| Triplet state exciton have a wide range of applications in electroluminescence,fluorescence molecular imaging,photodynamic therapy,and photocatalysis.In recent years,exploring the pathways to access the triplet excited states of organic chromophores has attracted much attention.Among the numerous photoinduced processes in organic chromophores,intersystem Crossing(ISC)is one of the most common exciton dynamics processes..The ISC process involves a spin-forbidden horizontal transition from an excited singlet state to a higher vibrational level of the isoenergetic triplet state.Therefore,ISC necessitates a strong driving force from efficient spin–orbit coupling(SOC)between the singlet and triplet wavefunctions.To enhance the spin-orbit coupling of molecules,researchers usually introduce heavy atoms into molecules,but triplet state molecules based on the heavy atom effect have limited their applications in numerous fields due to their high toxicity and high cost.Therefore,the development of triplet excited state organic chromophores without heavy atoms has important research significance.In this thesis,a series of thiomolecules were designed and synthesized based on perylene and picene derivatives,perylene tetrabutyl ester(PTBE)and picene tetrabutyl ester(PiTBE),using the design strategy of thionation of the carbonyl group in organic chromophore,to explore the effect of sulfur substitution on the intersystem crossing process and triplet state.The specific research contents are as following:(1)Firstly,the thio-molecule PTBE-S4 was designed and synthesized using PTBE as the basic unit,and the thio-dimer molecule PTBE2-S8 was synthesized as a control molecule to investigate the effect of sulfur substitution on molecules containing multiple chromophores.The UV-Vis steady-state absorption spectra,fluorescence emission spectra,cyclic voltammetry curves and density functional theory calculations showed that the steady-state spectra of the molecules exhibited a significant red shift after the oxygen atoms were replaced by sulfur atoms,and the energy gap difference decreased,indicating an increase in the electron affinity.The test results of transient spectroscopy show that the intersystem crossing process can be effectively promoted by sulfur substitution,and triplet state is generated.The fast intersystem crossing process is successfully achieved in PTBE with weak spin-orbital coupling.It is found that suitable exciton coupling can regulate the intersystem crossing process.The intersystem crossing rates of PTBE-S4 and PTBE2-S8 are 2.48μs and 5.05 μs,respectively.(2)To further verify the universality of strategy of thionation of the carbonyl group in organic chromophore,we designed and synthesized another polycyclic aromatic hydrocarbon PiTBE,and performed sulfur substitution experiments to obtain PiTBE-S4.The results show that PiTBE-S4 has a smaller energy gap compared to PiTBE.The transient spectroscopy test results show that the intersystem crossing rate of PiTBE-S4 is greatly improved compared with that of PiTBE,from 4.5 ns to about400 fs.In summary,the strategy of thionation of the carbonyl group in organic chromophore can effectively promote the intersystem crossing process and generate long-lived triplet states.Moreover,this strategy has good universality and can be extended to other organic chromophores,providing ideas for designing triplet state organic chromophores with fast intersystem crossing processes and long-lived triplet states. |
