Stable Quadruple Helical Tetraradicaloid with Thermally Induced Intramolecular Magnetic Switching

We report an air-stable tetraradicaloid based on a rarely explored perylenequinonoid (PQ) core, namely, tetrabenzo-annulated tetracyclopenta[b,e, k,n]perylene (TBCP), which has a quadruple helical structure. As validated by X-ray crystallographic analysis and theoretical calculations, the nonplanar TBCP possesses unique hybrid resonance structures of two open-shell singlet diradicaloids. Remarkably, magnetic measurements reveal that TBCP in powder form shows unusual magnetic hysteresis upon heating followed by cooling, corresponding to interconversion of structure isomers with different magnetic properties. Such electronic properties can be rationalized as the response of structural changes to external thermal stimuli, accompanied by a subtle balance of two types of intramolecular magnetic interactions between four-site spin centers. The results provide a novel organic polyradicaloid as an unprecedented example of a functional material with the potential for intramolecular magnetic switching.