Interfacial charge-transfer absorption: 3. Application to semiconductor-molecule assemblies

Interfacial charge-transfer absorption (IFCTA) provides information concerning the barriers to charge transfer between molecules and the energy levels of a metal/semiconductor and the magnitude of the electronic coupling and could thus provide a powerful tool for understanding interfacial charge-transfer kinetics. Here we utilize a previously published model (J. Phys. Chem. B 2005, 109, 10251) to predict the energetics of IFCTA spectra for semiconductors and compare literature observations to these predictions for n-type semiconductors (largely TiO2). In contrast to metals, where IFCTA has been only rarely observed, new absorption features due to IFCTA are common for semiconductors such as TiO2. At issue is whether the electron accepting states in the TiO2 are localized or delocalized over the conduction band.