Photolysis of an Amphiphilic Assembly by Calixarene-Induced Aggregation

Article abstract of DOI:10.1021/jacs.5b01566

Photosensitizers generally show great tendency for self-aggregation in aqueous media, leading to quenched fluorescence and lower photosensitizing ability. Herein, we report that amphiphilic anthracene is highly photoreactive after aggregation induced by p-sulfonatocalix[4]arene in water. The formation of a host-guest supramolecular assembly and the photolysis of the anthryl core are identified by UV-vis and NMR spectroscopy, dynamic light scattering, and transmission electron microscopy. Additionally, the assembly exhibited efficient photolysis with visible light in the presence of exogenous photosensitizers. This approach could be extended to various photoresponsive self-assemblies and applications in phototherapy and the design of photodegradable materials. (Chemical Equation Presented)

Full text of DOI:10.1021/jacs.5b01566

Article
pubs.acs.org/JACS
Photolysis of an Amphiphilic Assembly by Calixarene-Induced
Aggregation
Yi-Xuan Wang, Ying-Ming Zhang, and Yu Liu*
Department of Chemistry, State Key Laboratory of Elemento-Organic Chemistry, Collaborative Innovation Center of Chemical
Science and Engineering (Tianjin), Nankai University, Tianjin 300071, P. R. China
S
* Supporting Information
ABSTRACT: Photosensitizers generally show great tendency for
self-aggregation in aqueous media, leading to quenched
fluorescence and lower photosensitizing ability. Herein, we report
that amphiphilic anthracene is highly photoreactive after
aggregation induced by p-sulfonatocalix[4]arene in water. The
formation of a host−guest supramolecular assembly and the
photolysis of the anthryl core are identified by UV−vis and NMR
spectroscopy, dynamic light scattering, and transmission electron
microscopy. Additionally, the assembly exhibited efficient
photolysis with visible light in the presence of exogenous photosensitizers. This approach could be extended to various
photoresponsive self-assemblies and applications in phototherapy and the design of photodegradable materials.
excellent biocompatibilities, SCnAs are appealing candidates for
biological and pharmaceutical applications.11 Moreover, SCnAs
have a unique tendency to modulate the aggregation behavior
of aromatic or amphiphilic molecules by decreasing the critical
aggregation concentration, enhancing aggregate compactness,
and regulating the degree of order in the aggregates, which is
referred to as calixarene-induced aggregation (CIA) by our
group.12 Herein, we demonstrate a design strategy for a
photolyzable assembly, based on CIA between SC4A and
amphiphilic 9-alkoxy-substituted anthracene (AnPy). Anthra-
cenes are highly reactive upon light irradiation, and the
reversible anthracene dimerization is a model for photo-cross-
linking of functional materials.13 In addition, anthracene can
trap singlet oxygen and form stable endoperoxides, which is
useful for the detection of singlet oxygen.14 However,
application in the development of photolyzable assemblies
has not been fully explored.15 In this work, we fabricated a
photolyzable supramolecular assembly, employing SC4A as the
host and AnPy as the photoactive guest (Scheme 1). SC4A not
only induced compact packing between anthracenes but also
inhibited the fluorescence quenching of AnPy, which is
favorable for photosensitization. Interestingly, the photo-
decomposition of aggregated AnPy was significantly promoted,
while it was reported that the fluorescence of photosensitizers
could be generally self-quenched after aggregation,16 resulting
in greatly reduced ability for singlet oxygen generation and
lower photoreactivity.17 The supramolecular assembly exhibited
efficient photolysis with visible light in the presence of
exogenous photosensitizers. To the best of our knowledge,
INTRODUCTION
■
Benefiting from cleanness, high efficiency and low cost, light
has become one of the most desirable stimuli for regulating
molecular structures and aggregate behaviors of molecular
assemblies.1 Superior to other external signals, light is a
noninvasive stimulus that can be readily triggered from outside
of the system to adequately control the physicochemical
properties of multicomponent assemblies. Photoreactions can
be initiated, stopped, or even paused by the reversible switching
of the light’s wavelength and intensity without adding any
exogenous substances.2 Consequently, photoactive molecules
are widely used to construct photomodulated materials, which
are used in soft lithography,3 separation technology,4 and
photodynamic therapy.5
Among the various photoresponsive systems, photolyzable
matrices that can irreversibly decompose after irradiation have
received much attention in the design of degradable materials,
drug delivery vehicles, and tissue engineering systems.6
Supramolecular approaches are an alternative way to build
photolyzable materials. Such assemblies are held together by
multiple weak noncovalent interactions that can be easily tuned
by external stimuli, and more importantly, the tectons are
generally small molecules, which favor dissipation of the
assembly.7 Many studies have investigated the fabrication of
photoresponsive supramolecular assemblies,8 but photolytic
materials with high efficiency are still needed. Among the
numerous noncovalent interactions, the host−guest complex-
ation based on macrocyclic receptors is particularly advanta-
geous in constructing water-soluble supramolecular architec-
tures.9 p-Sulfonatocalix[n]arenes (SCnAs) are a prominent
family of water-soluble calixarene derivatives with versatile
inclusion/complexation properties for various types of guest
molecules in aqueous media.10 With high water solubilities and
Received: February 11, 2015
© XXXX American Chemical Society
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nonlinear least-squares curve-fitting method by analyzing the
sequential changes in the fluorescence intensity of AnPy in the
presence of varying concentrations of SC4A. The enhanced
fluorescence of the SC4A−AnPy complex may be ascribable to
a regulated intramolecular photoinduced electron transfer
(PET) process.18 For free AnPy, the PET process takes place
from the anthracene moiety as an electron-rich donor to the
pyridinium moiety as an electron-deficient acceptor. After
complexation with SC4A, the pyridinium moiety was included
in the electron-rich cavity of SC4A, and therefore the
nonradiative channel in the PET process was spontaneously
inhibited to a great extent, leading to an enhanced emission
intensity of the anthracene fluorophore.
Scheme 1. Schematic Illustration of the Photolyzable
Supramolecular Amphiphilic Assembly
Similar to many other amphiphilic molecules reported
before, AnPy could be induced by SC4A to form large
assemblies via host−guest interaction. The critical aggregation
concentration of AnPy in the presence of SC4A was measured
by monitoring the dependence of the optical transmittance at
600 nm on the concentration of AnPy. In the absence of SC4A,
the optical transmittance of AnPy at 600 nm showed no
appreciable change as the concentration increased from 0.01 to
0.20 mM (Figure S4, Supporting Information). However, upon
addition of SC4A, the optical transmittance decreased gradually
as the concentration of AnPy increased because of the
formation of the large amphiphilic assembly. According to the
plot of optical transmittance at 600 nm versus the
concentration of AnPy, the calixarene-induced critical aggrega-
tion concentration was obtained as ca. 0.06−0.10 mM (Figures
2a and S5, Supporting Information). There is no tendency for
SC4A to self-aggregate in aqueous solution.19 To determine the
optimal molar ratio of the intermolecular aggregation between
SC4A and AnPy, the optical transmittance of AnPy at a fixed
concentration (0.10 mM) was monitored while increasing the
concentration of SC4A. As shown in Figures 2b and S6
(Supporting Information), the transmittance at 600 nm first
gradually decreased until reaching a minimum at an SC4A/
AnPy ratio of 0.4 and then increased upon further addition of
SC4A. The decrease in the left-hand portion of inflection is due
to the formation of a higher-order complex of SC4A with AnPy,
further resulting in a supramolecular amphiphilic assembly.
However, the assembly converted into simple inclusion
complexes upon addition of excess SC4A. The strong
electrostatic repulsion among the complexes prevents them
from nanoaggregation, eventually leading to an increase in the
optical transmittance. Therefore, the optimal mixing ratio for
the amphiphilic assembly was SC4A:AnPy = 2:5. A clear
shoulder absorption band at ca. 408 nm was observed in the
UV−vis absorption spectrum of the SC4A−AnPy assembly,
which is attributed to aggregation of anthracene moieties
(Figure S7a, Supporting Information).20 However, this
absorption band was not observed for free AnPy, even at
high concentrations (Figure S7b, Supporting Information), or
the aggregates formed by similar 9-substituted amphiphilic
anthracene.21 The intrinsic electrostatic repulsion between the
pyridinium moieties is unfavorable for the π−π stacking
between the anthracene rings of AnPy, whereas the anthracene
rings can stack with each other more tightly once the
pyridinium head in AnPy is surrounded by the cavity of the
negatively charged SC4A through electrostatic attraction. A
control experiment showed that no assembly appeared when
replacing SC4A with its fragment 4-phenolsulfonic sodium
under comparable conditions (Figure S7, Supporting Informa-
tion), indicating that the cyclic tetramer structure of SC4A is
such a photolyzable system promoted by supramolecular
aggregation has not been reported to date.
RESULTS AND DISCUSSION
■
Construction and Characterization of the Amphiphilic
Supramolecular Assembly. SCnAs are thought to greatly
reduce electrostatic repulsion in the cationic head groups of the
amphiphilic guests and facilitate guest aggregation via host−
guest complexation. Therefore, the high binding affinities
between the SCnAs and the cationic head groups of the guests
are crucial for high-performance CIA.12a The binding constant
(Ka) between AnPy and SC4A was determined by the
fluorescence spectral titration. As shown in Figure 1, the
Figure 1. Alterations of the fluorescence spectra of AnPy (5.0 μM)
upon addition of SC4A (0−35 μM, from (a) to (i)) in aqueous
solution at 25 °C. Inset: the nonlinear least-squares analysis of the
variation of fluorescence intensity with the concentration of SC4A to
calculate the binding constant (λex = 365 nm and λem = 417 nm).
emission intensity of AnPy at 417 nm gradually increased upon
addition of SC4A. Furthermore, a peak was reached at a molar
fraction of 0.5 in the Job plot, indicating the 1:1 binding
stoichiometry between SC4A and AnPy (Figure S3, Supporting
Information). After validating the complex stoichiometry, the
Ka value could be calculated as 4.22 × 105 M−1 using a
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Figure 2. (a) Dependence of the optical transmittance at 600 nm on the AnPy concentration (0.03−0.10 mM) in the presence of SC4A (0.05 mM)
in water at 25 °C. (b) Dependence of the optical transmittance at 600 nm on the SC4A concentration (0−0.08 mM) with a fixed AnPy
concentration (0.10 mM) in water at 25 °C. Inset: Schematic illustration of the SC4A−AnPy assembly and the corresponding simple inclusion
complex. (c) DLS data of the SC4A−AnPy assembly at 25 °C. (d) TEM images of the SC4A−AnPy assembly. Inset: magnified TEM image.
Figure 3. 1H NMR spectra of AnPy in the (a) absence and (b) presence of SC4A, and (c) the SC4A−AnPy assembly after UV irradiation (365 nm)
in DMSO-d6 for 30 min ([SC4A] = 0.96 mM and [AnPy] = 2.4 mM). The peaks of unreacted AnPy, 1-(4-hydroxybutyl)pyridinium, anthraquinone,
and SC4A are denoted in blue, pink, orange, and green, respectively.
undoubtedly the critical factor in inducing the supramolecular
amphiphilic assembly.
cannot form any aggregates under comparable conditions
(Figure S8, Supporting Information), suggesting that the
complexation of SC4A with AnPy can induce the critical
decrease in aggregation concentration of amphiphilic AnPy.
Moreover, spherical nanoparticles with diameters ranging from
200 to 400 nm were observed in the TEM images, indicative of
the formation of the supramolecular aggregation in the SC4A−
AnPy system (Figure 2d). Meanwhile, the particles were found
Subsequently, dynamic light scattering (DLS) and trans-
mission electron microscopy (TEM) were employed to identify
the morphology and size distribution of the SC4A−AnPy
assembly. As shown in Figure 2c, SC4A−AnPy assemblies
exhibit a narrow size distribution with an average hydrodynamic
diameter of 266.72 nm at a scattering angle of 90°. Free AnPy
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to possess negative ζ potential, primarily due to the residual
negative charges on SC4A upon complexation with pyridinium-
bearing AnPy (Figure S9, Supporting Information).
NMR spectroscopy is a powerful tool to determine complex
1
structures. We performed H NMR measurements in DMSO-
d6 instead of D2O because undesirable intermolecular
aggregation drastically broadens the signals, making them
unidentifiable. As shown in Figure 3a,b, the proton signals of
pyridinium exhibited pronounced upfield shifts owing to the
ring current effect of the aromatic nuclei of calixarene,22 while
those of the anthracene rings were not appreciably affected.
These results demonstrate that the pyridinium moieties are
encapsulated in the calixarene cavity, while the anthracene
moieties remain outside. This molecular binding behavior
supports the claim that the intramolecular PET process in AnPy
is inhibited by complexation with SC4A, as validated by the
fluorescence titration experiments. Combining all the afore-
mentioned results, a plausible mechanism for SC4A−AnPy
assembling is deduced as illustrated in Scheme 1, where the
anthryl rings anchored by the SC4A−pyridinium complexation
are tightly packed to each other by the hydrophobic and π−π
interactions and the partly deprotonated phenol groups at the
lower rim of SC4A are exposed to the aqueous solution.23
Thermoresponsiveness and Photolysis of the Supra-
molecular Assembly. The thermoresponsive assembly/
disassembly processes are considered as one of the basic
properties in noncovalently linked system. Because the
complexation of SC4As with organic cations and the π−π
stacking of anthracenes are both dominantly enthalpy-driven
processes, the equilibrium speciation could shift toward the
enthalpically unfavorable partners upon heating.24 Therefore,
the SC4A−AnPy assembly is expected to respond to temper-
ature. As shown in Figure S10a (Supporting Information), the
scattering intensity of the solution decreased gradually with
temperature increases from 25 to 40 °C and reached a plateau
upon further increase in temperature, which reflects dis-
assembly. More powerful evidence comes from the optical
transmittance measurements (Figure S10b, Supporting In-
formation). After warming the assembly solution at 40 °C for
several minutes, the optical transmittance at long wavelengths
increased to approximately 100%, suggesting that the SC4A−
AnPy assembly completely disappeared. The reversible
assembly/disassembly process was easily repeated by simply
adjusting the temperature (Figure 4).
Upon excitation by UV irradiation, it was known that
anthracene could be capable of being directly excited and prone
to react with singlet oxygen to form stable cyclic endoper-
oxides.25 However, for 9-alkoxy-substituted anthracenes, the
rearrangement and further oxidation of their endoperoxides
lead to the formation of anthraquinone and relevant alkanols
(Scheme S1, Supporting Information).26 Accordingly, UV−vis
absorption measurements were performed to monitor the
decomposition of AnPy. As shown in Figure S7a (Supporting
Information), the absorption of the anthracene moiety in the
range of 300−400 nm slightly decreased after irradiation by UV
light at 365 nm for 30 min, implying that only a small amount
of AnPy had decomposed. Comparatively, the absorption of the
anthracene moiety in the SC4A−AnPy assembly decreased
significantly after UV irradiation with accompanying formation
of precipitates, which clearly implies that the photodecompo-
sition of AnPy is significantly enhanced after aggregation with
SC4A. Light irradiation at 365 nm cannot influence the
structural change of SC4A because SC4A alone shows no
Figure 4. Optical transmittance changes of the SC4A−AnPy assembly
at 600 nm over several cycles of thermal equilibration in water at 25
and 40 °C.
appreciable absorption above 300 nm.27 This photochemical
phenomenon is quite interesting because the aggregation of
photosensitizers always leads to a severe self-quenching of the
excited state, accompanied by a quenched fluorescence
intensity and reduced capability for singlet oxygen generation.28
To investigate the mechanism for this CIA-promoted photo-
decomposition, we first identified the photolytic products by
mass spectrometry (MS) and 1H NMR. After UV irradiation at
365 nm for 30 min, the sample of the SC4A−AnPy assembly
was lyophilized and then redissolved in DMSO-d6 for 1H NMR
measurements. Despite a residue of unreacted AnPy, peaks
corresponding to the pyridinium and alkyl chain of AnPy were
split into two groups, and new peaks at 8.71, 4.48, 3.37, 1.83,
and 1.32 ppm could be assigned to the 1-(4-hydroxybutyl)-
pyridinium product after irradiation (Figures 3c and S11c,
Supporting Information). The signal at 4.52 ppm that
disappeared upon addition of D2O could be assigned to the
proton of the hydroxyl group (Figure S11, Supporting
Information). The m/z peak of 1-(4-hydroxybutyl)pyridinium
at 152.1 was also observed in the ESI-MS spectrum (Figure
S12, Supporting Information). The precipitate product was
separated by filtration and confirmed as anthraquinone by EI-
MS and 1H NMR measurements (Figure S13, Supporting
Information). Combining all of the aforementioned results, we
can deduce that the AnPy in SC4A−AnPy assembly
decomposed into 1-(4-hydroxybutyl)pyridinium and anthraqui-
none, as illustrated in Scheme S1 (Supporting Information).
The photodecomposition rates of AnPy and the SC4A−
AnPy assembly were further examined by UV−vis spectrosco-
py. For free AnPy, photodecomposition proceeded very slowly,
and <20% of AnPy decomposed upon irradiation at 365 nm for
60 min (Figure 5a). Additionally, the photodecomposition
process at low AnPy concentrations (<0.10 mM) remained
unchanged but was gradually reduced as a function of
increasing AnPy concentrations (>0.10 mM). Irradiation was
performed under air, and the concentration of oxygen in
aqueous solution is ca. 0.28 mM, which can limit further
oxidation at high AnPy concentrations. For the SC4A−AnPy
assembly, 52% of AnPy decomposed after irradiation at 365 nm
for only 15 min, indicating that the photodecomposition rate of
AnPy was significantly enhanced in the presence of SC4A
(Figure 5b). After inletting argon for 10 min at room
temperature, photodecomposition proceeded more slowly.
However, an increased photodecomposition rate was observed
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anthryl rings in the SC4A−AnPy assembly facilitate commu-
nication with singlet oxygen to further self-oxidization, because
the efficacy of photosensitization relies on the proximity of
sensitizers and their targets.30
Finally, we further examined the photolysis of the SC4A−
AnPy assembly upon irradiation with visible light. Eosin Y, a
commonly used generator for singlet oxygen after exposure to
green light, was chosen as the auxiliary photosensitizer. The
absorption of eosin was broadened in the presence of AnPy or
the SC4A−AnPy assembly, possibly due to the π−π stacking
between eosin and anthracene (Figure 6a).15 DLS data further
Figure 5. Normalized absorbance of (a) AnPy (measured at 25 °C)
and (b) the SC4A−AnPy assembly (measured at 40 °C) at 368 nm
upon irradiation for different amounts of time.
when using oxygen instead of argon. Control experiments
showed no decrease in the absorption of AnPy when irradiating
the solution at 450 nm under comparable conditions,
suggesting that the photosensitization of anthracene is crucial
to the decomposition reaction (Figure 5b). Because AnPy
decomposes into insoluble anthraquinone and hydrophilic
alkanol, the SC4A−AnPy assembly is expected to dissipate after
irradiation. Indeed, DLS measurements gave a wide size
distribution (polydispersity: 0.548) with a large hydrodynamic
diameter (up to 1.3 μm) for the irradiated assemblies, and the
signal for the SC4A−AnPy assembly disappeared after
irradiation, corresponding to disassembly and precipitation
(Figure S14a, Supporting Information). Moreover, spherical
morphologies were not observed in the TEM image after
irradiation (Figure S14b, Supporting Information). Taken
together, these results suggest that the SC4A−AnPy assembly
photodissipated successfully.
The mechanisms of this CIA-promoted photodecomposition
were investigated by fluorescence spectrometry. The emission
intensity of the SC4A−AnPy assembly was comparable to free
AnPy, suggesting that the included AnPy retained its
photosensitivity with no quenched fluorescence upon aggrega-
tion (Figure S15a, Supporting Information). Even though a
relatively higher emission intensity of AnPy was observed when
the supramolecular assembly was transferred into the simple
SC4A−AnPy inclusion complex in the presence of excess
SC4A, the inclusion complex showed a similar decomposition
rate to that of free AnPy (Figure S15, Supporting Information).
Therefore, we assume that the photolysis enhancement is
possibly due to (i) the increased solubility of oxygen and/or the
elongated lifetime of singlet oxygen in the hydrophobic
assembly core than in bulk water;29 and (ii) the closely packed
Figure 6. (a) UV−vis absorption spectra of eosin (0.01 mM), eosin
with AnPy (0.10 mM), and eosin with the SC4A−AnPy assembly in
water at 25 °C (with 1% ethanol). (b) Absorbance of the SC4A−AnPy
assembly at 368 nm in the absence and presence of eosin upon
irradiation at 520 nm for different amounts of time (measured at 40
°C).
show that no obvious size change occurs in the presence of
eosin, indicating that the introduction of eosin at such a low
concentration does not make any negative effect on the
structural stability of binary assembly (Figure S16, Supporting
Information). Upon irradiation at 520 nm, the supramolecular
assembly exhibited higher efficiency in photodecomposition
than free AnPy (Figure 6b), confirming that the AnPy-involved
photolytic process was greatly accelerated by exogenous singlet
oxygen.
CONCLUSIONS
■
We constructed a supramolecular photolyzable assembly based
on the host−guest complexation between a macrocyclic
receptor SC4A and a photodecomposable guest AnPy. The
obtained nanoparticles possessed a narrow distribution and
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UV−vis Spectroscopy. The optical transmittance and absorbance of
the aqueous solution were measured in a quartz cell (light path, 10
mm) on a Shimadzu UV-3600 spectrophotometer equipped with a
PTC-348WI temperature controller.
could be reversibly modulated by temperature change. Upon
UV light irradiation, AnPy slowly decomposed into anthraqui-
none and alkanol, but its photodecomposition rate was
remarkably promoted after aggregation with SC4A, accom-
panied by the dissipation of the binary amphiphilic assembly.
Moreover, the SC4A−AnPy assembly exhibited efficient
photolysis with visible light in the presence of eosin Y as an
exogenous photosensitizer. This approach can be used to
construct various photoresponsive self-assembled materials,
thus making CIA a promising strategy in the fields of
photodynamic therapy and the photodegradation of pollutants.
Fluorescence Spectroscopy. Steady-state fluorescence spectra were
recorded in a conventional quartz cell (light path, 10 mm) on a Varian
Cary Eclipse equipped with a Varian Cary single-cell Peltier accessory
to control the temperature.
1
NMR Spectroscopy. H NMR spectra were recorded on a Bruker
AV400 spectrometer at 25 °C.
TEM Measurement. TEM images were acquired using a Tecnai 20
transmission electron microscope operating at an accelerating voltage
of 200 kV. The sample for TEM measurements was prepared by
dropping a sample solution onto a copper grid. The grid was then air-
dried.
EXPERIMENTAL SECTION
■
Materials. Anthrone (Aladdin), 1,4-dibromo butane (Aladdin), 4-
phenolsulfonic sodium (Acros Organics), and eosin Y (Sigma-Aldrich)
were used without further purification. SC4A was synthesized and
purified according to procedures reported previously.31 The storage
solution of SC4A (1 mM) was adjusted to pH 7.2 using aqueous
NaOH (1 M), and the pH value for the SC4A−AnPy assembly was
6.3, which is consistent with that of free AnPy. Such a slightly acidic
environment could facilitate the decomposition of 9-anthryl ether. The
mixing concentration for the amphiphilic assembly was 0.04 mM for
SC4A and 0.10 mM for AnPy throughout the work, unless mentioned
otherwise.
DLS Measurement. Solution samples were examined on a laser light
scattering spectrometer (BI-200SM) equipped with a digital correlator
(TurboCorr) at 636 nm at a scattering angle of 90°. The
hydrodynamic diameter (Dh) was determined by DLS experiments
at 25 °C.
Zeta (ζ) Potential Measurement. Zeta potential values were
determined at 25 °C on a Brookhaven ZetaPALS (Brookhaven
Instrument, USA). The instrument utilizes phase analysis light
scattering to provide an average over multiple particles. Doubly
distilled water was used as the background electrolyte for ζ potential
measurements.
Synthesis. 9-(4-Bromobutoxy)anthracene. A mixture of anthrone
(2.0 g, 10.3 mmol), 1,4-dibromo butane (9.0 g, 41.7 mmol) and
K2CO3 (14.0 g, 101.3 mmol) in 120 mL of acetone was heated to
reflux for 14 h under an argon atmosphere. After cooling to room
temperature, the solvent was removed via rotary evaporation under
reduced pressure, and the resulting residue was purified by column
chromatography (CH2Cl2:petroleum ether = 1:10) to yield 9-(4-
ASSOCIATED CONTENT
* Supporting Information
■
S
Characterization of compound AnPy, Job plot, additional
optical transmittance and UV−vis curves, ζ potential, and
photodecomposition product analysis are provided. This
material is available free of charge via the Internet at http://
pubs.acs.org.
1
bromobutoxy)anthracene (1.77 g, 52%) as a white powder. H NMR
(400 MHz, CDCl3): δ 8.31−8.18 (m, 3H), 8.07−7.95 (m, 2H), 7.55−
7.40 (m, 4H), 4.23 (t, 2H), 3.62 (t, 2H), 2.38−2.28 (m, 2H), 2.27−
2.17 (m, 2H). 13C NMR (400 MHz, CDCl3): δ 151.1, 132.4, 128.5,
125.5, 125.2, 124.6, 122.2, 74.9, 33.6, 29.7, 29.4.
AnPy. 9-(4-Bromobutoxy)anthracene (120 mg, 0.36 mmol) and
pyridine (1 mL) were dissolved in acetone (25 mL), and the solution
was heated to reflux for 24 h under an argon atmosphere (Scheme 2).
AUTHOR INFORMATION
Corresponding Author
*yuliu@nankai.edu.cn
■
Notes
The authors declare no competing financial interest.
Scheme 2. Synthesis of AnPy
ACKNOWLEDGMENTS
■
We thank the “973” Program (no. 2011CB932502) and
NNSFC (nos. 91227107, 21432004, and 21472100) for
financial support.
REFERENCES
■
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After cooling to room temperature, the mixture was poured into
anhydrous diethyl ether (300 mL) with vigorous stirring. The
precipitates produced were filtered and washed with diethyl ether.
The product was dried overnight under vacuum (yield: 100 mg, 67%).
MS: m/z 328.2 ([AnPy − Br]+, calcd for C23H22NO+, 328.2). 1H
NMR (400 MHz, D2O): δ 8.49 (d, 2H), 8.27 (t, 1H), 7.97−7.84 (m,
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