Fluoride-responsive organogel containing azobenzyl and cholesterol units

• Two new cholesterol-based compounds O1 and O2 were designed and synthesized.
• O2 could form opaque gel in 1,4-dioxane with red color.
• The gel could selectively response to fluoride ions with color and phase changes.

In this paper, two new cholesterol-based compounds O1 and O2 were designed and synthesized. The compound O2 could selectively gel in 1,4-dioxane with porous ribbon structure. The aggregation mode of O2 molecules were characterized by SEM, IR, UV–vis and XRD experiments. Interestingly, the gel of O2 was also fluoride-responsive. The addition of TBAF on the gel surface would trigger the gel–sol transition, and the collapse time could be controlled by amount of fluoride ions. The response process was also accompanied by dramatic color changes from orange to purple. From the NMR titration experiments, it was deduced that the hydrogen bonding competition between the anion-receptor and self-assembly of the receptor played an important role for the gel–sol transition.

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