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 (PT3) 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)2PT3-P,S](PF6)2 which decomposes. Emission lifetimes and transient absorption spectra and lifetimes have been obtained for all the complexes. These data support a PT3 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.