A Series of hyperbranched polytriazoles containing perfluoroaromatic rings from AB2-type monomers: Convenient syntheses by click chemistry under copper(I) catalysis and enhanced optical nonlinearity

Article abstract of DOI:10.1002/asia.201100379

In this paper, four new hyperbranched polytriazoles containing azo moieties, derived from different AB₂-type monomers, were successfully prepared through the "click" chemistry reaction under copper(I) catalysis by modifying the synthetic route. The polymers were soluble in organic solvents and exhibited good second-order nonlinear optical (NLO) properties. Thanks to the self-assembly of perfluoroaromatic moieties in the periphery, HP2 showed the best NLO properties, with the d₃₃ value as high as 145.0pmV^-1.

Full text of DOI:10.1002/asia.201100379

DOI: 10.1002/asia.201100379
A Series of Hyperbranched Polytriazoles Containing Perfluoroaromatic
Rings from AB2-Type Monomers: Convenient Syntheses by Click Chemistry
under Copper(I) Catalysis and Enhanced Optical Nonlinearity
Wenbo Wu,[a] Yingjie Fu,[a] Can Wang,[a] Cheng Ye,[b] Jingui Qin,[a] and Zhen Li*[a]
On the occasion of the 10th anniversary of click chemistry
Abstract: In this paper, four new hyperbranched polytriazoles containing azo moi-
eties, derived from different AB2-type monomers, were successfully prepared
Keywords: click chemistry · copper ·
through the “click” chemistry reaction under copper(I) catalysis by modifying the
hyperbranched polymers · second-
synthetic route. The polymers were soluble in organic solvents and exhibited good
order nonlinear optical effects
self-assembly
·
second-order nonlinear optical (NLO) properties. Thanks to the self-assembly of
perfluoroaromatic moieties in the periphery, HP2 showed the best NLO proper-
ties, with the d33 value as high as 145.0 pmVꢀ1.
Introduction
regardless of their structural imperfections in comparison
with dendrimers.[2] Fortunately, from AB2 monomers, but
not through the popular A2+B3 approach, hyperbranched
polymers with the controlled structure more like dendrim-
ers, could be achieved.[3]
Due to their unique architectural and functional features,
dendritic macromolecules (i.e., dendrimers and hyper-
branched polymers) are poised to make significant contribu-
tions in several areas of physical and biological science and
engineering.[1,2] Although dendrimers are perfect monodis-
persed macromolecules with a regular and highly branched
three-dimensional architecture, and demonstrate many spe-
cial properties, including nanometer size, globular shape,
multivalent character, and the modularity of the assembly,
the syntheses of dendrimers, either in convergent or diver-
gent approaches, are always relatively costly. Alternatively,
hyperbranched polymers, with similar unique properties to
dendrimers, have attracted much attention in recent years,
due to their convenient preparation by a single-step reaction
through a one-pot procedure in a large scale and quantity,
On the other hand, the copper-catalyzed azide–alkyne cy-
cloaddition, also named as the “click chemistry” reaction,
has aroused much interest among researchers because of its
remarkable features, such as nearly quantitative yields, mild
reaction conditions, broad tolerance toward functional
groups, low susceptibility to side reactions, and simple prod-
uct isolation.[4] As a powerful synthetic tool, this “click”
chemistry reaction was successfully applied to the construc-
tion of some new functional hyperbranched polymers, with
satisfying, even exciting results, generally by taking an
A2+B3 approach,[5] in which two monomers containing ter-
minal azido and yne groups were needed. However, related
reports were still a little scarce.[5] As for AB2 monomers, it
was difficult to construct the corresponding soluble hyper-
branched polymers through the CuI-catalyzed click polymer-
izations due to self-oligomerization.[6] Fortunately, by modi-
fying the synthetic procedure and adding the end-capped
groups, we have successfully prepared soluble azo-chromo-
phore-containing AB2-type hyperbranched polytriazoles,
HP-NO2 and HP-SO2 (see Chart S1 in the Supporting Infor-
mation), which acted as new second-order nonlinear optical
(NLO) polymeric materials (one kind of materials with the
promise of performance and cost improvements related to
telecommunications, computing, embedded network sensing,
[a] W. Wu, Y. Fu, C. Wang, Prof. J. Qin, Prof. Z. Li
Department of Chemistry, Hubei Key Laboratory on
Organic and Polymeric Opto-Electronic Materials
Wuhan University, Wuhan 430072 (China)
Fax : (+86)27-68756757
E-mail: lizhen@whu.edu.cn
[b] Prof. C. Ye
Organic Solids Laboratories, Institute of Chemistry
The Chinese Academy of Sciences
Beijing 100080 (China)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201100379.
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THz wave generation and detection, and many other appli-
cations), with very exciting results such as enhanced NLO
effects and simple syntheses.[3a] To pursue the relationship
between the structure and properties of this AB2-type hy-
perbranched polytriazoles and tackle the challenge in the
NLO field (how to efficiently translate the large b values of
the organic chromophores into high macroscopic NLO activ-
ities of polymers), we have introduced different sizes of the
end-capped groups to the periphery of the hyperbranched
polymers as isolation moieties to adjust their solubility,
processability, and NLO properties (see Chart S2 in the Sup-
porting Information).[3b] However, with some improvement
in their processability and structural adjustment,[3b] the NLO
properties of these hyperbranched polymers were not very
satisfying due to the reduced effective concentrations of the
chromophore moieties as a result of a large amount of bulky
groups in their periphery. Thus, it was required to find some
new approaches to improve the processability, solubility, and
other properties of the resultant hyperbranched polymers,
but without victimizing the possibly enhanced NLO effects.
In 2007, by utilizing the reversible self-assembly of aro-
matic/perfluoroaromatic dendron-substituted NLO chromo-
phores through the presence of complementary Ar–ArF in-
teractions, Jen and co-workers developed a new class of mo-
lecular glasses, which exhibited the improved poling efficien-
cy and much enhanced macroscopic NLO effects.[7] Inspired
by their wonderful results, also considering that the proper-
ties of the hyperbranched polymers were partially dominat-
ed by the nature of their large amounts of end groups in the
periphery[8] and there were no reports concerning the fluo-
roaromatic moieties containing NLO hyperbranched poly-
mers, we introduced some pentafluorophenyl moieties into
the above AB2-type hyperbranched polytriazoles and inves-
tigated their properties. As shown in Scheme 1, the fluoro-
phenyl groups containing four or five fluorine atoms were
introduced into the hyperbranched polymers conveniently
on the surface of the hyperbranched polymer (HP2), inside
(HP3), or both (HP4). For comparison, HP1 without the
fluorophenyl moieties was also prepared. Interestingly, the
synthetic procedure we reported previously should be modi-
fied here at to large degree,[3] since it was not good enough
for the preparation of HP1–HP4. The experimental results
demonstrated that the fluorophenyl moieties in the poly-
mers played an important role in their properties. For exam-
ple, with pentafluorophenyl moieties as end groups in the
periphery, HP2 exhibited about 24% higher macroscopic
NLO performance than that of HP1, no matter if the effec-
tive concentration of the chromophore moieties in HP2 was
reduced to about 15%. Similar phenomena were observed
in the case of HP3 and HP4. Furthermore, relative to HP-
NO2 and HP-SO2, the processability of HP1–HP4 was much
improved. Herein, we would like to present the syntheses,
characterization, and properties of these hyperbranched
polymers in detail.
Results and Discussion
Synthesis
The overall pathway of monomer M2 and the end-capped
chromophore C2 was given in Scheme 2, whereas monomer
M1 and the end-capped chromophore C1 were prepared
previously.[9] As shown in Scheme 2, compound S3 was pre-
pared through the esterification reaction between N-phenyl-
diethanol (S1) and pentafluorobenzoic acid (S2) under mild
conditions. As different fluorine atoms possessed different
activities in the pentafluorophenyl group in S3, compound
S4 could be prepared through a nucleophilic substitution re-
ꢀ
action by using NaN3 (N3 ) as the nucleophilic reagent while
other fluorine atoms were not involved in the reaction.
Then, under the normal azo coupling reaction conditions, es-
pecially at the low reaction temperature (08C), monomer
M2 and the end-capped chromophore C2 could be obtained
in satisfactory yields. Similar to those in M1, both of the
azido and yne groups were present in M2. Once the temper-
ature was a little higher than room temperature, these two
active groups could react with each other as a result of their
high reactivity. That was to say, if the reaction temperature
was a little higher, perhaps, this monomer could not be ob-
tained. Fortunately, according to our previous work of pre-
paring M1,[3a] we used the azo coupling reaction at 08C to
avoid the cycloaddition reactions at this stage. The pure mo-
nomer M2 was stable during its storage in the refrigerator
for about one year.
As mentioned in the Introduction, in some special cases,
the CuI-catalyzed click polymerizations of the AB2 mono-
mers failed to yield soluble hyperbranched polymers, due to
self-oligomerization.[6] Thus, the polymerization process of
the above monomers, M1 and M2, should be handled very
carefully. Previously, we found that AB2-type polytriazoles
could be successfully prepared by adjusting the synthetic
procedure of the click reaction from monomer M1 through
two stages: at the first stage of the polymerization process,
the hyperbranched polymeric intermediate HP-N3 (see
Chart S3 in the Supporting Information), which possessed a
large amount of unreacted azido groups in the periphery,
was synthesized; then, at the second stage, the end-capped
group and another batch of catalysts were added into the re-
action solution of HP-N3 to react with the peripheric azido
groups in HP-N3.[3] As shown in Scheme 1, the hyper-
branched polytriazoles HP1–HP4 were prepared from the
same monomer or similar monomer to that used previous-
ly,[3] thus they should be prepared according to the previous
procedure. However, in the polymerization process, as the
activities of the azido groups of the two monomers were dif-
ferent, the actual polymerization conditions were different,
that is, the amounts of catalysts used to prepare HP3 and
HP4 were not identical to those for HP1 and HP2. The spe-
cific reaction times and amounts of catalysts are presented
in Table 1 and the Experimental Section. The longer reac-
tion time and more catalysts needed disclosed the relatively
poor activity of the azido groups in monomer M2. This was
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Hyperbranched Polytriazoles Containing Perfluoroaromatic Rings
Scheme 1. Synthesis of NLO hyperbranched polymers. DMF=N,N-dimethylformamide.
reasonable, since the azido group was bonded to the aromat-
ic ring, unlike that linked with alkyl moieties in M1.
Structural Characterization
The overall synthetic route was simple and efficient, in
which different chromophore moieties and functional end-
capped groups could be easily introduced. Thus, these re-
sults confirmed the reproducibility, reliability, and extensity
of the controllable synthetic process for the hyperbranched
polymers from AB2 monomers through the CuI-catalyzed
click polymerization by modifying the synthetic procedure
and using end-capped groups once again. It was believed
that many other AB2-type hyperbranched polymers could
be obtained, inspired by our preliminary results.
The monomers and polymers were characterized by spectro-
scopic methods, and all gave satisfactory spectral data (see
Figures S1–S19 in the Supporting Information). Compounds
S3, S4, monomer M2, and the end-capped chromophore C2
were new compounds. From the H NMR and mass spectra,
the structure of S3 was confirmed by NMR spectroscopy,
1
mass spectroscopy, and elemental analyses. The structure of
1
S4 was similar to S3, thus the H (Figure 1) and 13C NMR
spectra just produced a little change. For example, the
chemical shift of methylene groups bonding to the oxygen
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Scheme 2. Synthesis of monomer M2 and end-capped chromophore C2. EDC=3-(ethyliminomethyleneamino)-N,N-dimethyl-propan-1-amine, DMAP=
4-dimethylaminopyridine.
Table 1. Some related data of polymerizations.
Figure S20 (Supporting Infor-
Compound no.
t1 [h][a]
t2 [h][b]
n1 [%][c]
n2 [%][d]
Yield [%]
mation) showed the IR spectra
of HP1–HP4, the absorption
bands associated with the nitro
groups were at about 1520 and
1340 cmꢀ1. However, it was
easily seen that there was a
weak absorption at about
HP1
HP2
HP3
HP4
16
16
24
24
12
12
24
24
10
10
10
10
3.3
3.3
5
88.7
72.6
58.9
60.2
5
[a] Polymerization time before the addition of the end-capped chromophore. [b] Reaction time after the addi-
tion of the end-capped chromophore. [c] Amount of catalyst before the addition of the end-capped chromo-
phore. [d] Amount of catalyst after the addition of the end-capped chromophore.
Figure 2. 19F NMR spectra of S3 and S4 conducted in [D]chloroform.
2100 cmꢀ1 in their spectra, which indicated that there were
still some azido groups that remained unreacted. Relative to
the corresponding absorption of the monomers and the ab-
sorption at about 1740 cmꢀ1 (C=O) in the same spectrum,
which was the absorption of the carbonyl of the end-capped
chromophore, the absorption bands of the azido groups
were very weak, disclosing that the amount of azido groups
was small. Actually, in the polymerization procedure, the
whole process of the click reaction was monitored by IR
spectroscopy, and only when the absorption peak of the
azido group at about 2095 cmꢀ1 disappeared was the reac-
tion was terminated. That is to say, during the synthesis of
the hyperbranched polymers, no peak of the azido groups
Figure 1. 1H NMR spectra of S3 and S4 conducted in [D]chloroform. The
solvent peaks are marked with asterisks (*).
atom of S4 was d=4.53 ppm, whereas that of S3 was at d=
4.54 ppm. To further confirm the structure of S4, 19F NMR
spectroscopy was conducted. As shown in Figure 2, one
peak in the 19F NMR spectra of S4 disappeared in compari-
son with S3, coupled with the appearance of an absorption
band at about 2095 cmꢀ1 ( N3) in the IR spectra (Figure 3),
ꢀ
the results verified that the reaction proceeded successfully.
Similar to this, the structures of monomer M2 and end-
capped chromophore C2 were confirmed (see Figures S5–
S10 in the Supporting Information).
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Hyperbranched Polytriazoles Containing Perfluoroaromatic Rings
using the click chemistry reaction was clear. For example,
there was no peak in the 19F NMR spectra of HP1 and its
corresponding monomer (see Figure S13 in the Supporting
Information), but there were three peaks in the 19F NMR
spectra of HP2 (see Figure S15 in the Supporting Informa-
tion), which should be ascribed to the pentafluorophenyl
end-capped chromophore. Interestingly, some more peaks
appeared in the 19F NMR spectra of HP3 (see Figure S17 in
the Supporting Information), than its corresponding mono-
mer M2 (see Figure S10 in the Supporting Information).
This should be ascribed to the different chemical environ-
ment of the internal fluorophenyl moieties, which might in-
dicate the possible presence of the self-assembly of perfluor-
oaromatic moieties inside the hyperbranched polymer of
HP3. Similar phenomena were observed in the case of HP4
(see Figure S19 in the Supporting Information). To obtain
more information, some control experiments were conduct-
ed: the 19F NMR spectra of different mixtures, including C1
and M2, C2 and M1, C2 and M2, and HP1 and HP2 were
measured. No additional peaks appeared in the 19F NMR
spectra (see Figures S21–S27 in the Supporting Informa-
tion), disclosing another possibility that the actual interac-
tion between the fluorophenyl group and the phenyl one
was totally different in the hyperbranched structure from
those in the physical mixtures, which indicated the special
properties of the dendritic structure.
The molecular weights of HP1–HP4 were determined by
gel-permeation chromatography (GPC) with THF as an
eluent and polystyrene standards as calibration standards.
As shown in the Experimental Section, these four hyper-
branched polymers possessed high molecular weights. Thus,
the polymerization method reported here was successful to
construct hyperbranched polymeric structures with high mo-
lecular weights and good solubility from AB2 monomers
through the click reaction. The polymers were thermally
stable, as shown in Figure 4, with the 5% weight loss tem-
perature of polymers listed in Table 2. Here, HP1 exhibited
the best thermal stability and HP4 the worst. The reason for
this might be that the pentafluorophenyl group was not so
Figure 3. FTIR spectra of S3, S4, and monomer M2.
was observed in the IR spectrum of the reaction mixture
when the reaction was stopped. However, the weak absorp-
tion of the azido groups was observed in the IR spectra.
This should be caused by the low concentration of azido
groups in the reaction mixture when monitored. Fortunately,
although the hyperbranched polymers contained some un-
reacted azido groups, they were very stable during the stor-
age and characterization process, which indicated that a
small amount of azido moieties would not lead to cross-link-
ing of the hyperbranched polymers. The reason for this
might be that the azido moieties were surrounded by other
bulky groups in the polymers. In fact, we also prepared a
similar hyperbranched polymer, HP5, without end-capped
groups (see Scheme S1 in the Supporting Information). As
expected, it could not dissolve in any solvent after about
one week, whereas HP1–HP4 still maintained a good solu-
bility after 12 months.
1
In all the H NMR spectra of the polymers, the chemical
shifts were consistent with the polymer structures demon-
strated in Scheme 2 (see Figures S11–S19 in the Supporting
Information). From their 1H NMR spectra, it was easy to
confirm the success of the polymerization by using a click
1
reaction. For example, in the H NMR spectra, there was a
separate peak observed at d=2.8–3.1 ppm, which should be
ascribed to the methylene groups bonded to the carbon
atom of the newly formed triazole rings, whereas in the
1H NMR spectrum of M2, those methylene groups bonded
to terminal alkyne moieties appeared at about d=2.5 ppm.
Also, a new peak at d=4.5 ppm appeared in HP1 and HP2,
which should be assigned to the methylene groups linked to
the nitrogen atom of the newly formed triazole rings and
the methylene groups bonded to the oxygen atom of the
end-capped chromophore. However, this phenomenon was
1
not apparent in the H NMR spectra of HP3 and HP4, be-
cause monomer M2 has the peak at the same chemical shift
assigned to the methylene groups bonded to the oxygen
atom in the 1H NMR spectrum. However, from their
19F NMR spectra, the success of the end-capping reaction by
Figure 4. TGA thermograms of HP1–HP4 measured in nitrogen at a
heating rate of 108Cminꢀ1
.
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FULL PAPERS
site-isolation effect.[3,10] Here, similar results were obtained,
and the better effective site-isolation effect could be ach-
ieved in HP1–HP4 rather than in HP-NO2. This should be
due to the different isolated groups (phenyl or pentafluoro-
phenyl) of the end-capped chromophore moieties, which
nearly constructed the primary interface between the hy-
perbranched polymers and the environment. The results
were similar to our previous work. However, HP3 and
HP4 demonstrated nearly the same maximum absorption
wavelength to HP1 and HP2, despite the fact that they
have different isolated groups. This meant that the size of
[1,2,3]-triazole rings should be big enough for them to be
used as good isolation moieties surrounding the chromo-
phore moieties and the superfluous pentafluorophenyl in
the interior architecture of hyperbranched polymers could
not make the effective site-isolation effect better.
Table 2. Characterization data of polymers.
Compd.no. Tg
Td
Te
ls
d33
d33(1)
F[g] N[h]
[8C][a] [8C][b] [8C][c] [mm][d] [pmVꢀ1
]
[pmVꢀ1
]
[e]
[f]
HP1
HP2
HP3
HP4
276
244
217
178
145
148
178
170
0.24
0.26
0.21
0.18
116.8
145.0
104.7
121.7
20.9
25.9
18.7
21.8
0.21 0.55
0.23 0.47
0.18 0.41
0.22 0.36
155
162
[a] Glass transition temperature (Tg) of polymers detected by the DSC analyses
under nitrogen at a heating rate of 108Cminꢀ1. [b] The 5% weight loss temper-
ature of polymers detected by the TGA analyses under nitrogen at a heating
rate of 108Cminꢀ1
. [c] The best poling temperature. [d] Film thickness.
[e] Second harmonic generation (SHG) coefficient. [f] The nonresonant d33
values calculated by using the approximate two-level model. [g] Order parame-
ter F=1 A1Aꢀ10, A1 and A0 are the absorbance of the polymer film after and
before corona poling, respectively. [h] The loading density of the effective chro-
mophore moieties.
stable. The glass transition temperatures (Tg) of the poly-
mers were also investigated by using a differential scanning
calorimeter (DSC) with the results summarized in Table 1.
HP3 and HP4 exhibited a high Tg values of 155 and 1628C,
respectively.
NLO Properties
To evaluate the NLO activity of the polymers, their poled
thin films were prepared. In our previous work, HP-NO2 ex-
hibited bad processability, and it could not form high-quality
thin films through spin-coating.[3a] In this work, we used the
chromophores with isolated groups as end-capped moieties
to prepare the polymers and improve their processability:
all the polymers could easily form high-quality thin films
through spin-coating.
All the hyperbranched polymers were soluble in common
polar organic solvents, such as THF, DMF, and DMSO.
Their solutions could be easily spin-coated into thin solid
films; therefore, it was convenient to test their NLO proper-
ties based on the thin films. The UV/Vis absorption spectra
of the chromophores and polymers in different solvents
were demonstrated in Figure 5 and Figures S28–S32 in the
Supporting Information, with the maximum absorption
wavelengths for the p–p* transition of the azo moieties in
them listed in Table S1 (Supporting Information). Figure 5
demonstrated the UV/Vis spectra of the hyperbranched
polymers in chloroform, and all the polymers exhibited
blue-shifted maximum absorption wavelength in comparison
with HP-NO2. Our previous work has demonstrated that the
[1,2,3]-triazole rings surrounding the chromophore moieties
could act as good isolation moieties, leading to the effective
The convenient technique to study the second-order NLO
activity was to investigate the second harmonic generation
(SHG) processes characterized by d33, an SHG coefficient.
The method for the calculation of the SHG coefficients (d33)
for the poled films has been reported previously.[11] From
the experimental data, the d33 values of polymers were cal-
culated at 1064 nm fundamental wavelength. To check the
reproducibility, we repeated the measurements three times
and nearly got the same results. As shown in Table 2, the d33
values of the polymers with the pentafluorophenyl groups as
the isolated groups in the periphery, HP2 and HP4, were
higher than their corresponding polymers with phenyl as the
isolated moieties, HP1 and HP3; this was reasonable. As
mentioned in the Introduction, many previous literature re-
ports have reported that there were strong intermolecular
interactions between aromatic rings and perfluoroaromatic
rings. Here, in comparison with HP1 or HP3, there were
many pentafluorophenyl groups in the periphery of HP2
and HP4. The role of self-assembly between that pentafluor-
ophenyl and phenyl groups would make the pentafluoro-
phenyl the perfect interface between the chromophores in
the interior architecture and environment. That is to say,
pentafluorophenyl groups, which are attached to the surface
of hyperbranched polymers, would be a good isolated inter-
face between two molecules and greatly reduce the intermo-
lecular dipole–dipole interactions between chromophores.
Also, just as reported by Jen et al.,[7] the complementary
Ar–ArF interactions could improve the poling efficiency of
the materials, leading to the enhanced d33 values. However,
the perfluoroaromatic rings in the interior architecture
Figure 5. UV/Vis spectra of polymers in chloroform (0.02 mgmLꢀ1).
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Hyperbranched Polytriazoles Containing Perfluoroaromatic Rings
didn’t result in higher d33 values, because in the interior ar-
chitecture, perfluoroaromatic rings were fixed between two
chromophore moieties; this special structure reduced the in-
termolecular interactions between perfluoroaromatic and ar-
omatic rings and made the perfluoroaromatic rings in the in-
terior architecture more like normal isolated groups; howev-
er, it might be too large. The large bulk of the pentafluoro-
phenyl moieties meant the low loading density of the effec-
tive chromophore moieties. It was well-known that in
theory, under identical experimental conditions, the d33
value was proportional to the density of the chromophore
moieties. So the d33 values of HP3 and HP4 were lower than
HP1 and HP2, as a result of the lower density of the chro-
mophore moieties. However, due to their outstanding site-
isolation effects and the presence of complementary Ar–ArF
interactions in some degree, the d33 values of HP3 and HP4
were much higher than other hyperbranched polymers,
which possessed similar structure and density to the chromo-
phore moieties. For example, the d33 value of HP4
Figure 6. Decay curves of the SHG coefficients of hyperbranched poly-
~
:
&
*
mers HP1–HP4 as a function of the temperature ( : HP1, : HP2,
^
HP3, : HP4).
Conclusions
(121.7 pmVꢀ1) was nearly two times that of P6 (63.7 pmVꢀ1
;
see Chart S1 in the Supporting Information),[3b] although
they possessed the same density of the chromophore moiet-
ies and similar chemical structure.
In summary, four new azo chromophore containing hyper-
branched polytriazoles, HP1–HP4, derived from different
AB2 monomers and bearing different end-capped chromo-
phores, were successfully prepared by click chemistry under
copper(I) catalysis by modifying the synthetic procedure.
All the polymers exhibited higher macroscopic NLO effects,
in comparison with other hyperbranched polytriazoles with
the similar structure and loading density of the effective
chromophore moieties, thanks to the additional complemen-
tary Ar–ArF interactions. Different chemical structures led
to different effects: the pentafluorophenyl in the periphery
produced higher d33 values than the normal phenyl in the
periphery, whereas the perfluoroaromatic rings in the interi-
or architecture produced slightly lower d33 values due to the
lower loading density of the effective chromophore moieties.
Compound HP2 with pentafluorophenyl in the periphery
and acceptable loading density of the effective chromophore
moieties has the highest d33 values (145.0 pmVꢀ1). Thus, the
introduction of the pentafluorophenyl groups into the pe-
riphery of hyperbranched polymer should be a new ap-
proach to enhance the macroscopic NLO effects of poly-
mers.
As there might be some resonant enhancement due to the
absorption of the chromophore moieties at 532 nm, the
NLO properties of HP1–HP4 should be much smaller as
shown in Table 2 (d33(1)), which were calculated by using
the approximate two-level model. Due to their relatively
good optical transparency, these hyperbranched polymers
exhibited good d33(1) values, with that of HP1 as high as
20.9 pmVꢀ1. Also, HP2 and HP4 demonstrated satisfactory
d33(1) values due to the pentafluorophenyl groups in the
periphery. To further explore the alignment of the chromo-
phore moieties in the polymers, we measured their order pa-
rameter (F). Figures S33–S36 in the Supporting Information
show the UV/Vis spectra of the films of HP1–HP4 before
and after corona poling. It was easily seen that after the
corona poling, the dipole moments of the chromophore moi-
eties in the polymers were aligned and the absorption
curves decreased due to birefringence. From the absorption
change, the F values for the polymers could be calculated
according to the equation presented in Table 2 (see footnote
[g]), and HP2 exhibited the highest value.
The dynamic thermal stabilities of the NLO activities of
HP1–HP4 were investigated by the depoling experiments, in
which the real time decays of their SHG signals were moni-
tored as the poled films were heated from room tempera-
ture to 1608C in air at a rate of 48Cminꢀ1. Figure 6 showed
the decay of the SHG coefficient of HP1–HP4 as a function
of temperature: as the chemical structure of them was simi-
lar, the onset temperatures for decays of them all was
around 1058C, higher than HP-NO2 (938C). The results in-
dicated that the long-term temporal stability of the hyper-
branched polymers was relatively good.
Experimental Section
Materials
THF was dried over and distilled from K/Na alloy under an atmosphere
of dry nitrogen. Dichloromethane (CH2Cl2) was dried over CaH2 and dis-
tilled under normal pressure before use. DMF was dried over CaH2 and
distilled under reduced pressure before use. Chromophores C1 and M1
were synthesized previously.[9] Pentafluorobenzoic acid (S2) was pur-
chased from Alfa-Aesar. All other reagents were used as received.
Instrumentation
1H and 13C NMR spectra were measured on a Varian Mercury300 spec-
trometer by using tetramethylsilane (TMS; d=0 ppm) as an internal
standard. 19F NMR spectra were measured on a Varian Mercury600 spec-
trometer. FTIR spectra were recorded on a Perkin–Elmer-2 spectrometer
Chem. Asian J. 2011, 6, 2787 – 2795
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
2793

Z. Li et al.
FULL PAPERS
in the region of 3000–400 cmꢀ1 on KBr pellets. UV/Vis spectra were ob-
tained by using a Shimadzu UV-2550 spectrometer. Elemental analyses
OCH2 ), 4.62 (t, J=5.4 Hz, 4H; OCOCH2 ), 6.87 (d, J=8.7 Hz, 2H;
ArH), 7.67 (d, J=8.7 Hz, 1H; ArH), 7.93 ppm (m, 4H; ArH); 13C NMR
(75 MHz, CDCl3, 298 K): d=15.0, 27.9, 49.5, 63.3, 68.0, 69.1, 83.1, 109.1,
111.7, 116.4, 117.3, 126.0, 139.4, 141.7, 145.0, 146.6, 148.4, 149.9, 155.2,
158.8 ppm; 19F NMR (564 MHz, CDCl3, 298 K): d=ꢀ138.16 (d, J=
1.69 Hz), ꢀ147.56 (t, J=2.04 Hz), ꢀ160.19 ppm (t, J=2.04 Hz); MS (EI):
m/z: calcd: 800.13 [M+]; found: 800.19; elemental analysis calcd (%) for
C35H22N4O7F10: C 52.87, H 2.92, N 6.89; found: C 52.51, H 2.77, N 7.00;
UV/Vis (THF, 1ꢁ10ꢀ5 mmolmLꢀ1): lmax =459 nm.
ꢀ
ꢀ
ꢀ
ꢀ
were performed by
a CARLOERBA-1106 microelemental analyzer.
GPC was used to determine the molecular weights of polymers. GPC
analysis was performed on a Waters HPLC system equipped with a
2690D separation module and a 2410 refractive index detector. Polystyr-
ene standards were used as calibration standards for GPC, THF was used
as an eluent, and the flow rate was 1.0 mLminꢀ1. Thermal analysis was
performed on a NETZSCH STA449C thermal analyzer at a heating rate
of 108Cminꢀ1 in nitrogen at a flow rate of 50 cm3 minꢀ1 for thermogravi-
metric analysis (TGA) and the thermal transitions of the polymers. The
thickness of the films was measured with an Ambios Technology XP-2
profilometer.
Chromophore M2
Compound S4 (615 mg, 1.00 mmol), diazonium salt (S5) (319 mg,
1.00 mmol). The crude product was purified by column chromatography
on silica gel by using ethyl acetate/petroleum ether (1:4, v/v) as the
Synthesis of S3
eluent to afford a deep-red solid (534 mg, 63.1%). IR (KBr): n˜ =3307
ꢀ1
(CꢁC H), 2129 ( N3), 1731 (C=O), 1516, 1334 cm ( NO2); 1H NMR
ꢀ
ꢀ
ꢀ
N-Phenyldiethanolamine (S1) (1.08 g, 6.0 mmol), pentafluorobenzoic acid
(S2) (3.18 g, 15.0 mmol), 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide
hydrochloride (EDC) (5.75 g, 30.0 mmol), and 4-(N,N-dimethyl)amino-
pyridine (DMAP) (288 mg, 2.40 mmol) were dissolved in dry CH2Cl2
(120 mL) and stirred at room temperature for 3 h and then treated with a
saturated solution of citric acid and extracted with CH2Cl2. The resulting
mixture was washed with brine and a saturated solution of citric acid.
After removal the organic solvent, the crude product was purified by
column chromatography on silica gel by using chloroform/petroleum
ether (1:1, v/v) as the eluent to afford a white solid (2.92 g, 84.2%). IR
ꢀ
(300 MHz, CDCl3, 298 K): d (TMS)=2.01 (s, 1H; CꢁCH), 2,15 (m,
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
2H; CH2 ), 2.51 (m, 2H, CH2C ), 3.93 (brs, 4H; NCH2 ), 4.36 (t,
ꢀ
ꢀ
ꢀ
ꢀ
J=5.7 Hz, 2H; OCH2 ), 4.60 (brs, 4H; OCOCH2 ), 6.87 (d, J=
8.7 Hz, 2H; ArH), 7.67 (d, J=8.7 Hz, 1H; ArH), 7.93 ppm (m, 4H;
ArH); 13C NMR (75 MHz, CDCl3, 298 K): d=15.0, 27.9, 49.5, 63.1, 68.0,
69.1, 83.1, 109.1, 111.7, 116.4, 117.3, 126.0, 138.6, 141.9, 145.0, 146.6,
148.4, 150.0 155.2, 159.1 ppm; 19F NMR (564 MHz, CDCl3, 298 K): d=
ꢀ138.69 (d, J=1.24 Hz), ꢀ150.98 ppm (d, J=1.24 Hz); elemental analysis
calcd (%) for C35H22N10O7F8: C 49.9, H 2.91, N 17.01; found: C 49.65, H
2.62, N 16.54; UV/Vis (THF, 1ꢁ10ꢀ5 mmolmLꢀ1): lmax =461 nm.
(KBr): n˜ =1732 cmꢀ1 (C=O); 1H NMR (300 MHz, CDCl3, 298 K):
d
ꢀ
ꢀ
(TMS)=3.79 (t, J=6.0 Hz, 4H; NCH2 ), 4.54 (t, J=6.0 Hz, 4H;
General Procedure for the Synthesis of Hyperbranched Polymers HP1–
HP4
ꢀ
ꢀ
OCH2 ), 6.78 (d, J=7.8 Hz, 2H; ArH), 7.26 ppm (m, 3H; ArH);
13C NMR (75 MHz, CDCl3, 298 K): d=49.5, 63.6, 112.1, 117.3, 129.4,
146.5, 158.9 ppm; 19F NMR (564 MHz, CDCl3, 298 K): d=ꢀ138.32 (d,
J=1.69 Hz), ꢀ148.20 (t, J=2.04 Hz), ꢀ160.50 ppm (t, J=1.86 Hz); MS
(EI): m/z: calcd: 569.07 [M+]; found: 569.07; elemental analysis calcd
(%) for C24H13NO4F10: C 50.85, H 2.62, N 2.34; found: C 50.63, 6.30,
2.46.
The hyperbranched polymers were synthesized by Cu-catalyzed cycload-
ditions from different monomers M1 or M2 and different end-capped
chromophores C1 or C2, respectively. A typical experimental procedure
for the preparation of HP1 is given below as an example.
Preparation of HP1
Synthesis of S4
Chromophore M1 (69.4 mg, 0.15 mmol) was dissolved in DMF (7.5 mL)
under nitrogen. Then aqueous solutions of CuSO4 (187.5 mL, 0.04m) and
NaAsc (187.5 mL, 0.08m) were dropped into the solution, respectively.
After the reaction had been stirred for 16 h at room temperature, the
end-capped chromophore C1 (111.7 mg, 0.18 mmol) was added and, at
the same time, another batch of CuSO4 (62.5 mL, 0.04m) and NaAsc
(62.5 mL, 0.08m) was also added. The reaction mixture left to stir for
12 h. After this time, a lot of water was poured into the mixture, which
was then filtered and washed with methanol and acetone. The obtained
solid was further purified by reprecipitation from its THF solution into
methanol to afford red powder HP1 (144.1 mg, 88.7%). Mw =6.04ꢁ104,
Mw/Mn =2.19 (GPC, polystyrene calibration); IR (thin film): n˜ =2098
Compound S3 (1.14 g, 2.0 mmol) and NaN3 (260 mg, 8.0 mmol) were dis-
solved in dry DMF (20 mL) and stirred at 808C for 12 h under an atmos-
phere of argon. Then, the reaction mixture was treated with distilled
water, 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 by using chloroform/petroleum ether (1:1, v/v) as the eluent to
ꢀ
afford a pale-yellow solid (1.17 g, 95.0%). IR (KBr): n˜ =2125 ( N3),
1728 cmꢀ1 (C=O); H NMR (300 MHz, CDCl3, 298 K): d (TMS)=3.80 (t,
1
ꢀ
ꢀ
ꢀ
ꢀ
J=6.0 Hz, 4H; NCH2 ), 4.53 (t, J=6.0 Hz, 4H; OCH2 ), 6.78 (d, J=
8.1 Hz, 2H; ArH), 7.26 ppm (m, 3H; ArH); 13C NMR (75 MHz, CDCl3,
298 K): d=49.5, 63.5, 112.1, 117.4, 129.4, 146.5, 159.1 ppm; 19F NMR
(564 MHz, CDCl3, 298 K): d=ꢀ138.82 (d, J=0.68 Hz), ꢀ151.17 ppm;
MS (EI): m/z: calcd: 615.03 [M+]; found: 615.09; elemental analysis
calcd (%) for C24H13N7O4F8: C 46.71, H 2.18, N 15.83; found: C 46.84, H
2.13, N 15.93.
( N3), 1716 (C=O), 1516, 1338 cmꢀ1 ( NO2); 1H NMR (300 MHz,
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ ꢀ
[D6]DMSO, 298 K): d=1.6–2.1 ( CH2 ), 2.6–2.8 ( CH2 ), 3.6–4.2 ( N
ꢀ
ꢀ
ꢀ
ꢀ
CH2 ), 4.2–4.6 ( O CH2 ), 6.6–6.8 (ArH), 6.9–7.1 (ArH), 7.2–8.0 ppm
(ArH); 13C NMR (75 MHz, [D6]DMSO, 298 K): d=21.9, 29.0, 47.3, 49.6,
51.7, 62.7, 68.4, 69.0, 79.6, 112.7, 117.5, 119.0, 123.3, 126.2, 127.9, 129.1,
129.7, 133.9, 144.7, 146.8, 155.3, 166.3 ppm; UV/Vis (THF, 0.02 mgmLꢀ1):
lmax =464 nm.
General Procedure for the Synthesis of Chromophores C2 and M2
Compound S3 or S4 and diazonium salt with equal equivalents were dis-
solved in DMF at 08C. The reaction mixture was stirred for 12 h at 08C
and then treated with H2O and 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.
Preparation of HP2
Chromophore M1 (69.4 mg, 0.15 mmol), C2 (144.1 mg, 0.18 mmol). After
the reaction had been stirred for 16 h, the end-capped chromophore C2
was added for the next 12 h reaction. Red powder (137.5 mg, 72.6%);
Mw =10.97ꢁ104, Mw/Mn =2.01 (GPC, polystyrene calibration); IR (thin
film): n˜ =2101 ( N3), 1737 (C=O), 1516, 1339 cm ( NO2); 1H NMR
ꢀ1
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
(300 MHz, [D6]DMSO, 298 K): d=1.7–2.2 ( CH2 ), 2.7–2.9 ( CH2 ),
Chromophore C2
ꢀ ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
3.6–4.2 ( N CH2 ), 4.2–4.6 ( O CH2 ), 6.6–6.8 (ArH), 6.9–7.1 (ArH),
7.2–8.0 ppm (ArH); 19F NMR (564 MHz, [D6]DMSO, 298 K): d=ꢀ139.2,
ꢀ150.0, ꢀ161.5 ppm; UV/Vis (THF, 0.02 mgmLꢀ1): lmax =461 nm.
Compound S3 (569 mg, 1.00 mmol), diazonium salt (S5) (319 mg,
1.00 mmol). The crude product was purified by column chromatography
on silica gel by using ethyl acetate/petroleum ether (1:4,v/v) as the eluent
to afford a deep-red solid (644 mg, 80.4%). 1H NMR (300 MHz, CDCl3,
ꢀ
ꢀ
ꢀ
298 K): d (TMS)=2.01 (s, 1H; CꢁCH), 2,15 (m, 2H; CH2 ), 2.51 (m,
ꢀ
ꢀ
ꢀ
ꢀ
2H; CH2C ), 3.94 (t, J=5.4 Hz, 4H; NCH2 ), 4.36 (t, J=5.7 Hz, 2H;
2794
www.chemasianj.org
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2011, 6, 2787 – 2795

Hyperbranched Polytriazoles Containing Perfluoroaromatic Rings
Preparation of HP3
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Chromophore M2 (84.6 mg, 0.10 mmol), C1 (74.5 mg, 0.12 mmol). After
the reaction had been stirred for 24 h, the end-capped chromophore C1
was added for the next 24 h reaction. Red powder (86.4 mg, 58.9%);
Mw =10.64ꢁ104, Mw/Mn =1.48 (GPC, polystyrene calibration); IR (thin
film): n˜ =2127 ( N3), 1735 (C=O), 1518, 1340 cm ( NO2); 1H NMR
ꢀ1
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
(300 MHz, [D6]DMSO, 298 K): d=1.8–2.4 ( CH2 ), 2.8–3.0 ( CH2 ),
ꢀ ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
3.6–4.0 ( N CH2 ), 4.0–4.6 ( O CH2 ), 6.6–7.1 (ArH), 7.1–8.1 (ArH),
8.2–8.4 ppm (ArH); 19F NMR (564 MHz, [D6]DMSO, 298 K): d=ꢀ138.5,
ꢀ140.3, ꢀ142.1, ꢀ146.7, ꢀ151.8 ppm; UV/Vis (THF, 0.02 mgmLꢀ1):
lmax =463 nm.
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Preparation of HP4
Chromophore M2 (84.6 mg, 0.10 mmol), C2 (96.1 mg, 0.12 mmol). After
the reaction had been stirred for 24 h, the end-capped chromophore C1
was added for the next 24 h reaction. Red powder (99.1 mg, 60.2%);
Mw =17.30ꢁ104, Mw/Mn =2.15 (GPC, polystyrene calibration); IR (thin
film): n˜ =2128 ( N3), 1738 (C=O), 1520, 1340 cm ( NO2); 1H NMR
ꢀ1
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
(300 MHz, [D6]DMSO, 298 K): d=1.8–2.0 ( CH2 ), 2.0–2.4 ( CH2 ),
ꢀ
ꢀ
ꢀ ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
2.8–3.2 ( CH2 ), 3.8–4.1 ( N CH2 ), 4.2–4.8 ( O CH2 ), 6.9–7.2
(ArH), 7.2–8.1 (ArH), 8.4–8.6 ppm (ArH); 19F NMR (564 MHz,
[D6]DMSO, 298 K): d=ꢀ138.6, ꢀ139.3, ꢀ140.3, ꢀ145.8, ꢀ146.8, ꢀ149.0,
ꢀ151.9, ꢀ161.5 ppm; UV/Vis (THF, 0.02 mgmLꢀ1): lmax =466 nm.
Preparation of Polymer Thin Films
The polymers were dissolved in THF (concentration ~3 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 ul-
trasonic bath before use. Residual solvent was removed by heating the
films in a vacuum oven at 408C.
NLO Measurements of Poled Films
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The second-order optical nonlinearity of the polymers was determined by
an in situ second harmonic generation (SHG) experiment by using a
closed temperature-controlled oven with optical windows and three
needle electrodes. The films were kept at 458 to the incident beam and
poled inside the oven, and the SHG intensity was monitored simultane-
ously. Poling conditions were as follows: temperature, different for each
polymer (Table 1); voltage, 7.7 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.
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Acknowledgements
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We are grateful to the National Science Foundation of China (no.
21034006) and the Fundamental Research Fund for the Central Universi-
ties for financial support.
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Received: April 14, 2011
Published online: August 22, 2011
Chem. Asian J. 2011, 6, 2787 – 2795
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
2795