Photoswitching of Conductance through Salicylidene Methylamine

Photoswitching of conductance through both stable isomers of salicylidene methylamine was investigated using nonequilibrium Greens function method combined with density functional theory. This study demonstrates how the optically induced intramolecular proton transfer between the hydroxyl group and the amino group of salicylidene methylamine can lead to molecular size photodiode with on/off current ratio of 1 order of magnitude. It was further elucidated that the optical switching alone is not sufficient to realize the molecular switch. Of primary importance was found to be the anchoring between the molecule and the metal electrodes. When the anchoring groups were connected to the benzene ring in para-orientation, minimal on/off current ratio was estimated. When the anchoring groups were connected to the benzene ring in meta-orientation, 1 order of magnitude on/off current ratio was calculated. Molecular orbital analysis was successfully employed to elucidate the difference in the photoswitching properties of the meta- and para-anchored isomers of salicylidene methylamine. This study demonstrates the potential application of aromatic Schiff bases as photodiodes in the field of molecular electronics.