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Photophysical Properties of Covalently Attached Ru(bpy)_3^(2+) and Mcyclam^(2+)(M = Ni, H_2) Complexes

Fujita, Etsuko and Milder, Steven J. and Brunschwig, Bruce S. (1992) Photophysical Properties of Covalently Attached Ru(bpy)_3^(2+) and Mcyclam^(2+)(M = Ni, H_2) Complexes. Inorganic Chemistry, 31 (11). pp. 2079-2085. ISSN 0020-1669. doi:10.1021/ic00037a019.

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Absorption and emission spectra, emission quantum yields, and excited-state lifetimes of the metal-to-ligand charge-transfer (MLCT) excited state(s) of Ru(bpy)_2(6-Mebpy)^(2+), Ru(bpyh(bpy-cyclamH_2)^(4+), and Ru(bpyh)_2(bpy-cyclamNi)^(4+) are reported. The absorption and emission spectra of these complexes are similar to those of Ru(bpy)_3^(2+) in H_2O at room temperature except for small shifts in the maxima. The emission lifetime decreases by a factor of about 80 for 6-Mebpy, and the emission quantum yield decreases by a factor of about 300 for the bpy-cyclam pendant complexes as compared to the parent Ru(bpy)_3^(2+) complex at 25 °C. Decay of the ^3MLCT excited state takes place by two independent channels: a temperature-independent pathway to the ground state and a thermally-activated pathway via a ligand-field excited state. Activation free energies, E_a, for the latter pathway were obtained from fits of the temperature-dependent emission lifetime measurements. Smaller E_a were observed for the 6-substituted complexes (1500-2300 cm^(-1)) relative to Ru(bpy)_3^(2+)(3000-3910 cm^(-1)) in EtOH and CH_3CN, indicating that either the energy difference decreases and/or the reorganization parameter changes between the emissive ^3MLCT and the ligand-field state to which it is strongly coupled. The smaller E_a can be attributed to the increased Ru-N bond distance in the 6-substituted complexes caused by steric hindrance that decreases the ligand-field strength and lowers the energy and/or reorganization parameter of the ligand-field excited state. For the bpy-cyclamNi^(2+) pendant complex, an energy-transfer pathway may also provide a deactivation channel.

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Brunschwig, Bruce S.0000-0002-6135-6727
Alternate Title:Photophysical properties of covalently attached tris(bipyridine)ruthenium(2+) and Mcyclam2+ (M = nickel, H2) complexes
Additional Information:© 1992 American Chemical Society. Received September 5, 1991. We thank Drs. Carol Creutz and Norman Sutin for helpful discussions, Dr. Siegfried Schindler for synthetic suggestions, and Elinor Norton for analyses for ruthenium, nickel, PF_6-, and ClO_4- and measurements of mass spectra. This research was carried out at Brookhaven National Laboratory under Contract DE-AC02-76CH00016 with the U.S. Department of Energy and supported by its Division of Chemical Sciences, Office of Basic Energy Sciences.
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Department of Energy (DOE)DE-AC02-76CH00016
Issue or Number:11
Record Number:CaltechAUTHORS:20180801-111158088
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Official Citation:Photophysical properties of covalently attached tris(bipyridine)ruthenium(2+) and Mcyclam2+ (M = nickel, H2) complexes. Etsuko Fujita, Steven J. Milder, and Bruce S. Brunschwig Inorganic Chemistry 1992 31 (11), 2079-2085. DOI: 10.1021/ic00037a019
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:88441
Deposited By: Tony Diaz
Deposited On:01 Aug 2018 18:25
Last Modified:16 Nov 2021 00:26

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