JP2010245179A - Organic electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic electroluminescent element the durability of which in long-time drive is improved. <P>SOLUTION: The organic electromuninescent element includes an organic compound layer sandwiched between at least a pair of electrodes. An amount of Pd contained in the organic compound layer is 1 ppm or less, and an amount of P is 0.5 ppm or less. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an organic electroluminescence element.

  Recent progress in organic electroluminescence elements is remarkable, and features include high luminance, a wide variety of emission wavelengths, high-speed response, and reduction in thickness and weight of light-emitting devices at a low applied voltage. From this, the organic electroluminescent element has suggested the possibility to a wide use.

  However, at present, there is a problem that the luminance deteriorates with time due to long-term use, and further improvement is required. As one of the causes of this deterioration over time, the influence of trace metal impurities in the material has become obvious.

  For example, in Patent Document 1, Pd contained in an organic material is cited as a cause of deterioration, and an example in which an organic material that defines the amount of Pd is used for an organic electroluminescence element has been reported. Patent Document 2 reports an example in which deterioration with time is suppressed by suppressing metal impurities to 2.5 ppm or less.

  However, even if the organic materials listed in these examples are used, it is difficult to say that the durability during long-time driving is sufficiently ensured, and the possibility that other deterioration factors are present cannot be wiped out. For this reason, it has been desired to further improve the durability in long-time driving by identifying factors that have an influence on deterioration over time and eliminating the influence.

JP 2005-240011 A Japanese Patent Laid-Open No. 2005-41982

  As described above, it is not possible to obtain sufficient durability in an organic electroluminescence element simply by defining the trace metal impurities reported so far. The present invention has been made to solve this problem, and it is an object of the present invention to specify a factor affecting the deterioration with time of an organic electroluminescence element and to eliminate it. Another object of the present invention is to provide an organic electroluminescence element having improved durability during long-time driving.

  The organic electroluminescent element of the present invention is an organic electroluminescent element having an organic compound layer sandwiched between at least a pair of electrodes, the amount of Pd contained in the organic compound layer is 1 ppm or less, and the amount of P is 0 It is characterized by being 5 ppm or less.

  ADVANTAGE OF THE INVENTION According to this invention, the organic electroluminescent element which the durability in long-time drive improved can be provided.

It is sectional drawing which shows 1st embodiment in the organic light emitting element of this invention. It is sectional drawing which shows 2nd embodiment in the organic light emitting element of this invention. It is sectional drawing which shows 3rd embodiment in the organic light emitting element of this invention.

  Hereinafter, the present invention will be described in detail.

  The organic electroluminescence device of the present invention has an organic compound layer sandwiched between at least a pair of electrodes, the amount of Pd contained in the organic compound layer is 1 ppm or less, and the amount of P is 0.5 ppm or less. It is characterized by being. The electrode that sandwiches the organic compound layer may be a reflective electrode or a light transmissive electrode. Moreover, a well-known material can be used as a constituent material of an electrode.

  Here, first, the organic electroluminescence element of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view showing a first embodiment of the organic electroluminescence element of the present invention. In the organic electroluminescence element 10 of FIG. 1, an anode 2, a light emitting layer 3, and a cathode 4 are sequentially provided on a substrate 1. This organic electroluminescent element 10 is effective when the light emitting layer 3 is comprised with the organic compound which has all the hole transport ability, electron transport ability, and luminous performance. In addition, the light emitting layer 3 may be configured by mixing a plurality of organic compounds having any one of hole transport ability, electron transport ability, and light emitting performance.

  FIG. 2 is a cross-sectional view showing a second embodiment of the organic electroluminescence element of the present invention. In the organic electroluminescence element 20 of FIG. 2, an anode 2, a hole transport layer 5, an electron transport layer 6, and a cathode 4 are sequentially provided on a substrate 1. In the organic electroluminescence device 20, it is preferable to use a combination of a light-emitting organic compound having either a hole transport property or an electron transport property and an organic compound having only an electron transport property or only a hole transport property. . In the organic electroluminescence element 20, the hole transport layer 5 or the electron transport layer 6 also serves as a light emitting layer.

  FIG. 3 is a cross-sectional view showing a third embodiment of the organic electroluminescence element of the present invention. The organic electroluminescence element 30 in FIG. 3 is obtained by inserting the light emitting layer 3 between the hole transport layer 5 and the electron transport layer 6 in the organic electroluminescence element 20 in FIG. 2. The organic electroluminescence element 30 has functions of separating carrier transport and light emission, and is used in appropriate combination with an organic compound having hole transport properties, electron transport properties, and light emission properties. For this reason, the degree of freedom of material selection is greatly increased, and various organic compounds having different emission wavelengths can be used, so that the emission hues can be diversified. Furthermore, each carrier or exciton can be effectively confined in the central light emitting layer 3 to improve the light emission efficiency.

  Further, in the organic electroluminescence element 30 of FIG. 3, a hole injection layer may be inserted between the anode 2 and the hole transport layer 5. In this case, it is effective for improving the adhesion between the anode 2 and the hole transport layer 5 or improving the hole injection property, and is effective for lowering the voltage.

  Further, in FIG. 3, a layer (hole block layer, exciton block layer) that prevents holes or excitons (exciton) from escaping to the cathode 4 side is inserted between the light emitting layer 3 and the electron transport layer 6. Also good. Use of a compound having a very high ionization potential as a constituent material of the hole block layer or exciton block layer is effective in improving the light emission efficiency.

  However, FIG. 1 thru | or FIG. 3 is a very basic element structure to the last, and the structure of the organic electroluminescent element of this invention is not limited to these. For example, an insulating layer is provided at the interface between the electrode and the organic compound layer, an adhesive layer or an interference layer is provided, the hole transport layer is composed of two layers having different ionization potentials, and the light emitting layer has a laminated structure of two or more layers. Various layer configurations can be taken, such as.

  The organic electroluminescence element of the present invention has an organic compound layer. This organic compound layer is suitably used as any one of the light emitting layer 3, the hole transport layer 5, and the electron transport layer 6 in the organic electroluminescence device as described above.

  The inventors of the present invention have made extensive studies in order to suppress the deterioration of luminance when the organic electroluminescence element is driven for a long time. As a result, it is found that the luminance deterioration of the organic electroluminescence element can be effectively suppressed by suppressing impurities contained in the organic compound layer, particularly Pd amount and P amount to a predetermined amount or less, and the present invention is completed. It came to.

  That is, it is an organic electroluminescence device in which the amount of Pd contained in the organic compound layer is 1 ppm or less and the amount of P is 0.5 ppm or less. Thereby, the luminance degradation of the organic electroluminescence element can be suppressed, and good luminance can be maintained for a long time.

  The reason why Pd and P are mixed as impurities in the organic compound layer is due to a method of synthesizing an organic compound that is a constituent material of the organic compound layer. As a material for an organic electroluminescence device, a compound having a skeleton with a condensed ring connected is generally used, and such a material is often synthesized using a coupling reaction. Among them, coupling reactions using Pd as a catalyst are often used, and this is caused by the mixing of Pd aggregates generated due to deactivation of the Pd catalyst during the reaction process. In general, it is considered that the Pd aggregate is formed only by Pd, with the P ligand coordinated to Pd being eliminated. However, analysis of the Pd aggregate by the present inventors revealed that the P component was incorporated into the Pd aggregate. Furthermore, it has been found that when a Pd aggregate is mixed in an organic compound even in a very small amount, Pd and P are mixed in the element formed using the organic compound, resulting in significant luminance deterioration. Therefore, removal of Pd aggregates, that is, Pd and P from the organic compound is indispensable for suppressing luminance deterioration.

  The purification method for removing Pd and P from the organic compound is not particularly limited as long as it can be used. Specific examples include a sublimation purification method, a recrystallization method, a reprecipitation method, a column purification method, an adsorption method, and a zone melting method. Furthermore, these methods may be combined. These purification methods may be appropriately selected depending on the nature and structure of the organic compound, and among them, the sublimation purification method, the recrystallization method, the column purification method, and the adsorption method are more preferably used. Moreover, when the Pd catalyst-derived Pd aggregate is the main factor of Pd and P contained in the organic compound, a method of devising the reaction conditions of the coupling reaction and suppressing Pd deactivation itself is also preferable. Although there is no restriction | limiting in particular as such a method, When the produced | generated organic compound melt | dissolves in a reaction solution completely at room temperature, the method of using the Pd catalyst carry | supported by the polymer is mentioned. On the other hand, in the case of an organic compound that dissolves less than 50% in the reaction solution at room temperature, a method using a Pd catalyst coordinated with a phosphine having a high coordination ability or an excessive phosphine ligand added to the Pd catalyst A method is mentioned. In addition to these innovations in the synthesis method, the above purification methods may be combined.

  The method for detecting, measuring and quantifying Pd and P in the present invention is carried out using a known method or apparatus, and is not particularly limited. Examples of such a method include high frequency inductively coupled plasma emission spectrometry (ICP-AES) and high frequency inductively coupled plasma mass spectrometry (ICP-MS). In these methods, not only ICP (Inductively Coupled Plasma) but also MIP (Microwave Induced Plasma) or the like may be used as an ion source or a light emission source. In addition, atomic absorption spectrometry (AAS), X-ray photoelectron spectroscopy (XPS), fluorescent X-ray analysis (XRF), nuclear magnetic resonance spectroscopy (NMR), electron spin resonance spectroscopy (ESR), electron beam Microanalyzer analysis method (EPMA) etc. are mentioned. Among these, ICP-AES, ICP-MS, and AAS are preferable from the viewpoints of versatility and quantitativeness.

For example, the above ICP-AES measurement is performed to quantify the amount of Pd and the amount of P contained in the organic compound. At this time, if the amount of Pd is 1 ppm or less and the amount of P is an organic compound of 0.5 ppm or less, an element manufactured using the organic compound has much less deterioration in luminance when driven for a long time. It has durability. Here, high durability means that the organic electroluminescence device is a device in which the time until the luminance reduction rate from the initial luminance is 10% exceeds 100 hours when the organic electroluminescence device is driven at a constant current of 100 mA / cm ² . Say that. On the other hand, as described in Comparative Example 1, the device manufactured using the organic compound containing 0.7 ppm of P had a time until the luminance reduction rate from the initial luminance became 10%, which was less than 100 hours. . Furthermore, Pd and P amount contained in the organic compound were correlated with Pd and P amount contained in the device produced using the organic compound. Therefore, in order to suppress the luminance deterioration of the element, it is important that the Pd amount is 1 ppm or less and the P amount is 0.5 ppm or less.

  The organic compound contained in the organic compound layer in the organic electroluminescence device of the present invention is synthesized, for example, by a reaction using a catalyst component containing Pd and P as described above. In particular, among organic compounds synthesized by such a method, a compound having a structure containing an aromatic hydrocarbon is preferable. Of the organic compounds containing aromatic hydrocarbons, compounds represented by the following general formula (1) are particularly preferred.

  In the formula (1), A to D are substituted or unsubstituted benzene ring, substituted or unsubstituted naphthalene ring, substituted or unsubstituted anthracene ring, substituted or unsubstituted phenanthrene ring, substituted or unsubstituted pyrene, respectively. A ring, a substituted or unsubstituted fluorene ring, a substituted or unsubstituted chrysene ring, a substituted or unsubstituted fluoranthene ring, and a substituted or unsubstituted benzofluoranthene ring;

  Substituents that the above benzene ring, naphthalene ring, anthracene ring, phenanthrene ring, pyrene ring, fluorene ring, chrysene ring, fluoranthene ring and benzofluoranthene ring may have include a methyl group, a tert-butyl group, etc. Examples thereof include aryl groups such as an alkyl group and a phenyl group.

  In formula (1), A to D may be the same or different.

In the formula _(1), n 1 and n ₂ is an integer of 0 or more. However, the sum of n ₁ and n ₂ is 0 or more and 3 or less. From the viewpoint of ease of synthesis and film formability, the sum of n ₁ and n ₂ is preferably 0 or more and 2 or less.

  As an organic compound containing the aromatic hydrocarbon mentioned above, the compound shown by following General formula (2) and Formula (3) other than the compound of Formula (1) is mentioned.

In Formula (2), A to D are the same as A to D in Formula (1). In the formula (2), n ₁ and n ₂ is an integer of 0 or more. However, the sum of n ₁ and n ₂ is 0 or more and 3 or less.

In Formula (3), A to D are the same as A to D in Formula (1). In the formula _{(3), n 1, n} 2 and n ₃ represent an integer of 0 or greater. However, the sum of n ₁ , n ₂ and n ₃ is 0 or more and 3 or less.

  In addition, this invention is applicable also to the compound obtained by other reaction using a Pd catalyst, for example, Pd catalyst amination reaction, Heck reaction, etc.

  Hereinafter, a preferable example is shown as an organic compound contained in the organic electroluminescent element of this invention. The compounds shown here are merely examples, and the compounds of the present invention are not limited to these.

  In addition to the compounds represented by the formulas (1) to (3), examples of the organic compound containing an aromatic hydrocarbon include compounds obtained by a Pd-catalyzed amination reaction. As a compound obtained by Pd catalyst amination reaction, the compound shown below is mentioned, for example.

  Examples are shown below. However, the present invention is not limited to these.

  [Synthesis Example 1] Synthesis of Compound-1 (Exemplary Compound c-20)

(Synthesis Example 1-1)
The following reagents and solvents were charged into the reaction vessel.
Raw material-1: 274 g (680 mmol)
Raw material-2: 366 g (715 mmo)
PdCl ₂ (PPh ₃ ) 2: 9.56 g (13.6 mmol)
Sodium carbonate: 108 g (1.02 mol)
Toluene: 4110 ml
Ethanol: 2055ml
Water: 1028ml

  Next, the reaction vessel was purged with nitrogen and stirred for 6 hours under reflux. Thereafter, the mixture was cooled and the precipitated crystals were collected by filtration to obtain a crude product. The crude product was washed with slurry in the order of water, methanol, ethyl acetate, and toluene. Next, the obtained crystals were dissolved in chlorobenzene by heating, and then filtered while hot to remove residual palladium and the like using Kiriyama filter paper (No. 5C). The filtrate was cooled, and the precipitated crystals were collected by filtration to obtain 403 g (yield 93%) of Compound-1 recrystallized product. Further, sublimation purification of the obtained compound-1 was performed to obtain a sublimation purified product.

(Synthesis Example 1-2)
In Synthesis Example 1-1, the Kiriyama filter paper used for hot filtration was No. Synthesis was performed according to Synthesis Example 1-1 except that 5C was changed to GFP. Next, sublimation purification of Compound-1 obtained in the same manner as in Synthesis Example 1-1 was performed to obtain a sublimation purified product.

(Synthesis Example 1-3)
After 2.0 g (mmol) of the recrystallized product obtained in Synthesis Example 1-1 was dissolved by heating in 150 ml of chlorobenzene, 10 g of Galleon Earth V2 (manufactured by Mizusawa Chemical Co., Ltd.) was added. Next, the mixture was stirred at 100 ° C. for 15 minutes and filtered while hot. Next, the filtrate was cooled, and the precipitated crystals were collected by filtration to obtain 1.6 g (yield 80%) of an active clay-treated product of Compound-1. Next, sublimation purification of Compound-1 obtained in the same manner as in Synthesis Example 1-1 was performed to obtain a sublimation purified product.

(Synthesis Example 1-4)
The following reagents and solvents were charged into the reaction vessel.
Raw material-1: 280 g (696 mmol)
Raw material-2: 374 g (731 mmo)
Triphenylphosphine: 36.5 g (139 mmol)
PdCl ₂ (PPh ₃ ) 2: 9.77 g (13.9 mmol)
Sodium carbonate: 111 g (1.04 mol)
Toluene: 4200 ml
Ethanol: 2100ml
Water: 1050ml

  Next, the reaction vessel was purged with nitrogen and stirred for 5 hours under reflux. Thereafter, the mixture was cooled and the precipitated crystals were collected by filtration to obtain a crude product. About this crude product, the heating slurry washing | cleaning was performed in order of water, acetone, and toluene. Next, the obtained crystal was recrystallized from chlorobenzene to obtain 384 g (yield 90%) of Compound-1. Next, sublimation purification of Compound-1 was performed in the same manner as in Synthesis Example 1-1 to obtain a sublimation purified product.

  [Synthesis Example 2] Synthesis of Compound-2 (Exemplary Compound c-21)

(Synthesis Example 2-1)
In a nitrogen atmosphere, the following reagents and solvents were charged in a reaction vessel.
Raw material-3: 0.60 g (1.16 mmol)
Raw material-4: 0.40 g (1.05 mmol)
Toluene: 20 mL
Ethanol: 10mL

Further, 10 mL of a 10 wt% aqueous sodium carbonate solution was added, and then the reaction solution was stirred at room temperature for 30 minutes. Subsequently, tetrakis (triphenylphosphine) palladium (0.006 g, 0.005 mmol) was added, and the reaction solution was stirred for 5 hours while being heated to reflux. Next, after cooling the reaction solution to room temperature, water was added to stop the reaction. Next, the product was extracted with chloroform by a liquid separation operation. Next, the extract was washed twice with pure water, dried over sodium sulfate, and concentrated under reduced pressure to obtain a crude product. Subsequently, this crude product was dissolved in chloroform and filtered while hot through a short alumina / silica gel laminated column to remove residual palladium and the like, and then the filtrate was concentrated under reduced pressure to obtain crude crystals. Next, this crude crystal is washed with a slurry in a heptane / toluene solvent, and then recrystallized with a toluene solvent. 0.67 g (yield 92%) was obtained. Further, sublimation purification was performed at 380 ° C. under reduced pressure of 10 ⁻⁴ Pa to obtain 0.45 g of sublimation purified product (sublimation purification yield 68%).

(Synthesis Example 2-2)
In Synthesis Example 2-1, synthesis was performed according to Synthesis Example 2-1, except that the hot filtration in the alumina / silica gel laminated column was changed to the hot filtration using Kiriyama filter paper (5C). Of sublimation products.

(Measurement of Pd and P concentration)
About the sublimation purified product of Compound-1 obtained in Synthesis Example 1-1 to Synthesis Example 1-4 and the sublimation purified product of Compound-2 obtained in Synthesis Example 2-1 to Synthesis Example 2-2, Pd and P concentration was measured by ICP-AES (manufactured by SPECTRO). As a pretreatment, acid decomposition was performed on 200 mg of each sample using 4 ml of nitric acid and 4 ml of sulfuric acid. Then, ultrapure water was added so that it might become 50 g in total, and it was set as the measurement sample. A calibration curve was created from three points of 0 ppb, 100 ppb, and 500 ppb, and Pd and P amount contained in each sample were quantified. The detection limit values were 1 ppm for Pd and 0.5 ppm for P. In addition, ultrapure water was added to 4 ml of nitric acid and 4 ml of sulfuric acid to make a total of 50 g as a blank, and Pd and P amount of the blank were subtracted. The results are shown in Table 1. In Table 1, when Pd was 1 ppm or less, Pd was defined as undetected, and when P was 0.5 ppm or less, P was defined as undetected.

Example 1
The organic electroluminescent element shown in FIG. 3 was produced by the method shown below. It was confirmed in advance that organic compounds other than Compound-1 did not contain Pd and P.

  On the glass substrate, indium tin oxide (ITO) was formed by sputtering to form the anode 2. At this time, the film thickness of the anode was set to 120 nm. Next, this anode-attached substrate was ultrasonically washed successively with acetone and isopropyl alcohol (IPA), then washed with pure water and dried. Next, what was UV / ozone cleaned was used as a transparent conductive support substrate.

  Next, Compound E-1 shown below and chloroform were mixed as the hole transport layer 5 to prepare a chloroform solution having a concentration of 0.1% by weight.

  This chloroform solution was dropped on the anode, and film formation was performed by first performing spin coating at a rotation speed of 500 rpm for 10 seconds and then at a rotation speed of 1000 rpm for 40 seconds. Thereafter, the film was dried in a vacuum oven at 80 ° C. for 10 minutes to completely remove the solvent in the thin film. Then, the compound E-1 was formed into a film by the vacuum evaporation method and the hole transport layer 5 was formed. At this time, the thickness of the hole transport layer 5 was 60 nm.

  Next, on the hole transport layer 5, the compound E-2 and the compound E-3 shown below, which are guests (light-emitting materials), and a compound-1 which is a host (obtained in Synthesis Example 1-2) are formed by vacuum deposition. The light-emitting layer 3 was formed by co-evaporation. At this time, the film thickness of the light emitting layer was 50 nm, and the contents of Compound E-2 and Compound E-3 with respect to the entire light emitting layer were 4% by weight and 16% by weight, respectively.

Next, 2,9-bis [2- (9,9′-dimethylfluorenyl)]-1,10-phenanthroline was formed on the light-emitting layer 3 by a vacuum deposition method to form the electron transport layer 6. At this time, the film was formed under the conditions that the thickness of the electron transport layer was 50 nm, the degree of vacuum during vapor deposition was 1.0 × 10 ⁻⁴ Pa, and the film formation rate was 0.1 nm / sec to 0.2 nm / sec.

  Next, KF was deposited to a thickness of 1 nm, and then Al was deposited to a thickness of 120 nm. Here, the KF film and the Al film function as the cathode 4.

  Next, a protective glass plate was placed in a dry air atmosphere and sealed with an acrylic resin adhesive so as not to cause element degradation due to moisture adsorption. An organic electroluminescence element was obtained as described above.

About the obtained organic electroluminescent element, durability of an element was evaluated by measuring the time until the luminance decreasing rate from an initial luminance became 10%, keeping a constant current density of 100 mA / cm < ² >. The results are shown in Table 3.

(Example 2)
In Example 1, an organic electroluminescence device was obtained according to Example 1 except that the sublimation purified product obtained in Synthesis Example 1-4 was used as Compound-1 (host). Similarly, the durability of the element was evaluated. The results are shown in Table 2.

Example 3
The organic electroluminescent element shown in FIG. 3 was produced by the method shown below. It was confirmed in advance that organic compounds other than Compound-2 did not contain Pd and P.

On the glass substrate (substrate 1), indium tin oxide (ITO) having a film thickness of 120 nm as an anode 2 was formed as a transparent conductive support substrate (ITO substrate) by sputtering. On the ITO substrate, the following organic compound layer and electrode layer were continuously formed by vacuum evaporation by resistance heating in a vacuum chamber of 10 ⁻⁴ Pa. Specifically, first, as the hole transport layer 5, a compound E-4 was formed to a film thickness of 18 nm. Next, as the light-emitting layer 3, the host compound-2 (sublimation purified product obtained in Synthesis Example 2-1) and the guest compound E-2 are co-evaporated to form a mixed film having a thickness of 30 nm. did. Here, content of the compound E-2 with respect to the whole light emitting layer 3 is 10 weight%. Next, as the electron transport layer 6, the compound E-5 was formed into a film with a film thickness of 40 nm. Next, KF was deposited to a thickness of 1 nm, and then Al was deposited to a thickness of 120 nm. Here, the KF film and the Al film function as the cathode 4. About the obtained organic electroluminescent element, durability of an element was evaluated by measuring the time until the luminance decreasing rate from an initial luminance became 10%, keeping a constant current density of 100 mA / cm < ² >. The results are shown in Table 2.

(Comparative Example 1)
In Example 1, an organic electroluminescence device was obtained according to Example 1 except that the sublimation purified product obtained in Synthesis Example 1-1 was used as Compound-1 (host). Similarly, the durability of the element was evaluated. The results are shown in Table 3.

(Comparative Example 2)
In Example 2, an organic electroluminescence device was obtained according to Example 2 except that the sublimation purified product obtained in Synthesis Example 2-2 was used as Compound-2 (host). Similarly, the durability of the element was evaluated. The results are shown in Table 3.

  From the above results, when the amount of Pd and P contained in the organic compound layer is less than the detection limit, that is, in an organic electroluminescence device in which Pd is less than 1 ppm and P is less than 0.5 ppm, the durability is remarkably high. Confirmed to improve.

  1: substrate, 2: anode, 3: light emitting layer, 4: cathode, 5: hole transport layer, 6: electron transport layer, 10, 20, 30: organic electroluminescence device

Claims (2)

  In an organic electroluminescence device having an organic compound layer sandwiched between at least a pair of electrodes, the amount of Pd contained in the organic compound layer is 1 ppm or less, and the amount of P is 0.5 ppm or less. Organic electroluminescence device. The organic electroluminescent device according to claim 1, wherein the organic compound layer contains a compound represented by the following general formula (1).

(In the formula (1), A to D each represent a substituted or unsubstituted benzene ring, naphthalene ring, anthracene ring, phenanthrene ring, pyrene ring, fluorene ring, chrysene ring, fluoranthene ring, or benzofluoranthene ring. A to D may be the same or different, and n ₁ and n _{2 each} represent an integer of 0 or more, provided that the sum of n ₁ and n ₂ is 0 or more and 3 or less.

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