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Resonance Raman spectroscopy of the lowest excited state of derivatives of tris(2,2'-bipyridine)ruthenium(II): substituent effects on electron localization in mixed-ligand complexes

Journal Article · · Inorg. Chem.; (United States)
DOI:https://doi.org/10.1021/ic00224a027· OSTI ID:5863199
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The one-electron nature of the lowest electronic excited state of (RuL/sub n/L'/sub 3-n/)/sup 2 +/ (L, L' = 2,2'-bipyridine (bpy), 4,4'-dimethyl-2,2'-bipyridine (Me/sub 2/bpy), 4,4'-dibromo-2,2'-bipyridine (Br/sub 2/bpy); n = 0, 1, 2, 3) as the PF/sub 6//sup -/ salts in CH/sub 3/CN at 25/sup 0/C has been investigated by optical absorption and emission spectral studies and by resonance raman spectroscopy. For all (RuL/sub 3/)/sup 2 +/ species the data are interpreted as revealing a lowest excited state that has the excited electron localized on one of the three equivalent ligands, as previously established for (Ru(bpy)/sub 3/)/sup 2 +/. The complexes (Ru(bpy)(Me/sub 2/bpy)/sub 2/)/sup 2 +/ and (Ru(bpy)/sub 2/(Br/sub 2/bpy))/sup 2 +/ show excited-state Raman spectra consistent with a mixture of excited species, only a fraction with the excited electron localized on the more easily reduced ligand. Optical emission spectra show that substituent effects can be important, even though the substituent variation occurs in a ligand that is not the ligand on which the excited electron is localized. For example, (Ru(bpy)(Me/sub 2/bpy)/sub 2/)/sup 2 +/ emits at lower energy (approx. 450 cm/sup -1/) than((Ru(bpy)/sub 3/)/sup 2 +/, though both excited species involve an excited electron localized on the 2,2'-bipyridine ligand. The lower energy excited state is due to the destabilization of the d-..pi..(HOMO) orbital in the ground-state 4,4'-dimethyl-2,2'-bipyridine species. Consistent with such an interpretation, the E/sup 0/' for the (Ru(Me/sub 2/bpy)/sub 3/)/sup 3+/2+/ redox couple is approx. 0.2 V negative of that for the 2,2'-bipyridine analogue.

Research Organization:
Massachusetts Institute of Technology, Cambridge
OSTI ID:
5863199
Journal Information:
Inorg. Chem.; (United States), Journal Name: Inorg. Chem.; (United States) Vol. 25:4; ISSN INOCA
Country of Publication:
United States
Language:
English

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Related Subjects

14 SOLAR ENERGY
140505* -- Solar Energy Conversion-- Photochemical
Photobiological
& Thermochemical Conversion-- (1980-)
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201 -- Chemical & Physicochemical Properties
400301 -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
AZINES
BIPYRIDINES
COMPLEXES
DATA
ENERGY LEVELS
ENERGY TRANSFER
EXCITED STATES
EXPERIMENTAL DATA
HETEROCYCLIC COMPOUNDS
INFORMATION
LASER SPECTROSCOPY
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PYRIDINES
RAMAN SPECTROSCOPY
RESONANCE
RUTHENIUM COMPLEXES
SPECTROSCOPY
TRANSITION ELEMENT COMPLEXES