Structure-property relationship in functionalized azobenzene photoswitches and their supramolecular behavior

Herein, we report the design, synthesis, and supramolecular behavior of 30 structurally diverse photoresponsive azobenzene molecular systems. To establish structure-property relationships, azobenzenes appended with N-picolinyl and/or N-benzyl groups tethered directly through carboxamides or via triazolylmethyl carboxamide linkages were explored. We have evaluated the photoswitching characteristics and thermal stability of the Z isomers through systematic studies. All the targets were also screened for their aggregation behavior and supramolecular aspects. Among all the derivatives, a few carboxamide-based systems formed microcrystals upon aggregation, showing light responsiveness. In contrast, the derivatives tethered via triazolylmethyl carboxamide linkage exhibited hydrogel formation with excellent water-absorbing capacity. All supramolecular aspects of the morphology of the microcrystal and hydrogel states and their stimuli-responsiveness have been studied using spectroscopy and various microscopic techniques.