Construction and photophysical properties of organic-inorganic nanonetworks based on oligo(phenylenevinylene) and functionalized gold nanoparticles

Article abstract of DOI:10.1002/cphc.200900734

Novel organic-inorganic nanonetworks of oligo(phenylenevinylene) (OPV) and gold nanoparticles (GNPs) have been synthesized by the amine-based epoxide ring-opening reaction. The resulting OPV-GNPs nanocomposites exhibit homogeneous and well-defined interfa

Full text of DOI:10.1002/cphc.200900734

DOI: 10.1002/cphc.200900734
Construction and Photophysical Properties of Organic–
Inorganic Nanonetworks Based on
Oligo(phenylenevinylene) and Functionalized Gold
Nanoparticles
Jien Yang, Xiaofeng Liu, Changshui Huang, Chunjie Zhou, Yuliang Li,* and Daoben Zhu[a]
Novel organic–inorganic nanonetworks of oligo(phenyleneviny-
lene) (OPV) and gold nanoparticles (GNPs) have been synthe-
sized by the amine-based epoxide ring-opening reaction. The
resulting OPV–GNPs nanocomposites exhibit homogeneous
and well-defined interfaces between the organic ligands and
the inorganic nanoparticles, thereby promoting efficient elec-
tronic interfacial interaction between the two constituents. The
functionalized gold nanoparticles serve as chemical reagents
for the construction of nanohybrids, while the epoxide-termi-
nated OPV acts as linkage between gold nanoparticles. The
new architecture provides a facile methodology for fabrication
of novel organic–inorganic nanohybrids under relatively mild
conditions, which facilitates further applications of hybrid ma-
terials.
1. Introduction
The design and fabrication of organic/inorganic nanostructures
have been investigated intensively in the past decades owing
to their significant promise in the area of catalysis,[1] photogra-
phy,[2] optoelectronics,[3] surface enhanced Raman scattering
(SERS),[4–5] and biomedical applications.[2,6–16] Metal nanoparti-
cles exhibit intense size- and shape-dependent properties due
to the surface plasmon resonance (SPR).[15–17] Therefore, they
are an increasing important colorimetric reporter[18–19] for indi-
cating the status of metal nanoparticles transferring from dis-
persion to aggregation.[4] Significant achievements have been
made in synthesis of diverse functionalized gold nanoparticles
(GNPs), referencing as monolayer protected gold clusters
(MPCs).[20–21] which are usually exploited as building blocks for
supramolecular structures and sensory applications.[22–26] The
construction of such composite materials on the nanoscale is
of great importantance in driving the development of nano-
technology. An appropriate architecture is appreciated for effi-
cient dispersion of metal nanoparticles in organic media with
well-defined interfaces and properties, in which the organic li-
gands effectively prevent metal nanoparticles from aggrega-
tion.[27]
Developing a methodology capable of efficiently and repro-
ducibly fabricating molecular structure on atomic and macro-
scopic dimensions is a key factor in designing materials with
pre-programmed activity, which remains a primary challenge in
nanotechnology. Current trends for preparation of hybrid ma-
terials mainly include mixing these two components or con-
structing them either physically or chemically. The defect is the
readily separation of the components and suppressing elec-
tronic interaction. This implies that the OPV–GNPs network
with homogeneous phases and well-controlled interfaces are
favorable for electronic communication and charge transporta-
tion, which is difficult to achieve just by utilizing conventional
blending approaches.[36–37]
The nucleophilic opening of epoxide rings by amines
(Scheme 1) is an important reaction for synthesis of poly-
mers[38] and pharmaceuticals[39], which can be expedited effec-
tively with zinc(II) perchlorate hexahydrate as a catalyst under
relatively mild conductions. Herein, we present a facile path-
way for fabrication of GNPs–OPV nanohybrids by utilizing an
oligo(phenylene vinylene) tailored with epoxide groups, which
acts as a linkage during the construction of nanohybrids with
amino-functionalized GNPs. The as-prepared hybrid nanonet-
works display homogeneous status and well-defined interfaces,
Hybrid nanomaterials of GNPs and organic ligands are re-
ceiving considerable attention.[22–23] The organic ligands play
an important part in fabrication of such systems, which include
low molecular weight ligands[28–30] and polymers (both conju-
gated[31–32] and nonconjugated).[33–34] Oligo(phenylenevinylene)
(OPV) and its derivatives are excellent candidates in linking the
inorganic functional centers owning to their remarkable optical
and electronic properties.[35] Thus, the combination of GNPs
and OPV may bring out unique materials holding novel chemi-
cal and physical properties that can be exploited for fabrica-
tion of novel nanoscale devices.
[a] J. Yang, Dr. X. Liu, Dr. C. Huang, C. Zhou, Prof. Y. Li, Prof. D. Zhu
Beijing National Laboratory for Molecular Sciences (BNLMS)
CAS laboratory of Organic Solids, Institute of Chemistry
Chinese Academy of Sciences and
Graduate School of Chinese Academy of Sciences
Beijing 100190 (Peoples Republic of China)
Fax: (+86) 10-82616576
E-mail: ylli@iccas.ac.cn
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cphc.200900734.
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659

Y. Li et al.
tionalized gold nanoparticles were obtained as the final
product after general workup.
The oligo (phenylenevinylene) was synthesized using the
Wittig–Horner reaction.[40] The absorption maximum of OPV is
located at 396 nm (Figure 1A), which is mainly due to p–p*
Scheme 1. Schematic illustration for the GNPs–OPV nanonetworks based on
the epoxide ring-opening reaction.
which facilitate the electronic interaction between GNPs and
OPV. Moreover, both the photophysical properties and mor-
phology are dramatically influenced, indicating the validity of
the combination between the two components.
2. Results and Discussion
2.1. Synthesis of Oligo(phenylenevinylene)
We adopted the Wittig–Horner reaction for olefin formation as
reported[31] to synthesize the oligo (phenylenevinylene) as
shown in Scheme 2. The bis-phosphonate 4[40] and 4-(oxiran-2-
ylmethoxy) benzaldehyde 1 were reacted in dry DMF in the
presence of excess amount of NaH to afford OPV ligand 5.
Figure 1. Spectrum of GNPs, GNPs–OPV, and OPV. A) the absorption spectra
of GNPs GNPs–OPV, and OPV. Inset pictures are the OPV, GNPs and GNPs–
OPV photographs. B) the emission spectra of GNPs–OPV and OPV. Inset pic-
tures are the fluorescence of OPV, GNPs and GNPs–OPV.
transition of the conjugated main chains. The as-prepared OPV
also acted as a fluorescent probe for indicating the reaction of
amino-functionalized GNPs with epoxide beyond the role of
linkage. The amino-functionalized GNPs were synthesized fol-
lowing a modified literature method, the TOAB protected
GNPs underwent a ligand-exchange process by mixing the
GNPs with quantitative amount of 4-ATP. The amino-functional-
ized GNPs are particularly prone to sedimentation within one
minute[43] in most solvents. Therefore the GNPs could not be
characterized by NMR due to poor solubility. So we demon-
strated the reliability of the reaction using a model reaction
(see Supporting Information). The sample was further inspect-
ed by transmission electron microscopy (TEM) and dynamic
light scattering (DLS).
Scheme 2. Synthesis of OPV. Conditions for reactions: a) K2CO3, DMF;
b) KOH, EtOH,C12H25Br; c) HBr(aq.), acetic acid; d) P(OEt)3; e) NaH, THF.
2.2. Synthesis of Amino-Functionalized Gold Nanoparticles
The GNPs were synthesized utilizing the modified Brust’s reac-
tion[41] followed by ligand place-exchange reaction of tetra-n-
octylammonium bromide (TOAB)-protected GNPs with 4-ATP.[42]
In the ligand place-exchange reaction, a new thiolate ligand
(4-ATP) was incorporated into nanoparticles by mixing the new
ligand and the TOAB-protected GNPs in THF. The amino-func-
The SPR band of GNPs locates at 605 nm, giving a light blue
coloration in transmission, which tends to suggest a distribu-
tion in the degree of aggregation in solution. The aggregation
of amino-terminated GNPs is attributed to H-bonding between
nanoparticles, leading to the formation of irregular fractal type
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Organic–Inorganic Nanonetworks
structures (Figure 5A). The existence of SPR demonstrates the
average diameter of GNPs larger than 5 nm, which also be con-
firmed by calculation from TEM observations. The DLS also
give an evidence of the aggregation (the average diameter of
GNPs larger than that of calculation from TEM) and the
relatively narrow distribution of GNPs.
opening reaction of the amine attaching to the epoxide, the
hydroxyl group emerges after the reaction. The presence of hy-
droxyl stretching modes at 3500 cmÀ1 is unambiguous
evidence of the amino attaching to the epoxide.
In the nanonetworks, the OPV acts as electron donor as well
as a linkage, while the amino-GNPs acts as electron acceptor
with amine attaching on the end of OPV. Unfortunately, the
formed GNPs–OPV nanohybrid cannot be directly characterized
by NMR spectroscopy because of its poor solubility. The UV/Vis
absorption spectroscopy and TEM provide more direct insights
for the reaction inducing the covalent combination of the two
components. In Figure 1 the surface plasmon resonance peak
of GNPs in the nanonetworks shifts from 605 nm to 538 nm
owning to the improvement of GNPs dispersity within the
system. The OPV acts as a spacer to prevent the GNPs from ag-
gregation, which is the main function in the construction of
the nanocomposites with wonderful interfaces. The formation
of hydroxyl also suppress H-bonding between nanoparticles.
The emission spectrum (Figure 1B) indicates that the fluores-
cence of OPV is quenched, which also indicates that the GNPs
are attached to the OPV effectively. The electronic transmission
from OPV to GNPs upon the irradiation of light brings about
the phenomenon.
2.3. Construction of the Nanonetworks of OPV and GNPs
The organic–inorganic nanonetworks are usually fabricated
using a common two-stage approach.[44] In the present study,
we also take two steps for preparation of the nanohybrid. We
have firstly prepared an epoxide-bearing OPV containing
double epoxide at its junction point (Scheme 2). In a separate
synthesis, we prepared amino-functionalized GNPs. Then, the
GNPs was covalently linked on the OPV under relatively mild
conditions in the presence of zinc perchlorate hexahydrate as
catalyst.[39] The strategy avoids sacrificing the stability and pho-
tophysical properties of the two components.[45] Briefly, the so-
lution of OPV (1ꢁ10À3 m) was mixed with an amount of amino-
GNPs in DMF. And the mixture was left to react at ambient
conditions with the presence of zinc perchlorate hexahydrate,
while the changes were monitored over time using TLC. The
quenching of fluorescence (Figure 1B) of the OPV shows the
progressive reaction procedure between the both compo-
nents, demonstrating the GNPs disturb the electron transition
of the conjugated main chains.
The results of DLS confirm the topography of the GNPs and
OPV–GNPs we draw from the TEM. From the histogram of Fig-
ure 3A, we can understand the poor distribution of 4-ATP pro-
Fourier transform infrared spectroscopy (FT–IR) is a powerful
tool to investigate the structures of molecules, which can iden-
tify certain functional groups. We explored the FT–IR of the 4-
ATP, GNPs, OPV and the GNPs–OPV nanonetworks respectively.
The IR spectra (Figure 2) shows the changes of critical function-
al groups before and after the reaction, verifying the combina-
tion of OPV and GNPs. From comparison the spectrum of 4-
ATP and GNPs, the lack of SÀH band at 3435 cmÀ1 support the
formation of SÀAu bond between the ligand of 4-ATP and the
nanoparticles, while the presence of the NÀH bond stretching
signal occurs at 3380 cmÀ1. This illustrates the structure detail
of the 4-ATP protected GNPs. As a consequent of the ring-
Figure 3. The size distribution of GNPs and OPV–GNPs nanonetworks: A) The
diameter distribution of GNPs; B) The diameter distribution of OPV–GNPs.
tected GNPs readily. The H-bonding forming between the
nanoparticle results in a minor aggregation network. The net-
works’ average diameter is larger than that of OPV–GNPs,
which also is a proof of the conformation of nanonetworks.
We have examined the effect of the molar ratio (r) between
GNPs and OPV. As shown in Figure 4A, the blue shift demon-
strates the role of OPV in constructing the nanonetworks as
the molar ratio decreases and the SPR and fluorescence in-
creases. There is a saturation ratio between the GNPs and OPV,
which most likely results from the space limits.
From the TEM images in Figure 5, we notice the distinct
changes happening between nanoparticles through the reac-
tion. The image of Figure 5A displays the aggregation of GNPs,
which mainly can be contributed to the H-bonding inter-nano-
particles. The amino groups stretch out of the surfaces of
Figure 2. FT–IR spectra of a) 4-ATP, b) GNPs, c) OPV and d) GNPs–OPV. The
samples were prepared by evaporating the solvent of the corresponding sol-
utions on NaBr disks.
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Y. Li et al.
nanonetworks do not lie in a plane but pile up. Consequently,
the crystal lattices of the nanoparticles in HR–TEM (Figure 5D)
appear discretely, which confirms the formation of nano-
networks.
We also adopt an analogous molecule (see Supporting Infor-
mation) as a comparison to confirm the role of the as-prepared
OPV in the construction of the nanonetworks. The analogous
molecule bearing double hydroxyl groups looses the ability to
react with amino functionalized GNPs, so it could not improve
the dispersivity of the GNPs in the system. This indirectly
proofs the ability of the as-prepared OPV in constructing the
GNPs–OPV nanonetworks (Figure 6). The reaction occurs on
the surfaces of the nanoparticles is critical to construct the
novel organic–inorganic nanonetworks.
Figure 4. Spectra of different molar ratio between the OPV and GNPs. A) Ab-
sorption spectra. B) Emission spectra. The spectra were obtained from the
solution of DMF of OPV and GNPs. The OPV solution was prepared by dis-
solving 4 mg in 10.00 mL DMF. Dissolving 4 mg GNPs in 10.00 mL DMF and
shocking to prepare the GNPs solution. The total volume is 2.00 mL.
Figure 6. TEM images of the two molecules’ role in the dispersivity of GNPs.
A) the hydroxyl-terminated OPV and GNPs, B) the epoxide-terminated OPV
and GNPS.
3. Conclusions
In summary, we have developed a novel strategy for the con-
struction of nanonetworks of OPV and GNPs. The functionaliza-
tion of nanoparticles with simple difunctional molecules serves
as chemical reagents in the synthesis of nanohybrids. This illus-
trates that the GNPs could be further explored for nanoscale
building blocks with modification by various simple ligands,
extending to interdisciplinary applications. The resulting GNPs–
OPV nanocomposites exhibit homogeneous and well-defined
interfaces between the organic ligands and the inorganic
nanoparticles, thereby promoting the efficient electronic inter-
facial interaction between the two constituents, facilitating the
fabrication of fantastic devices. The methodology also provides
a new application of amine reacting with epoxide beyond the
traditional usage in discipline of macromolecules.
Figure 5. TEM images A) amino-terminated GNPs, B) HR–TEM of amino-ter-
minated GNPs, C) the nanonetworks of GNPs–OPV, D) HR–TEM of GNPs–OPV.
GNPs, which generate the H-bonding leading to this aggrega-
tion. However, the reaction of amino with the epoxy groups at
the terminals of OPV eliminate (or decrease) the effect of H-
bonding. We can draw that conclusion easily from the image
of Figure 5C, because the nanoparticles embedded in the
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Organic–Inorganic Nanonetworks
Synthesis of Amino-Functionalizationed Gold Nanoparticles: The
functionlized GNPs were prepared according to previous meth-
ods,[41,47] specifically, solution of 50 mg of HAuCl4·4H2O in 2.0 mL of
deionized water and 300 mg of tert-n-octylammonium bromide in
5 mL of toluene were shaken in a separation funnel. The yellow
Experimental Section
Materials and methods: Chemicals were purchased from Alfa Aesar
and Aldrich, and utilized as received unless indicated otherwise. All
solvents were purified using standard procedures.
À
water layer becomes clear and the AuCl4 was phase transferred to
Synthesis and Characterization of 4-(oxiran-2-ylmethoxy)Benzalde-
hyde (1): 4-hydroxybenzaldehyde (1 g, 8.2 mmol) and potassium
carbonate (3.4 g, 24.6 mmol) were suspended in 30 mL of ethanol
and heated to 808C under nitrogen atmosphere. The mixture was
vigorously stirred and the epoxy chloropropane (1.8 g, 19 mmol)
was added dropwise within 10 min. After refluxing for 2 h, the re-
sulting mixture was filtered to remove potassium carbonate and
the filtrate was condensed on rotary evaporator. The residue was
dissolved in ethyl acetate, washed with water, dried over anhy-
drous sodium sulfate, evaporated solvent. The resulting solid
loaded on a silica column chromatography (eluent: petroleum
ether : ethyl acetate=5:1) to yield 1 (1.3 g, 89.3%) as white solid.
1H NMR (400 MHz, CDCl3 , TMS) d 2.79 (2H, J=65.72 Hz), 3.39(1H,
m), 4.35 (2H, J=132 Hz), 7.04 (2H, J=8.6 Hz), 7.85 (2H, J=8.6 Hz).
13C NMR(100 MHz, CDCl3, TMS) d 44.52, 49.85, 69.04, 114.92, 130.36,
131.98, 163.40, 190.75.
organic layer. The organic layer was transferred to a 10 mL round-
bottom bottle. Upon vigorously stirred, a freshly prepared solution
of 5 mg of NaBH4 in 1 mL of deionized water was added all at
once after which the solution darken. After 4 h of stirring the
water was removed by extracted and the organic layer was
washed several times. To the organic phase, 10 mg of 4-aminoben-
zenethiol (4-ATP) was added and the solution was stirred vigorous-
ly for 2 days. Subsequently, the toluene was evaporated and the
black residue was suspended in ethanol and washed extensively
over a glass frit with ethanol and acetone until the filtrate re-
mained colorless. The trace of 4-aminobenzenethiol was monitored
by TLC. The 4-ATP protected gold nanoparticles was obtained,
which was dried for further usage.
Preparation of GNPs–OPV Networks: The OPV (1.5 mg) and previ-
ous prepared GNPs (1 mg) were mixed in 3 mL of N,N-dimethyl form-
amide (DMF) and then zinc perchlorate (Cat.) was added. The solu-
tion was stirred for 2 h and the amino added to epoxide under the
catalysis of Zn(ClO4)2·6H2O.[39] The resulting solution was diluted
and prepared as samples without further treatment to remove re-
sidual OPV.
Synthesis of 1,4-Bis(dodecyloxy)benzene (2)[46]: To a suspension of
1,4-dihyroxyquinone (3.3 g, 10 mmol) and 1-bromododecane
(5.3 g, 21 mmol) in 60 mL ethanol under nitrogen atmosphere, po-
tassium hydroxyl (2.5 g, 45 mmol) was added all at once. After re-
fluxing for 8 h, the reaction mixture was cooled to room tempera-
ture and filtered off, washed with ethanol and dried in vacuum.
The crude product was recrystallized in methanol to yield 2 (4.1 g,
92.0%) as a white solid.
Characterizations: TEM samples were prepared by dropping DMF
solutions of GNPs on carbon coated copper grids (400 mesh) and
evaporated. Images of representative areas were recorded on a
JEOL JEM-2011 transmission electron microscope operating at 200
KV. The absorption spectra were obtained from DMF solutions of
the gold nanoparticles on a JASCO V-570 spectrophotometer. The
emission spectra were obtained on JASCO FP-6600 fluorimeter.
Quartz cuvettes of 1 cm path length were employed. Proton and
carbon nuclear magnetic resonance spectra (1H NMR and 13C NMR)
were recorded out on Bruker ARX300, ARX400 spectrometer using
tetramethylsilane (TMS) as an internal standard, chemical shifts are
given in ppm relative to TMS. Mass spectra were measured with
Bruker Biflex III MALDI-TOF spectrometer and APEX II FT-ICRMS
spectrometer. The nanoparticles diameter distribution was record-
ed on Zetasizer.
Synthesis of 1,4-Bis(bromomethyl)-2,5-bis(dodecyloxy)benzene (3)[46]
:
To a suspension of 1,4-bis(dodecyloxy)benzene (3.0 g, 6.7 mmol),
paraformaldehyde (0.404 g, 13.4 mmol) and hydrogen bromide
(2.00 mL, 45(wt)% in acetic acid, 13.4 mmol) was heated to 658C
for 5 h. The resulting solution was cooled to room temperature
and poured into 200 mL of water. The precipitate was filtered,
washed by water and methanol. The product 3 (3.5 g, 83.0%) was
obtained by recrystallizing from dichloromethane and methanol.
Synthesis
of
Tetraethyl(2,5-bis(dodecyloxy)-1,4-phenylene)bis-
(methylene) diphosphonate (4): The mixture of 1,4-bis(bromometh-
yl)-2,5-bis(dodecyloxy)benzene (3.2 g, 5 mmol) and triethyl phos-
phate (1.66 g, 10 mmol) was heated to 1408C for 8 h. The resulting
solution was cooled to room temperature and loaded on silica gel
chromatography (eluent: petroleum ether: ethyl acetate=2:1) to
give 4 (2.7 g, 72.2%) as a white solid.
Acknowledgements
This work was supported by the National Nature Science Founda-
tion of China (20831160507,10874187,20873155 and 20721061)
and the National Basic Research 973 Program of China.
Synthesis and Characterization of Oligo(phenylenevinylene) (5): To
the solution of compound 1 (1 g, 5.6 mmol) and compound 4
(2.1 g, 2.8 mmol) dissolved in fresh THF (40 mL), sodium hydride
(excess) was added slowly, and stirred for further 2 h. The excess
sodium hydride was quenched by water when the reaction com-
pleted. The solvent was removed on rotary evaporator and washed
by water (100 mL ꢁ 3) and brine, dried over Na2SO4. The residue
was loaded on silica gel chromatography (eluent: petroleum
ether:dichloromethane=1:1) after evaporation of the solvent. The
yellowish solid was obtained as OPV (5) (1.3 g, 59.5%) as light
Keywords: epoxides · gold nanoparticles · nanohybrids ·
nanonetworks · ring-opening reaction
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Received: September 18, 2009
Published online on January 18, 2010
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