Photoinduced intra-molecular electron transfer in aniline-containing Ru(II) polypyridine complexes

The photoinduced intra-molecular electron transfer in three aniline-containing Ru(II) polypyridine complexes, [Ru(bpy)2(bpy-bmam)](PF6)2 (2), Ru(dcbpy)(bpy-bmam)(NCS)2 (3), and Ru(dcbpy)(bpy-mam)(NCS)2 (4) (bpy-bmam=4,4′-bis(N-methyl-anilinomethyl)-2,2′-bipyridine, bpy-mam=4-methyl-4′-(N-methyl-anilinomethyl)-2,2′-bipyridine, dcbpy=4,4′-dicarboxyl-2,2′-bipyridine, bpy=2,2′-bipyridine), was investigated using steady-state and time-resolved absorption and emission spectra, and photoinduced inter-molecular electron transfer between [Ru(bpy)2(dmbpy)](PF6)2 (1) (dmbpy=4,4′-dimethyl-2,2′-bipyridine) and N,N-dimethylaniline was also studied for comparison. While inter-molecular reductive quenching of 1’s emission by aniline was less efficient, nearly half emission was quenched intra-molecularly in 2. Upon photoinduced electron injection onto the conduction band of TiO2 from 3 or 4 anchored on the TiO2 surface, intra-molecular electron transfer from aniline moiety to Ru(III) orbital occurred rapidly with rate constants of 3.4×107 and 2.6×107 s−1, respectively, restricting the interfacial recombination of injected electrons with Ru(III) and as a result improving the photoelectrochemical behavior of 3 or 4 when used in dye-sensitized nanocrystalline semiconductor solar cells.