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

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.