Ultrafast Intramolecular Relaxation and Wave-Packet Motion in a Ruthenium-Based Supramolecular Photocatalyst

摘要

The hydrogen-evolving photocatalyst [(tbbpy)(2)Ru(tpphz)Pd(Cl)(2)](2+) (tbbpy=4,4-di-tert-butyl-2,2-bipyridine, tpphz=tetrapyrido[3,2-a:2,3-c:3,2-h:2,3-j]phenazine) shows excitation-wavelength-dependent catalytic activity, which has been correlated to the localization of the initial excitation within the coordination sphere. In this contribution the excitation-wavelength dependence of the early excited-state relaxation and the occurrence of vibrational coherences are investigated by sub-20fs transient absorption spectroscopy and DFT/TDDFT calculations. The comparison with the mononuclear precursor [(tbbpy)(2)Ru(tpphz)](2+) highlights the influence of the catalytic center on these ultrafast processes. Only in the presence of the second metal center, does the excitation of a (MLCT)-M-1 state localized on the central part of the tpphz bridge lead to coherent wave-packet motion in the excited state.