Indandiazocines: Unidirectional molecular switches

We report theoretical investigations on azobenzene-based indandiazocines, novel chiral systems that perform unidirectional cis ↔ trans isomerizations upon photoexcitation. For three different systems of this kind, we have simulated excited-state surface-hopping trajectories for both isomerization directions, using a configuration-interaction treatment based on system-specifically reparametrized semiempirical AM1 theory. Our results are also compared to experimental and theoretical results for the parent system diazocine. We show that, as intended by design, the trans ! cis bending of the azo unit in these indandiazocines can only happen in one of the two possible directions due to steric constraints, which is a new feature for photoswitches and a necessary prerequisite for directional action at the nanoscale.