Self-Assembled Radicals

Switching of the spin-spin interactions in organic radicals is of particular interest for the development of molecular-scale magnetic devices and guest-tunable spin materials, such as new spin probe reagents and MRI contrast agents. Whereas spin-spin coupling via covalent bonds has been well studied, strong through-space interactions between organic radicals are more difficult to achieve because unpaired spins have to be located at a short distance. Here, we report some example of reversible introduction/suppression of spin-spin exchange in a self-recognising and self-assembling persistent radical controlled by external triggers. Non covalent assemblies play also an important role in stabilizing radicals life times leading to EPR signal enhancement and in increasing the partial resistance of the radical against biomimetic reductive conditions. It will be shown that EPR study of small paramagnetic probes included inside macrocyclic cavities represents a powerful tool for directly observing such type of non covalent aggregates in aqueous solutions.