Light-activation of molecular motors in polymersomes†

Light-activated synthetic organic molecular motors are emerging as an excellent prospect to actuate supramolecular assemblies such as polymersomes with spatiotemporal precision. The influence on these materials depends on the motor's frequency of rotation and concentration. Therefore, we determined the rotation frequency of a motor in a poly(dimethyl siloxane)-b-poly(ethylene glycol) (PDMS₁₃-b-PEG₁₃) polymersome and compared it to the frequency observed in different organic solvents. Using UV-vis spectrophotometry and nuclear magnetic resonance spectroscopy, we measured the rate of the thermal helix inversion step, which is the rate-determining step of the rotary cycle, and obtained the activation parameters. We found that the investigated motor's frequency of rotation did not significantly change in the polymersomes and remains at around 1 mHz. Moreover, dynamic light scattering results indicate that the rotation of the motors does not cause a significant change in the structure of this type of polymersome when used at a diblock copolymer : motor molar ratio of up to 100 : 2. Our findings provide a first insight into the effect of the polymersome on the motor's frequency of rotation and vice versa. Enhancing the polymersome composition with motors can lead to novel concepts, including light-activated nanopharmaceuticals, nanoreactors, and biomimetic artificial organelles and cells.