Quantum-Classical Simulation of Molecular Motors Driven Only by Light

Molecular motors that exhibit controlled unidirectional rotation provide great prospects for many types of applications, including nanorobotics. Existing rotational motors have two key components: photoisomerization around a π-bond followed by a thermally activated helical inversion, the latter being the rate-determining step. We propose an alternative molecular system in which the rotation is caused by the electric coupling of chromophores. This is used to engineer the excited state energy surface and achieve unidirectional rotation using light as the only input and avoid the slow thermally activated step, potentially leading to much faster operational speeds. To test the working principle, we employ quantum-classical calculations to study the dynamics of such a system. We estimate that motors built on this principle should be able to work on a subnanosecond time scale for such a full rotation. We explore the parameter space of our model to guide the design of a molecule that can act as such a motor.