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Torsional Bias as a Strategy To Tune Single-triplet Gaps in Organic Diradicals
Johns Hopkins Univ, Dept Chem, 3400 North Charles St, Baltimore, MD 21218 USA.
Univ Malaga, Dept Phys Chem, Campus Teatinos S-N, E-29071 Malaga, Spain.
Univ Malaga, Dept Phys Chem, Campus Teatinos S-N, E-29071 Malaga, Spain.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
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2018 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 23, p. 12148-12157Article in journal (Refereed) Published
Abstract [en]

Quinoidal compounds with proaromatic structures possess differing degrees of diradical character, where the open-shell diradical resonance form has restored aromaticity throughout the compound. Methods to tune the diradical character of these compounds have traditionally focused on altering the length and the molecular composition of the pi-conjugated backbones. However, other molecular design strategies to tune the singlet-triplet gap of pi-conjugated quinoidal molecules have not been extensively explored. We previously reported a strikingly small energy gap between the quinoidal and diradical states of a quinoidal small molecule containing methano[10]annulene (TMTQ) that was dictated in large part by the unusual aromaticity of the central annulene ring. Here, we report on two alkylated derivatives of TMTQthat present substantially different torsional biases to the planarity of the TMTQ pi-system. Using a combination of electronic and vibrational spectroscopies, magnetic measurements, and quantum chemical calculations, we demonstrate here how a steric effect rather than pi-electron compositional molecular engineering can dramatically narrow the singlet-triplet gap of a quinoidal compound to as small as -0.52 kcal/mol, determined experimentally. This study offers important insight for the continued development of open-shell diradical molecules that need not rely exclusively on the design of synthesis of new and complex conjugated systems.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC , 2018. Vol. 122, no 23, p. 12148-12157
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Physical Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-358520DOI: 10.1021/acs.jpcc.8b01905ISI: 000435611900003OAI: oai:DiVA.org:uu-358520DiVA, id: diva2:1244686
Funder
Carl Tryggers foundation , CTS 14:369Carl Tryggers foundation , CTS 17:347Available from: 2018-09-03 Created: 2018-09-03 Last updated: 2018-10-05Bibliographically approved

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Ottosson, Henrik

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