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

The rate constants (k(q)) for the photoinduced electron transfer reactions of Ru(ii)-polypyridyl complexes (Ru(NN)(3)(2+)) with 2,6-disubstituted phen olate ions in aqueous acetonitrile are highly sensitive to change in the bu lkiness of the ligand in Ru(NN)(3)(2+) as well as the phenolate ion. The de crease in k(q) value with the increase in the size of the ligand in Ru(NN)( 3)(2+) and the phenolate ion is ascribed to the decrease in the electronic coupling matrix element, \H-DA\, between the donor and acceptor with the in crease in the electron transfer distance. The hydrophobic interaction or po ssible pi-pi stacking between the pyridine rings of Ru(NN)(3)(2+) and the a ryl moiety of ArO- leads to less steric effect.