Coordination mode dependent excited state behavior in group 8 phosphino(terthiophene) complexes

The ground and excited state behavior of four Ru(II) and Os(II) bipyridyl complexes containing the 3'-(diphenylphosphino)-2,2':5',2'-terthiophene (PT(3)) ligand in two different coordination modes (P,S and P,C) is reported. The complexes are generally stable under extended photoirradiation, except for Ru(bpy)(2)PT(3)-P,S](PF(6))(2) which decomposes. Emission lifetimes and transient absorption spectra and lifetimes have been obtained for all the complexes. These data support a PT(3) ligand based lowest excited state in the case of both P,S bound complexes, and a charge separated lowest excited state in both P,C bound complexes, conclusions supported by Density Functional Theory (DFT) calculations.