JP2002275460A - Luminescent material and el luminescent layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a luminescent material suitable for an EL device or the like capable of being driven at a high energy efficiency with intermolecular energy transfer using polysilane as a sender. SOLUTION: The luminescent material has a recurring unit comprising one or more kinds out of polysilane compounds expressed by any of the general structural formulae (wherein, R<1> and R<2> are each a 2-9C alkyl). In an EL luminescent layer produced by mixing a luminescent molecule having an absorption excitation spectrum identical or near to the luminescent spectrum of the polysilane compound with a polysilane compound, EL luminescence having a high luminescent efficiency is realized awing to intermolecular energy transfer of the polysilane compound.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light-emitting material used for an EL (electroluminescence) display panel, a surface-emitting lighting, and the like.

[0002]

2. Description of the Related Art An organic EL device utilizing a light emission phenomenon caused by recombination of holes and electrons reproduces an image by surface emission unlike a display panel using a liquid crystal which requires a backlight. The image is clearer than a liquid crystal display panel and can be easily identified even in a dark place. Therefore, it is attracting attention as a next-generation display device replacing liquid crystal. For the light emitting layer of the organic EL device, an organic light emitting material such as 8-hydroxyquinoline, a rare earth complex, or the like is used.
Although the luminous efficiency of the luminescent molecule itself such as a dye molecule is high, the energy efficiency as a whole is low because the transmission efficiency of the process of delivering electric energy supplied by energization to the luminescent molecule in the organic EL element is low.

[0003]

DISCLOSURE OF THE INVENTION The present invention has been devised to solve such a problem. The present invention utilizes polysilane as a sender and utilizes intermolecular energy transfer to improve the efficiency of transfer to luminescent molecules. It is an object of the present invention to provide a light emitting material suitable for an EL device or the like which can be driven with high energy efficiency.

In order to achieve the object, the luminescent material of the present invention is characterized in that the repeating unit comprises one or more polysilane compounds represented by any of the following general structural formulas. When an EL light-emitting layer is prepared by mixing a light-emitting molecule having an absorption / excitation spectrum that matches or approximates the light-emission spectrum of the polysilane compound with the polysilane compound, intermolecular energy transfer of the polysilane compound is used to achieve high luminous efficiency. EL emission becomes possible. Here, R ¹ and R ² represent an alkyl group having 2 to 9 carbon atoms.
Among them, a polysilane compound having an alkyl group having 4 to 9 carbon atoms is soluble and can be easily formed into a film. However, when a film is formed by vapor deposition, a polysilane compound having an alkyl group having 2 to 9 carbon atoms can be used. n is 2
An integer greater than or equal to 8 is set, and is preferably set to 8 or more.

[0005]

[Function] Polysilane has electrical conductivity (especially hole conductivity).
And is an excellent material as a hole transport layer, and can also conduct electrons. Further, since it is a one-dimensional chain polymer having high ultraviolet light emission efficiency and high resonance energy transfer efficiency, the use of resonance energy transfer can excite all light-emitting molecules of the three primary colors R, G, and B having lower energy than ultraviolet light.

[0006] Polysilane is a one-dimensional polymer in which Si atoms are connected in a chain, and specifically, polydihexylsilane (PDHS) and poly [bis (p-propoxyphenyl) -silane] (PBPPS) described below. , Poly [bis (m-butoxyphenyl) -silane] (PBBPS), poly [(m-hexyloxyphenyl) -phenylsilane] (PmHPPS), poly [(m-hexyloxyphenyl) -phenylsilane] (PpHPPS) Is mentioned.

[0007] Si- forming the main chain of the polysilane compound
The σ bond electrons between Si are delocalized, and
Over the entire main chain region (segment)
ing. Therefore, holes are easily carried in the main chain direction,
Very high in the molecule 10 ^-Fourcm^Two/ Vs holes
It exhibits conductivity. In addition, crystal Si forming a three-dimensional lattice
Because it is a one-dimensional chain polymer different from
Intense light in the range from ultraviolet to visible light with the property of band structure
2 shows absorption and exciton emission. Moreover, the emission peak wavelength, etc.
The optical properties of an alkyl bonded to the main chain as a side chain
Can be controlled relatively easily depending on the group, phenyl group and the like. This
Polysilane compounds such as
A "), high electrical conductivity and high efficiency luminescence characteristics
Is particularly suitable as a light emitting material for EL devices.

In a light-emitting material in which a light-emitting molecule B having an absorption / excitation spectrum that matches the emission spectrum of the polysilane molecule A is mixed with the polysilane molecule A, resonance energy transfer occurs. In other words, in a system in which the light-emitting molecule B in the ground state exists near the polysilane molecule A in the excited state, a dipole is generated according to the energy overlap between the emission spectrum of the polysilane molecule A and the absorption (or excitation) spectrum of the light-emitting molecule B. Quantum mechanical multipole interactions such as dipole-dipole and dipole-quadrupole interactions act to produce polysilane molecules A.
Is excited and moves to the light-emitting molecule B in a resonant manner, so that the polysilane molecule A transitions to the ground state and the light-emitting molecule B transitions to the excited state. The luminescent molecule B in the excited state then transitions to the ground state with luminescence unique to the luminescent molecule B.

In order for the resonance energy transfer to occur, the luminescence (vibrator strength) of the polysilane molecule A and the luminescent molecule B
It is necessary that the emission spectrum of the polysilane molecule A and the absorption (or excitation) spectrum of the light-emitting molecule B overlap, and that the polysilane molecule A and the light-emitting molecule B be close to each other at an interval of 1 to several nm. It is. By mixing a polysilane compound A having a high electrical conductivity and a high efficiency ultraviolet emission characteristic with a light-emitting molecule B having an absorption (or excitation) spectrum consistent with the emission spectrum of the polysilane compound A, the polysilane compound A and the light-emitting property are mixed. When the polysilane compound A is excited by current injection in a state where the polymer B is close to the polymer B, the excitation energy is transmitted to the light-emitting molecule B using a resonance energy transfer process, and the visible three primary colors R and G are emitted from the light-emitting molecule B. , B emit light.

Since the light-emitting molecule B, which has excellent light-emitting properties, rarely has electric conductivity, it is possible to separate the functions of electric conductivity and light-emitting property, and the degree of freedom in designing materials and devices is greatly increased. Expanding. Polysilane compound A used as an energy donor as a hole-conducting material includes polydihexylsilane having an alkyl side chain group and poly [(m-hexyloxyphenyl) having a phenyl side chain group, as shown in the above structural formula. Phenylsilane], poly [bis (p-
[Propoxyphenyl) silane], poly [(p-hexyloxyphenyl) phenylsilane], poly [bis (m-butoxyphenyl) silane], and the like.

Light-emitting molecule B as an energy acceptor
Includes coumarin 6, perylene, 4-dicyanomethylene-2-
Methyl-6- (p-dimethylaminostyryl) -4H-pyran (DC
M), zinc tetraphenylporphyrin (ZnTPP), and other organic dyes, as well as the aforementioned poly [(m-hexyloxyphenyl) phenylsilane] and poly [bis (p-propoxyphenyl) silane]. The same molecule can be used as an energy donor or an energy acceptor depending on the partner to be combined.

When the light-emitting layer is formed as a mixed thin film of the polysilane compound A and the light-emitting molecule B, full-color light emission is possible because all of the three primary colors R, G, and B having lower energy than ultraviolet light are emitted. Becomes In fact, the present inventors have confirmed white light emission by experiments. In addition, polysilane molecules are low-cost because they are mainly made of Si, and do not adversely affect the environment. In addition, since it has high compatibility with a semiconductor Si crystal substrate and the like, it can be applied to a wide range of applications and can be combined with an electronic circuit. In addition, when a soluble polysilane is used, uniform mixing with other molecules and spin coating film formation are facilitated, and a functional thin film having no defect is formed.

[0013]

EXAMPLE Synthesis of dichloro (m-hexyloxyphenyl) -phenylsilane 3.64 g (150 mmol) of magnesium powder and 78 ml of dry ether were stirred in a 300 ml three-necked flask whose inside was maintained in an argon atmosphere. Then, 1-bromo-3-hexyloxybenzene was obtained from the syringe.
A solution of 8 g (135 mmol) of 60 ml of dry ether was added dropwise. After completion of the dropwise addition, the mixture is heated under reflux for 3 hours,
Hexyloxyphenyl Grignard reagent was prepared.

Similarly, 500 ml of which the inside is replaced with argon
23.7 g of trichlorophenylsilane in a three-necked flask
(112 mmol) and 100 ml of dry ether.
Then, the hexyloxyphenyl Grignard reagent prepared above was added dropwise while the three-necked flask was cooled in a water bath and stirred. After the dropwise addition, heating under reflux was continued for 2 hours, and then the solvent was distilled off under normal pressure. After further heating under reflux for 4 hours, the reaction solution was cooled to room temperature, 70 ml of dry hexane was added, and a salt was precipitated in a refrigerator. The precipitate was suction-filtered using a glass filter under an argon atmosphere, and distilled under reduced pressure to obtain dichloro (m-hexyloxyphenyl) -phenylsilane in a yield of 18.1 g and a yield of 45.6%.

Synthesis of Poly [(m-hexyloxyphenyl) -phenylsilane] The inside of a 200 ml three-necked flask equipped with a fluororesin seal stirrer, an Aline condenser and a serum cap was purged with argon, and 2.47 g (107 m2) of metallic sodium was added. Mol) and 25 μl of dried diglyme in a three-necked flask,
By heating and refluxing while stirring at high speed, a Na dispersion was prepared. After cooling the Na dispersion to room temperature, dichloro (m-hexyloxyphenyl) -phenylsilane 1 was injected from a syringe while maintaining the temperature at 70 ° C.
A solution of 8.1 g (51.2 mmol) of 5 ml of dry toluene was added dropwise to the Na dispersion. The Na dispersion gradually changed from colorless to dark purple during dropping.

After completion of the dropwise addition, the mixture was reacted at 70 ° C. for 2 hours, and then 20 ml of dry 2-propanol was added dropwise using a syringe.
Unreacted sodium and polymer terminals were deactivated by stirring for 20 minutes. The solution after the reaction was transferred to a separating funnel, water was added, and the mixture was shaken well to separate the organic layer, thereby removing sodium salts. After this operation was repeated twice, a saturated saline solution was added, and the mixture was similarly shaken well to separate an organic layer. Then, the aqueous layer was extracted twice with toluene, the extract was mixed with the organic layer, dried over anhydrous sodium sulfate, anhydrous sodium sulfate was removed by cotton plug filtration, and the filtrate was evaporated.

The residue was dissolved in 6 ml of toluene and reprecipitated by dropping into a mixed solution of 400 ml of 2-propanol and 40 ml of toluene. As a result, a thread-like white substance precipitated. The precipitate was separated by filtration, washed with methanol, and dried in a desiccator to obtain white solid poly [(m-hexyloxyphenyl) -phenylsilane]. The synthesized polysilane molecule is
The structure was determined by NMR spectrum. Also, GPC
As a result of analysis (based on polystyrene), a bimodal pattern was shown, and the weight average molecular weight was 420,000 each.
And 6,000, and the dispersities were 2.10 and 1.35. When the absorption spectrum was analyzed, absorption was observed at 396 nm, and a sharp emission peak was observed at 421 nm in a solid state and at 415 nm in a liquid state when excitation light of 330 nm was irradiated.

The synthesized poly [(m-hexyloxyphenyl) -phenylsilane] is soluble in an organic solvent such as chloroform, tetrahydrofuran, and toluene.
The problem of solubility, which is a drawback of polydiphenylsilane, has been solved while preserving the excellent properties of polydiphenylsilane, such as having a strong emission peak at m, and it has been found that the polydiphenylsilane can be used as a material utilizing film forming technology. .

Light-emitting layer 1: poly [(m-
[Hexyloxyphenyl) -phenylsilane] in tetrahydrofuran (THF) (15 g / l) is spin-coated on a quartz substrate with ITO (transparent electrode) at 1500 rpm for 1 minute, and vacuum-dried for 24 hours to form a thin film having a thickness of 100 nm. Was prepared. 5 nm thick Li on polysilane thin film
An F (lithium fluoride) thin film and an Al thin film (cathode) with a thickness of 200 nm were deposited by continuous vapor deposition to produce an EL device. Al at nitrogen temperature (77K) in a vacuum atmosphere
When a voltage was applied between the thin film and the ITO thin film to inject a current, an EL spectrum of poly [(m-hexyloxyphenyl) -phenylsilane] was obtained. This EL spectrum was the same as the photoluminescence spectrum and was observed at room temperature. FIG. 1 shows the IV characteristics at this time.
FIG. 1A shows the EL spectrum in FIG.

Light emitting layer 2: polydihexylsilane (PDHS)
Has a transconformation at room temperature (below 42 ° C), and its trans emission energy is almost equal to the emission excitation energy (corresponding to the absorption energy) of poly [bis (p-propoxyphenyl) -silane] (PBPPS) From the values (FIG. 2), energy transfer between them is expected. Therefore, a mixed thin film with polydihexylsilane was formed on a quartz substrate by the same spin coating method as in Film-forming Example 1, and the state of energy transfer was confirmed by photoluminescence measurement. Spectrum M1 at room temperature immediately after film formation
In this case, helix emission of polydihexylsilane was also observed, but when cooled to 77K and returned to room temperature, almost complete trans emission M2 was obtained (FIG. 3). Conversely, when the temperature was returned to room temperature after heating to 42 ° C. or higher, the trans emission disappeared, and helix emission M3 was observed.

Looking at the excitation spectrum of PBPPS, the state M
3 (dashed line in FIG. 4b) versus state M2 (solid line in FIG. 4b)
Since the trans peak of PDHS (solid line in FIG. 4A) is observed to overlap, it can be seen that energy transfer from PDHS to PBPPS occurs in a state of transformer emission with large energy overlap. Also, PDHS
The single thin film and the PBPPS / PDHS mixed thin film were pulse-excited with a nitrogen laser beam having a wavelength of 337 nm, and the response waveform of PDHS transformer emission was observed. As a result, the decay life of the PDHS single film was 1.10 ns, while the decay life of the mixed thin film was 0.93 n
m, and it was confirmed that energy transfer to PBPPS occurred (FIG. 5).

Light-Emitting Layer 3: Since the emission energy of poly [(m-hexyloxyphenyl) -phenylsilane] (PHPPS) and the absorption energy of perylene Perylene overlap (FIG. 6), a mixed thin film of both was prepared. When the mixed thin film and the PHPPS simple thin film were optically excited at 4.13 eV, the emission intensity of PHPPS was reduced in the mixed thin film as compared with the single thin film, and remarkable visible light emission of perylene was observed (FIG. 7). No perylene emission was observed in the PMMA / perylene mixed film without energy overlap.
It can be seen that energy transfer from HPPS to perylene occurred. This result was also demonstrated in the excitation spectrum and time-resolved photoluminescence.

Light-emitting layer 4: Since the emission energy of poly [(m-hexyloxyphenyl) -phenylsilane] and the absorption energy of coumarin 6 overlap (FIG. 8), a mixed thin film of both is prepared and poly [(m [Hexyloxyphenyl) -phenylsilane]. Upon photoexcitation at 4.13 eV, the emission intensity of poly [(m-hexyloxyphenyl) -phenylsilane] in the mixed thin film was lower than that of the single thin film, and remarkable visible light emission of coumarin 6 was observed (FIG. 9). Combined with the results of the excitation spectrum and the time-resolved photoluminescence, it was demonstrated that energy transfer from coumarin 6 from poly [(m-hexyloxyphenyl) -phenylsilane] occurred.

Light-emitting layer 5: Since the emission energy of poly [(m-hexyloxyphenyl) -phenylsilane] and the absorption energy of DCM overlap (FIG. 10), a mixed thin film of both is prepared and poly [(m- [Hexyloxyphenyl) -phenylsilane]. Upon photoexcitation at 4.13 eV, the emission intensity of poly [(m-hexyloxyphenyl) -phenylsilane] was reduced in the mixed thin film compared to the single thin film, and visible emission of DCM was observed (FIG. 11). Combined with excitation spectrum and time-resolved photoluminescence results,
It was demonstrated that energy transfer from DCM from poly [(m-hexyloxyphenyl) -phenylsilane] to DCM occurred.

Light emitting layer 6: Since the emission energy of poly [(m-hexyloxyphenyl) -phenylsilane] and the absorption energy of ZnTPP overlap (FIG. 12), a mixed thin film of both is prepared, and poly [(m- [Hexyloxyphenyl) -phenylsilane]. Upon photoexcitation at 4.13 eV, the emission intensity of poly [(m-hexyloxyphenyl) -phenylsilane] in the mixed thin film was lower than that of the single thin film, and visible light emission of ZnTPP was observed (FIG. 13). Combined with the excitation spectra and the results of time-resolved photoluminescence, it was demonstrated that energy transfer occurred from Zn [P] to poly [(m-hexyloxyphenyl) -phenylsilane].

Emitting layer 7: Perylene, coumarin and DCM are adjusted to 0.5 mol% in total by utilizing energy transfer from poly [(m-hexyloxyphenyl) -phenylsilane] to various visible light emitting dyes. In addition, emission color control by emission of a plurality of dyes was investigated. Perylene: Coumarin 6: DCM =
White light emission W1 in a mixed thin film of 5: 1: 4, yellow light emission W in a mixed thin film of perylene: coumarin 6: DCM = 4: 2: 4
Blue-green light emission W3 was observed in the mixed thin film of 2, perylene: coumarin 6: DCM = 6: 2: 2 (FIG. 14). In addition, the emission spectrum of each dye demonstrated energy transfer from poly [(m-hexyloxyphenyl) -phenylsilane].

Emitting layer 8: A mixture of 5 mg of poly [(m-hexyloxyphenylmethyl) -phenylsilane] and 5 mg of polydihexylsilane was mixed with 0.5 ml of hexane,
It was dissolved in a mixed solvent of 0.5 ml of tetrahydrofuran THF to prepare a solution. 30 mm x 30 mm pattern I
Seven drops of the solution were dropped on the TO substrate, spin-coated at 1500 rpm, and vacuum-dried for 24 hours to form a light emitting layer having a thickness of 100 °. On the light emitting layer formed on the ITO substrate, a LiF layer (protective layer for the hole blocking layer and the light emitting layer) having a thickness of 5 ° and an Al layer having a thickness of 1000 to 1500 ° were continuously deposited.

When a voltage was applied between the ITO electrode (anode) and the Al layer (cathode) to inject a current into the light emitting layer, and the EL light emission characteristics were observed, trans light emission of polydihexylsilane and poly [(m -Hexyloxyphenyl) -phenylsilane] was confirmed. FIG. 15A shows an IV characteristic of this EL device, and FIG. 15B shows an EL spectrum. Also, when compared with the photoluminescence spectrum at the same location (FIG. 15c), it can be seen that there is no change in the peak position. The emission and absorption energy range of poly [(m-hexyloxyphenyl) -phenylsilane] is poly [bis (p-
(Propoxyphenyl) -silane] (Fig. 16)
From this, it is understood that energy transfer occurs between polydihexylsilane / poly [(m-hexyloxyphenyl) -phenylsilane] in comparison with the result of the light emitting layer 2.

In an EL device, external energy is carried by an electric current. However, since the energy donor and the energy acceptor emit EL light at the same position as the photoluminescence spectrum, the subsequent light emission process and energy transfer process are performed in the photoluminescence state. Common to
Therefore, also in the EL device, it was demonstrated that energy transfer from polydihexylsilane to poly [(m-hexyloxyphenyl) -phenylsilane] occurred.

Light-emitting layer 9: A poly [(m-hexyloxyphenyl) -phenylsilane] concentration of 10 g / l chloroform solution and a coumarin 6 chloroform solution were mixed with polysilane 1
Coumarin 6 per unit (1 Si atom) 0.5 ~
They were mixed at a ratio of 2.0 mol%. The prepared mixed solution was dropped on an ITO substrate, spin-coated at 1500 rpm for 10 minutes, and then degassed in vacuo at room temperature to obtain a film thickness of 100 n.
m was obtained. On this luminescent thin film, a film thickness of 5 nm
Was deposited by continuous vapor deposition to produce an EL light-emitting device.

By applying a voltage between the ITO thin film and the Al layer to supply a current, coumarin 6, which is a luminescent molecule, was allowed to emit light. FIG. 17 shows the emission spectrum. Similarly, emission spectra of perylene and DCM when EL emission is performed are shown in FIGS. 18 and 19, respectively. It is difficult for these dyes themselves to emit light by directly receiving an electric current, and EL emission using excitation energy through energy transfer from polysilane enables new development of EL devices.

[0032]

As described above, the luminescent material for an EL device of the present invention efficiently transmits electric energy to luminescent molecules in the EL layer by utilizing the resonance energy transfer of polysilane molecules, and the ultraviolet light. Even the visible three primary colors R, G, and B, which have lower energies than those described above, are sufficiently excited to emit luminescent molecules. Therefore, an overall energy efficiency is improved, and an EL device capable of full color is obtained.

[Brief description of the drawings]

FIG. 1 shows IV characteristics (a) and emission spectrum (b) at 77 K of a light-emitting layer 1 produced in an example.

FIG. 2 is a graph showing that the excitation energy of PBPPS coincides with the emission energy of PDHS.

Fig. 3 Emission spectrum of PDHS / PBPPS mixed thin film

Fig. 4 Excitation spectrum of PDHS / PBPPS mixed thin film

Fig. 5 Time-resolved photoluminescence of PDHS / PBPPS mixed thin film

FIG. 6 is a graph showing that the absorption energy of perylene matches the emission energy of PHPPS.

Fig. 7 Emission spectrum of PHPPS / perylene mixed thin film

FIG. 8 is a graph showing that the absorption energy of coumarin 6 matches the emission spectrum of PHPPS.

Fig. 9: Emission spectrum of PHPPS / coumarin 6 mixed thin film

FIG. 10 is a graph showing that the absorption energy of DCM matches the emission spectrum of PHPPS.

Fig. 11 Emission spectrum of PHPPS / DCM mixed thin film

FIG. 12 is a graph showing that the absorption energy of ZnTPP matches the emission spectrum of PHPPS.

Fig. 13 Emission spectrum of PHPPS / ZnTPP mixed thin film

FIG. 14 is a graph showing the effect of the addition ratio of perylene, coumarin, and DCM on the emission spectrum.

FIG. 15 shows IV characteristics (a), EL spectrum (b) and fluorescence spectrum (c) of a PDHS / PmHPPS mixed thin film.

FIG. 16 is a graph showing that the emission and absorption energy regions of PBPPS and PHPPS are almost equal.

FIG. 17: EL spectrum of an EL device using a PHPPS / coumarin 6 mixed thin film as a light emitting layer

FIG. 18: EL spectrum of an EL device using a PHPPS / perylene mixed thin film as a light emitting layer

FIG. 19: EL spectrum of an EL device using a PHPPS / DCM mixed thin film as a light emitting layer

Claims (2)

[Claims] 1. A light emitting material utilizing intermolecular energy transfer with polysilane, wherein the repeating unit is composed of one or more polysilane compounds represented by any of the following general structural formulas. 2. An EL comprising a mixture of a light-emitting molecule having an absorption / excitation spectrum that matches or approximates the light-emission spectrum of the polysilane compound according to claim 1.
Light emitting layer.