Synthesis and co-assembly of gold nanoparticles functionalized by a pyrene-thiol derivative

Article abstract of DOI:10.1039/c4ra11932k

We successfully synthesized a series of gold nanoparticles capped with 11-(4-(pyren-1-yl)phenoxy)undecane-1-thiol (A-SH) and with 1-dodecanethiol. The homodispersed gold nanoparticles were fully verified by TEM, UV-Vis and PL spectroscopy. TEM images of the nanoparticles showed similar particle sizes at approximately 2.5 nm also evidenced by the absorption spectra. By solvent-exchange co-self-assembly of a pyrene derivative composited with these functionalized nanoparticles, the different arrangements of Au nanoparticles were observed. Compared to Au nanoparticles functionalized by 1-dodecanethiol (GNP), the pyrene-thiol-capped gold nanoparticles (GNP-A) showed better dispersity in the pyrene derivative matrix because of their π-π interactions. This journal is

Full text of DOI:10.1039/c4ra11932k

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Synthesis and co-assembly of gold nanoparticles
functionalized by a pyrene–thiol derivative
Cite this: RSC Adv., 2015, 5, 140
a
a
a
a
Yongsheng Mi, Pengxia Liang, Zhou Yang, Dong Wang, Wanli He,a Hui Caoa
*
*
and Huai Yangb
We successfully synthesized a series of gold nanoparticles capped with 11-(4-(pyren-1-yl)phenoxy)
undecane-1-thiol (A-SH) and with 1-dodecanethiol. The homodispersed gold nanoparticles were fully
verified by TEM, UV-Vis and PL spectroscopy. TEM images of the nanoparticles showed similar particle
sizes at approximately 2.5 nm also evidenced by the absorption spectra. By solvent-exchange co-self-
assembly of a pyrene derivative composited with these functionalized nanoparticles, the different
arrangements of Au nanoparticles were observed. Compared to Au nanoparticles functionalized by 1-
dodecanethiol (GNP), the pyrene–thiol-capped gold nanoparticles (GNP-A) showed better dispersity in
the pyrene derivative matrix because of their p–p interactions.
Received 7th October 2014
Accepted 24th November 2014
DOI: 10.1039/c4ra11932k
www.rsc.org/advances
xation on the 1D matrix by p–p interactions of the functional
groups such as pyrene derivatives.18
Introduction
Unlike other aromatic compounds, pyrene-based molecular
systems have proved to be a versatile class of probe molecule in
both chemistry and biology.19 Pyrene and its derivatives, in the
monomeric form, show structured absorption and emission
peaks, which are extremely sensitive to their environments.20
Besides, pyrene is known to form an electron donor–acceptor
complex with electron-acceptor molecules and already has been
incorporated into self-assembled systems owing to the strong
p–p interactions.21 Thus, it would be interesting to prepare gold
nanoparticles capped by alkanethiols containing pyrene units
and hence employ transmission electron microscopy to study
the molecular arrangements of alkanethiol ligands. Indeed,
thiols with pyrene units have been incorporated into the self-
assembled monolayer structures,22 but the co-assembly of pyr-
ene–thiol capped Au nanoparticles and pyrene derivatives has
been reported rarely.
Here, we presented the synthesis and characterization of a
kind of pyrene–thiol-capped gold nanoparticles and corre-
sponding gold nanoparticles capped with 1-dodecanethiol.12 In
particular, we have focused our attention on the self-assembly
properties of these nanoparticles composited with pyrene deriv-
ative which has well self-assembly behavior. By co-assembly of
the organic–metal composites, p–p interactions will be fully
exploited and regular morphologies could be observed by TEM.
Metal hybrids of chromophores assembled as two- or three-
dimensional assemblies provide routes for hybrid materials
with optical, electrical and photochemical properties.1–7 Most of
the earlier studies on the interaction between uorophores and
metals are limited to bulk gold surfaces, functionalized with
self-assembled monolayers.8 For instance, 1D arrays of gold NPs
have potential for the directional transfer of photons and/or
electrons, due to a dramatic increase of particle–particle inter-
action, leading to the construction of nanoscale devices,9 such
as plasmon waveguides, magnetic logic, quantum cellular
automata, and coulomb blockade devices.10,11
Since the important report by Brust et al. in 1994,12 extensive
chemical and physical studies have been carried out on
alkanethiols-capped gold nanoparticles, which are also referred
to three-dimensional monolayers protected clusters. These
investigations include new approaches to the synthesis of
monodispersed gold nanoparticles, preparation of superlattice
structures composed of nanoparticles, controllable arrange-
ments of nanoparticles with supramolecular chemistry prin-
ciple, in-place exchange reaction, and functionalization of
nanoparticles.13 Many groups are interested in the p–p inter-
actions of organic protective agents to control various types of
assembly of gold NPs.14 For example, spherical aggregates by
terthiophene15 and 2D assembly by pyrene units16 or by thio-
phene ligands.17 1D assembly of gold NPs can also be realized by
Results and discussion
Synthesis and TEM characterization
aDepartment of Materials Physics and Chemistry, School of Materials Science and
Engineering, University of Science and Technology Beijing, Beijing 100083, People's
Republic of China. E-mail: yangz@ustb.edu.cn; wangdong_ustb@foxmail.com; Fax:
+86-10-62333759; Tel: +86-10-62333759
Molecular structure of compound A-SH which had a phenyl
bDepartment of Materials Science and Engineering, College of Engineering, Peking
pyrene core connected with alkyl-thiol. The pyrene cores could
University, Beijing 100871, People's Republic of China. E-mail: yanghuai@pku.edu.cn provide well photophysical and self-assembly properties, as well
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as the alkyl-thiol group could be connected with Au nano-
particles by Au–SH interactions. The introduction of anisole
group could reduce the difficulty by typical Suzuki coupling
procedure. Synthetic routes of pyrene–thiol derivative A-SH was
presented in Scheme 1. As shown in Scheme 1, compound A-SH
was obtained by a combination of Suzuki coupling procedure,
nucleophilic substitution, etc. The pyrene–thiol derivative was
evidenced by typical peaks at 480.0 m/z in the mass spectra. In
addition, with the 1H-NMR and FI-IR spectra, the nal
compound was fully characterized.
Pyrene–thiol derivative A-SH and 1-dodecanethio were
functionalized on Au nanoparticles by adopting a biphasic
synthetic procedure similar to realize the morphology-control of
nanoparticle by the capped side groups, which was shown in
Scheme 2. Gold nanoparticles were functionalized with the
corresponding thiol derivatives in molar ratio of 1 : 10 to obtain
Au nanoparticles under 10 nm sizes. In the preparation of
functionalized gold nanoparticles, an aqueous solution of
hydrogen tetrachloroaurate(III) hydrate was stirred with tet-
raoctylammonium bromide, until all the aurate ions were
transferred into the toluene layer. To this was added a solution
of thiol derivatives and aer stirring for several minutes,
sodium borohydride was added to reduce the Au and the hybrid
nanoparticles were obtained.
Various methods adopted for the characterization of
monolayer-protected clusters of gold nanoparticles have been
reviewed recently by Murray and co-workers.3 In the present
case, the pyrene–thiol-capped Au nanoparticles were charac-
terized using High-Resolution Transmission Electron Micros-
copy (HRTEM). The HRTEM images of gold nanoparticles
functionalized with 1-dodecanethiol and A-SH is presented in
Fig. 1. Samples were prepared by drop casting the nanoparticles
suspension onto a carbon-coated copper grid (for details, see the
Scheme 2 Schematic representation of the functionalization of Au
nanoparticles with 1-dodecanethiol and pyrene–thiol derivative A-SH.
Experimental section). Images presented in Fig. 1 indicated the
presence that both 1-dodecanthiol functionalized Au nano-
particles (GNP) and A-SH functionalized Au nanoparticles (GNP-A)
showed average sizes of 2.5 nm. There was lager clusters (>3 nm)
observed on the grid which might be formed as a result of the
interparticle aggregation of smaller particles. Insets of the
images gave the particles size distributions of the samples.
UV-Vis and PL spectra
Absorption spectra of Au nanoparticles functionalized by 1-
dodecanethiol (GNP) and pyrene–thiol-capped Au nanoparticles
(GNP-A), as well as the emission spectra of GNP-A, were pre-
sented in Fig. 2. Absorption spectrum of GNP given in Fig. 2(a)
possessed a broad band in the visible region as well as a typical
structured absorption band at approximately 532 nm, which
were all attributed to the surface plasmon absorption and the
size of Au nanoparticles.23 The surface plasmon absorption
originated from the interaction of external electromagnetic
radiation with highly polarizable Au 5d10 electrons of Au
nanoparticles.24
Scheme 1 Molecular structures and synthetic routes of pyrene–thiol Fig. 1 TEM images of gold nanoparticles functionalized with (a) 1-
based derivatives. (a) AIBN, toluene, 85 ꢀC, 8 h; (b) (4-hydroxyphenyl) dodecanethiol (GNP) and (b) A-SH (GNP-A) after drop casting onto a
boronic acid, Pd(PPh3)4, THF/TEA, 80 ꢀC, 8 h; (c) K2CO3, DMF, 24 h; (d) carbon-coated copper grid. Inset shows the particle size distributions.
HCl, MeOH, rt, 8 h.
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enough to form excited state dimmers or in constrained/
heterogeneous media wherein the mobility of the polynuclear
aromatic hydrocarbon molecules was minimized.20 The
concentration dependence of pyrene chromophore binding to
Au nanoparticles was earlier investigated by Chen and Katz by
titrating Au nanoparticles with pyrene chromophore possessing
thioester/thiocarbonate functional group.26,27
Self-assembly properties
Fig. 3(a) gave the molecular structures of pyrene derivatives
1,3,6,8-tetra(pent-1-yn-1-yl) pyrene (RNT) that we synthesized
before, which showed well self-assembly behavior for the strong
p–p interactions. By using solvent-exchange method in solution
phase (for details, see the Experimental section), RNT molecules
could self-assembly into regular morphology as was shown in
Fig. 3(b). Rod-like structures of RNT molecules with ꢁ100 nm in
width could be observed by combined characterizations of SEM
and TEM.
Fig. 2 Absorption spectra of (a) Au nanoparticles functionalized by 1-
dodecanethiol, (b) A-SH and Au nanoparticles functionalized by A-SH;
emission spectra of (c) A-SH and the Au nanoparticles functionalized
by A-SH.
The absorption characteristics of compound A-SH and the
pyrene–thiol-capped nanoparticles GNP-A were shown in
Fig. 2(b). Pyrene–thiol derivative A-SH showed an obvious
absorption band at 345 nm, which was a typical structured
absorption band of pyrene chromophores. When functional-
ized on Au nanoparticles, the structured absorption band of
pyrene chromophore remained unperturbed, and the struc-
tured absorption band of Au nanoparticles appeared at
approximately 536 nm. Although surface capping by pyrene–
thiol ligands did cause a small shi in the plasmon band
maxima from that observed with GNP, the modied nano-
particles of GNP and GNP-A showed similar size and
morphology (Fig. 1). Indeed, the plasmon band energies of
both series of functionalized nanoparticles were, for the most
part, independent of the chemical identity of the appended
ligand.25
The emission spectral properties of GNP-A gold nano-
particles and compound A-SH in CH2Cl2 solutions were
compared in Fig. 2(c). By comparing to A-SH, GNP-A nano-
particles exhibited a new shoulder peak at 485 nm, which was
attributed to the excimer emission of pyrene chromophores.
Excimer emission was usually observed in the spectral region of
425–600 nm when the concentration of pyrene core was high
Fig. 3 Self-assembly morphologies of pyrene derivative composited
with gold nanoparticles. (a) Molecular structure of pyrene derivative
RNT; (b) TEM and SEM images of self-assembled RNT; (c) TEM image
of self-assembled RNT composited with GNP nanoparticles; (d) TEM
image of self-assembled RNT composited with GNP-A nanoparticles;
(e) the possible arrangement of self-assembled RNT–GNP composite;
(f) the possible arrangement of self-assembled RNT–GNP-A
composite.
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Fig. 4 gave the PL spectroscopic titration experiment of
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Conclusion
RNT solutions with quantitative addition of GNP-A. In Fig. 4,
the uorescence intensity of RNT in dichloromethane typi-
cally decreased with the addition of GNP-A, which may
attribute to the p–p interactions between the pyrene rings of
RNT and GNP-A in solutions. Co-assembly experiments of
these RNT-NPs composites were carried out by separately
mixing RNT with GNP and GNP-A in CH2Cl2 solutions. The
conformational exibility of the functional side groups of the
Au nanoparticles gave them sufficient solubility in hydro-
phobic solvent of CH2Cl2 and equal amount of GNP and GNP-
A was added into RNT solutions respectively. TEM images in
Fig. 3(c) and (d) showed the morphologies of self-assembled
RNT–GNP and RNT–GNP-A composites. In Fig. 3(c), RNT
molecules self-assembled into rod-like structures and GNP
nanoparticles were aggregated into nanocluster for the
limited solubility in poor solvent of ethanol. However, in
Fig. 3(d) GNP-A nanoparticles uniformly dispersed and
mostly arranged along the self-assembled RNT rods. By
comparing the self-assembled morphologies of these two
composites, it could be observed that GNP-A nanoparticles
showed better dispersity in the solvent than GNP nano-
particles. More importantly, unlike GNP nanoparticles, GNP-
A nanoparticles could have better interactions with RNT
molecules and this may be attributed to the p–p interactions
between the functional pyrene groups and the RNT mole-
cules as were shown in Fig. 3(e) and (f). Thus, this method to
form well co-assembly structures by modifying Au nano-
particles with functional groups we provided is applicable to
a wide variety of NP systems and we expect that this will have
potential for versatile applications in electronic and optical
nanodevices.
In summary, gold nanoparticles capped with 11-(4-(pyren-1-yl)
phenoxy)undecane-1-thiol and with 1-dodecanethiol were
prepared and characterized. The TEM images of these nano-
particles both showed similar particles size at approximately 2.5
nm as well as evidenced by the absorption spectra. By co-self-
assembly of pyrene derivative composited with these function-
alized nanoparticles, different morphologies of Au nano-
particles were observed by TEM. Comparing to Au nanoparticles
functionalized by 1-dodecanethiol, pyrene–thiol-capped gold
nanoparticles distributed well on the self-assembled nano-
structures of pyrene derivative for the p–p interactions. This
result reected the articial control of nanoparticles via versa-
tile functionalities, which might represent
advancement in small-scale device applications.
a substantial
Experimental section
Materials
Reagents were purchased from commercial sources and used
without further purication. Solvents were distilled in the
standard methods and purged with argon before use.
Synthesis of S-(11-bromoundecyl)ethanethioate (1)
350 mg of AIBN (98% 2.15 mmol) was added to a solution of
thioacetic acid (1.60 ml, 21.45 mmol) and 11-bromo-1-decene
(1.00 g, 4.29 mmol) in toluene (45 ml). The mixture was stir-
red and heated at 95 ꢀC for 4 h. Then, the volatiles were removed
in vacuo. The resulting orange oil was dissolved in CH2Cl2 (100
ml) and washed with a saturated solution of NaCl (50 ml) and
with a saturated solution of NaHCO3 (50 ml). The organic phase
was dried with anhydrous MgSO4 and the solvent was removed
under reduced pressure yielding a yellow solid. The product was
puried by chromatography on a silica gel column with PE/
CH2Cl2 (2 : 1) as eluent. The desired compound was obtained as
bright yellow oil. Yield: 1.30 g (98%). 1H-NMR (400 MHz,
CDCl3): d ¼ 3.42 (2H, m), 2.88 (2H, m), 2.34 (3H, s), 1.86 (2H, m),
1.59 (2H, m), 1.44 (2H, m), 1.36 (2H, m), 1.29 (2H, m) ppm. 13C-
NMR (100 MHz, CDCl3): d ¼ 194.9, 33.7, 32.6, 32.5, 30.5, 29.6,
29.3, 29.2, 28.7, 28.6, 28.0 ppm. FT-IR (KBr): 2926, 2854, 1694,
1463, 1353, 1251, 1134, 952, 722, 627 cmꢂ1. MALDI-TOF-MS
(dithranol): m/z: calcd for C13H25BrOS: 308.08 g molꢂ1, found:
309.3
13H25BrOS (309.20): C 51.47, H 8.11, S 10.38; found: C 51.50, H
g
molꢂ1 [MH]+. Elemental analysis calcd (%) for
C
8.09, S 10.40.
Synthesis of 4-(pyren-1-yl)phenol (2)
1-bromopyrene (1.00 g, 3.58 mmol) was dissolved in 30 ml of
anhydrous THF and the mixture was degassed via ultrasonic
under nitrogen atmosphere for 45 min. Then, 4-hydroxy-
phenylboronic acid (0.50 g, 3.58 mmol) and catalytic agents
Pd(PPh3)4 (0.04 g, 0.03 mmol), K3PO4 (15.20 g, 71.60 mmol) were
added and the reaction mixture was heated to 85 ꢀC and stirred
for 8 hours under nitrogen atmosphere. The cooled reaction
mixture was diluted with CH2Cl2 and extracted with water. The
Fig. 4 (a) Changes in the PL spectra of RNT in dichloromethane
excited by 428 nm with the addition of quantitative 0.5 mg mlꢂ1 GNP-A
solution and (b) the different PL intensities of RNT at 459 nm during the
PL spectroscopic titration experiment.
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organic phase was dried with MgSO4 and the solvent was (KBr): 2921, 2852, 1605, 1467, 1245, 1111, 844, 756 cmꢂ1
.
removed under reduced pressure. The crude product was puri- MALDI-TOF-MS (dithranol): m/z: calcd for C33H36OS: 480.25 g
ed by column chromatography (silica gel, dichloromethane/ molꢂ1, found: 480.7 g molꢂ1 [MH]+. Elemental analysis calcd
petroleum ether ¼ 1/1, v/v) to give compound 2. Yield: 0.95 g (%) for C33H36OS (480.25): C 82.45, H 7.55, S 6.67; found: C
(90%). 1H-NMR (400 MHz, CDCl3): d ¼ 8.24 (3H, d, J ¼ 6.8 Hz), 82.46, H 7.57, S 6.65.
8.20 (1H, m), 8.13 (2H, d, J ¼ 6.8 Hz), 8.06 (2H, d, J ¼ 6.8 Hz),
7.99 (1H, d, J ¼ 6.8 Hz), 7.56 (2H, d, J ¼ 6.8 Hz), 7.06 (2H, d, J ¼
Function of gold nanoparticles
6.8 Hz) ppm. 13C-NMR (100 MHz, CDCl3): d ¼ 157.4, 134.6,
Sized gold clusters capped with 1-dodecanethiol and pyrene–
133.9, 133.3, 132.2, 130.5, 128.8, 128.3, 126.6, 126.3, 125.6,
thiol A-SH were synthesized according to the Brust procedure.12
125.1, 123.3, 121.9, 116.4, 115.5 ppm. FT-IR (KBr): 3789, 1593,
In the preparation of A-SH functionalized gold nanoparticles,
1471, 1229, 835, 753, 504 cmꢂ1. MALDI-TOF-MS (dithranol): m/
an aqueous solution of hydrogen tetrachloroaurate(III) hydrate
z: calcd for C22H14O: 294.10 g molꢂ1, found: 294.3 g molꢂ1
(50 mmol in 2 ml) was stirred with tetraoctylammonium
[MH]+. Elemental analysis calcd (%) for C22H14O (294.10): C
bromide (250 mmol in 5 ml of toluene) for 5 min, until all the
89.76, H 4.76; found: C 89.79, H 4.77.
aurate ions were transferred into the toluene layer. To this was
added a solution of A-SH, in the molar ratio 1 : 10 in 2 ml of
toluene. Aer stirring for 2–3 min, sodium borohydride (2.5
mmol in 2 ml of water) was added and the mixture was stirred
Synthesis of S-(11-(4-(pyren-1-yl)phenoxy)undecyl)
ethanethioate (3)
Compound 2 (0.50 g, 1.70 mmol) and K2CO3 (0.71 g, 5.10 mmol) for 3 h. The hybrid nanoparticles formed were puried by
were added to a solvent of DMF (50 ml) and the mixture was repeated precipitation and ltration using ethanol (3 ꢃ 100 ml).
stirred under nitrogen atmosphere for 1 hour. Then compound The brown powder obtained was redispersed in toluene.
1 (1.57 g, 5.10 mmol) was added and the reaction mixture was
heated to 100 ꢀC and reacted for 24 hours. The cooled reaction
Preparations of the TEM grid
mixture was diluted with CH2Cl2 and extracted with water. The
For the characterization of Au nanoparticles by TEM, a carbon-
organic phase was dried with MgSO4 and the solvent was
supported copper grid (Okenshoji, Model: STEM100 Cu grid)
removed under reduced pressure. The crude product was puri-
was used. The grid was stored in a desiccator and used without
ed by column chromatography (silica gel, dichloromethane/
any treatment. An ethanol–toluene solution containing Au
petroleum ether ¼ 1/3, v/v) to give compound 3. Yield: 0.71 g
nanoparticles was aged for more than 2 days and dropped (0.05
(80%). 1H-NMR (400 MHz, CDCl3): d ¼ 8.24 (3H, d, J ¼ 6.8 Hz),
ml) onto the grid. All grids were dried naturally for 1 day before
8.20 (1H, m), 8.12 (2H, d, J ¼ 6.8 Hz), 8.06 (2H, d, J ¼ 6.8 Hz),
the TEM observation.
7.99 (1H, d, J ¼ 6.8 Hz), 7.58 (2H, d, J ¼ 6.8 Hz), 7.12 (2H, d, J ¼
6.8 Hz), 4.11 (2H, m), 2.90 (2H, m), 2.35 (3H, s), 1.90 (2H, m),
Self-assembly of gold nanoparticles and discotic molecules
1.60 (16H, m) ppm. 13C-NMR (100 MHz, CDCl3): d ¼ 194.9,
158.3, 133.9, 133.6, 133.3, 132.2, 129.7, 128.8, 128.3, 126.6, Self-assembly of the RNT and the RNT–GNP composites was
126.3, 125.6, 125.1, 123.3, 121.9, 115.5, 114.9, 68.7, 32.5, 30.5, conducted by using the solvent-exchange method in the solu-
29.6, 29.3, 29.2, 28.7, 25.9 ppm. FT-IR (KBr): 2923, 2851, 1688, tion phase, which transfers the molecules from a good solvent
1606, 1498, 1243, 836 cmꢂ1. MALDI-TOF-MS (dithranol): m/z: (CH2Cl2) into a poor solvent (ethanol) where the molecules have
calcd for C35H38O2S: 522.26 g molꢂ1, found: 522.7 g molꢂ1 limited solubility, and thus self-assembly occurs through p–p
[MH]+. Elemental analysis calcd (%) for C35H38O2S (522.26): C stacking. This approach takes the advantage of the strong
80.42, H 7.33, S 6.13; found: C 80.44, H 7.32, S 6.12.
intermolecular p–p interactions, which are enhanced in a poor
solvent where the molecules have minimum interaction with
the solvent. Similar methods have previously been used for self-
assembling 1D nano- or microstructures of p-conjugated
organic molecules.28–30 In our experiments, we used a solution-
injection method to facilitate the self-assembly in the ethanol
medium. Typically, a minimum volume (50 ml) of a concen-
trated CH2Cl2 solution (0.001 M) of RNT was injected rapidly
into a larger volume (5 ml) of ethanol, followed by immediate
mixing. Thus, the mixed solution contained only a slight
amount of toluene, resulting in the effective self-assembly of the
molecule. Such a solvent provided limited solubility for RNT
molecules, but on the other hand leaded to favorable molecular
p–p stacking.
Synthesis of 11-(4-(pyren-1-yl)phenoxy)undecane-1-thiol (A-
SH)
1.15 ml of concentrated HCl (37%, 13.94 mmol) were added to a
solution of 3 (0.56 g, 1.08 mmol) in MeOH (20 ml). The mixture
was heated to reux for 3 hours. Aer this time 30 ml of water
were added and the resulting solution was extracted with
diethyl ether (3 ꢃ 30 ml). The organic phase was dried with
anhydrous MgSO4 and the solvent was evaporated at reduced
pressure yielding A-SH. Yield: 0.39 g (75%). 1H-NMR (400 MHz,
CDCl3): d ¼ 8.24 (3H, d, J ¼ 6.8 Hz), 8.20 (1H, m), 8.12 (2H, d, J ¼
6.8 Hz), 8.06 (2H, d, J ¼ 6.8 Hz), 7.99 (1H, d, J ¼ 6.8 Hz), 7.58
(2H, d, J ¼ 6.8 Hz), 7.12 (2H, d, J ¼ 6.8 Hz), 4.11 (2H, m), 2.58
(2H, m), 1.90 (2H, m), 1.60 (13H, m), 0.90 (4H, m) ppm. 13C-
NMR (100 MHz, CDCl3): d ¼ 158.3, 133.9, 133.6, 133.3, 132.2,
Characterization
129.7, 128.8, 128.3, 126.6, 126.3, 125.6, 125.1, 123.3, 121.9, 1H-NMR spectra of the samples were recorded with a Varian 400
115.5, 114.9, 68.7, 34.2, 29.6, 28.9, 28.2, 25.9, 24.6 ppm. FT-IR MHz instrument. All UV-Visible spectra were recorded on a
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Acknowledgements
This work was supported by the National Natural Science
Foundation of China (Grant no. 51173017, 51373024, 51203011,
51103010, and 61370048), the Major Project of International
Cooperation of the Ministry of Science and Technology (Grant
no. 2013DFB50340), the Major Project of Beijing Science and
Technology Program (Grant no. Z121100006512002) and Beijing
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