DYE-CAPPED SEMICONDUCTOR NANOCLUSTERS - ONE-ELECTRON REDUCTION AND OXIDATION OF THIONINE AND CRESYL VIOLET H-AGGREGATES ELECTROSTATICALLY BOUND TO SNO2 COLLOIDS

SnO2 colloids are capped with the cationic dyes thionine and cresyl vi olet by electrostatic interaction. The close packing of these dyes on the negatively charged SnO2 colloids resulted in the formation of H-ag gregates. One-electron reduction and oxidation of these H-aggregates b ound to SnO2 colloids has been investigated by pulse radiolysis. The s pectral features of semireduced, (OH)-O-.-adduct, and semioxidized for ms of dye monomers and aggregates are compared by recording time-resol ved transient absorption spectra. The bimolecular rate constants for t he reaction of dye-capped SnO2 colloids with aqueous electrons (5-6 x 10(9) M(-1) s(-1)) and (OH)-O-. radicals (3.5 x 10(8) M(-1) s(-1)) are nearly an order of magnitude smaller than those for the corresponding reactions of dye monomers. The slower diffusion of colloidal particle s is likely to influence the diffusion kinetics of reactions involving dye-capped SnO2 colloids.