Catechol as an efficient anchoring group for attachment of ruthenium–polypyridine photosensitisers to solar cells based on nanocrystalline TiO2 films

The Ru(II)–polypyridyl complexes [Ru(H2L)(terpy)][PF6]2 (1) and [Bu4N][Ru(H2L)(NCS)3] (2) (H2L=4′-(3,4-dihydroxyphenyl)-2,2′:6′,2″-terpyridine), in which H2L is coordinated as a terpyridyl fragment with a catechol site pendant from the C4′ position, adhere effectively to nanocrystalline TiO2 (anatase) surfaces via the pendant catechol group; incident photon-to-current conversion efficiency values of up to 50% were obtained in their photocurrent action spectra, suggesting that the catechol unit may be a convenient and effective anchoring group for attaching dyes to TiO2-based photovoltaic cells.