Stable Cycloparaphenylene Diradical Dications with Macrocyclic Aromaticity

Comprehensive Summary Solid‐state structures and aromaticity of open‐shell cycloparaphenylene (CPP) dications remain elusive. This work reports the first isolation of open‐shell cycloparaphenylene dications [9]CPP 2•2+ and [11]CPP 2•2+ through weakly coordinating anion‐stabilized oxidation. X‐ray crystallography confirms radially oriented π‐delocalization, while EPR/SQUID analyses reveal antiferromagnetic coupling in open‐shell singlet ground states with significant diradical character. Bidirectional aromaticity modulation emerges upon oxidation: diminished local benzene character versus enhanced global in‐plane aromaticity, with macrocycle size governing diradical stability (Δ E OS‐T , –3.11, –1.30, –0.99 kcal·mol –1 for [9]CPP 2•2+ , [10]CPP 2•2+ and [11]CPP 2•2+ , respectively). Remarkably, size expansion preserves local aromaticity while reducing macrocyclic aromaticity, demonstrating electronic control over geometric constraints. These 3 D spin‐delocalized systems bridge Hückel aromaticity with curved π‐topology, offering design principles for carbon nanotube‐inspired organic spintronics and molecular multielectron storage architectures.