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: photoisomerisation around a pi-bond followed by a thermally activated helical inversion; the latter being the rate-determining step. We propose an alternative molecular system, where the rotation is caused by the electronic 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 thermal 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 build on this principle should be able to work on a sub-nanosecond timescale for such a full rotation. We explore the parameter space of our model to guide the design of a molecule which can act as such motor.