Synthesis,cis/trans Isomerization And Properties Of Several Amino-substituted Tetraphenylethene Derivatives

In past decades,tetraphenylethene?TPE?,as a classic aggregation-induced emission fluorophore,has attracted tremendous research interest due to its easy synthesis and functionalization.However,separation of the TPE isomers is challenging,and the isomerization and properties of the cis-and trans-isomers of TPE derivatives have been sparsely explored.In this work,a series of TPE derivatives with aggregation-induced emission characteristics have been designed and synthesized,and their cis-trans isomerization process and the properties of cis/trans isomers have been investigated.The preliminary results in this work are as follows:Firstly,for the diamino-functionalized TPE derivatives?NH₂-TPE-NH₂?:?1?they can readily undergo cis/trans isomerization in their solution state,but not in the solid state.?2?It was found that the cis/trans isomerization rate of NH₂-TPE-NH₂ in chloroform is faster than those in methanol and DMSO.?3?The isomerization process can speed up under acidic condition,heating,and UV irradiation.Moreover,the isomerization rates become slower with the increasing of the degree of N-acetylation of NH₂-TPE-NH₂ under the same conditions,,demonstrating that free amino groups play a great role in the isomerization process.We propose that the conversion is ascribed to the imine-enamine tautomerization.Secondly,two geometric isomers,cis-and trans-C₁₃H₂₇CO-Ala-TPE,have been synthesized by introducing alanine-containing attachments to the pheripheries of NH₂-TPE-NH₂.The cis/trans isomers show different UV-Vis absorption and solid state photoluminescence behaviours.The conformers exhibite different self-assembling behaviours under the same conditions,and stimuli-responsive behaviours upon exposure to solvent vapors and shear stress.The TPE-containing dipeptides,C₁₃H₂₇CO-Ala-Ala-TPE,display aggregation-induced circular dichroism effect.Their conformers show different luminescence and self-assembly behaivours,and mechano-and vapo-chromic effects.Thirdly,the pyridinyl-functionalized TPE derivatives,TPE-L/D-Val-11PyBr showed aggregation-induced emission and circular dichroism effects.They can easily form clear gels with good thermal reversibility.The fluorescence of TPE-L/D-Val-11PyBr gels can be reversibly regulated when a heating/cooling cycle are performed.