Strain Energy Induced Rotary Speed Acceleration in a Light‐Driven Molecular Motor

Abstract

Abstract Light‐driven molecular motors based on overcrowded alkenes represent a major type of molecular machines that are able to rotate unidirectionally. The regulation of the rotary speed without altering the core structure of a motor is crucial and remains a major challenge. In the present study, we reported that the rotary speed of molecular motors can be significantly enhanced by harnessing the strain energy of cycloparaphenylene (CPP). A series of molecular motors incorporated in CPP with varying sizes were synthesized, and their photochemical and thermal isomerization behaviors were meticulously examined using UV–vis and 1 H NMR spectroscopy. The remarkable increase of the acceleration effect of the rotary speed with decreasing macrocycle sizes, up to 389‐fold, can be attributed to the strain energy induced bending in the stator part, which reduces steric hindrance in the “ fjord region ” of the molecule, supported by a detailed computational study employing density functional theory. This work provides systematic insight into the behavior of molecular motors under strain energy, thereby paving the way for the application of motor‐incorporating CPPs as a general strategy to accelerate the rotary speed of molecular motors.