Concise Synthesis of Photoresponsive Polyureas Containing Bridged Azobenzenes as Visible-Light-Driven Actuators and Reversible Photopatterning

Linear photoresponsive polyurea of PbAzo containing bridged-azobenzene moieties in backbone was synthesized via polyaddition reaction between hexamethylene diisocyanate and cis-3,3′-diamino ethylene-bridged azobenzene. The bridged-azobenzene moieties endow the PbAzo polyurea advantages of visible-light-driven isomerization and fast and powerful photoresponse. Under irradiation with 405 nm blue light, stable cis-PbAzo converts into metastable trans-PbAzo accompanying the amorphous-to-crystalline transition and the yellow-to-red color change via cis-to-trans isomerization. With further illumination with 532 nm green light, trans-to-cis isomerization reversibly takes place. This photoresponsive polyurea is used in photopatterning, in which patterns can be reversibly written or erased alternatively by 405 nm blue light and 532 nm green light or heating. Besides, the polyurea film can act as qualified visible-light-driven actuators. Under irradiation with 405 nm blue light, it initially bends away the light source with the bending angle above 110 deg in several seconds, and then it recovers to its initial state with no attenuation under irradiation with 532 nm green light. Our photoresponsive polyurea is different from photoresponsive polymers including planar azobenzene moieties, and this polyurea is expected to be promising for smart materials.