CHARACTERIZATION OF EXCIPLEXES GENERATED BY EXCITED TRIS-DIIMINE-RUTHENIUM(II) COMPLEXES AND SILVER(I) ION OF GROUND-STATE

Luminescent bimolecular and termolecular exciplexes of [Ru(bpy)(3)](2 +) and [Ru(phen)(3)](2+) (bpy =2,2'-bipyridine, phen = 1,10-phenanthr oline) formed by silver ions have been characterized and compared. For mation constants, luminescence lifetime, radiative and nonradiative de cay constants were determined at room temperature. Oxidative quenching measurements in the [Ru(bpy)(3)](2+)-Ag+ system using MV2+ (MV2+ = 1, 1'-dimethyl-4,4'-bipyridinium) as an electron acceptor resulted in que nching rate constants, (3.1+/-0.2)x10(9), (3.1+/-0.3)x10(9), (1.6+/-0. 3)x10(9) and cage escape efficiencies, 0.11+/-0.01, 0.05+/-0.01, 0.06/-0.01, for [Ru(bpy)(3)](2+), *[Ru(bpy)(3)lAg(3+) and *[Ru(bpy)(3)]Ag -2(4+), respectively. Temperature-dependent luminescence lifetime in a queous solutions revealed that the exciplex formation causes a conside rable change in the deactivation pathways of the excited species. Exci plex formation results in a decrease in the efficiency of the thermall y activated decay through MLCT --> dd transition and in an increase of the efficiency of deactivation to the ground state via other non radi ative processes. The thermodynamic parameters of the exciplex formatio n have been estimated. (C) 1998 Elsevier Science S.A.