Theoretical Research On The Regulation Of Excited State Of Hybrid State (HLCT) Molecules

In a contemporary world with rapid development of information,organic electroluminescent devices(OLEDs)have achieved considerable development and gradual commercial applications.The research focus of OLEDs devices is organic light-emitting materials,so it is particularly important to design low-cost and high-efficiency light-emitting materials.The study of the excited state of light-emitting materials helps us better understand the formation process and design OLEDs with better performance.There are three main types of excited states:localized excited state(LE),charge-transfer state(CT),and hybridized local and charge-transfer excited state(HLCT).The LE state mainly affects the luminous efficiency of the material,and the CT state mainly affects the exciton utilization rate of the material.The HLCT state has the characteristics of both the LE state and the CT state,and can simultaneously satisfy high-efficiency luminescence and exciton utilization,and prepare ideal luminescent materials.Therefore,it has become a hot spot for scientists to research.In this thesis,a series of theoretical researches on the HLCT state were carried out using the method of quantum chemical calculation.Through calculation and comparison of the geometric configuration,absorption and emission spectra,energy and transition properties of the excited state of different molecules in the ground state and the excited state,the calculation method to accurately describe the HLCT state molecules was finally found.Then the excited state of the classical D-A structure molecule was explored.On this basis,the structure was expanded,a series of molecular systems with multiple receptors were designed,and the formation process and influencing factors of its HLCT state were studied.First,the anthracene,tetracene and pentacene molecules with simple structure and triplet high energy gap((?)E_(T1-T2))have been studied.In order to verify the accuracy of calculation methods and functionals,we employ the DFT method and ten different functionals(SVWN,PBE,BLYP,B3LYP,PBE0,BMK,BHand HLYP,M06-2X,M06HF,?B97X)to calculate.The results showed that the DFT/?B97X method can accurately calculate the triplet energy level.We further used the same 10 functionals above to calculate the configuration,absorption and emission spectra,excitation energy of the TPA-AC molecules with HLCT states,and compared them with the experimental values.The results showed that?B97X can almost accurately describe the HLCT state molecule.Based on this,it was determined that the calculation method of?B97X can basically accurately describe the HLCT state molecule.In order to study the formation process and characteristics of HLCT states,the typical TPA-NZP molecule with D-A structure was selected as the research object,and its excited state characteristics,NTOs and transition density matrix were calculated to understand the formation process of its HLCT state.The energy difference between the intrinsic LE state and the CT state of the molecule is small and the coupling is large,causing it to linearly combine and redistribute during the transition process,forming new excited states S₁ and S₂,these two newly formed states.The excited states are all typical HLCT states.Exploring the factors affecting the formation of the HLCT state of the molecule revealed that the torsion angle between the receptors has a great influence on the HLCT state.After the formation process and influencing factors of the HLCT of the classic D-A type TPA-NZP molecule were explored,the D-A structure was expanded and D-A-D,A-D-A,A-D-D-A,D-A-A-D,and A-D-A-D-A type molecules were designed.The calculations results indicate that the singlet hybridization in the D-A molecule will form a new HLCT state:the S₁ state dominated by the LE state and the S₂ state dominated by the CT state.It has been discovered that the excited states containing multiple acceptor molecular systems are divided into three types in the entire energy system,which provides a good idea for the design and regulation of new HLCT state molecules in the future.