Dual-Time Scale Photoinduced Electron Transfer from PbS Quantum Dots to a Molecular Acceptor

A combination of picosecond and microsecond transient absorption dynamics reveals the involvement of two mechanisms by which 1,4-benzoquinone (BQ) induces the decay of the excited state of PbS quantum dots (QDs): (i) electron transfer to BQ molecules adsorbed to the surfaces of PbS QDs and (ii) collisionally gated electron transfer to freely diffusing BQ. Together, these two mechanisms quantitatively describe the quenching of photoluminescence upon addition of BQ to PbS QDs in dichloromethane solution. This work represents the first quantitative study of a QD-ligand system that undergoes both adsorbed and collisionally gated photoinduced charge transfer within the same sample. The availability of a collisionally gated pathway improves the yield of electron transfer from PbS QDs to BQ by an average factor of 2.5 over that for static electron transfer alone.