Synthesis and Photophysical Analysis of Amphiphilic Azobenzene Surfactants for Photomechanical Actuation

Abstract

Photoswitchable amphiphiles are promising candidates for investigating light-responsive mechanical behavior in soft and biological systems, with potential applications in dynamic materials and adaptive interfaces. Azobenzene is the most studied photoactuator, but research typically focuses on its standard backbone, limiting control over its photophysical and kinetic properties. Modifying its conjugated core offers new opportunities for tuning its behavior. Here, the synthesis and characterization of water-soluble azobenzene derivatives featuring a hexaethylene glycol (OCH₂CH₂)₆ unit terminated with a sodium sulfate (OSO₃Na) group, alongside subtle electronic modifications to the conjugated backbone, are reported. Their steady-state photophysical properties and reversible photoisomerization kinetics in aqueous environments under real-time observation are demonstrated. Despite similar activation parameters for the thermal cis–trans isomerization in some derivatives, their half-lives vary significantly, underscoring the overlooked role of the transmission coefficient in isomerization kinetics. Finally, these photo-responsive amphiphiles are showcased as dynamic surfactants in oil-in-water and water-in-oil emulsions, visualizing their behavior through operando microscopy. These findings underscore their potential for tunable emulsions and adaptive soft matter applications.