Organic light-emitting device

Abstract

To provide an organic compound that can be suitably used as a light-emitting material for displays, and an organic light-emitting device that includes such an organic compound.SOLUTION: A light-emitting layer includes a dopant compound and a host compound, and the host compound has a lone pair of electrons and a π electron orbital, and an energy difference ΔEST obtained by subtracting an energy level ET1 of the lowest triplet excited state T1 from an energy level ES1 of the lowest singlet excited state S1 is negative or is 0 eV≤ΔEST<0.0090 eV.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to organic light emitting devices that can be used as light emitting materials. [Background technology]

[0002] An organic light-emitting diode is an example of an organic light-emitting device that uses an organic electroluminescence (hereinafter referred to as organic EL) material composed of organic compounds. Even now, when displays and lighting devices equipped with organic light-emitting diodes are being offered on the market, there is a high demand for new organic EL materials with higher luminous efficiency. An organic EL material is an example of a light-emitting material. Organic EL materials include fluorescent materials and phosphorescent materials. The theoretical internal quantum efficiency of phosphorescent materials is four times higher than that of fluorescent materials. Therefore, research and development of phosphorescent materials has been conducted in advance from the viewpoint of increasing the internal quantum efficiency. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2015 / 159971 [Non-patent literature]

[0004] [Non-Patent Document 1] Hiroki Uoyama et al. "Highly efficient organic light-emitting diodes from delayed fluorescence", Nature, 2012, 492, 234. [Non-Patent Document 2] Johannes Ehrmaier et. al.,"Singlet-Triplet Inversion in Heptazine and in Polymeric Carbon Nitrides", The Journal of Physical Chemistry A, 123, 8099-8108 (2019) Summary of the Invention [Problem to be solved by the invention]

[0005] However, phosphorescent materials have a problem of high cost because they contain expensive metals such as iridium.

[0006] [Regarding Patent Document 1 and Non-Patent Document 1] Thermally activated delayed fluorescence materials described in Patent Document 1 and Non-Patent Document 1 are known as luminescent materials that are less expensive than phosphorescent materials containing expensive metals such as iridium. Hereinafter, thermally activated delayed fluorescence materials are referred to as TADF (Thermally Activated Delayed Fluorescence) materials.

[0007] TADF materials have the lowest singlet excited state S1 energy level E S1 to the energy level E of the lowest triplet excited state T1 T1 Energy difference ΔE minus ST The TADF material is constructed so that the internal quantum efficiency of the organic electroluminescence material is small (for example, about 100 meV). By thermally inducing reverse intersystem crossing from the lowest triplet excited state T1 to the lowest singlet excited state S1, the lowest triplet excited state T1, which is normally deactivated as heat, is utilized as delayed fluorescence, and as a result, it is theoretically possible to increase the internal quantum efficiency of the organic electroluminescence material to 100%.

[0008] In addition, ΔE ST By reducing the energy of the delayed fluorescence to the same level as that at room temperature, the researchers were able to promote reverse intersystem crossing and shorten the emission lifetime of the delayed fluorescence to a few microseconds, which is comparable to that of conventional phosphorescent materials.

[0009] However, when considering the use of TADF materials in displays, the emission lifetime of TADF materials is far from a practical level: the emission lifetime of TADF materials is about three orders of magnitude longer than the typical emission lifetime of organic electroluminescence materials used in displays available on the market.

[0010] This long emission lifetime leads to degradation of the TADF material due to an increase in the triplet exciton density in the TADF material and a decrease in the luminous efficiency when emitting high luminance light.

[0011] [Regarding Non-Patent Document 2] Due to the exchange interaction in the excited state, the energy level E of the lowest triplet excited state T1 T1 is the energy level E of the lowest singlet excited state S1 In other words, ΔE ST is positive.

[0012] On the other hand, the calculated ΔE ST There have been reports of organic compounds in which ΔE ST <-0.23 eV (see Table 3 in Non-Patent Document 2). Thus, the negative and large absolute value of ΔE ST belongs to a region called the Marcus inversion region. In organic EL materials belonging to the Marcus inversion region, the rate constant of reverse intersystem crossing from the lowest triplet excited state T1 to the lowest singlet excited state S1 is considered to be small. The inventors of the present application have also experimentally confirmed that such organic EL materials exhibit very low luminescence intensity and luminescence quantum yield. Therefore, it is not practical to use organic EL materials belonging to the region called the Marcus inversion region as luminescent materials for displays.

[0013] One aspect of the present invention has been made in consideration of the above-mentioned problems, and an object of the present invention is to provide an organic compound that can be suitably used as a light-emitting material for a display, and an organic light-emitting device including such an organic compound. [Means for solving the problem]

[0014] In order to solve the above problems, the organic light-emitting device according to the first aspect of the present invention includes an emitting layer containing a dopant compound and a host compound. In this organic light-emitting device, the host compound is an organic compound having a lone pair of electrons and a π electron orbital, and has an energy level E of the lowest singlet excited state S1. S1 to the energy level E of the lowest triplet excited state T1 T1 Energy difference ΔE minus ST is negative or 0 eV ≤ ΔE ST <0.0090 eV.

[0015] In addition, in the organic light-emitting device according to the second aspect of the present invention, in addition to the configuration of the organic light-emitting device according to the first aspect described above, the host compound is a heptazine derivative having a lone electron pair and a π electron orbital, and is represented by the following formula (1) and has optional substituents R1, R2, and R3. [ka]

[0016] In addition to the configuration of the organic light-emitting device according to the first or second aspect of the present invention, the organic light-emitting device according to the third aspect of the present invention further comprises a radiative deactivation rate constant k r is 1.0×10 6 s -1 <k r It is.

[0017] Furthermore, in the organic light-emitting device according to the fourth aspect of the present invention, in addition to the configuration of the organic light-emitting device according to the second aspect described above, the substituents R1, R2, and R3 are each composed of two types of substituents.

[0018] Furthermore, in the organic light-emitting device according to the fifth aspect of the present invention, in addition to the configuration of the organic light-emitting device according to the second aspect described above, the substituents R1, R2, and R3 are each composed of three different types of substituents.

[0019] Furthermore, in an organic light-emitting device according to a sixth aspect of the present invention, in addition to the configuration of the organic light-emitting device according to the second aspect described above, the substituents R1, R2, and R3 are each composed of one type of substituent.

[0020] Furthermore, an organic light-emitting device according to a seventh aspect of the present invention has the same configuration as the organic light-emitting device according to the fourth aspect described above, and further has the same substituents R2 and R3 among the substituents R1, R2, and R3, and the substituent R1 has a structure represented by the following formula (2): -S-R31, -O-R31, or -N-(R32)R33...(2) Here, R31 to R33 are each independently a chain or cyclic hydrocarbon group having 20 or less carbon atoms, which may be substituted by a substituent, and each of the substituents R2 and R3 is a phenyl group or a phenyl group having 1 to 3 substituents.

[0021] Furthermore, an organic light-emitting device according to an eighth aspect of the present invention has the same configuration as the organic light-emitting device according to the second aspect, in addition to the above, wherein the substituent R1 has any one of the following structures: [ka] Each of the substituents R2 and R3 has one of the structures shown below. [ka] (However, the following exceptions apply.) [ka]

[0022] Furthermore, in addition to the configuration of the organic light-emitting device according to the ninth aspect of the present invention, the substituents R1, R2, and R3 have any of the structures shown below. [ka]

[0023] In order to solve the above problems, an organic light-emitting device according to a tenth aspect of the present invention includes an emitting layer containing a dopant compound and a host compound. In this organic light-emitting device, the dopant compound is an organic compound having a lone pair of electrons and a π electron orbital, and has an energy level E S1 to the energy level E of the lowest triplet excited state T1 T1 Energy difference ΔE minus ST is negative or 0 eV ≤ ΔE ST <0.0090 eV.

[0024] Further, an organic light-emitting device according to an eleventh aspect of the present invention has the same configuration as the organic light-emitting device according to the tenth aspect described above, in which the dopant compound is a heptazine derivative having a lone pair of electrons and a π electron orbital, and is represented by the following formula (1) and has optional substituents R1, R2, and R3. [ka]

[0025] In addition to the configuration of the organic light-emitting device according to the 12th aspect of the present invention, the organic light-emitting device according to the 10th or 11th aspect further comprises a radiative deactivation rate constant k r is 1.0×10 6 s -1 <k r It is.

[0026] Furthermore, in an organic light-emitting device according to a thirteenth aspect of the present invention, in addition to the configuration of the organic light-emitting device according to the eleventh aspect described above, the substituents R1, R2, and R3 are each composed of two types of substituents.

[0027] In addition, an organic light-emitting device according to a fourteenth aspect of the present invention has the same configuration as the organic light-emitting device according to the eleventh aspect described above, and further comprises three different types of substituents R1, R2, and R3.

[0028] Furthermore, in an organic light-emitting device according to a fifteenth aspect of the present invention, in addition to the configuration of the organic light-emitting device according to the eleventh aspect described above, the substituents R1, R2, and R3 are each composed of one type of substituent.

[0029] An organic light-emitting device according to a sixteenth aspect of the present invention has the same configuration as the organic light-emitting device according to the thirteenth aspect, and further has the same substituents among the substituents R1, R2, and R3 as the substituents R2 and R3, and the substituent R1 has a structure represented by the following formula (2): -S-R31, -O-R31, or -N-(R32)R33...(2) Here, R31 to R33 are each independently a chain or cyclic hydrocarbon group having 20 or less carbon atoms, which may be substituted by a substituent, and each of the substituents R2 and R3 is a phenyl group or a phenyl group having 1 to 3 substituents.

[0030] Furthermore, an organic light-emitting device according to a seventeenth aspect of the present invention has the same configuration as the organic light-emitting device according to the eleventh aspect, in which the substituent R1 has any one of the following structures: [ka] Each of the substituents R2 and R3 has one of the structures shown below. [ka] (However, the following exceptions apply.) [ka]

[0031] Furthermore, in addition to the configuration of the organic light-emitting device according to the 18th aspect of the present invention, the substituents R1, R2, and R3 have any of the structures shown below. [ka] Effect of the Invention

[0032] According to one aspect of the present invention, it is possible to provide an organic compound that can be suitably used as a light-emitting material for a display, and an organic light-emitting device including such an organic compound. [Brief description of the drawings]

[0033] [Figure 1] FIG. 2 is a schematic diagram of energy levels in an organic compound according to one embodiment of the present invention. [Diagram 2] 1 is a graph showing the emission spectrum, the temperature dependence of transient luminescence decay, and the temperature dependence of the rate constant kDF of a mixed thin film of organic compound A and PPF according to a first embodiment of the present invention. [Diagram 3] 1 is a graph showing the emission spectrum, temperature dependence of transient luminescence decay, and temperature dependence of rate constant kDF of a toluene solution of organic compound A which is a first reference example of the present invention. [Figure 4] 1 is a graph showing the correlation between the energy difference ΔEST and the oscillator strength f in organic compounds 1 to 38, which are the second reference example group of the present invention. [Diagram 5] FIG. 11 is a scatter plot showing the correlation between the energy difference ΔEST and the oscillator strength f in organic compounds pX-Y, ​​which are the third example group of the present invention. [Figure 6] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y No. 1 to No. 200 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 7]11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 201 to 400 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 8] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 401 to 600 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 9] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 601 to 800 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 10] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 801 to 1000 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 11] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 1001 to 1200 in ascending order of energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 12] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 1201 to 1400 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 13] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 1401 to 1600 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 14] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 1601 to 1800 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 15]11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 1801 to 2000 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 16] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 2001 to 2200 in ascending order of energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 17] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 2201 to 2400 in the order of smallest energy difference ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 18] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 2401 to 2600 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 19] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 2601 to 2800 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 20] 13 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 2801 to 3000 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 21] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 3001 to 3200 in ascending order of energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 22] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 3201 to 3400 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 23]13 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 3401 to 3600 in the order of smallest energy difference ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 24] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 3601 to 3800 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Diagram 25] 13 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 3801 to 4000 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 26] 13 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 4001 to 4200 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 27] 13 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 4201 to 4400 in the order of smallest energy difference ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 28] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 4401 to 4600 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 29] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 4601 to 4800 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Diagram 30] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 4801 to 5000 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Diagram 31]11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 5001 to 5200 in ascending order of energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Diagram 32] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 5201 to 5400 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Diagram 33] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 5401 to 5600 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Diagram 34] 13 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 5601 to 5800 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Diagram 35] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 5801 to 6000 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Diagram 36] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 6001 to 6200 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 37] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 6201 to 6400 in the order of smallest energy difference ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 38] 13 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 6401 to 6600 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 39]13 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 6601 to 6800 in the order of smallest energy difference ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Diagram 40] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 6801 to 7000 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Diagram 41] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y No. 7001 to No. 7200 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Diagram 42] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 7201 to 7400 in the order of smallest energy difference ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Diagram 43] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 7401 to 7600 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Diagram 44] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 7601 to 7800 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Diagram 45] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 7801 to 8000 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Diagram 46] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 8001 to 8200 in ascending order of energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 47]11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 8201 to 8400 in the order of smallest energy difference ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 48] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 8401 to 8600 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 49] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 8601 to 8800 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 50] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 8801 to 9000 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 51] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 9001 to 9200 in ascending order of energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 52] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 9201 to 9400 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 53] 13 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 9401 to 9600 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 54] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 9601 to 9800 in the order of smallest energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 55]13 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 9801 to 10000 in ascending order of energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 56] 11 is a table showing the energy differences ΔEST and oscillator strengths f of organic compounds pX-Y Nos. 10001 to 10006 in ascending order of energy differences ΔEST among the organic compounds pX-Y of the third embodiment group of the present invention. [Figure 57] 1 is a graph showing an emission spectrum of a toluene solution of organic compound C, which is an example of the present invention. [Figure 58] 1 is a graph showing the temperature dependence of transient luminescence decay of a toluene solution of organic compound C, which is an embodiment of the present invention. [Figure 59] 1 is a graph showing the temperature dependence of the delayed fluorescence rate constant kDF of a toluene solution of an organic compound C, which is an example of the present invention. [Figure 60] 1 is a graph showing an emission spectrum of a toluene solution of organic compound D, which is an example of the present invention. [Figure 61] 1 is a graph showing the temperature dependence of transient luminescence decay of a toluene solution of organic compound D, which is an embodiment of the present invention. [Figure 62] 1 is a graph showing the temperature dependence of the delayed fluorescence rate constant kDF of a toluene solution of an organic compound D, which is an example of the present invention. [Figure 63] 1 is a graph showing an emission spectrum of a toluene solution of organic compound E, which is an example of the present invention. [Figure 64] 1 is a graph showing transient luminescence decay of a toluene solution of organic compound E, which is an embodiment of the present invention. [Figure 65] 1 is a graph showing an emission spectrum of an organic light-emitting device using organic compound C according to an embodiment of the present invention. [Figure 66] 1 is a graph showing the current density-voltage-luminance characteristics of an organic light-emitting device using organic compound C, which is an embodiment of the present invention. [Figure 67]1 is a graph showing the external quantum efficiency-luminance characteristics of an organic light-emitting device using organic compound C, which is an embodiment of the present invention. [Figure 68] 1 is a graph showing transient luminescence decay of an organic light-emitting device using organic compound C according to an embodiment of the present invention, and an organic light-emitting device using 4CzIPN. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] [Organic compounds] <Summary> An organic compound according to an embodiment of the present invention is an organic compound having a lone electron pair and a π electron orbital. In the following, the organic compound according to an embodiment of the present invention is referred to as the organic compound of the present invention. The organic compound of the present invention can take at least a ground state S0, a lowest singlet excited state S1, and a lowest triplet excited state T1 (see FIG. 1). When electrons and holes are induced in the organic compound of the present invention, a part of them is excited to the lowest singlet excited state S1, and the remaining majority is excited to the lowest triplet excited state T1. In the following, the induced electrons and holes are collectively referred to as carriers.

[0035] The organic compound of the present invention has an energy level E S1 to the energy level E of the lowest triplet excited state T1 T1 Energy difference ΔE minus ST -0.20eV≦ΔE ST In FIG. 1, the energy level E T1 is the energy level E S1 That is, the energy difference ΔE ST is positive.

[0036] In addition, in the organic compound of the present invention, the energy difference ΔE ST is preferably negative, i.e., -0.20 eV ≤ ΔE ST It is preferably configured to be <0 eV.

[0037] In the organic compound of the present invention, the radiative deactivation rate constant k r is preferably 1.0×10 6 s -1 <k r .

[0038] In the organic compound of the present invention, the oscillator strength f is preferably 0.0050 < f

[0039] Note that each of the above-described energy difference ΔE ST , radiative deactivation rate constant k r , and oscillator strength f is described with two significant figures. When each of the energy difference ΔE ST , radiative deactivation rate constant k r , and oscillator strength f has three or more significant figures, the number of significant figures shall be made two by rounding off the third significant figure.

[0040] <Advantages of the organic compound> The lowest triplet excited state T1 is an unstable excited state. Therefore, for example, when the organic compound of the present invention is used as a light-emitting material for a display including an organic light-emitting diode, the longer the time that the excited carriers stay in the lowest triplet excited state T1, the more likely the organic compound is to deteriorate, and the shorter the driving life, which is the life that can be driven as a light-emitting material, is likely to be.

[0041] In the organic compound of the present invention, since the energy difference ΔE ST is less than 0.0090 eV, it is easier to undergo reverse intersystem crossing from the lowest triplet excited state T1 to the lowest singlet excited state S1 compared to the TADF materials described in Patent Document 1 and Non-Patent Document 1. That is, the reverse intersystem crossing rate constant k RISC of the organic compound of the present invention is larger than the rate constant k RISC of the TADF materials described in Patent Document 1 and Non-Patent Document 1. That is, the organic compound of the present invention can shorten the time that the excited carriers stay in the lowest triplet excited state T1 compared to the TADF materials described in Patent Document 1 and Non-Patent Document 1.

[0042] In addition, the luminescence lifetime of the fluorescent emission caused by the recombination of carriers in the lowest singlet excited state S1 is shorter than the luminescence lifetime of the fluorescent emission caused by the recombination of carriers from the lowest triplet excited state T1. Therefore, the organic compound of the present invention can have a shorter luminescence lifetime than the TADF materials described in Patent Document 1 and Non-Patent Document 1.

[0043] The organic compound of the present invention configured as described above can have higher durability than the TADF materials described in Patent Document 1 and Non-Patent Document 1, and as a result, can extend the operating life of organic light-emitting diodes and displays using the organic compound of the present invention.

[0044] In addition, in the organic compound of the present invention, the energy difference ΔE ST is -0.20 eV or more, the rate constant k RISC It is possible to increase the luminescence intensity and the luminescence quantum yield.

[0045] Energy difference ΔE ST Organic compounds with an energy difference ΔE ST is negative and its absolute value is too large, so it belongs to the Marcus inversion region. Organic compounds that belong to the Marcus inversion region have a rate constant k RISC It is predicted from the calculation results that the luminescence intensity and luminescence quantum yield of organic compounds belonging to the Marcus inversion region are very low. Therefore, it is not practical to use organic compounds belonging to the Marcus inversion region as luminescent materials for displays.

[0046] Therefore, the organic compound of the present invention can be suitably used as a light-emitting material for a display having an organic light-emitting diode, compared with the TADF materials described in Patent Document 1 and Non-Patent Document 1 and the organic compound described in Non-Patent Document 2. Note that an organic light-emitting diode is one aspect of an organic light-emitting device, and an organic light-emitting diode containing the organic compound of the present invention is included in the scope of the present invention.

[0047] <Energy difference ΔE ST Upper and lower limits> (Energy difference ΔE ST (Preferable lower limit of Reverse intersystem crossing in organic compounds occurs due to the weak spin-orbit interaction (H SO ), the rate constant k RISC can be expressed by the Marcus theory type equation, equation (1) (see Aizawa, N., Harabuchi, Y., Maeda, S., & Pu, Y.-J. Kinetic Prediction of Reverse Intersystem Crossing in Organic Donor-Acceptor Molecules. ChemRxiv. Preprint. https: / / doi.org / 10.26434 / chemrxiv.12203240.v1).

number

[0048] where

number

number

[0049] From equations (1) and (2), the rate constant k RISC is ΔE ST The theoretical value of λ by TDDFT calculation is 0.050 eV or more and 0.20 eV or less for a representative TADF material (see Aizawa et. al. above), and 0.0030 eV or more and 0.10 eV or less for a heptadine derivative, which is an example of the organic compound of the present invention. The organic compound of the present invention has an energy difference ΔE ST The lower limit of the rate constant k is -0.20 eV. RISC can be made larger.

[0050] In the organic compound according to one embodiment of the present invention, the energy difference ΔE ST may be below −0.20 eV.

[0051] (Energy difference ΔE ST (Upper limit of The rearrangement energy λ is always positive because it is based on the most stable energy of the lowest triplet excited state T1. To date, the smallest ΔE ST The energy difference between the electrons is reported to be 0.009 eV (see Hironori Kaji et al. "Purely organic electroluminescent material realizing 100% conversion from electricity to light", Nat. Commun. 6, 8476 (2015)). The exchange interaction between molecules is the energy difference ΔE ST The energy difference between the molecules is smaller than that within the molecule. ST The upper limit of 0.0090 eV means that the rate constant k RISC can be made larger than that of the TADF materials described in Patent Document 1 and Non-Patent Document 1.

[0052] <Radiation inactivation rate constant k r lower limit value> In the organic compound of the present invention, the radiation inactivation rate constant k r is 1.0×10 6 s -1 <k r ≦1×10 9 s -1 is preferable. According to this configuration, compared with typical light-emitting materials used in displays equipped with organic light-emitting diodes currently available on the market, it is possible to achieve quantum yields and emission lifetimes similar to theirs, or quantum yields and emission lifetimes of the same level.

[0053] Also, in the organic compound of the present invention, it is preferable that the oscillator strength f satisfies 0.0050 < f. According to this configuration, the intensity of fluorescence can be increased. Therefore, when the organic compound of the present invention is used as a light-emitting material constituting the light-emitting layer of an organic light-emitting diode, the luminance of the organic EL element can be increased.

[0054] <Regarding the wavelength of fluorescence>

[0055] The wavelength λ (nm) of the fluorescence emitted by the organic compound of the present invention is determined according to the energy difference ΔE S1 from the energy level E of the lowest singlet excited state S1 S0 to the energy level E of the ground state S0 S01 (eV). The wavelength λ is obtained by λ = 1240 / ΔE S01 .

[0056] In the organic compound of the present invention, the wavelength λ is not particularly limited.

[0057] <Preferred examples of organic compounds> Hereinafter, a preferred example of the organic compound of the present invention will be described more specifically. However, for the organic compound of the present invention, the energy difference ΔE ST is negative or 0 eV ≦ ΔE STThe chemical structure is not limited to the following examples as long as the organic compound of the present invention satisfies the relationship of -0.20 eV≦ΔE <0.0090 eV. ST It is preferable that the relationship of <0.0090 eV is satisfied.

[0058] In a preferred embodiment, the organic compound of the present invention has a structure represented by the following formula (2): [ka]

[0059] In formula (2), R1, R2, and R3 (hereinafter sometimes referred to as R1 to R3) are each independently any substituent. X1, X2, X3, X4, X5, and X6 (hereinafter sometimes referred to as X1 to X6) are each independently a nitrogen atom or CH. When X1 to X6 are nitrogen atoms, a preferred example is a heptazine derivative.

[0060] In the above formula (2), it is preferable that at least one of X1 to X6 is a nitrogen atom, more preferably two or more or three or more are nitrogen atoms, and further preferably all are nitrogen atoms. When all of X1 to X6 are nitrogen atoms, the structure is represented by the following formula (1). [ka]

[0061] In formula (1), the definitions of R1 to R3 are the same as those in formula (2).

[0062] A preferred example of R1 to R3 in the formulas (1) and (2) will be described more specifically below.

[0063] Although R1 to R3 may each be a different substituent, a structure in which two of R1 to R3 (for example, R2 and R3, or R1 and R3) are the same substituent and the remaining one is a different substituent may be preferable. That is, it may be preferable that R1 to R3 are each composed of three different types of substituents, or two types of substituents, or one type of substituent.

[0064] In particular, the symmetry in a preferred example is D 3h By lowering the energy difference ΔE ST is negative, i.e., -0.20 eV ≤ ΔE ST In some cases, it may be possible to realize an organic compound that satisfies the <0 eV relationship and has a high luminescence quantum yield.

[0065] (Examples of R1 to R3) An example of each of R1 to R3 is as follows. [ka] [ka] [ka] [ka]

[0066] (An example of R1) In a more preferred example, R1 has a structure shown in formula (3). -S-R31, -O-R31, or -N-(R32)R33...(3) In formula (3), R31 to R33 are each independently a chain or cyclic hydrocarbon group having 20 or less carbon atoms, which may be substituted by a substituent. In one example, the chain or cyclic hydrocarbon group may preferably have 10 or less carbon atoms. Furthermore, R32 and R33 bonded to the same nitrogen (N) may be bonded to each other to form a ring structure.

[0067] Specific examples of the chain or cyclic hydrocarbon group represented by R31 to R33 include a chain alkyl group, a chain alkenyl group, a chain alkynyl group, and a hydrocarbon ring group.

[0068] Examples of chain alkyl groups include linear or branched alkyl groups having 20 or less, preferably 15 or less, more preferably 10 or less, and even more preferably 5 or less, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, hexyl, and octyl groups.

[0069] Examples of chain alkenyl groups include linear or branched alkenyl groups having 20 or less, preferably 15 or less, and more preferably 10 or less, such as vinyl, propenyl, butenyl, 2-methyl-1-propenyl, hexenyl, and octenyl groups.

[0070] Examples of chain alkynyl groups include linear or branched alkynyl groups having 20 or less, preferably 15 or less, and more preferably 10 or less, such as ethynyl, propynyl, butynyl, 2-methyl-1-propynyl, hexynyl, and octynyl groups.

[0071] Examples of the hydrocarbon ring group include cycloalkyl groups having 3 or more, and preferably 5 or more, and 20 or less, preferably 15 or less, and more preferably 10 or less, such as a cyclopropyl group, a cyclohexyl group, or a tetradecahydroanthranyl group; cycloalkenyl groups having 3 or more, and preferably 5 or more, and 20 or less, preferably 15 or less, and more preferably 10 or less, such as a cyclohexenyl group; and aryl groups having 6 or more, and 18 or less, and preferably 10 or less, such as a phenyl group, an anthranyl group, a phenanthryl group, or a ferrocenyl group.

[0072] The chain alkyl groups, chain alkenyl groups, chain alkynyl groups, and hydrocarbon ring groups exemplified as R31 to R33 may have a substituent. Examples of the substituent of the chain alkyl group, chain alkenyl group, or chain alkynyl group include halogen groups (halogen atoms) such as a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

[0073] Examples of the substituent of the hydrocarbon ring group include, in addition to the above halogen groups, an amino group (-NH2), a nitro group (-NO2), a cyano group (-CN), a hydroxyl group (-OH), an alkyl group, a halogenated alkyl group, an alkoxy group, etc. Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, an isobutoxy group, a sec-butoxy group, a tert-butoxy group, a pentyloxy group, a hexyloxy group, an octyloxy group, etc. The alkyl portion of the alkyl group, the halogenated alkyl group, the alkoxy group, etc. preferably has 5 or less carbon atoms.

[0074] A more specific example of the structure represented by the above formula (3) is as follows. [ka]

[0075] (An example of R2) In a more preferred example, R2 is selected from a hydrocarbon ring group or a heterocyclic group.

[0076] Examples of the hydrocarbon ring group include cycloalkyl groups having 3 or more, and preferably 5 or more, and 20 or less, preferably 15 or less, and more preferably 10 or less, such as a cyclopropyl group, a cyclohexyl group, or a tetradecahydroanthranyl group; cycloalkenyl groups having 3 or more, and preferably 5 or more, and 20 or less, preferably 15 or less, and more preferably 10 or less, such as a cyclohexenyl group; and aryl groups having 6 or more, and 18 or less, and preferably 10 or less, such as a phenyl group, an anthranyl group, a phenanthryl group, or a ferrocenyl group.

[0077] Examples of the heterocyclic group include a heteroaryl group consisting of a 5- or 6-membered monocyclic ring or a fused ring formed by condensing 2 to 6 5- or 6-membered rings, and a heterocycloalkyl group consisting of a 5- or 6-membered monocyclic ring or a fused ring formed by condensing 2 to 6 5- or 6-membered rings, and examples of the heteroatom include a nitrogen atom, an oxygen atom, a sulfur atom, etc. Specific examples include a 5-membered monocyclic ring such as a thienyl group; a 6-membered monocyclic ring such as a pyridyl group, a 1-piperidinyl group, a 2-piperidinyl group, a 2-piperazinyl group, etc.; and a fused ring consisting of 2 to 6 5- or 6-membered rings such as a benzothienyl group, a carbazolyl group, a quinolinyl group, an octahydroquinolinyl group, etc.

[0078] A preferred example of R2 is a phenyl group which may have 1 to 5 substituents as described below, or a pyridyl group which may have 1 to 4 substituents. When it has a substituent, the number of the substituents is not particularly limited, but may be preferably 1 to 3.

[0079] These hydrocarbon ring groups or heterocyclic groups may have a substituent as described above. Examples of the substituent include halogen groups (halogen atoms) such as fluorine atom, chlorine atom, bromine atom, and iodine atom; amino group (-NH2); nitro group (-NO2); cyano group (-CN); hydroxyl group (-OH); linear or branched alkyl groups having 20 or less carbon atoms, preferably 15 or less, more preferably 10 or less, and even more preferably 5 or less carbon atoms, such as methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, sec-butyl group, tert-butyl group, hexyl group, and octyl group; halogenated alkyl groups; and alkoxy groups. Examples of alkoxy groups include methoxy group, ethoxy group, propoxy group, isopropoxy group, butoxy group, isobutoxy group, sec-butoxy group, tert-butoxy group, pentyloxy group, hexyloxy group, and octyloxy group. The alkyl moiety of the alkyl group, halogenated alkyl group, and alkoxy group preferably has 5 or less carbon atoms.

[0080] A phenyl group which may have 1 to 5 substituents or a pyridyl group which may have 1 to 4 substituents, which are preferred examples of R2, will be described in more detail below. The substituents of the phenyl group or pyridyl group are preferably the above-mentioned halogen group, hydroxyl group, alkyl group, halogenated alkyl group, or alkoxy group. In the phenyl group which may have 1 to 5 substituents, the number of the substituents is preferably 0, 1, 2, or 3. When the number of the substituents is 1, the substituent is preferably located at the 2-position or 4-position of the phenyl group. When the number of the substituents is 2, the substituents are preferably located at the 2- and 4-position or 2- and 6-position of the phenyl group. When the number of the substituents is 3, the substituents are preferably located at the 2-, 4-, and 6-position of the phenyl group. When the number of the substituents is 2 or 3, 2 or 3 substituents selected from the group consisting of an alkyl group, an alkoxy group, and a halogen group may be preferred. In the pyridyl group which may have 1 to 4 substituents, the number of the substituents is preferably 0, 1, 2 or 3, and in some cases 0, 1 or 2 is more preferable.

[0081] A more specific example of R2 is as follows: [ka]

[0082] (An example of R3) In a more preferred example, R3 is selected from the substituents exemplified as R1 or the substituents exemplified as R2. R1 to R3 may be different substituents, but it is more preferred that R3 and R1 are the same substituent or that R3 and R2 are the same substituent.

[0083] (An example of a preferred combination of R1, R2, and R3) In one preferred combination of R1, R2, and R3, R1 is a substituent satisfying the above formula (3), and R2 and R3 are phenyl groups optionally substituted with 1 to 3 substituents. Here, it is more preferred that R2 and R3 are the same group. It is even more preferred that R1 is any of the following: [ka] Furthermore, R2 and R3 are a combination selected from an unsubstituted phenyl group and a phenyl group substituted with 1 to 3 methyl groups (preferably R2 and R3 are the same group).

[0084] Particularly preferred examples of the organic compound of the present invention include the following. [ka] [ka] [ka]

[0085] Among the above, the organic compounds numbered 1, 2, 3, 4 (11), 6, 16, 23, 25, 27, and 29 (33) may be more preferred.

[0086] <An example of a method for synthesizing an organic compound represented by formula (1) or formula (2)> The method for synthesizing the organic compound is not particularly limited. For example, the organic compound can be synthesized by reacting a compound (precursor compound) in which R1 to R3 in formula (1) or formula (2) are halogen groups with a compound corresponding to R1, R2, and R3 in the presence of a Lewis acid catalyst (e.g., aluminum chloride, etc.). When two or more compounds are used as the compounds corresponding to R1, R2, and R3, different R1, R2, and R3 can be introduced by appropriately adjusting the amounts of these compounds used, the timing of their addition to the reaction system, and other reaction conditions. For details of the synthesis method, see the Examples section described below.

[0087] <Uses of the organic compound of the present invention> The organic compound of the present invention can be suitably used, for example, as a light-emitting material for the light-emitting layer of an organic light-emitting element or an organic light-emitting device. The organic compound of the present invention may form a light-emitting layer by itself, or may form a light-emitting layer as a composition (sometimes referred to as a "light-emitting composition") mixed with other compounds. An organic light-emitting element or an organic light-emitting device containing the organic compound of the present invention in the light-emitting layer also falls within the scope of the present invention.

[0088] In addition, the light-emitting layer often contains a host compound and a dopant compound. The dopant compound is sometimes called a guest compound. The host compound is responsible for transporting charges (electrons and holes). The dopant compound is responsible for emitting light. The organic compound of the present invention may be used as a host compound or a dopant compound in the light-emitting layer. In particular, the organic compound of the present invention is preferably a compound having an energy difference ΔE ST -0.20eV≦ΔE STThose satisfying the relationship of <0.0090 eV can be used as either the host compound or the dopant compound. Among the organic compounds of the present invention, the energy difference ΔE ST is ΔE ST <-0.20 eV are preferably used as the host compound.

[0089] Also, the method used for forming the light-emitting layer is not limited. As a method for forming the light-emitting layer, for example, a vacuum evaporation method may be employed, or a coating method may be employed. Examples of the coating method include an inkjet method, a gravure printing method, and a nozzle coating method. Further, the substrate constituting the organic light-emitting device may be any substrate having translucency, and may be a hard substrate typified by glass or a flexible substrate typified by resin.

[0090] <Other aspects> The present invention also includes the following aspects.

[0091] The organic compound according to the first aspect of the present invention is an organic compound having a lone pair and a π electron orbital, and the energy difference ΔE obtained by subtracting the energy level E S1 of the lowest singlet excited state from the energy level E T1 of the lowest triplet excited state is -0.20 eV ≤ ΔE ST <0.0090 eV. ST <0.0090 eV.

[0092] In addition, the organic compound according to the second aspect of the present invention has, in addition to the configuration of the organic compound according to the first aspect described above, a radiative decay rate constant k r of 1.0 × 10 6 s -1 <k r r .

[0093] In addition, the organic compound according to the third aspect of the present invention has, in addition to the configuration of the organic compound according to the first or second aspect described above, an oscillator strength f of 0.0050 < f.

[0094] Further, the organic compound according to the fourth aspect of the present invention has, in addition to the configuration of the organic compound according to any one of the first to third aspects described above, a configuration in which the organic compound is a heptazine derivative represented by the following formula (1) and has three independent substituents R1, R2, and R3. [ka]

[0095] Further, the organic compound according to the fifth aspect of the present invention has, in addition to the configuration of the organic compound according to the fourth aspect described above, a configuration in which the substituents R1, R2, and R3 are each composed of two types of substituents.

[0096] Further, the organic compound according to the sixth aspect of the present invention has, in addition to the configuration of the organic compound according to the fourth aspect described above, a configuration in which the substituents R1, R2, and R3 are each composed of three different types of substituents.

[0097] Further, the organic compound according to the seventh aspect of the present invention has, in addition to the configuration of the organic compound according to the fourth aspect described above, a configuration in which the substituents R1, R2, and R3 are each composed of one type of substituent.

[0098] In order to solve the above problems, the organic compound according to the eighth aspect of the present invention is an organic compound having a lone electron pair and a π electron orbital, and is a heptazine derivative represented by the following formula (1) and having three independent substituents R1, R2, and R3, and the substituents R1, R2, and R3 are composed of two or three types of substituents. [ka]

[0099] Moreover, an organic light-emitting device according to a ninth aspect of the present invention comprises an organic compound according to any one of the first to eighth aspects of the present invention.

[0100] An organic light-emitting device according to a tenth aspect of the present invention has, in addition to the configuration of the organic light-emitting device according to the ninth aspect described above, a light-emitting layer containing the organic compound functioning as a dopant compound and a host compound.

[0101] In order to solve the above problems, an organic light-emitting device according to an eleventh aspect of the present invention includes an emitting layer containing a dopant compound and a host compound. In this organic light-emitting device, the host compound is an organic compound having a lone pair of electrons and a π electron orbital, and has an energy level E of the lowest singlet excited state S1. S1 to the energy level E of the lowest triplet excited state T1 T1 Energy difference ΔE minus ST is negative or 0 eV ≤ ΔE ST <0.0090 eV.

[0102] In order to solve the above problems, an organic light-emitting device according to a twelfth aspect of the present invention includes an emitting layer containing a dopant compound and a host compound. In this organic light-emitting device, the host compound is a heptazine derivative having a lone pair of electrons and a π electron orbital, and is represented by the following formula (1) and has an optional substituent R1: [ka] EXAMPLES

[0103] [First embodiment] The organic compound A, which is a first embodiment of the present invention, will be described below. The organic compound A is a heptazine derivative represented by the following formula (4). That is, the organic compound A has a mother nucleus of heptazine, and three substituents R1, R2, and R3, in which R1 is a 1-piperidinyl group (i.e., -N-(R32)R33 represented by formula (4), and -R32 and -R33 are bonded to each other to form a ring structure), and R2 and R3 are both 4-methoxyphenyl groups. That is, the three substituents are composed of two types of substituents. [ka]

[0104] <Energy difference ΔE ST and calculation of oscillator strength f> (TDDFT calculation) Using TDDFT calculations, the structures of the lowest singlet excited state S1 and the lowest triplet excited state T1 of organic compound A are optimized, and the energy difference ΔE ST and the oscillator strength f were calculated. The TDDFT calculation was performed using the TDDFT calculation implemented in Gaussian16, with the ωB97X-D functional and the 6-31G(d) basis set.

[0105] (ADC(2) calculation) In the most stable structure of the lowest triplet excited state T1 of organic compound A obtained by the above-mentioned TDDFT calculation, the energy difference ΔE ST and the oscillator strength f were calculated. The ADC(2) calculation implemented in Q-Chem5.2 was used, and the basis set was 6-31G(d).

[0106] Energy difference ΔE of organic compound A calculated by TDDFT calculation and ADC(2) calculation ST and oscillator strength f are shown in Table 1. The energy difference ΔE of organic compound A calculated using the ADC(2) calculation, which can also take into account two-electron excitation, ST and the oscillator strength f are, respectively, ΔE ST =-0.35 eV and f=0.017. In other words, organic compound A has a negative energy difference ΔE ST and a relatively large oscillator strength f. [Table 1]

[0107] <Synthetic scheme> Organic compound A was obtained by the synthesis scheme shown below. That is, under an argon atmosphere, AlCl3 (1.83 mmol) is added to a dichloromethane solution (5 ml) of anisole (2.5 mmol) at 0°C. The mixture is left at that temperature for 40 minutes, and trichloroheptazine (0.83 mmol) is added at 0°C. After 10 minutes, the temperature is raised to room temperature and rotated overnight. After 20 hours, reflux is started and continued for 4 hours. When the temperature is returned to room temperature, 0.5 ml (excess amount) of piperidine is added. After 1 hour, water is added to quench. A yellowish-white organic compound A is isolated by column purification (1% AcOEt / DCM → 15% AcOEt / DCM). In this example, the yield of organic compound A was 15%. [ka]

[0108] <Light Emitting Characteristics> For the mixed thin film of organic compound A synthesized in this way and 2,8-bis(diphenylphosphoryl)dibenzo[b,d]furan (PPF), (1) the emission spectrum was measured using a Fluoromax-4 fluorescence spectrophotometer manufactured by HORIBA, (2) the emission quantum yield was measured using an integrating sphere C9920 manufactured by Hamamatsu Photonics, and (3) the emission lifetime τ of delayed fluorescence was measured using a Fluorolog-3 manufactured by HORIBA. In the mixed thin film of this example, the concentration of organic compound A was 5 wt%. The upper, middle, and lower rows of Figure 2 respectively show the emission spectrum, temperature dependence of transient luminescence decay, and rate constant k of delayed fluorescence of the mixed thin film of this example. DF 1 is a graph showing the temperature dependence of

[0109] The measurements of (1), (2), and (3) above were carried out under an inert nitrogen atmosphere. The measurement of (3) above was carried out by changing the temperature using a UNISOKU cryostat CoolSpeK. The temperature dependence of the obtained luminescence lifetime τ was analyzed using equation (3) assuming thermal equilibrium between the lowest singlet excited state S1 and the lowest triplet excited state T1, and the energy difference ΔE STand the radiative deactivation rate constant k r The experimental value of was estimated. In equation (3), k B is the Boltzmann constant, T is the absolute temperature, k DF is the rate constant of delayed fluorescence.

number

[0110] The mixed thin film of this example exhibited blue emission (CIE 0.16, 0.14) with a maximum emission wavelength of 442 nm (see the upper part of FIG. 2). In addition, the mixed thin film of this example exhibited a high luminescence quantum yield of 85%, a short luminescence lifetime τ of 1066 ns, and a radiative deactivation rate constant k r 1.2×10 8 s -1 From the temperature dependence of the luminescence lifetime τ, the energy difference ΔE ST ΔE ST = 0.004 eV (see the middle and bottom panels of Fig. 2). The radiative deactivation rate constant k r The oscillator strength f without taking into account the degeneracy, estimated using equation (4), was f = 0.35.

number

number

[0111] [First Reference Example] The toluene solution of organic compound A synthesized using the synthesis scheme described in the first embodiment is used as the first reference example. In the toluene solution of this reference example, the concentration of organic compound A is 8×10 -5M. As in the first embodiment, (1) the emission spectrum of the toluene solution of this reference example was measured using a Fluoromax-4 fluorescence spectrophotometer manufactured by HORIBA, (2) the emission quantum yield was measured using an integrating sphere C9920 manufactured by Hamamatsu Photonics, and (3) the emission lifetime τ of delayed fluorescence was measured using a Fluorolog-3 manufactured by HORIBA. The upper, middle, and lower panels of FIG. 3 respectively show the emission spectrum, temperature dependence of transient luminescence decay, and rate constant k of delayed fluorescence of the toluene solution of this reference example. DF 1 is a graph showing the temperature dependence of

[0112] The toluene solution of this reference example emitted blue light (CIE 0.16, 0.16) with a maximum emission wavelength of 442 nm (see the upper part of Figure 3). In addition, the toluene solution of this reference example showed a high emission quantum yield of 75% and a short emission lifetime τ of 588 ns. From the temperature dependence of the emission lifetime τ, the energy difference ΔE ST ΔE ST = 0.033 eV, and the radiative deactivation rate constant k r k r =2.2×10 7 s -1 (See the middle and bottom panels of Figure 3.)

[0113] [Second Example Group] Organic compounds 1 to 38, which are the second example group of the present invention, are described below. Each of organic compounds 1 to 38 is the 38 organic compounds described above as a particularly preferred example of the organic compound of the present invention.

[0114] As in the first embodiment, the structures of the lowest singlet excited state S1 and the lowest triplet excited state T1 of the organic compounds 1 to 38 are optimized using TDDFT calculations, and the energy difference ΔE ST and oscillator strength f were calculated. ST 4 is a graph showing the correlation between the frequency and oscillator strength f. Note that the solid line in FIG. (ΔEST) =(ΔE ST -0.18) × 0.3 (ΔEST)That is, each of the organic compounds 1 to 38 satisfies f≧(ΔE ST -0.18) × 0.3.

[0115] Energy difference ΔE of organic compound A, which is the first example ST is calculated as ΔE ST = 0.27 eV, but when calculated from the luminescence characteristics of the synthesized organic compound A, ΔE ST =0.0040 eV. In other words, the energy difference ΔE ST is the energy difference ΔE when using TDDFT calculation ST It was found that the shift was smaller compared to

[0116] Based on the results of the first embodiment described above, the energy difference ΔE ST The energy difference ΔE calculated using TDDFT calculations in the space spanned by and the oscillator strength f ST and the oscillator strength f is f ≧ (ΔE ST Each of the organic compounds 1 to 38 that satisfy the relational formula of −0.18)×0.3 is included in the scope of the present invention.

[0117] [First Comparative Example] The organic compound B described in Non-Patent Document 2 will be described below. Organic compound B is a heptazine derivative represented by the following formula (5). That is, organic compound B has a heptazine core and three substituents R1, R2, and R3, which are all 4-methoxyphenyl groups. [ka]

[0118] For organic compound B, the energy difference ΔE calculated using the ADC(2) calculation ST and the oscillator strength f are, respectively, ΔE ST =-0.250 eV and f=0.0000050.

[0119] On the other hand, a toluene solution was prepared for organic compound B, and in the same manner as in the first example, (1) the emission spectrum was measured using a Fluoromax-4 fluorescence spectrophotometer manufactured by HORIBA, (2) the emission quantum yield was measured using a C9920 integrating sphere manufactured by Hamamatsu Photonics, and (3) the emission lifetime τ was measured using a Fluorolog-3 manufactured by HORIBA. As a result, the radiative deactivation rate constant k r , and the oscillator strength f are k r =1.0×10 6 s -1 , and f = 0.0039. It was found that organic compound B did not exhibit delayed fluorescence. Therefore, the energy difference ΔE ST could not be evaluated.

[0120] As described above, organic compound B does not exhibit delayed fluorescence and has an energy difference ΔE ST Since it is not possible to evaluate the fluorescence intensity of organic compound B, it is not included in the scope of the present invention. Organic compound B has a very small oscillator strength, which results in low fluorescence intensity. Therefore, it is difficult to use organic compound B as a light-emitting material for displays.

[0121] [Third Example Group] The organic compounds pX-Y which are the third embodiment group of the present invention will be described below.

[0122] <Naming rules for organic compounds> In the organic compound pX-Y, ​​each of X and Y is an integer of 1 to 186, which corresponds to the numbers of the 186 types of substituents exemplified in the section (Examples of R1 to R3). In the structure of the following formula (1), the organic compound pX-Y employs a substituent specified by a common X as R2 and R3, and employs a substituent specified by Y as R1. [ka]

[0123] For example, the organic compound p37-151 is represented by the following formula (6). [ka]

[0124] <Screening calculation> In the organic compound pX-Y, ​​R2 and R3 are selected from 186 substituents, and similarly, R1 is selected from 186 substituents. Therefore, the organic compound pX-Y is a group of 34596 organic compounds in total.

[0125] For these 34596 organic compounds pX-Y, ​​the structure of T1 was optimized using the Unrestricted DFT implemented in Gaussian16. The functional was LC-BLYP and the domain decomposition parameter was 0.18 Bohr -1 The basis set was 6-31G. Using the obtained T1 optimized structure, the energy difference ΔE ST The oscillator strength f was calculated using the LC-BLYP functional and the domain decomposition parameter of 0.18 Bohr -1 The basis set used was 6-31G(d). In the following, this calculation is referred to as the screening calculation.

[0126] The results of the screening calculation for the organic compound pX-Y of 34596 are shown in Figure 5. Figure 5 shows the energy difference ΔE ST This is a scatter diagram showing the correlation between the energy difference ΔE ST 6 to 56 show the organic compounds pX-Y of 10006 selected in ascending order of energy difference ΔE ST and oscillator strength f. The numbers in Figs. 6 to 56 indicate the energy difference ΔE ST They are arranged in ascending order of size.

[0127] <High precision calculation> In addition, for the organic compounds pX-Y, ​​the following organic compounds C, D, and E were optimized for T1 using Unrestricted MP2 implemented in Gaussian16. The basis set was cc-pVDZ. Using the obtained T1 optimized structures, the energy difference ΔE ST and the oscillator strength f were calculated. The basis function used was cc-pVDZ. In the following, this calculation is referred to as the high-precision calculation.

[0128] Organic compounds C and D have a relatively small energy difference ΔE ST The organic compound E is an analogue of the organic compounds C and D.

[0129] Organic compound C is organic compound p37-151 and is represented by the following formula (7). [ka] Organic compound C was synthesized as follows. Intermediate I1 represented by the following formula (8) was dissolved in m-xylene, and aluminum chloride (1.0 g, 7.6 mmol) was added at 0°C. The mixture was stirred at 0°C for 2 hours and at room temperature for 17 hours, and water was added. Chloroform was then added and stirred for 30 minutes, after which the organic layer was separated, dried over sodium sulfate, and concentrated. Column purification was performed (CHCl3 100%) to obtain organic compound C. The obtained yellow solid organic compound C was 17 mg (0.224 mmol, 7.1%). 1H NMR (600 MHz, CDCl3) δ[ppm] = 2.39 (s, 6H), 2.73 (s, 6H), 4.88 (q, J = 8.2 Hz, 2H), 7.11 - 7.13 (m, 4H), 8.19 (d, J = 7.8 Hz, 2H) MS (MALDI-TOF): 478.60 [calcd:479.17] [ka]

[0130] Intermediate I1 was synthesized as follows. 2,2,2-trifluoroethanol (199 mL, 2.78 mmol) was dissolved in tetrahydrofuran (10 mL), and sodium hydride (121 mg, 3.0 mmol) was added at 0°C. After stirring for 30 minutes, cyameluric acid (700 mg, 2.53 mmol) was slowly added dropwise to a tetrahydrofuran solution (20 mL) at 0°C, and the mixture was stirred at 0°C for 2 hours and at room temperature for 1 hour. The reaction solution was concentrated under reduced pressure to obtain intermediate I1.

[0131] Organic compound D is organic compound p37-107 and is represented by the following formula (9). [ka] Organic compound D was synthesized as follows. Intermediate I2 represented by the following formula (10) was dissolved in m-xylene (20 mL), and aluminum chloride (980 mg, 0.79 mmol) was added at room temperature under an argon atmosphere, and the mixture was stirred for 17 hours. Water was added to stop the reaction. After extraction with chloroform, the organic layer was dried over sodium sulfate and concentrated. Purification was performed using a column (AcOEt: CHCl3 = 0:100 - 5:95) to obtain the target product. The obtained yellow solid organic compound D was 25 mg (0.054 mmol, 2.2%). 1 H NMR (600 MHz, CDCl3) δ[ppm] = 1.66 - 1.71 (m, 6H), 2.36 (s, 6H), 2.67 (s, 6H), 3.96 (br s, 4H), 7.06 - 7.07 (m, 4H), 7.99 (d, J = 8.4 Hz, 2H) MS (MALDI-TOF): 465.71 [calcd:464.24] [ka]

[0132] The synthesis of intermediate I2 was carried out as follows. Cyameluric acid chloride (677 mg, 2.45 mmol) was dissolved in tetrahydrofuran (20 mL) and piperidine (266 mL, 2.7 mmol) was added at room temperature. After 30 minutes, the temperature was raised to 50°C and stirred for 45 minutes. After returning to room temperature, the reaction solution was concentrated under reduced pressure to obtain intermediate I2.

[0133] Organic compound E is organic compound p37-37 and is represented by the following formula (11). [ka] The synthesis of organic compound E was carried out as follows. Cyameluric acid (623 mg, 2.26 mmol) was dissolved in m-xylene (20 mL), and diphenylamine (420 mg, 2.49 mmol) was added at room temperature. After stirring for 2.5 hours, the temperature was raised to 50°C and stirring was continued for another 2 hours. The mixture was cooled to 0°C, and aluminum chloride (904 mg, 6.8 mmol) was added. After stirring at room temperature for 17 hours, water was added. After 30 minutes, chloroform was added, and the organic layer was separated, dried over sodium sulfate, concentrated, and purified by column (CHCl3 100%) to obtain the target product. The obtained white solid organic compound p37-37 was 70 mg (0.14 mmol, 6.4%). 1 H NMR (600 MHz, CDCl3) δ[ppm] = 2.34 (s, 6H), 2.63 (s, 6H), 7.03 (br s, 4H), 7.28 - 7.31 (m, 6H), 7.38 (t, J = 7.8 Hz, 4H), 7.97 (d, J = 8.4 Hz, 2H) MS (MALDI-TOF): 549.94 [calcd:548.24]

[0134] The high-precision calculation results for organic compounds C, D, and E are shown in Table 2. [Table 2]

[0135] <Evaluation of light emission characteristics> Organic compound C in toluene (concentration 8.0 × 10 -5 The emission spectra of the mixed thin film (concentration 10 wt%) of organic compound C and 2,8-bis(diphenylphosphoryl)dibenzo[b,d]furan (PPF) prepared by vacuum deposition were measured using a Fluoromax-4 fluorescence spectrophotometer manufactured by HORIBA. The emission quantum yields of the toluene solution of organic compound C and the mixed thin film were measured using a Hamamatsu Photonics C9920 integrating sphere. The emission lifetimes τ of the toluene solution of organic compound C and the mixed thin film were measured using a Fluorolog-3 fluorescence lifetime measurement device manufactured by HORIBA. The emission lifetimes τ can also be called delayed fluorescence lifetimes. The above measurements were performed under an inert nitrogen atmosphere with an excitation light wavelength of 370 nm. The delayed fluorescence lifetimes τ were measured by changing the temperature using a cryostat CoolSpeK manufactured by UNISOKU. The temperature dependence of the obtained delayed fluorescence lifetimes τ was analyzed using equation (3) assuming thermal equilibrium between S1 and T1, and the energy difference ΔE ST and the radiative deactivation rate constant k r The experimental value was estimated.

number

[0136] Similar to organic compound C, toluene solutions of organic compounds D, E, F, G, H, I, J, K, L, and M were prepared and their luminescence properties were evaluated.

[0137] The organic compound F is the organic compound p1-151 and is represented by the following formula (12). [ka] The synthesis of organic compound F was carried out as follows. Intermediate I1 was dissolved in benzene (15 mL), and aluminum chloride (884 mg, 6.6 mmol) was added at 0°C and stirred for 5 minutes. The mixture was further stirred at room temperature for 10 minutes and at 70°C for 19 hours. Water was added and stirred for 30 minutes, after which chloroform was added and the organic layer was separated. After drying with sodium sulfate, the mixture was concentrated and purified with a column (CHCl3 100%) to obtain the target product. The obtained yellow solid organic compound F was 15 mg (0.035 mmol, 1.6%). 1 H NMR (600 MHz, CDCl3) δ[ppm] = 4.92 (q, J = 8 Hz, 2H), 7.53 (dd, J = 7.8 Hz, 4H), 7.68 (dd, J = 7.2 Hz, 2H), 8.56 (d, J = 7.2 Hz, 4H) MS (MALDI-TOF): 469.61 [calcd:468.20]

[0138] The organic compound G is the organic compound p7-151, and is represented by the following formula (13). [ka] The synthesis of organic compound G was carried out as follows. Intermediate I1 was dissolved in toluene (10 mL), and aluminum chloride (872 mg, 6.5 mmol) was added at 0°C. The mixture was stirred at 0°C for 30 minutes and at room temperature for 19 hours. Water and then chloroform were added, and the mixture was stirred for 30 minutes, after which the organic layer was separated. After drying with sodium sulfate, the mixture was concentrated and purified using a column (CHCl3 100%) to obtain the target product. The obtained yellow solid organic compound G was 90 mg (0.20 mmol, 9.2%). 1 H NMR (600 MHz, CDCl3) δ[ppm] = 2.46 (s, 6H), 4.90 (q, J = 8 Hz, 2H), 7.33 (d, J = 7.8 Hz, 4H), 8.45 (d, J = 8.4 Hz, 4H) MS (MALDI-TOF): 452.64 [calcd:451.14]

[0139] Organic compound H is organic compound p7-107 and is represented by the following formula (14). [ka] The synthesis of organic compound H was carried out as follows. Cyameluric acid chloride (100 mg, 0.36 mmol) was dissolved in toluene (3 mL) and piperidine (36 mL, 0.36 mmol) was added at room temperature. After 5 minutes, the temperature was raised to 100°C, stirred for 30 minutes, and then returned to room temperature. Aluminum chloride (106 mg, 0.79 mmol) was added, and the mixture was stirred at 100°C for 1 hour, then returned to room temperature and water was added. The organic layer was separated, dried over sodium sulfate, concentrated, and purified by column (AcOEt: CHCl3=0:100 - 1:20) to obtain the target product. The obtained yellow solid organic compound H was 19 mg (0.044 mmol, 12.1%). 1 H NMR (600 MHz, CDCl3) δ[ppm] = 1.68 - 1.72 (m, 6H), 2.44 (s, 6H), 3.99 (br s, 4H), 7.29 (d, J = 7.8 Hz, 4H), 8.44 (d, J = 7.8 Hz, 4H)

[0140] Organic compound I is organic compound p64-166 and is represented by the following formula (15). [ka] The synthesis of organic compound I was carried out as follows. To a solution of intermediate I3 (608 μL, 4.3 mmol) represented by the following formula (16) in dichloromethane (11.8 mL), aluminum chloride (616 mg, 4.6 mmol) was added at room temperature and stirred for 40 minutes. A solution of compound 2 in dichloromethane (12 mL) was slowly added and stirred at room temperature for 20.5 hours. 1M aqueous sodium hydroxide solution (16 mL) was added at 0°C, and the mixture was stirred at room temperature for 4 hours, and then filtered using Celite. After adding a 20% aqueous sodium chloride solution to the reaction solution, the organic layer was separated, dried over anhydrous sodium sulfate, concentrated, and purified by column (CH2Cl2- CH2Cl2: MeOH = 9: 1) to obtain a crude product (117 mg). The crude product was purified by a preparative column (SunFire, Hexane / EtOAc = 82: 18), and organic compound I was obtained as the first peak. The obtained yellow solid organic compound I was 8.4 mg (0.015 mmol, 1.4%). 1 H NMR (600 MHz, CDCl3) δ[ppm] = 0.80-0.92 (br, 2H), 1.20-1.38 (br, 2H), 1.38-1.50 (br, 2H), 1.69-1.79 (br, 2H), 2.01-2.11 (br, 2H), 2.41 (s, 12H), 3.80 (s, 6H), 3.87-3.96 (br, 1H), 6.60 (s, 4H) [ka]

[0141] Intermediate I3 was synthesized as follows. Diisopropylethylamine (93 μL, 0.54 mmol) and cyclohexanethiol (66 μL, 0.54 mmol) were added to a suspension of cyameloyl chloride·potassium trichloride (536 mg, 1.1 mmol) in toluene (8.9 mL) at room temperature, and the mixture was heated to reflux for 14 hours. After cooling to room temperature and filtering off insoluble matter, the mixture was concentrated under reduced pressure to obtain intermediate I3.

[0142] The organic compound J is organic compound p107-4 and is represented by the following formula (17). [ka] The synthesis of organic compound J was carried out as follows. To a solution of aluminum chloride (133 mg, 1.0 mmol) and methoxybenzene (41 μL, 0.38 mmol) in dichloromethane (3 mL), cyameluric acid chloride (70 mg, 0.25 mmol) was added at 0 °C. After 10 minutes, the reaction solution was warmed to room temperature and stirred for 17 hours. An excess of piperidine (0.5 mL) was added and stirred for 30 minutes, after which it was diluted with water and chloroform. The separated organic layer was concentrated and purified by column chromatography (CH2Cl2 100% - AcOEt:CH2Cl2 = 1: 4) to obtain the target product. The obtained yellow solid organic compound J was 6.8 mg (0.015 mmol, 6.1%). 1 H NMR (600 MHz, CDCl3) δ [ppm] = 1.64 - 1.69 (m, 12H), 3.91 (t, 4H), 3.95 (t, 4H), 6.93 (d, J = 9 Hz, 2H), 8.48 (d, J= 8.4 Hz, 2H) 13 C NMR (600 MHz, CDCl3) δ [ppm] = 24.44, 26.16, 45.50, 55.44, 113.47, 127.71, 132.10, 155.21, 156.09, 161.40, 163.88, 172.87 MS (FD-TOF): 445.2342 [M] + , calcd. for C 23 H 27 NO (445.2339)

[0143] The organic compound K is the organic compound p107-107 and is represented by the following formula (18). [ka] The synthesis of organic compound K was carried out as follows. To a solution of aluminum chloride (133 mg, 1.0 mmol) and methoxybenzene (41 μL, 0.38 mmol) in dichloromethane (3 mL), cyameluric acid chloride (70 mg, 0.25 mmol) was added at 0 °C. After 10 minutes, the reaction solution was warmed to room temperature and stirred for 17 hours. An excess of piperidine (0.5 mL) was added and stirred for 30 minutes, after which it was diluted with water and chloroform. The separated organic layer was concentrated and purified using a column (CH2Cl2 100% - AcOEt:CH2Cl2 = 1: 4) to obtain the target product. The obtained white solid organic compound K was 30 mg (0.071 mmol, 28.4%). 1 H NMR (600 MHz, CDCl3) δ [ppm] = 1.59 - 1.65 (m, 18H), 3.87 (t, 12H) 13 C NMR (600 MHz, CDCl3) δ[ppm] = 24.50, 26.12, 45.15, 155.11, 161.59 MS (FD-TOF): 422.2658 [M] + , calcd. for C 21 H 30 N 10 (422.2655)

[0144] The organic compound L is the organic compound p105-105 and is represented by the following formula (19). [ka] Organic compound L was synthesized as follows. Dicyclohexylamine (1.39 ml, 7.0 mmol) was added to a suspension of cyameloyl chloride·potassium trichloride mixture (501 mg, 1.0 mmol) in toluene (5.5 mL) at room temperature. The mixture was stirred at 100°C for 21 hours using a heat block. Dichloromethane and water were added to the reaction solution, and the organic layer was separated, dried over anhydrous sodium sulfate, and concentrated under reduced pressure to obtain a crude product (1.088 g). The crude product was recrystallized from dichloromethane and purified by column chromatography (CHCl). Organic compound L was obtained as a white solid, weighing 220.7 mg (0.310 mmol, 31.0%). 1 H NMR (600 MHz, CDCl3) δ[ppm] = 1.10-1.22 (br, 12H), 1.27-1.44 (br, 18H), 1.58-1.74 (br, 18H), 1.80 (d, J = 12.0 Hz, 12H), 2.08-2.94 (br, 6H) MS (MALDI-TOF): 712.251 [M+H = 712.067]

[0145] The organic compound M is the organic compound p144-144 and is represented by the following formula (20). [ka] The synthesis of organic compound M was carried out as follows. Cyameluric acid chloride (138 mg, 0.5 mmol) and dimethylaminopyridine (220 mg, 1.8 mmol) were placed in a flask, and cyclohexanol (3 mL) was added at room temperature under a nitrogen atmosphere. After 5 minutes, the temperature was raised to 60°C, and after another hour, to 70°C, and the mixture was stirred for 17 hours. After returning to room temperature and adding water, the mixture was extracted with chloroform, and the organic layer was dried over sodium sulfate and concentrated. The product was purified using a column (CHCl3 100%) to obtain the target product. The obtained white solid organic compound M was 41 mg (0.088 mmol, 18%). 1H NMR (600 MHz, CDCl3) δ[ppm] = 1.28 - 1.34 (m, 3H), 1.36 - 1.43 (m, 6H), 1.53 - 1.56 (m, 3H), 1.58 - 1.64 (m, 6H), 1.77 - 1.79 (m, 6H), 1.95 - 1.98 (m, 6H), 5.15 - 5.19 (m, 3H), MS (ESI): 468.27 [calcd:467.26]

[0146] (Luminescent properties of organic compound C) In a toluene solution, organic compound C emitted blue light with a maximum emission wavelength of 449 nm (see FIG. 57). The luminescence quantum yield of organic compound C in a toluene solution was high at 74%, and it showed a short luminescence lifetime τ of 214 ns. From the temperature dependence of the luminescence lifetime τ, the energy difference ΔE ST to -6 meV, and the radiative deactivation rate constant k r A 1.1 x 10 7 s -1 (See Figures 58 and 59.)

[0147] (Luminescent properties of organic compound D) In a toluene solution, organic compound D emitted blue light with a maximum emission wavelength of 442 nm (see FIG. 60). The luminescence quantum yield of organic compound D in a toluene solution was high at 67%, and it showed a short luminescence lifetime τ of 565 ns. From the temperature dependence of the luminescence lifetime τ, the energy difference ΔE ST is 47 meV, and the radiative deactivation rate constant k r 3.2 × 10 7 s -1 (See Figures 61 and 62.)

[0148] (Emission characteristics of organic compound E) In a toluene solution, organic compound E emitted green light with a maximum emission wavelength of 518 nm (see FIG. 63). The luminescence quantum yield of organic compound E in a toluene solution was 12%. No delayed fluorescence was observed from the transient luminescence decay measurement, and only fluorescence with a luminescence lifetime τ of 90 ns was observed (see FIG. 64).

[0149] (Emission properties of organic compounds F-M) Table 3 shows the luminescence characteristics of organic compounds F, G, H, I, J, K, L, and M. Table 3 also shows the luminescence characteristics of organic compounds C, D, and E described above.

[0150] As shown in Table 3, organic compounds F and G have a negative energy difference ΔE in toluene solution, just like organic compound C. ST Organic compound H, like organic compound D, shows a positive energy difference ΔE ST Organic compounds I, J, K, L, and M, like organic compound E, did not show delayed fluorescence. [Table 3]

[0151] <Evaluation of organic light-emitting devices> A glass substrate with indium tin oxide (ITO) of 130 nm thickness was ultrasonically cleaned in the following order: neutral detergent, ultrapure water, acetone, and 2-propanol. After boiling in 2-propanol, it was treated with UV ozone for 30 minutes. Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) (Clevious, Hereaeus) diluted to 60% with ultrapure water was placed on the glass substrate with ITO. TMA dispersion of PEDOT:PSS (CH8000) was spin-coated in air and then dried at 200°C for 10 minutes to form a PEDOT:PSS film with a thickness of 30 nm. Then, a 5-nm-thick layer of molybdenum trioxide (MoO3), a 3-nm-thick layer of 4,4′′-bis(triphenylsilanyl)-(1,1′,4′,1′′)-terphenyl (BST), a 10-nm-thick layer of bis(4-(dibenzo[b,d]furan-4-yl)phenyl)diphenylsilane (DBFSiDBF), a 15-nm-thick layer of 2,8-bis(diphenylphosphoryl)dibenzo[b,d]furan (PPF) and organic compound C (10 wt%), a 10-nm-thick layer of PPF, a 40-nm-thick layer of tris(8-hydroxyquinolinato)aluminium (Alq3), a 1-nm-thick layer of (8-hydroxyquinolinato)lithium (Liq), and a 100-nm-thick layer of aluminum were deposited by vacuum deposition to fabricate an organic light-emitting device. The light-emitting area of ​​the organic light-emitting device was 2.0 × 2.0 mm. 2 The structural formulas of PEDOT, PSS, BST, DBFSiDBF, PPF, Alq3, and Liq are as follows: [ka]

[0152] Similarly, an organic light-emitting device was fabricated using 2,4,5,6-tetra(carbazol-9-yl)isophthalonitrile (4CzIPN) instead of organic compound C.

[0153] The current density-voltage-luminance characteristics of the fabricated organic light-emitting devices were measured using a Tektronix Keithley 2400 source meter and a Konica Minolta CS-200 luminance meter. The EL spectra were measured using a Hamamatsu Photonics PMA-11 multichannel spectrometer. The transient luminescence decay was measured by applying a pulse voltage (maximum 8 V, minimum -4 V) at a frequency of 1 KHz using a Hamamatsu Photonics H7826 light sensor, an Agilent 33220A function generator, and a Tektronix DPO3052 oscilloscope.

[0154] The organic light-emitting device using organic compound C exhibited blue light emission from organic compound C at a current of 0.1 mA to 5.0 mA (see FIG. 65). This organic light-emitting device also exhibited good current density-voltage-luminance characteristics without leakage current or the like (see FIG. 66). In this organic light-emitting device, the maximum external quantum efficiency of organic compound C reached 17% (see FIG. 67). These results demonstrated that organic compound C converts triplet excitons to singlet excitons and can be used as an organic light-emitting device. Furthermore, compared to 4CzIPN, a common TADF material, organic compound C in this organic light-emitting device exhibited fast transient luminescence decay (see FIG. 68). This is due to the negative energy difference ΔE ST This is because triplet excitons can be rapidly converted to singlet excitons due to the above-mentioned property and can be used to emit light.

[0155] <Other organic compounds> In addition to the above-mentioned organic compounds C to M, organic compounds p4-107, p4-4, p37-118, p139-139, p141-141, p142-142, p140-140, p162-162, and p65-166 were synthesized.

[0156] The organic compound p4-107 is represented by the following formula (21). [ka] The synthesis of organic compound p4-107 was carried out as follows. Cyameryl chloride (70 mg, 0.3 mmol) was dissolved in dichloromethane (3 mL), and aluminum chloride (130 mg, 1.0 mmol) and methoxybenzene (80 mL, 0.8 mmol) were added at 0°C. After stirring for 15 minutes, the temperature was raised to room temperature and stirred for 18 hours. An excess amount of piperidine (1.0 mL) was added to the reaction solution, and after 30 minutes, water and dichloromethane were added to dilute it. The organic layer was separated, dried over sodium sulfate, concentrated, and purified by column (AcOEt:CH2Cl2=1:50 - 1:6) to obtain organic compound p4-107. The obtained yellow solid organic compound p4-107 was 5.4 mg (0.012 mmol, 4.6%). 1 H NMR (600 MHz, CDCl3) δ[ppm] = 1.68 - 1.72 (m, 6H), 2.44 (s, 6H), 3.99 (br s, 4H), 7.29 (d, J = 7.8 Hz, 4H), 8.44 (d, J = 7.8 Hz, 4H) MS (MALDI-TOF): 469.61 [calcd:468.20]

[0157] The organic compound p4-4 is represented by the following formula (22). [ka] The synthesis of organic compound p4-4 was carried out as follows. Cyameluric acid chloride (100mg, 0.36mmol) was dissolved in dichloromethane (3mL), and methoxybenzene (196mL, 1.8mmol) and aluminum chloride (173mg, 1.3mmol) were added at 0℃. After 5 minutes, the temperature was raised to room temperature and stirred for 24 hours. After adding water, the organic layer was separated and dried over sodium sulfate. After concentration, purification was carried out on a column (AcOEt: CHCl3=0:100 - 1:20) to obtain the target product. The obtained yellow solid organic compound p4-4 was 34.5mg (0.071mmol, 19.8%). 1H NMR (600 MHz, CDCl3) δ[ppm] = 3.92 (s, 9H), 6.99 (d, J = 9 Hz, 6H), 8.57 (d, J = 9 Hz, 6H) MS (MALDI-TOF): 492.65 [calcd:491.17]

[0158] The organic compound p37-118 is represented by the following formula (23). [ka] The synthesis of organic compound p37-118 was carried out as follows. Cyameluric acid (623 mg, 2.26 mmol) was dissolved in m-xylene (20 mL), and diphenylamine (420 mg, 2.49 mmol) was added at room temperature. After stirring for 2.5 hours, the temperature was raised to 50°C and stirring was continued for another 2 hours. The mixture was cooled to 0°C, and aluminum chloride (904 mg, 6.8 mmol) was added. After stirring at room temperature for 17 hours, water was added. After 30 minutes, chloroform was added, and the organic layer was separated, dried over sodium sulfate, concentrated, and purified by column (CHCl3 100%) to obtain the target product. The obtained yellow solid organic compound p37-118 was 318 mg (0.58 mmol, 25.6%). 1 H NMR (600 MHz, CDCl3) δ[ppm] = 2.34 (s, 6H), 2.63 (s, 6H), 7.03 (br s, 4H), 7.28 - 7.31 (m, 6H), 7.38 (t, J = 7.8 Hz, 4H), 7.97 (d, J = 8.4 Hz, 2H) MS (MALDI-TOF): 549.94 [calcd:548.24]

[0159] The organic compound p139-139 is represented by the following formula (24). [ka] The synthesis of organic compound p139-139 was carried out as follows. Cyameluric acid chloride (138 mg, 0.5 mmol) was dissolved in tetrahydrofuran (2 mL), and methanol (2 mL) and N,N-diisopropylethylamine (425 mL, 2.5 mmol) were added at room temperature under a nitrogen atmosphere. After 20 minutes, the temperature was raised to 60°C and stirred for 24 hours. After returning to room temperature and adding water, the precipitate was filtered and dried in vacuum. The product was dissolved in chloroform, filtered through silica gel, and washed with chloroform to obtain the target product. The obtained white solid organic compound p139-139 was 35 mg (0.133 mmol, 27%). 1 H NMR (600 MHz, CDCl3) δ[ppm] = 4.10 (s, 9H) MS (MALDI-TOF): 264.30 [calcd:263.08]

[0160] The organic compound p141-141 is represented by the following formula (25). [ka] The synthesis of organic compound p141-141 was carried out as follows. Intermediate I4 (228 mg, 0.5 mmol) represented by the following formula (26) was dissolved in 1-propanol (3 mL), and 2,4,6-trimethylpyridine (217 mL, 1.65 mmol) was added at room temperature under an argon atmosphere. After stirring for 10 minutes, the temperature was raised to 90°C and stirred for 3 hours. After returning to room temperature and adding water, the mixture was extracted with chloroform, and the organic layer was dried over sodium sulfate and concentrated. The product was purified using a column (AcOEt: CHCl3 = 5:95 - 15:85) to obtain the target product. The obtained white solid organic compound p141-141 was 107 mg (0.31 mmol, 62%). 1 H NMR (600 MHz, CDCl3) δ[ppm] = 1.00 (t, 9H), 1.80 (s, 6H), 4.43 (t, 6H) MS (MALDI-TOF): 348.50 [calcd:347.17] [ka]

[0161] The synthesis of intermediate I4 was carried out as follows. Cyameluric acid chloride (314 mg, 1.1 mmol) was dissolved in toluene (5 mL), and 3,5-dimethylpyrazole (362 mg, 3.8 mmol) and N,N-diisopropylethylamine (969 mL, 5.7 mmol) were added at room temperature under an argon atmosphere. After 40 minutes, the temperature was raised to 70°C, and after another 20 minutes, the temperature was raised to 90°C, and the mixture was stirred for 2 hours. After returning to room temperature and adding water, the mixture was extracted with chloroform, and the organic layer was dried over sodium sulfate and concentrated. The product was purified using a column (MeOH: CHCl3 = 1:99 - 10:90) to obtain the target product. The obtained pale yellow solid intermediate I4 was 490 mg (1.08 mmol, 94%). 1 H NMR (600 MHz, CDCl3) δ[ppm] = 2.34 (s, 9H), 2.76 (s, 9H), 6.11 (s, 3H) MS (MALDI-TOF): 456.54 [calcd:455.20]

[0162] The organic compound p142-142 is represented by the following formula (27). [ka] The synthesis of organic compound p142-142 was carried out as follows. Cyameryl chloride (358 mg, 1.3 mmol) was dissolved in tetrahydrofuran (3 mL), and 1-butanol (3 mL) and N,N-diisopropylethylamine (1.1 mL, 6.5 mmol) were added at room temperature under an argon atmosphere. After the addition, the temperature was raised to 70°C, and after 2 hours, it was heated to 90°C and stirred for 1.5 hours. After returning to room temperature and adding water, it was extracted with chloroform, and the organic layer was dried over sodium sulfate and concentrated. The product was obtained by purification using a column (AcOEt:CH2Cl2=1:99 - 10:90). The obtained white solid organic compound p142-142 was 374 mg (0.96 mmol, 74%). 1 H NMR (600 MHz, CDCl3) δ[ppm] = 0.95 (t, 9H), 1.45 (tq, 6H), 1.76 (tt, 6H), 4. 47 (t, 6H), MS (MALDI-TOF): 390.64 [calcd:389.22]

[0163] The organic compound p140-140 is represented by the following formula (28). [ka] The synthesis of organic compound p140-140 was carried out as follows. Cyameryl chloride (456 mg, 1.65 mmol) was dissolved in tetrahydrofuran (5 mL), and ethanol (5 mL) and N,N-diisopropylethylamine (1.4 mL, 8.3 mmol) were added at room temperature under an argon atmosphere. After 2 hours, the temperature was raised to 80°C and stirred for 17 hours. After returning to room temperature and adding water, the mixture was extracted with dichloromethane, and the organic layer was dried over sodium sulfate and concentrated. The product was purified using a column (AcOEt:CH2Cl2=5:95 - 15:85) to obtain the target product. The obtained white solid organic compound p140-140 was 172 mg (0.56 mmol, 34%). 1 H NMR (600 MHz, CDCl3) δ[ppm] = 1.41(t, 9H), 4.53(q, 6H) MS (MALDI-TOF): 306.47 [calcd:305.12]

[0164] The organic compound p162-162 is represented by the following formula (29). [ka] The synthesis of organic compound p162-162 was carried out as follows. Cyameryl chloride (221 mg, 0.8 mmol) was dissolved in toluene (5 mL), and ethanethiol (592 mg, 4.0 mmol) and N,N-diisopropylethylamine (680 mL, 5.7 mmol) were added at room temperature under an argon atmosphere. After 30 minutes, the temperature was raised to 35°C and the mixture was stirred for 17 hours. After returning to room temperature and adding water, the mixture was extracted with chloroform, and the organic layer was dried over sodium sulfate and concentrated. The product was purified using a column (AcOEt:CH2Cl2=0:100-5:95) to obtain the target product. The white solid organic compound p162-162 was obtained in an amount of 234 mg (0.66 mmol, 83%). 1 H NMR (600 MHz, CDCl3) δ[ppm] = 1.37 (t, 9H), 3.16(q, 6H) MS (MALDI-TOF): 354.43 [calcd:353.06]

[0165] The organic compound p65-166 is represented by the following formula (30). [ka] The synthesis of organic compound p65-166 was carried out as follows. To a solution of intermediate I3 (608 μL, 4.3 mmol) in dichloromethane (11.8 mL), aluminum chloride (616 mg, 4.6 mmol) was added at room temperature and stirred for 40 minutes. A solution of compound 2 in dichloromethane (12 mL) was slowly added and stirred at room temperature for 20.5 hours. 1M aqueous sodium hydroxide solution (16 mL) was added at 0°C, and the mixture was stirred at room temperature for 4 hours, and then filtered using Celite. After adding 20% ​​aqueous sodium chloride solution to the reaction solution, the organic layer was separated, dried over anhydrous sodium sulfate, concentrated, and purified by column (CH2Cl2- CH2Cl2: MeOH = 9 : 1) to obtain a crude product (117 mg). The crude product was purified by a preparative column (SunFire, Hexane / EtOAc = 82 : 18) to obtain organic compound p65-166 as the third peak. The obtained yellow solid organic compound p65-166 was 13.8 mg (0.025 mmol, 2.3%). 1H NMR (600 MHz, CDCl3) δ[ppm] = 0.80-0.92 (br, 2H), 1.20-1.38 (br, 2H), 1.38-1.50 (m, 2H), 1.66-1.76 (br, 2H), 2.00-2.08 (br, 2H), 2.31 (s, 6H), 2.32 (s, 6H), 3.78 (s, 6H), 3.89-3.98 (br, 1H), 6.57 (s, 2H), 6.63 (s, 2H)

[0166] The crude product was purified using a preparative column (SunFire, Hexane / EtOAc = 82:18) to obtain the second peak, which was the organic compound represented by the following formula (31). The obtained yellow solid organic compound was 22.4 mg (0.040 mmol, 3.8%). 1H NMR (600 MHz, CDCl3) δ[ppm] = 0.80-0.92 (br, 2H), 1.20-1.38 (br, 2H), 1.38-1.50 (m, 2H), 1.68-1.77 (br, 2H), 2.00-2.10 (br, 2H), 2.31 (s, 3H), 2.32 (s, 3H), 2.41 (s, 6H), 3.78 (s, 3H), 3.79 (s, 3H), 3.86-3.98 (br, 1H), 6.58 (s,1H), 6.59 (s, 2H), 6.64 (s, 1H) [ka]

[0167] [Additional Notes] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Industrial Applicability]

[0168] The present invention can be used as a light-emitting material.

Claims

1. The light-emitting layer includes a dopant compound and a host compound, The host compound is an organic compound having a lone pair of electrons and a π electron orbital, and is in the lowest singlet excited state S １ Energy level E Ｓ１ to the lowest triplet excited state T １ Energy level E Ｔ１ Energy difference ΔE minus ＳＴ is negative or 0 eV≦ΔE ＳＴ <0.0090 eV.

2. The organic light-emitting device according to claim 1, wherein the host compound is a heptazine derivative having a lone pair of electrons and a π electron orbital, and is represented by the following formula (1) and has optional substituents R1, R2, and R3. 【Chemistry 1】

3. The radiative deactivation rate constant k of the host compound ｒ is 1.0 x 10 ６ s －１ <k ｒ 2. The organic light-emitting device of claim 1 , wherein:

4. The organic light-emitting device according to claim 2 , wherein the substituents R1, R2, and R3 each consist of two types of substituents.

5. The organic light-emitting device according to claim 2 , wherein the substituents R1, R2, and R3 are each composed of three different types of substituents.

6. The organic light-emitting device according to claim 2 , wherein the substituents R1, R2, and R3 each consist of one type of substituent.

7. Among the substituents R1, R2, and R3, the same substituents are defined as the substituents R2 and R3, The substituent R1 has a structure represented by the following formula (2): -S-R31, -O-R31, or -N-(R32)R33... (2) Here, R31 to R33 each independently represent a chain or cyclic hydrocarbon group having 20 or less carbon atoms, which may be substituted by a substituent.

5. The organic light-emitting device of claim 4, wherein each of the substituents R2 and R3 is a phenyl group or a phenyl group having from one to three substituents.

8. The substituent R1 is any of the structures shown below: 【Chemistry 2】 3. The organic light-emitting device of claim 2, wherein each of the substituents R2 and R3 has one of the following structures: 【Chemistry 3】 (However, the following exceptions apply.) 【Chemistry 4】

9. The organic light-emitting device of claim 6 , wherein the substituents R1, R2, and R3 have any of the following structures: 【Chemistry 5】

10. The light-emitting layer includes a dopant compound and a host compound, The dopant compound is an organic compound having a lone pair of electrons and a π electron orbital, and is in the lowest singlet excited state S １ Energy level E Ｓ１ to the lowest triplet excited state T １ Energy level E Ｔ１ Energy difference ΔE minus ＳＴ is negative or 0 eV≦ΔE ＳＴ <0.0090 eV.

11. The organic light-emitting device according to claim 10, wherein the dopant compound is a heptazine derivative having a lone pair of electrons and a π electron orbital, and is represented by the following formula (1) and has optional substituents R1, R2, and R3. 【Chemistry 6】

12. The radiative deactivation rate constant k of the dopant compound ｒ is 1.0 x 10 ６ s －１ <k ｒ 11. The organic light-emitting device of claim 10, wherein:

13. The organic light-emitting device according to claim 11 , wherein the substituents R1, R2, and R3 each consist of two types of substituents.

14. The organic light-emitting device according to claim 11 , wherein the substituents R1, R2, and R3 are each composed of three different types of substituents.

15. The organic light-emitting device according to claim 11 , wherein the substituents R1, R2, and R3 each consist of one type of substituent.

16. Among the substituents R1, R2, and R3, the same substituents are defined as the substituents R2 and R3, The substituent R1 has a structure represented by the following formula (2): -S-R31, -O-R31, or -N-(R32)R33... (2) Here, R31 to R33 each independently represent a chain or cyclic hydrocarbon group having 20 or less carbon atoms, which may be substituted by a substituent.

14. The organic light-emitting device of claim 13, wherein each of the substituents R2 and R3 is a phenyl group or a phenyl group having from 1 to 3 substituents.

17. The substituent R1 is any of the structures shown below: 【Chemistry 7】 12. The organic light-emitting device of claim 11, wherein each of the substituents R2 and R3 has one of the following structures: 【Chemistry 8】 (However, the following exceptions apply.) 【Chemistry 9】

18. 16. The organic light-emitting device of claim 15, wherein the substituents R1, R2, and R3 have any of the following structures: 【Chemistry 10】

Images