Lifetimes of the lowest excited state of tris(2,2′-bipyridine)ruthenium(II) and its amphipathic derivative in micellar systems

Abstract

The luminescence decay lifetimes of tris(2,2′-bipyridine)ruthenium(II) ([Ru(bpy) 3] 2+) and its amphipathic derivative ( N,N′-di(dodecyl)-2,2′-bipyridine-4,4′-dicarboxyamide)bis(2,2′-bipyridine)ruthenium(II) ([RuC 2B] 2+) measured in H 2O, D 2O, CH 3OH, CD 3OH and CH 3OD solutions as well as in micellar solutions of sodium dodecylsulphate in H 2O and D 2O reveal the role of the protic solvent molecules in the deactivation of the excited ruthenium(II) complexes. The lifetimes of the complexes reduce with increasing size of the water pool in the inverted micellar solution. [Ru(bpy) 3] 2+ is present in the water pool, whereas [RuC 12B] 2+ is buried inside the anionic interface with its aliphatic side-chains penetrating deep into the hydrophobic domain. In aqueous micellar solution [Ru(bpy) 3] 2+ is on the micellar surface only of the anionic detergent, whereas [RuC 12B] 2+ is partially buried inside the micelles regardless of whether they are anionic, cationic or non-ionic. In fact N,N′-dimethylaniline, which dissolves only in the hydrocarbon region of the micelles, is a good quencher for [RuC 12B] 2+ in aqueous micellar solution but does not quench [Ru(bpy) 3] 2+.