Construction Of Photo-modulated Supramolecular Systems Driven By Halogen Bond

The subject of supramolecular chemistry is a complex of a plurality of molecules that forms an assembled structure by weak non-covalent interactions.At present,the formation of well-defined supramolecular structures through the self-assembly of functional molecules has become an important way to develop new materials and devices.Halogen bond,similar to hydrogen bond,has become an effective tool to construct supramolecular materials.Halogen bond possesses the features of directionality,tunability,hydrophobicity,donor atom size in favor of broadening applications.The features of light are remote control,fast response and exact location.Among the photoresponsive groups,azobenzene?azo?group is the most widely used.The azo-containing molecules can undergo reversible cis-trans isomerizations upon the alternate UV and visible light irradiations,so that the configuration change will lead to the variation of molecular assembly.Hence,the performance of the supramolecular system is regulated.An azopyridine derivative with a long alkyl end group,Azopy-C₁₀,has been designed and synthesized.The molecule has the following three characteristics:first,azopyridine has the photoresponsiveness;second,the N atom can form a halogen bond with the halogen atom;third,the long alkyl chain is beneficial to promote the formation of supramolecular systems such as gels and liquid crystals.The research results are listed as following:1.When Azopy-C₁₀ and 1,4-trafluorodiiodotebenzene?TFDIB?are put into the solvents such as acetonitrile or ethanol,the photoresponsive halogen-driven Azopy-C10·TFDIB supramolecular gels can be formed.The gels have reversible thermal responsiveness and one-way photo-responsiveness.Interestingly,when irradiated by UV light,the gels collapse on a macroscopic scale.At the same time,the morphology of such halogen bond driven assembly during gel-sol transition transforms from flake to fluffy bobble-like,and finally to peony-like.2.It has been confirmed by POM that the halogen bond complexes formed by Azopy-C₁₀ with TFDIB or 1,4-tetrafluorodibromobenzene?TFDBB?show a smectic A phase liquid crystal.However,only Azopy-C₁₀·TFDIB liquid crystal can realize the transformation of smectic phase to isotropic phase upon UV irradiation.The Azopy-C₁₀·TFDBB liquid crystal does not show such photoresponsiveness.