Study On Singlet Fission Properties Of Perylenediimide Derivatives

Singlet exciton fission(SF)is a process in which a high energy singlet exciton divides its energy among two neighboring molecules to from two lower energy triplet excitons.Singlet fission could overcome the Shockley-Quiesser limit on the theoretical efficiency of single-junction solar cells for power conversion efficiency from 33% to 45%.So far,scientists have not studied the singlet fission process clearly.because of its influence on solar cells,photoelectric conversion and other fields,it is significant to study on Singlet fission.In this thesis,we have designed and synthesized some Perylenediimides with different substituents,and explored the singlet fission properties of these molecules in different aggregation states.The thesis includes the following parts:1.We designed and synthesized five molecules with different bay-substituents,PDI-C5-2,PDI-C5-3,PDI-C5-4,PDI-C5-1N and PDI-C5-2N.They were subjected to basic optical characterization to determine the singlet state energy level and the driving force of the singlet fission.By comparing with the optical spectrum in the solution state,it is found that the perylenediimides derivative has some difference in absorption emission position,fluorescence quantum yield and fluorescence lifetime in the state of solid film,and there are other competitions with radiative decay.The decay pathway reveals the process by which singlet fission may occur.This work has guiding significance for the study of the basic properties of singlet fission materials.2.We studied the singlet fission properties of perylenediimide derivatives in the film state by femtosecond transient absorption.This process reveals the effect of singlet fission driving force and substituent effect on triplet yield.We tested the PDI derivatives in the solution and film state for the femtosecond transient absorption spectroscopy.It is found that in the solution state,the excited state molecules decay directly to the ground state through the fluorescent pathway.There was singlet fission process in the solid film state.The position of the triplet signal was determined by comparison with sensitization experiments.This work provides a basis for exploringthe nature of singlet splits.3.We prepared nanoparticles of PDI-C5-2,PDI-C5-3,PDI-C5-4,PDI-C5-1N and PDI-C5-2N molecules and characterized them by a series of optical properties.As well as the test of transient absorption,no singlet fission process was found.Investigating whether PDI derivatives nanoparticles can undergo singlet fission in order to judge the influence of molecular packing on singlet fission.By comparing the optical properties of the solution state and the solid film state,and the test of femtosecond transient absorption spectroscopy,it is found that the nanoparticle may not have a singlet fission process,and the molecular packing has a certain influence on the singlet fission.