Mechanical Strain-Controlled Aromaticity in Cyclo[n]Carbons

Abstract

Cyclocarbons have unique electronic and mechanical properties, but their extreme reactivity makes experimental studies and practical applications highly challenging. In this work, we use molecular modeling to investigate how mechanical strain, including uniaxial tension and radial contraction/expansion, affects the aromaticity of C₁₆ and C₁₈cyclocarbons. Aromaticity was evaluated using magnetic (NICS, GIMIC) and electronic (π-EDDB, AV1245) indices to provide a comprehensive assessment. Our results show that uniaxial tension slightly reduces the (anti)aromaticity of both cyclocarbons, with C₁₆becoming less antiaromatic and C₁₈ less aromatic. Radial expansion leads to almost complete loss of aromaticity, regardless of the initial electronic nature of the cyclocarbon. In turn, radial contraction appears to be an effective approach to enhance electronic delocalization in cyclocarbons, with a particularly notable effect for C₁₈. One of the most significant findings is that an 8% radial contraction transforms moderately aromatic C₁₈into a highly aromatic system with fully equalized bond lengths, offering a potential strategy for designing more stable cyclocarbon systems within mechanically strained architectures.