EQCM investigations of dye-functionalized nanocrystalline titanium dioxideelectrode solution interfaces: Does luminescence report directly on interfacial electron transfer kinetics?

Electrochemical quartz crystal microbalance (EQCM) experiments have been pe rformed on dye-functionalized nanocrystalline titanium dioxide electrode/so lution interfaces. The experiments show that reversible, potential-induced dye desorption occurs in both aqueous and nonaqueous environments at potent ials close to the conduction band edge. Previous experiments have reported that potentiostatic filling of empty conduction band or near-band-edge surf ace states has dramatic effects on the corresponding photophysical and phot ochemical behavior of surface-bound dyes. Most notably, apparent decreases in the efficiencies of charge injection and increases in dye luminescence y ield were found to accompany potential changes. Detailed analyses have emph asized the role of surface-state filling in decreasing the driving force fo r injection processes and thus, increasing the luminescence quantum yield. The electrochemically stimulated dye detachment phenomenon reported here pr ovides a compelling alternative or additional mechanistic explanation for t he profound potential dependence of the interfacial luminescence responses.