Sunlight-Driven Photomobile Polymer Materials Containing Push-Pull Azobenzene Moieties

Polymer materials that show macroscopic deformation upon irradiation with light are feasible as soft actuators. However, previous photomobile systems typically required artificial light sources for actuation. Herein, we develop photomobile polymer materials that can be deformed by natural sunlight. Azobenzenes functionalized with electron-donating and -withdrawing groups (push-pull azobenzenes) show trans-cis photoisomerization upon irradiation with sunlight and cis-trans thermal back isomerization after the cessation of irradiation. Push-pull azobenzenes are incorporated into crosslinked liquid-crystalline polymers, in which azobenzene moieties are uniaxially aligned. Upon irradiation with simulated sunlight, the polymer films exhibit bending toward the incident light and revert to the initial shapes after the discontinuation of irradiation. The time scales of the macroscopic bending and unbending are consistent with those of photoisomerization behaviors of azobenzene moieties. This result indicates that macroscopic deformation is induced through photochemical processes rather than photothermal processes. The development of sunlight-driven photomobile polymer materials would lead to the creation of autonomous and ecofriendly photoresponsive systems without the need for artificial optical elements, such as light sources, lenses, and filters.