Green light powered molecular state motor enabling eight-shaped unidirectional rotation

Peter Mayer,Henry Dube,Aaron Gerwien

doi:10.1038/s41467-019-12463-4

Abstract

Molecular motors convert external energy into directional motions at the nano-scales. To date unidirectional circular rotations and linear motions have been realized but more complex directional trajectories remain unexplored on the molecular level. In this work we present a molecular motor powered by green light allowing to produce an eight-shaped geometry change during its unidirectional rotation around the central molecular axis. Motor motion proceeds in four different steps, which alternate between light powered double bond isomerizations and thermal hula-twist isomerizations. The result is a fixed sequence of populating four different isomers in a fully unidirectional trajectory possessing one crossing point. This motor system opens up unexplored avenues for the construction and mechanisms of molecular machines and will therefore not only significantly expand the toolbox of responsive molecular devices but also enable very different applications in the field of miniaturized technology than currently possible.

Highlights

Molecular motors convert external energy into directional motions at the nano-scales
The HT motion was originally proposed as volume conserving photoreaction for the isomerization of retinal inside the opsin protein framework and proceeding as fully concerted process wherein a double bond and adjacent single bond rotate at the same time after photoexcitation[34,35,36,37,38]
Taking both thermal interconversions and photoreactions into account, a repetitive unidirectional motion of HTI 1 can be established in four distinct steps (Fig. 3a, b)

Summary

Introduction

Molecular motors convert external energy into directional motions at the nano-scales. Most recently we have introduced a light-only powered molecular motor enabling stepwise directional motions without thermal ratcheting in the ground state[33] To this end, the hula-twist (HT) photoreaction[34,35,36,37,38], as recently experimentally evidenced by our group[38], was employed in combination with simple double-bond isomerization (DBI) and single bond rotation (SBR) photoreactions. We present a simple molecular setup 1 that allows realization of a very precise and repetitive eight-shaped geometry change during unidirectional rotation of one molecular fragment around the other within a single switch architecture To this end, an unusual type of thermal HT motion is employed alternating with photoinduced DBI. The term “thermal hula-twist (HT)” motion refers here to a 180° rotation of both the double bond and the adjacent single bond in the ground state leading to concomitant E–Z isomerization, as well as atropisomerization without observable intermediates

Methods

Results

Conclusion