Photo-release of acetonitrile in ruthenium(II) complexes with various substituted terpyridine ligands.

The photo-release of acetonitrile is investigated in a series of ruthenium(II) complexes of the general formula [Ru(R-phtpy)(acac)(MeCN)](PF) (phtpy stands for 4'-phenyl-2,2':6',2''-terpyridine, and R = EtN, MeN, MeO, Me, H, NO). The experimental quantum yields of photo-release ( = MeCN released/photons absorbed) increases with the donating capability of R, with values ranging from = 0 (NO) to = 0.05 (EtN). The origin of this effect is investigated computationally using the density functional theory and compared to those reported recently by our group on related [Ru(R-phtpy)(acac)(NO)](PF) species capable of causing photo-release of NO. In the present case, the capability for MeCN release appears related to the relative energies of the metal-centered (MC) metal-ligand-charge-transfer (MLCT) triplet states. The MC state, in which the Ru-NC distance is elongated to 4.2 Å, is expected to be responsible for the release. Additionally, four crystal structures are reported for the compounds in which R = EtN, MeO, H, and NO.