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Multi-State Aromaticity: Aromatics in Both Ground and Lowest Excited States
1School of Chemistry, Chemical Engineering and Biotechnology, Nanyang Technological University, Singapore, 637371, Singapore.
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Aromaticity represents one of the most significant and widely applied concepts in modern chemistry. According to Hückel's rules, cyclic conjugated rings with [4n + 2] π electrons are aromatic in the ground state (S0) and anti-aromatic in the lowest excited state (S1/T1). Conversely, Baird's rule defines that cyclic molecules based on conjugated 4n π πelectrons exhibit anti-aromatic and aromatic properties in S0 and S1/T1, respectively. Do compounds showing aromaticity in both ground and lowest excited states─namely, multi-state aromaticity, exist? This review presents the recent advances in the area and uncovers the tricks that make multi-state aromaticity synthetically feasible.
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