Energetics of photoinduced electron-transfer reactions decided by Quantum confinement

The photophysics of linear CdSe-CdTe nanorod heterostructures are reported. Charge-transfer emission and absorption bands are identified. Analysis of these bands reveals the factors governing photoinduced electron transfer from CdTe to CdSe, and it is thereby shown how quantum confinement effects decide the thermodynamic parameters of the Marcus-Hush theory. An important finding is the very small reorganization energy associated with the nuclear degrees of freedom (similar to 20 meV in toluene), which seems to be a characteristic of these nanoscale donor-acceptor systems and differentiates them from most analogous molecular systems. Therefore Marcus "inverted region" behavior is found to be typical for these systems. By analyzing the mixing between the CdTe exciton and the charge-transfer states for one sample, we find the electronic coupling matrix element that promotes the charge separation to be similar to 50 meV.