Towards the use of Adaptive Feedback Control Pulse Shaping to Probe and Control Reactivity of the Metal-to-Ligand Charge Transfer Excited State in Ruthenium(II) Bis-Terpyridine Complexes.

摘要

A novel ruthenium(II) polypyridyl complex [Ru(bpy--An)(tpy--phi--MV)] 4+ (where tpy-An = 4'-(9-anthrcenyl)-2,2':6',2''-terpyridine and tpy--&phis;--MV 2+ = 4'-(1-(1'-methyl-4,4-bipyridinium-1-yl)-phenyl)-2,2':6',2''-terpyridine) capable of undergoing energy transfer (EnT) or electron transfer (E T) following photoexcitation to the metal-to-ligand charge transfer (MLCT) state is investigated. Adaptive feedback control (AFC) pulse shaping, which has proven to be a versatile experimental tool for probing photoinduced dynamics in a variety of chemical systems, is used try and control the En T and ET reactivity in this complex with the goal of informing the underlying EnT and ET dynamics. To allow for interpretation of the aforementioned AFC experiments the photophysics of [Ru(bpy--An)(tpy--phi--MV)]4+ and a family of six closely related bis-terpyridine Ru(II) complexes are characterized using static absorption, electochemical, and ultrafast pump-probe techniques. These experiments reveal previously unreported dynamics such as equilibration between the 3MLCT and 3MC (where MC = metal centered excited state) and interligand electron transfer. Furthermore, the EnT and ET reactions in [Ru(bpy--An)(tpy--phi--MV)] 4+ (and the associated model complexes) are found to occur on a sub-picosecond and picosecond timescale, respectively. These are the fastest EnT and ET timescales reported for any Ru(II) bis-terpyridine based complexes. As an addendum, photophysics of the mononuclear water oxidation catalysts [Ru(bpy)(tpy)(OH2)]2+ and [Ru(bpy)(tpy)(OD 2)]2+ in neat H2O and D2O solvent, respectively, are reported. Ultrafast pump-probe experiments reveal an inverse kinetic isotope effect with the excited state lifetime being shorter for the D2O complex than the H2O complex. This is attributed to interactions between the coordinated aqua (or D2O) and solvent in the MLCT excited state and suggests design principles applicable to synthesis of photo-driven water oxidation assemblies.