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An Unusually Small Singlet–Triplet Gap in a Quinoidal 1,6‐Methano[10]annulene Resulting from Baird’s 4n π‐Electron Triplet Stabilization |
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| Authors: | Dr Benjamin C Streifel Dr José L Zafra Guzmán L Espejo Prof Carlos J Gómez‐García Prof Juan Casado Prof John D Tovar |
| Affiliation: | 1. Department of Chemistry, Johns Hopkins University, Baltimore MD, 21218 (USA);2. Department of Physical Chemistry, University of Málaga, Campus de Teatinos s/n, 29071 Málaga (Spain);3. Instituto de Ciencia Molecular, Universidad de Valencia, 46980 Paterna (Spain) |
| Abstract: | Within the continuum of π‐extended quinoidal electronic structures exist molecules that by design can support open‐shell diradical structures. The prevailing molecular design criteria for such structures involve proaromatic nature that evolves aromaticity in open‐shell diradical resonance structures. A new diradical species built upon a quinoidal methano10]annulene unit is synthesized and spectroscopically evaluated. The requisite intersystem crossing in the open‐shell structure is accompanied by structural reorganization from a contorted Möbius aromatic‐like shape in S0 to a more planar shape in the Hückel aromatic‐like T1. This stability was attributed to Baird’s Rule which dictates the aromaticity of 4n π‐electron triplet excited states. |
| Keywords: | annulenes aromaticity Baird’ s rule diradical species quinoidal structures |
