Photochemical reactivity of diarylethenes: effects of carboxyl group derivatives

Diarylethenes provide light-controllable generation of reactive species (such as Brønsted and Lewis acids) to trigger various processes with high spatial and temporal resolution. At the same time, the opposite light-induced deactivation has not been developed yet. A promising way to achieve such controllable "removal" of acidity is the introduction of a carboxyl group at one of the reactive carbons. To address this issue, we studied the irreversible photoreactions of the corresponding substrates in the diphenylethene and phenyloxazolylethene series. Indeed, exposure to UV light led to the irreversible elimination of the carboxyl group during transformation to phenanthrene or naphthalene products. The efficiency of this reaction, competing processes, and the reactivity of the related esters and salts are discussed. Our results show that the carboxyl group (or its derivatives) can serve as the leaving group in the photochemical reactions of diarylethenes, thus providing "photoswitching-off" of acidity.