Synthesis And Properties Of Benzophenone Type Thermally Activated Delayed Fluorescent And Phosphorescent Materials

To date,organic light-emitting diode?OLED?technology has been through three generations which inclueconventional fluorescent OLED,organometallic complex phosphorescent OLED and thermally activated delayed fluorescent?TADF?OLED.Among them,TADF based OLEDs can accelerate 75%of first excited triplet?T₁?excitons up-converse to first singlet excited state?S₁?through reverse intersystem crossing?RISC?process without introducing heavy metal atoms,which allows 100%of excitons tobe utilized in fluorescence emission,andmakesTADF to be known as the“third generation”OLED with promising future.Beside,the purely organic room temperature phosphorescent?PORTP?materials can realize slow radiation transition from T₁ state to ground state?S₀?,result in phosphorescence with long lifetime.And PORTP materials are widely used in the field of photoelectric materials and biochemistry based on this unique luminescent mechanism.In the first chapter of thisdissertation,the development of organic light-emitting diodes was introduced,and the types of organic light-emitting materials were classified.Then we outlined the mechanism of TADF and PORTP.We summarized the research progress of various TADF materials based on the classification of red,green and blue light emitting and different electron accepters.Moreover,various PORTP materials were reviewed briefly.Then we pointed out the research content and design ideas of this dissertation.In the second chapter of thisdissertation,four electron donor-electron accepter?D-A?type molecules based on benzophenone derivatives electron acceptors that modified with benzofuran,benzothiophene and benzosulfone,conbined with carbazole,3,6–di–tert–butyl-carbazole and diphenylamine electron donorswere designed and synthesized,namely DBTBZCz,DBTBZtCz,DBFBZDPA and DPSZCz.Photoluminescence properties of four molecules were evaluated by theoretical calculations,UV-visible absorptionspectra,and transient/steady-state emission spectra.Their thermal stability was evaluated via TGA/DSC measurement,and cyclic voltammetry were used to measure their molecular frontier orbital energy levels.We found that DBTBZCz and DBTBZtCz demonstrated the smallest single-triplet energy gap,showed significant TADF properties.The characterization of OLED devices based on DBTBZCz and DBTBZtCz revealed that 20 wt%doped in DPEPO gave the best performance of devices:maximum current efficiency of DBTBZCz and DBTBZtCz based device is 5.32 cd·A^-1and 8.6 cd·A^-1,respectively;and 2.39 lm·W^-1and 5.0 lm·W^-1,respectively for maximum power efficiency;and 3.04%and 6.49%,respectively for maximum EQE.In the third chapter of thisdissertation,we designed and synthesized DBFBZF and DBFBZBr based on benzophenone and dibenzofuran.Their photoluminescence properties were evaluated by theoretical calculations,UV-visible absorption spectra,and transient/steady-state emission spectra.By measuring the phosphorescence of benzophenone,dibenzofuran,DBFBZF and DBFBZBr in 2-methyl-tetrahydrofuran solution at 77 K,we found that the triplet energy levels and the phosphorescent lifetime of DBFBZF and DBFBZBr were mainly dominated by the benzophenone unit whichdemonstrated a lower triplet energy level compared with dibenzofuran.Furthermore,we have found that DBFBZF and DBFBZBr showed negligible emission in solution at room temperature,while emitted phosphorescence dual emission origin from different triplet states in crystallined powder state,which may include a phosphorescence Phos.2 that origined from T₂ state with short emission wavelength at 450 nm⁴60 nm and short lifetime of 1.533 ms and 1.088 ms;and a phosphorescence Phos.1 that origined from T₁ state with long emission wavelength at 520nm⁵60 nm and long lifetime of around 170 ms and 75 ms for DBFBZF and DBFBZBr.