The concept of a macroscopic device can be extended to the molecular level by designing and synthesising (supra)molecular species capable of performing specific functions. Molecular devices operate via electronic and/or nuclear rearrangements and, like macroscopic devices, need energy to operate and signals to communicate with the operator. The energy needed to make a device work can be supplied as chemical energy, electrical energy, or light. Luminescence is one of the most useful techniques to monitor the operation of molecular-level devices. The extension of the concept of a 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. Molecular-level devices should find applications in information storage, display, and processing; in the long run, they are expected to lead to the construction of molecular-based (chemical) computers. In this perspective article, some of the most recent achievements in the field of photochemical molecular devices will be illustrated, with particular reference to (i) devices for photoinduced energy or electron transfer; (ii) devices for information processing based on photochemical or photophysical processes; (iii) devices designed to obtain extensive conformational changes upon photoexcitation (photochemically driven molecular machines).
