Photochemistry of Common Xanthene Fluorescent Dyes as Efficient Visible-light Activatable CO-Releasing Molecules

Xanthene derivatives are organic dyes, some of which are routinely used in different chemical and biological applications, including human medicine. In this work, we investigated the photochemistry of some of the most common ones, fluorescein, eosin Y, and rose bengal, and major products of their photodegradation using optical spectroscopy, NMR, chromatography and mass spectroscopy techniques. These substances, usually considered (photo)chemically stable, were found to liberate carbon monoxide (CO) in 40–80% chemical yields upon extensive irradiation with visible light in aqueous solutions during their multistep concomitant degradation processes. In addition, a number of low-mass secondary photoproducts, such as phthalic and formic acids, were identified in the irradiated mixtures. We demonstrate that these common fluorescent dyes can also be considered as visible-light activatable carbon monoxide (CO)-releasing molecules (photoCORMs) under specific conditions with potential biological implications.