Synthesis and Properties of Naphtho‐fused Fluorenyl Radical

Comprehensive Summary Open‐shell graphene fragments (OGFs) with non‐benzenoid topologies are attracting increasing attention due to their potential applications in organic light‐emitting diodes (OLEDs) and organic radical conductors. Herein, we report the synthesis of an air‐stable fluorenyl radical derivative ( AR1 ) containing a seven‐membered ring, achieving thermodynamic stabilization through the fusion of a naphthalene ring around its periphery and anthracene substituent. The half‐life times ( τ 1/2 ) of AR1 in air‐saturated solution is 71.9 h. The high stability was ascribed to kinetic blocking of reactive sites with high spin densities. The geometric and electronic structures of AR1 were systematically studied by combining various experimental methods and density functional theory (DFT) calculations, which include X‐ray crystallographic analysis, electron spin resonance (ESR), cyclic voltammetry, and UV−vis−NIR measurements.