1,721,119 research outputs found
Controlling molecular shuttling in a rotaxane with weak ring recognition sites
Full text linkWe describe a rotaxane molecular shuttle encompassing triazolium and tertiary ammonium units as weak recognition sites for the ring. Such a design, which differs from that of typical controllable rotaxanes, allows the precise tuning of the ring distribution among the two sites - i.e., the coconformational equilibrium - by changing the solvent polarity or the nature of the counteranions. Shuttling of the ring between the two stations can also be toggled by acid-base stimuli. Such an approach is paradigmatic to obtain rotaxanes that can sense environmental changes and transduce them into a coconformational response and opens avenues for novel applications in sensing and stimuli-responsive materials
Photoprocesses
No full textThe development of supramolecular chemistry has allowed the construction of structurally organized and functionally integrated chemical systems capable of elaborating the energy and information input of photons to perform complex functions. Model systems capable of mimicking the two fundamental steps of photosynthesis, namely light harvesting and photoinduced charge separation, have recently been developed
The bottom-up approach to molecular-level devices and machines
No full textThe macroscopic concepts of a device and a machine can be extended to the molecular level. Molecular-level devices and machines are constructed by a bottom-up approach. The atom-by-atom bottom-up approach is unrealistic from the chemical viewpoint. The bottom-up approach molecule-by-molecule following the guidelines of supramolecular (multicomponent) chemistry has proved to be successful. The extension of the concepts of a device and a machine to the molecular level is of interest not only for basic research, but also for the growth of nanoscience and the development of nanotechnology
Controlled disassembling of self-assembling systems: Toward artificial molecular-level devices and machines
No full textInvestigations on self-assembling/induced-disassembling systems have led to the design of molecular-level devices capable of performing a variety of functions. Some of the work carried out in this field is illustrated
Light-powered molecular-scale machines
No full textThe macroscopic concepts of a machine can be extended to the molecular level. Molecular-level machines are constructed by the molecule-by-molecule bottom-up approach following the guidelines of supramolecular chemistry. Like macroscopic machines, molecular machines are characterized by (i) the kind of energy 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, (v) the time needed to complete a cycle of operation, and (vi) the function performed. The most convenient way to supply energy to a molecular machine is through photochemical energy inputs. Photochemical techniques offer, indeed, several advantages: (i) photons can make a machine work without formation of waste products, (ii) light can be switched on/off easily and rapidly, (iii) lasers provide the opportunity of working in very small space and very short time domains, (iv) photons can be used to "read" the state of the system and to monitor the operation of the machine. The extension of the concepts of a machine to the molecular level is of interest not only for basic research, but also for the growth of nanoscience and the development of nanotechnology
Photochemistry and photophysics of coordination compounds: An extended view
No full textCoordination chemistry is much more than the coordination of transition-metal ions by organic or inorganic ligands. Its scope extends to the binding of all kinds of substrates (cationic, anionic, and neutral molecular species). Therefore coordination chemistry merges into the big field of supramolecular chemistry. Coordination compounds (with or without metals) exhibit by definition a high level of organization and therefore they are quite suitable to exploit the energy and information content of photons. In this paper we illustrate specific examples concerning the similarity between the photochemical behavior of classical coordination compounds (i.e. metal complexes) and supramolecular species not containing metals. We also describe coordination compounds not containing metals that undergo photochemically, electrochemically, or chemically induced mechanical movements (molecular-level machines) and behave as logic gates. (C) 1998 Elsevier Science S.A
Electrochemistry of coordination compounds: An extended view
No full textNowadays coordination chemistry has merged into the big field of supramolecular chemistry. In this paper we illustrate specific examples concerning analogies between the electrochemical behaviour of mononuclear metal complexes and supramolecular species containing metal complexes as component units. This similarity is extended to apparently very different systems, such as pseudorotaxanes, rotaxanes and catenanes not containing metal ions. In some cases the described compounds undergo electrochemically induced molecular movements and can be considered as prototypes of molecular-level machines. The importance of electrochemistry as a tool for obtaining information on the structure of the supramolecular system and as an energy input to induce mechanical movements at the molecular level is outlined. © 1999 Elsevier Science S.A. All rights reserved
Molecular-level devices
No full textIn everyday life we make extensive use of macroscopic devices. A macroscopic device is an assembly of components designed to achieve a specific function. Each component of the device performs a simple act, while the entire device performs a more complex function, characteristic of the assembly. For example, the function performed by a hairdryer (production of hot wind) is the result of acts performed by a switch, a heater, and a fan, suitably connected by electric wires and assembled in an appropriate framework. The concept of device can be extended to the molecular level. A molecular–level device can be defined as an assembly of a discrete number of molecular components (that is, a supramolecular structure) designed to achieve a specific function. Each molecular component performs a single act, while the entire supramolecular structure performs a more complex function, which results from the cooperation of the various molecular components. The extension of the concept of device to the molecular level is of interest not only for basic research, but also for the growth of nanoscience and the development of nanotechnology [4]. Looking at supramolecular chemistry from the viewpoint of functions with references to devices of the macroscopic world is a very interesting exercise that helps the development of chemistry by introducing new concepts
Molecular logic circuits
No full textMiniaturization has been an essential ingredient in the outstanding progress of information technology over the past fifty years. The next, perhaps ultimate, limit of miniaturization is that of molecules, which are the smallest entities with definite size, shape, and properties. Recently, great effort has been devoted to design and investigate molecular-level systems that are capable of transferring, processing, and storing information in binary form. Some of these nanoscale devices can, in fact, perform logic operations of remarkable complexity. This research - although far from being transferred into technology - is attracting interest, as the nanometer realm seems to be out of reach for the "top-down" techniques currently available to microelectronics industry. Moreover, such studies introduce new concepts in the "old" field of chemistry and stimulate the ingenuity of researchers engaged in the "bottom-up" approach to nanotechnology
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