Quenching of tris (2,2′-bipyridine) chromium (III) and tris(1,10-phenanthroline)chromium (III) excited states by phenols: Temperature and pH effect

Autor: Eduardo H. Staricco, Gerardo A. Argüello, Daniela Pagliero
Rok vydání: 1998
Předmět:
Zdroj: Journal of Photochemistry and Photobiology A: Chemistry. 115:199-206
ISSN: 1010-6030
DOI: 10.1016/s1010-6030(98)00262-7
Popis: The quenching rate constant kq of the excited states *Cr(bpy)33+ and *Cr(phen)33+ by several substituted phenols was investigated as a function of temperature using the time resolved luminescence quenching technique. The activation parameters showed a pH dependence. The most important contribution to the total activation entropy in basic media was found to be the electrostatic factor. The data obtained from log kq vs. ΔG0 plot were analyzed on the basis of the current theories for electron transfer processes. The best fitting analysis in the ΔG# vs. ΔG0 plot yielded reorganization energies of 59 and 55 kcal/mol for the bipyridine and phenanthroline chromium complexes, respectively. The high values of reorganization energies found (λ) were interpreted as a hydrogen bond term contribution (λH) to the outer-sphere reorganization energy, λo′, where λo′ = λo+ λH. The effect of the ionic strength and [Cl−] on the quenching rate constant for the reaction of *Cr(phen)33+ with 2,6-dimethylphenol was investigated. It was found that neither the ionic pair formation nor the [Cl−] concentration seem to affect the quenching mechanism.
Databáze: OpenAIRE
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