Mémoire, partim B: Study of a synthetic molecular motor by single molecule force spectroscopy

Abstract

In this work, a Feringa type molecular motor, known to perform unidirectional rotation when irradiated with ultraviolet (UV) light, is studied by Single Molecule Force Spectroscopy (SMFS) using Atomic Force Microscopy (AFM). First, the probed system is identified using forces and extensions taken at rupture events, as well as the persistence length calculated using the worm-like chain (WLC) model. Then, the analyses of profiles featuring at least two rupture events showed a population of revealed length that is similar to the motor’s width. This phenomenon could potentially result from an unexpected force triggered isomerization. Further irradiative experiments showed that the probability of encountering revealed lengths in the range of values of this population is reduced when the system is exposed to UV light. These results hint at an eased force triggered isomerization of the system. However, other plausible explanations could not be ruled out and require more experiments. The probing of the system during irradiative experiments also revealed patterns in the force curves that suggest rotation of the motor. While no quantitative data regarding the rotation mechanism could be extracted, several characteristics of the patterns observed corroborate the established theoretical rotation mechanism of Feringa type motors. Moreover, the possibility of measuring the rotation frequency and the width of the motor rotation was illustrated.