DOI: 10.1002/anie.201101013
Liquid Crystals
Complementary Hydrogen Bonding Between a Clicked C3-Symmetric
Triazole Derivative and Carboxylic Acids for Columnar Liquid-
Crystalline Assemblies**
Mi-Hee Ryu, Jin-Woo Choi, Ho-Joong Kim, Noejung Park,* and Byoung-Ki Cho*
Click chemistry has received much attention in organic and
polymeric materials chemistry, because it can provide a very
efficient synthetic pathway for designing soft materials.[1] To
date, click chemistry has been mostly utilized to simply bridge
organic building units into more complex architectures, such
as dendrimers, block copolymers, and cyclic compounds.[2]
However, more attention is now paid to the functionality of
click chemistry, and particularly in the use of the resulting
triazole ring. As an interesting example, several research
groups recently investigated the anion-binding properties of
triazole derivatives, although some research regarding metal
coordination were also reported.[3] Craig et al. demonstrated
that aryl triazole based oligomers can bind anions by utilizing
the electropositive CH group of the triazole group.[4] Con-
temporaneously, Hecht and Meudtner reported an unprece-
dented helix inversion in response to halide ions in triazole-
linked foldamers,[5] and Flood and Li observed a strong,
selective affinity of shape-persisted triazolophanes for chlo-
ride ions.[6] Such an anion-binding capability of clicked
triazole-based compounds can be understood as privileged
hydrogen bonding (H-bonding) between the anion and the
CH group of the triazole ring.
design of discotic LCs can be accomplished by supramolec-
ular approaches. Among the possible non-covalent strategies,
molecular recognition processes involving H-bonding inter-
actions could be the most efficient way to build a rigid discotic
mesogen by considering bonding directionality and
strength.[8]
In this regard, it would be interesting to design an
H-bonding motif using a clicked triazole derivative for the
construction of discotic LC materials. Considering the
H-bonding capability of the triazole ring toward anions, we
thought that the electropositive character of triazole hydro-
gen could allow an H-bonding formation with other
H-acceptors, such as carbonyl and imidazole groups.[9]
Herein, we present novel H-bonded complexes (HBCs)
consisting of a clicked C3-symmetric 1,3,5-tris(1-alkyl-1H-
1,2,3-triazol-4-yl)benzene (TTB) unit with 3,4,5-trioctyloxy-
benzoic acids (TBAs) in a 1:3 stoichiometry (Figure 1).
Taking into account the core structure of HBC, we suggest
that the nitrogen atom in TTB can be an H-acceptor with
respect to the donor from the terminal hydroxy group in TBA.
The corresponding H-bonding is assigned as OHc···N. The
aromatic hydrogen atoms in the triazolyl and benzenyl groups
of TTB can also form H-bonding pairs with the carbonyl
oxygen atom in TBA (depicted by CHa···O and CHb···O in
Figure 1b). Owing to these complementary H-bonding inter-
actions and the 1:3 stoichiometry, we intuitively thought that
the HBC complexes would be conformationally rigidified,
leading to supramolecular discs for the columnar stacking;
any other stoichiometry is less likely to afford this organ-
ization.
To confirm the aforementioned conjectures, we initially
performed the first-principles density functional calculations.
We used the Gaussian03 package, the PBE-type gradient-
corrected functional, and the B3LYP hybrid functional. The
cc-pVDZ basis set was used with the counterpoise correc-
tion.[10] The counterpoise-corrected binding energy between
TTB and TBA was found to be 57.9 (48.2) kJmolÀ1 when the
PBE (B3LYP) functional was employed. This result confirms
the known features of the PBE functional, which tends to
overestimate H-bonding interactions.[11] Nevertheless, the
results clearly show that the three complementary H-bonds
mediate the strong intermolecular binding between TTB and
TBAs. The H-bond lengths are 1.70, 1.98, and 2.41 ꢀ for
OHc···N, CHa···O, and CHb···O, respectively. For comparison,
we also calculated the interaction strength in the TBA dimer.
The H-bond length in the TBA dimer is 1.53 ꢀ, and the
binding energy of the dimeric H-bonding association was
calculated to be 36.7 (32.8) kJmolÀ1 with the PBE (B3LYP)
Discotic liquid crystals (LCs) consisting of a flat aromatic
core and flexible chains are known to form columnar
mesophases. The columnar architecture formed by discotic
LCs is very attractive because it provides a one-dimensional
conducting pathway for electrons, photons, or energy.[7] The
[*] M.-H. Ryu, J.-W. Choi, Prof. B.-K. Cho
Department of Chemistry, Dankook University
Jukjeon 126, Gyeonggi, 448-701 (Korea)
Fax: (+82)31-8005-3153
E-mail: chobk@dankook.ac.kr
Dr. H.-J. Kim
Department of Biomedical Engineering
Northwestern University (USA)
Prof. N. Park
Interdisciplinary School of Green Energy
Ulsan National Institute of Science and Technology
Ulsan, 689-798 (Korea)
E-mail: noejung@dku.edu
[**] This work was supported by the Core Research Program (2009-
0084501) and the Basic Science Research Program (2009-0070798)
through the National Research Foundation (NRF) funded by the
Ministry of Education, Science and Technology (MEST). We
acknowledge the Pohang Accelerator Laboratory (Beamline 10C1),
Korea.
Supporting information for this article is available on the WWW
Angew. Chem. Int. Ed. 2011, 50, 5737 –5740
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
5737