Covalent Linking Greatly Enhances Photoinduced Electron Transfer in Fullerene-Quantum Dot Nanocomposites: Time-Domain Ab Initio Study

Nonadiabatic molecular dynamics combined with time-domain density functional theory are used to study electron transfer (ET) from a CdSe quantum dot (QD) to the C-60 fullerene, occurring in several types of hybrid organic/inorganic nanocomposites. By unveiling the time dependence of the ET process, we show that covalent bonding between the QD and C-60 is particularly important to ensure ultrafast transmission of the excited electron from the QD photon-harvester to the C-60 electron acceptor. Despite the close proximity of the donor and acceptor species provided by direct van der Waals contact, it leads to a notably weaker QD-C-60 interaction than a lengthy molecular bridge. We show that the ET rate in a nonbonded mixture of QDs and C-60 can be enhanced by doping. The photoinduced ET is promoted primarily by mid- and low-frequency vibrations. The study establishes the basic design principles for enhancing photoinduced charge separation in nanoscale light harvesting materials.