Theoretical Study On Spectral Properties And Carrier Mobility Of Oligothiophene And Derivatives

Oligomeric thiophene compounds have the advantages of strong chemical stability,simple synthesis process,easy functionalization and wide color adjustability.Because of these excellent properties,it has been widely concerned and studied in organic photoelectric materials.However,in practical application,the efficiency of organic photovoltaic devices and electroluminescent devices based on oligothiophene is relatively low.It is found that the substitution of alkyl and electron-withdrawing groups can obviously improve its efficiency.However,at present,there are relatively few theoretical studies on oligothiophene and its related derivatives.Therefore,it is of great significance to discuss and summarize the relationship between the structure and properties of existing oligothiophene derivatives from the theoretical aspect,which can point out the direction for designing new oligothiophene derivatives.In this study,we mainly use density functional theory（DFT）,time-dependent density functional theory（TDDFT）,classical molecular dynamics,dynamic Monte Carlo（KMC）method and Marcus theory to explore the electronic structure,excited state properties,solid-state stacking morphology and carrier mobility of oligopentathiophene（T5）and its derivatives.The content is as follows:（1）Oligomeric thiophene materials are widely used in the field of organic electronics because of their excellent characteristics.Pentaphthene has high carrier mobility,solubility and stability,while alkylated and central thiophene ring S,S-dioxide pentathiophene derivatives have better photoelectric effect than T5.However,there is a lack of systematic research and mechanism explanation on how alkylation and S,S-dioxide affect their photoelectric properties.Therefore,the effects of alkylation and central thiophene ring S,S-dioxide on frontier molecular orbitals,dipole moments,electron distribution,ultraviolet-visible absorption spectra,fluorescence emission spectra and fluorescence quantum yield of T5 series molecular were systematically studied in this project.The results show that the S,S-oxidation of the central thiophene ring increases the electronegativity of the molecule,but also makes the planarity of the molecule worse,the dipole moment and D_CTincrease,and HOMO and LUMO decrease.In solution,the fluorescence quantum yield of pentathiophene with alkylation and central thiophene ring S,S-dioxide will decrease.（2）By molecular dynamics and quantum chemical calculation,we simulated the stacking form of alkylation and central thiophene ring-S,S-dioxide oligothiophene amorphous crystal films.The carrier mobility is calculated,which fills the theoretical gap in exploring alkylation and thiophene S,S-dioxide oligopentathiophene in solid state.We found that thiophene S,S-dioxide is beneficial to hole transport of oligothiophene,but not to electron transport.