ABSTRACT
The term photomagnetism describes a change in magnetization induced by light. There is currently great interest in obtaining photomagnetic materials whose magnetic properties may be controlled at will by light. Such control over magnetic properties by optical stimuli may have application in magneto-optical devices. Examples of photomagnetism in inorganic magnetic systems covalently linked organic polyradicals and organic/inorganic magnetic systems have already been reported. Indeed, Prussian blue analogues are examples of inorganic photomagnetic systems in which long-range magnetic ordering is modified by photons. Further examples of inorganic photoinduced magnetic systems are photoswitchable coordination compounds that interconvert reversibly between two isomers with different magnetic properties, such as spin-crossover or valence tautomerism. Different examples of photoinduced magnetization changes in purely organic materials have also been described. For instance, a diradical species bearing two stable nitroxide radicals connected through an isomerizable unit. The third family of photomagnetic molecular materials is composed of organic/inorganic hybrid systems where a magnetically active transition-metal ion is coordinated with a photoresponsive magnetic coupler.On the other hand, supramolecular self-organization is considered to be very important in the development of functional materials. Indeed, the construction of ordered arrays of nanostructures by employing organic self-assembly techniques provide alternative strategies for the production of nanodevices. From the magnetic point of view, supramolecular magnetic materials based on the self-assembly of open-shell molecules are very interesting. The construction of such solids requires that the structural subunits exhibit noncovalent interactions able to be controlled in a predictable manner. Hydrogen-bonding has emerged as a particularly useful and efficient tool for the construction of such solids. Moreover, transmission of magnetic interactions through hydrogen bonds has been demonstrated to be quite efficient in metal complexes and several hydrogen-bonded organic magnets. Despite the enormous interest of having switchable magnetic materials, hydrogen-bonded supramolecular magnetic materials whose properties may be systematically tuned and/or controlled by external stimuli are limited to few examples.This entry will describe some examples of molecular photomagnetic materials, including examples where the magnetic properties can be tuned by means of a light stimulus to induce self-assembly of the magnetic units. These materials represent an interesting example of a photomagnetic system based on a supramolecular phenomenon in which two doublet species are converted into one dimer with a singlet ground state.
