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.