Molecular and Supramolecular Devices

Molecular devices have been defined as structurally organized and functionally integrated chemical systems they are based on specific components arranged in a suitable manner, and may be built into supramolecular architectures [1.7,1.9]. The function performed by a device results from the integration of the elementary operations executed by the components. One may speak of photonic, electronic or ionic devices depending on whether the components are respectively photoactive electroactive or ionoactive, i.e., whether they operate with (accept or donate) photons, electrons, or ions. This defines fields of molecular and supramolecular photonics, electronics and ionics. 

Two basic types of components may be distinguished active components, that perform a given operation (accept, donate, transfer) on photons, electrons, ions, etc. structural components, that participate in the build-up of the supramolecular architecture and in the positioning of the active components, in particular through recognition processes in addition, ancillary components may be introduced to modify or perturb the properties of the other two types of components. A basic feature is that the components and the devices that they constitute should perform their function ) at the molecular and supramolecular levels as distinct from the bulk material. Incorporation of molecular devices into supramolecular architectures yields functional supermolecules or assemblies (such as layers, films, membranes, etc.). 

Molecular and supramolecular devices are by definition formed from covalently and non-covalently linked components, respectively. One might envisage that covalently built devices made up of distinct but interacting components, retaining at least in part their identity as if they were bound together in a non-covalent fashion, could also belong to the supramolecular domain. Such a case has been argued for supramolecular photochemistry [A. 10] and could be extended to other supramolecular functions. 

This may be perceived as a significant stretching of the basic definition of supramolecular species. This definition is essential to charactere the identity of the field. 

One may however consider that the integrated operation of its individual components confers to a molecular (covalently linked) device a flavour of supramolecular nature, since its function extends over the whole device in a sort of superstructure fashion. It then would appear justified to include in the domain of supramolecular chemistry systems that bear relation to supramolecular species on functional grounds, systems whose function is of supramolecular nature although they are clearly molecular in terms of structure and bonding. A further reason for not excluding such a possibility lies in the considerable enrichment that such an open view brings to the field  

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Molecular and supramolecular devices incorporated into ultra-micro-circuits represent potential hardware components of eventual systems that might qualify as molecular computers, whose highly integrated architecture and operation would not be of the von Neumann type. On the biological side, the fabrication of components for sensory and motor protheses could be considered. All these entities may result from the self-assembly of suitably instructed subunits so that computing via self-assembly may be envisaged. 

Fig. 1. From molecular to supramolecular chemistry molecules, supermolecules, molecular and supramolecular devices.

The photochemical and photophysical processes discussed above provide illustrations and incentives for further studies of photoeffects brought about by the formation of supramolecular species. Such investigations may lead to the development of photoactive molecular and supramolecular devices, based on photoinduced energy migration, electron transfer, substrate release, or chemical transformation. Coupling to recognition processes may allow the transduction of molecular infor-... 

Fig. 50. Chemionics as the chemistry of recognition-directed and self-organised photonic, electronic and ionic molecular and supramolecular devices generated by means of functional programmed chemical systems.

Comparable extension has been given to the research on molecular recognition, catalysis and transport processes (Chapters 2-6) on molecular and supramolecular devices (Chapter 8) and self-processes (Chapter 9). This was done to emphasize the more recently developed topics, despite the much larger volume of work on the former areas that have been described in many instances in the literature. The outline of Chapters 1-7 follows that of earlier reviews. Chapters 8 and 9 bring together approaches from various directions. Chapter 10 places the basic concepts into a broader perspective and is intended to make the score decidedly open ended. 

The area of molecular and supramolecular devices would desserve full treatment (see [25]) in view of the important developments one may predict for this field in the future. However we shall limit ourselves here to a few considerations concerning dynamic changes in mechano-devices which are the seat of motional processes. 

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