Stepwise "dark Photoswitching" of Photochromic Dimers in a Junction

Molecular photoswitches incorporated in a junction present a way to achieve light-controlled conductance switching by photoisomerization. Yet, the two isomers might also interconvert upon charging of the molecule if this results in a change in their relative energies. This behavior (current-induced switching) has been termed dark photoswitching and was observed for the dihydroazulene-vinylheptafulvene couple in a junction. In this theoretical study, we expand this concept to dimeric structures containing two dihydroazulene units linked through meta- or para-phenylene bridges and anchored to the electrodes through different linkers. In particular, we show how stepwise dark photoswitching can be achieved for certain redox states.