Artificial Redox-Driven Directionally Controlled Switches As a Basis for Redox-Driven Molecular Motors

Abstract

This review relates to artificial redox-driven molecular devices. The advantages of using very simple chemical building blocks for the bottom-up design of nanoleveled functional motors and the importance of the unidirectionality of a switching process for the development of redox-driven molecular motors are discussed. Furthermore, the crucial difference between artificial molecular switches and motors is explained. This review discusses few selected examples of redox-driven devices exhibiting partially complex-coupled movement sequences, which, however, due to the lack of an overall directionally controlled movement are not able to perform mechanical work on a molecular scale. Recent examples for redox-driven devices with at least one directionally controlled switching process as well as the proof for the unidirectionality of the switching process are presented. The challenge in designing directionally controlled switches is the fact that during the switching process, a configuration (or conformation) must be changed reversibly. This crucial process can be a flip caused by the change of the coordination sphere of a metal ion, a rotation around a C-C single bond, or around a C-C double bond. For future developments, we suggest designing artificial redox-based molecular motors in which the motion process of the presented directionally controlled switches are coupled with another switchable unit. The latter could also be switchable in a nondirected way.