Aromatic/perfluoroaromatic self-assembly effect: An effective strategy to improve the NLO effect

Article abstract of DOI:10.1039/c2jm33129b

In this paper, a facile route was designed to prepare four new second-order nonlinear optical (NLO) polyaryleneethynylenes containing normal aromatic or perfluoroaromatic rings as isolation groups via a simple Sonogashira coupling reaction. For comparison, their small molecule models were also synthesized to investigate the aromatic/perfluoroaromatic (Ar-Ar^F) self-assembly effect existing between the isolation groups and polymer main chain. Thanks to the presence of the self-assembly effect, the NLO effect and stability of these polymers were enhanced in a large degree. The NLO coefficient of P4 reached up to 166.7 pm V^-1, which is, to the best of our knowledge, the new record reported so far for linear polymers using simple azobenzenes as the chromophore moieties.

Full text of DOI:10.1039/c2jm33129b

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PAPER
Aromatic/perfluoroaromatic self-assembly effect: an effective strategy to
improve the NLO effect†
a
a
b
c
Wenbo Wu, Qi Huang, Guofu Qiu, Cheng Ye, Jingui Qin and Zhen Li
a
a
*
Received 16th May 2012, Accepted 12th July 2012
DOI: 10.1039/c2jm33129b
In this paper, a facile route was designed to prepare four new second-order nonlinear optical (NLO)
polyaryleneethynylenes containing normal aromatic or perfluoroaromatic rings as isolation groups via
a simple Sonogashira coupling reaction. For comparison, their small molecule models were also
synthesized to investigate the aromatic/perfluoroaromatic (Ar–ArF) self-assembly effect existing
between the isolation groups and polymer main chain. Thanks to the presence of the self-assembly
effect, the NLO effect and stability of these polymers were enhanced in a large degree. The NLO
coefficient of P4 reached up to 166.7 pm Vꢀ1, which is, to the best of our knowledge, the new record
reported so far for linear polymers using simple azobenzenes as the chromophore moieties.
high-speed electro-optic modulators, optical switches, frequency
Introduction
converters and so on.4 One major obstacle that is hindering the
rapid development of this field is the relatively low macroscopic
NLO activities, in comparison with large mb values of the organic
chromophores, because of the strong dipole–dipole interactions
among the chromophore moieties with the donor–p–acceptor
structure in the polymeric system. This interaction results in the
poling-induced noncentrosymmetric alignment of chromophore
moieties (necessary for the materials to exhibit the macroscopic
NLO effect), a daunting task during the poling process under an
electric field.5 Recently the aromatic/perfluoroaromatic (Ar–ArF)
self-assembly effect was first used in nonlinear optical (NLO)
materials by Jen and co-workers in 2007.6 By utilizing aromatic/
perfluoroaromatic dendron-substituted NLO chromophores
through the presence of these complementary Ar–ArF interac-
tions, they developed a new class of molecular glasses (Charts S1
There are various noncovalent intermolecular interactions that
can be used for the construction of supramolecular self-assem-
blies in molecular glasses, such as electrostatic interactions
between charges, multiple hydrogen bonds, metal–organic ligand
coordination, p–p aromatic interactions, van der Waals inter-
actions and so on.1 Among them, noncovalent interactions
between aromatic groups have been widely used in organic and
polymeric opto-electronic materials.2 Although a considerable
amount of work concerning the stacking of aromatic rings has
concentrated on phenyl–phenyl interactions, there is a growing
interest in the interactions of phenyl and perfluorophenyl groups.
Patrick and Prosser3a first recognized that a 1 : 1 mixture of
benzene (with a melting point of 5.5 ꢁC) and hexafluorobenzene
(with a melting point of 4 ꢁC) could form a complex, which melts
at 24 ꢁC, much higher than 5.5 or 4 ꢁC. Although pure benzene
adopts an edge-to-face structure in the solid-state, it has been
determined that the structure of the benzene/hexafluorobenzene
mixture consists of alternating stacks of these two molecules, due
to the electropositive activity of hexafluorobenzene (Chart 1).2c,3
In the field of opto-electronic materials science, most of
the second-order nonlinear optical (NLO) materials have
been developed for applications in photonic devices, such as
aDepartment of Chemistry, Wuhan University, Wuhan 430072, China.
E-mail: lizhen@whu.edu.cnor; lichemlab@163.com; Fax: +86 027
68755363
bCollege of Pharmacy, Wuhan University, Wuhan 430072, China
cInstitute of Chemistry, The Chinese Academy of Sciences, Beijing 100080,
China
† Electronic supplementary information (ESI) available: Structure of
some dendritic NLO chromophores containing perfluoroaromatic
rings, and some polymers containing isolation groups. The IR spectra,
NMR spectra, UV-vis spectra, TGA thermograms of polymers P1–P4
and their model molecules. See DOI: 10.1039/c2jm33129b
Chart 1 Different interactions between different aromatic rings.
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and S2†), which exhibited improved poling efficiency and greatly
enhanced macroscopic NLO effects.6 However, so far, there have
been no other successful cases reported. Thus, further research is
still needed to check the above mentioned exciting increase of the
macroscopic NLO effect derived from the Ar–ArF self-assembly
effect and understand this abnormal phenomenon in more depth.
From 2006, we have systematically designed many different
types of NLO dendronized polymers containing different isola-
tion groups with different sizes in the chromophore moieties
(Charts S3–S8†). 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.7
Considering the above mentioned aromatic/perfluoroaromatic
(Ar–ArF) self-assembly effect, we were wondering if this effect
could be coupled with the concept of a ‘‘suitable isolation
group’’, to further improve the NLO performance of the resul-
tant polymers. From this standpoint, four new simple NLO
polyaryleneethynylenes P1–P4 (Scheme 1) containing nitro-
based azobenzene as the chromophore were designed and
prepared successfully via the Sonogashira coupling reaction. In
P2 and P4, the isolation groups were perfluoroaromatic rings
instead of the normal phenyl rings in P1 and P3. This change
could only alter the loading density of the effective chromophore
moieties to a very limited degree, which would facilitate the
comparison of their properties on the same level. To aid the
investigation of the Ar–ArF self-assembly effect conveniently, six
small model molecules M1–M6 were also synthesized. Analyzing
the properties of P1 and P3 containing normal phenyl rings as
the isolation groups, its corresponding chromophore C2 and
model molecules, there was much evidence such as different
NMR and IR spectra, to confirm the presence of the self-
assembly in P2 and P4. Excitingly, these interactions resulted in
much higher NLO coefficients, with the d33 value of P4 reaching
up to 166.7 pm Vꢀ1, which is the highest value so far reported for
linear polymers using simple azobenzenes as the chromophore
moieties, to the best of our knowledge. Herein, we would like to
present the syntheses, characterization and properties of these
NLO polymers in detail.
Result and discussion
Synthesis
The overall pathway of the monomer synthesis is presented in
Scheme 2. Usually, in the azo-coupling reaction, diazonium
hydrochloride was used as the azo reagent, due to its high reac-
tion activity.8 However, for the synthesis of chromophore S3,
there was nearly no product yielded using this route, even when
we changed the reaction conditions including, the concentration
and pH values. Thus, fluoborate salt was used instead of the
normal hydrochloride salt as the azo reagent.9 Then, the mono-
mers (chromophores C1 and C2) were prepared by the esterifi-
cation of chromophore S3 with benzoic acid or
pentafluorobenzoic acid under mild conditions, in which the
phenyl or pentafluorophenyl groups act as isolation spacers.
Finally, the target NLO polymers P1–P4 could be prepared
successfully via a typical Sonogashira cross-coupling reaction
between different chromophores and aryl halides, catalyzed by
Pd(PPh3)4, PPh3, and CuI, similar to our previous work,8a as
shown in Scheme 1. The reactivity of different aryl halides was
very different during the Sonogashira cross-coupling procedure:
aryl iodide could react with terminal alkyne below room
temperature, while aryl bromide only reacts at higher tempera-
tures such as 50–60 ꢁC. However, to ensure there were no other
unnecessary groups to affect the self-assembly effect, N,N-bis-
(4-bromophenyl)benzenamine was still used as the comonomer
Scheme 1 The synthesis of NLO polymers P1–P4.
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Scheme 2 The synthesis of monomers C1 and C2.
(since the synthesis of N,N-bis(4-iodophenyl)benzenamine was
very difficult), although the aryl bromide had a lower reactivity.
Anyhow, the total route to the synthesis of the target poly-
aryleneethynylenes P1–P4 was very simple, making it convenient
to make a comparison of their tested NLO properties.
showed the FT-IR spectra of the polymers P1–P4, in which the
absorption bands associated with the nitro groups and carbonyl
groups were at about 1338, 1517 cmꢀ1 and 1720 cmꢀ1 or
1740 cmꢀ1 respectively, showing that the chromophore and
isolation groups were stable during the Sonogashira polymeri-
zation reactions. Different activities of phenyl groups or penta-
fluorophenyl groups led to different wavenumbers of the
carbonyl group. At the same time, an absorption band derived
from the ^C–H stretching vibrations disappeared at about
3277 cmꢀ1 in the FT-IR spectra of polymers P1–P4, indicating
that the polymerizations were successful.
The synthesis of the model molecules M1–M6 was similar to
the monomers C1–C2 and the NLO polymers P1–P4, and the
specific synthetic route is shown in Scheme 3: the azo based
chromophore S5 was prepared via the azo-coupling reaction
using fluoborate salt S2 as the azo reagent; and then, M1 and M2
were prepared by esterifications; at last, M3–M6 were also
obtained via the Sonogashira cross-coupling reaction.
NMR spectroscopy is an especially useful tool to illustrate the
successful synthesis of products in organic chemistry. Fig. 1 shows
the 1H NMR spectra of S3, C2 and P2, as well as their chemical
structures, as an example to show the successful synthesis, while
the original spectra of the other compounds are listed in Fig. S2–
S28 in the ESI.† In the spectrum of chromophore S3, no unex-
pected resonance peaks were observed, and the chemical shifts
Characterization and self-assembly effect
The prepared chromophores and polymers were characterized by
spectroscopic methods, and all gave satisfactory spectral data
(see experimental section and ESI† for detail data). Fig. S1†
Scheme 3 The synthesis of model molecules M1–M6.
18488 | J. Mater. Chem., 2012, 22, 18486–18495
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Fig. 2 1H NMR spectra of compounds containing pentafluorophenyl
groups. A: polymers and monomers; B: model molecules.
Fig. 1 1H NMR spectra of S3, C2 and NLO polymer P2 in chloroform-d.
the 1H NMR spectrum (Fig. 2B) of M4 or M6, respectively. Thus,
1
from their H NMR spectra, a preliminary conclusion could be
were consistent with the proposed structure (the corresponding
peaks are marked in Fig. 1). After esterification by penta-
fluorobenzoic acid, the –OH peak (marked 1) disappeared, while
the chemical shifts of the –COOCH2– group (marked 6) and
–OCH2– (marked 7) became larger, due to the electron with-
drawing activity of the pentafluorobenzoic groups. After poly-
merization, all the peaks of P2 showed an apparent inclination of
signal broadening, and the disappearance of the single peaks
associated with the protons of C^CH (marked 3) around 2.05
ppm, and some ArH from the comonomer appeared, confirming
that the polymerization was successful. The structure of the other
polymers could be also confirmed in a similar way. There was an
interesting phenomenon observed in the 1H NMR spectra. Except
the peaks assigned to the protons of the isolation groups (phenyl
or pentafluorophenyl), there was another difference between the
1H NMR spectra of C1 and C2: the chemical shift of the
–COOCH2– group in C1 was 4.80 ppm, but 4.88 ppm in C2. This
should be ascribed to the different electron behavior of the phenyl
and pentafluorophenyl groups. Due to the high electronegativity
of fluorine atom, the perfluoroaromatic rings were electropositive,
making the electron withdrawing activity of the penta-
fluorobenzoic groups much strongerthan that of the benzoic ones.
Thus, the chemical shifts of protons next to them were different.
After polymerization, the chemical shifts of protons next to the
pentafluorobenzoic (–COOCH2–) in the 1H NMR spectra of P2
and P4 became smaller, in comparison with its corresponding
chromophore C2 (Fig. 1 and 2A), disclosing that the electron
withdrawing activity of pentafluorobenzoic groups became
weaker, and the electron density distribution on the per-
fluoroaromatic rings became higher. This phenomenon could be
caused by the self-assembly effect between the perfluoroaromatic
rings and the aromatic ones in the comonomer units. Further-
more, the change of this peak in P2 was larger than that in P4,
indicating that the self-assembly effect in P2 was stronger than P4,
possibly due to its larger comonomer triphenylamine (TPA) unit.
obtained: in this case, the self-assembly was present between the
isolation groups and polymer main chain; the self-assembly effect
between pentafluorophenyl and TPA was stronger than that
between pentafluorophenyl and phenyl moieties; the self-
assembly effects in the polymers were stronger than those in small
molecules.
In their 13C NMR spectra a similar phenomenon was
observed. The C]O groups should show a characteristic peak at
about 160 ppm. In the 13C NMR spectra of C1, P1, P3, and even
the model molecules M1, M3 and M5, the chemical shifts of that
peak were all at about 166 ppm. In the 13C NMR spectrum of C2
was at 158.9 ppm, while after polymerization, it was at 154.7 ppm
in P2, while still about 159 ppm in P4. As we know, it is much
more difficult to measure the 13C NMR spectra of polymers than
small molecules, due to their special structure and relative poor
solubility. Thus, this changes should be more obvious in the 13
C
NMR spectra of model molecules. In the 13C NMR spectrum of
M2, the chemical shift was nearly the same as in C2, at 158.6
ppm. After the Sonogashira reaction, it was at 154.2 or 154.3
ppm in the 13C NMR spectrum (Fig. S24 and S28) of M4 or M6,
respectively. This could further confirm our speculations.
On the other hand, it was known in theory that penta-
fluorophenyl groups only have three types of F atom, and there
should only be three peaks observed in the corresponding 19F
NMR spectra. However, the Ar–ArF self-assembly effect might
change the environment of some F atoms. Therefore, if the Ar–
ArF self-assembly effect was strong enough, additional peaks
should also be observed in their 19F NMR spectra. As shown in
Fig. 3, along with the three original peaks, there were still some
more peaks appearing in the 19F NMR spectra of P2 and P4, and
the intensity in P2 was stronger than that in P4. In the 19F NMR
spectra of the model molecules (Fig. 3), there were only three
peaks in that of M2, while two more very weak peaks were
observed in that of M4 and M6 after the Sonogashira coupling
reaction, indicating that the self-assembly was between the
isolation groups and polymer main chain, which is consistent
1
To further prove this point, the H NMR spectra of the model
1
molecules were also tested. As expected, the chemical shifts of
protons next to the benzoic group (–COOCH2–) in M1, M3 and
M6 were the same. However, differences occur in the model
molecules bearing pentafluorophenyl groups. The chemical shift
of the –COOCH2– group in M2 was 4.88 ppm, the same as in C2.
Just after the Sonogashira reaction, it changed to 4.85 or 4.87 in
with the results of the H NMR.
The molecular weights of polymers were determined by gel
permeation chromatography (GPC) with THF as an eluent and
polystyrene standards as calibration standards. As shown in
Table 1 and the experimental section, P1 and P2 showed slightly
lower molecular weights than P3 and P4, possibly caused by the
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and the maximum absorption wavelengths (lmax) for the p–p*
transition of the azo moieties in them are listed in Table 2. All the
polymers exhibited similar lmax values, nearly identical to their
corresponding chromophores. This phenomenon indicated that
the self-assembly effect did not occur between perfluoroaromatic
rings and chromophore moieties, else the lmax for P2 and P4
should be different from those of P1 and P3. Thus, the self-
assembly effect should only be present between isolation groups
and polymer main chains as the 1H NMR spectra disclosed.
NLO properties
In the excellent work of Jen and co-workers, the complementary
Ar–ArF interactions could improve the poling efficiency of the
dendron-substituted NLO chromophores, leading to the
enhanced NLO activities.6 As mentioned above, it was confirmed
that the Ar–ArF self-assembly effect could exist between the
isolation groups and polymer main chains. Thus, how about this
Ar–ArF self-assembly effect? To answer this question, the NLO
activity of them should be measured. To evaluate the NLO
activity of the polymers, their poled thin films were prepared.
Due to its bad processability, P1 could not form high-quality
thin films through spin-coating. Therefore, its NLO coefficient
was also tested in the doped PMMA film with the concentration
of 50% (w/w). The most convenient technique to study the
second-order NLO activity was to investigate the second
harmonic generation (SHG) processes characterized by d33, an
SHG coefficient. 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:10
Fig. 3 19F NMR spectra of P2, P4 and their model molecules.
lower reaction activity of aryl bromide. This lower reactive
activity also made the yields of P1 and P2 much lower than those
of P3 and P4. Interestingly, P2 and P4 also exhibited slightly
lower molecular weights than their corresponding polymers P1
and P3, indicating that the introduction of perfluoroaromatic
rings would make the activity of the Sonogashira reaction a little
lower. However, the molecular weights of these four polymers
were on the same level, around 10 000 g mmolꢀ1, which would
facilitate the comparison of their properties on the same level.
The TGA thermograms are shown in Fig. S29 (ESI†), and the
5% weight loss temperature (Td) of the polymers is listed in Table
1. All the polymers were thermally stable with Td values higher
than 200 ꢁC. P2 and P4 exhibited a little worse thermal stability
than P1 and P3, indicating that the pentafluorophenyl group was
not as stable. But this was still good enough for NLO materials,
because the temperatures for their real application are generally
lower than 200 ꢁC. The glass transition temperatures (Tg) of the
polymers were also investigated using a differential scanning
calorimeter (DSC), with the results summarized in Table 1. P1
exhibited a Tg value of 73 ꢁC, while the Tg value of P2 increased
to a large degree (up to 139 ꢁC), indicating that the self-assembly
effect existed in P2, as is consistent with other phenomena.
The UV-vis absorption spectra of the chromophores and
polymers in different solvents are diplayed in Fig. S30–S35 (ESI†),
sffiffiffiffiffiffiffiffiffiffiffi
d33;s cðs2Þ
Is lc;q
Iq ls
¼
¼
F
cðq2Þ
d11;q
where d11,q is the 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 3).
Generally, the d33 value of the same NLO polymer could be
different when measured by different methods or different testing
systems at different times. To avoid the above-mentioned
Table 2 The maximum absorption of polymers and their corresponding
chromophores (lmax, nm)a
Table 1 Characterization data of polymers
Yield
(%)
a
a
b
c
Tg (ꢁC)
Td (ꢁC)
THF 1,4-Dioxane CHCl3 CHCl2 DMF DMSO Film
No.
Mw
Mw/Mn
P1 497
P2 491
P3 496
P4 494
C1 489
C2 489
477
476
479
482
478
479
488
488
491
496
493
493
490
488
493
496
494
495
497
496
503
501
500
500
504
499
507
508
507
507
508
500
503
504
P1
P2
P3
P4
51.3
30.7
68.6
68.0
9600
8900
11 400
9900
1.50
1.56
1.97
1.76
73
248
215
252
222
139
(—)d
77
a
Determined by GPC in THF on the basis of a polystyrene calibration.
Glass transition temperature (Tg) of polymers detected by the DSC
b
a
analyses under argon at a heating rate of 10 ꢁC minꢀ1
weight loss temperature of polymers detected by the TGA analyses
.
The 5%
c
The maximum absorption wavelength of the polymer (chromophore
molecule) solutions with the concentrations fixed at 0.02 mg mLꢀ1
(2.5 ꢂ 10ꢀ5 mol mLꢀ1).
under nitrogen at a heating rate of 10 ꢁC minꢀ1
.
Not obtained.
d
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possible deviations, the NLO properties of all the polymers were
tested at the same time.
It was well-known that in theory, under identical experimental
conditions, the NLO activities were proportional to the density
of the chromophore moieties.11 In P1, the comonomer unit of
TPA, which is much larger than the phenyl one in P3, resulted in
a much lower loading density of the chromophore moieties than
that in P3 (0.383 vs. 0.487). Therefore, the d33 value of P1
(21.4 pm Vꢀ1) was lower than that of P3 (50.4 pm Vꢀ1), since
their structures were similar. The d33 values of the polymers P2
and P4, with the pentafluorophenyl groups as isolation groups,
were much higher than the corresponding polymers with phenyl
as the isolation moieties, although they possessed a relatively
lower loading density of the azo chromophore moieties than
those in P1 and P3, respectively. This should be ascribed to the
presence of the self-assembly effect. As mentioned above, it was
confirmed that the Ar–ArF self-assembly effect in P2 using TPA
as comonomer was stronger than that in P4, thus, from P1 to P2,
the d33 value increased more than 6 times, while the d33 value of
P4 was only 3.3 times of P3. Excitingly, the d33 value of P4
reached up to 166.7 pm Vꢀ1, which is, to the best of our
knowledge, the highest value so far for linear polymers using
simple azobenzenes as chromophore moieties.
Fig. 4 Absorption spectra of the film of P3 (left) and P4 (right) before
and after poling.
minꢀ1. Fig. 5 shows the decay of the SHG coefficient of P1–P4 as
a function of temperature. It is very easy to see that the onset
temperatures for the decay of P2 and P4 with the penta-
fluorophenyl groups as the isolated groups, were much higher
than their corresponding polymers with phenyl as the isolation
moieties, especially P2, its onset temperatures for the decays
reached up to 104 ꢁC. That is to say, to destroy the alignment of
the chromophore moieties in P2 and P4, much more energy
should be needed, indicating that the Ar–ArF self-assembly effect
was still present after poling, and these interactions could
increase the stability of NLO polymers, which could contribute
to their practical application in the photonics field.
As there might be some resonant enhancement12 due to the
absorption of the chromophore moieties at 532 nm, the NLO
properties of P1–P4 should be much smaller as shown in Table 3
(d33(N)), which were calculated by using the approximate two-
level model. Since all the polymers exhibited nearly the same UV-
vis absorption behavior, their d33(N) values demonstrated the
same phenomena as their d33 values.
Thus, all the NLO behavior (including the poling and depoling
experiments) of P2 and P4 confirmed the poling procedure of
NLO materials with the self-assemble effect derived from Ar–
ArF interactions, is a little different to the normal poling proce-
dure (Fig. 6). Before poling, the chromophores was randomly
arranged; when the temperature increased, the self-assembly
effect from the Ar–ArF interactions was broken, if the electric
field was applied at that time, the chromophore could be induced
to a noncentrosymmetric alignment; after cooling, the self-
assembly effect could be resumed, which could improve the
stability of the NLO effect. It should be noted that the self-
assembly effect was always present both before and after poling.
Without poling, the self-assembly effect was present, but had
nothing to do with the orderly alignment of the chromophore
To further study the alignment behavior of the chromophore
moieties in the polymers, the order parameter (F) of the polymers
(Table 3) was measured and calculated from the change of the
UV-vis spectra of their films before and after poling under an
electric field (Fig. 4 and S36†), according to the equation
described in Table 3 (footnote e). The tested F values of P2 (0.15)
and P4 (0.24) were still higher than those of P1 (0.08) and P3
(0.11), indicating the better alignment of the chromophore
moieties in the poled film of P2 and P4, further confirming the
advantages of the self-assembly effect in NLO polymers.
The dynamic thermal stabilities of the NLO activities of the
polymers were investigated by depoling experiments, in which
the real-time decays of their SHG signals were monitored as the
poled films were heated from 40 to 130 ꢁC in air at a rate of 4 ꢁC
Table 3 NLO activities of hyperbranched polymers
No. Te (ꢁC) lsb (mm) d33c (pm Vꢀ1
)
d33(N) (pm Vꢀ1
)
Fe
Nf
a
d
P1
85
0.32
0.36
0.27
0.25
0.28
12.3
21.4
128.5
50.4
166.7
0.8
1.5
11.7
4.2
(—) 0.383
0.08
0.15 0.342
0.11 0.487
0.24 0.425
P1g 105
P2 130
P3
P4
90
95
13.7
a
b
The best poling temperature. Film thickness. Second harmonic
c
d
generation (SHG) coefficient. The nonresonant d33 values calculated
e
by using the approximate two-level model. Order parameter F ¼ 1 ꢀ
A1/A0, A1 and A0 are the absorbance of the polymer film after and
before corona poling, respectively. The loading density of the effective
f
g
chromophore moieties. Tested in the doped PMMA film with the
concentration of 50% (w/w).
Fig. 5 Decay curves of the SHG coefficients of P1–P4 as a function of
the temperature.
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previous work.7,8a 1,4-Diiodobenzene was purchased from Alfa
Aesar. All other reagents were used as received.
Instrumentation
1H NMR spectra were measured on a Varian Mercury300 or
Bruker ARX 400 spectrometer using tetramethylsilane (TMS;
d ¼ 0 ppm) as an internal standard. The Fourier transform
infrared (FTIR) spectra were recorded on a PerkinElmer-2
spectrometer in the region of 3000–400 cmꢀ1. UV-vis spectra
were obtained using
a Shimadzu UV-2550 spectrometer.
Elemental analyses (EA) were performed by a CARLOERBA-
1106 microelemental analyzer. Gel permeation chromatography
(GPC) was used to determine the molecular weights of polymers.
GPC analysis was performed on a Waters HPLC system equip-
ped with a 2690D separation module and a 2410 refractive index
detector. Polystyrene standards were used as calibration stan-
dards for GPC. THF was used as an eluent, and the flow rate was
1.0 mL minꢀ1. Thermal analysis was performed on NETZꢀSC1 H
ꢁ
STA449C thermal analyzer at a heating rate of 10 C min in
nitrogen at a flow rate of 50 cm3 minꢀ1 for thermogravimetric
analysis (TGA) and the thermal transitions of the polymers. The
thickness of the films was measured with an Ambios Technology
XP-2 profilometer.
Synthesis of chromophore S3
Fig. 6 Graphical illustration of the alignment formation of self-assem-
bled polymer P2 and P4 by Ar–ArF interactions.
N,N-Di(4-pentynyl)benzenamine (S1) (901.3 mg, 4.0 mmol) and
diazonium salt S2 (1.19 g, 4.0 mmol) were dissolved in 8 mL DMF/
THF (1/1, v/v) at 0 ꢁC. The reaction mixture was stirred for 12 h at
moieties. However, during the poling process, the self-assembly
effect could benefit the noncentrosymmetric alignment of the
chromophore moieties, thus, leading to the enhanced macro-
scopic NLO effect and the improved stability of the NLO effect.
0
ꢁC, and then treated with H2O, extracted with CH2Cl2, and
washed with brine. The organic layer was dried over anhydrous
sodium sulfate. After removal of the organic solvent, the crude
product was purified by column chromatography on silica gel
using ethyl acetate/petroleum ether (b.p. 60–90 ꢁC)(2/1, v/v) as the
Conclusions
1
eluent to afford a deep red solid (1.1 g, 63.3%). H NMR (400
MHz, CDCl3, 298 K), d (TMS, ppm): 1.88 (m, 4H, –CH2–), 2.05 (s,
2H, –C^C–H), 2.30 (m, 4H, –CH2–), 3.59 (t, J ¼ 6.0 Hz, 4H,
–NCH2–), 4.00 (t, J ¼ 4.0 Hz, 2H, –OCH2–), 4.37 (t, J ¼ 4.0 Hz,
2H, –OCH2–), 6.80 (d, J ¼ 8.0 Hz, 2H, ArH), 7.72 (d, J ¼ 8.0 Hz,
1H, ArH), 7.86 (d, J ¼ 8.0 Hz, 2H, ArH) 7.95 (m, 2H, ArH).
In this paper, a facile route was designed to prepare four new
NLO polyaryleneethynylenes P1–P4 containing normal
aromatic rings or perfluoroaromatic rings as isolation groups via
a simple Sonogashira coupling reaction. Thanks to the Ar–ArF
self-asembly effect, the d33 values and NLO stabilities of P2 and
P4 with the pentafluorophenyl groups as isolated groups were
much higher those of P1 and P3. The d33 value of P4 reached up
to 166.7 pm Vꢀ1, which is, to the best of our knowledge, the
highest value so far for linear polymers using simple azobenzene
as chromophore moieties. Thus, our successful example might
stimulate the utilization of the Ar–ArF self-assembly effect, to
construct new functional materials with good performance.
General procedure for the synthesis of chromophore C1 and C2
Chromophore S3 (1.00 equiv.), carboxyl-containing compound
(1.50 equiv.), 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide
hydrochloride (EDC) (2.00 equiv.), and 4-(N,N-dimethyl)ami-
nopyridine (DMAP) (0.20 equiv.) were dissolved in dry CH2Cl2
(0.1 mmol mLꢀ1 of chromophore S3) and stirred at room
temperature for 3 h, and then treated with a saturated solution of
citric acid and extracted with CH2Cl2, and washed with a satu-
rated solution of citric acid and brine. After removing all the
solvent and the crude product was purified by column chroma-
tography on silica gel.
Experimental
Materials
Tetrahydrofuran (THF) was dried over and distilled from K–Na
alloy under an atmosphere of dry nitrogen. Triethylamine (Et3N)
was distilled under normal pressure and kept over potassium
hydroxide. Dichloromethane (CH2Cl2, DCM) was dried over
CaH2 and distilled under normal pressure before use. N,N-Di-
(4-pentynyl)benzenamine (S1), diazonium fluoroborate S2 and
N-ethyl-N-(4-pentynyl)benzenamine (S4) were prepared in our
Chromophore C1. Chromophore S3 (499.7 mg, 1.15 mmol),
benzoic acid (211.3 mg, 1.73 mmol). The crude product was
purified by column chromatography on silica gel using ethyl
acetate/chloroform (1/20, v/v) as eluent to afford deep red solid
(614.3 mg, 99.2%). IR (KBr), y (cmꢀ1): 3267 (C^C–H), 1711
18492 | J. Mater. Chem., 2012, 22, 18486–18495
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1
(C]O), 1519, 1335 (–NO2). H NMR (400 MHz, CDCl3, 298
calibration). IR (KBr), y (cmꢀ1): 1739 (C]O), 1515, 1336 (–NO2).
1H NMR (300 MHz, CDCl3 298 K), d (TMS, ppm): 1.7–2.2
(–CH2–), 2.3–2.6 (–CH2–), 3.1–3.8 (–NCH2–), 4.4–4.6 (–OCH2–),
4.7–5.0 (–COOCH2–), 6.4–7.0 (ArH), 7.0–8.0 (ArH). 13C NMR
(75 MHz, CDCl3, 298 K), d (TMS, ppm): 17.04, 26.05, 50.35,
64.45, 66.34, 68.24, 110.64, 111.61, 117.80, 126.53, 148.20, 154.72.
K), d (TMS, ppm): 1.87 (m, 4H, –CH2–), 2.06 (s, 2H, –C^C–H),
2.30 (m, 4H, –CH2–), 3.58 (t, J ¼ 8.0 Hz, 4H, –NCH2–), 4.62 (t, J
¼ 4.0 Hz, 2H, –OCH2–), 4.80 (t, J ¼ 4.0 Hz, 2H, –COOCH2–),
6.74 (d, J ¼ 8.0 Hz, 2H, ArH), 7.40 (t, J ¼ 8.0 Hz, 2H, ArH), 7.55
(t, J ¼ 8.0 Hz, 1H, ArH), 7.69 (d, J ¼ 8.0 Hz, 1H, ArH), 7.86 (d,
J ¼ 8.0 Hz, 1H, ArH), 7.92 (m, 1H, ArH), 8.05 (m, 3H, ArH),
8.17 (d, J ¼ 8.0 Hz, 1H, ArH). 13C NMR (75 MHz, CDCl3, 298
K), d (TMS, ppm): 49.5, 61.7, 64.1, 67.9, 101.0, 110.2, 111.6,
117.3, 126.0, 128.7, 130.7, 137.6, 144.8, 147.0, 148.0, 150.7, 154.5,
165.7. C31H30N4O5 (EA) (found/calcd): C, 68.77/69.13; H, 6.06/
5.61; N, 10.06/10.40%.
P3. Chromophore C1 (107.7 mg, 0.20 mmol), 1,4-diiodo-
ꢁ
benzene (66.0 mg, 0.20 mmol), reaction temperature: 30 C. P3
was obtained as a deep red powder (83.9 mg, 68.6%). Mw
¼
11 400, Mw/Mn ¼ 1.97 (GPC, polystyrene calibration). IR (KBr),
y (cmꢀ1): 1719 (C]O), 1516, 1336 (–NO2). 1H NMR (300 MHz,
CDCl3 298 K), d (TMS, ppm): 1.2–2.1 (–CH2–), 2.2–2.6 (–CH2–),
3.3–3.7 (–NCH2–), 4.2–4.8 (–OCH2– and –COOCH2–), 6.5–6.8
(ArH), 7.0–7.2 (ArH), 7.2–8.2 (ArH). 13C NMR (75 MHz,
CDCl3, 298 K), d (TMS, ppm): 17.30, 26.33, 29.94, 32.45, 50.53,
63.38, 68.89, 81.64, 90.45, 110.94, 111.73, 117.80, 123.22, 126.63,
128.60, 129.98, 131.69, 132.24, 133.34, 137.69, 144.57, 148.15,
151.35, 155.06, 160.75, 166.63.
Chromophore C2. Chromophore S3 (499.7 mg, 1.15 mmol),
pentafluorobenzoic acid (365.8 mg, 1.73 mmol). The crude
product was purified by column chromatography on silica gel
using ethyl acetate/chloroform (1/20, v/v) as the eluent to afford a
deep red solid (686.2 mg, 94.9%). IR (KBr), y (cmꢀ1): 3299
(C^C–H), 1743 (C]O), 1516, 1336 (–NO2). 1H NMR (400
MHz, CDCl3, 298 K), d (TMS, ppm): 1.87 (m, 4H, –CH2–), 2.05
(s, 2H, –C^C–H), 2.30 (m, 4H, –CH2–), 3.58 (t, J ¼ 8.0 Hz, 4H,
–NCH2–), 4.56 (t, J ¼ 4.0 Hz, 2H, –OCH2–), 4.88 (t, J ¼ 4.0 Hz,
2H, –COOCH2–), 6.76 (d, J ¼ 8.0 Hz, 2H, ArH), 7.69 (d, J ¼ 8.0
Hz, 1H, ArH), 7.83 (d, J ¼ 8.0 Hz, 2H, ArH), 7.94 (m, 2H, ArH).
13C NMR (75 MHz, CDCl3, 298 K), d (TMS, ppm): 15.9, 25.7,
49.9, 64.2, 67.9, 69.4, 83.0, 110.2, 111.2, 117.5, 126.3, 144.1,
147.5, 147.8, 151.1, 154.4, 158.9. C31H25N4O5F5 (EA) (found/
calcd): C, 59.24/59.66; H, 3.95/4.01; N, 8.91/8.91%.
P4. Chromophore C2 (113.1 mg, 0.18 mmol), 1,4-diiodo-
benzene (59.4 mg, 0.18 mmol). P4 was obtained as a deep red
powder (86.1 mg, 68.0%). Mw ¼ 9900, Mw/Mn ¼ 1.76 (GPC,
polystyrene calibration). IR (KBr), y (cmꢀ1): 1740 (C]O), 1517,
1335 (–NO2). 1H NMR (300 MHz, CDCl3 298 K), d (TMS,
ppm): 1.8–2.2 (–CH2–), 2.3–2.7 (–CH2–), 3.4–3.8 (–NCH2–), 4.4–
4.7 (–OCH2–) 4.7–5.0 (–COOCH2–), 6.7–7.0 (ArH), 7.1–8.0
(ArH). 13C NMR (75 MHz, CDCl3, 298 K), d (TMS, ppm):
17.28, 26.34, 50.49, 64.47, 68.39, 81.59, 90.65, 107.91, 110.81,
111.62, 117.82, 123.24, 126.55, 128.75, 131.64, 132.32, 133.27,
136.95, 137.68, 138.62, 144.53, 144.93, 146.63, 147.84, 148.17,
151.50, 154.72, 159.10.
General procedure for the synthesis of P1–P4
A mixture of chromophore C1 or C2 (1.00 equiv.), aryl halide
(1.00 equiv.), copper iodide (CuI) (5 mol%), triphenylphosphine
(PPh3) (5 mol%), tetrakis(triphenylphosphine)palladium
(Pd(PPh3)4) (3 mol%), was carefully degassed and charged with
argon. THF (monomer C1 or C2 concentration was about
0.025 mmol mLꢀ1)/Et3N (3/1 by volume) was then added. The
reaction was stirred for 4 days at an appropriate temperature.
The mixture was passed through a cotton filter and dropped into
a large volume of methanol. The precipitate was collected,
further purified by several precipitations of its THF solution into
Synthesis of chromophore S5
N-Ethyl-N-(4-pentynyl)benzenamine (S4) (1.34 g, 4.5 mmol) and
diazonium salt S2 (1.34 g, 4.5 mmol) were dissolved in 8 mL DMF/
THF (1/1, v/v) at 0 ꢁC. The reaction mixture was stirred for 12 h at
0
ꢁC, and then treated with H2O and extracted with CH2Cl2,
washed with brine. The organic layer was dried over anhydrous
sodium sulfate. After removal of the organic solvent, the crude
product was purified by column chromatography on silica gel
using ethyl acetate/petroleum ether (2/1, v/v) as the eluent to
afford a deep red solid (1.62 g, 81.8%). IR (KBr), y (cmꢀ1): 3534
(–OH), 3218 (C^C–H), 1519, 1335 (–NO2). 1H NMR (300 MHz,
CDCl3, 298 K), d (TMS, ppm): 1.25 (t, J ¼ 6.6 Hz,3H, –CH3), 1.89
(m, 2H, –CH2), 2.08 (s, 1H, C^CH), 2.31 (m, 2H, –CH2–), 3.46–
3.57 (m, 5H, –NCH2– and –OH), 3.99 (s, br, 2H, –OCH2–), 4.37 (t,
J ¼ 4.2 Hz, 2H, –OCH2), 6.77 (d, J ¼ 9.0 Hz, 2H, ArH), 7.72 (d,
J ¼ 9.6 Hz, H, ArH), 7.86 (d, J ¼ 9.6 Hz 2H, ArH), 7.95 (m, 2H,
ArH). 13C NMR (75 MHz, CDCl3, 298 K) d(ppm): 12.27, 15.84,
25.89, 45.43, 49.14, 60.72, 69.43, 72.32, 83.03, 110.64, 111.07,
117.17, 117.69, 126.46, 143.59, 147.35, 147.61, 151.23, 154.38.
ꢁ
acetone, and dried in a vacuum at 40 C to a constant weight.
P1. Chromophore C1 (80.8 mg, 0.15 mmol), N,N-bis(4-bro-
mophenylꢁ)benzenamine (60.5 mg, 0.15 mmol), reaction temper-
ature: 60 C. P1 was obtained as a deep red powder (60.0 mg,
51.3%). Mw ¼ 9600, Mw/Mn ¼ 1.50 (GPC, polystyrene calibra-
tion). IR (KBr), y (cmꢀ1): 1718 (C]O), 1515, 1337 (–NO2).
1H NMR (300 MHz, CDCl3 298 K), d (TMS, ppm): 1.6–2.1
(–CH2–), 2.1–2.6 (–CH2–), 3.1–3.8 (–NCH2–), 4.3–4.8 (–OCH2–
and –COOCH2–), 6.4–6.8 (ArH), 7.0–8.1 (ArH). 13C NMR (75
MHz, CDCl3, 298 K), d (TMS, ppm): 17.10, 26.10, 50.35, 63.36,
66.48, 68.94, 111.06, 111.78, 117.79, 126.60, 128.61, 129.98,
132.76, 133.34, 144.67, 147.75, 148.25, 151.20, 155.09, 166.60.
General procedure for the synthesis of model molecules M1 and
M2
P2. Chromophore C2 (94.3 mg, 0.15 mmol), N,N-bis(4-bro-
mophenylꢁ)benzenamine (60.5 mg, 0.15 mmol), reaction temper-
ature: 60 C. P2 was obtained as a deep red powder (40.2 mg,
30.7%). Mw ¼ 8900, Mw/Mn ¼ 1.56 (GPC, polystyrene
Chromophore S5 (1.00 equiv.), carboxyl-containing compound
(1.50 equiv.), 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide
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hydrochloride (EDC) (2.00 equiv.), and 4-(N,N-dimethyl)ami-
nopyridine (DMAP) (0.20 equiv.) were dissolved in dry CH2Cl2
(0.1 mmol mLꢀ1 of chromophore S5) and stirred at room
temperature for 3 h, and then treated with saturated solution of
citric acid and extracted with CH2Cl2, and washed with a satu-
rated solution of citric acid and brine. After removal of all the
solvent, the crude product was purified by column chromatog-
raphy on silica gel.
acetate/chloroform (1/35, v/v) as the eluent to afford a deep red
solid (45 mg, 36.9%). IR (KBr), y (cmꢀ1): 1721 (C]O), 1515,
1336 (–NO2). 1H NMR (300 MHz, CDCl3 298 K), d (TMS,
ppm): 1.25 (t, J ¼ 6.9 Hz, 3H, –CH3), 1.95 (m, 2H, –CH2–), 2.51
(t, J ¼ 6.3 Hz, 2H, –CH2–), 3.52–3.58 (m, 4H, –NCH2–), 4.61 (t,
J ¼ 4.5 Hz, 2H, –OCH2–), 4.78 (t, J ¼ 4.8 Hz, 2H, –COOCH2–),
6.73 (d, J ¼ 9.6 Hz, 2H, ArH), 6.97–7.09 (m, 7H, ArH), 7.26 (m,
7H, ArH), 7.39 (m, 2H, ArH), 7.54 (m, H, ArH), 7.70 (d, J ¼ 8.7
Hz, 1H, ArH), 7.84–8.05 (m, 6H, ArH). 13C NMR (75 MHz,
CDCl3, 298 K), d (TMS, ppm): 12.42, 17.01, 26.46, 29.66, 45.56,
49.47, 63.11, 68.67, 81.68, 87.61, 110.77, 111.20, 116.50, 117.45,
122.54, 122.34, 124.75, 126.45, 128.31, 129.31, 129.73, 132.35,
133.04, 144.09, 147.20, 147.75, 151.18, 154.73, 166.37.
Chromophore M1. Chromophore S5 (396 mg, 1.0 mmol),
benzoic acid (183 mg, 1.5 mmol). The crude product was purified
by column chromatography on silica gel using ethyl acetate/
chloroform (1/20, v/v) as the eluent to afford a deep red solid (472
mg, 94.4%). IR (KBr), y (cmꢀ1): 3270 (C^C–H), 1713 (C]O),
1519, 1335 (–NO2). 1H NMR (300 MHz, CDCl3, 298 K),
d (TMS, ppm): 1.24 (t, J ¼ 6.9 Hz, 3H, –CH3), 1.88 (m, 2H,
–CH2–), 2.06 (s, 1H, –C^CH), 2.30 (m, 2H, –CH2–), 3.50 (m,
4H, –NCH2–), 4.62 (t, J ¼ 5.7 Hz, 2H, –O–CH2), 4.79 (t, J ¼ 5.7
Hz, 2H, –COOCH2–), 6.70 (d, J ¼ 8.4 Hz, 2H, ArH), 7.40 (m,
2H, ArH), 7.57 (m, 1H, ArH), 7.71 (d, J ¼ 8.7 Hz, 1H, ArH), 7.86
(d, J ¼ 9.0 Hz, ArH), 7.92 (d, 1H, ArH), 7.99–8.07 (m, 3H, ArH).
13C NMR (75 MHz, CDCl3, 298 K), d (TMS, ppm): 12.33, 15.90,
25.96, 45.48, 49.20, 63.10, 68.60, 69.42, 83.085, 110.67, 111.13,
117.42, 126.41, 128.30, 129.70, 133.04, 144.06, 147.58, 147.74,
151.07, 154.71, 166.37.
M4. Chromophore M2 (128 mg, 0.20 mmol), 4-iodo-N,N-
diphenylaniline (61 mg, 0.165 mmol). The crude product was
purified by column chromatography on silica gel using ethyl
acetate/chloroform (1/50, v/v) as the eluent to afford a deep red
solid (83 mg, 50.0%). IR (KBr), y (cmꢀ1): 1741 (C]O), 1515,
1335 (NO2). 1H NMR (300 MHz, CDCl3 298 K), d (TMS, ppm):
1.26 (t, J ¼ 6.9 Hz, 3H, –CH3), 1.96 (m, 2H, –CH2–), 2.52 (t, J ¼
6.3 Hz, 2H, –CH2–), 3.53–3.62 (m, 4H, –NCH2–), 4.55 (t, J ¼ 4.2
Hz, 2H, –OCH2–), 4.86 (t, J ¼ 4.2 Hz, 2H, –COOCH2–), 6.76 (d,
J ¼ 9.0 Hz, 2H, ArH), 7.00–7.11 (m, 7H, ArH), 7.26 (7H, ArH),
7.69 (d, J ¼ 9.3 Hz, 1H, ArH), 7.83 (d, J ¼ 8.7 Hz, 2H, ArH),
7.93(m, 2H, ArH). 13C NMR (75 MHz, CDCl3, 298 K), d (TMS,
ppm): 12.26, 16.90, 26.33, 45.48, 49.36, 64.09, 67.91, 81.58, 87.59,
110.23, 110.97, 116.44, 117.41, 117.51, 122.44, 123.25, 124.66,
126.32, 129.25, 132.27, 143.87, 147.12, 147.40, 147.60, 151.16,
154.27.
Chromophore M2. Chromophore S5 (515 mg, 1.3 mmol),
pentafluorobenzoic acid (413 mg, 1.95 mmol). The crude product
was purified by column chromatography on silica gel using ethyl
acetate/chloroform (1/20, v/v) as the eluent to afford a deep red
solid (632 mg, 82.4%). IR (KBr), y (cmꢀ1): 3313 (C^C–H), 1744
1
(C]O), 1518, 1334 (–NO2). H NMR (300 MHz, CDCl3, 298
M5. Chromophore M1 (106 mg, 0.21 mmol), iodobenzene
(34 mg, 0.165 mmol). The crude product was purified by column
chromatography on silica gel using ethyl acetate/chloroform
(1/35, v/v) as the eluent to afford a deep red solid (38 mg, 40.0%).
IR (KBr), y (cmꢀ1): 1719 (C]O), 1517, 1335 (–NO2). 1H NMR
(300 MHz, CDCl3 298 K), d (TMS, ppm): 1.26 (t, J ¼ 6.9 Hz, 3H,
–CH3), 1.96 (m, 2H, –CH2–), 2.52 (t, J ¼ 6.9 Hz, 2H, –CH2–),
3.50–3.62 (m, 4H, –NCH2–), 4.61 (t, J ¼ 4.5 Hz, 2H, –OCH2–),
4.79 (t, J ¼ 4.5 Hz, 2H, –COOCH2–), 6.74 (d, J ¼ 9.6 Hz, 2H,
ArH), 7.30 (m, 3H, ArH), 7.40 (m, 4H, ArH), 7.54 (m, H, ArH),
7.71 (d, J ¼ 9.0 Hz, H, ArH), 7.91–8.06 (m, 4H, ArH). 13C NMR
(75 MHz, CDCl3, 298 K), d (TMS, ppm): 12.38, 16.91, 26.33,
45.52, 49.40, 63.08, 68.63, 81.62, 88.63, 110.70, 111.16, 117.42,
123.43, 126.41, 127.81, 128.27, 129.67, 131.42, 133.01, 144.05,
147.58, 147.70, 151.12, 154.68, 166.32.
K), d (TMS, ppm): 1.26 (t, J ¼ 6.9 Hz, 3H, –CH3), 1.89 (m, 2H,
–CH2–), 2.07 (s, 1H, –C^CH), 2.30 (m, 2H, –CH2–), 3.53 (m, 4–
H, –NCH2–), 4.56 (t, J ¼ 4.5 Hz, 2H, –OCH2–), 4.88 (t, J ¼ 4.5
Hz, 2H, –COOCH2–), 6.73 (d, J ¼ 9.0 Hz, 2H, ArH), 7.69 (d, J ¼
9.0 Hz, 1H, ArH), 7.83 (d, J ¼ 9.0 Hz, 2H, ArH), 7.94 (m, 2H,
ArH). 13C NMR (75 MHz, CDCl3, 298 K), d (TMS, ppm): 12.03,
15.68, 25.76, 45.29, 49.01, 64.04, 67.79, 69.21, 82.96, 110.11,
110.79, 117.16, 117.26, 126.12, 143.73, 147.30, 147.48, 150.97,
154.21, 158.65.
General procedure for the synthesis of M3–M6
A mixture of chromophore M1 or M2 (1.10 equiv.), aryl halides
(1.00 equiv.), copper iodide (CuI) (5 mol%), triphenylphosphine
(PPh3) (5 mol%), tetrakis(triphenylphosphine)palladium
(Pd(PPh3)4) (3 mol%), was carefully degassed and charged with
argon. THF (the concentration M1 or M2 was about 0.025 mmol
mLꢀ1)/Et3N (3/1 by volume) was then added. The reaction was
stirred for 2 days at room temperature, and then treated with a
saturated solution of citric acid and extracted with CH2Cl2, and
washed with a saturated solution of citric acid and brine. After
removal of all the solvent, the crude product was purified by
column chromatography on silica gel.
M6. Chromophore M2 (118 mg, 0.20 mmol), iodobenzene
(34 mg, 0.165 mmol). The crude product was purified by column
chromatography on silica gel using ethyl acetate/chloroform
(1/50, v/v) as the eluent to afford a deep red solid (69 mg, 51.2%).
IR (KBr), y (cmꢀ1): 1740 (C]O), 1520, 1335 (–NO2). 1H NMR
(300 MHz, CDCl3 298 K), d (TMS, ppm): 1.27 (t, J ¼ 6.9 Hz, 3H,
–CH3), 1.96 (m, 2H, –CH2–), 2.52 (t, J ¼ 6.9 Hz, 2H, –CH2–),
3.4–3.7 (m, 4H, –NCH2–), 4.56 (t, J ¼ 4.2 Hz, 2H, –OCH2–), 4.87
(t, J ¼ 4.2 Hz, 2H, –COOCH2–), 6.77 (d, J ¼ 9.3 Hz, 2H, ArH),
7.31 (m, 2H, ArH), 7.42 (m, 2H, ArH), 7.70 (d, J ¼ 9.0 Hz, 2H,
ArH), 7.84 (d, 2H, J ¼ 9.0 Hz, ArH), 7.94 (m, 2H, ArH). 13C
NMR (75 MHz, CDCl3, 298 K), d (TMS, ppm): 12.30, 16.90,
M3. Chromophore M1 (106 mg, 0.21 mmol), 4-iodo-N,N-
diphenylaniline (61 mg, 0.165 mmol). The crude product was
purified by column chromatography on silica gel using ethyl
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View Article Online
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151.22, 154.31.
Preparation of polymer thin films
The polymers (or P1 and PMMA mixture) were dissolved in
THF (concentration ꢃ3 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 with DMF, acetone, distilled water, and THF sequen-
tially in an ultrasonic bath before use. Residual soꢁlvent was
removed by heating the films in a vacuum oven at 40 C.
NLO measurements of the poled films
The measuring procedure was similar to those reported previ-
ously.13,14 The second-order optical nonlinearity of the polymers
was determined by 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 45ꢁ 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
3); voltage, 7.8 kV at the needle point; gap distance, 0.8 cm. The
SHG measurements were carried out with an 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.
Acknowledgements
We are grateful to the National Science Foundation of China
(no. 21034006), and the Doctoral Fund of Ministry of Education
of China (20090141110043) for financial support.
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This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 18486–18495 | 18495