Control of spin–spin exchange interactions in polynitroxides through inclusion within c-cyclodextrin3

Supramolecular interactions of polynitroxides with c-cyclodextrin (c-CD) were used to control intramolecular electron spin–spin exchange couplings in these stable radicals. In the absence of c-CD, the binitroxide T2 and trinitroxide T3 showed strong spin–spin coupling as evidenced by the high exchange coupling constant of J = 120 MHz for T2 in its EPR spectra. Host/guest complexes are formed upon addition of c-CD to the polynitroxides where the nitroxide moiety interacts with the c-CD cavity, which causes suppression of spin exchange. By variation of the host/guest ratio, the nature of a trinitroxide spin system can be tuned from a three-spin to a two-spin to a one-spin system. In addition to the host/guest ratio, the spin exchange coupling can also be tuned by temperature, which shifts the equilibrium between CD-encapsulated nitroxides and free nitroxides.