Tetraphenylethylene-based expanded oxacalixarene: Synthesis, structure, and its supramolecular grid assemblies directed by guests in the solid state

Article abstract of DOI:10.1021/jo402884a

A novel TPE-based expanded oxacalixarene with typical aggregation-induced emission properties was synthesized by the S_NAr reaction of dihydroxytetraphenylethylene with 2,6-dichloropyrazine. The conformation of the oxacalixarene is adjusted by the encapsulated guests (benzene or THF), which results in different supramolecular grid structures in the solid state.

Full text of DOI:10.1021/jo402884a

Note
pubs.acs.org/joc
Tetraphenylethylene-Based Expanded Oxacalixarene: Synthesis,
Structure, and Its Supramolecular Grid Assemblies Directed by
Guests in the Solid State
Chun Zhang,*,† Zhen Wang,† Song Song,‡ Xianggao Meng,§ Yan-Song Zheng,*,‡ Xiang-Liang Yang,†
and Hui-Bi Xu†
†College of Life Science and Technology, Huazhong University of Science and Technology, and National Engineering Research
Center for Nanomedicine, Wuhan 430074, China
‡School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
§School of Chemistry, Central China Normal University, Wuhan 430079, China
S
* Supporting Information
ABSTRACT: A novel TPE-based expanded oxacalixarene with
typical aggregation-induced emission properties was synthe-
sized by the SNAr reaction of dihydroxytetraphenylethylene
with 2,6-dichloropyrazine. The conformation of the oxacalixar-
ene is adjusted by the encapsulated guests (benzene or THF),
which results in different supramolecular grid structures in the
solid state.
Tetraphenylethylene derivatives (TPEs)8,9 are a class of
interesting compounds that exhibit propeller-like and non-
planar conformations and have a well-known aggregation-
induced emission (AIE) effect. With the unique structure, TPE-
based porous materials have been constructed, including
conjugated microporous polymers10 and TPE-bridged metal−
organic frameworks.11 Taking advantage of the AIE feature
enables the construction of various TPE-based chemo/
biosensors.12 Although TPEs have attracted more and more
attention because of their AIE feature, construction of
calixarene scaffolds utilizing TPE as the skeleton building
blocks has been unexplored.13 Herein we report the efficient
synthesis, structure, and the AIE properties of TPE-based
expanded oxacalixarenes. Moreover, the conformation of the
TPE-based expanded oxacalixarenes was efficiently adjusted by
the encapsulated guests, resulting in different supramolecular
grid structures in the solid state.14
xacalixarenes,1,2 in which the carbon linkages between the
Oaromatic units are replaced by oxygen atoms, have
attracted increased interest in recent years because of their
availability, tunable cavities and potential applications in
supramolecular chemistry. Consequently, different methods
for the synthesis of oxacalixarenes, including the fragment
coupling approach (FCA)3 and one-pot macrocyclic con-
densation reactions,4 have been developed to tune the size and
electronic properties of the cavity and therefore to improve
their assembly and recognition abilities. For example, enlarged
oxacalix[n]arenes (n > 4) have been synthesized successfully by
different protocols in recent years.5 The other strategy to
enlarge the cavity of oxacalixarenes is to employ large-sized
building blocks. For instance, Katz and co-workers reported a
new class of naphthyridine-based or naphthalene-based
oxacalixarenes in which the two naphthalene units separated
by 7.0 Å could form a defined tweezerlike cavity for selective
binding of salicylic acid in solution and the incorporation of a
CH3CN molecule in the solid state.6 Chen and co-workers
introduced triptycene units into the oxacalix[4]arene system,
which resulted in several new oxacalix[4]arenes with enlarged
cavities and fixed conformations, and they found that this class
of oxacalix[4]arene compounds could assemble into tubular
structures in the solid state and encapsulate some interesting
guests such as fullerene.7 Recently, Wang2h and Wen2f
constructed m-terphenylene-based oxacalixarenes with enlarged
cavities. The introduction of novel building blocks into
oxacalixarene scaffolds has been recognized as one of the
most important driving forces to promote advances in
oxacalixarene chemistry.
The synthesis of the expanded oxacalixarene is depicted in
Scheme 1. Dihydroxytetraphenylethylene 2 was prepared
according to the literature method.13 The one-pot coupling
reaction of 2 with 2,6-dichloropyrazine (3) in the presence of
Cs2CO3 in DMSO at 120 °C for 10 h resulted in the formation
of the expected TPE-based oxacalixarene 1 in a yield of 42.2%.
The chemical structure of oxacalixarene 1 was characterized by
1H and 13C NMR spectroscopy, MALDI-TOF MS, and
elemental analysis.15
1
The H NMR spectrum of macrocycle 1 in CDCl3 shows
only one singlet at 8.07 ppm for the proton Ha of the pyrazine
Received: December 31, 2013
Published: February 28, 2014
© 2014 American Chemical Society
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Note
structure, single crystals of 1 were cultivated in different solvent
systems. Single crystals of 1·C6H6 and 1·0.5C4H8O were
obtained by slow evaporation of the benzene/CH3CN and
THF solutions, respectively.15 As shown in Figure 2, 1 is in a
Scheme 1. Synthesis of TPE-Based Oxacalixarene 1
moiety, while its 13C NMR spectrum showed only 12 signals for
the carbons. The presence of only one set of proton and carbon
signals in the corresponding 1H and 13C NMR spectra indicates
that the conformation of the macrocycle 1 is fixed. Moreover,
no significant spectral changes were observed in variable-
1
temperature H NMR experiments on oxacalixarene 1 (Figure
S3 in the Supporting Information), which furthermore
confirmed the fixed conformation of 1 in solution.
Oxacalixarene 1 shows typical AIE properties. The
fluorescence spectra of 1 in solution were measured. As
expected, the compound is almost nonfluorescent in solution
(Figure 1), in accordance with previous studies.9,12 However,
Figure 2. Crystal structures of (a) 1·C6H6 and (b) 1·0.5C4H8O.
Hydrogen atoms have been omitted for clarity.
Figure 1. Fluorescence spectra of oxacalixarene 1 in THF after the
addition of various amounts of water (excitation wavelength: 350 nm).
1,3-alternate conformation in the solid state, which is similar to
the conformational structures of most literature-documented
oxacalixarenes.2 In the crystal structure of 1·C6H6 and 1·
0.5C4H8O, the four bridging oxygen atoms are located in one
plane. Because of the encapsulation of different guests,
oxacalixarene 1 displayed different conformations in the solid
state. As shown in Figure 2, the two pyrazine rings are eclipsed
with dihedral angles of 62.67° and 76.09° in the crystals of 1·
C6H6 and 1·0.5C4H8O, respectively. The transannular N···N
distances for the lower and upper rims are 9.270 and 13.999 Å
for 1·C6H6 and 9.405 and 13.748 Å for 1·0.5C4H8O,
respectively.
the fluorescence of 1 “turns on” upon aggregation. Figure 1
shows the fluorescence spectra of 1 in THF after the addition
of different amounts of water. It was found that the
fluorescence intensity of 1 is significantly enhanced when the
water/THF volume ratio is larger than 3/1. Such fluorescence
enhancement can be detected by the naked eye, as shown in
Figure S5 in the Supporting Information, which presents
photographs of compound 1 in solutions with different water/
THF ratios under UV irradiation. The fluorescence enhance-
ment for 1 is due to the formation of aggregates because the
compound is not water-soluble, and thus, the addition of water
to its solution in THF induces its aggregation. As shown in
Figure S6 in the Supporting Information, the results of
transmission electron microscopy (TEM) and selected-area
electron diffraction (SAED) analysis indicated that oxacalixar-
ene 1 aggregated into amorphous nanoparticles with a size
distribution of 50−150 nm when the water/THF ratio was 10/
1.
Moreover, oxacalixarene 1 assembled into different supra-
molecular assemblies introduced by the different guests. In 1·
C6H6, two molecules of 1 with different directions form a dimer
structure by a couple of C−H···N interactions between the
aromatic protons of the TPE moiety and the nitrogen atom of
́
the pyrazine (dH···N = 2.477 Å, θC−H···N = 146.69°) and a π−π
stacking interaction between the pyrazine moieties of the
́
adjacent oxacalixarenes (dπ−π = 3.435 Å) (Figure 3a and Figure
To investigate the solid-state structure of oxacalixarene 1 and
to examine the guest-induced conformational changes in the
S7 in the Supporting Information). By another a couple of C−
́
H···N interactions (dH···N = 2.499 Å, θC−H···N = 136.59°) and a
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Note
on a 400 MHz NMR spectrometer. MALDI mass determination was
performed on a MALDI-TOF mass spectrometer with CCA.
Synthesis of 1. Under a dry argon atmosphere, a mixture of TPE 2
(100 mg, 0.28 mmol), 2,6-dichloropyrazine (3) (41 mg, 0.28 mmol),
and anhydrous Cs2CO3 (182 mg, 0.56 mmol) in anhydrous DMSO (5
mL) was stirred vigorously at 120 °C for 10 h and then cooled to rt.
The reaction mixture was partitioned between EtOAc (50 mL) and
H2O (40 mL) and then separated, and the aqueous layer was extracted
twice with EtOAc (20 mL). The combined organic layers were washed
with brine (100 mL), dried over anhydrous Na2SO4, filtered, and
concentrated in vacuo. The crude product was purified by column
chromatography over silica gel (eluent: 1/5 CH2Cl2/petroleum ether)
to give 1 as a white solid (51 mg, 42.2%). Mp: >300 °C. IR (KBr):
1640.54, 1582.37, 1538.86, 1501.44, 1450.85, 1405.09, 1315.37,
1260.27, 1205.76, 1172.57, 1103.35 cm−1. 1H NMR (400 MHz,
CDCl3): δ 6.83 (d, J = 8.0 Hz, 8H), 6.99 (d, J = 8.0 Hz, 8H), 7.07 (m,
8H), 7.10 (m, 12H), 8.07 (s, 4H). 13C NMR (CDCl3, 100 MHz): δ
121.0, 126.7, 127.3, 127.9, 131.4, 132.2, 132.6, 139.3, 140.3, 141.7,
143.9, 151.0. MALDI-TOF-MS: m/z 880.8 (M+). Anal. Calcd for
C60H40N4O4: C, 81.80; H, 4.58; N, 6.36. Found: C, 82.03; H, 4.41; N,
6.50. Crystallographic data for 1·C6H6 (C66H46N4O4): Mr = 959.07;
triclinic, space group P1; a = 12.024(3) Å, b = 12.744(3) Å, c =
̅
18.613(5) Å, α = 97.529(4)°, β = 98.367(4)°, γ = 115.203(3)°, V =
2493.1(11) Å3; Z = 2; ρcalcd = 1.278 g/cm3; μ = 0.080 mm−1;
reflections collected 20886; data/restraints/parameters 9747/0/667;
GOF on F2 0.971; final R1 = 0.0554, wR2 = 0.1236; R indices (all data)
R1 = 0.1294, wR2 = 0.1611; largest diffraction peak and hole 0.274 and
−0.297 e/Å3, respectively; CCDC-975767. Crystallographic data for 1·
0.5C H O (C H N O ): M = 959.07; triclinic, space group P1; a =
̅
4
8
62 44
4
4.5
r
12.237(4) Å, b = 12.745(4) Å, c = 17.157(6) Å, α = 79.464(6)°, β =
89.857(6)°, γ = 65.497(5)°, V = 2385.7(14) Å3; Z = 2; ρcalcd = 1.277
g/cm3; μ = 0.081 mm−1; reflections collected 17716; data/restraints/
parameters 8355/30/649; GOF on F2 0.951; final R1 = 0.0615, wR2 =
0.1291; R indices (all data) R1 = 0.1588, wR2 = 0.1738; largest
diffraction peak and hole 0.776 and −0.312 e/Å3, respectively; CCDC-
975768.
Figure 3. The dimer structures of oxacalixarene 1 in (a) 1·C6H6 and
(b) 1·0.5C4H8O and the grid structures assembled in (c) 1·C6H6 and
(d) 1·0.5C4H8O. Solvent molecules and hydrogen atoms have been
omitted for clarity.
ASSOCIATED CONTENT
■
́
couple of π−π stacking interactions (dπ−π = 3.248 Å) between
S
* Supporting Information
1H and 13C NMR, IR, and MS spectra of 1; TEM image of 1;
and X-ray crystallographic data and refinement parameters
(including CIF files) for 1·C6H6 and 1·0.5C4H8O. This material
is available free of charge via the Internet at http://pubs.acs.org.
adjacent dimers, oxacalixarene 1 assembles into a grid structure
́
with dimensions of 16.302 Å × 14.169 Å. In each grid, two
benzene molecules are located by a π−π stacking interaction
́
(dπ−π = 3.270 Å) (Figure 3c and Figure S8 in the Supporting
Information). In 1·0.5C4H8O, two molecules of 1 with different
directions also form a dimer structure by a couple of C−H···N
AUTHOR INFORMATION
Corresponding Authors
*E-mail: chunzhang@hust.edu.cn.
*E-mail: zyansong@hotmail.com.
Notes
■
́
interactions (dH···N = 2.547 Å, θC−H···N = 125.99°) and a couple
́
of C−H···π interactions (dH···π = 2.768 Å) (Figure 3b and
Figure S9 in the Supporting Information). By virtue of a couple
́
of C−H···N interactions (dH···N = 2.364 Å, θC−H···N = 155.91°),
adjacent dimers also assemble into a grid structure with
dimensions of 11.866 Å × 10.482 Å, which can contain only
́
The authors declare no competing financial interest.
one molecule of THF (Figure 3d and Figure S10 in the
Supporting Information). The difference in the oxacalixarene
assembly in 1·C6H6 and 1·0.5C4H8O might have resulted from
the different template effects of the guests (benzene and THF).
In conclusion, we have synthesized the novel TPE-based
expanded oxacalixarene 1 by the SNAr reaction of dihydrox-
ytetraphenylethylene with 2,6-dichloropyrazine. Oxacalixarene
1 shows typical AIE properties. Moreover, the conformation of
1 is efficiently adjusted by the encapsulated guests, resulting in
different supramolecular grid structures in the solid state. The
AIE properties of the novel TPE-based oxacalixarene would
render it an interesting host for the recognition of some guests.
ACKNOWLEDGMENTS
■
This work was supported by the National Natural Science
Foundation of China (20902031), the National Basic Research
Program of China (2012CB932500), the Fundamental
Research Funds for the Central Universities (HUST
2013YGYL003), the Natural Science Foundation of Hubei
Province (2013CFB163), and the Wuhan ChenGuang Program
(201150431118). We also thank the Analytical and Testing
Center of Huazhong University of Science and Technology for
related analysis.
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