Steric effects in the photoinduced electron transfer reactions of ruthenium(II)-polypyridine complexes with 2,6-disubstituted phenolate ions

Abstract

The rate constants (k_q) for the photoinduced electron transfer reactions of Ru(II)-polypyridyl complexes (Ru(NN)₃²⁺) with 2,6-disubstituted phenolate ions in aqueous acetonitrile are highly sensitive to change in the bulkiness of the ligand in Ru(NN)₃²⁺ as well as the phenolate ion. The decrease in k_q value with the increase in the size of the ligand in Ru(NN)₃²⁺ and the phenolate ion is ascribed to the decrease in the electronic coupling matrix element, ∣H_DA ∣, between the donor and acceptor with the increase in the electron transfer distance. The hydrophobic interaction or possible π–π stacking between the pyridine rings of Ru(NN)₃²⁺ and the aryl moiety of ArO⁻ leads to less steric effect.