The light-induced double-bond isomerization of the visual pigment rhodopsin operates a molecular-level optomechanical energy transduction, which triggers a crucial protein structure change. In fact, rhodopsin isomerization occurs according to a unique, ultrafast mechanism that preserves mode-specific vibrational coherence all the way from the reactant excited state to the primary photoproduct ground state. The engineering of such an energy-funnelling function in synthetic compounds would pave the way towards biomimetic molecular machines capable of achieving optimum light-to-mechanical energy conversion. Here we use resonance and off-resonance vibrational coherence spectroscopy to demonstrate that a rhodopsin-like isomerization operates in a biomimetic molecular switch in solution. Furthermore, by using quantum chemical simulations, we show why the observed coherent nuclear motion critically depends on minor chemical modifications capable to induce specific geometric and electronic effects. This finding provides a strategy for engineering vibrationally coherent motions in other synthetic systems.

A new family of light driven molecular rotary motors, which can be synthesized from easily available precursor compounds and which are capable of completing a full 360° revolution by two photoisomerization steps only, is proposed. The non-adiabatic molecular dynamic simulations show that the photoisomerization steps of the motor's working cycle occur on an ultrafast time scale (ca. 200–300 fs), have a very high quantum yield of isomerization (0.91–0.97), and display high selectivity of torsion in the same direction. It is expected that the new motor should remain operational at lower temperatures than the currently existing motors.