Photoinduced electron-transfer reactions of ruthenium(II) complexes. 1. Reductive quenching of excited Ru(bpy) sub 3 sup 2+ by aromatic amines
- Tokyo Institute of Technology, Yokohama (Japan)
The rate constants (k{sub q}) and activation parameters for reductive quenching of *Ru(bpy){sub 3}{sup 2+} (bpy = 2,2{prime}-bipyridine) by 19 aromatic amines were determined in acetonitrile. The activation enthalpies ({Delta}H{sub 23}{double dagger}) increased from +1 to +6 kcal/mol with decreasing k{sub q} while the activation entropies were almost constant around {minus}15 eu for all quenchers except for those of highly exoergic reactions. The mechanism of the reductive quenching is discussed on the basis of k{sub q} as well as of the activation parameters. The quenching was shown to depend on the nature of the aromatic amine; the quenching by tertiary amines was always faster than that by primary and secondary amines when k{sub q} are compared at the same free energy change. The results are explained by the variation of outer-sphere reorganization energy with the nature of a quencher. For the quenching by tertiary and primary/secondary amines, the radii of the quenchers (r{sub Q}{sup ex}) were estimated to be 3 and 2.4 {angstrom}, respectively, by analyzing free energy relationships of the activation free energy of the quenching. The difference in r{sub Q}{sup ex} between tertiary and primary or secondary amines (0.5-0.6 {angstrom}) was in good agreement with that between N,N-dimethylamino and anilino groups estimated by the space-filling model (0.7 {angstrom}). The solvent reorganization around the amino group is more relevant than that around an aromatic ring or a whole molecule to the actual outer-sphere reorganization energy.
- OSTI ID:
- 7171073
- Journal Information:
- Journal of Physical Chemistry; (USA), Journal Name: Journal of Physical Chemistry; (USA) Vol. 93:15; ISSN 0022-3654; ISSN JPCHA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360000 -- Materials
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400000* -- Chemistry
400500 -- Photochemistry
CHEMICAL REACTIONS
COMPLEXES
DATA
DATA ANALYSIS
ELECTRON TRANSFER
EXPERIMENTAL DATA
INFORMATION
MEASURING INSTRUMENTS
MEASURING METHODS
NUMERICAL DATA
ORGANIC COMPOUNDS
OXIDATION
PHOTOCHEMICAL REACTIONS
QUENCHING
RUTHENIUM COMPLEXES
TRANSITION ELEMENT COMPLEXES