Theoretical Studies On The Evolution Of Excited States And Luminescence Mechanism Of Advanced Organic Optoelectronic Materials

Organic light-emitting materials have attracted extensive attention due to their excellent photoelectric performance,low cost and easy to be synthetized.With the development of computer technology,quantum chemistry has become an effective way to explore the behavior of excitons in the molecules and predict the photoelectric properties of the materials.Based on the quantum chemistry methods,a series of theoretical studies on the evolution process and luminescence mechanism of the excited states for new concept organic optoelectronic materials were conducted to discuss the relationship between the molecular structures and their photoelectric performance and provide theoretical guidances for designing efficient organic light-emitting materials.The main research contents of this paper are summarized as follows:?1?Carbene-metal-amides?CMAs?are promising charge-transfer emitters,especially the CMA1reported in 2017,and it shows nearly 100%internal quantum efficienty in organic light-emitting diodes?OLEDs?because of the small singlet-triplet splitting(?E_ST)and large oscillator strength.However,the CMA materials having performance better than CMA1 are still rare.Here,by introducing N atoms into the carbazole of CMA1,four new CMA complexes were designed,and their ground and excited states properties were studied theoretically.From systemic investigation on molecular geometry,frontier molecular orbital,radiative and non-radiative rates,and so on,it was found that the two designed molecules?-N and 2?-N show larger reverse intersystem crossing?RISC?rates than CMA1,suggesting that they can quickly utilize the triplet excitons.Also,the two molecules have faster radiative rates at S₁ state,suggesting that they are potentially better luminescent molecules.This work will provide new clues for developing CMA-based luminescent materials.?2?Since the high-performance luminescent organic radicals are rare and the luminescence mechanism and molecular design strategies are still unclear,the photophysical properties of tris?2,4,6-trichlorophenyl?-methyl?TTM?-based radicals were studied in this section.It is found that the transition dipole moment of the radicals mainly depends on the substituent fragment.If the dihedral angle between the substituent and the TTM fragment of the radical is small,the transition dipole moment will be large.In addition,two potential high-efficiency luminescent radicals,TTM-3PPy ID and TTM-3NPy ID,were obtained,showing large fluorescence radiative rates.?3?Based on four smallest afterglow molecules of CN-substituted benzenes,the mechanism of the afteraglow molecules were investigated,and the ground state and excited state properties of the molecules were theoretically studied.Compared to the experimental values,it is found that the introduction of cyano groups not only enhances intersystem crossing,but also is favorable for?-?packing in the crystals to stabilize triplet excitons for high performance organic afterglow.