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Organic photochemistry

Exciting excited-state aromaticity

Nature Chemistry volume 4, pages 969–971 (2012)Cite this article

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In 1972, Baird published rules describing aromaticity and antiaromaticity in the lowest triplet excited states of annulenes. The fortieth anniversary of Baird's rules — which are the reverse of Hückel's rules for aromaticity and antiaromaticity in the ground state — ought to be celebrated before 2012 comes to an end.

Aromaticity is a key concept in organic chemistry, and can be used to explain a range of properties and processes. The most common form of aromaticity is that of planar fully π-conjugated (hetero)-annulenes, which comply with Hückel's 4n+2 π-electron rule; several other forms also exist, however, such as Möbius and spherical aromaticity. Forty years ago, Colin Baird published rules, developed using perturbation molecular orbital theory, that apply to aromaticity and antiaromaticity in the lowest triplet excited state1.

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Figure 1: Excited-state aromaticity.

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  1. Henrik Ottosson is in the Department of Chemistry – BMC, Uppsala University, Box 5 76, 751 23 Uppsala, Sweden,

    Henrik Ottosson

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  1. Henrik Ottosson
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Correspondence to Henrik Ottosson.

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Ottosson, H. Exciting excited-state aromaticity. Nature Chem 4, 969–971 (2012). https://doi.org/10.1038/nchem.1518

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