Ultrafast Electron Transfer from Photoexcited CdSe Quantum Dots to Methylviologen

The ultrafast charge separation at the quantum dot (QD)/molecular acceptor interface was investigated in terms of acceptor concentration and the size of the QD. Time‐resolved experiments revealed that the electron transfer (ET) from the photoexcited QD to the molecular acceptor methylviologen (MV2+) occurs on the fs time scale for large acceptor concentrations and that the ET rate is strongly reduced for low concentrations. The increase in the acceptor concentration is accompanied with a growth in the overlap of donor and acceptor wavefunctions, resulting in a faster reaction until the MV2+ concentration reaches a saturation limit of 0.3–0.4 MV2+ nm−2. Moreover, we found significant QD size dependence of the ET reaction, which is explained by a change of the free energy (ΔG). Quick, quick: The ultrafast charge separation at the quantum dot/molecular acceptor interface was investigated in terms of acceptor concentration (methylviologen) and the size of the quantum dot (see picture).