A Study on the Origin of the Radical in Fullerene and Graphene

We reported the electron spin resonance (ESR) signal in neutral low band gap semiconductors and C₆₀ in the Li Y., J. Phys. Chem. C 2017, 121, 8579–8588. Herein, further investigation on the origin of the radical of fullerene and its derivatives was conducted, and we proposed an open-shell diradical ground state of C₆₀ and its derivatives for the first time in this work. The radicals of fullerene are usually acknowledged as their impurities or radical cations/anions. Diradical ground states in polycyclic aromatic hydrocarbons including the zethrene family and others with fused five-/six-member rings motivate us to investigate the other potential origin of the radicals of fullerene. C₆₀ has 1812 sets of resonance structures, which is the key factor to stabilize its diradicals. Numerous sets of resonance structures and excellent electron delocalization of graphene play as the key factors in stabilizing its diradicals. The previously claimed ESR-silent C₆₀ after sublimation is due to the four-member ring formation and further self-polymerization. C₆₀ with higher purity exhibited a higher ESR signal intensity, and this further confirmed that the ESR might not come from the impurity. Previously published work confirmed the radical is not from a radical cation/anion; our proposal of the radical of fullerene is reasonable in understanding its basic properties. Moreover, the radical origin of graphene is also proposed similarly.