Switchable Multifunctional Materials

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Expectations of processing times and volumes of data are increasing exponentially as are energy demands. Key to addressing this is to do more with less, requiring faster and lower power electronics. Molecular (e.g. nanomagnets) or two-dimensional (e.g. graphene) materials have shown tremendous magnetic/conducting properties; triggering or harnessing these with the use of a small amount of energy can drastically cut energy consumption. Thus, systems in which physical properties can be switched is of great interest in the quest for superior next-generation functional materials to be employed as sensors, displays, etc. While switchable materials are intriguing fundamentally, to be commercially viable the responsive moiety must reversibly interconvert between two (or more) states to ensure the existence of bistable (or multistable) states (e.g. 0 and 1 in binary code). A method to couple the responsive and functional units must also be developed to produce switchable materials that satisfy the requirements of various applications. Thanks to their inherent bistability, spin crossover (SCO) complexes in which external stimuli (e.g. light, temperature, pressure) can induce switching between low (LS) and high (HS) spin magnetic states are promising candidates for the realization of molecule-based electronics and spintronics.    This proposal targets new materials by design to exploit key attributes of organic/inorganic systems and their implementation into molecular electronics. While rational design permits access to novel materials with new functionalities that combine magnetic, optical and transport properties, the dependence of physical properties on solid-state packing remains a challenge. This is especially pertinent in SCO systems, as efforts to fully harness these materials reveal the importance and difficulty of controlling solid-state packing, and hence targeted macroscopic properties in order to bridge the gap between laboratory and reality. Practical application of SCO materials requires strong, abrupt or hysteretic cooperativity. We will achieve this by enhancing intermolecular interactions through ligand design and the use of conjugated linkers in the generation of 1) polynuclear SCO complexes and 2) redox active Hofmann-type frameworks & Prussian-blue-Hofmann blends; features that are also anticipated to render multifunctionality to SCO systems by strengthening communication between the responsive and functional moieties coupled with controlled assembly in the solid-state. Given the high spatial and temporal resolution afforded to photoirradiation, interconversion between LS and HS states can be realized with high efficiency and good reversibility via light-induced spin transitions. Designing materials with magnetic and optical bistabilities, and combining these features with other physical attributes (e.g. porosity), enables exploration of smart multifunctional materials where the properties can be controlled via external stimuli.