Stiff-Stilbene-Linked\nBis-Cholesterol: Synthesis and\nInvestigation of Its Supramolecular Gelation and Photophysical Behaviors

Here, we report the design, synthesis, and comprehensive\ncharacterization\nof the bis-cholesterol supramolecular gelator, which contains photochromic\nstiff-stilbene as a bridging unit. The <i>cis</i>-isomer\nof stiff-stilbene bridged bis-cholesterol (<i>Z</i>-<b>D</b>) was first synthesized with a systematic design, which can\nbe further converted into its <i>trans</i>-isomer (<i>E</i>-<b>D</b>) with a high degree of efficiency (ca.\n100%) upon exposure to 385 nm UV light. Unusual gelation behavior\nwas observed for <i>Z</i>-<b>D</b>, which exhibited\nsupergelator properties in mixed solvents of acetonitrile (ACN)/dichloromethane\n(DCM) (v/v = 1:1), DCM/MeOH (v/v = 1:2), ACN/CHCl<sub>3</sub> (v/v\n= 2:1), and CHCl<sub>3</sub>/MeOH (v/v = 1:2), with minimum gelation\nconcentrations (MGCs) as low as 0.2 w/v%. These gels formed rapidly\nat room temperature without the aid of any mechanical forces upon\nthe addition of an antisolvent into the vial containing the gelator\nand its dissolving solvent. The formation of the self-assembled gel\nwas primarily driven by hydrogen bonding, van der Waals forces, and\ndipole–dipole interactions, as confirmed by <sup>1</sup>H NMR,\nFourier transform infrared spectroscopy (FT-IR), and UV–vis\nspectroscopies. The gelator molecule <i>Z</i>-<b>D</b> entraps organic solvents and organizes itself into three-dimensional\n(3D) fibrillar networks in various single and mixed solvents, as confirmed\nby scanning electron microscopy (SEM) analysis. Upon irradiation with\n385 nm light, the gel networks disintegrated into a precipitate suspension,\nresulting in the transformation of the fibrous structures into irregular\nspherical-like aggregates. This proves that the structural conformation\nchanges in the gelator significantly influence the resulting self-assembled\nstructures. Overall, the findings present in this study pave the way\nfor the future development of novel light-responsive bis-cholesterol-based\ngelators, especially in their <i>Z</i>-isomeric form.