Isomer-Dependent Franck–Condon Blockade in Weakly Coupled Bipyridine Molecular Junctions

Abstract

Franck–Condon blockade is an attractive functionality of molecular junctions, but its tunability is still a challenge that has not been fully addressed. We show here from first-principles calculations that the electron–vibration coupling strength of a weekly coupled bipyridine molecular junction can be largely tuned from weak to strong coupling regime through isomerization. Electron transport properties of four bipyridine isomers, namely 2,6′-bipyridine, 2,4′-bipyridine, 2,2′-bipyridine, and 4,4′-bipyridine, have been exclusively examined. A very strong Franck–Condon blockade is found to be associated with 2,2′-bipyridine and 4,4′-bipyridine molecules and should be observable experimentally. A gate-controlled conductance switch is proposed for a molecular junction with a 4,4′-bipyridine molecule. Our calculations have clearly demonstrated that bipyridine isomers are excellent candidates for the experimental study of vibration-mediated transport properties in a single molecule