Air Stable Chalcogen-Doped Rubicenes with Diradical Character

Abstract

Air stable diradicaloid polycyclic aromatic hydrocarbon (PAH) materials possess unique electronic and magnetic properties for various applications. In general, long conjugated distances between two radical centers are required to improve the air stability, thereby complicating the synthetic procedures. Herein, the chalcogen containing rubicenes (O-, S-, and Se-rubicenes) were systematically investigated to understand the chalcogen effects on chalcogen–rubicene physicochemical properties. Impressively, these rubicenes presented unprecedented diradical character within one simple benzene ring and excellent air stabilities. Their diradical character were manifested by single-crystal X-ray studies, variable-temperature nuclear magnetic resonance, and electron spin resonance. Furthermore, the nucleus independent chemical shifts and the anisotropy of the induced current density calculations revealed that the formation of diradical was caused by a pro-aromaticity driving force. Importantly, the diradical character of rubicenes are visualized by Fractional Occupation Number Weighted Electron Density (FOD) plots, which present high NFOD values from 1.651 to 1.830. This contribution provided distinctive insights into the structure and property relationship of PAH diradicals.