Modulating spin delocalization in phenoxyl radicals conjugated with heterocycles

Phenoxyl radicals were synthesized having heterocyclic substituents in the 4-position. Electron spin resonance spectroscopy shows spin density can be modulated by delocalization onto the heterocycle structure, to the extent that some of the largest spin density bearing sites in 3 and 4 lies in the heterocycle, not in the phenoxyl ring.