Molecular Devices: Energy Transfer

Devices are systems able to performs specific functions[1] which result from the coordinated operation of different components. The design of these systems is hence based on the identification or the development of the necessary parts and in their integration in a suitable supramolecular architecture. The main challenge in such a process is undoubtedly synthetical: the control of the mutual interactions between the molecular active units, in fact, requires a fine tuning of the distance and orientation of the components as well as of the electronic properties of the interconnecting linkers. Organization through covalent bonding has, in this context, several advantages and many examples of covalent supramolecular devices have been reported in the last two decades. Beside the covalent approach led to the design of fascinating and efficient prototypes it often made necessary the preparation of beautiful but complicated chemical systems which resulted from time demanding multistep synthetic paths and that are not suitable for large scale production. Many examples of devices derived from a more traditionally supramolecular approach based on self assembly and host-guest interactions has also been reported. In this chapter some relevant examples of both covalent and self-organizing supramolecular devices based on energy transfer (ET) processes will be reviewed. The basic principles of ET will also be discussed. Recently, the advent of nanomaterials offered to supramolecular chemists new active components and structural platforms suitable for the design of nanometric molecular devices. At the present stage, nanomaterials represents an ideal platform to achieve a reasonable degree of spatial organization especially when the integration of a large number of components is required or desired. This approach allows the achievement of complex, extensive devices otherwise not accessible. Moreover some nanomaterials have unique photophysical properties and can become themselves active nanosized component of the final device. Considered the huge literature in the field of hetero-supramolecular chemistry even when restricted to energy transfer based devices, we decided to focus the last part of this review chapter on discrete nanodevices, namely on systems which can be, at least in principle, isolated as individual nanometric (working) objects.