Photo-driven molecular devices

Abstract

In this critical review, we discuss switching of the light-powered bistable rotaxanes and catenanes and highlight the practical applications of some of these systems. Photoactive molecular and supramolecular machines are comprised of two parts-1) a switching element, based on noncovalent interactions within the recognition units, which is responsible for executing mechanical movement, and 2) a light-harvesting unit which utilizes light to control the competitive interactions between the recognition sites. We also survey another class of molecular devices, namely molecular rotary motors--i.e., those that behave like their macroscopic counterparts--in which photochemically and thermally induced mechanical movement relies on isomerizations of a pivotal C=C bond, leading to a rotation of the top propeller part with respect to the stationary bottom part of the helical shaped chiral molecule. (146 references.).

Molecular, Supramolecular, and Macromolecular Motors and Artificial Muscles

“…These types of molecules can be designed to expand or to contract linearly in response to different stimuli, such as chemical, 18,79-83 electrochemical, [84][85][86][87][88] and optical stimuli. 20,21,[89][90][91][92] Depending on the design (vide infra), switchable rotaxanes are capable of contracting up to 67% of their initial (extended) length, [93][94][95] suggesting that artificial molecular muscles could be harnessed by tethering to a solid support to perform macroscale work. This section describes recent advances and future prospects for controlling the artificial molecular muscles on both single-molecule and microscopic levels and developing them into nanomechanical devices.…”

“…Like their macroscopic counterparts, molecular machines must be powered by electrical, 1,3 chemical, 18 electrochemical, 19 or optical [20][21][22][23] means. Although certain key examples of such mechanical coupling are already understood, new strategies for energetic coupling at the nanoscale will enable new applications.…”

Chemical reactions induced by oscillating external fields in weak thermal environments

“…34 Knowledge of the mechanism by which these interactions mediate reactive flow provides a methodological tool in the design of molecular devices with unique functionality. [35][36][37] Materials that undergo conformational changes in response to an external trigger offer examples of such emergent technology. 36,[38][39][40][41] Stimuli such as thermal variations, electric fields, and photoinduction have been used as triggers for the conversion of chemical energy into mechanical work.…”

“…37,[42][43][44] Assemblies that convert chemical energy into directional motion can be achieved through isomerization reactions which are induced either from light or applied electric fields. 35,45,46 In these responsive materials, controlling the rate and pathway at which reactants transform to products is fundamental to harness mechanical actions for applicative purposes.…”

Orthogonal switching of a single supramolecular complex

“…The highly dynamic nature of supramolecular non-covalent processes offers versatile tools to utilize and amplify external stimuli in the manipulation of material properties through reversible stimuli-responsive molecular switching 5 . Recent efforts have been dedicated to gaining orthogonal control over supramolecular systems, whereby different responses can be triggered on demand with a specific order of input stimuli, representing versatility and complexity beyond unifunctional systems 6 .…”