Supramolecular light-switchable triazole-hosts for photoresponsive anion binding

Abstract

A series of photoreversible anion binding hosts is developed, combining either an azobenzene or an arylazopyrazole as a central photoswitch unit and tetrakis-triazoles as anion binding motifs. By broad structural variations, including different linker types and positions between the triazoles, the anion binding contrast of both isomers is maximized, with the Z isomer exhibiting a binding constant of up to a factor of 16 larger than that of the E isomer. Back-isomerisation Z → E is studied with respect to the influence of a bound anion. Anion binding stabilizes the Z-isomer against thermal isomerization, providing a two-fold lifetime of the Z isomer. A reduced photoisomerization rate and an enhanced Z/E ratio in the photostationary state correlate with the anion binding constant of the Z isomer, which is probably due to the modified photophysical processes.