Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2019 Jan 7;24(1):201.
doi: 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

Hyomin Jin  1 , Seonah Kim  2 , Hye Jin Bae  3 , Ji Hye Lee  4 , Hyonseok Hwang  5 , Myung Hwan Park  6 , Kang Mun Lee  7
Affiliations

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

Hyomin Jin et al. Molecules. .

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.

Keywords: intramolecular charge transfer; o-carborane; radiative decay; structural fluctuation.

PubMed Disclaimer

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Synthetic procedure for o-carboranyl compounds (CB1, CB2, CB1B, and CB2B). Reaction conditions: (i) 1-hexyne, CuI, PdCl2(PPh3)2, NEt3/toluene, r.t., 24 h. (ii) Pd(PPh3)4, Na2CO3, THF/H2O (4:1, v/v), 80 °C, 24 h. (iii) B10H14, Et2S, toluene, 110 °C, 72 h. (iv) BBr3, (i-Pr)2NEt, DCM, r.t., 48 h. (v) AlMe3, toluene, r.t., 0.5 h.
Figure 2
Figure 2
X-ray crystal structures of CB2 (left) and CB2B (right) (50% thermal ellipsoids). H atoms are omitted for clarity.
Figure 3
Figure 3
(a) UV-vis absorption spectra in toluene (5.0 × 10−5 M). Photoluminescence (PL) spectra in toluene (5.0 × 10−5 M) at (b) 298 and (c) 77 K. (d) PL spectra in film state (poly(methylmethacrylate) (PMMA) film doped with 5 wt % o-carbonyl compound). Inset figures show the color of the emission of each state under UV irradiation (λex = 354 nm).
Figure 4
Figure 4
Relative energies of frontier molecular orbitals of o-carboranyl compounds at the first excited singlet state (S1) calculated by density functional theory (DFT) (isovalue = 0.04). The transition energy (in nm) was calculated at the TD-B3LYP/6-31G(d) level.
See this image and copyright information in PMC

References

    1. Spokoyny A.M. New ligand platforms featuring boron-rich clusters as organomimetic substituents. Pure Appl. Chem. 2013;85:903–919. doi: 10.1351/PAC-CON-13-01-13. - DOI - PMC - PubMed
    1. Bregadze V.I. Dicarba-closo-dodecaboranes C2B10H12 and their derivatives. Chem. Rev. 1992;92:209–223. doi: 10.1021/cr00010a002. - DOI
    1. González-Campo A., Juárez-Pérez E.J., Viñas C., Boury B., Sillanpää R., Kivekäs R., Núñez R. Carboranyl Substituted Siloxanes and Octasilsesquioxanes: Synthesis, Characterization, and Reactivity. Macromolecules. 2008;41:8458–8466. doi: 10.1021/ma801483c. - DOI
    1. Issa F., Kassiou M., Rendina L.M. Boron in Drug Discovery: Carboranes as Unique Pharmacophores in Biologically Active Compounds. Chem. Rev. 2011;111:5701–5722. doi: 10.1021/cr2000866. - DOI - PubMed
    1. Wee K.-R., Cho Y.-J., Jeong S., Kwon S., Lee J.-D., Suh I.-H., Kang S.O. Carborane-Based Optoelectronically Active Organic Molecules: Wide Band Gap Host Materials for Blue Phosphorescence. J. Am. Chem. Soc. 2012;134:17982–17990. doi: 10.1021/ja3066623. - DOI - PubMed