Details

Autor(en) / Beteiligte

• Streifel, Benjamin C.
• Zafra, José L.
• Espejo, Guzmán L.
• Gómez-García, Carlos J.
• Casado, Juan
• Tovar, John D.

Titel

An Unusually Small Singlet-Triplet Gap in a Quinoidal 1,6-Methano[10]annulene Resulting from Baird's 4n π-Electron Triplet Stabilization

Ist Teil von

• Angewandte Chemie (International ed.), 2015-05, Vol.54 (20), p.5888-5893

Ort / Verlag

Weinheim: WILEY-VCH Verlag

Erscheinungsjahr

2015

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• 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 methano[10]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. Topological chameleon: A small ΔEST gap in a 1,6‐methano[10]annulene‐based tetracyanoquinodimethane results from an antiaromatic (but Möbius aromatic‐like) singlet ground electronic state based on a [10]annulene dication and a Hückel aromatic‐like triplet excited state. The small gap is a result of the net stabilization of the triplet excited state in accordance with Baird's rule.