Please use this identifier to cite or link to this item: https://hdl.handle.net/10356/87937
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dc.contributor.authorLuo, Dingen
dc.contributor.authorLee, Sangsuen
dc.contributor.authorZheng, Binen
dc.contributor.authorSun, Zheen
dc.contributor.authorZeng, Wangdongen
dc.contributor.authorHuang, Kuo-Weien
dc.contributor.authorFurukawa, Koen
dc.contributor.authorKim, Donghoen
dc.contributor.authorWebster, Richard D.en
dc.contributor.authorWu, Jishanen
dc.date.accessioned2018-08-20T02:12:58Zen
dc.date.accessioned2019-12-06T16:52:30Z-
dc.date.available2018-08-20T02:12:58Zen
dc.date.available2019-12-06T16:52:30Z-
dc.date.issued2014en
dc.identifier.citationLuo, D., Lee, S., Zheng, B., Sun, Z., Zeng, W., Huang, K. W., . . . Wu, J. (2014). Indolo [2,3-b] carbazoles with tunable ground states : how Clar's aromatic sextet determines the singlet biradical character. Chemical Science, 5(12), 4944-4952. doi:10.1039/C4SC01843Een
dc.identifier.issn2041-6520en
dc.identifier.urihttps://hdl.handle.net/10356/87937-
dc.description.abstractPolycyclic hydrocarbons (PHs) with a singlet biradical ground state have recently attracted extensive interest in physical organic chemistry and materials science. Replacing the carbon radical center in the open-shell PHs with a more electronegative nitrogen atom is expected to result in the more stable aminyl radical. In this work, two kinetically blocked stable/persistent derivatives (1 and 2) of indolo[2,3-b]carbazole, an isoelectronic structure of the known indeno[2,1-b]fluorene, were synthesized and showed different ground states. Based on variable-temperature NMR/ESR measurements and density functional theory calculations, it was found that the indolo[2,3-b]carbazole derivative 1 is a persistent singlet biradical in the ground state with a moderate biradical character (y0 = 0.269) and a small singlet–triplet energy gap (ΔES–T ≅ −1.78 kcal mol−1), while the more extended dibenzo-indolo[2,3-b]carbazole 2 exhibits a quinoidal closed-shell ground state. The difference can be explained by considering the number of aromatic sextet rings gained from the closed-shell to the open-shell biradical resonance form, that is to say, two for compound 1 and one for compound 2, which determines their different biradical characters. The optical and electronic properties of 2 and the corresponding aromatic precursors were investigated by one-photon absorption, transient absorption and two-photon absorption (TPA) spectroscopies and electrochemistry. Amphoteric redox behaviour, a short excited lifetime and a moderate TPA cross section were observed for 2, which can be correlated to its antiaromaticity and small biradical character. Compound 2 showed high reactivity to protic solvents due to its extremely low-lying LUMO energy level. Unusual oxidative dimerization was also observed for the unblocked dihydro-indolo[2,3-b]carbazole precursors 6 and 11. Our studies shed light on the rational design of persistent aminyl biradicals with tunable properties in the future.en
dc.description.sponsorshipASTAR (Agency for Sci., Tech. and Research, S’pore)en
dc.description.sponsorshipMOE (Min. of Education, S’pore)en
dc.language.isoenen
dc.relation.ispartofseriesChemical Scienceen
dc.subjectGround Stateen
dc.subjectPolycyclic Aromatic Hydrocarbonsen
dc.subjectDRNTU::Science::Chemistryen
dc.titleIndolo [2,3-b] carbazoles with tunable ground states : how Clar's aromatic sextet determines the singlet biradical characteren
dc.typeJournal Articleen
dc.contributor.schoolSchool of Physical and Mathematical Sciencesen
dc.identifier.doi10.1039/C4SC01843Een
dc.description.versionAccepted versionen
item.grantfulltextnone-
item.fulltextNo Fulltext-
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