TW202340422A - Delayed fluorescence material, laser oscillation material, and laser element - Google Patents

Abstract

This delayed fluorescence material expressed by formula (1) has a long sustained laser oscillation time and is useful as a laser oscillation material. In the formula, [sigma]em is the stimulated emission cross-sectional area, [sigma]TT is the absorption cross-sectional area in the excited triplet state, kISC is the intersystem crossing rate from the excited singlet state to the excited triplet state, and kRISC is the reverse intersystem crossing rate from the excited triplet state to the excited singlet state.

Description

Delayed fluorescent materials, laser oscillation materials and laser components

The invention relates to a laser oscillation delayed fluorescent material. Furthermore, the present invention also relates to a laser oscillation material and a laser element using such a delayed fluorescent material. Furthermore, the present invention also relates to an evaluation method of a delayed fluorescent material, a design method of a delayed fluorescent material using the delayed fluorescent material, a design method of a laser oscillation material, and a design method of a laser element. In addition, the present invention also relates to a database and a program for the above.

Organic lasers are attracting attention due to their wide wavelength tunability and the ease of keeping manufacturing costs low. They are expected to be used in augmented reality (AR) devices incorporating micro laser displays into contact lenses, light sources for spectrometers, and biosensing. Applications of technology, etc. In response to such expectations, as a result of active research on laser materials and resonator structures, light-excited organic solid-state lasers (OSSL) and current-excited organic semiconductor lasers using organic fluorescent materials as oscillation materials have been developed. Diode (OSLD). However, conventional organic lasers have the following problem. That is, whether the excitation light is continuously irradiated or the current is continuously passed, the laser oscillation will end in a short time. This is because while the organic fluorescent material is in an excited state, long-lived triplet excitons accumulate, causing absorption in the excited triplet state, and the induced emission process is hindered (see Non-Patent Document 1 to Non-Patent Document 7). Therefore, in order to achieve efficient continuous laser oscillation using organic fluorescent materials under photoexcitation or current excitation, it is necessary to suppress the accumulation of excited triplet states.

[Non-patent document 1] Forget, S.; Chénais, S.; Organic Solid-State Lasers; Springer, 2013. [Non-patent document 2] Org. Electron. 2011, 12, 8, 1346-1351. [Non-patent document 3] Phys. Rev. B 2010, 81, 165206. [Non-patent document 4] Phys. Rev. B 2011, 84, 241301. [Non-patent document 5] J. Appl. Phys. 2007, 101, 023107. [Non-patent document 6] Nat. Commun. 2020, 11, 5623. [Non-patent document 7] ACS Nano 2011, 5, 12, 9958-0065.

As a method of suppressing the accumulation of excited triplet states, a method of converting triplet excitons into a singlet excited state using reverse intersystem crossing of a thermally activated delayed fluorescent material has been proposed. However, regarding efficient continuous laser oscillation, The required conditions and materials are unknown. Therefore, intensive research has been conducted for the purpose of providing conditions and materials that can realize efficient continuous oscillation solid-state laser elements and current-excitation laser semiconductor elements by using thermally activated delayed fluorescent materials.

Through theoretical investigation, we investigated the conditions required for efficient continuous laser oscillation using thermally activated delayed fluorescence, and as a result of actually examining its validity using numerical calculations, we discovered for the first time that Using delayed fluorescent materials that meet specific conditions can enable long-term laser oscillation.

The present invention is proposed based on such knowledge, and specifically includes the following contents. [1] A delayed fluorescent material satisfying the following formula (1). [Formula 1] Formula (1) σ _em : Induced emission cross-sectional area σ _TT : Absorption cross-sectional area k of the excited triplet state _ISC : Intersystem crossing speed k from the excited singlet state to the excited triplet state _RISC : From the excited triplet state to the excited singlet state Inverse intersystem crossing velocity [2] The delayed fluorescent material as described in [1], in which the energy difference ΔE _ST between the lowest excited singlet state and the lowest excited triplet state at 77K is less than 0.3 eV. [3] The delayed fluorescent material as described in [1], wherein the energy difference ΔE _ST between the lowest excited singlet state and the lowest excited triplet state at 77K is 0.2 eV or less. [4] The delayed fluorescent material as described in [1], wherein the energy difference ΔE _ST between the lowest excited singlet state and the lowest excited triplet state at 77K is 0.1 eV or less. [5] The delayed fluorescent material according to any one of [1] to [4], wherein k _RISC is 1×10 ⁶ sec ^-1 or more. [6] The delayed fluorescent material according to any one of [1] to [4], wherein k _RISC is 1×10 ⁷ s ^-1 or more. [7] The delayed fluorescent material according to any one of [1] to [6], which is composed only of carbon atoms, hydrogen atoms, nitrogen atoms, oxygen atoms, sulfur atoms, boron atoms, silicon atoms, It is composed of atoms in the group of phosphorus atoms and fluorine atoms. [8] The delayed fluorescent material according to any one of [1] to [7], which has a boron-containing polycyclic aromatic skeleton with multiple resonance effects. [9] The delayed fluorescent material according to any one of [1] to [7], which has a donor group and an acceptor group. [10] A laser oscillation material containing the delayed fluorescent material according to any one of [1] to [9]. [11] A laser element using the delayed fluorescent material according to any one of [1] to [9]. [12] The laser element as described in [11], which is a current driven type. [13] The laser element as described in [11], which is a solid-state laser element. [14] A method for evaluating delayed fluorescent materials, which includes the following steps: measuring σ _em , σ _TT , k _ISC , and k _RISC of the delayed fluorescent material. [15] The evaluation method of delayed fluorescent material as described in [14], which includes the following steps: measuring σ _em , σ _TT , k _ISC , and k _RISC of the delayed fluorescent material, and determining whether the aforementioned formula (1) is satisfied. [16] The method for evaluating a delayed fluorescent material as described in [15], wherein the material is evaluated to be useful as a laser oscillation material when the aforementioned formula (1) is satisfied. [17] The method for evaluating delayed fluorescent materials as described in [15] or [16], wherein delayed fluorescent materials satisfying the aforementioned formula (1) are sorted. [18] The evaluation method of delayed fluorescent material as described in any one of [14] to [17], which includes the following steps: measuring σ _em , σ _TT , k _ISC , k _RISC of the delayed fluorescent material, and calculating The difference Δ is represented by the following formula (2). [Formula 2] Formula (2) [19] The method for evaluating delayed fluorescent materials according to [18], wherein those with a large difference Δ are highly evaluated. [20] The evaluation method of a delayed fluorescent material as described in [18] or [19], wherein the relationship between the chemical structure of the delayed fluorescent material and the difference Δ is accumulated. [21] The evaluation method of delayed fluorescent material as described in [20], wherein the relationship between the chemical structure of the new delayed fluorescent material and the difference Δ is predicted using the accumulated aforementioned relationship. [22] The evaluation method of a delayed fluorescent material as described in [20] or [21], wherein the chemical structure of the delayed fluorescent material with a large difference Δ is predicted using the accumulated aforementioned relationship. [23] The method for evaluating delayed fluorescent materials according to any one of [20] to [22], wherein the chemical structure of the delayed fluorescent material satisfying the aforementioned formula (1) is predicted using the accumulated aforementioned relationships. [24] The method for evaluating delayed fluorescent materials according to any one of [21] to [23], wherein the delayed fluorescent materials to be accumulated are a group of delayed fluorescent materials having a common specific partial structure. . [25] The method for evaluating delayed fluorescent materials according to any one of [21] to [23], wherein the delayed fluorescent materials to be accumulated are a group of delayed fluorescent materials having a specific donor group . [26] The method for evaluating a delayed fluorescent material according to any one of [21] to [23], wherein the delayed fluorescent material to be accumulated is a group of delayed fluorescent materials having a specific acceptor group. . [27] The method for evaluating a delayed fluorescent material as described in any one of [21] to [23], wherein the delayed fluorescent material to be accumulated is a boron-containing polycyclic aromatic skeleton with multiple resonance effects. Delayed fluorescent material group. [28] A method for designing delayed fluorescent materials using the evaluation method described in any one of [14] to [27]. [29] A method for designing a laser oscillation material using the evaluation method described in any one of [14] to [27]. [30] A method for designing a laser element using the evaluation method described in any one of [14] to [27]. [31] A database that accumulates the relationship between the chemical structure of delayed fluorescent materials and σ _em , σ _TT , k _ISC , and k _RISC . [32] A database that accumulates the relationship between the chemical structure of the delayed fluorescent material described in [20] and the difference Δ. [33] A database that accumulates chemical structures of delayed fluorescent materials that satisfy the aforementioned formula (1). [34] An evaluation method for delayed fluorescent materials, which uses the database described in any one of [31] to [33] and implements the evaluation method described in any one of [14] to [27]. [35] A method for designing delayed fluorescent materials using the database described in any one of [31] to [33]. [36] A method for designing laser oscillation materials using the database described in any one of [31] to [33]. [37] A method for designing a laser element using the database described in any one of [31] to [33]. [38] A program that implements the evaluation method described in any one of [21] to [27] and [34]. [39] A method to shorten the time until the laser operation reaches a stable state, which includes the following steps: using a delayed fluorescent material with a higher k _RISC and satisfying the aforementioned formula (1) for the laser element . [40] The method as described in [39], wherein the k _RISC of the delayed fluorescent material used for the laser element is 1×10 ⁷ s ^-1 or more. [41] The method as described in [39], wherein the k _RISC of the delayed fluorescent material used for the laser element is 1×10 ⁸ s ^-1 or more. [42] The method according to any one of [39] to [41], wherein the delayed fluorescent material used for the laser element further satisfies the following formula (1a). [Formula 3] Formula (1a) k _ISC : The intersystem crossing velocity from the excited singlet state to the excited triplet state k _RISC : The inverse intersystem crossing velocity from the excited triplet state to the excited singlet state [43] A method in which the laser action reaches stability A method for designing a laser element with a short time to state, which includes the following steps: according to the k _RISC of the delayed fluorescent material, select one from a group including at least two delayed fluorescent materials that satisfy the aforementioned formula (1) Delayed fluorescent material; and using the selected delayed fluorescent material as the laser element. [44] The method described in [43], wherein when selecting one delayed fluorescent material from the aforementioned group, the delayed fluorescent material with the highest k _RISC is selected. [45] A program that implements the method described in any one of [39] to [44]. [Effects of the invention]

According to the present invention, a laser oscillation delayed fluorescent material can be provided. Furthermore, it is also possible to evaluate the laser oscillation characteristics of the delayed fluorescent material, or to design a delayed fluorescent material that emits laser oscillation. Furthermore, the time required for the laser operation to reach a stable state can be shortened. Furthermore, laser components can also be provided or designed.

Hereinafter, the contents of the present invention will be described in detail. The description of the constituent elements described below may be based on representative embodiments and specific examples of the present invention, but the present invention is not limited to such embodiments and specific examples. In addition, the numerical range expressed using "～" in this specification means a range including the numerical values before and after "～" as the lower limit and the upper limit.

＜Delayed fluorescent material＞ The delayed fluorescent material of the present invention is characterized by satisfying the following formula (1).

[Formula 4] Formula (1) σ _em : Induced emission cross-sectional area σ _TT : Absorption cross-sectional area k of the excited triplet state _ISC : Intersystem crossing speed k from the excited singlet state to the excited triplet state _RISC : From the excited triplet state to the excited singlet state Inverse intersystem crossing speed

The "delayed fluorescent material" in the present invention refers to an organic compound that can cause reverse intersystem crossing from an excited triplet state to an excited singlet state. In such organic compounds, photons are naturally emitted upon transition from an excited singlet state resulting from inverse intersystem crossing to the ground state. This naturally emitted light is usually observed with a delay compared with the naturally emitted light from the excited singlet state resulting from direct excitation from the ground state, hence the name "delayed fluorescence". In the present invention, when the luminescence lifetime is measured with a fluorescence lifetime measurement system (such as a fringe camera system manufactured by Hamamatsu Photonics K.K.), a phosphor whose luminescence lifetime is 100 ns (nanoseconds) or more is observed is called delayed fluorescence. Material. In addition, the "delayed fluorescent material" in the present invention is also an organic material that can cause induced emission by generating an inversion distribution when excitation energy is applied at a certain or higher excitation intensity and by incident electromagnetic waves (photons) in this state. compound. That is, the delayed fluorescent material of the present invention is an organic compound that exhibits both reverse intersystem crossing and induced emission.

Among delayed fluorescent materials, the difference ΔE _ST between the lowest excited singlet energy and the lowest excited triplet energy at 77K is preferably 0.3eV or less, more preferably 0.25eV or less, 0.2eV or less, even better, and 0.15eV or less. It is good, 0.1 eV or less is still better, 0.07 eV or less is even better, 0.05 eV or less is even better, 0.03 eV or less is even better, and 0.01 eV or less is extremely good. Organic compounds with a small ΔE _ST easily transition from the excited singlet state to the excited triplet state through the absorption of thermal energy, and therefore function as a thermally activated delayed fluorescent material. The thermally activated delayed fluorescent material absorbs the heat emitted by the device and relatively easily travels backward from the excited triplet state to the excited singlet state, thereby effectively suppressing the accumulation of triplet excitons. ΔE _ST can be measured by the method described in column [b4] below.

Furthermore, the delayed fluorescent material of the present invention is characterized by satisfying formula (1) in particular. In the formula (1), the induced emission cross-sectional area (σ _em ) is a measure of the likelihood of induced emission of delayed fluorescent material molecules. The larger σ _em means the easier it is for induced emission to occur. On the other hand, the absorption cross-sectional area (σ _TT ) of the excited triplet state is a measure of the susceptibility of absorption of the excited triplet state. Here, "excited triplet state absorption" is a phenomenon in which triplet excitons absorb emitted light from singlet excitons and transform into a higher-order excited triplet state, which causes light loss. Therefore, the larger σ _TT is, the easier it is to produce light loss caused by absorption in the excited triplet state. In the delayed fluorescent material of the present invention, since σ _em and σ _TT satisfy the relationship between the speed constants (k _ISC , k _RISC ) of intersystem crossing and inverse intersystem crossing and equation (1), the induced emission speed exceeds The speed of absorption in the excited triplet state enables long-term continuation of laser oscillations. The measurement methods of σ _em , σ _TT , k _ISC , and k _RISC will be described later.

In a delayed fluorescent material satisfying equation (1), long-term continuation of laser oscillation can be explained using the gain coefficient (Gain Coefficient) represented by the following equation (2). [Formula 5] Formula (2) S: Excited singlet state T: Excited triplet state σ _em : Induced emission cross-sectional area σ _TT : Absorption cross-sectional area of the excited triplet state Γ: Light confinement factor α _cav : Propagation loss

The gain coefficient includes three terms: the light amplification term represented by Γσ _em S, the propagation loss term represented by α _CAV , and the excited triplet state absorption term represented by Γσ _TT T. When the gain coefficient is above 0, it means that the optical amplification mechanism operates and laser oscillation occurs. On the other hand, when the gain coefficient is negative, the loss process (propagation loss and excited triplet state absorption) is better than the optical amplification term, which means that it will not cause laser oscillation. Furthermore, even if the gain coefficient temporarily becomes 0 or more and laser oscillation is generated by applying excitation energy exceeding the laser oscillation critical value, triplet excitons are accumulated as time passes, and the triplet state absorption term is excited (Γσ _TT T) dominates, the final gain coefficient becomes less than 0, and the laser oscillation stops. Therefore, by simulating the time change of the gain coefficient and finding the time when the gain coefficient is equal to or greater than 0, the laser oscillation duration can be evaluated. Here, in conventional organic laser materials that do not cause inverse intersystem crossing, triplet excitons generated from intersystem crossing from the excited singlet state are accumulated as they are to cause absorption in the excited triplet state, so laser oscillation exists Short time problem. In this regard, in the delayed fluorescent material, inverse intersystem crossing from the excited triplet state to the excited singlet state occurs, so the triplet excitons generated by the intersystem crossing are not accumulated at high density and are converted to the singlet state. exciton. Moreover, especially if the delayed fluorescent material satisfies equation (1), by converting equation (1) with the density ratio S/T=k _RISC /R _ISC in the steady state to σ _em S>σ _TT T, the amplification term ( Γσ _em S) dominates the excited triplet state absorption term (Γσ _TT T). Therefore, the delayed fluorescent material that satisfies equation (1) maintains a gain coefficient above 0 even if time passes, and can sustain laser oscillation for a long period of time.

Here, each parameter of Formula (1) takes various values depending on the chemical structure of the delayed fluorescent material, but σ _em is usually about 10 ^-16 levels (cm ² ). Regarding σ _TT , in most cases it is about 10 ^-17 levels (cm ² ), and in very rare cases it is about 10 ^-19 levels (cm ² ). However, the delayed fluorescent material of the present invention that satisfies the formula (1) is not limitedly interpreted as having σ _em and σ _TT of this level. The k _RISC system of the delayed fluorescent material is preferably 1×10 ⁶ s ^-1 or more, more preferably 1×10 ⁷ s ^-1 or more, and further preferably 1×10 ⁸ s ^-1 or more. The k _ISC of the delayed fluorescent material is preferably 1×10 ¹⁰ s ^-1 or less, more preferably 1×10 ⁹ s ^-1 or less, and further preferably 1×10 ⁸ s ^-1 or less.

Hereinafter, through simulation using a laser element model, the mechanism of the delayed fluorescent material display effect that satisfies equation (1) of the present invention will be explained. The laser element model uses 4,6-bis((E)-4-(diphenylamino)styrene)-2,2-difluoro-2H-1λ ³ ,3,2λ ⁴ -dioxy Borane-5-carboxylic acid ethyl ester (TPA-BCm) was used as a delayed fluorescent material model (guest) and 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP) DFB laser element model as the gain medium of the subject-object system. Here, TPA-BCm is a compound having both delayed fluorescence properties and laser properties. Hereinafter, this laser element model is called "CBP-TADF element model".

The chemical structures of CBP and TPA-BCm, their energy level diagrams and energy transfer processes are shown in Figure 1. In Figure 1, S ₀ represents the ground state singlet energy level, S ₁ represents the lowest excited singlet energy level, T ₁ represents the lowest excited triplet energy level, and T _n represents the higher-order excited triplet energy level. CBP (T ₁ :2.6eV) has a higher lowest excited triplet energy level than TPA-BCm (T ₁ :1.6eV), and therefore exhibits a triplet confinement effect that confines the excited triplet energy within the guest molecule. In addition, k ^S _ET represents the rate constant of the excited singlet state energy transfer from the host to the guest molecule, k ^T _ET represents the rate constant of the excited triplet state energy transfer from the host to the guest molecule, and k _r,CBP represents the radiative attenuation constant of CBP. , k _r,TB represents the radiative attenuation constant of TPA-BCm, k ^T _nr,CBP represents the non-radiative attenuation constant of the excited triplet state of CBP, k ^S _nr,TB represents the non-radiative attenuation of the excited singlet state of TPA-BCm Constant, k ^T _nr,TB represents the non-radiative attenuation constant of the excited triplet state of TPA-BCm, k _ISC,CBP represents the intersystem crossing speed constant of CBP, k _ISC,TB represents the intersystem crossing speed of TPA-BCm The constant, k _RISC represents the speed constant of the inverse intersystem crossing of TPA-BCm.

The parameter values of the CBP-TADF component model used for simulation are shown in Table 1. The measurement method and numerical analysis method of parameters will be described later.

[Table 1]

In Table 1, k _st represents the rate constant of singlet-triplet elimination (STA), Γ represents the confinement coefficient, n _eff represents the refractive index, β represents the ratio of light to cavity mode, and α _cav represents the propagation loss. For the definition of other parameters, please refer to the description of equation (1) and Figure 1. In addition, in the simulation, the value of TPA-BCm was used as a parameter of the delayed fluorescent material except k _RISC , but the value of k _RISC was variously changed. Calculations of the laser oscillation critical value, laser oscillation duration, and various efficiencies were performed using numerical processing system software (Mathematica: manufactured by Wolfram Research Corporation). In addition, the simulation shown below is appropriate based on the laser oscillation critical value (55Wcm ⁻² ) of 4'4-bis[( N -carbazole)styrene]biphenyl (BSB-Cz) obtained through the same simulation. ) is confirmed to be equal to the reported laser oscillation critical value (70Wcm ⁻² ).

First, the process of stopping laser oscillation due to the accumulation of triplet excitons was simulated by calculating the induced emission efficiency (Φ _Stim ) defined by the following equation (3).

[Formula 6] Formula (3) Φ _Stim : induced emission efficiency k _Stim : induced emission velocity constant c: light speed P: photon density

The results of simulating the time changes of the intersystem crossing efficiency (Φ _ISC ) and the induced emission efficiency (Φ _Stim ) are shown in Figure 2. In Figure 2, Figure 2(a) shows the time change of each efficiency obtained by setting the excitation light intensity to 5kWcm ⁻² , and Figure 2(b) shows the time changes of each efficiency obtained by setting the excitation light intensity to 10kWcm ⁻² . Temporal changes in efficiency.

As shown in Figure 2, after the laser oscillation starts, Φ _Stim reaches the maximum value immediately, and at the same time, Φ _ISC decreases significantly. At this time, singlet excitons are rapidly consumed, so just after Φ _Stim reaches the maximum value, the laser oscillation is instantly suppressed, causing Φ _Stim to decrease and Φ _ISC to increase sharply. Afterwards, the singlet exciton density and photon density recovered rapidly, causing laser oscillation again. Such temporal changes in Φ _Stim and Φ _ISC show a vibratory structure called relaxation oscillation, and are caused by a sharp increase and decrease in singlet density just after the start of laser oscillation. In this system, the intersystem crossing velocity cannot follow the oscillation velocity, so the instantaneous rise of Φ _ISC in the relaxation oscillation will not have a strong impact on the excited triplet generation process. Furthermore, Φ _Stim approaches 1 value while oscillating, and the relaxation oscillation converges. Subsequently, a quasi-stable state is formed and Φ _Stim decreases. Here, the intersystem crossing process competes with induced emission, so Φ _Stim decreases, whereby the intersystem crossing process proceeds and triplet excitons are gradually accumulated. As a result, Φ _Stim gradually decreases and the laser oscillation stops within tens of nanoseconds. That is, it is known from this simulation that the laser oscillation attenuates and stops because triplet excitons accumulate after intersystem crossing proceeds after a quasi-stable state is formed.

Next, the attenuation of the laser oscillation caused by the accumulation of the triplet state was suppressed by using a delayed fluorescent material that satisfies the equation (1), and simulations using the CBP-TADF element model were used to verify the change in the duration of the laser oscillation. long. The results of simulating the laser characteristics of the CBP-TADF element model are shown in Figure 3. In Figure 3, Figure 3(a) shows the case where the k _RISC of the delayed fluorescent material is set to 1.0×10 ⁴ s ^-1 (actual measurement value) of TPA-BCm and is changed to 1.0×10 ⁷ s ^-1 and For the case of 1.0×10 ⁸ s ^-1 , the luminescence intensity is plotted against the excitation light intensity. In each figure, the excitation light intensity corresponds to the laser oscillation critical value in terms of the change in the slope of the plotted fit line. Figure 3(b) is a graph obtained by simulating the time change of the gain coefficient by setting the k _RISC of the delayed fluorescent material to 1.0×10 ⁸ s ^-1 and the excitation light intensity to 15kWcm ^-2 . Figure 3(c) ) To set the k _RISC of the delayed fluorescent material to 1.0×10 ⁴ s ^-1 , 1.0×10 ⁷ s ^-1 and 1.0×10 ⁸ s ^-1 , the excitation light intensity is set to 5.0kWcm ^-2 and 4.0kWcm ^{- 2} and 3.0kWcm ^-2 , the curve obtained by simulating the time change of the gain coefficient. In Figures 3(b) and 3(c), the period in which the gain coefficient is equal to or greater than 0 corresponds to the laser oscillation duration. In addition, in the simulation here, the values shown in Table 1 were used for parameters other than k _RISC . The relationship between σ _em /k _ISC and σ _TT /k _RISC under each condition is shown in Table 2.

[Table 2] K _RISC (s ^-1 ) _{σTT/ KRISC} The relationship between σ _em /k _ISC and σ _TT /k _RISC 1.0×10 ⁴ 3.9× ^10-21 2.6×10 ^-24 <3.9×10 ^-21 1.0×10 ⁷ 3.9× ^10-24 2.6×10 ^-24 <3.9×10 ^-24 1.0×10 ⁸ 3.9× ^10-25 2.6×10 ^-24 >3.9×10 ^-25

As shown in Figure 3(a), the critical value of laser oscillation is 3.3kWcm ^-2 in both the case of k _RISC =1.0×10 ⁴ s ^-1 and the case of k _RISC =1.0×10 ⁷ s ^-1 . In the case of k _RISC =1.0×10 ⁸ s ^-1, it is also 2.7kWcm ^-2 , which is slightly smaller than the critical value of laser oscillation. Regarding the laser oscillation duration, it is the same as about 20 ns at the excitation light intensity of 5kWcm ^-2 in both the case of k _RISC =1.0×10 ⁴ s ^-1 and the case of k _RISC =1.0×10 ⁷ s ^-1 degree. In this regard, if k _RISC =1.0×10 ⁸ s ^-1 and σ _TT /k _RISC is smaller than σ _em /k _ISC (σ _em /k _ISC > σ _TT /k _RISC ), then the magnitude relationship is opposite The situation is different. After the gain coefficient exceeds 0 at an excitation light intensity of 5 kWcm ^-2 , relaxation oscillation and its convergence, quasi-stable state follow, and the state where the gain coefficient is 0 continues and continuous wave (CW) oscillation occurs. Based on the above simulation results, it was confirmed that by using a delayed fluorescent material that satisfies σ _em /k _ISC >σ _TT /k _RISC σ _TT /k _RISC as a laser oscillation material, triplet accumulation in a quasi-stable state is suppressed. The absorption of the excited triplet state is suppressed, thereby enabling a laser element that can sustain laser oscillation for a long time.

(Measurement method and calculation method of parameters) The following describes the measurement method and numerical analysis method of parameters used in the above simulation. [a1] Rate constant ( k ^S _ET , k _r,CBP , k _ISC,CBP , k _r,TB , k _RISC ) based on photoluminescence of CBP film doped with 6 mass% TPA-BCm and CBP single film The rate constant was found for quantum yield (PLQY) and luminescence lifetime. As a result, the radiation attenuation speed constant of CBP (k _r,CBP ) is 2.4×10 ⁸ s ⁻¹ , the intersystem crossing speed constant of CBP (k _ISC,CBP ) is 3.7×10 ⁸ s ⁻¹ , and the radiation from the main body (CBP ) to the guest molecule (TPA-BCm), the singlet energy transfer rate constant (k ^S _ET ) is 1.8×10 ⁹ s ⁻¹ , and the radiation decay rate constant (k _r,TB ) of TPA-BCm is 2.3×10 ⁸ s ⁻¹ . Furthermore, it is inferred that the nonradiative decay rate constant (k ^S _nr,CBP ) of singlet excitons of CBP is small enough to be ignored, and the inverse intersystem crossing rate constant (k _RISC ) of TPA-BCm is 1×10 ⁴ s ^{− 1} . The numerical adequacy of k _RISC was confirmed by comparing the theoretical values of external quantum efficiency calculated using k _RISC and other parameters with reported experimental data of organic electroluminescent devices (Nat. Photonics 2018, 12, 98- 104.).

[a2] Density of CBP molecules and TPA-BCm molecules Regarding the density of CBP molecules and TPA-BCm molecules in the membrane, assuming that the density of the membrane is 1.1gcm ^-3 , the calculations are respectively 1.3×10 ²¹ cm ^-3 and 2.7× 10 ¹⁹ cm ^-3 .

[a3] Induced emission cross-sectional area ( σ _em ) of TPA-BCm and absorption cross-sectional area ( σ _TT ) of the excited triplet state. The σ _em of TPA-BCm was calculated by calculating the following equation (4).

[Formula 7] Formula (4) F _D (λ): Fluorescence spectrum λ: Wavelength n (λ): Refractive index at λ Φ _F : Photoluminescence quantum yield of 6 mass% TPA-BCm doped CBP film

The σ _TT of TPA−BCm was inferred from the transient absorption enhanced by the triplet sensitizer according to the method described in Nat. Mater. 2014, 13, 938-946.

Figure 4 shows the wavelength dependence of σ _em and σ _TT of TPA-BCm. As shown in Figure 4, the maximum values of σ _em and σ _TT are 2.6×10 ⁻¹⁶ cm ² and 3.9×10 ⁻¹⁷ cm ² respectively.

[a4] Rate constant of singlet - triplet annihilation ( k _st ) Singlet-triplet annihilation (STA) is caused by the Foerster energy transfer from the excited singlet state to the excited triplet state. Therefore, the speed constant (k _st ) of the STA is determined by calculating the following equation (5) using R ⁶ _F calculated by substituting σ _TT into the following equation (6). Here, substituting 3.9×10 ⁻¹⁷ cm ² into σ _TT , k _st is calculated as 2.1×10 ⁻¹⁰ cm ³ s ⁻¹ . For the derivation methods of equations (5) and (6), please refer to Jpn. J. Appl. Phys. 2015, 54, 071601. and Phys. Rev. Lett. 2007, 98, 197402.

[Formula 8] Formula (5) Formula (6) τ _s : Fluorescence lifetime of TPA-BCm N _A : Avogajer constant k ² : Directivity factor (direction coefficient) considered to be 2/3

[a5] Other rate constants ( k ^S _nr,TB , k ^T _nr,TB , k _ISC , k ^T _ET ) Regarding the nonradiative decay rate constant (k ^S _nr,TB ) of singlet excitons of TPA-BCm, triplet The non-radiative decay rate constant of state excitons ( k ^T _nr,TB ), the intersystem crossing rate constant (k _ISC ), and the triplet energy transfer rate constant from the host to the guest molecule (k ^T _ET ) are calculated by fitting It is obtained by measuring the transient photoluminescence (PL) curve of luminescence under long pulse excitation. Figure 5 shows the transient PL curve (solid line) measured at each excitation light intensity of 6 W/cm ² , 31 W/cm ² and 57 W/cm ² for a 6 wt% TPA-BCm doped CBP film and its adaptation. Curve (dashed line). For the excitation light, a long pulse laser with a wavelength of 355 nm and a pulse interval of 40 μs was used. As shown in Figure 5, the gradual accumulation of triplet excitons and the enhanced luminescence decay caused by singlet-triplet elimination were observed. Under the constraint of k _ISC,TB +k ^S _nr,TB =2×10 ⁸ s ⁻¹ estimated based on Φ _F and τ _s , the following formulas (7) to (10) and P=k _r,TB are used S _TB (assuming a non-cavity structure) analyzed these measured data. As a result, by using k _ISC,TB =1.0×10 ⁸ s ⁻¹ , k ^S _nr,TB =1.0×10 ⁸ s ⁻¹ , k ^T _nr,TB =1.0×10 ⁵ s ⁻¹ and k ^T _ET =5×10 ⁴ s ⁻¹ , the simulation results consistent with the measured data can be obtained, and the values used in the simulation are used as each speed constant.

[a6] Propagation loss ( α _cav ) Regarding the propagation loss (α _cav ), by using the parameter values calculated from [a1] to [a5], the simulation is performed for a 2-pass DFB laser (grating period Λ ₂ =450nm) The output intensity of the excitation light intensity is calculated as 80cm ^-1 . α _cav , Γ and b are respectively set to 80cm ^-1 , 0.7, 1×10 ^-4 and the oscillation critical value calculated through simulation is 3.2kWcm ^-2 , which is consistent with the measured oscillation under pulse light excitation of nitrogen laser. The critical value (I _th ) of 3.5kWcm ⁻² is roughly consistent.

[a7] Each rate equation for exciton density and photon density used in the simulation: singlet exciton density ( _SCBP ) and triplet exciton density ( _TCBP ) of CBP, singlet exciton density (S) of TPA-BCm _TB ) and triplet exciton density (T _TB ), and the rate equation for photon density (P) are given by the following equations (7) to (11).

[Formula 9] Formula (7) Formula (8) Formula (9) Formula (10) Formula (11)

G represents the excitation speed, R _CBP represents the ground state saturation probability of CBP, and R _TB represents the ground state saturation probability of TPA-BCm. For the definitions of other parameters, please refer to the descriptions of formulas (1), (3) and Table 1. For the exciton generation rate, it is assumed to be proportional to the saturation probability of G and the ground state (R=[N _molecule - (S+T)]/N _molecule ). Again, in this model of the rate equation, the output intensity is proportional to the photon density. Therefore, the oscillation threshold is determined by the nonlinear increase in P plotted against G.

(Methods for making films and laser elements used in measurement, and methods for measuring their characteristics) The following shows the production method of 6 mass% TPA-BCm doped CBP film and CBP single film for measuring parameters, the production method of laser element for measuring laser characteristics, and the measurement method of various characteristics.

[b1] Preparation of 6 mass % TPA-BCm- doped CBP film and CBP single film. A chloroform solution containing TPA-BCm and CBP was coated on a quartz substrate by spin coating and dried. A 6 mass% TPA-BCm doped CBP film was formed with a film thickness of 100 nm. In addition, a CBP single film was formed with a film thickness of 100 nm in the same manner except that a chloroform solution in which only CBP was dissolved was used instead of the chloroform solution of TPA-BCm and CBP.

[b2] The 6 mass % TPA-BCm doped CBP film was used for the production of a laser element as a gain medium. A glass substrate with a secondary DFB pattern was prepared. The secondary DFB pattern is formed using electron beam lithography (JBX-5500SC: manufactured by JEOL Ltd.) and etching so that the grating period satisfies the Bragg equation below. Bragg equation: mλ _Bragg =2 _neff Λ _m Here, m is the number of diffraction, λ _Bragg is the Bragg wavelength, and Λ is the period of the diffraction grating. A chloroform solution in which TPA-BCm and CBP were dissolved was applied to the glass substrate by a spin coating method and then dried to form a 6 mass % TPA-BCm doped CBP film with a film thickness of 200 nm. Next, the TPA-BCm-doped CBP film was covered with sapphire glass and sealed with CYTOP (manufactured by AGC Inc., registered trademark), thereby producing a laser element.

[b3] Measurement method of absorption characteristics, luminescence characteristics and laser oscillation characteristics For 6 mass% TPA-BCm doped CBP film and CBP single film, the ultraviolet-visible absorption spectrum, emission spectrum, photoluminescence quantum yield and luminescence were measured lifespan. For the measurement, a UV-visible spectrophotometer (LAMDA950: manufactured by PerkinElmer Co., Ltd.), a spectrofluorophotometer (FP-8600: manufactured by JASCO Corporation), and an absolute PL quantum yield measuring device (Quantaurus-QY: Hamamatsu Photonics KK), fluorescence lifetime measurement device (Quantaurus-tau: Hamamatsu Photonics KK). In addition, for the 6 mass % TPA-BCm doped CBP film, the transient luminescence characteristics were measured using a 355 nm CW laser as the excitation light source. A nitrogen laser (KEN-2020: USHO, wavelength = 337nm, pulse width = 0.8ns, irradiation area = 6.8×10 ^-3 cm ² ) and a photon multi-channel analyzer ( PMA50: Hamamatsu Photonics KK). The transient absorption measurement was performed by the pump-probe method using a time-resolved absorption spectrum analysis system (manufactured by Hamamatsu Photonics KK), using an excitation light source (YAG laser, wavelength = 355 nm) and a detection light source (hernia lamp).

[b4] Measurement method of ΔE _ST Regarding the difference (ΔE _ST ) between the lowest excited singlet energy (E _S1 ) and the lowest excited triplet energy ( _ET1 ) of each material, the lowest excited singlet energy (E _S1 ) and the lowest excited triplet energy, and are found by ΔE _ST =E _S1 -E _T1 . (1) Minimum excited singlet energy E _S1 Co-evaporate the measurement target compound and mCBP [3,3'-bis(9H-carbazol-9-yl)] so that the measurement target compound has a concentration of 6% by weight, In this way, a sample with a thickness of 100 nm was produced on the Si substrate. The fluorescence spectrum of the sample was measured at normal temperature (300K). By integrating the luminescence from just after the excitation light is incident to 100 nanoseconds after the incident, a fluorescence spectrum is obtained in which the vertical axis represents the luminous intensity and the horizontal axis represents the wavelength. In the fluorescence spectrum, the vertical axis represents emission and the horizontal axis represents wavelength. A tangent line is drawn with respect to the protrusion on the short-wave side of the emission spectrum, and the wavelength value λedge [nm] at the intersection of the tangent line and the horizontal axis is found. Let the value that converts the wavelength value into an energy value using the conversion formula shown below be E _S1 . Conversion formula: E _S1 [eV] = 1239.85/λedge In the measurement of the emission spectrum, a streak camera (Hamamatsu Photonics KK, manufactured by Hamamatsu Photonics KK) can be used as a detector using a nitrogen laser (MNL200 manufactured by Lasertechnik Berlin) as the excitation light source. C4334) etc. (2) Minimum excited triplet energy E _T1 Cool the sample that is the same as the minimum excited singlet energy E _S1 to 77 [K], irradiate the excitation light onto the sample for phosphorescence measurement, and use a fringe camera to measure the phosphorescence intensity. By integrating the luminescence from 1 millisecond after the incident of the excitation light to 10 milliseconds after the incident, a phosphorescence spectrum in which the vertical axis represents the emission intensity and the horizontal axis represents the wavelength is obtained. A tangent line is drawn with respect to the protrusion on the short wavelength side of the phosphorescence spectrum, and the wavelength value λedge [nm] at the intersection of the tangent line and the horizontal axis is obtained. Let the value that converts the wavelength value into an energy value using the conversion formula shown below be E _T1 . Conversion formula: E _T1 [eV]=1239.85/λedge The tangent line to the protrusion on the short wavelength side of the phosphorescence spectrum is drawn as follows. When moving on the spectrum curve from the short wavelength side of the phosphorescence spectrum to the maximum value on the shortest wavelength side among the maximum values of the spectrum, tangent lines at each point on the curve toward the long wavelength side are considered. The tangent increases in slope as the curve bulges (that is, as the vertical axis increases). A tangent line drawn at a point where the value of the slope takes a maximum value is defined as a tangent line to the protrusion on the short wavelength side of the phosphorescence spectrum. In addition, regarding the maximum point of the peak intensity that is 10% or less of the maximum peak intensity of the spectrum, the slope value closest to the maximum value on the shortest wavelength side that is not included in the maximum value on the shortest wavelength side is taken as the maximum. The tangent line drawn at the point of value serves as the tangent line to the bump with respect to the short wavelength side of the phosphorescence spectrum.

(Chemical structure of delayed fluorescent material) Next, the chemical structure of the delayed fluorescent material will be described. The structure of the delayed fluorescent material of the present invention is not particularly limited as long as it satisfies formula (1). In one aspect of the present invention, the delayed fluorescent material satisfying formula (1) is selected from the group consisting of carbon atoms, hydrogen atoms, nitrogen atoms, oxygen atoms, sulfur atoms, boron atoms, silicon atoms, phosphorus atoms and fluorine atoms. A compound composed of atoms in a group. In a preferred aspect of the present invention, the delayed fluorescent material that satisfies formula (1) is selected from the group consisting of carbon atoms, hydrogen atoms, nitrogen atoms, oxygen atoms, sulfur atoms, boron atoms and fluorine atoms. In a more preferred aspect of the present invention, the delayed fluorescent material satisfying formula (1) is selected from the group consisting of carbon atoms, hydrogen atoms, nitrogen atoms, oxygen atoms, boron atoms and fluorine atoms. A compound composed of atoms in a group.

The delayed fluorescent material satisfying Formula (1) can be selected from compounds having a boron-containing polycyclic aromatic skeleton having a multiple resonance effect, for example. Examples of such compounds include compounds having a skeleton structure represented by the following general formula (I).

[Chemical formula 1] (In the general formula (I), A ring, B ring and C ring are independently aromatic rings or heteroaromatic rings. At least one hydrogen atom in these rings can be substituted. Y ¹ is B, X ¹ and X ² are independently O, NR, S or Se. The R of the aforementioned NR is an optionally substituted aryl group, an optionally substituted heteroaryl group or an alkyl group, and the R of the aforementioned NR can be connected through a connecting group or a single bond. Bonded to the aforementioned A ring, B ring and/or C ring, and at least one hydrogen atom in the compound or structure represented by the general formula (I) may be replaced by a halogen atom or a deuterium atom.) Delayed fluorescence of the present invention The optical material may be a polymer having a plurality of unit structures represented by general formula (I).

The compound represented by the general formula (I) is preferably a compound represented by the following general formula (II) or a polymer having a plurality of unit structures represented by the following general formula (II).

[Chemical formula 2]

The A ring, B ring and C ring in the general formula (I) are each independently an aromatic ring or a heteroaromatic ring, and at least one hydrogen atom in these rings may be substituted by a substituent. The substituent is a substituted or unsubstituted aryl group, a substituted or unsubstituted heteroaryl group, a substituted or unsubstituted diarylamine group, a substituted or unsubstituted diarylamine group, a substituted or unsubstituted aryl group. Preferred are heteroarylamino groups (amine groups having an aryl group and a heteroaryl group), substituted or unsubstituted alkyl groups, substituted or unsubstituted alkoxy groups, or substituted or unsubstituted aryloxy groups. When these groups have a substituent, examples of the substituent include an aryl group, a heteroaryl group, or an alkyl group. Moreover, the above-mentioned aromatic ring or heteroaromatic ring has a covalent bond with the fused bicyclic structure (hereinafter, this structure is also referred to as "D structure") in the center of the general formula (I) consisting of Y ¹ , X ¹ and X ² A 5-member ring or a 6-member ring is better.

Here, the "fused bicyclic structure (D structure)" refers to a structure in which two saturated hydrocarbon rings including Y ¹ , X ¹ and X ² shown in the center of the general formula (I) are fused. Moreover, "the 6-membered ring covalently bonded to the fused bicyclic structure" refers to, for example, the a ring (benzene ring (6-membered ring)) fused to the aforementioned D structure as shown in the aforementioned general formula (II). Furthermore, "the aromatic ring or heteroaromatic ring (as the A ring) has the 6-membered ring" means that the A-ring is formed only from the 6-membered ring, or other rings are further combined with the 6-membered ring by including the 6-membered ring. The member rings fuse to form ring A. In other words, "an aromatic ring or heteroaromatic ring having a 6-membered ring (as the A ring)" referred to here means that the 6-membered ring constituting all or part of the A ring is fused with the aforementioned D structure. The same instructions apply to "B ring (b ring)", "C ring (c ring)" and "5-member ring".

Ring A (or ring B or ring C) in the general formula (I) corresponds to ring a and its substituents R ¹ to R ³ (or ring b and its substituents R ⁴ to R ⁷ ) in the general formula (II) , c ring and its substituents R ⁸ ~ R ¹¹ ). That is, the general formula (II) corresponds to the case where "A to C rings having 6-membered rings" are selected as the A to C rings of the general formula (I). In this sense, each ring of the general formula (II) is represented by lowercase letters a to c.

In the general formula (II), the adjacent groups among the substituents R ¹ to R ¹¹ of the a ring, b ring and c ring can be bonded to each other to form an aromatic ring or a heterocyclic ring together with the a ring, b ring or c ring. Aromatic ring, at least one hydrogen atom in the formed ring can be aryl, heteroaryl, diarylamine, diarylamine, arylheteroarylamine, alkyl, alkoxy or aryloxy substituted, at least 1 hydrogen atom in these may be substituted by aryl, heteroaryl or alkyl. Therefore, the polycyclic aromatic compound represented by the general formula (II) is as shown in the following formula (2-1) and formula (2-2) based on the mutual bonding form of the substituents in the a ring, b ring and c ring. In general, the ring structure of the compound changes. The A' ring, B' ring and C' ring in each formula correspond to the A ring, B ring and C ring in the general formula (I) respectively.

[Chemical formula 3]

When the A' ring, B' ring and C' ring in the above formula (2-1) and formula (2-2) are described in the general formula (II), they represent the substituents R ¹ to R ¹¹ The adjacent groups are bonded to each other to form an aromatic ring or a heteroaromatic ring together with the a ring, b ring and c ring respectively (it can also be called other ring structures formed by fusion with a ring, b ring or c ring) fused ring). In addition, although not shown in the formula, there are also compounds in which all a ring, b ring and c ring are changed to A' ring, B' ring and C' ring. Moreover, as can be seen from the above formulas (2-1) and formula (2-2), for example, R ⁸ of the b ring and R ⁷ of the c ring, R ¹¹ of the b ring, R ¹ of the a ring, and c ring R ⁴ and R ³ of the a ring do not belong to "adjacent groups" and they will not bond. That is, "adjacent groups" refers to groups that are adjacent on the same ring.

The compounds represented by the above formulas (2-1) and formula (2-2) correspond to, for example, structures represented by formulas (1-2) to (1-17) described in WO2015/102118 as ring skeletons. of compounds. That is, for example, it is an A' ring (or B' ring or C' ring) compound, the fused ring A' (or fused ring B' or fused ring C') formed is naphthalene ring, carbazole ring, indole ring, dibenzofuran ring or dibenzofuran ring. Benzothiophene ring.

X ^{1 and} R can be bonded to the aforementioned B ring and/or C ring through a linking group or a single bond. As the linking group, -O-, -S- or -C(-R) ₂ - is preferred. In addition, R in the aforementioned "-C(-R) ₂ -" is a hydrogen atom or an alkyl group. This description is also the same for X ¹ and X ² in the general formula (II).

Here, the requirement that "R of NR is bonded to the aforementioned A ring, B ring and/or C ring through a linking group or a single bond" in the general formula (I) corresponds to "the R of NR" in the general formula (II) "R is bonded to the aforementioned a ring, b ring and/or c ring through -O-, -S-, -C(-R) ₂ - or a single bond." This requirement can be expressed by a compound represented by the following formula (2-3-1) and having a ring structure in which X ¹ and X ² are introduced into fused ring B' and fused ring C'. That is, for example, it has a B' ring (or C ^' ring) formed by introducing X ¹ (or ) compound. This compound corresponds to, for example, a compound including a structure represented by formulas (1-451) to (1-462) as a ring skeleton and a compound including formulas (1-1401) to (1-1460) described in WO2015/102118 The structure represented is a compound with a ring skeleton, and the fused ring B' (or fused ring C') formed is, for example, a phenyl ring, a phenyl ring or an acridine ring. In addition, the above-mentioned regulations can also be represented by the following formula (2-3-2) and the compound having a ring structure in which X ¹ and/or X ² is introduced into the fused ring A', represented by the formula (2-3-3). Express. That is, for example, it is a compound having an A′ ring formed by introducing X ¹ (and/or X ² ) to the benzene ring as the a ring in the general formula (II) and condensing other rings. This compound corresponds to a compound described in WO2015/102118, for example, which includes a structure represented by formulas (1-471) to (1-479) as a ring skeleton, and the fused ring A' formed is, for example, a phenyl ring. , thiophene 𠯤 ring or acridine ring.

[Chemical formula 4]

Examples of the A ring, B ring, and C ring of the general formula (I), that is, the "aromatic ring" include an aromatic ring having 6 to 30 carbon atoms, preferably an aromatic ring having 6 to 16 carbon atoms, and an aromatic ring having 6 carbon atoms. An aromatic ring having ∼12 carbon atoms is more preferred, and an aromatic ring having 6 to 10 carbon atoms is particularly preferred. In addition, the "aromatic ring" corresponds to "an aromatic ring formed by the adjacent groups among R ¹ to R ¹¹ bonded to each other together with the a ring, b ring or c ring" specified in the general formula (II), In addition, the a ring (or b ring, c ring) is already composed of a benzene ring with a carbon number of 6, so the total carbon number of the 5-membered ring and the fused ring to which it is fused, 9, becomes the lower limit of carbon number.

Specific "aromatic rings" include a benzene ring as a monocyclic system, a biphenyl ring as a bicyclic system, a naphthalene ring as a fused bicyclic system, and a terphenyl ring as a tricyclic system (m-terphenyl ring, o-terphenyl ring, p-terphenyl ring), acenaphthylene ring, fluorine ring, pyrene ring, phenanthrene ring as a fused tricyclic system, biterphenyl ring, pyrene ring, fused tetraphenyl ring as a fused tetracyclic system Ring, perylene ring as a fused pentacyclic ring system, fused pentaphenyl ring, etc.

Examples of the A ring, B ring and C ring of the general formula (I), that is, the "heteroaromatic ring", include a heteroaromatic ring having 2 to 30 carbon atoms, and a heteroaromatic ring having 2 to 25 carbon atoms is preferred. A heteroaromatic ring having 2 to 20 carbon atoms is more preferred, a heteroaromatic ring having 2 to 15 carbon atoms is still more preferred, and a heteroaromatic ring having 2 to 10 carbon atoms is particularly preferred. Examples of the "heteroaromatic ring" include a heterocyclic ring containing 1 to 5 heteroatoms selected from oxygen, sulfur, and nitrogen in addition to carbon as ring constituent atoms. In addition, the "heteroaromatic ring" corresponds to a heteroaromatic ring in which adjacent groups among R ¹ to R ¹¹ are bonded to each other to form a heteroaromatic ring together with the a ring, b ring or c ring specified in the general formula (II). ”, and the a ring (or b ring, c ring) is already composed of a benzene ring with a carbon number of 6, so the total carbon number of the 5-membered ring and the fused ring to which it is fused, 6, becomes the lower limit of carbon number.

Specific "heteroaromatic rings" include, for example, a pyrrole ring, an ethazole ring, an isothiazole ring, a thiazole ring, an isothiazole ring, an imidazole ring, an ethadiazole ring, a thiadiazole ring, a triazole ring, and a tetrazole ring. Azole ring, pyrazole ring, pyridine ring, pyrimidine ring, pyridine ring, pyridine ring, tri-pyridine ring, indole ring, isoindole ring, 1H-indazole ring, benzimidazole ring, benzothiazole ring , benzothiazole ring, 1H-benzotriazole ring, quinoline ring, isoquinoline ring, quinoline ring, quinazoline ring, quinoline ring, pyridine ring, purine ring, pyridine ring, carbazole ring, acridine ring, phenoxathiine ring, phenoxathiine ring, phenoxathiine ring, phenoxathiine ring, phenoxathiine ring, indino ring, furan ring, benzofuran ring, isobenzofuran ring, Dibenzofuran ring, thiophene ring, benzothiophene ring, dibenzothiophene ring, furoxan ring, thien ring, etc.

At least one hydrogen atom in the above-mentioned "aromatic ring" or "heteroaryl ring" may be substituted or unsubstituted "aryl", substituted or unsubstituted "heteroaryl", substituted or unsubstituted "aryl" as the first substituent. Unsubstituted "diarylamine", substituted or unsubstituted "diarylamine", substituted or unsubstituted "arylheteroarylamine", substituted or unsubstituted "alkyl", Substituted with a substituted or unsubstituted "alkoxy group" or a substituted or unsubstituted "aryloxy group", examples of the first substituent include "aryl", "heteroaryl" and "diaryl" The aryl group of "amine group", the heteroaryl group of "diheteroarylamino group", the aryl group and heteroaryl group of "arylheteroarylamine group" and the aryl group as "aryloxy group" are as described above. A monovalent group of "aromatic ring" or "heteroaromatic ring".

In addition, the "alkyl group" as the first substituent may be either linear or branched, and examples thereof include a linear alkyl group having 1 to 24 carbon atoms or a branched alkyl group having 3 to 24 carbon atoms. . An alkyl group having 1 to 18 carbon atoms (branched alkyl group having 3 to 18 carbon atoms) is preferred, and an alkyl group having 1 to 12 carbon atoms (branched alkyl group having 3 to 12 carbon atoms) is more preferred. An alkyl group having 1 to 6 carbon atoms (branched chain alkyl group having 3 to 6 carbon atoms) is more preferred, and an alkyl group having 1 to 4 carbon atoms (branched chain alkyl group having 3 to 4 carbon atoms) is particularly preferred.

Specific alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, secondary butyl, tertiary butyl, n-pentyl, isopentyl, neo Pentyl, tertiary pentyl, n-hexyl, 1-methylpentyl, 4-methyl-2-pentyl, 3,3-dimethylbutyl, 2-ethylbutyl, n-heptyl, 1 -Methylhexyl, n-octyl, tertiary octyl, 1-methylheptyl, 2-ethylhexyl, 2-propylpentyl, n-nonyl, 2,2-dimethylheptyl, 2, 6-Dimethyl-4-heptyl, 3,5,5-trimethylhexyl, n-decyl, n-undecyl, 1-methyldecyl, n-dodecyl, n-tridecyl, 1- Hexyl heptyl, positive fourteen bases, positive fifteen bases, positive sixteen bases, positive seventeen bases, positive eighteen bases, positive twenty bases, etc.

Examples of the "alkoxy group" as the first substituent include a linear alkoxy group having 1 to 24 carbon atoms or a branched alkoxy group having 3 to 24 carbon atoms. An alkoxy group having 1 to 18 carbon atoms (branched chain alkoxy group having 3 to 18 carbon atoms) is preferred, and an alkoxy group having 1 to 12 carbon atoms (branched chain alkoxy group having 3 to 12 carbon atoms) is more preferred. Preferably, an alkoxy group having 1 to 6 carbon atoms (branched chain alkoxy group having 3 to 6 carbon atoms) is even more preferable, and an alkoxy group having 1 to 4 carbon atoms (branched chain alkoxy group having 3 to 4 carbon atoms) is more preferable. ) is particularly good.

Specific alkoxy groups include methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, secondary butoxy, tertiary butoxy, and pentoxy. base, hexyloxy, heptyloxy, octyloxy, etc.

As the first substituent, a substituted or unsubstituted "aryl group", a substituted or unsubstituted "heteroaryl group", a substituted or unsubstituted "diarylamine group", a substituted or unsubstituted "diheteroaryl group" "amine", substituted or unsubstituted "arylheteroarylamine", substituted or unsubstituted "alkyl", substituted or unsubstituted "alkoxy", or substituted or unsubstituted "aryloxy" "Group" means whether it is substituted or unsubstituted, at least one hydrogen atom among them may be substituted by a second substituent. Examples of the second substituent include an aryl group, a heteroaryl group, or an alkyl group. For specific examples of these, refer to the monovalent group of the above-mentioned “aromatic ring” or “heteroaryl ring” and the first Description of "alkyl" substituent. In addition, in the aryl group and heteroaryl group as the second substituent, at least one hydrogen atom in these is replaced by an aryl group such as phenyl (specific examples are the above), an alkyl group such as methyl (specific examples are the above) ) substituents are also included in the aryl group and heteroaryl group as the second substituent. As an example, when the second substituent is a carbazolyl group, a carbazolyl group in which at least one hydrogen atom at position 9 is substituted by an aryl group such as phenyl or an alkyl group such as methyl is also included as the second substituent. In the heteroaryl group of the base.

As an aryl group, a heteroaryl group, an aryl group of a diarylamine group, a heteroaryl group of a diarylamine group, or an aryl group of an arylheteroarylamine group in R ¹ to R ¹¹ of the general formula (II) Examples of the aryl group such as an aryl group and a heteroaryl group or an aryloxy group include an "aromatic ring" or a "heteroaryl ring" monovalent group described in the general formula (I). In addition, as the alkyl group or alkoxy group in R ¹ to R ¹¹ , refer to the description of “alkyl group” and “alkoxy group” as the first substituent in the description of the general formula (I) above. Furthermore, the same applies to the aryl group, heteroaryl group or alkyl group that is a substituent for these groups. Furthermore, when adjacent groups among R ¹ to R ¹¹ are bonded to each other to form an aromatic ring or a heteroaromatic ring together with the a ring, b ring or c ring, heteroaryl as a substituent for these rings Aryl, diarylamine, diarylamine, arylheteroarylamine, alkyl, alkoxy or aryloxy and aryl, heteroaryl or alkyl as further substituents are also same.

R in NR in X ^{1 and} For example, they may be substituted by alkyl or aryl groups. Examples of the aryl group, heteroaryl group and alkyl group include those mentioned above. In particular, aryl groups with 6 to 10 carbon atoms (such as phenyl, naphthyl, etc.), heteroaryl groups with 2 to 15 carbon atoms (such as carbazolyl, etc.), alkyl groups with 1 to 4 carbon atoms (such as methyl, Ethyl, etc.) are preferred. This description is also the same for X ¹ and X ² in the general formula (II).

R in "-C(-R) ₂ -", which is the linking group in the general formula (I), is a hydrogen atom or an alkyl group. Examples of the alkyl group include those mentioned above. In particular, an alkyl group having 1 to 4 carbon atoms (eg, methyl group, ethyl group, etc.) is preferred. This description is also the same for "-C(-R) ₂ -" which is the coupling group in general formula (II).

Furthermore, the compound contained in the laser element of the present invention may be a polymer having a plurality of unit structures represented by the general formula (I), preferably a polymer having a plurality of unit structures represented by the general formula (II). Polymer. The polymer is preferably a dimer to a hexamer, a dimer to a trimer is more preferred, and a dimer is particularly preferred. Regarding the polymer, it suffices as long as it has a plurality of the above-mentioned unit structures in one compound. For example, in addition to the above-mentioned unit structures through a single bond, an alkylene group having 1 to 3 carbon atoms, a phenyl group, or a naphthylene group. In addition to the form in which the linking group has a plurality of bonds, it can also be covalently composed of a plurality of unit structures and any ring included in the above unit structure (A ring, B ring or C ring, a ring, b ring or c ring) The bonding form may also be a form in which any of the rings included in the above unit structure (A ring, B ring or C ring, a ring, b ring or c ring) are fused to each other and bonded.

Examples of such a multipolymer include the following formula (2-4), formula (2-4-1), formula (2-4-2), formula (2-5-1) to formula (2 -5-4) or a polymer compound represented by formula (2-6). The polymer compound represented by the following formula (2-4) corresponds to a compound including a structure represented by the formula (1-21) as a ring skeleton described in WO2015/102118, for example. That is, if it is described in the general formula (II), it is a polymer compound having a plurality of unit structures represented by the general formula (II) in one compound with a benzene ring covalently serving as the a ring. In addition, the polymer compound represented by the following formula (2-4-1) corresponds to a compound including a structure represented by the formula (1-2665) as a ring skeleton described in WO2015/102118, for example. That is, if it is described in the general formula (II), it is a polymer compound having two unit structures represented by the general formula (II) in one compound with the benzene ring covalently serving as the a ring. In addition, the polymer compound represented by the following formula (2-4-2) corresponds to a compound including a structure represented by the formula (1-2666) as a ring skeleton described in WO2015/102118, for example. That is, if it is described in the general formula (II), it is a polymer compound having two unit structures represented by the general formula (II) in one compound with the benzene ring covalently serving as the a ring. In addition, the polymer compound represented by the following formula (2-5-1) to formula (2-5-4) corresponds to the formulas (1-22) to (1) described in WO2015/102118, for example. -25) The structure represented is a compound with a ring skeleton. That is, if it is described in the general formula (II), it is a polymer having a plurality of unit structures represented by the general formula (II) in one compound as a benzene ring covalently serving as the b ring (or c ring). compounds. In addition, the polymer compound represented by the following formula (2-6) corresponds to, for example, the structure represented by the formulas (1-31) to (1-37) described in WO2015/102118 as a ring skeleton. compound. That is, if it is explained in the general formula (II), for example, a benzene ring of b ring (or a ring, c ring) which is a certain unit structure and a b ring (or a ring, c ring) which is a certain unit structure c ring) The benzene ring is fused to form a polymer compound having a plurality of unit structures represented by the general formula (II) in one compound.

[Chemical formula 5]

The polymer compound can be a polymerized form expressed by combined formula (2-4), formula (2-4-1) or formula (2-4-2) and formula (2-5-1) ~ formula ( Any one of 2-5-4) or the polymerized form expressed by formula (2-6) can also be a combination of formula (2-5-1) to formula (2-5- The polymer formed by the polymerization form expressed by any one of 4) and the polymerization form expressed by formula (2-6) can also be a combination of formula (2-4) and formula (2-4) -1) or the multimerization form expressed by formula (2-4-2), the multimerization form expressed by any one of formula (2-5-1) to formula (2-5-4), and the formula (2-6) Polymers formed by the expressed polymerization form.

In addition, all or part of the hydrogen atoms in the chemical structure of the compound represented by the general formula (I) or (II) and its polymer may be deuterium atoms.

In addition, all or part of the hydrogen atoms in the chemical structure of the compound represented by the general formula (I) or (II) and its polymer may be halogen atoms. For example, in the general formula (I), A ring, B ring, C ring (A to C rings are aromatic rings or heteroaromatic rings), substituents for A to C rings, Y ¹ is Si-R or Ge- The hydrogen atoms in R (i.e. alkyl, aryl) when R, and R (i.e. alkyl, aryl) when X ¹ and X ² are NR may be substituted by halogen atoms, but in these cases Examples include examples in which all or part of the hydrogen atoms in an aryl group or a heteroaryl group are substituted by halogen atoms. The halogen atom is a fluorine atom, a chlorine atom, a bromine atom or an iodine atom, preferably a fluorine atom, a chlorine atom or a bromine atom, and more preferably a chlorine atom.

In the compound represented by the general formula (II), at least one of R ¹ to R ¹¹ may be a specific substituent specified in the general formula (II). Among the substituents that can be used for R ¹ to R ¹¹ specified in the general formula (II), an aryl group and a diarylamine group are preferred, and an aryl group and a diarylamine group having 6 to 30 carbon atoms (however, More preferably, the aryl group is an aryl group having 6 to 12 carbon atoms).

Regarding the synthesis method of the compound represented by the general formula (I), please refer to paragraphs [0281] to [0316] of WO2015/102118.

Regarding the delayed fluorescent material that satisfies the formula (1), it is also possible to select a donor group (typically, a group with a negative Hammett σp value) and an acceptor group (typically, Hammett’s σp value is negative). Select from a group of compounds with a structure in which a group with a positive σp value is bonded to a linking group (typically, a conjugated linking group such as an aromatic group).

Hammett's σp value was proposed by LP Hammett and quantified the influence of substituents on the acid dissociation equilibrium of para-substituted benzoic acid. Specifically, the following formula is established between the substituent in para-substituted benzoic acid and the acid dissociation equilibrium constant: σp=logK _x -logK Constant unique to the substituent in _H (σp). In the above formula, K _H represents the acid dissociation equilibrium constant of benzoic acid having no substituent, and K _X represents the acid dissociation equilibrium constant of benzoic acid substituted with a substituent at the para position. For an explanation of Hammett's σp and the numerical values of each substituent, please refer to Hansch, C. et. al., Chem. Rev., 91, 165-195 (1991). A positive value of Hammett's σp means that its substituent is an acceptor group (electron withdrawing group), and a negative value of Hammett's σp means that its substituent is a donor group (electron withdrawing group). ).

Preferable examples of the substituent having a positive Hammett's σp value include a fluorine atom, a hydroxyl group, a hydroxyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, a cyano group, a phosphine oxide group, and a sulfonate group. Cyl group, perfluoroalkyl group, acylamino group, alkoxy group, pyridyl group, pyrimidinyl group, triazolyl group, etc. Preferable examples of the substituent having a negative Hammett σp value include a substituted amino group and a substituted aminoaryl group. The substituted amino group here is preferably a substituted or unsubstituted diarylamine group, and the two aryl groups constituting the substituted or unsubstituted diarylamine group may be linked to each other. The connection can be through a single bond (in this case, a carbazole ring is formed), or through -O-, -S-, -N (R ⁷¹ ) -, -C (R ⁷² ) (R ⁷³ ) -, -Si (R ⁷⁴ ) (R ⁷⁵ ) - and other connecting groups. Here, R ⁷¹ to R ⁷⁵ represent a hydrogen atom or a substituent, and R ⁷² and R ⁷³ and R ⁷⁴ and R ⁷⁵ may be connected to each other to form a cyclic structure. Examples of the aryl group of the "substituted aminoaryl group" include a group in which one hydrogen atom is removed from the aromatic ring exemplified as an example of the A ring of the general formula (I).

Examples of the conjugated linking group include aromatic hydrocarbon groups and heteroaromatic groups. For a description, preferred range, and specific examples of the aromatic hydrocarbon ring (aromatic ring) constituting the aromatic hydrocarbon group, please refer to the description of the aromatic ring in the A ring of the general formula (I), etc., and for the description of the aromatic ring constituting the heteroaromatic group For the description, preferred range, and specific examples of the heteroaromatic ring (heteroaromatic ring), please refer to the description of the heteroaromatic ring in the A ring of the above-mentioned general formula (I), etc. Regarding the valency of the aromatic hydrocarbon group and the heteroaromatic group, when the number of substitutable hydrogen atoms of the corresponding aromatic hydrocarbon ring or heteroaromatic ring is n, each can be selected from an integer of 2 or more and n or less. . For example, the valence of the aromatic hydrocarbon group composed of a benzene ring is selected from an integer of 2 to 6.

Moreover, as a preferable example of a conjugated coupling group, the coupling group represented by the following general formula (III) can be mentioned.

[Chemical formula 6]

In the general formula (III), R ⁸¹ to R ⁸⁵ each independently represent the bonding position of a donor group or an acceptor group. It is preferable that R ⁸¹ and R ⁸³ are bonded with donor groups, and it is more preferable that R ⁸² , R ⁸⁴ and R ⁸⁵ are bonded with acceptor groups. Preferable examples of the donor group bonded to R ⁸¹ and R ⁸³ include a substituted aminoaryl group. Preferable examples of the acceptor group bonded to R ⁸² include an alkoxycarbonyl group (for example, an alkoxycarbonyl group having 2 to 25 carbon atoms). Examples of the acceptor group bonded to R ⁸⁴ and R ⁸⁵ include Preferable examples of the acceptor group include a halogen atom (for example, a fluorine atom).

＜Laser oscillation material＞ The laser oscillation material of the present invention contains the delayed fluorescent material of the present invention. For a description of the delayed fluorescent material of the present invention, please refer to the description in the above column of <Delayed Fluorescent Material>. By satisfying equation (1), the delayed fluorescent material of the present invention can suppress the light loss caused by the absorption of the excited triplet state during the laser oscillation process, thereby enabling the laser oscillation to continue for a long time. Therefore, the delayed fluorescent material of the present invention is highly useful as a laser oscillation material, and is particularly suitable as a laser oscillation material for CW laser. The laser oscillation material may only be composed of delayed fluorescent materials that satisfy equation (1), or may include other components.

＜Laser Components＞ The laser element of the present invention uses the delayed fluorescent material of the present invention. For a description of the delayed fluorescent material of the present invention, please refer to the description in the above column of <Delayed Fluorescent Material>. In the laser element of the present invention, it is preferable to use a delayed fluorescent material that satisfies formula (1) as the laser oscillation material constituting the gain medium. This makes it possible to realize a laser element with a long duration of laser oscillation. The laser element of the present invention can be a liquid laser in which the gain medium is liquid, or a solid-state laser in which the gain medium is solid (active layer). Furthermore, the laser element of the present invention may be a light-excited laser element that radiates laser light by irradiating the gain medium with excitation light, or may be generated by injecting holes and electrons into the gain medium and recombination of these. The energy radiation laser light is a current-excited laser element. The photoexcited laser element has a structure in which at least an active layer (gain medium) is formed on a substrate. Furthermore, the current excitation type laser element has a structure including at least an anode, a cathode, and an organic layer formed between the anode and the cathode. The organic layer may include at least an active layer (gain medium), may include only the active layer, or may include one or more organic layers in addition to the active layer. Examples of such other organic layers include a hole transport layer, a hole injection layer, an electron blocking layer, a hole blocking layer, an electron injection layer, an electron transport layer, an exciton blocking layer, and the like. The hole transport layer can be a hole injection transport layer with a hole injection function, and the electron transport layer can be an electron injection transport layer with an electron injection function. As a specific structural example of a laser element, there can be mentioned a structure in which substrate/anode/hole injection layer/hole transport layer/active layer/electron transport layer/cathode are laminated in this order. In a current-excited laser element, the laser light generated in the active layer can be taken out to the outside through the anode, the cathode can be taken out to the outside, the anode and the cathode can be taken out to the outside, or it can be taken out from the organic layer. The end face is taken out to the outside. Furthermore, each of the photoexcitation type and current excitation type laser elements may further include an optical resonator that amplifies the induced emission light from the active layer at a specific wavelength. Each component and each layer of the current excitation laser element will be described below. In addition, the description of the substrate and active layer also corresponds to the substrate and active layer of the photo-excited laser element.

(Substrate) The laser element of the present invention is preferably supported on a substrate. As the substrate, when the laser element has a structure that takes out the laser light from the substrate side, it is preferable to use a substrate that is translucent to the laser light, and it is preferable to use a transparent substrate including glass, transparent plastic, quartz, etc. On the other hand, when the laser element is configured to take out laser light from the side opposite to the substrate, the substrate is not particularly limited. In addition to the above-mentioned transparent substrate, substrates including silicon, paper, and cloth can also be used.

(Anode) As the anode in the laser element, metals, alloys, conductive compounds, and mixtures thereof with a large work function (4 eV or more) can be preferably used as electrode materials. Specific examples of such electrode materials include metals such as Au, conductive transparent materials such as CuI, indium tin oxide (ITO), SnO ₂ , ZnO, and TiN. In addition, amorphous materials capable of producing transparent conductive films such as IDIXO (In ₂ O ₃ -ZnO) can be used. The anode can be formed by depositing the electrode materials into a film by evaporation, sputtering or other methods. In addition, on the formed thin film, a pattern of a desired shape can be formed by photolithography to serve as an anode. Alternatively, when pattern accuracy is not required (about 100 μm or more), the above-mentioned electrode material can be vapor-deposited. , the pattern is formed through a mask of the desired shape during sputtering. Alternatively, when a material that can be coated such as an organic conductive compound is used, a wet film-forming method such as a printing method or a coating method can also be used. However, in the case where the laser element has a structure that transmits the anode and extracts the laser light, the anode needs to be translucent to the laser light. The transmittance of the laser light is preferably greater than 1%, and the transmittance of the laser light is greater than 10%. Better. Specifically, it is preferable to use the above-mentioned conductive transparent material for the anode, or to use a thin film of metal or alloy with a thickness of 10 to 100 nm for the anode. The sheet resistance of the anode is preferably several hundred Ω/□ or less. Furthermore, the film thickness also depends on the material, but is usually selected within the range of 10 to 1000 nm, preferably 10 to 200 nm.

(Cathode) On the other hand, as the cathode, a metal having a smaller work function than the material used for the anode (called an electron-injecting metal), an alloy, a conductive compound, or a mixture thereof can be used as the electrode material. Specific examples of such electrode materials include sodium, sodium-potassium alloy, magnesium, lithium, magnesium/copper mixture, magnesium/silver mixture, magnesium/aluminum mixture, magnesium/indium mixture, aluminum/aluminum oxide (Al ₂ O ₃ ) mixtures, indium, lithium/aluminum mixtures, rare earth metals, etc. Among these, a mixture of an electron-injecting metal and a second metal having a larger and more stable work function value than the electron-injecting metal, such as a magnesium/silver mixture, is used from the viewpoint of electron injection properties and durability against oxidation, etc. , magnesium/aluminum mixture, magnesium/indium mixture, aluminum/aluminum oxide (Al ₂ O ₃ ) mixture, lithium/aluminum mixture, aluminum, etc. are suitable. The cathode can be formed by depositing the electrode materials into a film by evaporation, sputtering or other methods. However, in the case where the laser element has a structure that transmits the cathode and extracts the laser light, the cathode needs to be transparent to the laser light. The transmittance of the laser light is preferably greater than 1%, and the transmittance of the laser light is greater than 10%. Better. Specifically, it is preferable to use a thin film of the above electrode material with a thickness of 10 to 100 nm for the cathode. The sheet resistance of the cathode is preferably several hundred Ω/□ or less, and the film thickness is usually selected in the range of 10 nm to 5 μm, preferably 50 to 200 nm.

(active layer) The active layer is a layer that causes induced emission after recombination of holes and electrons injected from the anode and cathode to generate excitons, forming an inversion distribution. The active layer may be composed only of the laser oscillation material, but preferably includes the laser oscillation material and the host material. As the laser oscillation material, one or two or more types selected from delayed fluorescent materials that satisfy equation (1) can be used. In order to further reduce the critical current density of the laser element of the present invention, it is important to limit the singlet excitons and triplet excitons generated in the laser oscillation material to the laser oscillation material. Therefore, it is preferable to use a host material in addition to the laser oscillation material in the active layer. As the host material, an organic compound having at least one of an excited singlet energy and an excited triplet energy higher than that of a delayed fluorescent material used as a laser oscillation material can be used. As a result, the singlet excitons and triplet excitons generated in the laser oscillation material can be confined in the molecules of the laser oscillation material, and the critical current density for generating laser oscillation can be reduced. However, even if the singlet excitons and triplet excitons cannot be sufficiently confined, it may still contribute to lowering the critical value and improving the laser characteristics. Therefore, as long as the system can achieve lowering the critical value and improving the laser characteristics. The host material can be used in the present invention without particular limitations. In the laser element of the present invention, the light induced by the laser oscillation material becomes laser light by the action of the optical resonator and the like and is emitted to the outside. The light emitted by the laser element may include natural emission light from the laser oscillation material, natural emission amplified light, or light emitted from the host material, but it is better if laser light is the main component. When a host material is used, the amount of the delayed fluorescent material used for the laser oscillation material in the active layer is preferably 0.1% by weight or more, more preferably 1% by weight or more, and 50% by weight or less. Preferably, it is 25% by weight or less, more preferably 20% by weight or less, still more preferably 20% by weight or less, and particularly preferably 15% by weight or less. As the host material in the active layer, organic compounds that have hole-transporting capabilities, electron-transporting capabilities, prevent long-wavelength emission of light, and have a high glass transition temperature are preferred.

(injection layer) The injection layer refers to the layer placed between the electrode and the organic layer in order to reduce the driving voltage and increase the luminous brightness. There are hole injection layers and electron injection layers, which can exist between the anode and the active layer or hole transport layer, and Between the cathode and the active layer or electron transport layer. The injection layer can be configured as needed.

(barrier layer) The barrier layer is a layer that can block charges (electrons or holes) and/or excitons existing in the active layer from diffusing out of the active layer. The electron blocking layer can be disposed between the active layer and the hole transport layer to block electrons from passing towards the hole transport layer and passing through the active layer. Similarly, the hole blocking layer can be disposed between the active layer and the electron transport layer to block holes from passing through the active layer towards the electron transport layer. The barrier layer can also serve to block the diffusion of excitons to the outside of the active layer. That is, the electron blocking layer and the hole blocking layer can each also serve as an exciton blocking layer. The electron blocking layer or exciton blocking layer mentioned in this specification is used in the sense of including a layer having the functions of an electron blocking layer and an exciton blocking layer.

(hole blocking layer) The hole blocking layer has the function of an electron transport layer in a broad sense. The hole blocking layer has the function of transporting electrons and blocking holes from reaching the electron transport layer, thereby increasing the probability of recombination of electrons and holes in the active layer. As the material of the hole blocking layer, the material of the electron transport layer described below can be used if necessary.

(electron blocking layer) The electron blocking layer has the function of transporting holes in a broad sense. The electron blocking layer has the function of transporting holes and blocking electrons from reaching the hole transport layer, thereby increasing the probability of recombination of electrons and holes in the active layer.

(Exciton blocking layer) The exciton blocking layer refers to a layer that blocks the excitons generated by the recombination of holes and electrons in the active layer from diffusing to the charge transport layer. By inserting this layer, the excitons can be effectively confined in the active layer. Within the layer, the luminous efficiency of the element can be improved. The exciton blocking layer can be inserted into either the anode side or the cathode side adjacent to the active layer, or both can be inserted at the same time. That is, when there is an exciton blocking layer on the anode side, the hole transport layer and the active layer can be inserted adjacent to the active layer. When it is inserted on the cathode side, the hole transport layer can be inserted between the active layer and the cathode. This layer is inserted adjacent to the active layer. Furthermore, a hole injection layer, an electron blocking layer, etc. can be provided between the anode and the exciton blocking layer adjacent to the anode side of the active layer, and between the cathode and the exciton blocking layer adjacent to the cathode side of the active layer. , can have an electron injection layer, an electron transport layer, a hole blocking layer, etc. When a barrier layer is provided, it is preferable that at least one of the excited singlet energy and the excited triplet energy of the material used as the barrier layer is higher than the excited singlet energy and excited triplet energy of the laser oscillation material.

(hole transport layer) The hole transport layer includes a hole transport material with the function of transporting holes. The hole transport layer can be provided with a single layer or multiple layers. The hole transport material has either injection or transport properties of holes or barrier properties for electrons, and may be either an organic substance or an inorganic substance. Examples of known hole transport materials that can be used include triazole derivatives, oxadiazole derivatives, imidazole derivatives, carbazole derivatives, indolocarbazole derivatives, and polyarylalkane derivatives. Pyrazoline derivatives and pyrazolone derivatives, phenylenediamine derivatives, aromatic amine derivatives, amino-substituted chalcone derivatives, ethazole derivatives, styrene scallion derivatives, quinone derivatives, hydrazones Derivatives, stilbene derivatives, silazane derivatives, aniline copolymers and conductive polymer oligomers, especially thiophene oligomers, etc. However, porphyrin compounds, aromatic tertiary amine compounds and styrylamines are used It is preferable to use an aromatic tertiary amine compound.

(electron transport layer) The electron transport layer contains a material with the function of transporting electrons, and the electron transport layer can be provided with a single layer or multiple layers. As an electron transport material (sometimes also used as a hole blocking material), it only needs to have the function of transferring electrons injected from the cathode to the active layer. Examples of the electron transport layer that can be used include nitro-substituted fluorine derivatives, diphenylquinone derivatives, thiopyran dioxide derivatives, carbodiimides, and fluorylidenemethane derivatives. Anthraquinone dimethane and anthrone derivatives, oxadiazole derivatives, etc. Furthermore, among the above-mentioned 㗁adiazole derivatives, thiadiazole derivatives in which the oxygen atom of the 㗁adiazole ring is substituted with a sulfur atom, and quintiline derivatives having a quintiline ring known as an electron-withdrawing group can also be used. As electron transmission material. Furthermore, a polymer material in which these materials are introduced into a polymer chain or used as a main chain of a polymer can also be used.

(Optical resonator) The optical resonator has the function of amplifying the induced emission light from the active layer through resonance to generate laser light. The optical resonator can be a distributed feedback (DFB) optical resonator that reflects light from a diffraction grating, a distributed reflection (DBR) optical resonator, or it can be composed of mirrors and partial mirrors arranged to face each other. Brimpero type optical resonator. The diffraction grating constituting the resonator only needs to be disposed adjacent to the layer constituting the waveguide. It may be disposed between the active layer and its adjacent layer (organic layer or electrode), or between organic layers other than the active layer. Between organic layers other than the active layer and electrodes. In a Fabry-Perot type optical resonator, the reflectivity of the reflecting mirror is preferably about 100%, and the reflectivity of the partial reflecting mirror is preferably 50 to 95%. Thereby, the partial reflecting mirror also functions as an output mirror, and laser light can be extracted from the side of the partial reflecting mirror. When a Fabry-Perot type optical resonator is used, the anode and the cathode can have the function of a reflector or a partial reflector, or the reflector and the partial reflector can be provided separately.

The laser element as described above radiates laser light by flowing a current exceeding a critical value current density between the anode and the cathode. At this time, in the laser element of the present invention, by including a delayed fluorescent material that satisfies equation (1), the absorption of the excited triplet state caused by triplet accumulation is suppressed, so that laser oscillation can be sustained for a long period of time.

When producing the laser element of the present invention, the film forming method of each layer constituting the laser element is not particularly limited, and can be produced by either a dry process or a wet process.

<Evaluation method of delayed fluorescent material> The evaluation method of the present invention includes a step (measurement step) of measuring σ _em , σ _TT , k _ISC , and k _RISC of the delayed fluorescent material. The delayed fluorescent material used for measuring each parameter (σ _em , σ _TT , k _ISC , k _RISC ) can be selected from the compound group as delayed fluorescent material described in the above column (Chemical Structure of Delayed Fluorescent Material), for example. Select in. For the definition of delayed fluorescent material, the definition of each parameter and the measurement method, you can refer to the corresponding description in the above column "Delayed fluorescent material". Hereinafter, the first and second embodiments of the evaluation method of the present invention will be described.

(First Embodiment of Evaluation Method) The evaluation method of the first embodiment includes a step of determining whether σ _em , σ _TT , k _ISC , and k _RISC measured in the measurement step satisfy the equation (1) (judgment step). ). Regarding the formula (1), please refer to the description of the formula (1) in the column of <Delayed Fluorescent Material> mentioned above. The evaluation method of the first embodiment includes a step of evaluating a delayed fluorescent material that is judged to satisfy equation (1) in the judgment step to be useful as a laser oscillation material (first evaluation step), and a step of sorting and judging in the judgment step. It is preferable that at least one of the steps (sorting step) of the delayed fluorescent material satisfy the formula (1). As shown in the "Delayed Fluorescent Material" column above, in the delayed fluorescent material that satisfies equation (1), laser oscillation continues for a long time. Therefore, by performing the above steps, delayed fluorescent materials that can perform laser oscillation for a long time can be identified using a simple calculation formula, and delayed fluorescent materials can be easily screened.

(Second Embodiment of Evaluation Method) The evaluation method of the second embodiment includes calculating the difference Δ represented by the following formula (2) using σ _em , σ _TT , k _ISC , and k _RISC measured in the measurement step. steps (calculation steps). σ _em , σ _TT , k _ISC , k _RISC of formula (2) have the same meaning as the corresponding parameters of formula (1).

[Formula 10] Formula (2)

The larger the difference Δ calculated from equation (2) is, the more reliable the laser oscillation is for a long period of time, and the higher the usefulness as a laser oscillation material. Therefore, by calculating the difference Δ, the laser oscillation sustaining performance of the delayed fluorescent material can be quantitatively evaluated. The evaluation method of the second embodiment includes a step of highly evaluating a delayed fluorescent material with a large difference Δ based on the difference Δ calculated in the calculation step (second evaluation step), and accumulating the chemical structure of the delayed fluorescent material. At least one of the steps (accumulation steps) related to the difference Δ is preferred. The second evaluation step may include a process of repeating the following steps: comparing the difference Δ between two delayed fluorescent materials, highly evaluating the delayed fluorescent material with the larger difference Δ, and then comparing the difference between the highly evaluated delayed fluorescent materials. The difference Δ between the quantity Δ and another delayed phosphor material is Δ, and the delayed phosphor material with a larger difference Δ is more highly evaluated. Furthermore, the second evaluation step may include a step of setting a difference Δ as a reference (standard Δ) and highly evaluating a delayed fluorescent material whose difference Δ is larger than the reference Δ. In the accumulation step, examples of the delayed fluorescent material group to be accumulated include a delayed fluorescent material group having a common specific partial structure, a delayed fluorescent material group having a specific donor group, A group of delayed fluorescent materials with specific acceptor groups and a group of delayed fluorescent materials with boron-containing polycyclic aromatic skeletons with multiple resonance effects. By performing the accumulation process, it is possible to identify the partial structure, donor group, and acceptor group that tend to increase the difference Δ of the delayed fluorescent material, and in "boron-containing polycyclic aromatic compounds with multiple resonance effects, "Skeleton Delayed Fluorescent Material", the characteristics of the structure showing a tendency to increase the difference Δ can be understood. For an explanation of the delayed fluorescent material having a donor group and an acceptor group and a boron-containing polycyclic aromatic skeleton with multiple resonance effects, please refer to the description in the (Chemical Structure of Delayed Fluorescent Material) column. In addition, when the evaluation method of the second embodiment includes an accumulation step, it may further include a step of predicting the relationship between the chemical structure of the new delayed fluorescent material and the difference Δ using the relationship accumulated in the accumulation step (first step). Prediction step), the step of using the cumulative relationship to predict the chemical structure of the delayed fluorescent material with a large difference Δ (the second prediction step), and using the cumulative relationship to predict the chemistry of the delayed fluorescent material that satisfies the formula (1) At least 1 step in the structure step (3rd prediction step). For example, in the first prediction step, when the difference Δ between delayed fluorescent materials having a specific partial structure is within the range of A±α in a cumulative relationship, it is possible to predict a new group of delayed fluorescent materials having the same partial structure. The difference Δ of the delayed fluorescent material is also within the range of A±α. Furthermore, in the second prediction step and the third prediction step, the chemistry of the delayed fluorescent material including a donor group, an acceptor group, and a partial structure that tend to increase the difference Δ of the delayed fluorescent material can be The structure is predicted to be a chemical structure of a delayed fluorescent material with a large difference Δ or a chemical structure of a delayed fluorescent material that satisfies formula (1). Here, the predicted chemical structure may include only any one of a donor group, an acceptor group, and a partial structure showing a tendency to increase the difference Δ, or may include a structure showing an increase in the difference Δ. Two or more of the preferred donor groups, acceptor groups, and partial structures.

Furthermore, the evaluation method of the second embodiment may further include each step of the first embodiment. In this case, the evaluation method of the second embodiment may include only a part of the steps described in the above column (First Embodiment of Evaluation Method), or may include all of them.

＜Design methods for delayed fluorescent materials, laser oscillation materials and laser components＞ The characteristic of the design method of delayed fluorescent materials, laser oscillation materials and laser elements of the present invention is that the evaluation method of the present invention is used. Regarding the evaluation method of the present invention, please refer to the description in the above column "Evaluation Method of Delayed Fluorescent Material". In the method for designing delayed fluorescent materials of the present invention, for example, molecularly designed delayed fluorescent materials can be screened using the evaluation method of the first embodiment. Thereby, a delayed fluorescent material with a long laser oscillation duration can be easily identified from a molecularly designed delayed fluorescent material group. Furthermore, in the method for designing a delayed fluorescent material of the present invention, in the evaluation method of the second embodiment, it is possible to have a chemical structure of "a delayed fluorescent material with a large difference Δ" predicted in the second prediction step. , carry out molecular design of the delayed fluorescent material according to the chemical structure of the "delayed fluorescent material satisfying formula (1)" predicted in the third prediction step. Furthermore, the method for designing a laser oscillation material and a laser element of the present invention may include the following steps: using the delayed fluorescent material designed in the method for designing a delayed fluorescent material of the present invention as a laser oscillation material. In the design method of the laser element, the design other than the laser oscillation material can be carried out by referring to the structure described in the <Laser Element> column above.

<Database> The first database of the present invention is a database that accumulates relationships between the chemical structure of delayed fluorescent materials and σ _em , σ _TT , k _ISC , and k _RISC . The second database of the present invention is a database that accumulates the relationship between the chemical structure of the delayed fluorescent material and the difference Δ. The third database of the present invention is a database that accumulates chemical structures of delayed fluorescent materials that satisfy formula (1). For the chemical structure of the delayed fluorescent material, you can refer to the description in the above (Chemical Structure of the Delayed Fluorescent Material) column. For the definitions of formula (1) and σ _em , σ _TT , k _ISC , k _RISC , you can refer to the above < Delayed fluorescent materials> column. Regarding the difference Δ, refer to the description in the above (Second Embodiment of Evaluation Method) column. The database of the present invention can be recorded on a recording medium so that it can be read by a computer. The recording medium may be any of a magnetic recording medium, an optical recording medium, and a semiconductor memory. Specific examples include a flexible disk, a hard disk, an optical disk, a magneto-optical disk, and a CD-ROM (Read Only Memory). (body), CD-R, DVD-ROM, magnetic tape, non-volatile memory card, ROM, EEPROM, silicon disk, etc.

The database of the present invention can be used to implement the evaluation method of the present invention, and the database of the present invention can be used to implement the design method of delayed fluorescent materials, laser oscillation materials and laser elements of the present invention. Regarding the methods of the present invention, please refer to the descriptions in the column "Evaluation Methods of Delayed Fluorescent Materials" and the descriptions in the column "Design Methods of Delayed Fluorescent Materials, Laser Oscillation Materials and Laser Elements".

＜Program (1st program)＞ The program (first program) of the present invention is a program for implementing the evaluation method of the present invention. That is, the program of the present invention is a program for causing a computer to execute each step included in the evaluation method of the present invention. Regarding the evaluation method of the present invention and its respective steps, please refer to the description in the above column "Evaluation Method of Delayed Fluorescent Material". The program of the present invention can be recorded on a recording medium so that it can be read by a computer. For descriptions and specific examples of recording media, please refer to the corresponding records in the <Database> column above.

<Method of shortening the time until the laser operation reaches the stable state> The method of the present invention is a method of shortening the time until the laser operation reaches the stable state, and includes the following steps: converting a laser with a higher k _RISC and satisfying the equation (1) Delayed fluorescent materials are used in laser components. For the definitions of delayed fluorescent materials and k _RISC that satisfy equation (1), you can refer to the description in the above <Delayed fluorescent material> column. Regarding the structure of the laser element, you can refer to the description in the above <Laser element> column. . In the present invention, "the time until the laser operation reaches a stable state" (hereinafter referred to as "the time for the laser operation to reach a stable state") refers to the time from when the relaxation oscillation converges to when the output becomes time until constant. However, when relaxation oscillation is not observed, the time from the start of laser oscillation until the output becomes constant is the "stable state attainment time of the laser operation." If delayed fluorescent materials with higher k _RISC and satisfying equation (1) are used in laser components, the time to reach the steady state is shortened, the laser output reaches the steady state in advance, and stable laser operation can be achieved. Below, it is verified that such an effect can be obtained by using DABNA-2 for the simulation of the delayed fluorescent material model. In the following structural formula, Ph represents a phenyl group. The velocity constants of DABNA-2 are k _r =1.7x10 ⁸ (s ^-1 ), k _ISC =1x10 ⁸ (s ^-1 ), k _RISC =1x10 ⁴ (s ^-1 ), σ _em =9.1x10 ^-17 (cm ² ), σ _TT =0.

[Chemical Formula 7]

Regarding the case where k _r =1.7x10 ⁸ (s ^-1 ) and k _ISC =1x10 ⁸ (s ^-1 ) are set, k _RISC is changed within the range of 5×10 ³ to 1×10 ⁹ (s ^-1 ). When k _RISC is changed to 1×10 ⁹ (s ^-1 ) or 1×10 ⁹ (s ^-1 ), the results of simulating the time change of the photon density after excitation are shown in Figures 6 and 7 respectively. In addition, the relationship between the steady state duration ω and k _RISC calculated based on the simulation results in Figure 6 is shown in Figure 8 . In Figure 8, the dashed line is the plotted fit curve. The rate equation obtained by the Euler method of this fitting curve is y=1E×10x ^-1.231 . As shown in Fig. 8, it is found that the steady state reaching time ω becomes shorter as k _RISC becomes larger, and when k _RISC becomes 1×10 ⁷ s ^-1 or more, ω becomes approximately 0. In addition, as shown in Fig. 7, when k _RISC becomes 1×10 ⁹ s ^-1 or more, the relaxation oscillation is significantly reduced. Based on the simulation results, it was confirmed that by using a delayed fluorescent material that has a higher k _RISC and satisfies equation (1) for the laser element, the time for the laser operation to reach a stable state is shortened and the laser operation is stabilized in advance. Furthermore, it was confirmed that in the delayed fluorescent material used for the laser element in the method of the present invention, k _RISC is preferably 1×10 ⁷ s ^-1 or more, more preferably 1×10 ⁸ s ^-1 or more, and 1 It is more preferable that it is ×10 ⁹ s ^-1 or more, and it is also preferable that it satisfies the following formula (1a).

[Formula 11] Formula (1a) k _ISC : The intersystem crossing velocity from the excited singlet state to the excited triplet state k _RISC : The inverse intersystem crossing velocity from the excited triplet state to the excited singlet state

<Design method of laser element with short time to reach stable state of laser operation> The method of designing the laser element of the present invention is to shorten the time until the time of laser operation to reach stable state (the time to achieve stable state of laser operation). The design method of the emissive element, and includes: the step of selecting one delayed fluorescent material from a group including at least two delayed fluorescent materials that satisfy the following formula (1) according to the k _RISC of the delayed fluorescent material (selecting Step); and the step of applying the selected delayed fluorescent material to the laser element (application step). For the definitions of delayed fluorescent materials and k _RISC that satisfy equation (1), you can refer to the records in the <Delayed Fluorescent Materials> column above. For the structure of the designed laser element, you can refer to the <Laser Elements> column above. column records. In the design method of the present invention, when selecting a delayed fluorescent material from a group including delayed fluorescent materials that satisfy equation (1), the retardation with the highest k _RISC among the delayed fluorescent materials constituting the group is selected. Fluorescent materials are preferred. As explained in the above column "Methods to shorten the stable state arrival time of laser operation", if a delayed fluorescent material with a higher k _RISC and satisfying equation (1) is used for a laser element, the laser The time to reach the steady state of the action is shortened. Therefore, by using the delayed fluorescent material selected in this way for a laser element, it is possible to design a laser element that takes a short time to reach a stable state of the laser operation and stabilizes the laser operation in advance.

＜Program (2nd program)＞ The program (second program) of the present invention is to implement the "method of shortening the time until the laser operation reaches the stable state" of the present invention or the "design method of the laser element with short time until the laser operation reaches the stable state" of the present invention. ” program. That is, the program of the present invention is a program used to cause a computer to execute each step included in each method of the present invention. Regarding each method and each step of the present invention, please refer to the description in the above column "Method to shorten the time to reach the steady state of the laser operation" and the above "Design of a laser element with a short time to reach the steady state of the laser operation". Record in the Method> column. The program of the present invention can be recorded on a recording medium so that it can be read by a computer. For descriptions and specific examples of recording media, please refer to the description in the <Database> column above.

<Modifications of the present invention> In addition, at least one of the following formulas (3) to (6) can be used instead of formula (1) or formula (2).

[Formula 12] Formula (3) σ _em (induced emission cross-sectional area) > σ _TT (absorption cross-sectional area of the excited triplet state)

[Formula 13] Formula (4) k _RISC (Inverse intersystem crossing speed from excited triplet state to excited singlet state) > k _ISC (Intersystem crossing speed from excited singlet state to excited triplet state)

[Formula 14] Formula (5) Δ=σ _em (induced emission cross-sectional area) >σ _TT (absorption cross-sectional area of the excited triplet state)

[Equation 15] Formula (6) Δ=k _RISC (Inverse intersystem crossing speed from excited triplet state to excited singlet state) > k _ISC (Intersystem crossing speed from excited singlet state to excited triplet state) )

Furthermore, equations (3) to (6) can also be combined appropriately. Furthermore, "σ _em (induced emission cross-sectional area)", "σ _TT (absorption cross-sectional area of the excited triplet state)" and "k _RISC (from the excited triplet state)" that constitute formulas (1) to (6) can also be used. The inverse intersystem crossing speed from the excited singlet state to the excited singlet state) "k _ISC (the intersystem crossing speed from the excited singlet state to the excited triplet state)""Δ".

[Industrial availability] The delayed fluorescent material satisfying formula (1) of the present invention is useful as a laser oscillation material. By using the delayed fluorescent material of the present invention, a laser element with a long duration of laser oscillation can be realized. Furthermore, by utilizing this relational expression, screening of delayed fluorescent materials, molecular design, and laser element design can also be performed. Therefore, the present invention has high industrial applicability.

Figure 1 is a diagram showing the chemical structures, energy level diagrams and energy transfer processes of CBP and TPA-BCm. Figure 2 is a graph obtained by simulating the time changes of the intersystem crossing efficiency (Φ _ISC ) and induced emission efficiency (Φ _Stim ) of the CBP-TADF element model. Figure 2 (a) sets the excitation light intensity to 5kWcm ⁻² As for the time change of each efficiency calculated, Figure 2(b) shows the time change of each efficiency calculated by setting the excitation light intensity to 10kWcm ⁻² . Figure 3 is a graph obtained by simulating the laser characteristics of the CBP-TADF element model. Figure 3 (a) is a plot of the luminous intensity relative to the excitation light intensity and its fitting line. Figure 3 (b) is a k _RISC Time changes of the gain coefficient when set to 1.0×10 ⁸ s ^-1 . Figure 3(c) shows k _RISC set to 1.0×10 ⁴ s ^-1 , 1.0×10 ⁷ s ^-1 and 1.0×10 ⁸ s ^- Time variation of the gain coefficient at ¹ . FIG. 4 is a graph showing the wavelength dependence of σ _em and σ _TT of TPA-BCm. Figure 5 shows the transient PL curve (solid line) and its fitting curve measured at various excitation light intensities of 6W/cm ² , 31W/cm ² and 57W/cm ² for a 6 wt% TPA-BCm doped CBP film. (dashed line) graph. Figure 6 shows that k _r is set to 1.7x10 ⁸ (s ^-1 ), k _ISC is set to 1x10 ⁸ (s ^-1 ), and k _RISC is set to 5×10 ³ to 1×10 ⁹ (s ^-1 ). Within the range, the curve obtained by simulating the time change of photon density after excitation. Figure 7 shows that k _r is set to 1.7x10 ⁸ (s ^-1 ), k _ISC is set to 1x10 ⁸ (s ^-1 ), and k _RISC is set to 1×10 ⁹ or 1×10 ⁹ (s ^-1 ). , a curve obtained by simulating the time change of photon density after excitation. FIG. 8 is a graph showing the relationship between the steady state duration ω and k _RISC calculated based on the simulation results in FIG. 6 .

Claims (45)

A delayed fluorescent material that satisfies the following formula (1), [Formula 1] Formula (1) σ _em : Induced emission cross-sectional area σ _TT : Absorption cross-sectional area k of the excited triplet state _ISC : Intersystem crossing speed k from the excited singlet state to the excited triplet state _RISC : From the excited triplet state to the excited singlet state Inverse intersystem crossing speed. The delayed fluorescent material as described in claim 1, wherein the energy difference ΔE _ST between the lowest excited singlet state and the lowest excited triplet state at 77K is less than 0.3 eV. The delayed fluorescent material as described in claim 1, wherein the energy difference ΔE _ST between the lowest excited singlet state and the lowest excited triplet state at 77K is less than 0.2 eV. The delayed fluorescent material as described in claim 1, wherein the energy difference ΔE _ST between the lowest excited singlet state and the lowest excited triplet state at 77K is less than 0.1 eV. The delayed fluorescent material as described in claim 1, wherein k _RISC is 1×10 ⁶ sec ^-1 or more. The delayed fluorescent material as described in claim 1, wherein k _RISC is 1×10 ⁷ s ^-1 or more. The delayed fluorescent material of claim 1, which is composed only of atoms selected from the group consisting of carbon atoms, hydrogen atoms, nitrogen atoms, oxygen atoms, sulfur atoms, boron atoms, silicon atoms, phosphorus atoms and fluorine atoms. composition. The delayed fluorescent material described in claim 1 has a boron-containing polycyclic aromatic skeleton with multiple resonance effects. The delayed fluorescent material according to claim 1, which has a donor group and an acceptor group. A laser oscillation material containing the delayed fluorescent material described in any one of claim 1 to claim 9. A laser element using the delayed fluorescent material according to any one of claims 1 to 9. The laser element according to claim 11, which is a current driven type. The laser component as described in claim 11 is a solid-state laser component. An evaluation method for delayed fluorescent materials, which includes the following steps: measuring σ _em , σ _TT , k _ISC , and k _RISC of the delayed fluorescent materials. The evaluation method of delayed fluorescent material as described in claim 14, which includes the following steps: measuring σ _em , σ _TT , k _ISC , and k _RISC of the delayed fluorescent material, and determining whether the aforementioned formula (1) is satisfied. The evaluation method for delayed fluorescent materials as described in claim 15, wherein When the above formula (1) is satisfied, it is evaluated that it is useful as a laser oscillation material. The evaluation method for delayed fluorescent materials as described in claim 15, wherein Sort delayed fluorescent materials that satisfy the aforementioned formula (1). The evaluation method of delayed fluorescent material as described in claim 14, which includes the following steps: measuring σ _em , σ _TT , k _ISC , and k _RISC of the delayed fluorescent material, and calculating the difference represented by the following formula (2) Δ, [Formula 2] Formula (2) . The evaluation method for delayed fluorescent materials as described in claim 18, wherein Those with a large difference Δ are highly evaluated. The evaluation method for delayed fluorescent materials as described in claim 18, wherein The relationship between the chemical structure of the cumulative delayed fluorescent material and the difference Δ. The evaluation method for delayed fluorescent materials as described in claim 20, wherein The relationship between the chemical structure of the new delayed fluorescent material and the difference Δ is predicted using the accumulated aforementioned relationships. The evaluation method for delayed fluorescent materials as described in claim 20, wherein The accumulated aforementioned relationships are used to predict the chemical structure of the delayed fluorescent material with a large difference Δ. The evaluation method for delayed fluorescent materials as described in claim 20, wherein The chemical structure of the delayed fluorescent material satisfying the aforementioned formula (1) is predicted using the accumulated aforementioned relationships. The evaluation method for delayed fluorescent materials as described in claim 21, wherein The delayed fluorescent materials to be accumulated are a group of delayed fluorescent materials having a common specific partial structure. The evaluation method for delayed fluorescent materials as described in claim 21, wherein The delayed fluorescent materials to be accumulated are a group of delayed fluorescent materials having a specific donor group. The evaluation method for delayed fluorescent materials as described in claim 21, wherein The delayed fluorescent materials to be accumulated are a group of delayed fluorescent materials having a specific acceptor group. The evaluation method for delayed fluorescent materials as described in claim 21, wherein The delayed fluorescent materials targeted for accumulation are a group of delayed fluorescent materials having a boron-containing polycyclic aromatic skeleton with multiple resonance effects. A method for designing delayed fluorescent materials using the evaluation method described in any one of claims 14 to 27. A method for designing a laser oscillation material using the evaluation method described in any one of claims 14 to 27. A method for designing a laser element using the evaluation method described in any one of claims 14 to 27. A database that accumulates the relationship between the chemical structure of delayed fluorescent materials and σ _em , σ _TT , k _ISC , and k _RISC . A database that accumulates the relationship between the chemical structure of the delayed fluorescent material described in claim 20 and the difference Δ. A database that accumulates chemical structures of delayed fluorescent materials that satisfy the aforementioned formula (1). An evaluation method for delayed fluorescent materials, which uses the database described in any one of claims 31 to 33 and implements the evaluation method described in any one of claims 14 to 27. A method for designing delayed fluorescent materials, which utilizes the database described in any one of claims 31 to 33. A method for designing laser oscillation materials, which uses the database described in any one of claims 31 to 33. A method for designing a laser component using the database described in any one of claims 31 to 33. A program that implements the evaluation method described in any one of claims 21 to 27. _[ Formula 3] Formula (1) σ _em : Induced emission cross-sectional area σ _TT : Absorption cross-sectional area k of the excited triplet state _ISC : Intersystem crossing speed k from the excited singlet state to the excited triplet state _RISC : From the excited triplet state to the excited singlet state Inverse intersystem crossing speed. The method of claim 39, wherein the k _RISC of the delayed fluorescent material used for the laser element is 1×10 ⁷ s ^-1 or more. The method of claim 39, wherein the k _RISC of the delayed fluorescent material used for the laser element is 1×10 ⁸ s ^-1 or more. The method according to claim 39, wherein the delayed fluorescent material used for the laser element further satisfies the following formula (1a), [Formula 4] Formula (1a) k _ISC : The intersystem crossing speed from the excited singlet state to the excited triplet state k _RISC : The inverse intersystem crossing speed from the excited triplet state to the excited singlet state. A method for designing a laser element with a short time until the laser action reaches a stable state, which includes the following steps: Based on the k _RISC of the delayed fluorescent material, from including at least 2 elements that satisfy the following formula (1) Select one delayed fluorescent material from the group of delayed fluorescent materials; and use the selected delayed fluorescent material for the laser element, [Formula 5] Formula (1) σ _em : Induced emission cross-sectional area σ _TT : Absorption cross-sectional area k of the excited triplet state _ISC : Intersystem crossing speed k from the excited singlet state to the excited triplet state _RISC : From the excited triplet state to the excited singlet state Inverse intersystem crossing speed. The method of claim 43, wherein when selecting a delayed fluorescent material from the aforementioned group, the delayed fluorescent material with the highest k _RISC is selected. A program that implements the method described in any one of claims 39 to 44.