Photochemistry on Surfaces. Intermolecular Energy and Electron Transfer Processes between Excited Ru(bpy)32+ and H-Aggregates of Cresyl Violet on SiO2 and SnO2 Colloids

Abstract

Cresyl violet, a cationic dye (CV{sup +}), forms H-aggregates on the negatively charged SiO{sub 2} and SnO{sub 2} colloids. These aggregates exhibit broad absorbance around 520 nm. By coadsorbing a sensitizer, Ru(bpy){sub 3}{sup 2+}, we are able to characterize the triplet excited state and reduced form of dye-aggregates on the colloidal SiO{sub 2} and SnO{sub 2} suspensions. On SiO{sub 2} surfaces, the excited state quenching of Ru(bpy){sub 3}{sup 2+} by dye-aggregates proceeds via an energy transfer mechanism. Picosecond laser flash photolysis experiments indicate that such a surface-promoted energy transfer is completed within 20 ps. On the other hand dye-aggregates adsorbed onto SnO{sub 2} colloids undergo photosensitized reduction since the excited sensitizer, Ru(bpy){sub 3} {sup 2+}, is efficiently quenched by the semiconductor support. The role of support material in promoting energy and electron transfer processes is described. 87 refs., 11 figs.