An Artificial Molecular Switch that Mimics the Visual Pigment and Completes its Photocycle in Picoseconds

Single molecules that act as light-energy transducers (e.g. converting the energy of a photon into atomic-level mechanical motion) are examples of minimal molecular devices. Here, we focus on a molecular switch designed by merging a conformationally locked diarylidene skeleton with a retinal-like Schiff base and capable to mimic, in solution, different aspects of the transduction of the visual pigment Rhodopsin. Complementary ab initio multiconfigurational quantum chemistry based computations and time-resolved spectroscopy are used to follow the light-induced isomerization of the switch in methanol. The results show that, similar to Rhodopsin, the isomerization occurs on a 0.3-ps time scale and is followed by < 10-ps cooling and solvation. The entire (two-photon-powered) switch cycle was traced by following the evolution of its infrared spectrum. These measurements indicate that a full cycle can be completed within 20 ps