From supramolecular photochemistry to the molecular computer

A molecule and its noncovalently bonded solvent shell can be termed “supermolecule”. It is assumed that its ground-state hypersurrace consists of many shallow local minima which have approximately the same energy and correspond to different arrangements of the solvent shell. At cryogenic temperatures each supermolecule sits in one of the different minima. Supermolecules might show different physical properties, specifically a spread in their absorption frequencies. This property forms the basis for spectral holeburning, a special type of photochemistry Spectral hole-burning not only allows high resolution spectroscopy of matrix isolated organic molecules, it also opens a wide field of technical applications, especially with respect to frequency selective information storage. Recently more than 2000 images were stored in a single polymer film at different frequencies of the visible spectrum. More general this type of wavelength-selective photochemistry allows the storage of all the properties associated with an optical wave field, such as frequency, polarization, direction of propagation, intensity, and, in conjunction with holographic methods, also the phase. One might say that supermolecular photochemistry freezes in all the properties of light. It is often claimed that the top end of the current generation of electronic computers will be replaced by optical computers having fast parallel computing capacities. A further development might be a molecular computer. The properiies of light are transferred to photochemical changes in the material and the stored patterns can then be operated on by logical operations at will. The interaction of the molecular energy levels with an external electric field provides dynamical responses. A functional model of a molecular processor which is based on spectral hole-burning and on the spectroscopic properties of a dye doped polymer film is described here. Hole-burning materials can be used for image recording as well as for parallel processing of stored information.