Azobenzene photomechanics: prospects and potential applications

The change in shape inducible in some photo-reversible molecules using light can effect powerful changes to a variety of properties of a host material. This class of reversible light-switchable molecules includes molecules that photodimerize, such as coumarins and anthracenes; those that allow intra-molecular photo-induced bond formation, such as fulgides, spiro-pyrans, and diarylethenes; and those that exhibit photo-isomerization, such as stilbenes, crowded alkenes, and azobenzenes. The most ubiquitous natural molecule for reversible shape change, however, and perhaps the inspiration for all artificial bio-mimics, is the rhodopsin/ retinal protein system that enables vision, and this is the quintessential reversible photo-switch for performance and robustness. Here, the small retinal molecule embedded in a cage of rhodopsin helices isomerizes from a cis geometry to a trans geometry around a C=C double bond with the absorption of just a single photon. The modest shape change of just a few angstroms is quickly amplified and sets off a cascade of larger shape and chemical changes, eventually culminating in an electrical signal to the brain of a vision event, the energy of the input photon amplified many thousands of times in the process. Complicated biochemical pathways then revert the trans isomer back to cis, and set the system back up for another cascade upon subsequent absorption. The reversibility is complete, and many subsequent cycles are possible. The reversion mechanism back to the initial cis state is complex Z. Mahimwalla C. J. Barrett (&) Department of Chemistry, McGill University, Montreal, Canada e-mail: [email protected] K. G. Yager Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY, USA J. Mamiya A. Shishido A. Priimagi Chemical Resources Laboratory, Tokyo Institute of Technology, Yokohama, Japan A. Priimagi Department of Applied Physics, Aalto University, Aalto, Finland 123 Polym. Bull. DOI 10.1007/s00289-012-0792-0