Helicene Radicals: Molecules Bearing a Combination of Helical Chirality and Unpaired Electron Spin. Issue 9 (16th September 2020) - Tani, Fumito
Abstract: Chiral helicenes that have helical π‐conjugated frameworks comprised of ortho ‐fused aromatic rings have been intensively investigated for several decades owing to their attractive properties and high potential for a variety of applications. In contrast, studies concerning helicene radicals (open‐shell helicenes) formed by redox reactions have been severely limited due to inherent high reactivity of organic radicals. However, open‐shell helicenes possessing a combination of chirality and unpaired electron spin(s) delocalized on helical π‐conjugated orbital(s) are promising for novel synergic magnetic functions. Recently, several kinds of isolable air‐stable helicene radicals have been prepared to enable their detailed analysis of the crystal structures and physicochemical properties. This Minireview describes the recent advances and future prospects of organic‐based helicene radicals categorized into three groups: 1) ionic radicals, 2) neutral radicals, and 3) diradicals. Abstract : Helicene radicals that realize both helical chirality and unpaired electron spin are intriguing components for novel synergic functions based on their electronic, photonic, and magnetic properties. This Minireview presents the synthesis, structures, and physicochemical properties of organic‐based helicene radicals to provide valuable knowledge for their further developments.