A Hybrid Quantum Mechanical Approach: Intimate Details of Electron Transfer between Type-I CdSe/ZnS Quantum Dots and an Anthraquinone Molecule

We report a hybrid computational approach to calculate electron transfer between a type-I CdSe/ZnS core/shell quantum dot (QD) with a varying shell thickness and the functionalized anthraquinone (AQ) molecule. This novel approach combines the traditional electron/hole confinement theory in the effective mass approximation for the QD and molecular orbital theory for the AQ molecule. In the present study, the QD's electron and hole envelope wave functions are solutions of the effective-mass Schrodinger equation, and the AQ wave function is obtained at the density functional level. Electron-transfer rate calculations are based on Marcus's theory with the coupling strength computed according to an one-electron orbital perturbation model. We show that in a heptane solution, the LUMO of AQ and the ISe electron orbital of QD are involved in the charge separation (CS) process. The charge recombination (CR) process, on the other hand, occurs from the singly occupied molecular orbital of the AQ radical (which corresponds to the LUMO in AQ) to a trapped hole state of the QD within the band gap. The calculations support previously reported interpretations of the role of the ZnS shell as a hindrance in the CS and CR process.