Intrinsically Visible Light-Responsive Liquid Crystalline Physical Gels Driven by a Halogen Bond.

Photoresponsive physical gels using liquid crystals (LCs) as solvents have attracted great interest owing to their potential applications. But, current investigations mainly focus on UV light, which is not environment-friendly enough. On the other hand, the halogen bond is a novel tool for constructing supramolecular gels because of good hydrophobicity, high directionality, tunable strength, and large size of halogen atoms. Herein, to construct an LC physical gel with both the advantages of a halogen bond and visible light response, azopyridine-containing Azopy-C is chosen as a halogen bond acceptor, while 1,2-bis(2,3,5,6-tetrafluoro-4-iodophenyl)diazene is selected both as the halogen bond donor and for the intrinsically visible light response. Such a binary gelator can self-assemble in the anisotropic solvent of nematic LC 5CB to form an LC physical gel. It experiences the gel-to-sol transition by green light irradiation. As the gelator concentration increases, the saturation voltage increases, but the switch-off time decreases. The combination of the halogen bond and controllable visible light-responsive LC physical gel provides the feasibilities of manipulating these smart soft materials.