Strain-Induced Quinoidal Character in a Carbon Nanoring Embedding Anthracene Units

We report a carbon nanoring, [2.2]cyclo(9,10)anthrylene-paraphenylene ([2.2]CAPP), featuring alternating anthracene and phenylene units within a [4]cycloparaphenylene (CPP) framework. The molecule was synthesized via a six-step metal-free route and structurally characterized by single-crystal X-ray diffraction. The high ring strain induces significant distortion in the anthracene units, resulting in a quinoidal electronic structure with a suppressed aromaticity. Despite possessing a 16π-electron conjugation pathway, no global antiaromaticity was observed. This work demonstrates that strain engineering in carbon nanorings enables control over the aromaticity and open-shell character through rational molecular design.