EQCM Investigations of Dye-Functionalized Nanocrystalline Titanium Dioxide Electrode/Solution Interfaces: Does Luminescence Report Directly on Interfacial Electron Transfer Kinetics?

Abstract

Electrochemical quartz crystal microbalance (EQCM) experiments have been performed on dye-functionalized nanocrystalline titanium dioxide electrode/solution interfaces. The experiments show that reversible, potential-induced dye desorption occurs in both aqueous and nonaqueous environments at potentials close to the conduction band edge. Previous experiments have reported that potentiostatic filling of empty conduction band or near-band-edge surface states has dramatic effects on the corresponding photophysical and photochemical behavior of surface-bound dyes. Most notably, apparent decreases in the efficiencies of charge injection and increases in dye luminescence yield were found to accompany potential changes. Detailed analyses have emphasized the role of surface-state filling in decreasing the driving force for injection processes and thus, increasing the luminescence quantum yield. The electrochemically stimulated dye detachment phenomenon reported here provides a compelling alternative or additional mechanistic explanation for the profound potential dependence of the interfacial luminescence responses.