Rational Manipulation And Application Of Donor-Acceptor Organic Optoelectronic Materials

The electron donor（Donor,D）-electron acceptor（Acceptor,A）materials are widely uesd in the fields of organic light-emitting diode（OLED）,organic photovoltaic cell（OPV）,organic field-effect transistor（OFET）and so on.The study of the molecular structures and related properties are crucial for the design and development of highly efficient D-A molecules.Based on the current research status,this paper used density functional theory（DFT）and time-dependent density functional theory（TD-DFT）to study the charge transfer and the interaction between donor and acceptor in D-A materials through theory and experiment.The main findings of this work are summarized as follows:Through the calculation of D-A bipolar host materials and thermally-actived delayed fluorescene（TADF）materials,the TADF molecules have more charges on the donor and acceptor fragments from the charge distribution analysis in the ground state.Quantitative parameters were introduced to further distinguish and proved that charge transfer is more effective in TADF molecules.In the lowest triplet（T₁）excited states,the hole-electron overlap degrees S of TADF molecules are all less than 50%,and the hole-electron center distances D_CT are greater than 1（?）.The differences of root-mean-square for distribution of hole-electronΔσ_CT are also above 1（?）.These values prove that the interaction is one of the most important factors which will affect D-A molecules,which can also give a theoretical guide to design them.By researching the TADF oligomers and non-TADF oligomers,the twist angles of TADF oligomers and these monomers between D and A are larger than those of non-TADF oligomers and those monomers.It results in the essential separation of the the highest occupied molecular orbital（HOMO）and the lowest unoccupied molecular orbital（LUMO）distribution,while still providing a nonvanishing frontier orbital overlap for a stronger radiative transition moment.When we added benzene ring to the acceptor units,it maked their structures change greatly,and also relatively reduced the values ofΔE_ST.The properties of HONTO and LUNTO of the lowest singlet（S₁）excited states are the main factors which influenceΔE_ST when it comes to natural transition orbitals analysis（NTOs）.Researches find that after polymerization,the absorption and emission spectra will have a certain redshift.This work provides theoretical support for the design and development of new TADF polymers.Through the analysis of a series parameters of two phosphorescent host materials with D-A structures and the classical host material m CP（N,N’-dicarbazolyl-3,5-benzene）,such as frontier molecular orbitals,exciton formation ratio on the singlet state and triplet state,and related experimental data.And we studied the charge transfer amount q of them in the optimal configuration of the ground state,the lowest excited singlet state,the lowest excited triplet state,the cation and the anion state.The exciton generation model is constructed based on Marcus-Hush theory pattern,and the recombination energy under the model was calculated.The results verified that in the phosphorescent host materials,the host materials with low triplet exciton formation cross-section are an alternative choice for high efficient blue and deep-blue phosphorescene organic light-emitting devices.