The self-assembly effect in NLO polymers containing isolation chromophores: Enhanced NLO coefficient and stability

Article abstract of DOI:10.1039/c3nj00048f

In this paper, a facile route was designed to prepare four new NLO polyaryleneethynylenes, which were constructed by two different chromophore moieties with the regular AB structure, to achieve a high NLO coefficient according to our recent work on isolation chromophores . Meanwhile, normal aromatic rings or perfluoroaromatic rings were also introduced as isolation groups to investigate the aromatic/perfluoroaromatic (Ar-Ar ^F) self-assembly effect in these NLO polymers. Thanks to the helpful self-assembly effect, the NLO effect and stability of P2, with perfluorophenyl groups as isolation groups, were improved to a large degree, in comparison with its analog P1 containing normal phenyl groups as isolation groups.

Full text of DOI:10.1039/c3nj00048f

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The self-assembly effect in NLO polymers containing
isolation chromophores: enhanced NLO coefficient and
stability†
Cite this: NewJ.Chem., 2013,
37, 1789
Wenbo Wu,a Zhen Xu,a Ying Xiong,*a Shaohui Xin,a Hongding Tang,a Cheng Ye,b
Guofu Qiu,c Jingui Qina and Zhen Li*a
In this paper, a facile route was designed to prepare four new NLO polyaryleneethynylenes, which were
constructed by two different chromophore moieties with the regular AB structure, to achieve a high
NLO coefficient according to our recent work on ‘‘isolation chromophores’’. Meanwhile, normal
aromatic rings or perfluoroaromatic rings were also introduced as isolation groups to investigate the
aromatic/perfluoroaromatic (Ar–ArF) self-assembly effect in these NLO polymers. Thanks to the helpful
self-assembly effect, the NLO effect and stability of P2, with perfluorophenyl groups as isolation groups,
were improved to a large degree, in comparison with its analog P1 containing normal phenyl groups as
isolation groups.
Received (in Montpellier, France)
11th January 2013,
Accepted 28th March 2013
DOI: 10.1039/c3nj00048f
www.rsc.org/njc
materials, such as ‘‘H-type’’ chromophores,4a,5 ‘‘six branched’’
Introduction
chromophores6 and ‘‘star-type’’ chromphores,7 etc., have been
Organic second-order nonlinear optical (NLO) materials are actively
pursued due to their increasing potential for applications in
photonic devices, such as high-speed electro-optic modulators,
optical switches and frequency converters.1 For device applications,
NLO polymers should possess large NLO activity, low optical loss,
good temporal stability and processibility.2 Among them, how to
efficiently translate the large b values of the organic chromophores
into high macroscopic NLO activities of polymers, are the major
problems encountered in optimizing organic NLO materials.3 On
the basis of the site isolation principle proposed by Dalton and Jen
et al., since 2006, with an attempt to partially solve this challenge in
NLO materials, we prepared different kinds of NLO polymers, in
which the size of the isolation groups in the NLO chromophore
moieties was changed from small to large. Based on the obtained
experimental results, we proposed the concept of a ‘‘suitable
isolation group’’, for the enhancement of the macroscopic NLO
effect of polymers.4 Based on the ‘‘site isolation principle’’ and the
concept of a ‘‘suitable isolation group’’, many new concepts of NLO
proposed to enhance the NLO coefficient in recent years.
However, nearly all the isolation groups before 2012 were
designed to only adjust the shape of the chromophore and decrease
the strong interactions between the chromophore moieties,
according to the ‘‘site isolation principle’’ and the concept of a
‘‘suitable isolation group’’. In fact, the interactions between two
chromophores or two isolation groups should also be considered in
the design of NLO materials. In 2012, for the first time, our group
developed a new method by using the interactions between two
chromophores: isolation chromophores.8 The results showed that if
the NLO polymer consists of two types of chromophore moieties
with regular structures, its NLO coefficient could be improved by a
large degree, in comparison with its analog just containing one type
of chromophore (Chart S1, ESI†). On the other hand, different from
normal aromatic rings, perfluoroaromatic rings were electropositive,
and this activity could lead to the reversible self-assembly between
these two types of aromatic rings. In 2007, this Ar–ArF self-assembly
effect was first used in NLO materials by Jen and co-workers.9
By utilizing aromatic/perfluoroaromatic dendron-substituted NLO
chromophores in the presence of complementary Ar–ArF inter-
actions, they developed a new class of molecular glasses (Chart
S2, ESI†), which exhibited an improved poling efficiency and
much enhanced macroscopic NLO effect. Very recently, these
interactions between two types of isolation groups were also
used in NLO polymers (Chart S3, ESI†), and a very large NLO
coefficient has been achieved.10
a Department of Chemistry, Wuhan University, Wuhan 430072, China.
E-mail: lizhen@whu.edu.cn, lichemlab@163.com, yingxiong@whu.edu.cn;
Fax: +86 27 68755363
b Institute of Chemistry, The Chinese Academy of Sciences, Beijing 100080, China
c College of Pharmacy, Wuhan University, Wuhan 430072, China
† Electronic supplementary information (ESI) available: Chemical structures of
some NLO polymers, TGA, UV-vis spectra of polymers P1–P4. See DOI: 10.1039/
c3nj00048f
c
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polymers, demonstrating the much better NLO stability, thanks
to the Ar–ArF self-assembly effect. Herein, we would like to
present the synthesis, characterization and properties of these
NLO polymers in detail.
Result and discussion
Synthesis
The nitro chromophore-based monomers, C3 and C4, have
already been synthesized in our previous work,10a,d while the
synthetic route to the sulfonyl chromophore-based monomer is
presented in Scheme 2. The donor compound S1 was prepared
by esterification of N-phenyldiethanol and 4-iodobenzoic acid.
The esterification is a simple reaction, and there are many
reports in the literature concerned with the reaction using
different catalysts, giving high yields. However, this reaction
was not satisfied because of the poor solubility of the product
Chart 1 The original idea of this work.
How about the combination of these two new methods? S1. We tried to synthesize it according to our previous work,
Would the self-assembly effect work in the NLO polymers using dicyclohexylcarbodiimide (DCC) as the dehydrating
containing isolation chromophores? (Chart 1) However, so agent, DMAP as the catalyst, CH2Cl2–THF as the solvent.
far, there was little work concerning it. Therefore, in this However, because of the poor solubility of the product and
paper, we attempted to design a new series of NLO polymers DCC, 7 days later, the amount of product was only a little,
(Scheme 1), in which two different types of NLO chromophores as determined by thin layer chromatography (TLC). Thus, 1-(3-
(sulfonyl- and nitro-based chromophores) were arranged. dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC),
Meanwhile, the isolation groups in them were changed with better solubility and much easier separation than DCC, was
between aromatic and perfluoroaromatic to investigate the used as the dehydrating agent instead of DCC. Even so, the
Ar–ArF self-assembly effect in these NLO polymers containing reaction still lasted 3 days with the providing the satisfactory yield
isolation chromophores. Excitingly, as the concentration of the at last. Under normal azo coupling reaction conditions, by using
pentafluorophenyl groups increased, the self-assembly effect the diazonium fluoroborate as the azo-reagent, chromophore S3
became stronger, and the NLO effect and stability became with the sulfonyl group as an acceptor was conveniently prepared.
better and better. In particular, the NLO coefficient of P2, with Finally, the monomers (chromophores C1 and C2), containing
pentafluorophenyl as the isolation groups, was more than three different isolation groups, were yielded by the esterification of
times higher than that of P1 which just contained normal chromophore S3 with benzoic acid or pentafluorobenzoic acid
phenyl groups, and its onset temperature for the decay in the under mild conditions. It is worth pointing out that the solubility
d33 value was more than 40 1C higher than those of the other of the chromophores containing the donor S1 units became
Scheme 1 Synthesis of the NLO polymers P1–P4.
c
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Scheme 2 Synthesis of the monomers C1 and C2.
improved after the introduction of the branched structure, and
chromophores C1 and C2 could be dissolved in common polar
solvents such as CHCl3, CH2Cl2 and THF, etc., making the
polymerization convenient. At last, the target NLO polymer P1–P4
could be prepared successfully via a typical Sonogashira cross-
coupling reaction between the two corresponding chromophores,
catalyzed by Pd(PPh3)4, PPh3, and CuI, as shown in Scheme 1,
which is similar to our previous work. Thus, the total route to
the target polyaryleneethynylenes P1–P4 was simple, making it
convenient to compare their NLO properties.
Fig. 2 13C NMR spectra of polymer P1 and its corresponding monomers.
single peaks associated with the protons of CRCH (marked b in
ꢀ
C3) at 2.06 ppm, again confirming the successful polymerization.
The structures of the other polymers could be also confirmed in a
similar way.
Here, the successful polymerization could be confirmed
more obviously from their 13C NMR spectra. Still using P1 as
a typical example, as shown in Fig. 2, in comparison with its
monomers C1 and C3, nearly all the peaks were still present in
P1, except the characteristic peaks assigned to the functional
groups of the monomers. For example: after polymerization the
Characterizations
The prepared chromophores and polymers were characterized
by spectroscopic methods, and all gave satisfactory spectral
data (see experimental section for detailed analysis data). NMR
spectroscopy was an especially useful tool for illustrating the
successful synthesis of the products in organic chemistry. Fig. 1
peak at 65.9 ppm (the typical signal of the –CRCH group)
ꢀ
moved to 92.7 ppm, indicating that the terminal alkynes in C2
have been substituted by aromatic rings. In addition, the peak
at 101.3 ppm, which was associated with iodobenzene, disappeared
in the 13C NMR spectra of P1, again confirming the successful
polymerization.
1
shows the H NMR spectra of C1, C3 and P1, as well as their
chemical structures, as an example to illustrate the successful
1
synthesis. In the H NMR spectra of monomers C1 and C3, no
unexpected resonance peaks were observed, and the chemical
shifts were consistent with the proposed structure (the corres-
ponding peaks were marked in Fig. 1, 1–13 for C1 while a–o for
C3). After polymerization, all the peaks of P1 showed an apparent
inclination of signal broadening, and the disappearance of the
This standpoint could be also confirmed by the FT-IR
spectra. As shown in Fig. 3, after polymerization, the absorption
band derived from the CRC–H stretching vibrations at about
3277 cmꢀ1 in the FT-IR spectrum of chromophores C3 disap-
peared in the spectrum of its corresponding polymer P1, while
the peak at about 2150 cmꢀ1 (–CRC–) appeared, indicating the
successful polymerization.
Fig. 1 1H NMR spectra of polymer P1 and its corresponding monomers.
Fig. 3 FT-TR spectra of polymer P1 and its corresponding monomers.
c
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The 19F NMR spectra were also used to investigate the Ar–ArF
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self-assembly effect in these NLO polymers. However, it was a
pity that besides the three original peaks from the pentafluoro-
phenyl group, no other signals appeared in their 19F NMR
spectra (Fig. S1, ESI†). On the other hand, it was evidence to
confirm the chemical structure of these polymers.
The molecular weights of P1–P4 were determined by gel-
permeation chromatography (GPC) with THF as the eluent and
polystyrene standards as the calibration standards. As shown in
Table 1 and the experimental section, the weight-average
molecular weights (Mw) of these polymers were nearly the same
(around 12 000), with polydispersity indexes lying in the range of
1.54–1.62. These similar molecular weights could perhaps facilitate
the comparison of their properties on the same level.
Fig. 4 UV-vis spectra of polymers P1–P4 in THF solution (0.02 mg mLꢀ1).
Their TGA thermograms are shown in Fig. S2 (ESI†), and the
5% weight loss temperature (Td) of the polymers are listed in
Table 1. All the polymers were thermally stable, with Td values
higher than 225 1C. Similar to our previous work on the Ar–ArF
self-assembly effect,10 P2–P4, bearing pentafluorophenyl
groups as the isolation groups, exhibited a slightly worse
thermal stability than P1, since the thermal stability of the
pentafluorophenyl group was slightly worse than the normal
phenyl one. However, this temperature (higher than 225 1C)
was good enough for NLO materials, because the temperature
for the real applications was generally lower than 200 1C. The
glass transition temperatures (Tg) of the polymers were also
investigated by using a differential scanning calorimeter (DSC),
with the results summarized in Table 1. As expected, as the
concentration of pentafluorophenyl groups increased, the Ar–
ArF self-assembly effect became stronger, and this interaction
could result in a higher Tg value. For P2, its glass transition
temperature was up to 158 1C, which is 37 1C higher than that
of P1, which just contained normal phenyls as isolation groups.
Furthermore, this higher Tg value could lead to the better
stability of the NLO activity, which could contribute to the
practical applications in photonics fields.
consisted of the same chromophores. This phenomenon also
indicated that the self-assembly effect did not occur between
the perfluoroaromatic rings and chromophore moieties, or the
lmax for P2–P4, with the self-assembly effect in them, should be
different from those of P1 more or less. Thus, the self-assembly
effect should only be present between the isolation groups and
the benzene rings in the main polymer chains, similar to our
previous work.10a
NLO properties
The NLO coefficient is the most important parameter for NLO
materials. In the excellent work of Jen’s group,9 as well as our
recent work,10 the complementary Ar–ArF interactions could
improve the poling efficiency, leading to enhanced NLO activities.
Thus, it was very important to check if this useful interaction
could still work in NLO polymers containing isolation chromo-
phore moieties. To evaluate the NLO activity of the polymers, their
poled thin films were prepared. The most convenient technique to
study the second-order NLO activity was to investigate the second
harmonic generation (SHG) processes characterized by d33, a SHG
coefficient. The test procedure was similar to that reported
previously,11 and to check the reproducibility, we repeated the
measurements at least three times for each sample. Calculation of
the SHG coefficients (d33) for the poled films is based on the
following equation:12
All the polymers were soluble in common polar organic
solvents such as CHCl3, CH2Cl2, THF, DMF, and DMSO.
The UV-vis absorption spectra of these polymers in different
solvents are demonstrated in Fig. 4 and S3–S6 (ESI†), and the
maximum absorption wavelengths (lmax) for the p–p* transition
of the azo moieties are listed in Table S1 (ESI†). It was easily
seen that the lmax of the chromophore moieties in these
polymers were nearly the same, since these four polymers
sffiffiffiffiffiffiffiffiffiffiffi
d33;s wðs2Þ
Is Ic;q
Iq Is
¼
¼
F
wðq2Þ
d11;q
where d11,q is d11 of the quartz crystals, which is equal to
0.45 pm Vꢀ1. Is and Iq are the SHG intensities of the sample
and the quartz, respectively, lc,q is the coherent length of the
quartz, ls is the thickness of the polymer film, and F is the
correction factor of the apparatus and is equal to 1.2 when lc is
much greater than ls. From the experimental data, the d33
values of P1–P4 were calculated at a fundamental wavelength
of 1064 nm (Table 2). Generally, the d33 value of the same NLO
polymer can be different when measured by different methods
or different testing systems at different times. To avoid the
above-mentioned possible deviations, the NLO properties of all
the polymers were tested at the same time.
Table 1 Characterization data of polymers P1–P4
a
a
b
c
No.
Yield (%)
Mw
Mw/Mn
Tg (1C)
Td (1C)
P1
P2
P3
P4
92.8
70.0
69.9
87.6
11 900
12 800
13 700
10 400
1.54
1.56
1.62
1.56
121
158
144
142
256
225
246
231
a
Determined by GPC in THF on the basis of a polystyrene calibration.
Glass transition temperature (Tg) of polymers detected by the DSC
b
analyses under argon at a heating rate of 10 1C minꢀ1
.
The 5% weight
c
loss temperature of polymers detected by the TGA analyses under
nitrogen at a heating rate of 10 1C minꢀ1
.
c
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Table 2 NLO activities of polymers P1–P4
No. Te (1C) ls (mm) d33 (pm Vꢀ1
)
d33(N) (pm Vꢀ1
)
Fe
N f
a
b
c
d
P1 125
P2 160
P3 130
P4 135
0.26
0.23
0.26
0.25
27.9
93.6
45.3
53.2
4.9
17.1
8.1
0.08 0.519
0.18 0.453
0.11 0.484
0.13 0.484
9.5
a
b
c
The best poling temperature. Film thickness. Second harmonic
d
generation (SHG) coefficient. The nonresonant d33 values calculated
e
using the approximate two-level model. Order parameter F = 1 ꢀ A1/
A0, A1 and A0 are the absorbance of the polymer film after and before
corona poling, respectively. f The loading density of the effective chromo-
phore moieties.
Fig. 5 Absorption spectra of the film of P1 (left) and P2 (right) before and after
poling.
The results were encouraging. As shown in Table 2, the d33
value of P1, with normal benzene rings as the isolation groups,
was only 27.9 pm Vꢀ1, and the d33 values increased to 45.3 and
53.2 pm Vꢀ1 in P3 and P4, in which half of the isolation groups
were changed to pentafluorophenyl groups. More excitingly,
when the concentration of the pentafluorophenyl groups was
further increased, the self-assembly effect became stronger, and
the d33 value was further increased to 93.6 pm Vꢀ1 in P2, which is
more than three times that of P1. The results showed that this
powerful Ar–ArF self-assembly effect should also work in the NLO
system containing isolation chromophores. Similar to our pre-
vious case,10a the enhanced NLO coefficient should be ascribed
to the slightly different poling procedure with the Ar–ArF self-
assembly effect (Fig. S7, ESI†): before poling, the chromophores
were randomly arranged; when the temperature increased, the
self-assembly effect from the Ar–ArF interactions was broken, if
an electric field was added at that time, the chromophores could
be induced into noncentrosymmetric alignment; after cooling,
the self-assembly effect could be resumed, which could improve
the stability of the NLO effect. This was consistent with the work
of Jen et al. (Fig. S8, ESI†). Meanwhile, in comparison with our
previous work on the NLO polymers, also using nitro-based
azobenzene as the chromophore, containing normal suitable
isolation groups (some examples are shown in Chart S4, ESI†),
93.6 pm Vꢀ1 was still a high value, confirming the advantages of
the self-assembly effect and isolation chromophore once again.
Since the films of the polymers still had some absorptions at
the wavelength of 532 nm (double the frequency of the 1064 nm
fundamental wavelength), the NLO properties of P1–P4 should
be much smaller, as shown in Table 2 (d33(N) values), which were
calculated using the approximate two-level model.13 Since all the
polymers exhibited almost the same UV-vis spectra, their d33(N)
values demonstrated the same phenomena as their d33 values.
To further study the alignment behaviour of the chromo-
phore moieties in the polymers, the order parameter (F) of the
polymers (Table 2) was measured and calculated from the
change of the UV-vis spectra of their films before and after
poling under an electric field (Fig. 5 and Fig. S6 and S7, ESI†),
according to the equation described in Table 2 (footnote e). The
tested F value of P2 (0.18) was still much higher than that of P1
(0.08), indicating the better alignment of the chromophore
Fig. 6 Decay curves of the SHG coefficients of P2–P4 as a function of the
temperature.
expected, the F values of P3 and P4 were tested to be 0.11 and
0.13, respectively, which are between the values of P1 and P2.
The dynamic thermal stabilities of the NLO activities of the
polymers were investigated by depoling experiments,14 in which the
real-time decays of their SHG signals were monitored as the poled
films were heated from 40 to 160 1C in air at a rate of 4 1C minꢀ1
.
Fig. 6 shows the decay of the SHG coefficient of P2–P4 as a function
of temperature. Since the SHG signal of P1 was low, its depoling
experiment was not successful. Even so, it was very easy to see that
the onset temperatures for the decay in the d33 value of P2 was
much higher than that of P3 and P4. This was understandable: due
to the strong Ar–ArF self-assembly effect, which destroys the align-
ment of the chromophore moieties in P2, much more energy
should be needed. This should be treated as important evidence
that confirms the existence of the Ar–ArF self-assembly effect in this
series of polymers containing isolation chromophores. Further-
more, the high Tonset value of P2 (up to 132 1C) indicated that the
long-term temporal stability was relatively good,13 which was
beneficial to its practical NLO applications.
Conclusions
moieties in the poled thin film of P2, further confirming the In summary, a facile route was designed to prepare four new
advantages of the self-assembly effect in NLO polymers. As NLO polyaryleneethynylenes containing isolation chromophores
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via the simple Sonogashira coupling reaction. Meanwhile, solvent, the crude product was recrystallized from a lot of acetone
different types of isolation chromophores (normal aromatic to afford a white solid (3.80 g, 98.8%). 1H NMR (300 MHz, DMSO-
and perfluoroaromatic rings) were also introduced to investi- d6, 298 K), d (TMS, ppm): 3.79 (t, J = 5.1 Hz, 4H, -NCH2-), 4.41 (t, J =
gate the Ar–ArF self-assembly effect in these NLO polymers. 5.1 Hz, 4H, -OCH2-), 6.63 (t, J = 7.2 Hz, 1H, ArH), 6.88 (d, J = 8.4 Hz,
Thanks to the powerful self-assembly effect, the NLO coefficient 2H, ArH), 7.17 (t, J = 7.8 Hz, 2H, ArH), 7.63 (d, J = 8.1 Hz, 4H, ArH),
of P2 was more than three times that of its analog P1 with 7.87 (d, J = 8.1 Hz, 4H, ArH). 13C NMR (75 MHz, DMSO-d6, 298 K), d
normal phenyl groups as the isolation groups. The onset (ppm): 50.4, 64.1, 103.6, 113.7, 117.9, 130.6, 130.8, 132.5, 139.3,
temperatures for the decay in the d33 value of P2 was up to 149.0, 167.1.
132 1C, demonstrating the much better stability of the NLO
activity than that of P1. These results showed that the powerful
Compound S3
Ar–ArF self-assembly effect could also work in the NLO systems Compound S1 (897 mg, 1.40 mmol) and diazonium salt S2
containing isolation chromophores. Further research on the (420 mg, 1.40 mmol) were dissolved in DMF/THF (15 mL/
applications of this conclusion to dendritic macromolecules 15 mL) at 0 1C. The reaction mixture was stirred for 36 h at
are in progress in our laboratory.
0 1C, and then treated with H2O and extracted with a lot of
CHCl3, washed with brine. The organic layer was dried over
anhydrous sodium sulfate. After the removal of all the organic
solvent, the crude product was purified by column chromatography
on silica gel using ethyl acetate/petroleum ether (60–90 1C) (2/3, v/v)
Experiment
Materials
Tetrahydrofuran (THF) was dried over and distilled from K–Na alloy as eluent and then recrystallized from ethyl acetate to afford an
under an atmosphere of dry nitrogen. Triethylamine (Et3N) orange solid (980 mg, 82.2%). 1H NMR (300 MHz, CDCl3, 298 K), d
was distilled under normal pressure and kept over potassium (TMS, ppm): 2.76 (s, br, 1H, –OH), 3.40 (s, br, –SCH2–, 2H), 3.92 (s,
hydroxide. Dichloromethane (CH2Cl2, DCM) was dried over CaH2 br, –NCH2–, 4H), 4.04 (s, br, –OCH2–, 2H), 4.57 (s, br, –COOCH2–,
and distilled under normal pressure before use. Nitro chromophore 4H), 6.96 (d, J = 8.4 Hz, 2H, ArH), 7.68 (d, J = 7.5 Hz, 4H, ArH), 7.79
based monomers C3 and C4 have been prepared in our previous (d, J = 7.5 Hz, 4H, ArH), 7.92 (d, J = 8.1 Hz, 2H, ArH), 8.02 (m, 4H,
work.10a,d All the other reagents were used as received.
ArH). 13C NMR (75 MHz, CDCl3, 298 K), d (ppm): 49.47, 56.09,
58.21, 61.83, 101.13, 111.80, 122.81, 125.87, 128.84, 130.79, 137.63,
138.41, 144.07, 150.76, 156.00, 165.78.
Instrumentation
NMR spectra were measured on a Varian Mercury300 or Bruker
Chromophore C1. Compound S3 (213 mg, 0.25 mmol),
ARX 400 spectrometer using tetramethylsilane (TMS; d = 0 ppm) as benzoic acid (45.8 mg, 0.375 mmol). 1-(3-Dimethylaminopropyl)-
the internal standard. 19F NMR spectra were measured on a Varian 3-ethylcarbodiimide hydrochloride (EDC) (95.9 mg, 0.50 mmol),
Mercury600 spectrometer. The Fourier transform infrared (FT-IR) and 4-(N,N-dimethyl)aminopyridine (DMAP) (6.1 mg, 0.050 mmol)
spectra were recorded on a PerkinElmer-2 spectrometer in the were dissolved in 10 mL dry CH2Cl2 and stirred at room tempera-
region of 3000–400 cmꢀ1. UV-vis spectra were obtained using a ture for 3 h, and then treated with saturated solution of citric acid
Shimadzu UV-2550 spectrometer. Elemental analyses (EA) were and extracted with CH2Cl2, washed with brine and a saturated
performed by a CARLOERBA-1106 microelemental analyzer. Gel solution of citric acid. After the removal of all the solvent, the
permeation chromatography (GPC) was used to determine the crude product was purified by column chromatography on silica
molecular weights of the polymers. GPC analysis was performed gel using ethyl acetate–chloroform (1/15, v/v) as eluent to afford an
on a Waters HPLC system equipped with a 2690D separation orange solid (213.6 mg, 89.2%). IR (KBr), n (cmꢀ1): 1716 (CQO),
module and a 2410 refractive index detector. Polystyrene standards 1132 (–SO2). 1H NMR (400 MHz, CDCl3, 298 K), d (TMS, ppm): 3.65
were used as calibration standards for GPC. THF was used as an (s, br, 2H, –SCH2–), 3.93 (t, J = 8.0 Hz, 4H, –NCH2–), 4.58 (t, J =
eluent, and the flow rate was 1.0 mL minꢀ1. Thermal analysis was 8.0 Hz, 4H, –COOCH2–), 4.70 (t, J = 8.0 Hz, 2H, –COOCH2–), 6.95
performed on a NETZSCH STA449C thermal analyzer at a heating (d, J = 8.0 Hz, 2H, ArH), 7.26 (m, 2H, ArH), 7.43 (s, br, 1H, ArH),
rate of 10 1C minꢀ1 in nitrogen at a flow rate of 50 cm3 minꢀ1 for 7.69 (d, J = 8.0 Hz, 4H, ArH), 7.79 (d, J = 8.0 Hz, 4H, ArH), 7.91(m,
thermogravimetric analysis (TGA) and the thermal transitions of 4H, ArH), 8.02 (d, J = 8.0 Hz, 2H, ArH). 13C NMR (100 MHz, CDCl3,
the polymers. The thickness of the films was measured with an 298 K), d (ppm): 49.78, 55.51, 58.29, 61.98, 101.25, 112.3, 123.07,
Ambios Technology XP-2 profilometer.
125.97, 128.93, 131.01, 137.89, 139.17, 144.44, 150.86, 156.23,
166.00. C39H33N3O8SI2 (EA) (%, found/calcd): C, 49.02/48.92; H,
3.63/3.47; N, 4.22/4.39.
Syntheses
Compound S1. N-Phenyldiethanolamin (1.08 g, 6.0 mmol),
Chromophore C2. The procedure was similar to the synth-
4-iodobenzoic acid (4.46 g, 18.0 mmol), 1-(3-dimethylamino- esis of chromophore C1. Compound S3 (213 mg, 0.25 mmol),
propyl)-3-ethylcarbodiimide hydrochloride (EDC) (4.60 g, pentafluorobenzoic acid (79.5 mg, 0.375 mmol). The crude
24.0 mmol), and 4-(N,N-dimethyl)aminopyridine (DMAP) (288 mg, product was purified by column chromatography on silica gel
2.40 mmol) were dissolved in dry CH2Cl2 (120 mL) and stirred at using ethyl acetate/chloroform (1/20, v/v) as eluent to afford a
room temperature for 3 days, and then treated with a saturated red solid (233.2 mg, 89.0%). IR (KBr), n (cmꢀ1): 1736 (CQO),
1
solution of citric acid and extracted with CH2Cl2, washed with brine 1130 (–SO2). H NMR (400 MHz, CDCl3, 298 K), d (TMS, ppm):
and a saturated solution of citric acid. After the removal of all the 3.55 (s, br, 2H, –SCH2–), 3.86 (t, J = 8.0 Hz, 4H, –NCH2–), 4.51
c
1794 New J. Chem., 2013, 37, 1789--1796
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(t, J = 8.0 Hz, 4H, –COOCH2–), 4.66 (t, J = 8.0 Hz, 2H, –COOCH2–), (75 MHz, CDCl3, 298 K), d (ppm): 16.12, 25.11, 45.83, 48.75,
6.90 (d, J = 8.0 Hz, 2H, ArH), 7.69 (d, J = 8.0 Hz, 4H, ArH), 7.79 49.32, 60.98, 62.16, 67.79, 80.09, 91.48, 100.18, 110.56, 110.99,
(d, J = 8.0 Hz, 4H, ArH), 7.91 (m, 4H, ArH), 8.02 (d, J = 8.0 Hz, 2H, 116.41, 116.62, 121.98, 124.99, 125.37, 127.39, 127.64, 128.04,
ArH). 13C NMR (100 MHz, CDCl3, 298 K), d (ppm): 48.71, 53.93, 128.77, 130.00, 132.08, 130.57, 132.08, 136.87, 137.60, 138.29,
58.72, 60.98, 100.2, 110.99, 121.68, 125.04, 128.01, 128.15, 143.49, 146.59, 147.08, 150.04, 153.92, 155.13, 164.88, 165.37.
129.98, 136.86, 137.92, 143.39, 150.05, 155.25, 164.96. 19F NMR 19F NMR (564 MHz, CDCl3, 298 K), d (ppm): ꢀ137.81, ꢀ148.45,
(376 MHz, CDCl3, 298 K), d (ppm): ꢀ137.27, ꢀ146.74, ꢀ159.84. ꢀ160.70.
C39H28F5N3O8SI2 (EA) (%, found/calcd): C, 44.54/44.72; H, 2.87/
2.69; N, 4.13/4.01.
P4. Chromophore C1 (86.2 mg, 0.090 mmol), chromophore
C4 (56.6 mg, 0.090 mmol), P4 was obtained as red powder
General procedure for P1–P4. A mixture of chromophore C1 (104.8 mg, 87.6%). Mw = 10 400, Mw/Mn = 1.56 (GPC, polystyrene
or C2 (1.00 equiv.), chromophore C3 or C4 (1.00 equiv.), copper calibration). IR (KBr), n (cmꢀ1): 1726 (CQO), 1517, 1339 (–NO2),
1
iodide (CuI) (5 mol%), tetrakis(triphenylphosphine)palladium 1132 (–SO2). H NMR (400 MHz, CDCl3 298 K), d (TMS, ppm):
(Pd(PPh3)4) (3 mol%) and triphenylphosphine (PPh3) (5 mol%) 1.7–2.0 (–CH2–), 2.3–2.5 (–CH2–), 3.5–3.7 (–SCH2–), 3.8–4.0
was carefully degassed and charged with argon. THF/Et3N (9/1, (–NCH2–), 4.3–4.7 (–OCH2–), 4.8–4.9 (–COOCH2–), 6.7–6.8
v/v, concentration: 0.02 mmol mLꢀ1 C1 or C2 in THF) was then (ArH), 6.9–7.0 (ArH), 7.2–7.4 (ArH), 7.6–7.7 (ArH), 7.8–8.1
added. The reaction was stirred for 4 days at room temperature. (ArH). 13C NMR (75 MHz, CDCl3, 298 K), d (ppm): 17.27,
The mixture was passed through a cotton filter and dropped 26.17, 49.82, 50.48, 51.06, 55.65, 58.51, 62.08, 64.40, 68.14,
into a lot of methanol. The precipitate was collected, further 81.25, 92.71, 110.42, 111.55, 112.14, 112.71, 117.80, 123.24,
purified by several precipitations of its THF solution into 126.20, 126.54, 128.51, 128.71, 129.03, 129.33, 129.61, 129.77,
acetone, and dried in a vacuum at 40 1C to a constant weight. 131.22, 131.58, 131.74, 132.27, 133.51, 138.06, 139.23, 144.46,
P1. Chromophore C1 (95.7 mg, 0.10 mmol), chromophore 146.57, 147.66, 148.17, 151.04, 154.69, 156.37, 165.97. 19F NMR
C3 (53.8 mg, 0.10 mmol), P1 was obtained as a red powder (564 MHz, CDCl3, 298 K), d (ppm): ꢀ137.81, ꢀ148.45, ꢀ160.70.
(115.2 mg, 92.8%). Mw = 11 900, Mw/Mn = 1.54 (GPC, polystyrene
calibration). IR (KBr), n (cmꢀ1): 1719 (CQO), 1517, 1338 (–NO2),
Preparation of polymer thin films
1
1132 (–SO2). H NMR (400 MHz, CDCl3 298 K), d (TMS, ppm):
1.8–2.1 (–CH2–), 2.4–2.6 (–CH2–), 3.5–3.7 (–SCH2–), 3.8–4.0
(–NCH2–), 4.4–4.7 (–OCH2– and –COOCH2–), 6.6–6.7 (ArH),
6.9–7.0 (ArH), 7.2–7.6 (ArH), 7.6–7.7 (ArH), 7.8–8.1 (ArH). 13C
NMR (75 MHz, CDCl3, 298 K), d (ppm): 17.30, 26.25, 49.82,
50.51, 55.62, 58.49, 62.03, 63.35, 68.82, 81.25, 92.71, 110.87,
111.72, 112.14, 117.61, 117.76, 123.24, 126.22, 126.61, 128.57,
128.78, 129.32, 129.77, 129.95, 131.76, 132.20, 132.27, 132.34,
133.50, 139.23, 144.57, 147.67, 148.17, 151.24, 155.07, 156.36,
166.1, 166.58.
The polymers P1–P4 were dissolved in THF (concentration
B3 wt%), and the solutions were filtered through syringe
filters. Polymer films were spin coated onto indium–tin–oxide
(ITO)-coated glass substrates, which were cleaned by DMF,
acetone, distilled water, and THF sequentially in an ultrasonic
bath before use. Residual solvent was removed by heating the
films in a vacuum oven at 40 1C.
NLO measurement of poled films
The second-order optical nonlinearity of the polymers was
determined by an in situ second harmonic generation (SHG)
experiment using a closed temperature-controlled oven with
optical windows and three needle electrodes. The films were
kept at 451 to the incident beam and poled inside the oven,
and the SHG intensity was monitored simultaneously. Poling
conditions were as follows: temperature, different for each polymer
(Table 2); voltage, 7.8 kV at the needle point; gap distance, 0.8 cm.
The SHG measurements were carried out with a Nd:YAG laser
operating at a 10 Hz repetition rate and an 8 ns pulse width at
1064 nm. A Y-cut quartz crystal served as the reference.
P2. Chromophore C2 (80.6 mg, 0.077 mmol), chromophore
C4 (48.4 mg, 0.077 mmol), P2 was obtained as red powder
(76.7 mg, 70.0%). Mw = 12 800, Mw/Mn = 1.56 (GPC, polystyrene
calibration). IR (KBr), n (cmꢀ1): 1729 (CQO), 1518, 1337 (–NO2),
1
1130 (–SO2). H NMR (400 MHz, CDCl3 298 K), d (TMS, ppm):
1.8–2.1 (–CH2–), 2.4–2.6 (–CH2–), 3.5–3.7 (–SCH2–), 3.8–4.0
(–NCH2–), 4.4–4.6 (–OCH2–), 4.7–4.8 (–COOCH2–), 6.6–6.7
(ArH), 6.8–6.9 (ArH), 7.3–7.4 (ArH), 7.5–7.6 (ArH), 7.7–8.0
(ArH). 13C NMR (75 MHz, CDCl3, 298 K), d (ppm): 16.00,
24.93, 48.59, 49.24, 60.80, 63.17, 66.95, 79.99, 91.43, 109.25,
110.32, 110.90, 116.54, 121.91, 124.94, 125.26, 126.85, 127.55,
127.91, 128.48, 130.45, 137.37, 138.07, 143.22, 146.40, 153.45,
164.81. 19F NMR (564 MHz, CDCl3, 298 K), d (ppm): ꢀ137.81,
ꢀ148.46, ꢀ160.70.
Acknowledgements
We are grateful to the National Science Foundation of China
(no. 21034006), academic award for excellent PhD Candidates
funded by Ministry of Education of China (no. 5052012203002)
for financial support.
P3. Chromophore C2 (94.2 mg, 0.090 mmol), chromophore
C3 (48.4 mg, 0.090 mmol), P3 was obtained as red powder
(83.3 mg, 69.9%). Mw = 13 700, Mw/Mn = 1.62 (GPC, polystyrene
calibration). IR (KBr), n (cmꢀ1): 1726 (CQO), 1516, 1339 (-NO2),
1131 (-SO2). 1H NMR (400MHz, CDCl3 298 K), d (TMS, ppm):
1.7–2.0 (–CH2–), 2.4–2.5 (–CH2–), 3.4–3.6 (–SCH2–), 3.7–4.0
(–NCH2–), 4.3–4.5 (–OCH2–), 4.6–4.7 (–COOCH2–), 6.6–6.7
(ArH), 6.8–6.9 (ArH), 7.3–7.4 (ArH), 7.5–8.0 (ArH). 13C NMR
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