Quantitative Mono‐Formation and Crystallographic Characterization of Pyrazole‐ and Pyrrole‐Ring Fused Derivatives of C₆₀

Abstract

Nitrogen‐heterocyclic fullerene derivatives have received great interest in the past years due to their potential biological activities and optical properties. Herein, we report a quantitative mono‐formation of the pyrazole‐ and pyrrole‐ring fused derivatives of fullerene C60, i.e., C60 (C13N2H10) (3) and C60 (C9NH11) (4), from the respective reactions between C60 and diphenylnitrilimine (1) and N‐benzylazomethine ylide (2). Single‐crystal X‐ray diffraction (XRD) crystallographic results unambiguously confirm the formation of [6,6]‐closed derivatives (3 and 4). Interestingly, the intermolecular π–π interactions between the phenyl groups and C60 spheres are observed in the crystal of 3, but they are absent from 4, indicating that the number of the external phenyl groups has an important influence on the stacking pattern of derivatives during crystallization. Electrochemical results show that the reduction potentials of 3 are positively shifted compared with the corresponding values of pristine C60, while the reduction potentials of 4 are all cathodically shifted, revealing the redox processes of C60 can be selectively modulated by changing the structures of the addends. Notably, our theoretical results demonstrate that the quantitative formation of merely one mono‐adduct without any bis‐ or multi‐adducts detected in both reactions is a direct result from the steric hindrance of the existing bulky pyrazole‐ or pyrrole‐ring moiety on the C60 cage. This work thus presents a quantitative way for the mono‐formation of the pyrrole‐ and pyrazole‐ring fused derivatives of C60, which are potentially useful as organic photovoltaic devices and biological reagents.