  The 'open' and 'closed' isomers of the diarylethene molecule that can be
converted between each other upon photo-excitation are found to have
drastically different current-voltage characteristics when sandwiched between
two graphene nanoribbons (GNRs). More importantly, when one GNR is metallic and
another one is semiconducting, strong rectification behavior of the 'closed'
diarylethene isomer with the rectification ratio >10^3 is observed. The
surprisingly high rectification ratio originates from the band gap of GNR and
the bias-dependent variation of the lowest unoccupied molecular orbital (LUMO)
of the diarylethene molecule, the combination of which completely shuts off the
current at positive biases. Results presented in this paper may form the basis
for a new class of molecular electronic devices.
