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

2015; Wiley; Volume: 21; Issue: 21 Linguagem: Inglês

10.1002/chem.201406350

1521-3765

Maria Wächtler, Julien Guthmuller, Stephan Kupfer, Margherita Maiuri, Daniele Brida, Jürgen Popp, Sven Rau, Giulio Cerullo, Benjamin Dietzek,

Metal-Catalyzed Oxygenation Mechanisms

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-20 fs 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 (1) MLCT state localized on the central part of the tpphz bridge lead to coherent wave-packet motion in the excited state.