Photochemical and Photophysical Studies of Rose Bengal Poly(vinylpyrrolidone) — Application to the Photoreduction of Water

Abstract

The photophysics and photochemistry of the xanthen dye rose bengal have been studied both free in aqueous solution and when bound to poly( vinylpyrrolidone ) ( pvp ). Fluorescence, picosecond spectroscopy and laser flash photolysis measurements have been undertaken. The singlet and triplet excited state lifetimes of the dye are increased and the dye photostability is enhanced upon binding to the polymer. These observations may be explained on the basis of changes in the microenvironment surrounding the dye and restrictions on molecular diffusion in the polymer. The reduced rate of non- radiative decay and higher photostability of rose bengal in the presence of polymer leads to improved overall yields of hydrogen production during the photoreduction of water in reaction systems which incorporate the dye and pvp as a light-harvesting pigment. One of the most efficient systems for the photoreduction of water at pH 9 and above is reported.