Micellar effect on the photoinduced electron-transfer reactions of ruthenium(II)–polypyridyl complexes with phenolate ions. Effect of cetyltrimethylammonium chloride

Abstract

Although the emission spectra and excited-state lifetime of Ru(bpy) ₃ ²⁺ (bpy=2,2′-bipyridine), Ru(dmbpy) ₃ ²⁺ (dmbpy=4,4′- dimethyl-2,2′-bipyridine) and Ru(phen) ₃ ²⁺ (phen=1,10-phenanthroline) are little affected by the addition of the cationic surfactant cetyltrimethylammonium chloride (CTAC), an appreciable shift in λ _max ^em , emission intensity and emission lifetime are observed for Ru(dtbpy) ₃ ²⁺ (dtbpy=4,4′-di-tert-butyl-2,2′-bipyri dine) and Ru(dpphen) ₃ ²⁺ (dpphen=4,7-diphenyl-1,10-phenanthroline). These results point out the importance of hydrophobic interactions over the coulombic repulsion thereby bringing the ruthenium(II) complexes close to the cationic micelles. The rate of luminescence quenching of five *Ru(NN) ₃ ²⁺ complexes, with alkyl-substituted phenolate ions in the presence of CTAC, follows different trends depending on the nature of the ligand in Ru(NN) ₃ ²⁺ as well as the quencher. The micellar inhibition is explained by considering ArO ^- being strongly associated with CTAC leaving Ru(NN) ₃ ²⁺ in the aqueous phase. The micellar catalysis at high [CTAC] with Ru(dtbpy) ₃ ²⁺ and Ru(dpphen) ₃ ²⁺ may be due to the operation of predominant hydrophobic interaction over the electrostatic repulsion.