Abstract
Charge transfer (CT) across the interface of TiO2, 3,4,9,10-perylene tetracarboxylic acid (PTCA) molecules and Ag with three models (TiO2/PTCA, TiO2/PTCA/Ag, and Ag/PTCA/TiO2) has been investigated using surface-enhanced Raman scattering (SERS). It is found that CT from PTCA molecules to TiO2 takes place in the TiO2/PTCA interface. After compositing with Ag, we find that the SERS spectra of TiO2/PTCA/Ag show an unexpected dramatic enhancement at 785 nm and reveal an unusual wavelength dependence. On the basis of our results, we propose a new pathway of charge separation, which is induced by not only a CT resonance but also a D−π–A CT mode. We demonstrate this mechanism in the TiO2/PTCA/Ag system, in which the silver electron can be transferred to TiO2 through two CT processes in series. Thus, it is a typical example of the CT system to enrich the chemical mechanism of SERS, which also provides a new advance toward a better understanding of the interface between dye and TiO2.
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