Air-stable radical polycyclic aromatic hydrogen-bonded organic frameworks

Abstract

Air-stable radical materials have emerged as promising candidates for next-generation electronic materials. Traditionally, constructing radical materials has required the intricate design and prolonged synthesis of radical building blocks. Herein, we have discovered a group of polycyclic aromatic monomers, previously considered to be air-unstable radicals, that can be oxidized to air-stable radical materials according to a post-synthetic protocol when they are incorporated into solid porous hydrogen-bonded organic frameworks (HOFs). The inherent porosity and crystallinity of HOFs facilitate extensive interactions with redox agents, such as tetravalent cerium(IV). These radical HOF materials exhibit high radical concentrations with paramagnetic behavior equivalent to two monomers sharing an unpaired electron. The HOFs can maintain their radical nature under ambient conditions on account of spin delocalization along the [π···π] stacked units. The radical formation transforms the HOFs from insulators to typical n-type semiconductors. This discovery opens up avenues for exploring stable radical materials with diverse applications.