Investigation Of The Spin Distribution Properties Of Push-Pull Asymmetric Diradicals

In recent years,open-shell diradical compounds have become a hot research topic in the field of materials due to their unique optical,electrical and magnetic properties.Compared with conventional organic materials,open-shell diradical compounds have two-photon absorption and narrow band gap,which have a wide range of applications in spintronic,organic optoelectronic and energy storage devices.So far,most of the research on open-shell diradicals has focused on symmetric systems,and much less research has been carried out on asymmetric molecules in the form of D-π-A structures.D-π-A type asymmetric molecules may also have zwitterionic resonance structures,and this structural form has a certain influence on the electronic properties of diradical molecules.Particularly around the structure of the coupling unit,the study of the modulation of spin coupling has become a central focus of research in the field of organic magnetic materials.Sulfur-containing organic radical molecules are the focus of research in the field of organic spin materials.Therefore,different types of D-π-A diradicals with benzo-1,3-dithio-2-ylidene as the key radicals center has been designed,and the nature of the spin distribution has been systematically investigated.The research in this thesis covers the following two main aspects.1.Using phenoxyl radicals as acceptor,the SBP series and heterocyclic series molecules were designed and synthesized to investigate the modulation of the spin distribution of D-π-A type molecules by different benzene ring linkage sites and heterocycles.For the SBP series molecules,because the donor-acceptor at the benzene ring linkage site influences the degree of spin coupling between the two radicals centres,thus achieving the modulation of the spin distribution of this series of diradical molecules.In addition,the ESR test and Density Functional Theory calculations confirm that Meta-SBP is a diradical molecule with high spin characteristics and a triplet ground state.UV absorption spectra indicate the existence of zwitterions for Meta-SBP and Ortho-SBP molecules.For the heterocyclic series,the single crystal structures of HeteroSFP and Hetero-STP show closed-shell quinone structures,while the UV absorption spectra confirm the existence of zwitterions for both molecules.2.Using imidazole radicals as acceptors,molecules based D-π-A structures with different numbers of thiophene π-bridges were designed and synthesized to investigate the influence of thiophene bridge length on the spin distribution of D-π-A type molecules.Combining experiment with theory,it was found that as the length of the thiophene bridges varied,in addition to modulating the spin distribution of the diradical molecules,it also generates unique optical properties to the molecules.