Excitation-Wavelength Dependence of Photoinduced Charge Injection at the Semiconductor-Dye Interface: Evidence for Electron Transfer from Vibrationally Hot Excited States
Heterodyad systems composed of a redox photosensitizer adsorbed on the surface of a wide band gap semiconductor were designed in a way that the ν'=0 energy level of the electronically excited state of the dye lies below the bottom of the conduction band of the solid. Under these conditions, the quantum yield of the charge injection from the sensitizer into the conduction band of the solid was found to depend upon the excitation photon energy. This observation provides an evidence that interfacial charge transfer is occurring prior to nuclear relaxation of the sensitizer's excited state. It allows the use of a simplified kinetic model and offers an easy experimental path to the determination of the electronic coupling that controls the rate of the ultrafast injection process.
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