The pH effect on the luminescence quenching of tris(2,2'-bipyridine)Ruthenim(II) by phenolic compounds

D. MARIANO A. VERA; GERARDO A. ARGUELLO; GUSTAVO A. ARGUELLO; HÉCTOR E. GSPONER

JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY

Elsevier

Lugar: New York; Año: 1993 vol. 76 p. 13 - 19

1010-6030

The effect of pH on the luminescence quenching of the excited state (3CT) of tris(2,2′-bipyridine) ruthenium (II) by a series of phenols was studied in aerated aqueous solutions at constant temperature and ionic strength. The experimental rate constants (kq) were obtained separately from static (luminescence intensity) and dynamic (lifetime measurements) methods and they were coincident. In all the systems studied the pH was carefully controlled and the obtained Stern—Volmer constants (Ksv) showed a marked increase when the pH increases. The lifetime in the absence of any quencher (τ0) was found to be constant in the pH range tested. An electron transfer mechanism was assumed for the quenching process. Since the reactivity of the phenolic compound in this quenching process is affected by the position of its acid—base equilibrium, it is possible to estimate kqs from the Ksv data at different pHs for the ionized (kq(PhO−)) and non-ionized (kq(PhOH)) forms of the quencher. A computer program developed for this purpose allowed us to get a good fit of the experimental data and to obtain the values of kq(PhO−), kq(PhOH) and the acid dissociation constant for each studied phenolic compound. The proposed method may be used to extrapolate the quenching rate constant value in media that is either too acid or too basic when direct experimental measurement is difficult to obtain. Moreover, the effect of substitution in the phenolic compounds upon the quenching process has also been examined.