Persistent and Stable Organic Radicals: Design, Synthesis, and Applications

Open-shell radicals are usually thermodynamically and kinetically unstable due to their incompletely satisfied valency. However, the rapid development of radical chemistry in the past 100 years has demonstrated the possibility to prepare persistent and even stable radicals through rational design and appropriated chemical constructions. The existence of unpaired electrons of open-shell materials endows them with some unique physicochemical properties, which are difficult to be achieved in well-studied, closed-shell materials. This critical review summarizes some typical persistent and stable organic radicals, together with the presentations of their chemical synthesis and physicochemical properties. Furthermore, the up-to-date practical applications in magnetic, electronic, optoelectronic, and biologic fields based on functional organic radicals are presented. Finally, we carefully revise the critical limitations and challenges in radical chemistry and material functionalization, covering some core issues, including stability and commercialization perspectives, that need to be systematically considered in future.