TIME-RESOLVED LUMINESCENCE INVESTIGATION OF THE ADSORPTION OF RU(BPY)(3)(2-DOPED SNO2 COLLOIDAL PARTICLES() ONTO ANTIMONY)

The adsorption of Ru(bpy)(3)(2+) (bpy = 2,2'-bipyridine) onto negative ly charged antimony-doped SnO2 colloidal particles (ca. 4-nm diameter) was monitored by time-resolved luminescence. Electron injection from photoexcited Ru(bpy)(3)(2+) into the conduction band of the semiconduc tor particle results in luminescence quenching predominantly within th e laser pulse when the complex is bound to the particle, whereas the l uminescence of the unbound complex decays with a lifetime of several h undred nanoseconds. The relative concentrations of the bound and free species are thus readily obtained by determining the relative contribu tions of the quenched and unquenched components in the luminescence de cay curve. Binding of Ru(bpy)(3)(2+) to the particles conforms to the Frumkin adsorption isotherm and suggests that the adsorbed Ru(bpy)(3)( 2+) molecules self-associate with a free energy of interaction equal t o -1.9 +/- 0.7 kcal mol(-1). The average maximal capacity of each part icle for adsorbed Ru(bpy)(3)(2+) determined by the binding data, 29 +/ - 10, is in agreement with the value obtained by ion exchange, 30 +/- 4, but is smaller than predicted for a close-packed monolayer.