Molecular framework materials recently have been shown to possess immensely rich host-guest chemistry; their porous lattices are capable of highly selective host-guest properties that include reversible guest and ion exchange, heterogeneous catalysis, and gas storage and separation. It was realized that by further exploitation of the porous nature of metal-organic frameworks in combination with spin crossover centres, molecular sensing materials can be generated, whereby the spin crossover sites can be switched ‘on’, ‘off’ or altered by the presence, absence or exchange of solvent guest molecules. The challenge in this exciting new area is to generate such materials with a focus on real and timely application. Light is one of the most promising ways to reversibly direct and control the physical properties of organic and inorganic materials. Spin crossover materials are a convenient class of compounds to make this possible as they are known to exhibit a light induced transition from a low spin to metastable high spin state, and indeed can show infinite lifetimes of the high spin state under certain conditions. The overall object of this proposal is to develop inorganic nanoporous materials and supramolecular clusters which have inbuilt light initiated switches, in the form of iron(II) spin crossover centers, for use as optical switches and storage devices, molecular sensors, chemical detectors, drug delivery, data storage, displays and other electron devices. The project makes use of the complementary skills and expertise of the research groups in Bordeaux, Melbourne and Sydney to achieve the first detailed investigations of this novel co-existence of spin crossover and nanoporous materials towards ‘nano-scale’ light initiated switching applications. The impact of even a small advance in such materials could translate into a major impact on the environment, economy, public health and national security.