Unimolecular submersible nanomachines
(USNs) bearing light-driven motors and fluorophores are synthesized.
NMR experiments demonstrate that the rotation of the motor is not
quenched by the fluorophore and that the motor behaves in the same
manner as the corresponding motor without attached fluorophores. No
photo or thermal decomposition is observed. Through careful design
of control molecules with no motor and with a slow motor, we found
using single molecule fluorescence correlation spectroscopy that only
the molecules with fast rotating speed (MHz range) show an enhancement
in diffusion by 26% when the motor is fully activated by UV light.
This suggests that the USN molecules give ∼9 nm steps upon
each motor actuation. A non-unidirectional rotating motor also results
in a smaller, 10%, increase in diffusion. This study gives new insight
into the light actuation of motorized molecules in solution.