Molecular assembly of a pyridine functionalized janusarene

Article abstract of DOI:10.1016/j.cclet.2021.06.057

We describe a janusarene derivative PyJ, which forms micrometer-scale one-dimensional metallo-supramolecular polymer through coordination driven self-assembly. PyJ is a well-preorganized dodecatopic pyridyl ligand built on a hexaphenylbenzene platform. The two-face structural feature of PyJ allows for a delicate control over multiple Py-Ag⁺-Py coordination interactions, leading to assembled structure of PyJ-Ag⁺, which was characterized by dynamic light scattering, atomic force microscopy, and transmission electron microscopy.

Full text of DOI:10.1016/j.cclet.2021.06.057

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Chinese Chemical Letters
journal homepage: www.elsevier.com/locate/cclet
Communication
Molecular assembly of a pyridine functionalized janusarene
Zhibo Yin, Luoyi Fan, Chaojun Lin, Haonan Shi, Bangyuan Xiong, Jiajian Gu, Yanpeng Zhu,
∗
Jiaobing Wang
School of Chemistry, Sun Yat-sen University, Guangzhou 510275, China
a r t i c l e i n f o
a b s t r a c t
Article history:
We describe a janusarene derivative PyJ, which forms micrometer-scale one-dimensional metallo-
Received 6 May 2021
Revised 11 June 2021
Accepted 21 June 2021
Available online xxx
supramolecular polymer through coordination driven self-assembly. PyJ is a well-preorganized dode-
catopic pyridyl ligand built on a hexaphenylbenzene platform. The two-face structural feature of PyJ
+
allows for a delicate control over multiple Py-Ag -Py coordination interactions, leading to assembled
+
structure of PyJ-Ag , which was characterized by dynamic light scattering, atomic force microscopy, and
Keywords:
transmission electron microscopy.
Janusarene
© 2021 Published by Elsevier B.V. on behalf of Chinese Chemical Society and Institute of Materia
Medica, Chinese Academy of Medical Sciences.
Supramolecular polymer
Assembly
Coordination
Helical
Coordination-driven self-assembly is a highly modular and flex-
ible approach for the rational construction of various metallo-
supramolecular structures such as molecular cages, knots, and
helicates [1–13]. In addition to these discrete molecular enti-
ties, some well-organized metallo-supramolecular polymers were
also constructed, providing access to novel functional and stimuli-
responsive materials [14–23]. No matter which final structures are
targeted, well-preorganized metallo-ligands hold the key for the
successful endeavor in these directions.
calcd. for C186 H236N12O48: 1703.8224). The isotopic pattern is iden-
tical with that of the simulated one. In the 1H NMR spectrum
(CDCl ), resonance signals corresponding to the hexaphenylben-
3
d
e
zene (HPB) protons of PyJ (7.44, H ; 7.33, H ) are observed. Other
resonance signals on the pyridyl unit can be well assigned with
expected integrations.
Coordination-driven molecular assembly of PyJ was first inves-
tigated by using UV-vis absorption spectroscopy (Fig. 3A). When
+
Ag is titrated to a methanol solution of PyJ, the absorption band
In 2017, we reported a homoditopic molecular host, named
janusarene (Fig. 1, top left) [24], which can bind and align various
guest compounds concurrently in the solid state. During the course
of this study, we realized that a simple phenyl-to-pyridyl structural
modification will result in an unusual dodecatopic pyridyl ligand
PyJ, whose two-face structural feature might be particularly suit-
able for the construction metallo-supramolecular polymer (Fig. 1,
shifts from 293 nm to 300 nm, giving a sharp isosbestic point at
+
303 nm, suggesting a clean transformation from PyJ to the PyJ-Ag
assembly. The titration curve levels off after the addition 6 equiv.
+
of Ag (Fig. 3A, inset), a theoretical stoichiometry for the proposed
one-dimensional supramolecular assembly (Fig. 1, right).
1H NMR result (Fig. S3 in Supporting information) is consistent
with the UV-vis measurement. The resonance signals of PyJ grad-
ually vanish upon AgBF4 titration, in deuterated methanol, indicat-
ing the formation of larger assembly, which prohibits fast molecu-
lar tumbling. In addition, no evident change in the chemical shift
is observed, implying a slow exchange in the NMR time scale. The
absence of notable resonance signals, corresponding to the short
oligomers, e.g. dimer and trimer, probably suggests a nucleation-
elongation assembling process, as occurs in many supramolecu-
lar polymerization systems [29], in which the formation of short
oligomers is more energetic demanding, because restricted confor-
mational switching in the initial assembling state might promote
further elongation. This is consistent with the S-shaped titration
curve (Fig. 3A, inset) [30], observed in the UV-vis studies. Dynamic
light scattering reveals the formation of an assembled species
+
right), taking advantage of the well-established linear Py-Ag -Py
coordination chemistry [25–28]. Therefore, we initiated this study,
which is detailed below.
PyJ was synthesized via a cobalt catalyzed cyclotrimerization
reaction (Fig. 1). Detailed synthesis and characterization are de-
scribed in Supporting information. The identity of PyJ is unam-
biguously confirmed by using high resolution mass spectroscopy
(
HRMS) and a combination of different nuclear magnetic reso-
nance (NMR) techniques (Fig. 2). HRMS shows an ionic species (m/z
2
+
,
1703.8224) fully consistent with the theoretical value ([M + 2H]
∗
Corresponding author.
E-mail address: wangjb5@mail.sysu.edu.cn (J. Wang).
https://doi.org/10.1016/j.cclet.2021.06.057
001-8417/© 2021 Published by Elsevier B.V. on behalf of Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences.
1
Please cite this article as: Z. Yin, L. Fan, C. Lin et al., Molecular assembly of a pyridine functionalized janusarene, Chinese Chemical
Letters, https://doi.org/10.1016/j.cclet.2021.06.057

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Fig. 2. High resolution mass (top) and 1H NMR spectra of PyJ (CDCl3).
+
Fig. 4. (A) AFM height image of PyJ-Ag , prepared by casting a dilute solution
+
of PyJ (1.0 μmol/L) and Ag (6.0 μmol/L) in methanol on a silica surface (scale
1
.5 μm × 1.5 μm). Inset, cross-section profile along the white line in the image.
+
(B) TEM image of PyJ-Ag negatively stained with uranyl acetate.
from the AFM image, the height profile of individual polymer chain
3.0 nm, Fig. 4A, inset) matches the expected value if the attached
(
tg chains and counterion species are taken into account. In con-
Fig. 1. Synthesis and structure of the pyridine functionalized janusarene PyJ. The
+
trast, control AFM experiment using PyJ, in the absence of Ag ,
triethylene glycol monomethyl ether (tg) chain, attached to improve the solubility
+
reveals dot-like structures without the formation of fiber-shaped
of PyJ, is omitted for clarity. Structure of the assembled PyJ-Ag (right) is optimized
using the Spartan software, MM force field.
objects (Fig. S2 in Supporting information).
+
TEM examination of a negatively stained PyJ-Ag reveals bun-
dles of parallelly aligned fibres (Fig. 4B; Fig. S4 in Supporting in-
formation), in agreement with that found in the AFM image. The
polymer chains display a uniform diameter of ca. 4.0 nm, which is
which has an average hydrodynamic radius of ca. 120 nm (Fig. 3B).
An evident Tyndall effect is observed, accordingly (Fig. 3A, inset).
Coordination-driven one-dimensional assembly of PyJ is proved
directly by using atomic force microscopy (AFM, Fig. 4A) and trans-
+
reasonable considering that PyJ-Ag is surrounded by a layer of tg
chains and the counterions.
+
+
mission electron microscopy (TEM, Fig. 4B). AFM image of PyJ-Ag ,
When molecular assembly is carried out in a chiral solvent like
+
obtained by casting a dilute solution of PyJ (1.0 μmol/L) and Ag
(R)-methyl lactate, optically active PyJ-Ag is successfully obtained
(
6.0 μmol/L) in methanol on a silica surface, shows fibrous struc-
[31]. As shown in Fig. 5, free PyJ is essentially optically inactive, in
keeping with its dynamic conformation in solution. In a sharp con-
trast, evident circular dichroism (CD) signals at 285 and 305 nm
tures of several micrometers in length, with the majority bundled
in parallel. Although detailed molecular arrangement is not evident
Fig. 3. UV-vis (A) spectral changes of PyJ (1 × 10− mol/L) toward AgBF4 titration in methanol. Inset, absorption at 293 nm as a function of the concentration of Ag , and
4
+
+
the Tyndall effect observed using a laser pointer. (B) DLS data in the absence and presence of Ag
.
2

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Declaration of competing interest
There are no conflicts to declare.
Acknowledgments
This work was supported by the National Natural Science Foun-
dation of China (Nos. 21871298, 91956118) and the Sun Yat-sen
University.
Supplementary materials
Supplementary material associated with this article can be
found, in the online version, at doi:10.1016/j.cclet.2021.06.057.
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[
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[
+
HPB units in assembled PyJ-Ag can be biased in a chiral solvent,
[
[
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other metallo-supramolecular polymer with attractive chiroptical
and dynamic properties.
3