Using Light-Switching Molecules to Modulate Charge Mobility in a Quantum Dot Array

We have studied the electron hopping in a two-CdSe quantum dot system linked by an azobenzene-derived light-switching molecule. This system can be considered as a prototype of a QD supercrystal. Following the computational strategies given in our recent work [Chu et al. J. Phys. Chem. C 115, 21409 (2011)], we have investigated the effects of molecular attachment, molecular isomer (trans and cis) and QD size on electron hopping rate using Marcus theory. Our results indicate that molecular attachment has a large impact on the system for both isomers. In the most energetically favorable attachment, the cis isomer provides significantly greater coupling between the two QDs and hence the electron hopping rate is greater compared to the trans isomer. As a result, the carrier mobility of the QD array in the low carrier density, weak external electric field regime is several orders of magnitude higher in the cis compared to the trans configuration. This is the first demonstration of mobility modulation using QDs and azobenzene that could lead to a new type of switching device.