Design And Piezochromic Properties Of Donor-Acceptor Molecules Contanining Benzothiadiazole

In recent years,deep red/near-infrared organic light-emitting materials?LOMs?have attracted the attention of researchers due to their potential applications in night vision devices,bio-imaging,sensors and lasers.However,most of the reported deep red/near-infrared photoluminescence?PL?efficiencies are low.And near-infrared emitters with high exciton utilization have long been hampered.Recently,Ma Yuguang's group used local excitation?LE?and CT states to form a special hybrid localized charge transfer?HLCT?excited state,which can effectively solve the deep red/near infrared low luminous efficiency problem,in which local excitation?LE?state contributes to high fluorescence quantum efficiency,while the CT state ensures a narrow band gap.However,the number of D-A deep red/near-infrared chromochromic dyes with HLCT properties is limited and the types are few,due to lack of deep understanding of the piezochromic mechanisms at the molecular-level.Therefore,it was of great significance and challenge to study the molecular packing modes and optical properties for obtaining the practical high-intensity deep red/near-infrared stimuli-responsive material.Based on the above analysis,a series of new organic?-conjugated materials with benzothiadiazole were desighed and synthesized in this thesis.Then the relationship among single molecule properties,supramolecular structure,external environmental factors?force and temperature?,and photophysical properties was systematically studied.Firstly,an organic deep red/near-infrared luminescent small molecule BTA-DMeO with benzothiadiazole?BTA?as a receptor and 3,5-dimethoxybenzene as a donor has been designed and synthesized.The properties of single molecule BTA-DMeO were studied by solvation effect,transient spectroscopy,theoretical calculation and 0.1%PMMA doped film.The target single molecule with HLCT luminescence properties was verified.In addition,crystal BTA-DMeO was obtained by slow evaporation from a mixed solution of dichloromethane/n-hexane and analyzed.It was found that the strong emission single molecule BTA-DMeO is self-assembled with H-type stacking due to?-?overlap and strong secondary bond.Under pressure conditions,this supramolecular self-assembly is easily destroyed,resulting in a material with significant fluorescence induced fluorescence enhancement?PIEE?and high sensitivity piezochromic?PRF?properties.Further,the disappearance of H-type stacking and molecular planarization is responsible for PIEE properties by transient spectroscopy,absorption spectroscopy,XRD,IR spectroscopy and theoretical calculations.Interestingly,this change can be effectively restored upon heating,indicating that these materials have great potential for use in practical installations.Subsequently,the organic deep red/near-infrared luminescent small molecule BTA-TPA with benzothiadiazole?BTA?as acceptor and triphenylamine as donor has been designed and synthesized.The solvation effect,theoretical calculation and 0.1%PMMA doped film were used to investigate the HLCT properties of single molecule BTA-TPA.In addition,BTA-TPA crystals with high fluorescence quantum efficiencies(?_PL=62.5%)were obtained by slow evaporation from a mixed solution of dichloromethane/n-hexane and analyzed.It was found that the strongly emitted deep red dye was self-assembled with discrete?-?dimers.Further,the HLCT properties of single molecules and the supramolecular interaction of discrete?-?dimers are responsible for high luminescence of deep red dyes by fluorescence spectroscopy,absorption spectroscopy,transient spectroscopy and theoretical calculations.In addition,in-situ high-pressure absorption spectroscopy,fluorescence spectroscopy and infrared spectroscopy experiments on crystal BTA-TPA were carried out at room temperature by diamond force chamber technology.The results show that the material has strong discoloration characteristics.And the sensitivity?of Piezochromic is 14.9 nm.GPa^-1,16.6 nm.GPa^-1,respectively.Therefore,the use of highly luminescent deep red dyes in practical defect detection,mechanical sensors and deformation detection has great potential.