ORGANIC MOLECULES HAVING TWO NON-CONJUGATED BRIDGES BETWEEN A DONOR AND AN ACCEPTOR FOR EFFECTIVE THERMALLY ACTIVATED DELAYED FLUORESCENCE FOR USE IN OPTOELECTRONIC DEVICES

Abstract

The invention relates to purely organic emitter molecules of a new type according to formula I and to the use thereof in optoelectronic devices, in particular in organic light-emitting diodes (OLEDs), comprising donor D: an aromatic or heteraromatic chemical group on which the HOMO is located and which optionally has at least one substitution; acceptor A: an aromatic or heteromatic chemical group on which the LUMO is located and which optionally has at least one substitution; bridge B1, bridge B2: organic groups that link the donor D and the acceptor A in a non-conjugated manner; wherein in particular the energy difference E(S.sub.1T.sub.1) between the lowest excited singlet (S1) state of the organic emitter molecule and the triplet (T1) state of the organic emitter molecule lying thereunder is less than 2000 cm.sup.1.

Claims

1. An organic molecule for luminescence, in particular for use as a luminophore in optoelectronic devices, comprising or consisting of a structure of the formula I, ##STR00037## Receptor A is an aromatic or heteraromatic chemical group, the HOMO is located on the group and the group optionally has at least one substitution; Bridge B1, bridge B2 connect organic groups of the donor D and acceptor A in a non-conjugated manner.

2. The organic molecule according to claim 1, wherein the donor D and/or the acceptor A are each selected from aromatic or heteroaromatic groups of the formulas II and III, ##STR00038## wherein the molecular fragments of the donor D and the acceptor A are different, wherein the formula II and/or formula III are optionally part of a fused ring system, having # positions, and the donor D and acceptor A are linked to the bridge B1 and bridge B2 via the positions, and Y1, Y2, Y3 and Y4 are independently selected from C and N; X1 to X7 are independently selected from N, O, S, SE, CH, NH, CR1 and NR2; wherein R1 and R2 groups are each independently selected from H, alkyl (particularly methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, adamantyl), cycloalkyi (particularly cyclopropyl, cyclopentyl, cyclohexyl), alkenyl (particularly vinyl, allyl), alkynyl (particularly ethynyl), aryl (particularly phenyl, tolyl, naphthyl), heteroaryl (particularly furyl, thienyl, pyrrolyl), chemically substituted alkyl, alkenyl, alkynyl, aryl, or heteroaryl, alkoxy (OR), thioalkyl (SR), sulfonyl (SO.sub.2R), acyl (COR), formyl (CHO), carboxyl (CO.sub.2R), boryl (BRR), sulfinyl (SOR), amine (NRR), phosphino (PRR), phosphinyl (PORR), amido (NRCOR), silyl (SiRRR), cyano and (CN), nitro (NO.sub.2), nitroso (NO), isocyanato (NCO), thiocyano (NCS) or halogen (F, Cl, Br, I); wherein R1 and R2 of the fragments X1 to X3 and X4 to X7 are optionally linked to each other in such a way as to form an additional aliphatic, aromatic or heteroaromatic ring system; wherein the residues R, R, and R are defined as R1 and R2, wherein the residues R, R, and R are optionally linked to each other in such a way as to form an additional aliphatic, aromatic or heteroaromatic ring system.

3. The organic molecule according to claim 2, wherein the groups R1 and R2 are independently selected from alkyl-C.sub.nH.sub.n+1 (1n8, particularly 1n4), cycloalkyl-CnH2n1 (3n6), substituted alkyl/cycloalkyl, alkoxy-OC.sub.nH.sub.n+1 (1n8), thioalkyl-SC.sub.nH.sub.n+1 (3n6), or alkylated amine groups, N(C.sub.nH.sub.2n+1)(C.sub.nH.sub.2n+1) (n and n=1 to 8) or N(C.sub.nH2.sub.n1)(CnH2n1) (n and n=3, 4, 5 or 6), wherein n is an integer respectively.

4. The organic molecule according to claim 1, wherein the donor D has at least one substituent and the substituent is independently selected from O, NH-alkyl, N (alkyl).sub.2, NH.sub.2, OH, ONH (CO)-alkyl, O (CO)-alkyl, alkyl, aryl, heterocyclyl, (CH)C-alkyl, phenothiazinyl, phenoxathiazinyl, carbazolyl, dihydrophenazinyl, N(R) (R), wherein all aryl and heterocyclyl groups are optionally substituted by alkyl and/or aryl groups, wherein all alkyl groups are also optionally substituted by F, Cl, Br and/or I; wherein R, RH, alkyl, aryl, haloalkyl or haloaryl.

5. The organic molecule according to claim 1, wherein the acceptor A has at least one substituent and the substituent is selected from halogen, (CO) H, (CO)-alkyl, (CO) OH, (CO) Cl, CF.sub.3, BF.sub.2, CN, S(O).sub.2OH, S(O).sub.2O-alkyl, NH.sub.3.sup.+, N(R)(R)(R).sup.+, NO.sub.2, haloalkyl and B(R)(R); wherein R, RH, alkyl, aryl, haloalkyl or haloaryl.

6. The organic molecule according to claim 1, comprising at least one Cl, Br and/or I atom(s), in particular for increasing spin orbit coupling.

7. The organic molecule according to claim 1, wherein the bridges B1 and B2 independently of one another have a structure according to one of the formulas IV and V: ##STR00039## wherein # is labeled as a linking site of the donor D or acceptor A of the molecule with other groups; A1 is selected from ##STR00040## O, S and ##STR00041## wherein R3-R7 are each independently selected from H, alkyl (particularly methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, adamantyl), cycloalkyi (particularly cyclopropyl, cyclopentyl, cyclohexyl), alkenyl (particularly vinyl, allyl), alkynyl (particularly ethynyl), aryl (particularly phenyl, tolyl, naphthyl), heteroaryl (particularly furyl, thienyl, pyrrolyl), chemically substituted alkyl, alkenyl, alkynyl, aryl, or heteroaryl, alkoxy (OR), thioalkyl (SR), sulfonyl (SO.sub.2R), acyl (COR), formyl (CHO), carboxyl (CO.sub.2R), boryl (BRR), sulfinyl (SOR), amine (NRR), phosphino (PRR), phosphinyl (PORR), amido (NRCOR), silyl (SiRRR), cyano and (CN), nitro (NO.sub.2), nitroso (NO), isocyanato (NCO), thiocyano (NCS) or halogen (F, Cl, Br, I), where R, R, and R are each have the same definition as R1 or R2; Chemical groups A2 and A3 are: A2 is selected from ##STR00042## O, S and ##STR00043## A3 is selected from ##STR00044## S and ##STR00045## wherein one or more of the chemical groups A2 to A3 are optionally selected from ##STR00046## wherein R8 to R22 are are each independently selected from H, alkyl (particularly methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, adamantyl), cycloalkyi (particularly cyclopropyl, cyclopentyl, cyclohexyl), alkenyl (particularly vinyl, allyl), alkynyl (particularly ethynyl), aryl (particularly phenyl, tolyl, naphthyl), heteroaryl (particularly furyl, thienyl, pyrrolyl), chemically substituted alkyl, alkenyl, alkynyl, aryl, or heteroaryl, alkoxy (OR), thioalkyl (SR), sulfonyl (SO.sub.2R), acyl (COR), formyl (CHO), carboxyl (CO.sub.2R), boryl (BRR), sulfinyl (SOR), amine (NRR), phosphino (PRR), phosphinyl (PORR), amido (NRCOR), silyl (SiRRR), cyano and (CN), nitro (NO.sub.2), nitroso (NO), isocyanato (NCO), thiocyano (NCS) or halogen (F, Cl, Br, I), where R, R, and R are each have the same definition as R1 or R2, and wherein the bridges B1 and B2 link the donor D or acceptor A and in the presence of A2 to A3 according to formula V, the groups of formula V are linked to each other via atoms C, Si, O, S, N, P, B or Ge.

8. The organic molecule according to claim 7, comprising or consisting of a structure selected from formulas VI to XVII ##STR00047## wherein Y1-Y4 are defined as Y1-Y4; X1-X7 are defined as X1-X7; A1, A2 and A3 are defined as A1 to A3; Z, a chemical group for linking the fragments A1 to A3 of the bridges B1 and B2 to one another, is selected from CH.sub.2, C(CH.sub.3).sub.2, O, C.sub.6H.sub.4 (phenylene) C.sub.5H.sub.8-(Cyclopentyl), CO (carbonyl), SO.sub.2 and N(CH.sub.3); wherein Y1-Y4 and X1-X7 are each independently selected from H, alkyl (particularly methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, adamantyl), cycloalkyi (particularly cyclopropyl, cyclopentyl, cyclohexyl), alkenyl (particularly vinyl, allyl), alkynyl (particularly ethynyl), aryl (particularly phenyl, tolyl, naphthyl), heteroaryl (particularly furyl, thienyl, pyrrolyl), chemically substituted alkyl, alkenyl, alkynyl, aryl, or heteroaryl, alkoxy (OR), thioalkyl (SR), sulfonyl (SO.sub.2R), acyl (COR), formyl (CHO), carboxyl (CO.sub.2R), boryl (BRR), sulfinyl (SOR), amine (NRR), phosphino (PRR), phosphinyl (PORR), amido (NRCOR), silyl (SiRRR), cyano and (CN), nitro (NO.sub.2), nitroso (NO), isocyanato (NCO), thiocyano (NCS) or halogen (F, Cl, Br, I), where R, R, and R are each have the same definition as R1 or R2.

9. The organic molecule according to claim 1, comprising a structure according to formula XVIII or consisting of a structure according to formula XVIII, ##STR00048## wherein, Q1 to Q6 are each independently selected from H, CH.sub.3, C.sub.2H.sub.5, C.sub.3H.sub.7, C.sub.4H.sub.9, C.sub.5H.sub.11, C.sub.6H.sub.13, phenyl, tolyl, xylyl, benzyl, thienyl, pyrazolyl, diazolyl, triazolyl, tetrazolyl, oxazolyl, oxadiazolyl, furyl, and carbazolyl; wherein Q1 and Q2, Q3 and Q4, and Q5 and Q6 are optionally linked, thereby forming a cycloalkyl system or an aromatic spirocyclic system; Alk1 to Alk10 are, independently of each other, H or an unbranched or branched aliphatic group or a cycloalkyl group.

10. The organic molecule according to claim 1, comprising one structure according to formula XIX or consisting of a structure according to formula XIX, ##STR00049## wherein Q1, Q2, Q3, Q4, Q5, and Q6 are each independently selected from H, CH.sub.3, C.sub.2H.sub.5, C.sub.3H.sub.7, C.sub.4H.sub.9, C.sub.5H.sub.11, C.sub.6H.sub.13, phenyl, tolyl, xylyl, benzyl, thienyl, pyrazolyl, diazolyl, triazolyl, tetrazolyl, oxazolyl, oxadiazolyl, furyl, and carbazolyl; wherein Q1 and Q2, Q3 and Q4, and Q5 and Q6 are optionally linked, thereby forming a cycloalkyl system or an aromatic spirocyclic system; Alk2, Alk3, Alk4, Alk5, Alk7, Alk8, Alk9, and Alk10 are, independently of each other, H or an unbranched or branched aliphatic group or a cycloalkyl group.

11. Applications of the organic molecule according to claim 1 in a light-emitting device, especially in an emitter layer of optoelectronic device, and in particular, in organic light-emitting diodes (OLEDs).

12. A method for manufacturing optoelectronic devices, wherein the molecules according to claim 1 are used.

13. An optoelectronic device, having the molecules according to claim 1.

14. The organic molecules according to claim 1 wherein the optoelectronic device is selected from an organic light-emitting diode (OLED), a light emitting electrochemical cell (LEEC or LEC), an OLED sensor, especially an unsealed shielded gas and vapor sensor, an optical temperature sensor, an organic solar cell (OSC), an organic field effect transistor, an organic laser, an organic diode, an organic photodiode and a down-conversion system.

Description

DETAILED DESCRIPTIONS OF EMBODIMENTS

[0056] ##STR00011##

[0057] The molecular structure of the emitter material having the formula I according to the invention is further explained by means of the structural formulas VI to XVII. These structural formulas represent examples of emitter materials according to the invention. Y1-Y4 and X1-X7 are defined as Y1-Y4 and XI-X7 (formulas II and III). A1, A2, A3 groups are defined as A1 to A3. The bridge fragments A1 and A1, A2 and A2, A3 and A3, respectively, may be the same or different.

[0058] Additional bridging groups Z are, for example, CH.sub.2, C(CH.sub.3).sub.2, O, C.sub.6H.sub.4-(phenylene), C.sub.5H.sub.8-(cyclopentylene), CO-(carbonyl), SO.sub.2, N(CH.sub.3). They represent the mutual connection of fragments A1 to A3 and A1 to A3 of bridges B1 and B2.

[0059] In a particular embodiment, the organic molecules according to the invention have a structure of Formula XVIII.

##STR00012##

[0060] In the donor region, the emitter molecule has an aromatic amine group. The acceptor moiety is a dicyanophenyl group in which two CN-substituents may be ortho, meta or para to each other and may be adjacent to a bridged aliphatic group.

[0061] Q1 to Q6 are each independently selected from the group consisting of H, CH.sub.3, C.sub.2H.sub.5, C.sub.3H.sub.7, C.sub.4H.sub.9, C.sub.5H.sub.11, C.sub.6H.sub.13, phenyl, tolyl, xylyl, benzyl, thienyl, oxazolyl, oxadiazolyl, triazolyl, tetrazolyl, oxazolyl, oxadiazolyl, furyl, and carbazolyl.

[0062] Q1 and Q2, Q3 and Q4, and Q5 and Q6 may be linked together to form a cycloalkyl- or aromatic spiro system (e.g., to stabilize the molecular structure).

[0063] Alk1 to Alk10 are H or a straight-chain or branched-chain (C.sub.nH.sub.2n+1; n=1, 2, 3, 4, 5, or 6) aliphatic group or a cycloalkyl group (C.sub.nH.sub.2n+1; n=5 or 6), independently of one another.

[0064] In addition, Alk1 and Alk6 can be omitted and the two benzene rings of the donor system are covalently bonded together to form a carbazole unit, as shown in Formula XIX.

##STR00013##

[0065] The formula XVIII illustrates the substituent.

EMBODIMENTS

[0066] The molecules in the following examples of the present invention may have at least one substitutions of Cl, Br and/or I to increase spin-orbit coupling (SBK). The appropriate position for substitutions can be determined by quantum mechanical calculations, and a computational program including SBK (eg, ADF, ORCA program) is used herein. To know the trend, DFT or CC2 calculation can be conducted, so as to identify the substitution position of halogen, i.e. the halogen atom orbitals with a significant proportion in HOMO, HOMO-1, HOMO-2 and/or LUMO, LUMO+1, LUMO+2. For the substitution pattern identified by this way, it should be noted that, for example, when calculated by TDDFT or CC2, the energy difference E (S.sub.1T.sub.1) of organic molecules between the lowest excited singlet state (S.sub.1) and it below triplet state (T.sub.1) is less than 2,000 cm-.sup.1, in particular less than 1500 cm-.sup.1, preferably less than 800 cm-.sup.1, more preferably less than 400 cm-.sup.1 and most preferably less than 200 cm-.sup.1.

[0067] The materials in the present invention can be synthesized using catalytic coupling reactions (e.g. Suzuki coupling reactions, Buchwald-Hartwig cross-coupling reactions) or various condensation reactions that are known to those skilled in the art.

Embodiment 1

[0068] ##STR00014##

[0069] Example Molecule 1

[0070] The molecules according to the invention shown in Example 1 would be detailed below. As shown from the frontier orbital in FIG. 3, the HOMO and LUMO were located in distinctly different spatial regions of the molecule. It was expected that the gap between the lowest triplet state and the singlet state above it was small enough that the molecule exhibited a significant TADF effect. The calculation of the example molecule 1 within the range of TD-DFT calculation (function B3LYP, basis set 6-31G (d, p)) showed that the energy level difference of the optimized triplet-state geometrical structure was E(S.sub.1T.sub.1)=75 cm-.sup.1. Therefore, the example molecule 1 was a good TADF emitter. The following reaction scheme illustrated the chemical synthesis of example molecule 1:

##STR00015##

[0071] Reactants and reaction conditions:

(1) (t-C.sub.4H.sub.9C.sub.6H.sub.5).sub.2NH, Pd(CH.sub.3COO).sub.2, P[(C(CH.sub.3).sub.3].sub.3, (CH.sub.3).sub.3CONa, 90 C., 19 hours.
(2) K.sub.4[Fe(CN).sub.6], Pd(CH.sub.3COO).sub.2, P[(C(CH.sub.3).sub.3].sub.3, Na.sub.2CO.sub.3, (CH.sub.3).sub.2NCHO, 140 C., 12 hours.

[0072] Synthesis can be performed according to the following detailed reaction scheme:

##STR00016##

[0073] Reactants and reaction conditions:

(1) CH.sub.3CO.sub.2Na, 230 C., 3 hours
(2) HPO.sub.2, I.sub.2, red phosphorus, CH.sub.3COOH, 80 C., 24 hours
(3) (H.sub.3PO.sub.4)n, 175 C., 5 hours
(4) Al[OCH(CH.sub.3).sub.2].sub.3, 275 C., 3 hours
(5) (t-C.sub.4H.sub.9C.sub.6H.sub.5).sub.2NH, Pd(CH.sub.3COO).sub.2, P[(C(CH.sub.3).sub.3].sub.3, (CH.sub.3).sub.3CONa, 90 C., 19 hours
(6) K.sub.4[Fe(CN).sub.6], Pd(CH.sub.3COO).sub.2, P[(C(CH.sub.3).sub.3].sub.3, Na.sub.2CO.sub.3, (CH.sub.3).sub.2NCHO, 140 C., 12 hours

[0074] Chemical Analysis:

[0075] R.sub.f(cyclohexane/ethyl acetate 10:1): 0.52. .sup.1H NMR (CDCl.sub.3, 300 MHz, ppm): 1.31 (s, 18H), 3.13 (m, 4H), 4.05 (s, 2H), 6.84 (dd, J=3.6 Hz, J=12.0 Hz, 1H), 6.90 (s, 1H), 6.95 (s, 1H), 6.95 (d, J=9 Hz, 5H), 7.22 (d, J=9 Hz, 4H), 7.55 (s, 2H). 13C-NMR (300 MHz CDCl.sub.3, ppm): 30.72 (CH2), 31.46 (CH3), 32.80 (CH2), 34.31 (CH2), 40.56 (Cquat), 113.16 (Cquat), 113.73 (Cquat), 115.59 (Cquat), 122.35 (Cquat), 123.48 (CH), 123.78 (CqUat), 126.03 (CH), 130.57 (CqUat), 130.94 (CH), 133.86 (CH), 134.48 (CH), 136.63 (Cquat), 144.91 (CqUat), 145.40 (Cquat), 145.69 (Cquat), 146.31 (Cquat).

[0076] MS (ES-MS=electrospray ionization mass spectrometry) m/z: 523 (M.sup.+). MS (HR-ES-MS=high resolution electrospray ionization mass spectrometer) m/z: C.sub.37H.sub.37N.sub.3 Calculation: 523.2979, Measurement: 523.2980 (M+). C.sub.37H.sub.37N.sub.3 Calculation: C 84.86, H 7.12, N 8.02%, Measurement: C 84.54, H 7.36, N 7.90%.

[0077] The example molecule 1 could be dissolved in many organic solvents such as methylene chloride (CH.sub.2Cl.sub.2), toluene, hexane, n-octane, tetrahydrofuran (THF), acetone, dimethylformamide (DMF), acetonitrile, ethyl alcohol, methanol, xylene or benzene. The excellent solubility in methylene chloride made polymethylmethacrylate (PMMA) or polystyrene (PS) doping possible.

[0078] The emitter material according to Embodiment 1 could be sublimated (temperature 170 C., pressure 10-.sup.3 mbar).

[0079] Photophysical measurements of example molecule 1 in PMMA or PS (doping concentration c1 wt %) demonstrated the occurrence of TADF and the favorable emission properties. At very low temperatures, for example when T=2K, thermal activation was not possible. Thus, the emission showed two very different decay times, namely, a very short component, which corresponded to an S.sub.1.fwdarw.S.sub.0-fluorescence transition, about 4 ns in PMMA, 25 ns in PS, and a very long component, which was classified as phosphorescence of T.sub.1.fwdarw.S.sub.0 transitions, (phos)550 ms in PMMA and (phos)450 ms in PS. (Note: nitrogen purging of samples)

[0080] FIG. 4 showed the corresponding time-resolved emission spectra in PS, i.e. no delay time (t=0 ns), detection time window t=100 ns, corresponding to short-term spectra of fluorescence, and corresponding to the long-term spectra of phosphorescence (t=500 and t=900 ms).

[0081] When the temperature rose to T=300K, drastic changes in spectra and decay behavior may occur, which would support the occurrence of TADF. FIG. 5 showed the short time domain (spontaneous fluorescence) and long time domain time-resolved emission spectra of example molecule 1 dissolved in PS. Since both spectra had approximately the same peak positions, long-lived components could also be interpreted as fluorescence-TADF emission in this case. The fluorescence decay time in PMMA was about 4 ns, and the fluorescence decay time in PS was about 25 ns. However, in PMMA, its long-lived component was greatly shortened to about 10 s, and the long-lived component in PS was also shortened to about 10 s.

[0082] It was of significance to compare the emission quantum efficiency at T=300K with the value obtained in ambient air under nitrogen purging (PMMA-doped samples). pL (nitrogen)=40%, pL (air)=25%. The result showed that the triplet state was involved in the emission process, because oxygen in the air usually only caused quenching of long-lived triplet states (A. M. Prokhorov et al, J. Am. Chem. Soc. 2014, 136, 9637). Since triplet state occupation was a prerequisite for generating TADF, this behavior again showed that example molecule 1 had the desired TADF properties. Notes: The emission maximum in PMMA at T=300K within the blue-white range was (max)=486 nm (CIE x: 0.198, y: 0.287), and the emission maximum in PS at T=300K within the blue range was (max)=450 nm (CIE x: 0.174; y: 0.154).

[0083] When studying substances dissolved in toluene, other photophysical properties of the emitter molecule according to Embodiment 1 can be identified. This further demonstrated that, for a simple measurement of the emitted quantum efficiency, as mentioned above, it was expected that the molecules dissolved in the toluene produced TADF because the emission quantum efficiency in air was significantly reduced. The corresponding measured values: .sub.PL(nitrogen)=30% and .sub.PL(air)=5%.

[0084] FIGS. 6a and 6b showed the emission attenuation behavior at T=300K in the ns region (FIG. 6a) and the s region (FIG. 6b). Spontaneous fluorescence decayed with (fluorine)=60 ns. (FIG. 6a) In addition, there were two attenuation components of (TADF 1)=270 ns and (TADF 2)=9 s. Both components were classified as TADF emissions.

[0085] FIG. 7 showed the time resolved emission spectra of example molecule 1 dissolved in toluene in three time domains, namely, the short time domain (spontaneous fluorescence) and two long time domains. These spectra were given of the attenuation components as shown in FIG. 6. Since all three spectra had the same peak position and the same spectral shape within the measurement accuracy range, the long-lived component could also be interpreted as fluorescence, i.e. two TADF emissions.

[0086] If the study was carried out in the non-phase-change temperature range of toluene and the sample that was remained liquid, the attenuation behaviors of the long-lived components emitted from example molecule 1 (concentration c10-.sup.5 mol/l) dissolved in toluene could be obtained. A temperature range of about 200K to 300K was very suitable. The measured values of the corresponding attenuation components were shown as Arrhenius diagrams (Boltzmann diagrams) in FIG. 8. Using Equation 2, Equation 3 could be approximated as the experimentally derived emission decay time .sub.exp (see C. Baleizao, M. N. Berberan-Santos, J. Chem. Phys, 2007, 126, 204510):

[00002]$\begin{array}{cc}\ln \left(\frac{1}{{}_{\exp }}\right)=A-\frac{.Math..Math.E_1\left(S_1-T_i\right)}{k_B.Math.T}& \left(3\right)\end{array}$

[0087] Where, A was a constant, i represented the TADF process 1 with E1 activation energy in triplet state T.sub.1 or TADF process 2 with activation energy E2 in triplet state T.sub.2.

[0088] The linear fitting of two time domain measurement points, ie two TADF emissions, was performed using Equation 3 according to FIG. 6. From the slope of the straight line, the activation energy could be obtained (E[(S.sub.1T.sub.1), TADF1]=310 cm-.sup.1 and E [(S.sub.1-T.sub.2), TADF2]=85 cm-.sup.1).

[0089] When cooled to T=77K, the long-lived unstructured emissions was frozen. There was only one structured phosphorescence, the decay time was very long, (phos)=450 ms (not shown in the figure). However, for long-lived components, the structure of the spectrum could also be observed in FIG. 4. This spectral structure could be attributed to the emission of donor or acceptor fragments. No charge transfer (CT) transition was involved in this case. If it is assumed that the correlation 0-0 transition at the intersection of the energetic (extrapolated) sides of the emission curve is reflected by the abscissa, these spectra could be used to roughly estimate the energy difference associated with the occurrence of TADF. The result was that the E was about (300100) cm-.sup.1, which also showed that the embodiment 1 was a TADF substance.

[0090] Therefore, the experiment demonstrated that the example molecule 1 produced TADF according to invention. The corresponding results of TADF behaviors for example molecule 1 doped in PMMA were also available.

[0091] It should be emphasized that this also showed that the energy difference 75 cm-.sup.1 calculated for the CT transitions (see the description of FIG. 3) was very consistent with the activation energy of TADF 2 process determined in the experiments.

[0092] FIG. 9 schematically summarized the measurement results in a formal energy level diagram. The emission behavior of example molecule 1 was described by three excitation energy states. There was another triplet state T1 (Lok) that could be assigned to local emission under two CT states 5.sub.1 (CT) and T.sub.2 (CT) with an experimentally determined energy difference of 85 cm.sup.1. The S.sub.1 (CT) state showed transient spontaneous fluorescence and two emissions of long decay time but different time-lasting at room temperature, which were generated from the thermal activation of T.sub.2 (CT) and T.sub.1 (lok), respectively, thus representing different TADF emissions. The formal model described here was based on long-lived TADF components longer than 9 s for the relaxation process between triplet states.

[0093] Here also illustrated one aspect for the naming of triplet state. It was based on the numbering by energy order, rather than by the type of electron excitation. Therefore, in the case of example molecule 1, the energy gap E (S.sub.1T.sub.1) between the CT states used was referred to as E [S.sub.1(CT)T.sub.2(CT)] due to the generation of the state T.sub.1(Iok) of low energy.

Embodiment 2

[0094] ##STR00017##

[0095] Example Molecule 2

[0096] The example molecule 2 according to the invention would be detailed below. As shown from the frontier orbital in FIG. 10, the HOMO and LUMO were located in distinctly different spatial regions of the molecule. It was expected that the gap between the lowest triplet state and the singlet state above it was small enough that the molecule exhibited a significant TADF effect. The calculation of the example molecule 2 within the range of TD-DFT calculation (function B3LYP, basis set 6-31G (d, p)) showed that the energy level difference of the optimized triplet-state geometrical structure was E(S.sub.1T.sub.1)=85 cm-.sup.1. Therefore, the example molecule 2 was a good TADF emitter. The following reaction scheme illustrated the chemical synthesis of example molecule 2.

##STR00018##

[0097] Reactants and reaction conditions:

(1) CH.sub.3CO.sub.2Na, 230 C., 3 hours
(2) HPO.sub.2, 1.sub.2, red phosphorus, CH.sub.3COOH, 80 C., 24 hours
(3) (H.sub.3PO.sub.4)n, 175 C., 5 hours
(4) Al[OCH(CH.sub.3).sub.2].sub.3, 275 C., 3 hours
(5) (t-C.sub.4H.sub.9C.sub.6H.sub.5).sub.2NH, Pd(CH.sub.3COO).sub.2, P[(C(CH.sub.3).sub.3].sub.3, (CH.sub.3).sub.3CONa, 90 C., 19 hours
(6) K.sub.4[Fe(CN).sub.6], Pd(CH.sub.3COO).sub.2, P[(C(CH.sub.3).sub.3].sub.3, Na.sub.2CO.sub.3, (CH.sub.3).sub.2NCHO, 140 C., 12 hours

Embodiment 3

[0098] ##STR00019##

[0099] Example Molecule 3

[0100] The molecules according to the invention shown in Embodiment 3 would be detailed below. As shown from the frontier orbital in FIG. 11, the HOMO and LUMO were located in distinctly different spatial regions of the molecule. It was expected that the gap between the lowest triplet state and the singlet state above it was small enough that the molecule exhibited a significant TADF effect. The calculation of the example molecule 3 within the range of TD-DFT calculation (function B3LYP, basis set 6-31G (d, p)) showed that the energy level difference of the optimized triplet-state geometrical structure was E (S.sub.1T.sub.1)=55 cm-.sup.1. Therefore, the example molecule 3 was a good TADF emitter.

[0101] The following reaction scheme illustrated the chemical synthesis of example molecule 3.

##STR00020## ##STR00021##

[0102] Reactants and reaction conditions:

(1) CH.sub.3CO.sub.2Na, 230 C., 3 hours.
(2) HPO.sub.2, I.sub.2, red phosphorus, CH.sub.3COOH, 80 C., 24 hours
(3) (H.sub.3PO.sub.4)n, 175 C., 5 hours
(4) (C.sub.2H.sub.5).sub.2O, 30 C., 24 hours NH.sub.4Cl, H.sub.2O; F.sub.3CCO.sub.2H, 3 hours, 50 C.
(5) Carbazole, Pd(CH.sub.3COO).sub.2, P[(C(CH.sub.3).sub.3].sub.3, (CH.sub.3).sub.3CONa, 90 C., 19 hours
(6) K.sub.4 [Fe(CN).sub.6], Pd(CH.sub.3COO).sub.2, P[(C(CH3).sub.3].sub.3, Na.sub.2CO.sub.3, (CH.sub.3).sub.2NCHO, 140 C., 12 hours

Embodiment 4

[0103] ##STR00022##

[0104] Example Molecule 4

[0105] The example molecule 4 according to the invention would be detailed below. As shown from the frontier orbital in FIG. 12, the HOMO and LUMO were located in distinctly different spatial regions of the molecule. It was expected that the gap between the lowest triplet state and the singlet state above it was small enough that the molecule exhibited a significant TADF effect. The calculation of the example molecule 4 within the range of TD-DFT calculation (function B3LYP, basis set 6-31G (d, p)) showed that the energy level difference of the optimized triplet-state geometrical structure was E(S.sub.1T.sub.1)=88 cm-.sup.1. Therefore, the example molecule 4 was a good TADF emitter.

[0106] The following reaction scheme illustrated the chemical synthesis of example molecule 4.

##STR00023## ##STR00024##

[0107] Reactants and reaction conditions

(1) CH.sub.3CO.sub.2Na, 230 C., 3 hours
(2) HPO.sub.2, I.sub.2, red phosphorus, CH.sub.3COOH, 80 C., 24 hours
(3) (H.sub.3PO.sub.4).sub.n, 175 C., 5 hours
(4) Al[OCH(CH.sub.3).sub.2].sub.3, 275 C., 3 hours
(5) (t-C.sub.4H.sub.9C.sub.6H.sub.5).sub.2NH, Pd(CH.sub.3COO).sub.2, P[(C(CH3).sub.3].sub.3, (CH.sub.3).sub.3CONa, 90 C., 19 hours
(6) K.sub.4[Fe(CN).sub.6], Pd(CH.sub.3COO).sub.2, P[(C(CH3).sub.3].sub.3, Na.sub.2CO.sub.3, (CH.sub.3).sub.2NCHO, 140 C., 12 hours

Embodiment 5

[0108] ##STR00025##

[0109] Example Molecule 5

[0110] The example molecule 5 according to the invention would be detailed below. As shown from the frontier orbital in FIG. 13, the HOMO and LUMO were located in distinctly different spatial regions of the molecule. It was expected that the gap between the lowest triplet state and the singlet state above it was small enough that the molecule exhibited a significant TADF effect. The calculation of the example molecule 5 within the range of TD-DFT calculation (function B3LYP, basis set 6-31G (d, p)) showed that the energy level difference of the optimized triplet-state geometrical structure was E(S.sub.1T.sub.1)=150 cm-.sup.1. Therefore, the example molecule 5 was a good TADF emitter. The following reaction scheme illustrated the chemical synthesis of example molecule 5.

##STR00026## ##STR00027##

[0111] Reactants and reaction conditions:

(1) CH.sub.3CO.sub.2Na, 230 C., 3 hours
(2) HPO.sub.2, I.sub.2, red phosphorus, CH.sub.3COOH, 80 C., 24 hours
(3) (H.sub.3PO.sub.4).sub.n, 175 C., 5 hours
(4) Al[OCH(CH.sub.3).sub.2].sub.3, 275 C., 3 hours
(5) (t-C.sub.4H.sub.9C.sub.6H.sub.5).sub.2NH, Pd(CH.sub.3COO).sub.2, P[(C(CH3).sub.3].sub.3, (CH.sub.3).sub.3CONa, 90 C., 19 hours
(6) K.sub.4[Fe(CN).sub.6], Pd(CH.sub.3COO).sub.2, P[(C(CH3).sub.3].sub.3, Na.sub.2CO.sub.3, (CH.sub.3).sub.2NCHO, 140 C., 12 hours

Embodiment 6

[0112] ##STR00028##

[0113] Example Molecule 6

[0114] The example molecule 6 according to the invention would be detailed below. As shown from the frontier orbital in FIG. 14, the HOMO and LUMO were located in distinctly different spatial regions of the molecule. It was expected that the gap between the lowest triplet state and the singlet state above it was small enough that the molecule exhibited a significant TADF effect. The calculation of the example molecule 6 within the range of TD-DFT calculation (function B3LYP, basis set 6-31G (d, p)) showed that the energy level difference of the optimized triplet-state geometrical structure was E(S.sub.1T.sub.1)=30 cm-.sup.1. Therefore, the example molecule 6 was a good TADF emitter.

Embodiment 7

[0115] ##STR00029##

[0116] Example Molecule 7

[0117] FIG. 15 showed the frontier orbitals HOMO and LUMO of example molecule 7. Since these orbitals were located in distinctly different spatial regions of the molecule, it could be expected that the gap between the lowest triplet state and the singlet state above it was small enough that the molecule exhibited a significant TADF effect. The calculation of the example molecule 7 within the range of TD-DFT calculation (function B3LYP, basis set 6-31G (d, p)) showed that the energy level difference of the optimized triplet-state geometrical structure was E(S.sub.1T.sub.1)=550 cm-.sup.1. Therefore, the example molecule 7 was a good TADF emitter.

[0118] The following reaction scheme illustrated the chemical synthesis of example molecule 7.

##STR00030##

[0119] Reactants and reaction conditions:

(1) CH.sub.3CO.sub.2Na, 230 C., 3 hours
(2) HI (57% aqueous solution), red phosphorus, 80 C., 24 hours
(3) (H.sub.3PO.sub.4).sub.n, 175 C., 5 hours
(4) Al[OCH(CH.sub.3).sub.2].sub.3, 275 C., 3 hours
(5) (CH.sub.3).sub.2NH, Pd (CH.sub.3COO).sub.2, P[(C(CH.sub.3).sub.3].sub.3, (CH.sub.3).sub.3CONa, 90 C., 19 hours

Embodiment 8

[0120] ##STR00031##

[0121] Example Molecule 8

[0122] As shown from the frontier orbitals in FIG. 16, the HOMO and LUMO were located in distinctly different spatial regions of the molecule. It was expected that the gap between the lowest triplet state and the singlet state above it was small enough that the molecule exhibited a significant TADF effect. The calculation of the example molecule 8 within the range of TD-DFT calculation (function B3LYP, basis set 6-31G (d, p)) showed that the energy level difference of the optimized triplet-state geometrical structure was E(S.sub.1T.sub.1)=540 cm-.sup.1. Therefore, the example molecule 8 was a good TADF emitter.

[0123] The following reaction scheme illustrated the chemical synthesis of example molecule 8.

##STR00032##

[0124] Reactants and reaction conditions:

(1) CH.sub.3CO.sub.2Na, 230 C., 3 hours
(2) HI (57% aqueous solution), red phosphorus, 80 C., 24 hours
(3) CH.sub.2N.sub.2, SO.sub.2Cl.sub.2, 80 C., 2 hours; (CH.sub.3).sub.3COH, C.sub.6H.sub.5COOAg, Et.sub.3N, 90 C., 2 hours
(4) (H.sub.3PO.sub.4).sub.n, 175 C., 5 hours
(5) Al[OCH(CH.sub.3).sub.2].sub.3, 275 C., 3 hours
(6) (CH.sub.3).sub.2NH, Pd(CH.sub.3COO).sub.2, P[(C(CH3).sub.3].sub.3, (CH.sub.3).sub.3CONa, 90 C., 19 hours
(7) K.sub.4[Fe(CN).sub.6], Pd(CH.sub.3COO).sub.2, P[(C(CH3).sub.3].sub.3, Na.sub.2CO.sub.3, (CH.sub.3).sub.2NCHO, 140 C., 12 hours

Embodiment 9

[0125] ##STR00033##

[0126] Example Molecule 9

[0127] FIG. 17 showed the frontier orbitals HOMO and LUMO of example molecule 9. Since these orbitals were located in distinctly different spatial regions of the molecule, it could be expected that the gap between the lowest triplet state and the singlet state above it was small enough that the molecule exhibited a significant TADF effect. The calculation of the example molecule 9 within the range of TD-DFT calculation (function B3LYP, basis set 6-31G (d, p)) showed that the energy level difference of the optimized triplet-state geometrical structure was E(S.sub.1T.sub.1)=550 cm-.sup.1. Therefore, the example molecule 9 was a good TADF emitter.

Embodiment 10

[0128] ##STR00034##

[0129] Example Molecule 10

[0130] FIG. 18 showed the frontier orbitals HOMO and LUMO of example molecule 10. Since these orbitals were located in distinctly different spatial regions of the molecule, it could be expected that the gap between the lowest triplet state and the singlet state above it was small enough that the molecule exhibited a significant TADF effect. The calculation of the example molecule 10 within the range of TD-DFT calculation (function B3LYP, basis set 6-31G (d, p)) showed that the energy level difference of the optimized triplet-state geometrical structure was E(S.sub.1T.sub.1)=140 cm-.sup.1. Therefore, the example molecule 10 was a good TADF emitter.

Embodiment 11

[0131] ##STR00035##

[0132] Example Molecule 11

[0133] FIG. 19 showed the frontier orbitals HOMO and LUMO of example molecule 11. Since these orbitals were located in distinctly different spatial regions of the molecule, it could be expected that the gap between the lowest triplet state and the singlet state above it was small enough that the molecule exhibited a significant TADF effect. The calculation of the example molecule 11 within the range of TD-DFT calculation (function B3LYP, basis set 6-31G (d, p)) showed that the energy level difference of the optimized triplet-state geometrical structure was E(S.sub.1T.sub.1)=420 cm-.sup.1. Therefore, the example molecule 11 was a good TADF emitter.

Embodiment 12

[0134] ##STR00036##

[0135] Example Molecule 12

[0136] FIG. 20 showed the frontier orbitals HOMO and LUMO of example molecule 12. Since these orbitals were located in distinctly different spatial regions of the molecule, it could be expected that the gap between the lowest triplet state and the singlet state above it was small enough that the molecule exhibited a significant TADF effect. The calculation of the example molecule 12 within the range of TD-DFT calculation (function B3LYP, basis set 6-31G (d, p)) showed that the energy level difference of the optimized triplet-state geometrical structure was E(S.sub.1T.sub.1)=1250 cm-.sup.1. Therefore, the example molecule 12 was a good TADF emitter.

[0137] FIG. 21 showed other example molecules.

BRIEF DESCRIPTION OF THE DRAWINGS

[0138] FIG. 1 shows a schematic diagram of the energy level of the thermally activated delayed fluorescence (TADF) process. k.sub.BT represents thermal energy with a Boltzmann constant k.sub.B and an absolute temperature T. This figure shows both the radiative and non-radiative (marked by wavy lines) attenuation processes of the radiation TADF process and the low-temperature observable T.sub.1 state. The figure does not mark the spontaneous S.sub.1.fwdarw.S.sub.0 fluorescence process.

[0139] FIG. 2 shows a schematic diagram of orbital energies of molecules with donor fragments and receptor fragments (D-A molecules) according to the present invention. Due to non-conjugated bridges, the interaction between the donor and acceptor tracks is small. Thus, the electronic properties of the D and A fragments can be approximated separately, that is, the D orbital energy is approximately equal to the energy of the corresponding free (unlinked) donor molecule, and the A orbital energy is approximately equal to the energy of the corresponding free (unlinked) acceptor molecule. The HOMO energy of the isolated donor (electron-rich) is significantly higher than HOMO energy of the isolated acceptor (electron-deficient). The LUMO of an isolated donor is much higher than the LUMO energy of an acceptor. Therefore, the HOMO of the D-A molecule is mainly located on the D fragment, while the LUMO of the D-A molecule is mainly located on the A fragment.

[0140] FIG. 3 shows an isosurface of the frontier orbital of the example molecule 1 (see Embodiment 1), HOMO: left, LUMO: right. The electronic ground state S.sub.0 geometry is optimized. Calculation method: DFT and TD-DFT, function: B3LYP, basis set: 6-31G (d, p), calculation software: Gaussian 09. The calculation result showed that the energy difference between the singlet state-CT state and the triplet state-CT state is 75 cm-.sup.1 (S.sub.0-geometry). This value indicates that the example molecule 1 is a good TADF emitter.

[0141] FIG. 4 shows time-resolved emission spectra of example molecule 1 doped about 1% by weight in PS at T=2K. Record the short-term spectrum in case of no time delay (t=0 ns) and detection time window 1 t=100 ns and record the long-term spectrum in case of a time delay t=500 s (time window t=900 ms). Excitation: short-time spectrum: 375 nm, pulse width 70 ps; long-time spectrum, excitation: 365 nm, pulse width: 10 ns.

[0142] FIG. 5 shows time-resolved emission spectra and decay time of example molecule 1 doped about 1% by weight in PS at T=300K. Record the short-term spectrum in case of no time delay (t=0 ns) and detection time window t=100 ns and record the long-term spectrum in case of a time delay t=1 s (time window t=100 s). Excitation: short-time spectrum: 375 nm, pulse width 70 ps; long-time spectrum, excitation: 355 nm, pulse width: 2.9 ns.

[0143] FIG. 6 shows the emission decay behaviors of example substance 1 dissolved in toluene, (a) short time domain (spontaneous fluorescence) and (b) long time domain, T=300K. Record the spontaneous fluorescence emission decay time (fluorescence)=60n and TADF decay time (TADF 1)=270 ns and (TADF 2)=9 s of respective components. Introduce nitrogen for 120 min to degas the solution. Excitation wavelength: 355 nm, pulse duration: 2.9 ns, and concentration: about 10-.sup.5 mol/l.

[0144] FIG. 7 shows the time-resolved emission spectra of example molecule 1 at a concentration of 10-.sup.5 M dissolved in toluene when T=300K. Record (a) short-time spectra (spontaneous fluorescence) of no time delay (t=0 ns) and test time window t=50 ns, (b) long-term spectrum (TADF1) with time delay t=300 s (time window t=600 ns) and (c) long time spectrum (TADF2) with time delay t=5 s (time window t=30 s). Excitation: Short-time spectrum: 375 nm, pulse width 70 ps, long-time spectrum, excitation: 355 nm, pulse width: 2.9 ns.

[0145] FIG. 8 shows the Boltzmann diagram (Arrhenius diagram) of long-lived composition of the corresponding emission decay time of example molecule 1 dissolved in toluene according to equation 3. The activation energy E(S.sub.1T.sub.1)=(31010)cm-.sup.1 and E(S.sub.1T.sub.2)=(855)cm.sup.1 obtained by fitting. The T1 state is the local state, and the T2 is classified as the charge donor transfer state.

[0146] FIG. 9 shows the formal energy level diagram, used to schematically describe the experimental emission decay time and activation energy. T.sub.1(lok) represents the local state, while T.sub.2(CT) and S.sub.1(CT) represent the charge transfer state. The heat returns from T.sub.1(lok) and T.sub.2(CT) to the S.sub.1(CT) state, resulting in two TADF processes.

[0147] FIG. 10 shows an isosurface of the frontier orbital of the example molecule 2 (see Embodiment 2), HOMO: left, LUMO: right. Optimization of the lowest triplet state T.sub.1 geometry. Calculation method: DFT and TD-DFT, function: B3LYP, basis set: 6-31G (d, p), calculation software: Gaussian 09. The result: E(S.sub.1T.sub.1)=85 cm-.sup.1 Both values indicate that example molecule 2 is a good TADF emitter.

[0148] FIG. 11 shows an isosurface of the frontier orbital of the example molecule 3 (see Embodiment 3), HOMO: left, LUMO: right. Optimization of the lowest triplet state T.sub.1 geometry. Calculation method: DFT and TD-DFT, function: B3LYP, basis set: 6-31G (d, p), calculation software: Gaussian 09. The result: E(S.sub.1T.sub.1)=55 cm-.sup.1 The result indicates that example molecule 3 is a good TADF emitter.

[0149] FIG. 12 shows an isosurface of the frontier orbital of the example molecule 4 (see Embodiment 4), HOMO: left, LUMO: right. Optimization of the lowest triplet state T.sub.1 geometry. Calculation method: DFT and TD-DFT, function: B3LYP, basis set: 6-31G (d, p), calculation software: Gaussian 09. The result: E(S.sub.1T.sub.1)=88 cm-.sup.1 The result indicates that example molecule 4 is a good TADF emitter.

[0150] FIG. 13 shows an isosurface of the frontier orbital of the example molecule 5 (see Embodiment 5), HOMO: left, LUMO: right. Optimization of the lowest triplet state T.sub.1 geometry. Calculation method: DFT and TD-DFT, function: B3LYP, basis set: 6-31G (d, p), calculation software: Gaussian 09. The result: E(S.sub.1T.sub.1)=150 cm-.sup.1 The result indicates that example molecule 5 is a good TADF emitter.

[0151] FIG. 14 shows an isosurface of the frontier orbital of the example molecule 6 (see Embodiment 6), HOMO: left, LUMO: right. Optimization of the electron ground state S.sub.0 and the lowest triplet state T.sub.1 geometry. Calculation method: DFT and TD-DFT, function: B3LYP, basis set: 6-31G (d, p), calculation software: Gaussian 09. The result: E(S.sub.1T.sub.1)=35 cm-.sup.1 (S.sub.0-geometry) and 30 cm.sup.1 (T.sub.1-geometry). Both values indicate that example molecule 2 is a good TADF emitter.

[0152] FIG. 15 shows an isosurface of the frontier orbital of the example molecule 7 (see Embodiment 7), HOMO: left, LUMO: right. Optimization of the lowest triplet state T.sub.1 geometry. Calculation method: DFT and TD-DFT, function: B3LYP, basis set: 6-31G (d, p), calculation software: Gaussian 09. The result: E(S.sub.1T.sub.1)=550 cm-.sup.1 The result indicates that example molecule 7 is a good TADF emitter.

[0153] FIG. 16 shows an isosurface of the frontier orbital of the example molecule 8 (see Embodiment 8), HOMO: left, LUMO: right. Optimization of the lowest triplet state T, geometry. Calculation method: DFT and TD-DFT, function: B3LYP, basis set: 6-31G (d, p), calculation software: Gaussian 09. The result: E(S.sub.1T.sub.1)=540 cm-.sup.1 (T, geometry) The result indicates that example molecule 8 is a good TADF emitter.

[0154] FIG. 17 shows an isosurface of the frontier orbital of the example molecule 9 (see Embodiment 9), HOMO: left, LUMO: right. Optimization of the lowest triplet state T.sub.1 geometry. Calculation method: DFT and TD-DFT, function: B3LYP, basis set: 6-31G (d, p), calculation software: Gaussian 09. The result: E(S.sub.1T.sub.1)=550 cm.sup.1 (T.sub.1-geometry) The result indicates that example molecule 9 is a good TADF emitter.

[0155] FIG. 18 shows an isosurface of the frontier orbital of the example molecule 10 (see Embodiment 10), HOMO: left, LUMO: right. Optimization of the electron ground state geometry. Calculation method: DFT and TD-DFT, function: B3LYP, basis set: 6-31G (d, p), calculation software: Gaussian 09. The result: E(S.sub.1T.sub.1)=140 cm-.sup.1 The result indicates that example molecule 10 is a good TADF emitter.

[0156] FIG. 19 shows an isosurface of the frontier orbital of the example molecule 11 (see Embodiment 11), HOMO: left, LUMO: right. Optimization of the electron T.sub.1 state geometry. Calculation method: DFT and TD-DFT, function: B3LYP, basis set: 6-31G (d, p), calculation software: Gaussian 09. The result: E(S.sub.1T.sub.1)=420 cm.sup.1 The result indicates that example molecule 11 is a good TADF emitter.

[0157] FIG. 20 shows an isosurface of the frontier orbital of the example molecule 12 (see Embodiment 12), HOMO: left, LUMO: right. Optimization of the lowest triplet state T.sub.1 geometry. Calculation method: DFT and TD-DFT, function: B3LYP, basis set: 6-31G (d, p), calculation software: Gaussian 09. The result: E(S.sub.1T.sub.1)=1250 cm-.sup.1 (T.sub.1 geometry) The result indicates that example molecule 12 is a good TADF emitter.

[0158] FIG. 21 shows schematic representation of other molecules according to the invention.