(Invited) Domino Killing Isomerization of Azobenzene Embedded in Rigid Polymer Gel

Abstract

Photoisomerization reactions of azobenzene derivatives have become the most common power source for molecular machines and photoresponsive polymers. Among photomechanical polymeric materials, a large response has been achieved exclusively using azobenzene-containing liquidcrystalline elastomers (azo-LCEs) and networks (azo-LCNs). Thus, although a number of efforts have been done to develop polymeric materials capable of transducing light to mechanical work, successful examples of bottom-up direct photomechanical transduction are still limited. Here we demonstrate that azobenzene containing rigid polymer networks, which consist of aromatic poly(amide acid) or polyimide backbones, show remarkable macroscopic deformation in response to blue (405 nm) and visible light (>532 nm) irradiation. The bending motion of the cantilever was recorded by a video camera and analyzed on a computer. Although, the centimeter-long cantilever of PAA gel rapidly bends and forms a 90° angle within 4 s upon 405nm laser irradiation at one point, that of PI gels deflect 90 degree within 1.5 s. The bent cantilever cannot smoothly return to a straight shape upon visible light (> 532 nm) irradiation at one point. Surprisingly, in order to return the polymer rod of PI gels to the upright state, it is necessary to irradiate the entire rod with visible light. We believe that this is because trans-cis isomerization of azobenzene at the light irradiation site induces domino killing isomerization of the polymer gel at the non-irradiated site. In this research, we discuss the possibility that domino killing isomerization of azobenzene is induced by laser irradiation from various evidence.