Surface Tension Manipulation with Visible Light through Sensitized Disequilibration of Photoswitchable Amphiphiles

The light-induced N=N double bond isomerization of azoarenes lies at the heart of numerous applications ranging from catalysis, energy storage, or drug release to optogenetics and photopharmacology. While efficient switching between their E and Z states has predominantly relied on direct UV light excitation, a recent study by Klajn and co-workers introduced visible light sensitization of E azoarenes and subsequent isomerization as a tool coined disequilibration by sensitization under confinement (DESC) to obtain high yields of the out-of-equilibrium Z isomer. This host-guest approach is, however, still constrained to small, minimally substituted azoarenes with limited applicability and functionality in advanced multicomponent molecular systems. Herein, we expand the DESC concept to steer the supramolecular assembly of surfactants at the air-water interface. Leveraging our expertise with photoswitchable arylazopyrazole amphiphiles, we induce substantial alterations of the surface tension and surface excess of water through their reversible E-Z isomerization. After studying the binding of positively and negatively charged surfactants to the host, we find that the extent of surface activity differences upon visible light irradiation for both isomer states is comparable to those observed for direct UV light excitation. The method is demonstrated on a large range of concentrations (from µM to mM) and can be equally activated using green or red light, depending on the sensitizer chosen. The straightforward implementation of visible light photoswitch sensitization in a complex molecular network showcases how DESC enables the improvement of existing light-responsive systems and allows for the development of novel applications driven exclusively with visible light.