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There is an ever-growing interest in the design and study of molecular switching materials because of their applicability in modern technologies such as active data expansion, storage and communication elements and optics. Molecular switches can be reversibly shifted between at least two different states with distinct properties by the application of external input energy (e.g., mechanical, magnetic, electrical, optical etc.).

The groups’ primary focus is on molecular switching based on the spin crossover phenomenon which can occur in certain d⁴-d⁷ transition metal complexes under external stimuli, such as temperature, pressure and light-irradiation. This particularly elegant example of molecular switching is accompanied by striking changes in colour, structure and magnetic signal and thus has been flagged for interest in a diverse array of advanced technologies. Following is an example of the spin crossover process for iron(II), highlighting the impressive colour change between high spin and low spin electronic states, alongside the distinct structure and magnetic signal shifts.

The group focuses on the strategic design and synthesis of poly-nuclear complexes, such as dinuclear, square, cage, 1-D chain, 2-D layered and 3-D framework materials, some of which are depicted below. These metallosupramolecular materials are prepared using the molecular building block approach, which exploits the directionality and flexibility of coordination bonds to target certain shapes and topologies (much like molecular lego). We carefully select metal and ligand combinations to produce metal ion coordination environments with molecular switching capacity. The direct coordination bridges between spin crossover metal ions act to enhance the spin state switching in efforts to produce optimal switching characteristics (i.e., room temperature working capacity, thermal hysteresis, etc).

The group has recently developed a unique strategic platform to induce multiple stepped spin crossover transitions into coordination materials. Materials displaying multi-stepped spin crossover transitions are pursued both fundamentally and with an interest in exploring their novel electronic functionalities for applications such as ternary and higher-order information storage. 

In this structural platform, we focus on 2-D Hofmann-type materials which include a mixture of antagonistic interactions to strategically induce structural deformations. By this approach, with temperature variation the spin transition pathway must proceed via a cascade of steps comprised of varying ratios of high and low spin states (nHS:mLS). We now have examples of two-step, three-step and four-step spin crossover materials by this method.