Temperature dependent photoisomerization kinetics of semicrystalline poly(azobenzene)s

Among the variety of photomechanical materials studied to date, photoresponsive semicrystalline polymers provide a potential route to enhance performance by combining a high degree of molecular ordering of polymer crystallites with facile material processing and actuator fabrication. However, the regular packing of azobenzene units within the crystalline lattice can hinder the trans-cis isomerization, a process which requires a substantial amount of free volume, thus deteriorating the photomechanical performance. We have studied the temperature-dependent kinetics of photoisomerization in poly(azobenzenes) with both alkyl and ethylene glycol chain extenders. Interestingly, while the amorphous component switches readily in both cases, the former polymers show a dramatic decrease in rate for the crystalline phase near room temperature. Understanding these temperature dependent photoisomerization kinetics is expected to enable control of photomechanical response time-scales, improve the energy efficiency of photo-actuation.