Open-shell molecules, such as radicals bearing unpaired electrons, are typically highly reactive and unstable species. However, with appropriate stabilization strategies—such as steric protection around the radical center or delocalization of the unpaired electron—these species can be rendered sufficiently stable to handle under ambient conditions, much like conventional organic compounds. Owing to their singly occupied molecular orbitals (SOMOs), open-shell molecules can readily participate in electron transfer processes, leading to various electronic functions such as electrical conductivity, organic battery applications, and redox catalysis.

Focusing on the unique electronic structures of radicals, our group has been developing functional molecules based on stable nitroxyl diradicals. Specifically, we are exploring multistep redox behavior and near-infrared (NIR) absorption arising from complexation between nitroxyl radicals and boron centers. In addition, we have enhanced the electron-accepting properties and red-shifted the emission wavelengths of HTTM-type radicals by π-extension of their peripheral structures.