Ab initio study of the transport properties of a light-driven switching molecule azobenzene substituent

A first-principles computational approach is applied to study the transport properties of a light-sensitive molecular switch. The molecule of azobenzene substituent can convert between a trans and a cis configuration upon photoexcitation, which is the basis of the switch. The current–voltage (I–V) curves of the two configuration systems vary dramatically. The current across the cis configuration system is much bigger than that across the trans configuration in a rather wide applied bias window. The ON:OFF current ratio is bigger than 27 at the bias range [−1.3, −1.9]V and [1.6, 2.4]V and reaches 107 at the bias voltage −1.7 V. A detailed analysis of the projected density of states of the two configurations in the environment of two Al (1 0 0) nanoscale electrodes and the transmission spectra of the system reveals the mechanism of the switch.

► The azobenzene substituent molecule has trans and cis configurations under light.
► The electron transport through these two configurations is studied.
► The current across the cis case is much bigger than that across the trans one.
► It arises from the much different molecule length, HOMO–LUMO gap and lead coupling.