Title:	Design of molecular motors that exploit excited-state aromaticity and can be attached to surfaces
DNr:	SNIC 2018/3-589
Project Type:	SNIC Medium Compute
Principal Investigator:	Bo Durbeej <bo.durbeej@liu.se>
Affiliation:	Linköpings universitet
Duration:	2018-12-01 – 2019-12-01
Classification:	10407 21001 10405
Homepage:	http://liu.se/en/employee/bodu88
Keywords:

Abstract

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 these systems have enormous potential for 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 light-driven molecular motors are designed through computational studies in theoretical chemistry. Thereby, we have found a number of ways to improve both the speed (rotational frequencies) and the efficiency (quantum yields (QYs)) of such motors. In particular, we have discovered that the ability of molecular motors to become aromatic in the photoactive excited state has a very favorable effect on their performance (Org Lett 2017, ChemPlusChem 2018, ChemistryOpen 2018). Therefore, the long-neglected, but nowadays revived, concept of excited-state aromaticity (ESA) has the potential to play a key role for the future development of the field. In the present project, this concept will be used for the design of new molecular motors with greater speed and higher QYs than current ones. Besides this goal, it is also desirable to gain an understanding of how organic molecular motors can be attached to inorganic surfaces. Indeed, in order to harvest the collective rotary motion produced by an ensemble of motors, rather than just the rotary motion of a single motor, attaching the motors to surfaces is an absolute requirement. However, the challenge here is that most chemical procedures for surface attachment distort the very motor properties that enable fast rotary motion in solution. Therefore, in this project, we will identify new such procedures that allow the motors to function well also when surface-bound. Having recently found that the speed and QYs of molecular motors can be increased by enabling one of the two motor halves to become aromatic in the photoactive excited state, the approach that will be taken to further improve the motors is to facilitate a similar process also in the other motor half. In particular, we will design motors where the onset of ESA in one motor half triggers (through intramolecular electron transfer) the onset of ESA in the other. The potency of the motor prototypes will then be assessed by modeling their rotary motion and calculate their QYs through demanding non-adiabatic molecular dynamics (NAMD) simulations. The approach that will be taken to develop new chemical procedures for attaching the motors to surfaces, in turn, is to optimize the choices of target surface and "linker" molecule between the motor and the surface. Specifically, by modeling the electronic structure of the motors when bound 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.