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)₃²⁺ (bpy=2,2′-bipyridine), Ru(dmbpy)₃²⁺ (dmbpy=4,4′- dimethyl-2,2′-bipyridine) and Ru(phen)₃²⁺ (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)₃²⁺ (dtbpy=4,4′-di-tert-butyl-2,2′-bipyri dine) and Ru(dpphen)₃²⁺ (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)₃²⁺ complexes, with alkyl-substituted phenolate ions in the presence of CTAC, follows different trends depending on the nature of the ligand in Ru(NN)₃²⁺ as well as the quencher. The micellar inhibition is explained by considering ArO^- being strongly associated with CTAC leaving Ru(NN)₃²⁺ in the aqueous phase. The micellar catalysis at high [CTAC] with Ru(dtbpy)₃²⁺ and Ru(dpphen)₃²⁺ may be due to the operation of predominant hydrophobic interaction over the electrostatic repulsion.

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