Molecular machines operated by light

Abstract

Abstract:The bottom-up construction and operation of machines and motors of molecular size is a topic of great interest in nanoscience, and a fascinating challenge of nanotechnology. Researchers in this field are stimulated and inspired by the outstanding progress of molecular biology that has begun to reveal the secrets of the natural nanomachines which constitute the material base of life. Like their macroscopic counterparts, nanoscale machines need energy to operate. Most molecular motors of the biological world are fueled by chemical reactions, but research in the last fifteen years has demonstrated that light energy can be used to power nanomachines by exploiting photochemical processes in appropriately designed artificial systems. As a matter of fact, light excitation exhibits several advantages with regard to the operation of the machine, and can also be used to monitor its state through spectroscopic methods. In this review we will illustrate the design principles at the basis of photochemically driven molecular machines, and we will describe a few examples based on rotaxane-type structures investigated in our laboratories. © Versita Warsaw and Springer-Verlag Berlin

Photo- and Redox-Driven Artificial Molecular Motors

“…The Z stereoisomer of azobenzene and the E → Z photoisomerization reaction were discovered in 1937 by G. S. Hartley . Since then, the interest in and popularity of the photochemistry of azobenzene derivatives in the scientific community have continuously increased, establishing them as a common choice when photocontrol has to be achieved in chemical species and materials. − ,− ,,,,,,− ,,,,,,− ,− The E configuration of azobenzene is ca. 42 kJ mol –1 more stable that the Z form; thus, at equilibrium in the dark, azobenzene is present almost exclusively as its E stereoisomer.…”

“…What chemists have been doing is making simple prototypes consisting of a few molecular components that can move relative to one another in a controllable way and tackling the challenging problems posed by the interfacing of such devices with the macroscopic world in terms of energy supply, information exchange, and in more recent years, the task performed. The many remarkable achievements in this area have been evidenced in several reviews − (including some focused on redox-driven − and light-driven − systems), themed issues, − edited books, − and monographs. − The scientific value of molecular machines was highlighted by the award of the 2016 Nobel Prize in Chemistry to Jean-Pierre Sauvage, Fraser Stoddart, and Ben Feringa well before these systems could impact significantly on people’s lives . Clearly, besides the relevance for fundamental science, the Nobel Committee recognized the huge potential of molecular machines for major progress in several areas of technology and medicine, with ground-breaking applications limited only by imagination…”

Oligomeric “Catastrophe Machines” with Thermally Activated Bistability and Stochastic Resonance

“…Nanosystems capable of reversible transitions between two states in response to applied stimuli are attracting greater attention given the pursuit of miniaturization of trigger-type and switch-type elements. These elements are key units of many functional nanodevices (e.g., molecular and macromolecular switches, single molecular sensors, molecular actuators, electric and optoelectric devices, and logic gates). − Mechanical and electromechanical nanodevices are also attracting attention because of the growing desire to make platforms for “algorithmic chemistry” with machinelike actions at the molecular level. − Despite recent progress in micro- and nanomechanics, practical mastery of bistable systems with sizes ranging from a few nanometers to several tens of nanometers has not yet been achieved. Therefore, the search for nanoscale molecular structures with the dynamics inherent in bistable mechanical systems is of particular interest.…”

Two‐Color Reversible Switching in a Photochromic Ruthenium Sulfoxide Complex

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Reversible, external triggering of molecules between two ground states is central to the operation of modern molecular machines. Although light is commonly employed for the formation of many different types of metastable states, [4][5][6][7][8] in practice it is difficult to employ light to regenerate the initial ground state. Although light is commonly employed for the formation of many different types of metastable states, [4][5][6][7][8] in practice it is difficult to employ light to regenerate the initial ground state.

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“…[1][2][3] A desirable trigger is light, as it provides an ample amount of energy in a short burst of time. Although light is commonly employed for the formation of many different types of metastable states, [4][5][6][7][8] in practice it is difficult to employ light to regenerate the initial ground state. The enthalpic and entropic factors that favor the photochemical generation of the metastable state from the ground state must necessarily be disfavored for the opposing photochemical reaction.…”