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Modeling the Physical Properties of Environmentally-Friendly Optical Magnetic Switches: DFT and TD-DFT

The dominant majority of the hundreds of available spin-crossover compounds, including the technologically most promising ones, are based on the Earth-abundant metal iron, making these switches particularly appealing in terms of sustainable technology. Furthermore, it has recently been established that these materials may be synthesized using the techniques of Green Chemistry. Spin crossover in transition metal complexes can be induced by a change of temperature, by the application of an external pressure, or a magnetic field, and also by photoexcitation. Given the wide variety of functionalities to which these bistable photomagnetic systems could give access, they may be viewed as the prototypes of molecular-scale optomagnetic switches. Hence, in response to the growing demand for storing and treating increasingly-dense information, much effort has been devoted over several decades to the design of transition metal materials exhibiting spin crossover in technologically-accessible temperature ranges. The cornerstone for designing new efficient photoactive spin-crossover materials remains the ability to predict the magnetic behaviour and the photoresponse of any first-row transition complex, and the manner in which its properties are influenced by its environment. This is a challenge for the inorganic chemist and also, most notably, for the theoretical and the computational chemist. This chapter gives an overview of the issues tied to the application of DFT and TD-DFT to the characterisation of transition metal complexes in the framework of spin-crossover and related phenomena.