Design Synthesis And Application Of The Novel Organic Light-emitting Molecules With High Exciton Utilization

In order to improve the exciton utilization,different organic blue light-emitting molecules were designed and synthesized in this paper.The structures of the target compounds were characterized by NMR,MS and X-ray single crystal diffraction.The photophysical properties,electrochemical properties and thermal stability of the compounds were studied.The effects of the structures of the compounds on the properties were discussed.The applications of compounds in devices and corresponding systems were also investigated.By applying imidazole derivatives as electron acceptors and carbazole as electron donors,bridging with biphenyl,changing the type of substituents and conjugation degree of molecules,three compounds with HLCT excited states were designed and synthesized:2-（4’-（9H-carbazol-9-yl）-[1,1’-biphenyl]-4-yl）-1-（4-methoxyphenyl）-1H-phenanthro[9,10-d]imidazole（Cz B-MOPPI）,2-（4’-（9H-carbazol-9-yl）-[1,1’-biphenyl]-4-yl）-1-（4-（trifluoromethyl）phenyl）-1H-phenanthro[9,10-d]imidazole（Cz B-FMPPI）and 9-（4’-（4,5-diphenyl-1-（4-（trifluoromethyl）phenyl）-1H-imidazol-2-yl）-[1,1’-biphen-yl]-4-yl）-9H-carbazole（Cz B-FMPIM）.The decomposition temperature values of three materials were determined to be 480,431 and 414°C,respectively.The glass transition temperatures of three compounds were determined to be 480,431 and 414°C.The relative fluorescence quantum yield of them were evaluated to be 0.90,0.92 and0.83.What’s more,the maximum emission peak of three molecules are 421,420 and445 nm,respectively.The compounds have good electron and hole transporting abilities contributing to the introduction of electron donors and acceptors in the molecule.Non-doped OLED devices based on three materials as luminescent layers achieved the maximum luminance of 6450,6667 and 3084 cd/m²,and the maximum external quantum efficiency of 5.97%,4.10%and 3.97%.The devices emit deep blue with the CIE coordinates as（0.16,0.08）,（0.15,0.12）,（0.15,0.07）,respectively.A series of TADF materials were designed and synthesized by applying carbazole and its derivatives as electron donors,diphenyl sulfone,pyridine and N heterocycles as electron acceptors,respectively.The electron distributions of molecular orbitals of the TADF materials were employed by quantum chemical calculation.TheΔE_ST was evaluated by studing the absorption,fluorescence and low temperature luminescence characteristics of the materials.In which,the smallestΔE_ST was 0.18 e V.The effects of different electron donors,steric hindrance,the conjugate size and position of the substituents onΔE_ST were discussed.All the experimental data could provide beneficial information for future optimal design of TADF materials.Three small organic blue-light emitting molecules with anthracene and fluorene as the main framework were synthesized:1-（9H-fluoren-9-yl）anthracene（1HFA）,9-（9H-fluoren-9-yl）anthracene（9HFA）and 9,10-di（9H-fluoren-9-yl）anthracene（DFA）.Through the analysis and comparison of their photophysical properties,the promising one,DFA,was selected to be further studied.It is found that DFA has high fluorescence quantum efficiency as 96%in chloroform.The fluorescence emission characteristics of DFA in aggregated state were studied and its optimal concentration range was determined.A TTA-UP system employing Pd OEP as sensitizer,DFA as annihilator was constructed.After adjusting the concentration of sensitizer and annihilator in TTA-UP system,the optimum condition for up-conversion efficiency reached 43%（theoretical maximum efficiency:50%）was obtained.By analyzing and studying the up-conversion spectra and the up-conversion fluorescence lifetime of the system,it is proved that the energy transfer between sensitizer and annihilator is 100%.