Phosphonate-Derivatized Porphyrins for Photoelectrochemical Applications

A series of phosphonate-derivatized, high redox potential porphyrins with mesityl, pentafluorophenyl, and heptafluoropropyl meso-substituents were synthesized by acid-catalyzed condensation reactions. Ground and excited state redox potentials in the series were varied systematically with the electron-donating or electron-accepting nature of the meso-substitutents. The extent of excitation and injection by porphyrin singlet excited states surface-bound to SnO2/TiO2 core/shell metal oxide nanoparticle films varies with the excited state reduction potential, E-o'(P+/P*). With the mesityl-substituted porphyrin, high current density and sustained photocurrents are observed at pH 7 with the addition of the electron transfer donor hydroquinone.