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Direct observation of metal-to-ligand charge-transfer (MLCT) excited states of pentaammineruthenium(II) complexes

Journal Article · · J. Am. Chem. Soc.; (United States)
DOI:https://doi.org/10.1021/ja00242a023· OSTI ID:6629357
; ; ;
Excited-state difference spectra and lifetimes are reported for Ru(tpy)/sub 2//sup 2 +/ (tpy = 2,2',2''-terpyridine) and a series of pentaammineruthenium(II) complexes. The initially formed excited states (generated by approx. 25-ps excitation with 532-nm light) are well modeled by a Ru/sup III/(L/sup .-/) electronic configuration (L is an aromatic, N-heterocyclic ligand) since an excellent correspondence is found between their absorption features and those of (L/sup .-)H/sup +/ radicals. The transients are, therefore, assigned as MLCT states. The Ru(tpy)/sub 2//sup 2 +/ excited-state lifetime is 250 ps. The Ru(NH/sub 3/)/sub 5/L/sup 2 +/ excited-state lifetimes vary from less than or equal to 20 (L = protonated pyrazine, protonated 4,4'-bipyridine, and 4-acetylpyridine) to approx. 200 (L = pyrazine, isonicotinamide, 4,4'-bipyridine) ps in water at approx. 22/sup 0/C. Ammine aquation products, Ru(NH/sub 3/)/sub 4/(H/sub 2/O)L/sup 2 +/, are also observed and are shown to result from multiphoton absorption of the ps-excitation pulses. The MLCT states of Ru(NH/sub 3/)/sub 5/L/sup 2 +/ (L = pz or 4,4'-bpy) undergo protonation by solvent water and deactivation to Ru(NH/sub 3/)/sub 5/LH/sup 3 +/; rate constants for proton loss from the protonated species (Ru(NH/sub 3/)/sub 5/LH/sup 3 +/ + H/sub 2/O ..-->.. Ru(NH/sub 3/)/sub 5/L/sup 2 +/ + H/sub 3/O/sup +/) are (2-3) x 10/sup 7/ s/sup -1/ and 2 x 10/sup 5/ s/sup -1/ for L = pz and 4,4'-bpy, respectively. The Ru(NH/sub 3/)/sub 5/L/sup 2 +/ MLCT-excited-state lifetimes are discussed in terms of the lowest excited state tuning model of Ford and co-workers.
Research Organization:
Brookhaven National Lab., Upton, NY
DOE Contract Number:
AC02-76CH00016
OSTI ID:
6629357
Journal Information:
J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 109:8; ISSN JACSA
Country of Publication:
United States
Language:
English

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Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500* -- Photochemistry
ABSORPTION SPECTRA
ABSORPTION SPECTROSCOPY
AMMINES
AZINES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHEMISTRY
COMPLEXES
DATA
DECOMPOSITION
ENERGY LEVELS
EXCITED STATES
EXPERIMENTAL DATA
HETEROCYCLIC COMPOUNDS
INFORMATION
KINETICS
LIFETIME
LIGANDS
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOCHEMISTRY
PHOTOLYSIS
PULSE TECHNIQUES
PYRIDINES
REACTION KINETICS
RUTHENIUM COMPLEXES
SPECTRA
SPECTROSCOPY
TRANSITION ELEMENT COMPLEXES