In situ infrared spectroscopic analysis of the adsorption of ruthenium(II) bipyridyl dicarboxylic acid photosensitisers to TiO2 in aqueous solutions

Internal reflection spectroscopy has been used to obtain the in situ infrared spectra of ruthenium(II) bipyridyl dicarboxylic acid photosensitiser species adsorbed to Degussa P25 and sol-gel TiO2 films from dilute aqueous solutions. The spectra indicate that adsorption is via the carboxylate groups which bridge surface titanium ions. Adsorption isotherms and binding constants have been derived from the spectral data. The ruthenium(II) cis-di(thiocyanato)-N,N′-bis(2,2′-bipyridyl-4,4′-dicarboxylic acid) complex, which is an efficient sensitiser, has the highest binding constant. This suggests a link between the strength of surface binding and the solar energy conversion efficiency.