Dynamics of the 3MLCT in Ru(II) Terpyridyl Complexes Probed by Ultrafast Spectroscopy: Evidence of Excited-State Equilibration and Interligand Electron Transfer

Ground- and excited-state properties of [Ru(tpy)2]2+, [Ru(tpy)(ttpy)]2+, and [Ru(ttpy)2]2+ (where tpy = 2,2′:6′,2″-terpyridine and ttpy =4′-(4-methylphenyl)-2,2′:6′,2″-terpyridine) in room temperature acetonitrile have been investigated using linear absorption, electrochemical, and ultrafast transient pump–probe techniques. Spectroelectrochemistry was used to assign features observed in the transient spectra while single wavelength kinetics collected at a variety of probe wavelengths were used to monitor temporal evolution of the MLCT excited state. From these data, the excited-state lifetime of each complex was recovered and the rate limiting decay step was identified. In the bis-heteroleptic complex [Ru(tpy)(ttpy)]2+, photoexcitation to the 1MLCT manifold generates both tpy-localized and ttpy-localized excited states. Accordingly, interligand electron transfer (ILET) from tpy-localized to the ttpy-localized 3MLCT excited states is observable and the time scale has been measured to be 3 ps. For the homol...