Franck-Condon Blockade and Aggregation-Modulated Conductance in Molecular Devices Using Aggregation-Induced Emission-Active Molecules.

We report an effective modulation of the quantum transport in molecular junctions consisting of aggregation-induced-emission(AIE)-active molecules. Theoretical simulations based on combined density functional theory and rate-equation method calculations show that the low-bias conductance of the junction with a single tetraphenylethylene (TPE) molecule can be completely suppressed by strong electron-vibration couplings, that is, the Franck-Condon blockade effect. It is mainly associated with the low-energy vibration modes, which is also the origin of the fluorescence quenching of the AIE molecule in solution. We further found that the conductance of the junction can be lifted by restraining the internal motion of the TPE molecule by either methyl substitution on the phenyl group or by aggregation, a mechanism similar to the AIE process. The present work demonstrates the correlation between optical processes of molecules and quantum transport in their junction, and thus opens up a new avenue for the application of AIE-type molecules in molecular electronics and functional devices.