Coulombic-enhanced hetero radical pairing interactions

Spin-spin interactions between two identical aromatic radicals have been studied extensively and utilized to establish supramolecular recognition. Here we report that spin-pairing interactions could also take place between two different pi-electron radicals, namely a bipyridinium radical cation (BPY+center dot) and a naphthalene-1,8:4,5-bis(dicarboximide) radical anion (NDI-center dot). The occurrence of this type of previously unreported hetero radical-pairing interactions is attributed to enhancement effect of Coulombic attraction between these two radicals bearing opposite charges. The Coulombic-enhanced hetero radical pairing interactions are employed to drive host-guest recognition, as well as the reversible switching of a bistable [2]rotaxane.