Can Baird's and Clar's Rules Combined Explain Triplet State Energies of Polycyclic Conjugated Hydrocarbons with Fused 4nπ- and (4n + 2)π-Rings?Show others and affiliations
2017 (English)In: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 82, no 12, p. 6327-6340Article in journal (Refereed) Published
Abstract [en]
Compounds that can be labeled as "aromatic chameleons" are π-conjugated compounds that are able to adjust their π-electron distributions so as to comply with the different rules of aromaticity in different electronic states. We used quantum chemical calculations to explore how the fusion of benzene rings onto aromatic chameleonic units represented by biphenylene, dibenzocyclooctatetraene, and dibenzo[a,e]pentalene modifies the first triplet excited states (T1) of the compounds. Decreases in T1 energies are observed when going from isomers with linear connectivity of the fused benzene rings to those with cis- or trans-bent connectivities. The T1 energies decreased down to those of the parent (isolated) 4nπ-electron units. Simultaneously, we observe an increased influence of triplet state aromaticity of the central 4n ring as given by Baird's rule and evidenced by geometric, magnetic, and electron density based aromaticity indices (HOMA, NICS-XY, ACID, and FLU). Because of an influence of triplet state aromaticity in the central 4nπ-electron units, the most stabilized compounds retain the triplet excitation in Baird π-quartets or octets, enabling the outer benzene rings to adapt closed-shell singlet Clar π-sextet character. Interestingly, the T1 energies go down as the total number of aromatic cycles within a molecule in the T1 state increases.
Place, publisher, year, edition, pages
American Chemical Society , 2017. Vol. 82, no 12, p. 6327-6340
Keywords [en]
Aromatization, Benzene, Electronic states, Electrons, Excited states, Isomers, Quantum chemistry, Aromaticities, Aromaticity indices, Closed shells, Electron distributions, Quantum chemical calculations, Triplet excitation, Triplet state, Triplet state energies, Quantum theory, hydrocarbon, polycyclic aromatic hydrocarbon derivative, Article, conjugation, electron, excitation, geometry, magnet
National Category
Organic Chemistry
Identifiers
URN: urn:nbn:se:ri:diva-57308DOI: 10.1021/acs.joc.7b00906Scopus ID: 2-s2.0-85020926872OAI: oai:DiVA.org:ri-57308DiVA, id: diva2:1616687
Note
Funding details: European Commission, EC; Funding details: Generalitat de Catalunya, 2014SGR931; Funding details: Ministerio de Economía y Competitividad, MINECO, CTQ2014-54306-P; Funding details: Institució Catalana de Recerca i Estudis Avançats, ICREA, 2014FI-B00429; Funding details: European Regional Development Fund, FEDER; Funding details: National Supercomputer Centre, Linköpings Universitet, NSC, SNIC-2016-1-74, SNIC-2016/7-21; Funding text 1: The Swedish Infrastructure for Computing (SNIC) at NSC and UPPMAX (Grants SNIC-2016-1-74 and SNIC-2016/7-21) are greatly acknowledged for the generous allotment of computer time. M.S. and O.E.B. acknowledge the Ministerio de Economia y Competitividad (MINECO) of Spain (Project CTQ2014-54306-P), the Generalitat de Catalunya (Project 2014SGR931, Xarxa de Referencia en Quimica Teorica i Computacional, ICREA Academia 2014 Prize for M.S. and Grant No. 2014FI-B00429 to O.E.B.), and the EU under the FEDER GrantUNGI10-4E-801 (European Fund for Regional Development).
2021-12-032021-12-032021-12-15Bibliographically approved