Tenfold increase in the photostability of an azobenzene guest in vapor-deposited glass mixtures

Abstract

Improvements to the photostability of organic glasses for use in electronic applications have generally relied on modification of chemical structure. We show here that the photostability of a guest molecule can also be significantly improved - without chemical modification - by using physical vapor deposition to pack molecules more densely. Photoisomerization of the substituted azobenzene, 4,4’-diphenyl azobenzene (DPA), was studied in a vapor-deposited glass matrix of celecoxib. We directly measure photoisomerization of trans- to cis- states via UV-Vis spectroscopy and show that the rate of photoisomerization depends upon the substrate temperature used during co-deposition of the glass. Photostability correlates with the density of the glass, where the optimum glass is about tenfold more photostable than the liquid-cooled glass. Molecular simulations, which mimic photoisomerization, also demonstrate that photoreaction of a guest molecule can be suppressed in vapor-deposited glasses. From the simulations, we estimate that the region that is disrupted by a single photoisomerization event encompasses approximately 5 molecules.