Investigation Of Radical Properties Based On Asymmetric Imidazole Molecules

In recent years,diradicals have received growing attention from scientists.In principle,they possess interesting electronic,magnetic,and optical properties,leads to great prospects for organic electronics and spintronics.The study of diradicals are mainly concentrated in symmetric molecular system.Molecules that have symmetrical radical centers,show a certain delocalization of radicals,and generally have good stability due to good conjugation.Also,these molecules often show strong near infrared absorption.On the other hand,photoexcited molecular system usually refers to molecule forms a closed-shell structure in the ground state,under a certain wavelength of light excitation,break the bond to form a diradical,and the process is reversible.Because of the closed-shell structure of the ground state,this kind of molecule has better stability and can control the lifetime of its excited state by changing the structure,which has the research prospect of designing photocontrolled materials.In contrast,the asymmetric diradical system is much less explored.In addition,most of the photoexcited molecular systems belong to even number of radicals,that is,the superposition of multiple diradicals,while there are few studies on odd number of radicals,which will help to better understand the spin-spin interaction of diradicals.Therefore,in this thesis,imidazole radical is combined with phenyl radical to study the interaction of diradicals in an asymmetric system and the influence of odd number of radicals on the excited state of photoexcited molecules.The content of this thesis includes the following two aspects:1.Design and synthesis a series of asymmetric diradical structures with different length of thiophene π Bridges and phenoxyl and imidazoyl groups as two radical centers.The structures exhibit excellent near-infrared absorption properties with the extension of thiophene π bridges,and the maximum absorption wavelength reaches 1105 nm.It was found that cis-trans isomerism existed when π-bridge was composed of two thiophenes,and the triplet in the progress of cis-trans isomerism was observed by ESR signal for the first time.By measuring the ESR of these molecules from 130 to 350 K and combining with DFT calculation,the exchange interaction characteristics of diradicals with different π bridge length were studied.2.A variety of asymmetric photoexcited molecules with monoradical in ground state and triradical in the excited state were designed and synthesized.The ESR signal was measured before and after the light excitation at low temperature.With the change of the position of the radical group,the structure showed different ESR characteristics,and one of the structures showed high spin excited state.In addition,the absorption spectra and spin properties of these molecules were characterized respectively.