PHOTOCHEMISTRY ON SURFACES - INTERMOLECULAR ENERGY AND ELECTRON-TRANSFER PROCESSES BETWEEN EXCITED RU(BPY)(3)(2-AGGREGATES OF CRESYL VIOLETON SIO2 AND SNO2 COLLOIDS() AND H)

Cresyl violet, a cationic dye (CV+), forms H-aggregates on the negativ ely charged SiO2 and SnO2 colloids. These aggregates exhibit broad abs orbance around 520 nm. By coadsorbing a sensitizer, Ru(bpy)(3)(2+), we are able to characterize the triplet excited state and reduced form o f dye-aggregates on the colloidal SiO2 and SnO2 suspensions. On SiO2 s urfaces, the excited state quenching of RU(bpy)(3)(2+) by the dye-aggr egates proceeds via an energy transfer mechanism. Picosecond laser fla sh photolysis experiments indicate that such a surface-promoted energy transfer is completed within 20 ps. On the other hand dye-aggregates adsorbed onto SnO2 colloids undergo photosensitized reduction since th e excited sensitizer, RU(bpy)(3)(2+), is efficiently quenched by the semiconductor support. The role of support material in promoting energ y and electron transfer processes is described.