Light-driven actuators are widely used for smart devices such as soft robots.One of the main challenges for actuators is achieving rapid responsiveness,in addition to ensuring favorable mechanical properties.Herein,we focused on photoresponsive polyurethane(CD-Azo-PU)based on controlling the crystallization of the hard segments in polyurethane(PU)by complexation between azobenzene(Azo)and cyclodextrins(CDs).CD-Azo-PU incorporated polyurethane as the main chain and a 1:2 inclusion complex between Azo andγCD as a movable crosslink point.Upon ultraviolet light(UV,λ=365 nm)irradiation,the photoresponsiveness of CD-Azo-PU bent toward the light source(defined as positive),while that of the linear Azo polyurethane(Azo-LPU)without peracetylatedγ-cyclodextrin diol(TAcγCD-diOH)as a movable crosslinker bent in the direction opposite the light source.The bending rates were determined to be 0.25◦/s for CD-Azo-PU and 0.083◦/s for Azo-LPU,indicating that the bending rate for CD-Azo-PU was faster than that for Azo-LPU.By incorporating movable crosslinks into CD-Azo-PU,we successfully achieved specific photoresponsive actuation with an enhanced rate.
Photoresponsive materials are considered as promising systems for intelligent technology applications owing to the contactless spatial and temporal control.Herein,controllable multi-photoresponsive behaviors are realized in benzo[b]thiophene derivatives(o-DMP-S,o-DMP-SO,and o-DMP-SO_(2))by modulating the sulfur oxidation state.Among them,o-DMP-S is photo-unreactive but possesses denser molecular packing upon ultraviolet(UV)light irradiation,exhibiting photoenhanced room-temperature phosphorescence properties.Through stoichiometric oxidation of the sulfur atom in o-DMP-S,the resulting sulfoxide compound o-DMP-SO undergoes a radical photolysis reaction involving photodeoxygenation and photochemical rearrangement,thereby leading to the photomechanical effect.The sulfone compound o-DMP-SO_(2)displays prominent reversible photochromism,resulting from the radical photocyclization under 365 nm UV light irradiation.Based on comprehensive experimental and computational investigations,the diverse photoresponsive behaviors of these benzo[b]thiophene derivatives are demonstrated to depend on the intersystem crossing efficiency and radical-mediated photochemical reaction activity in excited states due to the different sulfur oxidation states.This work provides an insightful understanding of the relationship between molecular structure and photoresponsive behavior and opens up the opportunity for the development of photoresponsive materials with potential applications.
