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Molecules 2019, 24(1), 201; https://doi.org/10.3390/molecules24010201

Effect of Planarity of Aromatic Rings Appended to o-Carborane on Photophysical Properties: A Series of o-Carboranyl Compounds Based on 2-Phenylpyridine- and 2-(Benzo[b]thiophen-2-yl)pyridine

1
Department of Chemistry, Institute for Molecular Science and Fusion Technology, Kangwon National University, Chuncheon 24341, Korea
2
Department of Chemistry, KAIST, Daejeon 34142, Korea
3
Department of Chemistry Education, Chungbuk National University, Cheongju 28644, Korea
These authors contributed equally to this work.
*
Authors to whom correspondence should be addressed.
Received: 5 December 2018 / Revised: 31 December 2018 / Accepted: 3 January 2019 / Published: 7 January 2019
(This article belongs to the Special Issue Advances in Materials Derived from Polyhedral Boron Clusters)
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Abstract

Herein, we investigated the effect of ring planarity by fully characterizing four pyridine-based o-carboranyl compounds. o-Carborane was introduced to the C4 position of the pyridine rings of 2-phenylpyridine and 2-(benzo[b]thiophen-2-yl)pyridine (CB1 and CB2, respectively), and the compounds were subsequently borylated to obtain the corresponding CN-chelated compounds CB1B and CB2B. Single-crystal X-ray diffraction analysis of the molecular structures of CB2 and CB2B confirmed that o-carborane is appended to the aryl moiety. In photoluminescence experiments, CB2, but not CB1, showed an intense emission, assignable to intramolecular charge transfer (ICT) transition between the aryl and o-carborane moieties, in both solution and film states. On the other hand, in both solution and film states, CB1B and CB2B demonstrated a strong emission, originating from π-π * transition in the aryl groups, that tailed off to 650 nm owing to the ICT transition. All intramolecular electronic transitions in these o-carboranyl compounds were verified by theoretical calculations. These results distinctly suggest that the planarity of the aryl groups have a decisive effect on the efficiency of the radiative decay due to the ICT transition. View Full-Text
Keywords: o-carborane; intramolecular charge transfer; structural fluctuation; radiative decay o-carborane; intramolecular charge transfer; structural fluctuation; radiative decay
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Jin, H.; Kim, S.; Bae, H.J.; Lee, J.H.; Hwang, H.; Park, M.H.; Lee, K.M. Effect of Planarity of Aromatic Rings Appended to o-Carborane on Photophysical Properties: A Series of o-Carboranyl Compounds Based on 2-Phenylpyridine- and 2-(Benzo[b]thiophen-2-yl)pyridine. Molecules 2019, 24, 201.

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