Superior grafting and state-of-the-art interfacial electron transfer rates for newly designed geminal dicarboxylate bound ruthenium(II)– and osmium(II)–polypyridyl dyes on TiO₂ nanosurface

Two new Ru(II)–/Os(II)–polypyridyl based sensitizer dyes with geminal dicarboxylic acid group as the binding unit for superior grafting of the dye to TiO₂ have been designed and synthesized. Steady-state photochemical studies of the two sensitizer dyes in presence of TiO₂ in water confirm strong binding of the dyes to TiO₂. Femtosecond transient absorption studies of these newly synthesized dyes on TiO₂ nanosurface have been carried out in water and the results have been compared with those for the corresponding 4,4′-dicarboxy-2,2′-bipyridine analogues of the dyes. While the charge recombination rates are considerably slower, interestingly, the electron injection rates are very fast for multiple saturated C–C linkages present between the chromophoric core and the anchoring moiety. The origin and the consequences of such profound effects on the ultrafast interfacial dynamics are discussed. This is the first report on the ultrafast transient absorption studies of dyes with geminal dicarboxylic acid binding groups, which we believe will add significantly to the present research efforts toward the development of robust and efficient dyes for use in dye solar applications