Oxidation of a Molecule by the Biexcitonic State of a CdS Quantum Dot

This paper describes spectroscopic evidence for the photoinduced transfer of a hole from the biexcitonic state of a CdS quantum dot (QD) to a phenothiazine (PTZ) molecular acceptor, covalently linked to the QD through phenyldithiocarbamate (PTC), with power-dependent yields of 8–21%. Visible and near-infrared transient absorption spectroscopy (TA) data suggest that the mechanisms of hole extraction include direct hole transfer from the QD’s valence band to PTZ in 2.4 ± 0.2 ps, or trapping of holes at the QD surface in ∼1 ps, followed by sequential hole transfer to PTZ. Both of these mechanisms potentially out-compete Auger recombination of biexcitonic states, which occurs within these QDs in 20 ± 1 ps. These results suggest that the PTC linkage will be useful for extracting multiple holes from a QD photosensitizer or solo photocatalyst to drive multistep oxidation reactions.