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RESEARCH PRODUCT

Resonance Raman Studies of Bis(terpyridine)ruthenium(II) Amino Acid Esters and Diesters

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Resonance Raman (rR) spectroscopy in combination with DFT calculations was used to elucidate the nature of the 1metal-to-ligand charge-transfer states (1MLCT) of ester derivatives of homo- and heteroleptic bis(terpyridine)ruthenium(II) complexes [RuII(tpy–COOC2H5)(tpy–R)](PF6)2 with R = NH2 (1a), R = COOC2H5 (1b) and R = NHCOCH3 (1c). The rR spectra provide evidence that the 1MLCT states of 1b and 1c are well described by the expected 1[(“t2g”)5{π*(tpy–COOC2H5)}1] electron configuration, while the 1MLCT state of the donor/acceptor-substituted complex 1a also involves the amine-substituted terpyridine ligand. The excited state of 1a can be described by a 1[{dyz/π(tpy–NH2)}1{π*(tpy–COOC2H5)}1] electron configuration with ligand-to-ligand charge-transfer (1LLCT) character. The mixed MLCT/LLCT character of the singlet excited state of 1a is characterized by a low-energy absorption maximum (λmax = 500 nm). The π-donor character of the tpy–NH2 ligand is also corroborated by DFT calculations on model compounds (small HOMO/LUMO gap, short C–N bond, longer Ru–N bond). The emitting triplet state features a low-energy emission maximum (λmax = 744 nm) as well as a longer lifetime of the emitting state (τ = 33.7 ns) at room temperature in acetonitrile as compared to the data of 1b and 1c.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)