Meta-substituted RuII rigid rods for sensitization of TiO2

Ruthenium polypyridyl rigid-rod compounds with phenylene–ethynelene (OPE) spacers and an isophthalic acid (Ipa) binding group were synthesized and characterized for sensitization of nanocrystalline TiO2 (anatase) thin films. Density functional theory predicted that the most stable structure oriented the isophthalic group about 45° from normal to the TiO2 surface. Comparative experimental studies of meta- and para-isomers revealed small changes in the ground state absorption spectra and very similar excited state and redox properties. The excited state injection yields (inj = 0.15 ± 0.03) into nanocrystalline TiO2 and the subsequent charge recombination rates were found to be insensitive to the isomer utilized. Meta-substitution enabled the synthesis of sensitizers with two RuII sensitizers that displayed enhanced sunlight absorption relative to the monomeric compound.