Molecular motors are molecules that can perform work by absorbing energy and converting the energy into directed mechanical motion such as rotation around a chemical bond. Because of this ability, it has long been recognized that molecular motors have enormous potential for a wide variety of applications in nanotechnology and medicine. Fittingly, the 2016 Nobel Prize in Chemistry was awarded to three scientists who have made outstanding contributions to the design and synthesis of molecular motors.
In the last few years, we have initiated a line of research unique to Swedish academia in which more powerful molecular motors are designed through computational studies in theoretical chemistry. Thereby, we have found a number of ways to improve the performance (i.e., increase the rotational frequencies) of already existing motors driven by UV light and heat (Phys. Chem. Chem. Phys. 2015, 17, 21740; ChemPhysChem 2016, 17, 3399). Furthermore, and more importantly, we have also designed entirely new types of motors that produce rotary motion in a purely photochemical fashion with UV light as the only input energy source (Phys. Chem. Chem. Phys. 2017, 19, 6952; Org. Lett. 2017, 19, 4818). Accordingly, the performance of these motors does not depend on temperature, which is a considerable advantage for many applications.
However, it is also desirable to design molecular motors that do not require UV light for their function, but rather can be powered by visible light. This holds true particularly for applications in medicine, because visible light is much less harmful to human tissue than UV light. Furthermore, in order to be able to exploit the collective rotary motion produced by ensembles of motors, it is necessary to understand how the motors can be attached to surfaces. The challenge in this regard is that the surface attachment invariably distorts the very motor properties that give rise to the rotary motion in the first place. Using as starting points the aforementioned UV-powered motors designed in our own previous research, the present project aims to make progress toward both these goals.
The approach that will be taken to make our motor designs work also when subjected to visible light is to increase the number of conjugated double bonds in the motors, which is well known to red-shift the light absorption. Furthermore, we will also introduce motor substituents thought to have a red-shifting effect. The potency of the resulting motor prototypes will then be assessed by modeling their photoinduced rotary motion through demanding first-principles non-adiabatic molecular dynamics (NAMD) simulations.
The approach that will be taken to make the motors surface-mountable, in turn, is to focus more on the choices of target surface and "linker" molecule between the motor and the surface, than on optimizing the actual properties of the motors themselves. Specifically, by modeling the electronic structure of the motors when attached to surfaces, ideal combinations of surface and linker molecule will be identified based on the criterion that they together distort the intrinsic motor properties as little as possible.