Singlet and triplet energy transfer processes in ruthenium(II) bipyridine complexes containing covalently bound arenes

Singlet and triplet energy transfer processes in [Ru(bipy)2(4-methyl-4′-(2-arylethyl)-2,2′-bipyridine)]2+ have been investigated, where aryl = 2-naphthyl (Ru-Naph), 9-anthryl (Ru-Anth) and 1-pyrenyl (Ru-Pyrene). In each case fluorescence from the aromatic chromophore is quenched by intramolecular energy transfer to Ru(bipy)32+ whereas emission from the Ru(bipy)32+ moiety is controlled by the relative energy of its 3MLCT state and the pendant arene triplet states. Consequently 3MLCT emission is observed for Ru-Naph whereas it is fully quenched for Ru-Anth. When the two states are isoenergetic (e.g. Ru-Pyrene) a long-lived 3MLCT emission is observed which delays with the same lifetime as the pyrene triplet state (5.23 μs).