Artificial molecular‐level machines with [Ru(bpy)3]2+ as a “light‐fueled motor”

Abstract

Abstract.A molecular-level machine is an assembly of a discrete number of molecular components (that is, a supramolecular structure) designed to perform mechanical-like movements (output) as a consequence of appropriate external stimuli (input). Like macroscopic machines, molecular-level machines are characterized by (i) the kind of energy input supplied to make them work, (ii) the kind of movement performed by their components, (iii) the way in which their operation can be controlled and monitored, (iv) the possibility to repeat the operation at will and establish a cyclic process, (v) the time scale needed to complete a cycle of operation, and (vi) the function performed. The most convenient way to supply energy to an artificial molecular-level machine is through a photochemical reaction. [Ru(bpy) 3 ] 2+ (bpy=2,2'-bipyridine) can be used as a photosensitizer to power mechanical movements in machines based on pseudorotaxanes, rotaxanes and catenanes. Besides being used as an external photosensitizer, [Ru(bpy) 3 ] 2+ can be incorporated in one of the machine components as a "light-fueled" motor. Three types of photochemically driven piston/cylinder systems and a photocontrollable molecular abacus are described. Other kinds of more sophisticated molecular-level machines based on rotaxanes and catenanes are proposed. The extension of the concept of machine to the molecular level is important not only for the sake of basic research, but also for the growth of nanoscience and the development of nanotechnology.

From the photochemistry of coordination compounds to light-powered nanoscale devices and machines

“…Derivatives of the [Ru(bpy) 3 ] 2+ -type photosensitizer can be incorporated in catenated structures [91] and in suitably designed catenanes of this type it is possible to cause photochemical switching between two different conformations [92]. For example, in catenane 16 6+ (Fig.…”

Artificial Molecular Motors Powered by Light

“…This compound has a modular structure; its ring component R is an electron donor bis-p-phenylene [34]crown-10, whereas its axle component is made of a Ru(ii) polypyridine complex (P) covalently linked to a 4,4 -bipyridinium (A1) and a 3,3 -dimethyl-4,4bipyridinium (A2) electron-accepting stations by means of a p-terphenyl-type rigid spacer (S); the axle component is finally stoppered by a tetraarylmethane group (T). The ruthenium-based unit plays the dual role of a light-fuelled power station [100] and a stopper, whereas the mechanical switch consists of the two electron-accepting stations and the electron donor macrocycle. The strategy devised in order to obtain the photoinduced shuttling movement of the macrocycle between the two stations A1 and A2 is based on a 'four stroke' synchronized sequence of electronic and nuclear processes.…”

Artificial Photochemical Devices and Machines

“…In supramolecular species, photoinduced electron-transfer reactions can often cause large displacement of molecular components [6,7,10,57]. Indeed, working with suitable systems, an endless sequence of cyclic molecular-level movements can in principle be performed making use of light-energy inputs without generating waste products [55,58].…”