Probing the energetic distribution of injected electrons at quantum dot-linker-TiO ₂ interfaces

We have used steady-state and time-resolved emission measurements to characterize interfacial electron transfer, or electron injection, from CdSe quantum dots (QDs) to molecularly linked TiO ₂ nanoparticles. Electrons were injected from both band-edge and trap states on relatively fast (<10 ^-8 s) and slow (>10 ^-8 s) time scales. The quantum yield of electron injection from trap states decreased as the trap-state distribution was shifted, by varying excitation energy, to lower energies. This effect probably arose from a driving-force dependence of the rate constant for electron injection. In contrast, the quantum yield of electron injection from band-edge states was independent of excitation energy. Our results highlight the key role of trapped carriers in interfacial charge-transfer processes of QDs and the influence of the energies and densities of trap states on the efficiencies of such processes.