Photochemical reactions such as cis-trans isomerization, ring-opening/closing, and cyclo-addition reactions allow organic crystals convert microscopic changes in their crystal lattices to macroscopic displacements, with potential applications as photomechanical actuators. Previous studies by our group have demonstrated actuation with diarylethene (DAE) derivatives in anodic alumina oxide (AAO) templates, utilizing a ring-closing reaction. Since the absorbance of the photoproduct leads to poor penetration depth of the excitation beam, positive photochromes such as DAE will fundamentally limit the performance of photomechanical actuators. These drawbacks are compounded by the variation and incompleteness in the filling rates of these porous templates. This work seeks to resolve these shortcomings using a negative photochrome, thereby allowing complete reaction of the organic, and improving the filling rates using solvent assisted annealing and surface functionalization of commercial AAO templates. 9-methylanthracene (9MA) undergoes a [4+4] cycloaddition to form a photo-dimer when irradiated with near UV light. Reaction progress is tracked via UV-VIS absorbance and the actuation is measured by both Michelson interferometry and beam displacement. Optimization of the solvent annealing process leads to more than a two-fold increase in the overall loading of the organic, but surface functionalization has a negligible impact on the loading. Crystal orientation is verified by grazing incidence wide angle x-ray spectroscopy (GIWAXS) and the nanowires exhibit expansion parallel to the long axis of the rod. Despite these optimizations, actuation of the 9MA-AAO template is found to be a combination of angular and linear displacement and is limited by incomplete filling of the template.

Optimizing composite organic-inorganic photomechanical actuators through interfacial chemistry

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.