Spectroscopic, structural, computational and (spectro)electrochemical studies of icosahedral carboranes bearing fluorinated aryl groups

Tricas, Hugo; Colón, Marta; Ellis, David; Macgregor, Stuart A.; McKay, David; Rosair, Georgina M.; Welch, Alan J.; Glukhov, Ivan V.; Rossi, Fulvio; Laschi, Franco; Zanello, Piero

doi:10.1039/c0dt01798a

Cited by 38 publications

(30 citation statements)

References 57 publications

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“…These ICT states are notable for their flexible carboranyl C−C bond, which can vibrate and relax non‐radiatively, or radiatively with a highly red‐shifted emission 24, 25, 26, 27, 28, 29, 30. Such systems often exhibit aggregation‐induced emission (AIE),13, 14, 15, 17, 18, 19, 20, 22, 31, 32 that is, in an aggregated state where molecular motion is restricted, non‐radiative relaxation pathways from the ICT state are inhibited, leading to a significant increase in emission efficiency.…”

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“…When di‐substituted with two naphthyl donor groups, the imposed proximity of the aryl systems allows for an overlap of the aromatic wavefunctions, such that dimerization occurs readily when one naphthalene is in the excited state 27. In other cases where o ‐carborane has been attached to pyrene, the bulky carborane moiety was found not to inhibit the π–π stacking required for pyrene excimer formation 19, 20, 23.…”

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Carborane‐Induced Excimer Emission of Severely Twisted Bis‐o‐Carboranyl Chrysene

et al. 2018

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The synthesis of a highly twisted chrysene derivative incorporating two electron deficient o‐carboranyl groups is reported. The molecule exhibits a complex, excitation‐dependent photoluminescence, including aggregation‐induced emission (AIE) with good quantum efficiency and an exceptionally long singlet excited state lifetime. Through a combination of detailed optical studies and theoretical calculations, the excited state species are identified, including an unusual excimer induced by the presence of o‐carborane. This is the first time that o‐carborane has been shown to induce excimer formation ab initio, as well as the first observation of excimer emission by a chrysene‐based small molecule in solution. Bis‐o‐carboranyl chrysene is thus an initial member of a new family of o‐carboranyl phenacenes exhibiting a novel architecture for highly‐efficient multi‐luminescent fluorophores.

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Carborane‐Induced Excimer Emission of Severely Twisted Bis‐o‐Carboranyl Chrysene

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“…With regard to the many closo-and nido-carboranes, carborane-based radical anions featuring a 2n+3 electron count are somewhat rare. [8][9][10][11][12][13] In a more recent report on the photophysics of ortho-carboranes with donating arylcarbazolyl substituents it was suggested that the species in their excited states consist of carbazolyl radical cations and radical cluster anions. This assumption was based on absorption spectroscopy where a transient band at 415 nm with a similar spectral profile as the corresponding radical anion was observed 13 (Scheme 2).…”

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Electrochemical and spectroelectrochemical studies of C-benzodiazaborolyl-ortho-carboranes

et al. 2013

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. (2013) 'Electrochemical and spectroelectrochemical studies of C-benzodiazaborolyl-ortho-carboranes.', Dalton transactions., 42 (6). pp. 2266-2281.Further information on publisher's website:http://dx.doi.org/10.1039/c2dt32378hPublisher's copyright statement: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. AbstractFifteen C-diazaborolyl-ortho-carboranes, 1-R ′ -2-R ″ -1,2-C 2 B 10 H 10 , where R′ represents the groups 2-(1,3-Et 2 -1,3,2-N 2 BC 6 H 4 )-, 2-(1,3-Ph 2 -1,3,2-N 2 BC 6 H 4 )-, 2-(1,3-Ph 2 -5,6-Me 2 -1,3,2-N 2 BC 6 H 2 )-, 2-(1,3-i Pr 2 -1,3,2-N 2 BC 6 H 4 )-, and 2-(1,3,2-N 2 BC 6 H 6 )-and where R ″ equals to H, Me, Ph, t Bu or SiMe 3 were synthesized. Cyclovoltammetric studies of the compounds showed irreversible oxidation waves which are caused by the oxidation of the heterocycle. Those C-diazaborolyl-ortho-carboranes with Ph, tBu SiMe 3 substituents at the adjacent C-atom of the cage displayed two one-electron reduction waves reflecting the formation of stable radical monoanions with unusual (2n+3) skeletal electron counts. The geometries of these anions were determined by combinations of infrared, UV-visible spectroelectrochemical and computational studies. Additionally the structures of seven new C-diazaborolyl-ortho-carboranes and one new 2-bromo-1,3,2-benzodiazaborole were determined by X-ray crystallography and compared with previously obtained structures.

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“…When di-substituted with two naphthyl donor groups,t he imposed proximity of the aryl systems allows for an overlap of the aromatic wavefunctions, such that dimerization occurs readily when one naphthalene is in the excited state. [27] In other cases where o-carborane has been attached to pyrene,t he bulky carborane moiety was found not to inhibit the p-p stacking required for pyrene excimer formation. [19,20,23] In these few cases,h owever, the carborane can be considered essentially electronically isolated from the aromatic excimer species,s ave for some electron-withdrawing inductive effects.…”

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“…Ak ey property of o-carborane is its ability to accept an excited charge via intramolecular charge transfer (ICT) from an aryl donor group,o ccurring most efficiently when the carborane has its C À Cb ond perpendicular to the aromatic plane.T hese ICT states are notable for their flexible carboranyl CÀCb ond, which can vibrate and relax nonradiatively,o rr adiatively with ah ighly red-shifted emission. [24][25][26][27][28][29][30] Such systems often exhibit aggregation-induced emission (AIE), [13-15,17-20, 22, 31, 32] that is,i na na ggregated state where molecular motion is restricted, non-radiative relaxation pathways from the ICT state are inhibited, leading to as ignificant increase in emission efficiency. It has been demonstrated that incorporation of bulky carboranes on the long edges of linear acenes creates al arge steric hinderance between the carboranes and proximal protons,l eading to aconsiderable deformation of the ring system.…”

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Carborane‐Induced Excimer Emission of Severely Twisted Bis‐o‐Carboranyl Chrysene

et al. 2018

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The synthesis of ahighly twisted chrysenederivative incorporating two electron deficient o-carboranyl groups is reported. The molecule exhibits ac omplex, excitation-dependent photoluminescence,i ncluding aggregation-induced emission (AIE) with good quantum efficiency and an exceptionally long singlet excited state lifetime.T hrough ac ombination of detailed optical studies and theoretical calculations,the excited state species are identified, including an unusual excimer induced by the presence of o-carborane.T his is the first time that o-carborane has been shown to induce excimer formation ab initio,aswell as the first observation of excimer emission by achrysene-based small molecule in solution. Bis-o-carboranyl chrysene is thus an initial member of an ew family of ocarboranyl phenacenes exhibiting an ovel architecture for highly-efficient multi-luminescent fluorophores.Atfirst glance,b ulky boron-rich spheroids appear to be an anathema to the two-dimensional, p-conjugated world of organic electronics.O nt he contrary,m otivated by their unique three-dimensional s-delocalization, electron-withdrawing ability (when substituted at the carbon vertices), [1] and high thermal and chemical stability,c arboranes,a nd principally o-carborane (C 2 B 10 H 12 ), have now been incorporated in aw ide range of molecular and polymeric semiconductors. Ak ey property of o-carborane is its ability to accept an excited charge via intramolecular charge transfer (ICT) from an aryl donor group,o ccurring most efficiently when the carborane has its C À Cb ond perpendicular to the aromatic plane.T hese ICT states are notable for their flexible carboranyl CÀCb ond, which can vibrate and relax nonradiatively,o rr adiatively with ah ighly red-shifted emission. [24][25][26][27][28][29][30] Such systems often exhibit aggregation-induced emission (AIE), [13-15,17-20, 22, 31, 32] that is,i na na ggregated state where molecular motion is restricted, non-radiative relaxation pathways from the ICT state are inhibited, leading to as ignificant increase in emission efficiency. It has been demonstrated that incorporation of bulky carboranes on the long edges of linear acenes creates al arge steric hinderance between the carboranes and proximal protons,l eading to aconsiderable deformation of the ring system. [15][16][17] With this comes alarge increase in the carborane rotation barrier, and generally am ore rigid structure;aproperty known to be useful for AIE.o-Carborane has also been shown, to av ery limited extent, to aid excimer emission. When di-substituted with two naphthyl donor groups,t he imposed proximity of the aryl systems allows for an overlap of the aromatic wavefunctions, such that dimerization occurs readily when one naphthalene is in the excited state.[27] In other cases where o-carborane has been attached to pyrene,t he bulky carborane moiety was found not to inhibit the p-p stacking required for pyrene excimer formation. [19,20,23] In these few cases,h owever, the carborane can be considered essentially electronica...

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Spectroscopic, structural, computational and (spectro)electrochemical studies of icosahedral carboranes bearing fluorinated aryl groups

Cited by 38 publications

References 57 publications

Carborane‐Induced Excimer Emission of Severely Twisted Bis‐o‐Carboranyl Chrysene

Carborane‐Induced Excimer Emission of Severely Twisted Bis‐o‐Carboranyl Chrysene

Electrochemical and spectroelectrochemical studies of C-benzodiazaborolyl-ortho-carboranes

Carborane‐Induced Excimer Emission of Severely Twisted Bis‐o‐Carboranyl Chrysene

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