Supramolecular assembly of H-bonded copolymers/complexes/nanocomposites and fluorescence quenching effects of surface-modified gold nanoparticles on fluorescent copolymers containing pyridyl H-acceptors and acid H-donors

Article abstract of DOI:10.1039/b823450g

A series of photoluminescent (PL) and liquid crystalline (LC) self-H-bonded side-chain copolymers (P1-P3) consisting of pyridyl H-acceptors and isomeric acid H-donors (i.e., para-, meta-, and ortho-benzoic acids) were synthesized. Supramolecular H-bonded

Full text of DOI:10.1039/b823450g

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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
Supramolecular assembly of H-bonded copolymers/complexes/
nanocomposites and fluorescence quenching effects of surface-modified gold
nanoparticles on fluorescent copolymers containing pyridyl H-acceptors and
acid H-donors†
*
Tzung-Chi Liang and Hong-Cheu Lin
Received 6th January 2009, Accepted 20th April 2009
First published as an Advance Article on the web 22nd May 2009
DOI: 10.1039/b823450g
A series of photoluminescent (PL) and liquid crystalline (LC) self-H-bonded side-chain copolymers
(P1–P3) consisting of pyridyl H-acceptors and isomeric acid H-donors (i.e., para-, meta-, and ortho-
benzoic acids) were synthesized. Supramolecular H-bonded complexes were also obtained by mixing
the photoluminescent H-acceptor homopolymer PBT1 (containing pyridyl pendants) with isomeric
H-donor homopolymers P7–P9. The formation of H-bonds was confirmed by FTIR, DSC, and XRD
measurements. Moreover, PL and LC properties of the H-bonded copolymers and complexes were
affected not only by the H-bonding effect of the supramolecular structures but also by the acid-
substituted positions of isomeric H-donors. In combination with different functionalized gold
nanoparticles (which bear acid or acid-free surfactants), the emission intensities of nanocomposites
containing self-H-bonded copolymer P1 (bearing both H-acceptor and H-donor moieties) and non-
self-H-bonded copolymer P4 (bearing acid-protected moieties), were quenched to different extents by
varying the concentration of gold nanoparticles. The copolymeric H-acceptors and surface-modified
gold nanoparticles demonstrated diverse morphological and PL quenching effects on the
supramolecular architectures of the nanocomposites, which result from competition between the
H-donors from the acid pendants on copolymers and the acid surfactants on the gold nanoparticles.
chains have been successfully used for sensing ions and biological
Introduction
species.19–25 The design and synthesis of fluorescent side-chain
conjugated polymers which supramolecularly assemble and are
able to exhibit either chromogenic and/or fluorogenic responses
due to non-covalent interactions have gained considerable
attention recently.26–32
Self-assembled phenomena through molecular recognition
between complementary constituents have been explored in
various areas, such as biomaterials, liquid crystalline (LC)
materials, and materials for electro-optical applications.1–8 Not
only can innovative LC properties of novel supramolecules
consisting of two different components be generated through the
intermolecular hetero-hydrogen-bonding interaction, but also
the directed self-assembly of nano-scale building blocks using
non-covalent interactions (e.g. hydrogen bonding, acid–base
proton transfer, and electrostatic forces) has been amplified into
macroscopically observable phenomena.9 More recently, there
has been considerable interest in conjugated polymers as highly
sensitive chemosensors due to their potential applications in
chemistry and biology.10–15 This is based on the different fluo-
rescence quenching capabilities caused by the varying degrees of
supramolecular interactions with particular chemical or biolog-
ical systems.16–18 Poly(p-phenylene)s, poly(p-phenylene ethyny-
lene)s, poly(p-phenylene vinylene)s, polythiophenes, and
polyfluorenes with receptor groups, such as crown ethers, pyri-
dine derivatives, and ionic groups, in the side-chains or main-
Self-assembly of nanoparticles into nanocomposites provides
a direct pathway for incorporating the particles’ unique physical
properties into the functional materials.33 Due to the stability
and biocompatibility of gold, gold nanoparticles protected by
a mixed monolayer provide highly attractive models for biolog-
ical and fluorescent conjugated polymers.34,35 Many high
performance fluorescence assay methods have been developed by
taking advantage of this superquenching ability of gold nano-
particles for optically sensing biologically important ions and
molecules. Gold nanoparticles can be functionalized so as to
become soluble in water as well as in organic solvents with
readily variable monolayer structures. Rotello and co-workers
reported the synthesis and self-assembly of gold nanoparticles
with inherent optical properties.36–43 Murray and co-workers
have investigated the quenching of fluorophores that are
attached to monolayer-protected gold nanoparticles, and also
the electron transfer from exited fluorophores to gold nano-
particles.44,45 Direct binding between a fluorophore and a metal
surface often results in the quenching of the fluorophore’s excited
states. In this scenario, both energy transfer and electron transfer
processes are considered to be the major deactivation pathways
for excited fluoroprobes on a metal surface.46 Furthermore, in
Department of Materials Science and Engineering, National Chiao Tung
University, Hsinchu, Taiwan, ROC. E-mail: linhc@cc.nctu.edu.tw; Fax:
+8863-5724727; Tel: +8863-5712121 ext.55305
† Electronic supplementary information (ESI) available: Synthesis and
characterization of monomers, polymers, and surface-functionalized
gold nanoparticles AuSC10 and AuSCOOH. See DOI: 10.1039/b823450g
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the presence of other metal ions, such as Cu2+, Co2+, Fe3+, Ni2+,
Zn2+, Pb2+ and Ag+, the gold nanoparticles of the quenched
nanocomposites (containing fluorophores) can be replaced with
the metal ions to different extents due to the stronger re-coor-
dination or re-complexation of the metal ions with fluorophores,
and therefore recover the fluorescence of the chromophores to
behave as chemosensors.47a,b In addition, the gold nanoparticles
of the quenched nanocomposites can also be reacted with
reduced glutathione in the presence of a glutathione reductase
enzyme, and then recover the fluorescence of the chromophores
to behave as biosensors.47c The sensor applications from this
work can be further developed to detect metal ions and
biomolecules based on the modulation of fluorescence quenching
and recovery.
distinct fluorescent quenching effects upon the addition of
surface-functionalized gold nanoparticles (i.e., AuSCOOH and
AuSC10, which contain acid and acid-free surfactants, respec-
tively). To our knowledge, this approach (as shown in the sche-
matic illustration of Fig. 1) is the first exploration of the
supramolecular assembly of nanocomposites via fluorescence
quenching and TEM morphological analysis. The competition
between H-donors from the acid surfactants on the gold nano-
particles and the acid pendent groups on the copolymers to form
H-bonds with the pyridyl pendants (as H-acceptors) of the
copolymers will be surveyed.
Experimental section
Materials
Previously, several series of H-bonded fluorescent complexes/
dendrimers and side-chain supramolecular polymers consisting
of pyridyl fluorophores (small molecular H-acceptors) and
various non-luminescent acid H-donors (including small mole-
cules, dendrimers, and side-chain polymers) have been generated
through intermolecular H-bonded interactions.48,49 The purpose
of this study was to explore photoluminescent (PL) self-H-
bonded copolymers (P1–P3), consisting of para-, meta-, and
ortho-benzoic acids (M1–M3) and fluorescent pyridyl (PBT)
units (with an expected molar ratio of 1 : 1), for their potential
application as proton donors (H-donors) and acceptors (H-
acceptors), repectively. In order to evaluate the proton donating
(H-donor) capabilities of the benzoic acid moieties, acid-pro-
tected monomers M4–M6 (containing para-, meta-, and ortho-
benzoic acid methyl ester units) and its successive acid-protected
(non-self-H-bonded) copolymers P4–P6 were synthesized.
Subsequently, it is more interesting to develop a two-stage self-
assembly process in which the recognition (or sensing) of
different surface-functionalized gold nanoparticles (with acid
and acid-free surfactants) is proceeded by light-emitting copol-
ymers, i.e., self-H-bonded copolymer P1 (bearing both
H-acceptor and H-donor moieties) and non-self-H-bonded
copolymer P4 (bearing acid-protected moieties), correspondingly.
Hence, side-chain conjugated copolymers bearing fluorescent
pyridyl H-acceptor pendants not only behave as highly selective
chemosensors for carboxylic acid H-donors, but also exhibit
Chemicals and solvents were reagent grade and purchased from
Aldrich, ACROS, TCI, TEDIA, and Lancaster Chemical Co.
Dichloromethane and THF were distilled before use. The other
chemicals were used without further purification.
General synthetic procedures for monomers (M1–M6)
The synthetic route of the H-acceptor monomer PBT is described
in the ESI† and isomeric H-donor monomers M1–M3 (i.e., para-,
meta-, and ortho-benzoic acids) were prepared according to the
procedure reported by Portugall et al.50 Monomers M4–M6, with
methyl-ester protecting groups, were also successfully synthe-
sized by the same synthetic method as the H-donor monomers
M1–M3. The chemical structures for all the products were
confirmed by 1H NMR spectroscopy and elemental analysis. The
chemical characteristics of monomers M1–M6, i.e., H-donor
monomers (M1–M3) and acid-protected monomers (M4–M6),
are outlined in the ESI.†
General synthetic procedures for copolymers (P1–P6)
According to Scheme 1, copolymers P1–P6 were synthesized
from monomers M1–M6 (H-donor monomers M1–M3 and acid-
donor-protected monomers M4–M6) and the H-acceptor
monomer PBT. Equal ratios of PBT (50%) and monomers M1–
M6 (50%), total amounts ꢀ1.2 g, were dissolved in THF (6 mL)
with AIBN (3 mol%) added as the initiator. The reaction mixture
was flushed with nitrogen for 5 min, and then heated in a water
bath at 60 ꢁC to initiate polymerization. After 24 h, the reaction
was terminated and the polymer was precipitated in a large
amount of ether. The resulting copolymers P1–P6 were re-dis-
solved several times in THF and re-precipitated in ether–hexane
(1 : 1). The yields of the copolymers P1–P6 were in the range 45–
67%. The molecular weights and polydispersity index (PDI)
values, relative to polystyrene standards, of copolymers P1–P6
are presented in Table S1 (ESI†). The output compositions of
copolymers P1–P6, i.e., the molar ratios of monomer PBT to (H-
donor or acid-protected) monomers M1–M6, which were esti-
mated by NMR experiments, are also listed in Table S1. The 1H
NMR spectra of copolymers P1–P6 are illustrated in Fig. S1
(ESI†). In the 1H NMR spectra of copolymers P1–P6, the
disappearance of proton peaks in the region of the vinyl units
(chemical shifts at 5.4–6.1 ppm of methacrylate and acrylate
groups) indicated that no monomers were present. The
Fig. 1 Schematic illustration of acid-functionalized gold nanoparticles
(AuSCOOH) blended with self-H-bonded copolymer P1 and non-self-H-
bonded copolymer P4.
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Scheme 1 Synthetic routes for copolymers P1–P6.
copolymer compositions in copolymers P1–P6 were estimated by
comparing the relative integration areas of the peak at 8.5 ppm,
which belongs to the two protons of the a-pyridyl groups in PBT.
The overlapped peaks from 6.7 to 7.9 ppm are assigned to the
other aromatic proton regions in PBT groups as well as benzoic
groups in M1–M6, respectively. The copolymer compositions (x/
y ¼ 1/y) were calculated by the following equation: x/y ¼ 1/y ¼ 1/
[(total integration areas of aromatic protons in copolymer ꢂ
total integration areas of aromatic protons in PBT)/(total
integration areas of aromatic protons in M1–M6)] ¼ 1/[(total
integration areas of the aromatic protons in copolymer ꢂ 12)/4].
This is based on the assumption that the total integration area of
the pyridyl protons nearest the heterocyclic N atom in each
copolymer is equal to 2, i.e., 2 protons. The chemical charac-
teristics of polymers P1–P6, i.e., H-donor polymers (P1–P3) and
acid-protected polymers (P4–P6), are outlined in the ESI.†
Homopolymers PBT1 and P7–P9
Scheme 2 Synthetic routes for H-acceptor homopolymer PBT1 and H-
donor homopolymers P7–P9.
By following Scheme 2, the H-acceptor monomer PBT, or H-
donor monomers M1–M3 (1 g) were dissolved in THF (5 mL)
with AIBN (3 mol%) added as the initiator. The reaction mixture
was flushed with nitrogen for 5 min and then heated in a water
bath at 60 ꢁC to initiate polymerization. After 24 h, the reaction
was terminated and the polymer was precipitated into a large
amount of ether. The homopolymers PBT1 and P7–P9 were re-
dissolved in THF and re-precipitated in hexane several times.
The yields were in the range 49–85%. The molecular weights and
polydispersity index (PDI) values of homopolymers PBT1 and
P7–P9 (i.e., H-donor homopolymers PBAp, PBAm, and PBAo)
are presented in Table S1 (ESI†).
dried for several hours in a vacuum oven at 60 ꢁC. During solvent
evaporation, the complexation through hydrogen bonding
occurred between the H-donor and H-acceptor homopolymers.
H-bonded complexes PBT1/P7, PBT1/P8, and PBT1/P9, which
possess equal molar amounts of both pyridyl (H-acceptor) and
carboxylic acid (H-donor) groups (1 : 1 molar ratio), were
produced.
Preparation of nanocomposites consisting of gold nanoparticles
and polymers
Preparation of H-bonded complexes (PBT1/P7–P9)
The surface-functionalized gold nanoparticles, AuSCOOH and
AuSC10, which contain acid and acid-free surfactants, respec-
tively, were synthesized according to the ESI.†Nanocomposites
were prepared by mixing solutions (0.5 mg mLꢂ1) of surface-
functionalized gold nanoparticles AuSCOOH and AuSC10 in
All H-bonded complexes were fabricated from equal molar ratios
of H-acceptor homopolymer PBT1 and H-donor homopolymers
P7–P9 (PBAp, PBAm, and PBAo). The complexes were dis-
solved in THF to make a clear solution, and then subsequently
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THF. This was then mixed with solutions of copolymers P1 and
P4 in DMF (2 mg mLꢂ1). The gold nanoparticles began to
assemble into nanocomposites within 2 min. The mixed solutions
became visibly turbid, indicating that an aggregation process had
occurred. After 24 h, the solid precipitates were collected and
washed extensively with hexane. The nanocomposites were then
dried overnight before being subjected to transmission electron
microscopy (TEM) measurements.
Results and discussion
Synthesis and characterization
Proton acceptor monomer PBT containing three-conjugated
aromatic rings was successfully synthesized via Sonogashira
coupling and Wittig–Horner reactions, whose synthetic route is
illustrated in the ESI.†Two series of H-donor monomers M1–
M3 and acid-protected monomers M4–M6 were synthesized.
The molecular structures of monomers M1–M6 were confirmed
1
by H NMR and elemental analysis. According to the synthetic
Characterizations
routes shown in Scheme 1, copolymers P1–P6 were synthesized
from the H-acceptor monomer PBT along with monomers
M1–M6 (H-donor M1–M3 and acid-protected M4–M6), with
approximately 1 : 1 molar ratio, via the conventional synthesis
of random free radical copolymerization. The random free
radical polymerization of H-donor homopolymers P7–P9
(PBAp–PBAo) and H-acceptor homopolymer PBT1, depicted
in Scheme 2, were performed under the same conditions used
in Scheme 1. The H-bonding effects on these two series of
analogous copolymers, i.e., self-H-bonded copolymers P1–P3
and non-self-H-bonded copolymers P4–P6 (containing H-
donor monomers M1–M3 and acid-protected monomers
M4–M6, respectively), were evaluated for their thermal,
mesogenic, and optical properties. The average molecular
weights measured by gel permeation chromatography (GPC),
relative to polystyrene standards, are displayed in Table S1
(ESI†). The number average molecular weights (Mn) of all
polymers are between 5300 and 7100 g molꢂ1, and the poly-
dispersity index (PDI) values are between 1.4 and 2.6. Their
thermal stabilities were measured under nitrogen by thermog-
ravimetric analyses (TGA), and these results are also summa-
rized in Table S1 (ESI†). The thermal decomposition
temperatures (Td) of 5% weight loss are between 284 and 389
ꢁC, where the Td values of polymers P3 and P9 exhibit the
lowest thermal stability (284 and 294 ꢁC, respectively) due to
the isomeric effect from steric hindrance in the ortho-acid.
1H NMR spectra were recorded on a Varian unity 300 MHz
spectrometer using CDCl3, DMSO-d6, d-dioxane, and d-THF as
solvents. Elemental analyses were performed on a HERAEUS
CHN-OS RAPID elemental analyzer. Fourier transform
infrared (FT-IR) spectra were performed on a Nicolet 360 FT-IR
spectrometer. The textures of mesophases were characterized by
a Leica DMLP polarizing optical microscope (POM) equipped
with a hot stage (Linkam LTS350). Temperatures and enthalpies
of phase transitions were determined by differential scanning
calorimetry (DSC, model: PerkinꢁElmer Pyris 7) under N2, at
a heating and cooling rate of 10 C minꢂ1. Thermogravimetric
analyses (TGA) were conducted on a Du Pont Thermal Analyst
2100 system with a TGA 2950 thermogravimetric analyzer under
N2, at a heating rate of 20 ꢁC minꢂ1. Molecular weights and
molecular weight distributions were determined through gel
permeation chromatography (GPC) using a Waters 510 HPLC,
equipped with a 410 differential refractometer, a refractive index
(RI) detector, and three Ultrastyragel columns (100, 500, and
103) connected in series in order to increase different pore sizes,
with DMF as eluent at a flow rate of 0.6 mL minꢂ1. The
molecular weight calibration curve was obtained using poly-
styrene standards. UV-visible absorption spectra in dilute THF
solutions (10ꢂ6 M) were recorded on a HP G1103A spectro-
photometer, and photoluminescence (PL) spectra in dilute THF
solutions (10ꢂ6 M) were obtained on a Hitachi F-4500 spectro-
photometer. Thin films for UV-vis and PL measurements were
spin-coated (3000 rpm) on quartz substrates from THF solutions
with a concentration of 1 wt%. The fluorescence quantum yields
(FPL) of the chromophores and H-bonded complexes were
determined relative to a standard film of 9,10-diphenylan-
thracene dispersed in PMMA (F ¼ 0.83).51 Synchrotron powder
X-ray diffraction (XRD) measurements were performed at
beamline BL17A1 of the National Synchrotron Radiation
Research Center (NSRRC), Taiwan, where the X-ray wave-
FT-IR spectroscopic studies
H-bonding effects in mesogenic copolymers P1–P6 along with
H-bonded complexes PBT1/P7–P9 (H-acceptor homopolymer
PBT1 blended with H-donor homopolymers P7–P9 in equal
molar ratios) were confirmed by FT-IR spectroscopy. The IR
spectra of the H-acceptor homopolymer PBT1, H-donor
homopolymer P7, and their H-bonded complexes PBT1/P7,
shown in Fig. 2(a), are compared in order to analyze the
formation of H-bonds. In contrast to the O–H band of pure H-
donor homopolymer P7 (PBAp) at 2658 and 2543 cmꢂ1, the
weaker O–H bands observed at 2528–2491 and 1931–1912 cmꢂ1
in H-bonded complexes PBT1/P7, PBT1/P8, and PBT1/P9 are
indicative of stronger H-bonds formed between pyridyl groups
of the H-acceptor homopolymer PBT1 and acid groups of H-
donor homopolymers P7–P9 in their H-bonded complexes
PBT1/P7–P9. On the other hand, a C]O stretching vibration
appeared at 1730–1727 cmꢂ1 in H-bonded complexes PBT1/P7–
P9 (a shoulder appeared at 1690 cmꢂ1 for H-bonded complex
PBT1/P7). This shows that the carbonyl group is in a more
associated state than that it is in the pure H-donor homopol-
ymer P7, which contains a weaker C]O stretching vibration at
˚
length was 1.32633 A. The XRD data were collected using
imaging plates (IP, of an area ¼ 20 ꢃ 40 cm2 and a pixel reso-
lution of 100) curved with a radius equivalent to the sample-to-
image plate distance of 280 mm, and the diffraction signals were
accumulated for 3 min. The powder samples were packed into
a capillary tube and heated by a heat gun, where the temperature
controller was programmable by a PC with a PID feedback
system. The scattering angle theta was calibrated by a mixture of
silver behenate and silicon. Transmission electron microscopy
(TEM) analyses were performed using a JEOL 2011 electron
microscope with an acceleration voltage of 200 keV. The samples
were prepared from THF solutions with a concentration of 1
wt%, and the aggregates were precipitated on TEM sample grids
(200 Cu mesh–carbon films).
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Table 1 Thermal properties of polymers and H-bonded homopolymer
complexes
Polymer/complex
Phase transition/ꢁCa
PBT1b
P1
P2
P3
P4
Glass 51 N 145c I
Glass 57 Sc 149 (3.7) I
Glass 52 N 80c I
Glass 42 N 69c I
Glass 22 N 58c I
P5
P6
Glass 22 N 47c I
Glass 24 N 45c I
PBT1/P7d
PBT1/P8d
PBT1/P9d
Glass 53 Sc 167 (4.3) I
Glass 30 N 94 (1.8) I
Glass 24 N 80c I
a
Phase transition temperatures (ꢁC) and enthalpies (in parentheses, kJ
molꢂ1) were determined by DSC at a heating rate of 10 ꢁC minꢂ1
.
b
Phase transitions of PBT (monomer of homopolymer PBT1): K 42c
N 71c I. Phase transition temperatures were obtained by POM and
confirmed by XRD. No detectable Tg temperatures (by DSC) were
observed in homopolymers P7–P9.
c
d
Phase characterization
The thermal properties (including glass transition temperatures
(Tg) and isotropization temperatures (Ti) with corresponding
enthalpies) of these copolymers and H-bonded complexes,
determined by DSC and POM, are shown in Fig. S2 (ESI†) and
Table 1. The glass transition temperatures of copolymers P1–P6
and H-bonded complexes PBT1/P7, PBT1/P8, and PBT1/P9 (H-
acceptor homopolymer PBT1 blended with H-donor homopol-
ymers P7–P9 in equal molar ratios) are ca. 22–57 ꢁC. Moreover,
all the self-H-bonded copolymers P1–P3 containing H-donors
have higher Tg and Ti values than their corresponding non-self-
H-bonded copolymers P4–P6, which do not contain H-donors.
This is because the self-H-bonded cross-linking polymer struc-
tures, in copolymers P1–P3, have a longer rigid core than the
non-H-bonded side-chain polymer structures in acid-protected
copolymers P4–P6. Both Tg and Ti values of H-bonded
complexes PBT1/P7, PBT1/P8, and PBT1/P9 show a similar
trend (i.e., PBT1/P7 > PBT1/P8 > PBT1/P9) as those of self-H-
bonded copolymers P1–P3 (para-acid-substituted copolymer P1
> meta-acid-substituted copolymer P2 > ortho-acid-substituted
copolymer P3). Overall, the para-substituted copolymer P1 and
the H-bonded complex PBT1/P7 exhibit the highest Tg and Ti
values because they have the most linear H-bonded (cross-linked)
structures.
Fig. 2 Infrared spectra of (a) H-acceptor homopolymer PBT1, H-donor
homopolymer P7, and H-bonded homopolymer complexes PBT1/P7; (b)
copolymers P1 and P4 in solid films.
1720 and 1669 cmꢂ1. All results suggest that H-bonds were
generated in the solid state of H-bonded complexes PBT1/P7,
PBT1/P8, and PBT1/P9. As seen in Fig. 2(b), self-H-bonded
copolymers P1–P3 reveal similar IR spectral profiles to those
[Fig. 2(a)]of H-bonded complexes PBT1/P7–P9, respectively.
This suggests that analogous H-bonded structures formed in the
self-H-bonded copolymers P1–P3 and in the H-bonded
complexes PBT1/P7–P9.52 However, in comparison with self-H-
bonded copolymers P1, acid-protected copolymer P4 in
Fig. 2(b) shows a weaker C]O stretching vibration at 1720
cmꢂ1 because of the lack of a H-bonding interaction. The C]O
stretching peak is sharper because there is less resonance for
C]O stretching in the non-self-H-bonded copolymer P4, as
well as acid-protected copolymers P5–P6 because of a lack of
H-bonds. Meanwhile, a shifted peak at 1600 cmꢂ1 from
a disturbance of the 1590 cmꢂ1 ring mode, was observed
in Fig. 2(a), which indicates a change in the strength of the
acid–pyridine interactions.
Because of the linear H-bonded structures of self-H-bonded
copolymer P1 and H-bonded complex PBT1/P7 (containing
para-acid-substituted homopolymer P7), the smectic phase was
only generated in the para-acid-substituted copolymer P1 with
a mesomorphic range of 92 ꢁC and in the H-bonded complex
ꢁ
PBT1/P7 with a mesomorphic range of 114 C. The H-bonded
complex PBT1/P7 had a wider mesophase range than the self-H-
bonded copolymer P1, because the H-bonded complex (PBT1/
P7) contains highly ordered H-bonded mesogens (from homo-
polymer blends) in the smectic arrangement. Due to the same
reason of highly ordered H-bonds in H-bonded complexes, the
nematic phases observed in nonlinear H-bonded structures (with
non-para-acid-substituted H-donors) of H-bonded complexes
PBT1/P8 and PBT1/P9 were wider than those of self-H-bonded
copolymers P2–P3. This result suggests that the steric factor
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related to the isomeric acid-substituted positions in H-donors is
decisive for the formation of mesomorphism in all H-bonded
structures. In addition, the acid-protected copolymers P4–P6
(which lack H-bonds) possess the nematic phase adopted from
the H-acceptor PBT moieties (with the nematic phase between 42
the formation of the supramolecular structures, the smectic layer
arrangements for copolymer P1 and H-bonded complex PBT1/
P7 were characterized by d-spacing values of XRD measure-
ments. The theoretical value of the fully-extended molecular
˚
length of copolymer P1 is 57.8 A, estimated using CS ChemO-
ꢁ
ꢁC and 71 C), which is similar to observations with the homo-
ffice. The d-spacing valuesꢁof copolymer P1 and the H-bonded
˚
complex PBT1/P7 at 130 C are 50.3 and 52.4 A, respectively
polymer PBT1. However, non-self-H-bonded copolymers P4–P6
have lower phase transition temperatures (including the iso-
tropization temperature Ti) than homopolymer PBT1 due to the
dilution effect of the acid-protected monomer moieties (M4–M6)
in copolymers P4–P6.
[Fig. 3(a)]. These XRD measurements support the hypothesis
that the copolymer P1 and H-bonded complex PBT1/P7 are
suitable to be identified as the tilted smectic C phase with tilt
angles of 29.6ꢁ and 25.0ꢁ, respectively. On the other hand, the
absence of d-layer spacing peaks, for copolymers P2–P6 and H-
bonded complexes PBT1/P8 and PBT1/P9, indicates that these
species possess the nematic phase. For instance, Fig. 3(b) shows
the XRD intensity against angle profiles obtained in the nematic
phase of copolymer P2 at 70 ꢁC.
To further elucidate the mesomorphic behavior in Table 1,
POM and XRD measurements were performed at the meso-
phasic ranges of all copolymers and H-bonded complexes. The
mesophases of copolymer P1 and H-bonded complex PBT1/P7
were characterized by POM. The textures of copolymers P1 and
P2 identified by POM are shown in Fig. S3 (ESI†). To confirm
Optical properties
The absorption and PL spectral data of all copolymers P1–P6 (in
both THF solutions and solid films) and H-bonded complexes
PBT1/P7, PBT1/P8, and PBT1/P9 (in solid films) are summa-
rized in Table 2 and Fig. S4 (ESI†). As shown in Table 2, the
maximum absorption peaks of copolymers P1–P6, near 350 nm
(in THF solutions), are mainly attributed to the PBT units. In
Table 2 and Fig. S4 (ESI†), PL emissions at 444–447 nm (in THF
solutions) and at 515–529 nm (in solids for self-H-bonded
copolymers P1–P3) are all red-shifted in contrast to PL emissions
of acid-protected copolymers P4–P6 (without H-bonds) at 429–
431 nm (in THF solutions) and at 466–472 nm (in solids).
Therefore, compared with PL emissions of non-self-H-bonded
copolymers P4–P6, the H-bonding effects on PL emission
wavelengths (lmax) of self-H-bonded copolymers P1–P3 are
further enhanced in solids (red-shifted 43–63 nm) than in solu-
tions (red-shifted 15–16 nm). However, due to the PL quenching
effect by the aggregation of longer self-H-bonded chromophores
in copolymers P1–P3, the acid-protected copolymers P4–P6
(without H-bonds) exhibit higher PL quantum yields (in both
solutions and solid films) than the self-H-bonded copolymers
P1–P3. For all copolymers (P1–P6), it is apparent that more p–p
stacking and molecular aggregation occur in solid films than in
solutions. The aggregation phenomena are even more
pronounced for P1–P3 in solid films due to the self-H-bonded
structures.
On the basis of our findings, non-luminescent acids are
important for inducing various wavelength shifts in PL emissions
of luminescent H-acceptors by tuning the pKa values of H-
donors in self-H-bonded copolymers and homopolymer
complexes. The H-donor moieties with different pKa values, i.e.,
para-H-donor (M1): pKa ꢀ4.36; > meta-H-donor (M2): pKa
ꢀ4.19; > ortho-H-donor (M3): pKa ꢀ4.15,53 offer a solid solvent
environment in the H-bonded copolymers and complexes.
Therefore, the PL emission wavelengths of H-bonded complexes
in solid films are related to the pKa values as follows: PBT1/P7 <
PBT1/P8 < PBT1/P9. Additionally, in contrast to self-H-bonded
copolymers P2 and P3, the para-substituted acid has the smallest
acidity, and therefore the weakest H-donor effect which induces
the smallest red-shifted PL emission in the solid film of copol-
ymer P1. However, both acidic and steric effects of isomeric
Fig. 3 (a) X-Ray diffraction (XRD) patterns of copolymer P1 and H-
bonded complex PBT1/P7 in the Sc phase at 130 ꢁC. (b) XRD intensity
against angle profiles obtained in the nematic phase of copolymer P2 at
70 ꢁC.
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Table 2 Absorption and PL emission spectral data of polymers and H-bonded homopolymer complexes in THF solutions and solid films
Absorption lmax/nm
PL emission lmax/nmb
Polymer/complex
Solutiona
Film
Solutiona
Film
F (%) (sol)c
F (%) (film)d
PBT1
P1
P2
P3
P4
P5
P6
PBT1/P7
PBT1/P8
PBT1/P9
350
349
349
350
347
348
349
—
357
359
361
361
359
360
360
358
363
360
440
447
445
444
431
429
429
—
487
515
529
523
472
466
466
514
522
525
40
43
39
35
58
60
60
—
—
—
20
17
14
16
22
23
26
18
16
15
—
—
—
—
a
b
Absorption and PL emission spectra were recorded in dilute THF solutions at room temperature. PL emissions were excited at the maximum
c
d
absorption peaks. PL quantum yield of 9,10-diphenylanthracene in THF (10ꢂ6 M) as the reference quantum yield in solution. PL quantum yield
of 9,10-diphenylanthracene blended in PMMA as the reference quantum yield in the solid film.
H-donors play important roles on the PL properties of H-bonded
structures. The molecular p–p stacking in the H-bonded bending
structures consisting of meta- and ortho-substituted H-donors
were suppressed owing to the steric hindrance of meta- and ortho-
substitution. Thus, the PL emission wavelengths of copolymers
P2 and P3 in solid films have the following order: meta-P2 (529
nm) > ortho-P3 (523 nm), which is in the reverse order of acidity.
In general, the results demonstrate that similar red-shifted PL
emissions occur when isomeric H-donors are complexed to form
supramolecular structures in both self-H-bonded copolymers
(P1–P3) and H-bonded homopolymer complexes (PBT1/P7–
P9). Moreover, the acidities and steric structures of the isomeric
H-donors do affect the molecular packing and PL emission
wavelengths of the H-bonded supramolecular architectures.
Therefore, the lmax values, which correspond to the emission
colors, of the photoluminescence in the supramolecular systems
can be tuned not only by adjusting the emitting cores but also by
changing the isomeric structures of the H-donors.
P1 were easily H-bonded with the pyridyl H-acceptor groups and
competed with the acid H-donor surfactants on AuSCOOH
nanoparticles. However, as shown in Fig. 4(b), the titration of
acid-protected copolymer P4 by AuSCOOH nanoparticles
displays a similar PL quenching trend as Fig. 4(a). This suggests
that the complexation of acid-protected copolymer P4 and
AuSCOOH nanoparticles has a similar H-bonding interaction as
that in the nanocomposite P1–AuSCOOH. Unlike the self-H-
bonded copolymer P1, there is no H-donor competition from the
acid-protected copolymer P4 during the H-bonding complexa-
tion process in the nanocomposite P4–AuSCOOH. Hence, the
excitons of acid-protected copolymer P4 are more easily trapped
by the charge-transfer quenching of AuSCOOH than those of
the self-H-bonded copolymer P1. As a comparison, the solutions
of copolymers P1 and P4 were titrated with another nanoparticle
counterpart, alkyl-functionalized gold nanoparticles (AuSC10,
which bear acid-free surfactants). Both PL titrations of copoly-
mers P1 and P4 by AuSC10 nanoparticles [Fig. 4(c) and
4(d)]resulted in similar PL reductions after increasing the
concentration of AuSC10 nanoparticles. However, due to less H-
bonding interactions of non-acid-modified AuSC10 nano-
particles (containing acid-free surfactants) with copolymers P1
and P4, AuSC10 nanoparticles have much weaker PL quenching
effects on P1 and P4 than acid-modified AuSCOOH nano-
particles [Fig. 4(a) and 4(b), respectively]. Comparing the insets
of Fig. 4(a)–(d), the fluorescence quenching curves for copoly-
mers P1 and P4 titrated by AuSCOOH [Fig. 4(a) and (b)] are
totally different from those titrated by AuSC10 [Fig. 4(c) and
(d)]. The lower quenching effects observed for PL titrations of
AuSC10 nanoparticles on copolymers P1 and P4 are owed to the
absence of H-bonding interactions between copolymers (P1 and
P4) and the acid-free surfactants on AuSC10 nanoparticles.
The PL quenching behavior follows the Stern–Volmer relation
I0/I ¼ 1 + KSV[Q],54 where I0 and I are the emission intensities of
the fluorescent copolymers (P1 and P4) in the absence and
presence of the quencher Q (surface-modified gold nano-
particles), respectively, KSV is the Stern–Volmer quenching
constant, and [Q] is the concentration of the quencher. Fig. 5
demonstrates Stern–Volmer plots of copolymers P1 and P4 for
various concentrations of acid-modified AuSCOOH nano-
particles and non-acid-modified AuSC10 nanoparticles, which
Fluorescence quenching effects of copolymers by surface-
modified gold nanoparticles
In the fluorescence quenching studies, where acid-donor-modi-
fied AuSCOOH nanoparticles and non-acid-modified AuSC10
nanoparticles (diameter ca. 5–6 nm) were doped, the photo-
luminescence (PL) spectra of copolymers P1 and P4 were
monitored in the presence of different concentrations of surface-
modified gold nanoparticles (Fig. 4). The fluorescence spectra of
pure copolymers P1 and P4 exhibit maximum PL emissions at
447 nm and 431 nm with corresponding quantum yields of 43%
and 58%, respectively. In Fig. 4(a) and 4(b), copolymers P1 and
P4 demonstrated dramatic decreases in fluorescence intensities
upon the addition of AuSCOOH nanoparticles (which contain
21% carboxylic acid surfactants). Upon the addition of AuS-
COOH, progressive fluorescence quenching effects on copolymer
P1 (blended with AuSCOOH) were observed by increasing the
concentration of AuSCOOH. It is conceivable that the polymer
nanocomposite P1–AuSCOOH reduced the fluorescence emis-
sion intensities by H-bonding complexation of the fluorescent
pyridyl units with the acid surfactant on AuSCOOH. The H-
donor (para-benzoic acid) units in the self-H-bonded copolymer
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Fig. 4 Fluorescence quenching spectra of copolymers P1 and P4 titrated by surface-functionalized nanoparticles (AuSCOOH and AuSC10) in THF
solutions: (a) P1 and (b) P4 by varying the concentration of acid-donor-modified gold nanoparticles (AuSCOOH); (c) P1 and (d) P4 by varying the
concentration of non-acid-modified gold nanoparticles (AuSC10).
are replotted from the insets of Fig. 4(a)–(d). The quenching
constants (KSV) of copolymers P1 and P4 titrated with different
nanoparticle quenchers (AuSCOOH and AuSC10) in THF
solutions are obtained from the slope of Fig. 5 and listed in Table
3. In comparison with the fluorescence quenching effects of the
AuSCOOH nanoparticles on copolymers P1 and P4, the
quenching constant (KSV ¼ 1.20 ꢃ 105 Mꢂ1) of P1 is smaller than
that (KSV ¼ 1.41 ꢃ 105 Mꢂ1) of P4. This can be explained by the
partial self-quenching effect of H-bonds in copolymer P1 (with
a lower quantum yield than the non-self-H-bonded copolymer
P4) which is induced by the higher aggregation of luminescent H-
acceptor moieties in P1 H-bonded to its own H-donor moieties.
Similar to the previous results of copolymers P1 and P4 titrated
with AuSCOOH, as copolymers were titrated with the AuSC10
nanoparticles, the quenching constant (KSV ¼ 1.32 ꢃ 104 Mꢂ1) of
P1 was slightly smaller (KSV ¼ 1.57 ꢃ 104 Mꢂ1) than that of P4.
Due to the reduced supramolecular interactions between
AuSC10 and copolymers P1 and P4 in the nanocomposites, both
KSV constants of copolymers P1 and P4 (1.32 ꢃ 104 and 1.57 ꢃ
104 Mꢂ1 without H-bonds) blended with non-acid-modified gold
nanoparticles (AuSC10) are much smaller than those (1.20 ꢃ 105
and 1.41 ꢃ 105 Mꢂ1 with H-bonds) H-bonded with acid-donor-
modified gold nanoparticles (AuSCOOH). Hence, the H-
bonding interactions play an important role in our study of the
fluorescence quenching effect. Moreover, it will be more inter-
esting to develop a multicomponent self-assembly process
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be ignored. The major source of fluorescence quenching is then
attributed to energy transfer between fluorescent copolymers (P1
and P4) and Au nanoparticles (AuSCOOH).
TEM analysis
To further confirm the modulation of fluorescence quenching
effects on copolymers P1 and P4 by acid-donor-modified gold
nanoparticles (AuSCOOH), transmission electron microscopy
(TEM) analysis was carried out on copolymer nanocomposites
containing AuSCOOH nanoparticles. This provides a further
insight into the morphology of the nanoparticle aggregation.
Solutions of copolymer nanocomposites, consisting of P1 and P4
(2 mg mLꢂ1) blended with AuSCOOH (0.5 mg mLꢂ1) in THF
solvent, were drop-cast onto TEM grids. The morphologies of
the copolymer nanocomposites into structural ensembles were
controlled by supramolecular self-assembly. Both carboxylic
Fig. 5 Corresponding Stern–Volmer plots of copolymers P1 and P4 for
increasing concentrations of acid-modified gold nanoparticles (AuS-
COOH) and non-acid-modified gold nanoparticles (AuSC10) in THF
solutions.
Table 3 Stern–Volmer constants (KSV) of copolymers P1 and P4 titrated
with different nanoparticle quenchers (AuSCOOH and AuSC10) in THF
solutions
a
KSV (Mꢂ1
)
P1
P4
AuSCOOH
AuSC10
1.20 ꢃ 105
1.32 ꢃ 104
1.41 ꢃ 105
1.57 ꢃ 104
a
The quenching behavior follows the Stern–Volmer relation I0/I ¼ 1 +
KSV[Q], where I0 and I are the emission intensities of the fluorescent
copolymer (P1 or P4) in the absence and presence of the quencher Q
(surface-functionalized gold nanoparticles), respectively, KSV is the
Stern–Volmer quenching constant, and [Q] is the concentration of the
quencher.
involving fluorescence quenching of pyridyl H-acceptors specif-
ically by both acid H-donors from copolymer P1 and acid-
donor-modified gold nanoparticles (AuSCOOH). In general, the
significant supramolecular interactions between various surface-
modified gold nanoparticles and fluorescent polymers can be
distinguished by the distinct fluorescence quenching behavior
with specific quenching constants (KSV). In order to confirm the
fluorescence quenching effects on copolymers P1 and P4 by
AuSCOOH, UV-visible absorption analyses of copolymer
nanocomposites, containing AuSCOOH, were carried out. We
would expect the UV-visible absorption spectra to change if the
aggregation of fluorescent polymers is induced by the addition of
AuSCOOH. In the UV-visible absorption spectra (Fig. S5,
ESI†), the absorption peaks of copolymers P1 and P4 (350 and
520 nm in THF solutions) titrated by AuSCOOH do not red shift
with increasing Au nanoparticle concentrations (from 0 to 121
mM). These were the same processing conditions used for the
quenching titrations of fluorescent polymers P1 and P4 by Au
nanoparticles. The reasonably low concentrations (smaller than
121 mM) of AuSCOOH were maintained to avoid the aggrega-
tion of fluorescent copolymers and AuSCOOH nanoparticles.
Therefore, the aggregation effects on fluorescence quenching can
Fig. 6 TEM images of acid-functionalized gold nanoparticles (AuS-
COOH) blended with (a) self-H-bonded copolymer P1, (b) acid-pro-
tected copolymer P4, and (c) alkyl-functionalized gold nanoparticles
(AuSC10) blended with self-H-bonded copolymer P1.
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acid units in surface-functionalized gold nanoparticles (AuS-
COOH) and copolymer P1 of nanocomposite P1–AuSCOOH
will compete with each other to form H-bonds with the pyridyl
groups on the copolymer P1. The addition of acid-modified gold
nanoparticles (AuSCOOH) to copolymers P1 and P4 created
two distinct aggregated structures. In Fig. 6(a), AuSCOOH
nanoparticles (incompletely H-bonded to P1) were only partially
dispersed in copolymer P1. This was due to the self-H-bonded
copolymeric structures of the pendent pyridyl H-acceptors self-
assembled with its own pendent H-donors in P1. Therefore, the
layered self-H-bonded copolymeric structures of P1 were clearly
visible in this TEM micrograph. On the other hand, as AuS-
COOH nanoparticles were blended with the non-self-H-bonded
copolymer P4, more carboxylic acid surfactants from AuS-
COOH nanoparticles were directly H-bonded with the pyridyl
H-acceptor groups of the acid-protected copolymer P4. AuS-
COOH nanoparticles were well distributed among copolymer
P4, as shown in Fig. 6(b). The self-assembled phenomena of H-
bonding between H-donors (from both copolymers and nano-
particles) and polymeric H-acceptors are dependent on all
existing carboxylic acid groups (H-donors) available for the
supramolecular architectures. Hence, AuSCOOH nanoparticles
are more homogeneously dispersed in the acid-protected copol-
ymer P4 and less uniformly dispersed in self-H-bonded copol-
ymer P1. Besides, as shown in Fig. S6 (ESI†), a similar
aggregation trend of AuSCOOH nanoparticles was observed in
the TEM images of nanocomposites containing various isomeric
copolymers (self-H-bonded copolymers P2 and P3 and non-self-
H-bonded copolymers P5 and P6). In order to distinguish the
contribution from the acid and acid-free surfactants on surface-
modified nanoparticles (AuSCOOH and AuSC10, respectively),
the self-H-bonded copolymer P1 was blended with non-acid-
modified AuSC10 nanoparticles (without H-bonds between
copolymer P1 and AuSC10 nanoparticles). Thus, it is clearly
observed in Fig. 6(c) that non-acid-modified nanoparticles
(AuSC10) aggregate more extensively. This suggests that no H-
bonding interactions occurred between AuSC10 nanoparticles
and copolymer P1. Overall, the TEM morphologies of H-bonded
architectures demonstrate the versatility of the self-assembly
processes in supramolecular nanocomposites of H-acceptor
polymers and H-donor nanoparticles.
further confirmed by FT-IR spectroscopy and XRD measure-
ments. Furthermore, the H-bonding interactions between acid-
modified gold nanoparticles (AuSCOOH) and acid-protected
copolymer P4 affect the fluorescence quenching more effectively,
when compared with the fluorescence titrations of acid-free-
modified gold nanoparticles (AuSC10). Moreover, in contrast to
the self-H-bonded copolymer P1, the acid-protected copolymer
P4 more readily captures acid-modified gold nanoparticles
(AuSCOOH) in the supramolecular assembly of nano-
composites. The H-bonding interactions between the pyridyl H-
acceptor (from the copolymers) and the acid H-donor units
(from both nanoparticles and copolymers) can explain the
similarities in fluorescence quenching effects on both copolymers
P1 and P4. Various nanocomposites containing two kinds of
fluorescent copolymer counterparts (self-H-bonded copolymer
P1 and acid-protected copolymer P4) and surface-modified
nanoparticles (acid-modified AuSCOOH and acid-free-modified
AuSC10) were developed to display distinct aggregation
phenomena in TEM images. The pyridyl H-acceptor units of
copolymer P1 would not only bind with its own para-benzoic
acid groups but also with the other proton donor surfactants
from AuSCOOH nanoparticles. Overall, this study is the first to
explore the supramolecular assembly behavior of nano-
composites between fluorescent copolymers and surface-func-
tionalized gold nanoparticles via both PL quenching phenomena
and TEM morphologies. Based on the fluorescence quenching
and recovery of gold nanocomposites, further chemosensor and
biosensor applications of this study can be developed in the near
future.
Acknowledgements
We are grateful to the National Center for High-performance
Computing for computer time and facilities. The powder XRD
measurements are supported by beamline BL17A (charged by Dr
Jey-Jau Lee) of the National Synchrotron Radiation Research
Center (NSRRC), in Taiwan. The TEM measurements are sup-
ported by the Sinica, in Taiwan. The financial support provided
by the National Science Council of Taiwan (ROC) through NSC
96-2113-M-009-015 and Chung-Shan Institute of Science and
Technology (in Taiwan) are acknowledged for this project.
Conclusions
References
In conclusion, the mesomorphic and photoluminescent proper-
ties of H-bonded copolymers and homopolymer complexes are
affected by the isomeric H-donors with different acid-substituted
(para, meta, and ortho) positions. These H-bonded complexes
can generate supramolecular architectures either through self-H-
bonded copolymers or by p-conjugated H-acceptor homopoly-
mers blended with H-donor homopolymers. The supramolecular
structures have the nematic and smectic C (Sc) phases that are
related to their bent and linear H-bonded structures, respectively.
The photoluminescent properties of self-H-bonded copolymers,
as well as the H-bonded homopolymer complexes, can be tuned
by the isomeric H-donor moieties, and red-shifted PL emissions
are expected in the H-bonded structures. Supramolecular archi-
tectures that contain H-bonds in self-H-bonded copolymers P1–
P3 and H-bonded homopolymer complexes PBT1/P7–P9 are
1 O. Ikkala and G. T. Brinke, Science, 2002, 295, 2407.
2 S. I. Stupp, S. Son, H. C. Lin and L. S. Li, Science, 1993, 259, 59.
3 T. Kato, N. Mizoshita and K. Kishimoto, Angew. Chem., Int. Ed.,
2006, 45, 38.
4 (a) X. J. Ma, Y. T. Shen, K. Deng, H. Tang, S. B. Lei, C. Wang,
Y. L. Yang and X. Z. Feng, J. Mater. Chem., 2007, 17, 4699; (b)
X. J. Li, R. B. Wen, Y. Zhang, L. R. Zhu, B. L. Zhang and
H. Q. Zhang, J. Mater. Chem., 2009, 19, 236; (c) T. Kajitani,
S. Kohmoto, M. Yamamoto and K. Kishikawa, J. Mater. Chem.,
2004, 14, 3449.
ˇ
ꢀ
5 W. Pisula, Z. Tomovic, M. Wegner, R. Graf, M. J. Pouderoijen,
E. W. Meijer and A. P. H. J. Schenning, J. Mater. Chem., 2008, 18,
2968.
6 Y. G. Liang, H. B. Wang, S. W. Yuan, Y. G. Lee, L. Gan and
L. P. Yu, J. Mater. Chem., 2007, 17, 2183.
7 T. Kato, T. Matsuoka, M. Nishii, Y. Kamikawa, K. Kanie,
T. Nishimura, E. Yashima and S. Ujiie, Angew. Chem., Int. Ed.,
2004, 43, 1969.
4762 | J. Mater. Chem., 2009, 19, 4753–4763
This journal is ª The Royal Society of Chemistry 2009

View Article Online
8 H. Mamlouk, B. Heinrich, C. Bourgogne, B. Donnio, D. Guillon and
D. Felder-Flesch, J. Mater. Chem., 2007, 17, 2199.
9 (a) M. Wanunu, R. P. Biro, H. Cohen, A. Vaskevich and
I. Rubinstein, J. Am. Chem. Soc., 2005, 127, 9207; (b) S. O. Obare,
R. E. Hollowell and C. J. Murphy, Langmuir, 2002, 18, 10407.
10 T. M. Swager, Acc. Chem. Res., 1998, 31, 201.
33 (a) M. C. Daniel and D. Astruc, Chem. Rev., 2004, 104, 293; (b)
C. Burda, X. Chen, R. Narayanan and M. A. El-Sayed, Chem.
Rev., 2005, 105, 1025.
34 B. C. Sih and M. O. Wolf, Chem. Commun., 2005, 3375.
35 M. K. Corbierre, N. S. Cameron, M. Sutton, S. G. J. Mochrie,
€
L. B. Lurio, A. Ruhm and R. B. Lennox, J. Am. Chem. Soc., 2001,
123, 10411.
11 L.-J. Fan and W. E. Jones Jr., J. Am. Chem. Soc., 2006, 128, 6784.
´
ꢀ~
ꢀ
12 R. Martınez-Manez and F. Sancenon, Chem. Rev., 2003, 103, 4419.
13 S. J. Broadwater, M. K. Hickey and D. T. McQuade, J. Am. Chem.
Soc., 2003, 125, 11154.
36 A. K. Boal, F. Ilhan, J. E. DeRouchey, T. Thurn-Albrecht,
T. P. Russell and V. M. Rotello, Nature, 2000, 404, 746.
37 R. Shenhar and V. M. Rotello, Acc. Chem. Res., 2003, 36, 549.
38 A. K. Boal, T. H. Galow, F. Ilhan and V. M. Rotello, Adv. Funct.
Mater., 2001, 11, 461.
14 L. J. Fan and W. E. Jones Jr., J. Phys. Chem. B, 2006, 110, 7777.
15 A. Trabolsi, M. Elhabiri, M. Urbani, J. L. D. de la Cruz, F. Ajamaa,
ꢀ
N. Solladie, A.-M. Albrecht-Gary and J. F. Nierengarten, Chem.
Commun., 2005, 5736.
39 O. Uzun, B. L. Frankamp, A. Sanyal and V. M. Rotello, Chem.
Mater., 2006, 18, 5404.
16 S. W. Thomas III, G. D. Joly and T. M. Swager, Chem. Rev., 2007,
107, 1339.
40 J. B. Carroll, B. L. Frankamp and V. M. Rotello, Chem. Commun.,
2002, 1892.
17 (a) H. R. Li and S. Valiyaveettil, Macromolecules, 2007, 40, 6057; (b)
M. H. Nurmawati, P. K. Ajikumar, L. A. Heng, H. R. Li and
S. Valiyaveettil, Chem. Commun., 2008, 4945.
18 C. Tan, M. R. Pinto and K. S. Schanze, Chem. Commun., 2002, 446.
19 B. S. Harrison, M. B. Ramey, J. R. Reynolds and K. S. Schanze, J.
Am. Chem. Soc., 2000, 122, 8561.
41 G. Cooke, J. F. Garety, S. G. Hewage, G. Rabani, V. M. Rotello and
P. Woisel, Chem. Commun., 2006, 4119.
42 J. B. Carroll, B. L. Frankamp, S. Srivastava and V. M. Rotello, J.
Mater. Chem., 2004, 14, 690.
43 B. L. Frankamp, O. Uzun, F. Ilhan, A. K. Boal and V. M. Rotello, J.
Am. Chem. Soc., 2002, 124, 892.
20 W. H. Binder, R. Sachsenhofer, C. J. Straif and R. Zirbs, J. Mater.
Chem., 2007, 17, 2125.
21 C. Fan, K. W. Plaxco and A. J. Heeger, J. Am. Chem. Soc., 2002, 124,
5642.
22 R. D. McCullough, P. C. Ewbank and R. S. Loewe, J. Am. Chem.
Soc., 1997, 119, 633.
23 B. S. Gaylord, A. J. Heeger and G. C. Bazan, J. Am. Chem. Soc., 2003,
125, 896.
44 T. Huang and R. W. Murray, Langmuir, 2002, 18, 7077.
45 P. P. H. Cheng, D. Silvester, G. Wang, G. Kalyuzhny, A. Douglas
and R. W. Murray, J. Phys. Chem. B, 2006, 110, 4637.
46 B. I. Ipe, K. G. Thomas, S. Barazzouk, S. Hotchandani and
P. V. Kamat, J. Phys. Chem. B, 2002, 106, 18.
47 (a) X. He, H. Liu, Y. Li, S. Wang, Y. Li, N. Wang, J. Xiao, X. Xu and
D. Zhu, Adv. Mater., 2005, 17, 2811; (b) X. H. Zhou, J. C. Yan and
J. Pei, Macromolecules, 2004, 37, 7078; (c) X. He, Z. Zhong,
Y. Guo, J. Lv, J. Xu, M. Zhu, Y. Li, H. Liu, S. Wang, Y. Zhu and
D. Zhu, Langmuir, 2007, 23, 8815.
24 J. Kim, D. T. McQuade, S. K. McHugh and T. M. Swager, Angew.
Chem., 2000, 112, 4026.
25 M. Kimura, T. Horai, K. Hanabusa and H. Shirai, Adv. Mater., 1998,
10, 459.
48 (a) H. C. Lin, H. Y. Sheu, C. L. Chang and C. Tsai, J. Mater. Chem.,
2001, 11, 2958; (b) H. C. Lin, Y. S. Lin, Y. S. Lin, Y. T. Chen, I. Chao
and T. W. Li, Macromolecules, 1998, 31, 7298.
49 (a) H. C. Lin, C. M. Tsai, G. H. Huang and Y. T. Tao,
Macromolecules, 2006, 39, 557; (b) C. W. Wu and H. C. Lin,
Macromolecules, 2006, 39, 7985.
26 K. G. Thomas and P. V. Kamat, Acc. Chem. Res., 2003, 36, 888.
27 A. Bayir, B. J. Jordan, A. Verma, M. A. Pollier, G. Cooke and
V. M. Rotello, Chem. Commun., 2006, 4033.
28 S. Barazzouk, P. V. Kamat and S. Hotchandani, J. Phys. Chem. B,
2005, 109, 716.
50 M. Portugall, H. Ringsdorf and R. Zentel, Makromol. Chem., 1982,
183, 2311.
ꢀ
29 T. Hasobe, K. Saito, P. V. Kamat, V. Troiani, H. Qiu, N. Solladie,
K. S. Kim, J. K. Park, D. Kim, F. D’Souza and S. Fukuzumi, J.
Mater. Chem., 2007, 17, 4160.
51 G. G. Guilbault, Practical Fluorescence, Marcel Dekker Inc., New
York, 1990.
30 B. Gadenne, I. Yildiz, M. Amelia, F. Ciesa, A. Secchi, A. Arduini,
A. Credi and F. M. Raymo, J. Mater. Chem., 2008, 18, 2022.
31 A. C. W. Leung and M. J. MacLachlan, J. Mater. Chem., 2007, 17,
1923.
52 (a) S. E. Odinokov, A. A. Mashkovshky, V. P. Glazunov,
A. V. Iogansen and B. V. Rassadin, Spectrochim. Acta, 1976, 32A,
1355; (b) J. Y. Lee, P. C. Painter and M. M. Coleman,
Macromolecules, 1988, 21, 954.
32 (a) H. Tong, L. Wang, X. Jing and F. Wang, Macromolecules, 2003,
36, 2584; (b) D. Wang, J. Wang, D. Moses, G. C. Bazan and
A. J. Heeger, Langmuir, 2001, 17, 1262; (c) X. H. Zhou, J. C. Yan
and J. Pei, Macromolecules, 2004, 37, 7078.
53 B. G. Tehan, E. J. Lloyd, M. G. Wong, W. R. Pitt, J. G. Montana,
D. T. Manallack and E. Gancia, Quant. Struct.-Act. Relat., 2002,
21, 457.
54 E. L. Cabarcos and S. A. Carter, Macromolecules, 2005, 38, 4409.
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