Interesting Aromaticity of Franck–Condon Excited States of Cyclo[16]Carbon

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Inspired by the realization of cyclo[16]carbon (C16) and driven by curiosity about its properties in excited states, a comprehensive theoretical study was conducted on the aromatic characteristics in the Franck–Condon states of C16. This work demonstrates that at the ground‐state (S0 state) geometry, C16 exhibits aromaticity not only in the triplet states (T1(in→out), T2(out→out), and T3(in→in)), but also more prominently in the quintet state (Q1 state), and different electronic transition modes result in different essential sources of aromaticity for each excited state. Quantitatively, C16 is about three times more aromatic in the quintet state than in the triplet states. These conclusions are supported by multiple robust indicators such as atomic force, induced current, and magnetic shielding, from qualitative, quantitative, and graphical perspectives.