Alternative copolymerization of a conjugated segment and a flexible segment and fabrication of a fluorescent sensing film for HCl in the vapor phase

Article abstract of DOI:10.1002/asia.201200561

A novel fluorescently active co-oligomer (P1) was designed and prepared by alternative co-polymerization of oligo(p-phenyleneethynylene) (OPE), possessing two cholesterol-containing side chains, and ethanediamine. A control co-oligomer (P2) possessing similar structure to P1 was also prepared, but in this case the OPE bears no side chains. P1 and P2 have been used for the fabrication of two fluorescent films, film 1 and film 2, respectively. Fluorescence studies demonstrated that the emission of film 1 is sensitive and selective to the presence of trace amounts of HCl in air. In contrast, film 2 shows no such response. The quenching has been attributed to the protonation of the imino groups within the oligomer chains, and the difference in the sensing behaviors of the two films was rationalized by supposing the existence of molecular channels in film 1. The proposed mechanism is supported by the results from additional experiments and theoretical calculations. Furthermore, the film as fabricated is robust, and thereby it is believed that film 1 has the potential to be developed into a new generation of sensitive and selective HCl sensor. Copyright

Full text of DOI:10.1002/asia.201200561

FULL PAPER
DOI: 10.1002/asia.201200561
Alternative Copolymerization of a Conjugated Segment and a Flexible
Segment and Fabrication of a Fluorescent Sensing Film for HCl
in the Vapor Phase
Hongyue Wang, Hong Cui, Xinglei Liu, Lanlan Li, Yuan Cao, Taihong Liu, and
Yu Fang*[a]
Abstract: A novel fluorescently active
co-oligomer (P1) was designed and
prepared by alternative co-polymeri-
zation of oligo(p-phenyleneethynylene)
(OPE), possessing two cholesterol-con-
taining side chains, and ethanediamine.
A control co-oligomer (P2) possessing
similar structure to P1 was also pre-
pared, but in this case the OPE bears
no side chains. P1 and P2 have been
used for the fabrication of two fluores-
cent films, film 1 and film 2, respective-
ly. Fluorescence studies demonstrated
that the emission of film 1 is sensitive
and selective to the presence of trace
amounts of HCl in air. In contrast,
film 2 shows no such response. The
quenching has been attributed to the
protonation of the imino groups within
the oligomer chains, and the difference
in the sensing behaviors of the two
films was rationalized by supposing the
existence of molecular channels in
film 1. The proposed mechanism is sup-
ported by the results from additional
experiments and theoretical calcula-
tions. Furthermore, the film as fabricat-
ed is robust, and thereby it is believed
that film 1 has the potential to be de-
veloped into a new generation of sensi-
tive and selective HCl sensor.
Keywords: cholesterol
·
fluores-
cence · hydrogen chloride · oligo-
mers · sensors
Introduction
from HCl.[4] Therefore, sensitive and selective detection of
HCl in air is of great importance for monitoring the quality
of air and for the protection of our atmosphere.
The anthropogenic emission of chlorine has become an im-
portant issue in the monitoring and protection of the
Earthꢀs atmosphere.[1] Determination of the concentration
of hydrogen chloride (HCl) in air has attracted special at-
tention due to the hazardous potential of this compound,[2]
such as causing acid rain, contributing to the formation of
dioxin,[3] and catalytically destroying tropospheric ozone.[1,4]
Thornton and co-workers reported that HCl is present in air
It is known that HCl in air is primarily produced by burn-
ing fuels and wastes, which contain chlorine in various
states.[5] HCl is also widely used in industries, such as manu-
facturing processes for electronics. Direct release is also an
important source for HCl in air. HCl is not only a destroyer
to tropospheric ozone, but it is also toxic and corrosive to
the human body. This might be the reason why HCl concen-
tration in workplace is strictly regulated. In Japan, for exam-
ple, the limit is 5 ppm with a short exposure period.[6] There-
fore, for emission control and air-quality monitoring, various
types of HCl vapor sensors have been developed and report-
ed.[3,6,7]
Traditionally, chemical species in air are measured by
wet-chemical methods, which means that the target chemi-
cals are extracted from the source, preconditioned, and sent
into a suitable chemical reactor where the concentration is
deduced.[8] Sasso and co-workers reported an absorption
spectrometer based on tunable diode lasers in the near-in-
frared region that allows sensitive detection of HCl.[8] Naka-
gawa et al. reported some HCl-sensitive photoactive compo-
site films, which were produced by embedding tetraphenyl-
porphyrin (TPPH2) or its derivatives in various polymer ma-
trixes.[9–11] However, these methods suffer from one or sever-
al drawbacks, for example, sensing has to be performed at
high temperatures, the sensing process is relatively slow, in-
terference from other compounds is common, and some-
times sophisticated instruments are needed.[3,12] Therefore,
at parts-per-billion (10À9, ppb) or parts-per-trillion (10À12
,
ppt) levels, on the basis of results from cavity ring-down
spectroscopy (CRDS) measurements.[4] Their study shows
that night-time reaction of nitrogen oxides (NOx) with HCl
produces chlorine atom precursor, ClNO2. This compound
then decomposes into atomic Cl and NOx under the sun-
light. Atomic Cl is very reactive and destroys ozone over
a long period of time. The NOx as produced recycles to
react again with HCl at night. Clearly, the primary destroyer
of tropospheric ozone is atomic Cl, which mainly comes
[a] H. Wang, H. Cui, X. Liu, L. Li, Y. Cao, Dr. T. Liu, Prof. Dr. Y. Fang
Key Laboratory of Applied Surface and Colloid Chemistry (Ministry
of Education)
School of Chemistry and Chemical Engineering
Shaanxi Normal University
Xi’an 710062 (P. R. China)
Fax : (+86)29-85310097)
E-mail: yfang@snnu.edu.cn
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201200561.
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development of new HCl sensors with superior performance
remains a challenge.
introduce biding sites into the films. One way is to introduce
imide groups by alternative co-polymerization of OPE with
an organic diamine. Accordingly, in this work, cholesterol
has been purposely introduced into OPE as a side chain via
a relatively long alkyl chain, and then the functionalized
OPE was copolymerized with ethanediamine. In this way,
a fluorescently active copolymer possessing both rigid and
soft structural segments was prepared and utilized for the
fabrication of fluorescent sensing film. It was found that the
film as fabricated shows a super-sensitive response to HCl in
the vapor phase.
Conjugated polymers (CPs) or oligomers have been
widely adopted as sensing fluorophores owing to the fact
that they are not only fluorescently active but also possess
the so-called super-quenching effect because of their unique
structure, which allows them to respond to a quencher in
a “one-point contact, multipoint response” manner.[12–15]
However, diffusion of analytes to be tested within the films
fabricated by using conjugated polymers as sensing fluoro-
phores is always a severe problem to affect the performance
of the films, in particular the response time and the sensitivi-
ty.[16–18] To solve this problem, various efforts have been
made, for example, the introduction of bulky side groups
and the fabrication of films in the presence of surfactants to
create molecular channels.[18] A few years ago, our group
proposed a new strategy to solve the problem. In the effort,
conjugated oligomers rather than conjugated polymers were
adopted as sensing fluorophores, and they were chemically
immobilized in a monomolecular layer way onto a substrate
surface. It is believed that in this way diffusion problems
should be automatically avoided. In fact, several fluores-
cence sensing films with superior performances have been
created accordingly.[19–22] However, a new challenge appears:
creation of new sensing films becomes very hard because of
the difficulties in synthesis. To keep the advantages of the
proposed strategy and avoid the difficulties, we recently pro-
posed another idea. If the conformation of the side chains
of an immobilized conjugated oligomer is sensitive to the
changes in its microenvironment, then a corresponding film
should act as a sensor, because the fluorescence behavior of
the oligomer should change accordingly. Again, on the basis
of this idea, a few sensing films were created.[23,24] During
the studies, we found that introduction of cholesterol side
chains via a long alky chain into a conjugated oligomer or
other fluorophore, specifically oligo(p-phenyleneethynylene)
(OPE) or perylene imide,[25] imparts the oligomer or the flu-
orophore an excellent ability to form films, which is crucial
for fabrication of sensing films.
Results and Discussion
Characterization of Film 1
Figure 1 shows the AFM image of film 1 and the SEM
image of film 2. The images reveal that P1 aggregated into
microparticles with an average diameter of about 0.5 mm.
Figure 1. a) An AFM image of film 1, and b) an SEM image of film 2.
This may not be a very surprising result considering that
THF is a good solvent for the oligomer but methanol is not.
Therefore, addition of the THF solution of the oligomer to
methanol must result in flocculation of the oligomer. Clear-
ly, the particles as observed must be the aggregates from the
flocculation. In comparison, P2 aggregated into much bigger
particles and even flakes due to the poor solubility of P2 in
both THF and methanol. As expected, the morphologies of
the aggregates of the oligomers on the substrate surface are
stable no matter how long the films were exposed to air or
immersed in water. Furthermore, both the intensity and the
profile of the fluorescence emission are independent of the
exposure or immersing time, suggesting that the films can be
considered for sensing applications in air and in aqueous
medium.
No doubt, combination of the advantages of the conjugat-
ed oligomers and those of the cholesterol may bring new op-
portunities for creating fluorescent sensing films with good
performance. For HCl sensing, it should be a bright idea to
Abstract in Chinese:
Steady-State Excitation and Emission of the Films
The fluorescence excitation and emission spectra of the olig-
omers P1 and P2 in THF and the films fabricated by using
them as fluorophores were recorded, and the results are de-
picted in Figure 2. It is seen that the maximum excitation
and emission of film 1 appear at 370 and 490 nm, respective-
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Yu Fang et al.
ly (Figure 2a), which are significantly red-shifted from those
of film 2. The red shift might be attributed to the higher de-
grees of aggregation of oligomer P1 due to its bulky side
chains, which makes the oligomer aggregate even in its good
solvent, THF.[26] For P2, neither THF nor methanol is
a good solvent, and thereby it may remain solid during the
fabrication of film 2 (c.f. Scheme 1). To elucidate this tenta-
tive explanation further, the fluorescence excitation and
emission spectra of the two oligomers in THF were also re-
corded (Figure 2b). The absorption and emission maxima of
P1 are significantly red-shifted from those of P2, indirectly
suggesting that the red shift observed in the film measure-
ments originates not only from aggregation in the fabrica-
tion process but also from differences in the aggregation of
the two oligomers in THF. The strong aggregation tendency
of P1 in THF may be attributed to the introduction of cho-
lesterol, although it only promotes formation of loosely
packed aggregates of the backbones of the molecules of P1.
Furthermore, the fluorescent films are robust and photo-
chemically stable, which is a prerequisite for sensing applica-
tions.
HCl Vapor Sensing Studies
Figure 3a depicts the fluorescence emission spectra of film 1
in the presence of different concentrations of HCl vapor.
Exposing the film to 5 ppb HCl results in significant fluores-
cence quenching, and exposure to 140 ppb HCl results in
nearly 90% reduction of the initial emission intensity of
film 1 at 490 nm. Further increase of the HCl concentration
Figure 2. The excitation and emission spectra of a) film 1 and film 2, and
b) P1 and P2 in THF (10 mgmLÀ1).
Scheme 1. a) Synthetic routes to P1 with cholesterol in its side-chains and to P2. b) Fabrication of a fluorescent sensing film (film 1) or a control film
(film 2) with P1 or P2 as the fluorophore.
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Figure 3. a) Fluorescence emission spectra of film 1 in the presence of dif-
ferent concentrations (from top to bottom: 0, 5, 10, 55, 70, 100, 125, 140,
150, 280, and 560 ppb) of HCl. b) Fluorescence emission spectra of film 1
recorded at different times (from top to bottom: 0, 10, 20, 40, 60, 120,
240, 720, 960, 1800 s) after addition of 140 ppb of HCl (lex =370 nm).
Figure 4. a) Quenching efficiencies of various acids in the vapor state
(140 ppb) to the fluorescence emission of the films. b) Quenching effi-
ciencies of various acids in solution (THF, 50 mm) to the fluorescence
emission of P1 (0.1 mgmLÀ1; lex =370 nm). The results are averages from
three measurements.
does not quench the emission any further. Figure 3b shows
the time dependence of the fluorescence emission of the
film in the presence of 140 ppb HCl vapor. About 240 s are
needed for the quenching to reach equilibration. The detec-
tion limit (DL) of film 1 to HCl in air is about 0.9 ppb. The
details of the calculation of DL are provided in the Support-
ing Information.
To understand the effects of other acids, including HF,
HCl, HBr, HI, HCOOH, CH3COOH, and HNO3, to the
fluorescence emission of film 1 in vapor phase, similar meas-
urements as described for HCl were also conducted (Fig-
ure 4a). For comparison, the sensing performance of film 2
was also examined, and the results are also shown. It may
be concluded that the quenching efficiencies of the gases to
the fluorescence emission of film 1 follow the order of
HCl>HCOOH>CH3COOH>HNO3 >HF, HBr, and HI.
The differences in the quenching abilities of the compounds
to the emission of film 1 might be a result of acidity and mo-
lecular size effects.
molecules that it contacts. Thus, poor diffusion means lower
quenching efficiency, explaining why film 2 shows almost no
ability to sense the presence acid, because the particles from
P2 are likely too dense owing to their lack of side chains.
For the quenching of the fluorescence emission of the two
oligomers prepared in the present study, another prerequi-
site is the protonation of the imino groups within the oligo-
mer chains, as will be discussed later. Similarly, for film 1,
the size of the analyte molecules must also be one of the im-
portant factors affecting their quenching efficiencies. Of the
compounds studied, HF and HCl are smaller than others
(Table S1 in the Supporting Information), and they should
exhibit higher quenching efficiencies. However, HF almost
shows no effect on the emission of the film. This result
might be understood by considering the weakly acidic
nature of HF (Table S1 in the Supporting Information), and
for this reason protonation of the imino groups within the
oligomer becomes impossible. For HCl, its small size and
strongly acidic nature guarantee its highest quenching effi-
ciency to the fluorescence emission of film 1. Similar explan-
ation can be also applied to the quenching behaviors of
other acids (Figure 4a). The better compatibility of
HCOOH and CH3COOH to the polymeric particles might
As mentioned earlier, diffusion of analyte within a film
layer, for the present case within the particles, is a crucial
factor to determine the performance of a film sensor. The
analyte can only quench the emission of the fluorophore
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be another important factor to explain their high quenching
efficiencies. This tentative explanation is supported by the
results from fluorescence quenching studies of P1 in THF
(Figure 4b). In this case, the quenching efficiencies of the
acids are very different from those in the vapor phase (Fig-
ure 4a). In solution, generally speaking, the inorganic acids
show much higher quenching efficiencies than the organic
acids do. This might be understood by considering that or-
ganic acids possess much higher solubility in THF than the
inorganic acids; in other words, their compatibility to the
solvent is good. Furthermore, in this solvent the ionization
tendency to produce protons is weak, and thereby protona-
tion of the imino groups within the oligomer chains is hard
to realize. This should explain why these acids show no sig-
nificant quenching effect to the emission of the film. For the
inorganic acids, the order of the quenching efficiencies may
be a reflection of the hardness of ionization of protons from
the acid molecules (see Table S1 in the Supporting Informa-
tion). This tentative explanation was further confirmed by
X-ray photoelectron spectroscopy (XPS) measurements. Fig-
ure 5a depicts the XPS spectra of film 1 treated with differ-
ent acids vapors. The signals of Cl 2p, F 1s and I 3d3, I 3d5
have been detected after treatment by HCl, HF, and HI, re-
spectively, but the I 3d3 and I 3d5 signals are very weak, thus
providing direct evidence that HI does not readily diffuse
into the fluorescent particles. Furthermore, careful study of
the high-resolution XPS traces suggests that the intensities
of the N 1s signal (Figure 5b–d) are dependent upon the
nature of the acids which were employed for the treatment
of the film. It is clear that the signal of the protonated N 1s
of the film treated by HCl is significant, but the others treat-
ed by HF or HI are relatively weak, a result explaining why
HCl is an efficient quencher of the fluorescence emission,
but HF and HI are not.
Figure 5. a) XPS traces of film 1 treated with HCl, HF, and HI, respec-
tively, and b–d) the N 1s signal of film 1 treated with HCl (b), HF (c),
and HI (d).
Sensing Mechanism Studies
As mentioned above, it is believed that protonation of the
imino groups within the oligomer chains necessary for the
quenching of their fluorescence emission (Figure 6a). To
elucidate this point, quantum-chemical calculations of the
energies of the highest occupied molecular orbital (HOMO)
and the lowest unoccupied molecular orbital (LUMO) of P1
and those of the protonated state, P1H at the DFT/B3LYP/
6-31G* level using Gaussian 09 were conducted. Figure 6c
depicts the results. Clearly, protonation alters the structures
of the frontier orbitals greatly, and in particular the gap be-
tween the two orbitals changes from 3.45 to 2.51 eV, which
Figure 6. a) Schematic representation of the proton-transfer mechanism for the quenching of the fluorescence emission of film 1. b) Fluorescent micro-
graphs of film 1 before and after exposure to HCl vapor. c) The frontier orbital energy correlation diagram and the frontier molecular orbitals of P1 in
neutral and protonated states.
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Synthesis of 1
may explain why protonation quenches the fluorescence
emission at the original position.
A mixture of cholesterol (6 g, 15.5 mmol), 1,8-dibromo-octane (14.29 mL,
77.5 mmol), KOH (3.48 g, 62 mmol), and dry THF (50 mL) was stirred
under argon at 808C for 48 h. The solvent was evaporated under reduced
pressure, and the residue was diluted with CH2Cl2 (50 mL), washed with
brine (50 mL), and then dried over MgSO4. The MgSO4 was removed by
vacuum filtration, and the filtrate was evaporated to dryness. The result-
ing yellow oil was purified by column chromatography on silica gel
column with petroleum ether:CH2Cl2 (v:v, 1:1) as eluent to afford com-
pound 1 as white solid (yield 64%). Melting point : 69–718C. IR (KBr):
Conclusions
A novel derivative of OPE was produced by introducing
two cholesteryl structures into its side positions via two rela-
tively long alky chains. An alternative co-oligomer based on
OPE was synthesized by simple condensation of a fluores-
cent active compound with ethanediamine. The co-oligomer
as obtained was successfully used for the fabrication of a su-
persensitive fluorescence sensing film for HCl in the vapor
phase. Comparison studies demonstrated that both the
bulky side chains and the flexible segments containing imino
groups are crucial for the formation and for the superior
performance of the film. Quantum chemical calculations
reveal that the quenching is due to protonation of the imino
groups within the oligomer chains. Furthermore, the present
study shows that the film as designed and fabricated has the
potential to be developed into an HCl film sensor.
n˜ =2931, 2852, 1461, 1381 cmÀ1 1H NMR (300 MHz, CDCl3): d=5.33 (s,
.
1H), 3.46–3.37 (m, 4H), 3.10–3.12 (m, 1H), 2.34–0.67 ppm (m, 55H).
Synthesis of 2
A mixture of compound 1 (2 g, 3.5 mmol), 2,5-diiodobenzene-1,4-diol[29]
(0.5 g, 1.4 mmol), KOH (0.63 g, 11.2 mmol), dry THF (10 mL) and dry
DMSO (30 mL) was stirred under argon atmosphere at room tempera-
ture for 48 h. Then, the reaction mixture was poured onto water
(300 mL), resulting in precipitation of a white solid. The residue was col-
lected, washed with water, dried, and purified by column chromatogra-
phy on silica gel column with petroleum ether: CH2Cl2 (v:v, 2:3) to
afford compound 2 as white solid (yield 55%). Melting point : 149–
1518C. IR (KBr): n˜ =2931, 2852, 1461, 1381, 1213 cmÀ1
.
1H NMR
(300 MHz, CDCl3): d=7.16 (s, 2H), 5.33 (s, 2H), 4.01–3.95 (m, 4H),
3.44–3.39 (m, 4H), 3.10–3.12 (m, 2H), 2.34–0.67 ppm (m, 110H). Elemen-
tal anal. (%) calcd. for C76H124O4I2: C 67.34, H 9.22; found: C 66.99,
H 9.50.
Experimental Section
Materials
Synthesis of 3
Compound
2
(500 mg, 0.37 mmol), 4-ethynylbenzaldehyde (144 mg,
(PPh3)4] (21.3 mg, 0.018 mmol), and CuI (3.5 mg,
1.1 mmol), [PdACHTUNGTRENNUNG
4-Ethynylbenzaldehyde (Alfa, 98%), 1,4-diiodobenzene (Alfa, 98%),
0.018 mmol) were added to a solution of diisopropylamine (3 mL) in tol-
uene (7 mL). The reaction mixture was stirred under argon at 708C for
48 h, then diluted with CH2Cl2 (50 mL), and then washed with brine
(50 mL), and finally dried over MgSO4. The MgSO4 was removed by
vacuum filtration, and the filtrate was evaporated to dryness. The result-
ing yellow solid was purified by column chromatography on silica gel
column with THF:CH2Cl2 (v:v, 1:60) to afford compound 3 as a yellow
solid (yield 72%). Melting point : 119–1218C. IR (KBr): n˜ =3433, 2931,
1,4-di-methoxybenzene (Sigma, 99%), [PdACHTNUTRGNE(UNG PPh3)4] (Alfa, 99%), and CuI
(Alfa, 98%) were used as received. All manipulations for the preparation
of the relevant compounds were performed using a standard vacuum line
and Schlenk technique under a purified-argon atmosphere. THF and tol-
uene were distilled from sodium benzophenone ketyl under argon prior
to use.
Measurements
2852, 2730, 2208, 1707, 1604, 1461, 1381, 1213 cmÀ1 1H NMR (300 MHz,
.
Fluorescence measurements were performed at room temperature on
a time-correlated single-photon-counting Edinburgh FLS 920 fluores-
cence spectrometer with a front-face method. The fabricated film was in-
serted into a quartz cell with its surface facing the excitation light source.
The position of the film was kept constant during each set of measure-
ments. Pressed KBr disks for the powder samples were used for the
transmission infrared (FTIR) spectroscopy measurements, and their
CDCl3): d=10.0 (s, 2H), 7.88–7.85 (d, 4H), 7.68–7.65 (d, 4H), 7.02–7.01
(d, 2H), 5.33 (s, 2H), 4.05–4.01 (m, 4H), 3.44–3.39 (m, 4H), 3.10–3.12
(m, 2H), 2.34–0.67 ppm (m, 110H). MS: (m/z, [M+Na]+): calculated:
1382.02, Found: 1382.97.
Synthesis of 4
This compound was synthesized according to a literature method.[30]
FTIR spectra were obtained with
a Bio-Rad FTIR spectrometer.
1H NMR spectra were measured on Bruker AV 300 NMR spectrometers.
The MALDI-TOF mass spectra were recorded in a Microflex mass ana-
lyzer (Bruker, USA) using dithranol as the MALDI matrix. AFM meas-
urements of the films were conducted on a SOLVER P47 PRO system.
SEM pictures of the films were obtained on a Quanta 200 scanning elec-
tron microscope (Philips-FEI). X-ray photoelectron spectroscopy (XPS)
measurements were carried out on an ESCAPHI5400 photoelectron
spectrometer. Molecular weights of the polymers or oligomers were de-
Synthesis of P1
Compound
3 (100 mg, 0.073 mmol) and ethanediamine (0.005 mL,
0.073 mmol) were added to THF (20 mL). The mixture was stirred under
argon at 708C for 48 h. After cooling to room temperature, NaBH4
(0.1 g, 2.6 mmol) was added and stirred for another 48 h. Then, the reac-
tion mixture was diluted with CH2Cl2 (50 mL), washed with brine
(50 mL), and then dried over MgSO4. The MgSO4 was removed by
vacuum filtration, and the filtrate was evaporated to dryness. The solid
was washed repeatedly with hot methanol and then dried overnight at
508C to afford P1 as yellow solid (yield 75%). IR (KBr): n˜ =3433, 2931,
termined on
a GPC instrument. This instrument is equipped with
a Waters 717 plus autosampler, a Waters 1515HPLC pump, three m-Styra-
gel columns, and a Waters 2414 refractive index (RI) detector. During
the measurements, the instrument was calibrated with polystyrene stand-
ards. The fluorescence tests were conducted in the following way: first,
a film to be tested was adhered to one inner side of a quartz cell, the
fluorescence emission spectrum of the system was recorded, and then the
quartz cell was placed in a bottle containing a specific concentration of
HCl vapor. Five minutes later, the fluorescence spectrum of the system
was recorded.[27, 28]
2852, 1604, 1461, 1381, 1213 cmÀ1 1H NMR (300 MHz, CDCl3): d=7.50–
.
7.47 (d, 4H), 7.17–6.98 (d, 4H) 5.33 (s, 2H), 4.05–4.01 (m, 4H), 3.44–3.39
(m, 4H), 3.10–3.12 ppm (m, 2H). Mn =1.86ꢂ104 by gel permeation chro-
matography (GPC, polydispersity index 2.1).
Synthesis of P2
Compound
4
(10 mg, 0.03 mmol) and ethanediamine (0.002 mL,
0.03 mmol) were added to THF (20 mL). The mixture was stirred under
argon at 708C for 48 h. NaBH4 (0.1 g, 2.6 mmol) was added and stirred
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Yu Fang et al.
for another 48 h. After the mixture was cooled to room temperature,
a precipitate formed. The precipitate was collected and washed repeated-
ly with methanol to afford P2 as yellow solid. However, the 1H NMR
spectral and GPC data for this co-polymer or oligomer cannot be ob-
tained because of its poor solubility in common solvents.
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ly dried at 1008C in
a dust-free oven for 1 h. P1 or P2 in THF
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Acknowledgements
The authors thank the Natural Science Foundation of China (Nos.
20927001, 20803046, 91027017 and 21173142), the 13115 Project of
Shaanxi Province (2010-ZDKG-89) and Program for Changjiang Scholars
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Received: June 22, 2012
Published online: October 10, 2012
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