Determination of exchange coupling constants in the electronic ground and excited states of molecular multi-spin systems

The interaction between unpaired electrons determines the magnetic properties of molecular materials and consequently their applicability. In particular, for applications of organic multi-spin systems in the emerging field of molecular spintronics, being able to control such electronic interactions is desirable, as this would pave the way for the creation of materials with tailor-made magnetic properties. Inter-spin interactions can be divided into two different categories, namely, dipolar and exchange interactions. Dipolar interactions are well predictable due to their defined distance dependence, while exchange interactions are difficult to determine since they exhibit a complex dependence on the molecular structure. Any approaches to tune the magnetic properties of molecular multi-spin systems, thus, need to focus on controlling the magnitude of the exchange interaction. In this tutorial review, we outline the theoretical background of exchange coupling and provide an overview of different experimental and computational methods available for the determination of exchange coupling constants in the electronic ground and excited states of molecular materials. We conclude by discussing the current limitations and challenges in the determination of exchange coupling parameters in these materials.