Theoretical Study And Molecular Design Of Hybridized Local And Charge-transfer Excited State In Thiazole Molecules

In recent years,Organic light emitting diodes（OLEDs）have been developed rapidly and gradually realized commercial applications.The research of organic light-emitting materials is the core technology of OLEDs devices,so designing cost-effective and feasible light-emitting materials is the focus of current research.In 2012,academician Ma Yuguang’s research team proposed"hot exciton,hybridized local and charge-transfer excited state"material,which can maximize exciton utilization and luminescent efficiency.It is a new material with broad development prospects and independent intellectual property rights."Hot exciton"materials are characterized by the exciton channel(T_CT→S_CT)at higher energy levels,that is,the energy gap between the higher triplet and singlet states is small and almost zero(ΔE_ST≈0),which can realize the process of reverse intersystem crossing（RISC）.At the same time,there is a large energy gap between the triplet states(T_CT→T_LE),which can theoretically achieve high luminescence efficiency and exciton utilization.The photoelectric properties of organic materials are essentially determined by the properties of their excited states,which are mainly divided into three types:localized excited state（LE）,which determines the luminous efficiency of molecules;Charge transfer state（CT）determines exciton utilization;Hybrid local and charge transfer excited state（HLCT）.HLCT state is a new excited state formed by the linear combination after hybridization of intrinsic LE state and intrinsic CT state.It has the properties of both LE state and CT state.The molecule we designed is to ensure that it has high luminous efficiency and exciton utilization at the same time,so as to meet the principle of HLCT state and the characteristics of hot exciton molecules.In this thesis,a series of theoretical studies on luminescent molecules with donor receptor（D-A）structure are carried out by using quantum chemical calculation method.We chose time-dependent density functional theory（TD-DFT）method and selected HLCT state molecule PCZ-AN-PPI to verify its different functional,including local functional:SVWN、PBE;Hybrid functional:BLYP（0%HF）、B3LYP（20%HF）、PBE0（25%HF）、BMK（42%HF）、BHand HLYP（50%）、M06-2X（56%HF）、M06HF（100%HF）and long range correction functional:Cam-B3LYP,wB97XD（Base groups are commonly used 6-31+G（d,p））,calculated from the ground state,excited state configuration,absorption,emission spectra and excited state properties,by comparing with the experimental values,the calculated results of the long-range correction functionalwB97XD are highly consistent with the experimental values,in other words,this functional can accurately describe and calculate the molecules of HLCT state.Different from the classical D-A molecular structure system,we extend D-A system to X-B-D system.In order to ensure a large energy gap between the triplet states(ΔE_T1–T2),we selected the naphthothiazole（NZ）group as the core B;and screened the donor and acceptor molecular groups,10H-phenoxazine and 1,3,4,6,7,9,9^b-heptaazaphenalene were selected as the electron acceptor X₁ and X₂ parts,and 10 donor groups were selected as the D part,the molecules of X₁-B-D and X₂-B-D were designed.By simulating the ground state and excited state properties of these 20 molecules,we found that the excited state of these molecules are more the transitions of HLCT state dominated by CT state,and while maintaining a large enoughΔE_T1–T2,the number of multipleΔE_ST was very small,which also means that the number of channels of the reverse intersystem crossing increased from one to multiple,which can carry out the reverse intersystem crossing of excitons more efficiently and improve the utilization rate of excitons,which may provide new ideas for the design of new"hot exciton"multichannel materials and provide sufficient theoretical support for future experiments.