Novel nanomaterials for enhanced applications
Molecular framework materials have recently been shown to possess immensely rich host-guest chemistry. Their porous lattices are capable of highly selective host-guest properties that include reversible ion exchange, heterogeneous catalysis, and gas storage and separation. Molecular sensing materials can be generated by further exploiting the porous nature of metal-organic frameworks in combination with spin crossover (SCO) centres. SCO sites can be switched on, off or altered by the presence, absence or exchange of solvent guest molecules. Light is one of the most promising ways to reversibly direct and control the physical properties of organic and inorganic materials. SCO materials are known to exhibit a light-induced transition from a low-spin to metastable high-spin state. The aim of the project 'Nanoporous materials and supramolecular clusters for light induced electronic switches' (Light Induced Switch) was to design and investigate the properties of new materials that have inbuilt light-initiated switches in the form of iron(II) SCO centres, for use as optical switches and storage devices. The project examined the light- and thermally-induced SCO properties of these materials as particle size was reduced from the macroscopic to microscale to nanoscale domains. Results showed that the spin transition becomes more gradual, more incomplete and the transition temperature (T½) decreases as particle size reduces. These results are the first photo-induced magnetic studies on a nanoparticle SCO system and show that, even on the nanoscale, photo-conversion of the low-spin species to a metastable high-spin state is possible. Furthermore, particle size reduction appeared to have little effect on the temperature at which the stored photomagnetic information was erased. This indicated that the light-induced SCO properties are governed by direct metal coordination environment at the molecular scale. The project achieved the first detailed investigations of these novel SCO and nanoporous materials in nanoscale light-initiated switching applications. The impact of even a small advance in such materials could open significant new opportunities for environmental, economic, public health and/or national security applications.
