From nitro- to sulfonyl-based chromophores: Improvement of the comprehensive performance of nonlinear optical dendrimers

Article abstract of DOI:10.1002/chem.201203567

Through the combination of the divergent and convergent approaches, coupled with the utilization of the powerful Sharpless "click-chemistry" reaction, two series of sulfonyl-based high-generation NLO dendrimers were conveniently prepared with high purity

Full text of DOI:10.1002/chem.201203567

FULL PAPER
DOI: 10.1002/chem.201203567
From Nitro- to Sulfonyl-Based Chromophores: Improvement of the
Comprehensive Performance of Nonlinear Optical Dendrimers
Wenbo Wu,[a] Guohua Xu,[b] Conggang Li,*[b] Gui Yu,[c] Yunqi Liu,[c] Cheng Ye,[c]
Jingui Qin,[a] and Zhen Li*[a]
Abstract: Through the combination of
the divergent and convergent ap-
proaches, coupled with the utilization
of the powerful Sharpless “click-chem-
istry” reaction, two series of sulfonyl-
based high-generation NLO dendrim-
ers were conveniently prepared with
high purity and in satisfactory yields.
Thanks to the perfect three-dimension-
al (3D) spatial isolation from the
highly branched structure and the iso-
lation effect of the exterior benzene
moieties and the interior triazole rings,
these dendrimers exhibited large
second harmonic generation coefficient
(d33) values up to 181 pmVꢀ1, which, to
the best of our knowledge, is the high-
est value so far for polymers containing
sulfonyl-based chromophore moieties.
Meanwhile, compared with the nitro-
chromophore-based analogues, their
optical transparency and NLO stability
were improved in a large degree, due
to the lower dipole moment (m) and
the special main-chain structure of sul-
fonyl-based chromophore in these den-
drimers.
Keywords: click chemistry · chro-
mophores · dendrimers · nonlinear
optics · sulfonyl
Introduction
polar chromophore moieties and enhancing the poling effi-
ciency, with a spherical shape, which was proposed by
Dalton and Jen et al. as being the most ideal conforma-
tion.[2d,3] Applying this site isolation principle, many dendrit-
ic NLO materials, including hyperbranched polymers,
dendronized polymers, and dendrimers have been prepared
and exhibited large EO coefficients, in which some bulky
groups were linked to chromophores as the isolation moiet-
ies.[4,5] Also, based on these excellent results in the NLO
field, as well as our systematic work on the concept of the
“suitable isolation group”,[6,7] our group have recently pre-
pared a new series of nitro-based chromophore-containing
NLO dendrons G1 to G5 (Schemes S1–S3, see the Support-
ing Information) and dendrimers G1-TPA to G3-TPA
(Chart S1 and Schemes S4 and S5, the Supporting Informa-
tion) through a “double-stage” method by using the “click-
chemistry” reaction.[8] These dendrimers demonstrated very
large d33 values (NLO coefficient, which could express the
magnitude of NLO effect) of 193.1 pmVꢀ1 (G5) and
246.0 pmVꢀ1 (G3-TPA), and the observed NLO effects in-
creased with an increase of the loading density of the chro-
mophore moieties, indicating that the frequently observed
asymptotic dependence of EO activity on the chromophore
number density may be overcome through rational design,
which is in accordance with the prediction of Sullivan and
co-workers.[9] This also confirmed our idea of the formed tri-
azole rings as suitable isolation groups to enhance the mac-
roscopic NLO effect.[10] However, as mentioned above, in
addition to the large optical nonlinearity, the optical trans-
parency and the stability of NLO coefficients were also im-
portant for NLO materials but less explored by scientists. In
fact, there are so-called nonlinearity-transparency trade-offs
and nonlinearity-stability trade-offs present in the NLO
In the past decades, large efforts have been made to investi-
gate organic and polymeric second-order nonlinear optical
(NLO) materials, due to their huge potential applications in
photonic devices, such as high-speed electro-optic (EO)
modulators, optical switches, and frequency converters.[1]
Thanks to the great efforts of scientists, many strategies and
approaches have been reported for the development of or-
ganic/polymeric NLO materials to meet the basic require-
ments of practical applications: large optical nonlinearity,
low optical loss, and excellent temporal stability of dipole
orientation.[2] In particular, controlling the shape of the
chromophore has proved to be an efficient approach for
minimizing the strong electronic interaction among the high
[a] W. Wu, Prof. J. Qin, Prof. Z. Li
Department of Chemistry
Hubei Key Laboratory on Organic and
Polymeric Opto-Electronic Materials
Wuhan University, Wuhan 430072 (China)
E-mail: lizhen@whu.edu.cn
[b] Dr. G. Xu, Prof. C. Li
China State Key Laboratory of Magnetic Resonance
and Atomic and Molecular Physics
Wuhan Institute of Physics and Mathematics
The Chinese Academy of Sciences, Wuhan, 430071 (China)
E-mail: conggangli@wipm.ac.cn
[c] Prof. G. Yu, Prof. Y. Liu, 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/chem.201203567.
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Figure 1. Differences between sulfonyl- and nitro-based-chromophores in NLO dendrimers.
fields,[11] that is to say, the improvement of the NLO proper-
ties often accompanies the decreased transparency or NLO
stability. Therefore, so far, it is still very difficult to demon-
strate all of these properties for NLO materials simultane-
ously.
as expected. However, so far, there a no reports concerning
this.
Therefore, in this paper, we designed and synthesized a
new series of sulfonyl-chromophore-based NLO dendrons
G1-S to G5-S (in which S represents that these dendrons
consist of sulfonyl-based chromophores, as to differentiate
G1 to G5 in our previous work) and a new series of sulfon-
yl-chromophore-based NLO dendrimers G1-S-GL to G4-S-
GL (in which GL represents that the topological structures
of these dendrimers are global-like, as to differentiate G1-S
to G5-S), through a “double-stage” method through the
“click-chemistry” reaction. As expected, these dendrimers
demonstrated a large NLO effect, good optical transparency,
and the improved stability of NLO coefficients simulta-
On the other hand, similar to the nitro-based azo chromo-
phore, the sulfonyl-based azo chromophore was another
normal NLO chromophore, and has a similar chemical
structure to its nitro-based counterpart. Considering the suc-
cessful examples of nitro-chromophore-based NLO den-
drimers, we hypothesized about the utilization of the sulfon-
yl-based chromophore moieties instead of the nitro-based
ones. In our opinion, perhaps, there should be at least two
advantages (Figure 1). First, in contrast to the nitrogen atom
in nitro groups that have sp2 hybrid orbitals, the molecular
orbitals of the sulfur atom in the sulfonyl groups are sp3
hybrid orbitals, which could lead to a little less conjugation
with the donor, and decrease the dipole moment (m) of the
chromophore, thus, improve the transparency of this kind of
NLO chromophore.[12] Secondly, different from the nitro-
based chromophore in NLO dendrimers G1 to G5 or G1-
TPA to G3-TPA, the whole sulfonyl-based chromophore
could be bonded into the dendrimers, which could limit the
relaxation of the chromophore, and further increase the sta-
bility of the alignment of the sulfonyl-based chromophore.
Meanwhile, this special main-chain structure could also
change the topological structure of NLO dendrimers. How-
ever, the effect of this change to the performance of NLO
dendrimers is very difficult to predict. Considering all of the
differences of these two types of chromophores, it was thus
very interesting and important to design and synthesize the
sulfonyl-chromophore-based high-generation dendrimers, to
check whether this change could improve the optical trans-
parency and the stability of NLO coefficients simultaneously
AHCTUNGTREGnNNUN eously, thus validating our original idea. More excitingly,
the NLO coefficient of G3-S-GL was 181 pmVꢀ1, which is,
to the best of our knowledge, the highest value so far for
the polymers containing the sulfonyl-based chromophore
moieties. Herein, we present the syntheses, characterization,
and properties of these new dendrimers in detail.
Results and Discussion
Synthesis: As shown in Schemes 1–3, the synthetic route to
G1-S–G5-S was very similar to our previous syntheses of G1
to G5 (Schemes S1–S3, the Supporting Information). In ad-
dition, the sulfonyl-based chromophore was used instead of
nitro-based one. At first, G1-S was synthesized between G0-
[6i]
and N,N-bis(2-azidoethyl)aniline (S1),[8] which has
ꢁ
-S
been already prepared in our previous work by using “click
chemistry” under room temperature. Then, through the effi-
cient azo-coupling reaction at 08C, another constructing
ꢁ
block of chromophore was formed to yield G1- -S. Simulta-
neously, another reactive alkyne group was introduced for
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Nonlinear Optical Dendrimers
FULL PAPER
proach, because of the large
steric hindrance of the reactive
segments. Therefore, with the
aim to obtain high-generation
dendrons, the divergent ap-
proach was also used to synthe-
size the dendronized core G2-
8N3-S from the AB2-type mono-
mer G0-2Cl-S, which was craft-
ed to contain two chloroethyl
groups and one terminal alkyne
group (Scheme 2). After the
“click-chemistry” reaction be-
tween G0-2Cl-S and N,N-bis(2-
azidoethyl)aniline (S1), the first
generation dendron G1-4Cl-S
was yielded conveniently. Then,
through the substitution of the
chloride groups in G1-4Cl-S,
dendron G1-4N3-S was pro-
duced in high yield. The subse-
quent click reaction between
azides of G1-4N3-S and the ter-
minal alkyne in chromophore
G0-2Cl-S gave the second gen-
eration dendrimer of G2-8Cl,
which could further undergo
the substitution reaction of the
chloride groups to produce the
core G2-8N3-S in high yield. At
last, the target high-generation
dendrons G3-S to G5-S could
be
conveniently
obtained
through “click chemistry” by
the utilization of the “double-
stage” approach (Scheme 3).
Even the preparation of G5-S,
which has a large steric effect,
could proceed completely in
about 6 h, as monitored by the
FTIR spectra (the peak cen-
tered at 2096 cmꢀ1 correspond-
ing to the azido groups gradual-
ly disappears).
The synthetic route was next
improved to give a more effi-
cient preparation of the den-
drimers. In our previous case
regarding the synthesis of G1-
TPA to G3-TPA (Scheme S4,
the Supporting Information),[8c]
due to the low reactivity of the
ꢁ
ꢁ
Scheme 1. The synthesis of end-capped dendrons (G1- -S and G2- -S). VC=vitamin C
the further growth of the dendrimers. Just repeating these
procedures, the low generation dendrons G1-S and G2-S,
Sonogashira coupling reaction used and the difficult purifi-
cation, the yields of the three-branched core were very low
(the total yield of two steps was only 8.99%). However, in
this case, the “click-chemistry” reaction, with nearly quanti-
tative yields and simple product isolation, was used instead
ꢁ
ꢁ
and end-capped dendrons G1- -S and G2- -S could be
easily prepared (Scheme 1). However, the higher generation
dendrimers could not be obtained in this convergent ap-
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C. Li, Z. Li et al.
CHCl3,
THF,
DMF,
and
DMSO, and their solutions
could be easily spin-coated into
thin solid films. Thus, it was
convenient to test their NLO
and other properties based on
the solutions and thin films.
Characterizations: The den-
drimers were well characterized
by spectroscopic analysis, and
all gave satisfactory data, in ac-
cordance with their expected
molecular structures (see the
Experimental Section and the
Supporting Information for de-
tails). The elemental analysis
technology was used to further
evaluate the purity of the final
target dendrons G1-S to G5-S
and dendrimers G1-S-GL to
G4-S-GL. In the FTIR spectra
(Figures S1 and S2, the Sup-
porting Information), all the
dendrimers showed absorption
bands associated with the sul-
fonyl groups at about 1316 and
1130 cmꢀ1, indicating the suc-
cessful introduction of sulfonyl-
chromophore moieties into
these dendrimers. Meanwhile,
the peak of azido groups (at
about 2098 cmꢀ1) disappeared
in the spectra of the target
NLO dendrimers, coupled with
the appearance of a carbonyl
group absorption at 1717 cmꢀ1,
disclosing that the target den-
drimers were yielded through
the “double-stage” approach
successfully.
All the NMR spectra (includ-
1
ing H and 13C NMR spectra) of
these dendrimers are shown in
Figure S2–S38 (the Supporting
Scheme 2. The synthesis of core G2-8N3-S.
Information). The structures of
(Scheme 4). As expected, in this work the total yield of G1-
6N3-S through two synthetic steps was up to 67.9%. Mean-
while, to avoid the large isolation effect of the new formed
triazoles, the core was changed to phenyl rings (but not the
previous TPA units), according to the concept of the “suita-
ble isolation group” (Scheme 4).[6] At last, the target den-
drimers G1-S-GL to G4-S-GL could be conveniently ob-
tained by using the “click chemistry” reaction, by the utiliza-
tion of the “double-stage” approach. (Scheme 5) These two
series of sulfonyl-chromophore-based dendrimers are readily
soluble in common polar organic solvents, such as CH2Cl2,
these dendrimers could be confirmed by the changes of the
peaks, associated with the reaction sites, in the 1H NMR
spectra. For example, through the convergent approach, the
“click chemistry” and azo-coupling reactions were used.
Thus, by the presence and absence of the signal of the
phenyl proton at the para position to the amino group in
the benzene ring at about d=6.8 ppm before (in G1-S and
ꢁ
ꢁ
G2-S) and after (G1- -S and G2- -S) the azo-coupling reac-
tions, the dendritic growth could be confirmed. On the other
hand, the substitution of the chloride groups to azide groups
and the “click chemistry” reaction were the typical reactions
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Scheme 3. The synthesis of high-generation dendrons (G3-S to G5-S).
1
through the divergent approach. In the H NMR spectrum
even broader peaks. As shown in their 1H NMR spectra
(Figure S19, S21, S23, the Supporting Information), after the
“click-chemistry” reaction, the signal at about d=3.6 ppm,
which can be assigned to the protons of -CH2N3, disap-
peared, whereas their characteristic peaks, such as about d=
of G1-4N3-S (Figure S13, the Supporting Information) and
G2-8N3-S (Figure S17, the Supporting Information), the
original peak at d=3.72 ppm of chloromethyl groups in G1-
4Cl-S (Figure S11, the Supporting Information) and G2-8Cl-
S (Figure S15, the Supporting Information) disappeared,
whereas the signal at d=3.60 ppm was enhanced, indicating
that the cores of dendrons have been synthesized successful-
ly. For high-generation dendrons G3-S to G5-S, due to their
ꢀ
ꢀ
ꢀ
ꢀ
3.1 ( CH2S ), 4.5 ppm ( COOCH2 ), 6.7 (ArH) and so on,
were still present, confirming the successful “click-chemis-
try” reaction. The structures of dendrimers G1-S-GL to G4-
S-GL could be confirmed in the similar way. Figure 2
1
1
ꢁ
large molecular weights, the peaks in their H NMR spectra
became broad, and the larger molecular weights resulted in
showed the H NMR spectra of G1- -S, G1-6N3-S-GL, and
G3-S-GL as an example to illustrate the successful synthesis
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C. Li, Z. Li et al.
ꢁ
G1- -S),
and
53.1 ppm
(-CH2N3, G1-6N3-S-GL) disap-
peared, whereas the peak corre-
sponding to the ester groups
from the end-capped dendrons
(d=166.7 ppm) was still pres-
ent, again confirming the suc-
cessful synthesis of high-genera-
tion dendrimers. In addition,
the 2D NMR spectra (including
H,H-COSY, C,C-COSY and
HMBC spectra) of high-genera-
tion dendrimers were per-
formed to further confirm the
structures of high-generation
dendrimers once more, and all
gave
satisfactory
results.
Figure 4 shows the NMR spec-
tra of G3-S-GL as a representa-
tive example, whereas the other
spectra are presented in the
Supporting Information (Fig-
AHCTUNGTRENNUNG
be a good method to confirm
the exact molecular weights of
the dendrimers. Figures S48–
S61 (the Supporting Informa-
tion) showed the MALDI-
TOF-MS spectra of the ob-
tained dendrimers, and all the
experimental results were in
good agreement with the ex-
pected molecular weights for
Scheme 4. The synthesis of core G1-6N3-S-GL.
the structures. However, the
MALDI-TOF-MS spectra of
of high-generation dendrimers. Besides this, the integration
of the signals of 1H NMR spectra was another piece of
strong evidence to confirm the perfection of the high-gener-
the azide-containing dendrimers did not give clear signals,
which could be caused by fragment ions arising due to the
fragmentation of unstabilized azide groups during the
MALDI analysis. For example, in the MALDI-TOF-MS
spectrum of G1-4N3-S (Figure S53, the Supporting Informa-
tion), except for the peaks at m/z 1184.7 ([M+Na]+) and
1162.7 ([M+H]+), there was only one other apparent peak
at 1134.6 ([M+Hꢀ28]+), possibly due to one of the four
azide groups that had degraded to nitrene. Unfortunately,
we failed to detect any signals within the appropriate mass
range for high-generation dendrimers G4-S, G5-S, and G4-
S-GL, and the possible reason might be that their larger mo-
lecular weight resulted in much lower peak intensity. In fact,
the MALDI-TOF-MS spectrum of G3-S-GL (Figure S61,
the Supporting Information), with much lower molecular
weight than G4-S-GL, was still unclear. Alternatively, the
laser light-scattering (LLS) measurement was conducted to
evaluate their absolute molecular weights. As shown in
Table 1, the tested values of these dendrimers were similar
to (or a little higher than) the calculated values, confirming
their structures again. Meanwhile, the gel permeation chro-
1
ation dendrimers. We also took the H NMR spectra of G3-
S-GL as an example. As shown in Figure 2, the peaks at d=
5.33 ppm should be assigned to the protons of the methylene
group linked to triazoles from the core G1-6N3-GL, whereas
the broad peaks at d=4.3–4.7 ppm should be assigned to
the protons of the methylene group linked to triazoles and
ester groups from the dendrons. The integral ratio of these
two peaks was 0.26:7.68, which was very similar to the theo-
retical value 1:28 (0.26:7.28). Thus, according to their inte-
gral ratio, the perfection of these high-generation dendrim-
ers could be confirmed. A similar phenomenon was also ob-
served in their 13C NMR spectra. Still using G3-S-GL as an
example, as shown in Figure 3, with the exception of some
characteristic peaks of functional groups, the 13C NMR spec-
ꢁ
tra of G1- -S, G1-6N3-S-GL and G3-S-GL were very simi-
lar, because they were all composed of sulfonyl-chromo-
phore moieties and triazole groups. After the “click-chemis-
try” reaction, the peaks at d=70.1, 81.6 (terminal alkynes,
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1
ꢁ
Figure 2. H NMR spectra of G1- -S, G1-6N3-S-GL and G3-S-GL in CDCl3 (the peaks from residual solvents, water, and TMS were marked with *).
relative molecular weights of polymers should be that the
efflux time of polymers with different molecular weight
Table 1. Molecular-weight-tested data of dendrimers.
[a]
[a]
[c]
[f]
Compound Mw
Mw/Mn
m/z[b]
Mw
m/z (calcd) Mc/Mw
should be different, since their size in dilute solution is dif-
ferent. However, the molecular weight was not the only
factor to affect the hydrodynamic radius of polymers. For
example, for the same molecular weight, the hydrodynamic
radius of dendritic structures should be much smaller than
the linear structures, and the hydrodynamic radius of the
dendritic structures with spherical shape should be the
G1-S
G2-S
G3-S
G4-S
1510 1.03
3800 1.05
6060 1.04
9340 1.04
12200 1.08
2160 1.05
4840 1.03
8150 1.10
11800 1.07
30300 1.36
1501.5
3679
2020
5550
12100
1501.7[d]
3680[d]
8036[d]
0.979
0.962
1.322
1.791
2.799
0.978
0.926
1.465
2.118
1.121
1.672
8038
[g]
–
–
19200 16728[e]
41200 34152[e]
[g]
G5-S
G1-S-GL
G2-S-GL
G3-S-GL
G4-S-GL
G5[h]
2135.4
5406
3650
6800
2135.7[d]
4505[d]
11954
14300 11941[d]
34600 24989[e]
33966
[g]
smallest one. Therefore, GPC analysis, using linear poly
ACHTUNGTRENNUNGsty-
–
AHCTUNGTREGrNNUN enes as calibration standards, often underestimates the mo-
G3-TPA[h] 14850 1.09
24813
lecular weights of dendrimers with a 3D branched struc-
ture,[13] thus, the tested molecular weights of higher-genera-
tion dendrimers were all lower than their true values. Here,
by the utilization of this special feature, the GPC results
might be used to characterize the 3D branched structure of
dendrimers in some sense: if the difference between the
tested and true values was higher, its hydrodynamic radius
should be more different from that of linear polymers, and
its topological structure should be much closer to spherical.
A Mc/Mw value (in which Mc is the calculated molecular
weight, whereas Mw is the weight average molecular weight
determined by GPC) was used to describe this difference
and the values were listed in Table 1. As expected, accompa-
nied with the generation increase of dendrimers, the Mc/Mw
values also increases, and the topology of the 3D branched
[a] Determined by GPC in THF on the basis of a polystyrene calibration.
[b] Measured by MALDI-TOF mass spectroscopy. [c] Determined by
LLS technique. [d] Calculated for [M+Na]+. [e] Calculated for [M]+.
[f] Mc was the calculated molecular weight. [g] Not obtained. [h] Tested
in our previous work, ref. [8].
matography (GPC) measurement was also conducted. All
the GPC curves of the dendrimers showed narrow peaks
with polydispersity indexes (PDI) of less than 1.10 (Table 1),
indicating that the products possessed monodispersed mo-
lecular weights. Meanwhile, the increasing trend in the
tested GPC results was also consistent with the actual mo-
lecular weights. In fact, GPC was one type of size exclusion
chromatography in essence, and its mechanism to test the
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C. Li, Z. Li et al.
Scheme 5. The synthesis of dendrimers (G1-S-GL to G4-S-GL).
structures was improved. Also, the Mc/Mw values of high-
generation dendrimers were higher than normal dendrons of
the same generation (for example: the Mc/Mw value of G4-
S-GL was 2.118, but for G4-S the value was 1.791), indicat-
ing that the topological structure of dendrimers should be
better than the normal dendrons, and further confirming our
previous idea on dendrimers in NLO fields. More excitingly,
when the molecular weights were similar, the Mc/Mw values
of these sulfonyl-chromophore-based dendrimers were all
higher than their nitro-chromophore-based counterparts (for
example: the Mc/Mw value of G5-S was 2.799, whereas only
1.121 for G5). This result indicated that the 3D topological
structure of these sulfonyl-chromophore-based dendrimers
should be better than that of nitro-based ones in our previ-
ous work, which should be very beneficial to their NLO
effect; this point was unexpected at the very beginning of
this work.
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Nonlinear Optical Dendrimers
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Figure 3. 13C NMR spectra of G1- -S, G1-6N3-S-GL and G3-S-GL in CDCl3 (the peaks from residual solvents were marked with *).
ꢁ
As mentioned above, the original idea of this paper was
the usage of the sulfonyl chromophore, to improve the opti-
Table 2. The maximum absorption of dendrimers in films.
Compound
lmax [nm]
Compound
lmax [nm]
cal transparency and the stability of NLO dendrimers. To
evaluate the optical transparency of these dendrimers, their
UV/Vis spectra (Figure 5 and the Supporting Information,
S62–S72 and Table S1) in different solvents were tested. The
maximum absorption wavelengths (lmax) for the p–p* transi-
tion of the azo moieties in films are listed in Table 2. Excit-
ingly, in comparison with the nitro-chromophore-based den-
drimers, the lmax values of all the dendrimers in this paper
were blueshifted by about 35 nm, demonstrating much
better optical transparency, which could contribute much to
their practical applications in photonics fields. Meanwhile,
accompanying with the generation increase of dendrimers,
the lmax was further blueshifted, due to more perfect 3D
structures of higher-generation dendrimers. However, since
these sulfonyl-chromophore-based dendrimers have better
3D topological structures than the nitro-based chromophore
dendrimers, the differences of lmax between low-generation-
G1-S
G2-S
G3-S
G4-S
438
434
433
432
432
436
434
433
433
G1
G2
G3
G4
479[a]
482[a]
480[a]
470[a]
470[a]
470[a]
470[a]
470[a]
G5-S
G5
G1-S-GL
G2-S-GL
G3-S-GL
G4-S-GL
G1-TPA
G2-TPA
G3-TPA
[a] Tested in our previous work, ref. [8].
and high-generation dendrimers were not so obvious as in
the nitro-based ones (for example: a blueshift of 12 nm from
G2 to G5, but only 2 nm from G2-S to G5-S).
These dendrimers were thermally stable (Figure S73 and
S74, the Supporting Information), with their 5% weight loss
temperatures listed in Table 3. The glass transition tempera-
Chem. Eur. J. 2013, 00, 0 – 0
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C. Li, Z. Li et al.
Table 3. The thermal properties of dendrimers.
[a]
[b]
Compound
Tg
[8C]
Td
[8C]
Compound
Tg
[8C]
Td
[8C]
G
E
N
ACHTUNGTRENNUNG
[c]
G1-S
G2-S
G3-S
G4-S
–
311
314
313
304
295
281
308
299
293
G1[d]
56
76
90
117
125
62
300
295
278
262
275
280
292
286
119
126
134
156
71
117
–
138
G2[d]
G3[d]
G4[d]
G5-S
G5[d]
G1-S-GL
G2-S-GL
G3-S-GL
G4-S-GL
G1-TPA[d]
G2-TPA[d]
G3-TPA[d]
74
92
[c]
[a] Glass transition temperature (Tg) of polymers detected by the DSC
analyses under argon at a heating rate of 108Cminꢀ1. [b] 5% weight loss
temperature of polymers detected by TGA analyses under nitrogen at a
heating rate of 108Cminꢀ1. [c] Not obtained. [d] Tested in our previous
work in ref. [8].
main-chain structure of the sulfonyl-chromophore moieties
in these dendrimers, the thermally stabilities of G1-S to G5-
S and G1-S-GL to G4-S-GL were improved relative to the
nitro-chromophore-based dendrimers. Considering that the
stability of the NLO effect was associated with the glass
transitions, the higher Tg values should benefit to their sta-
bility in the practical applications.
NLO properties: The NLO effect was the most important
parameter for NLO materials. If the NLO effects of these
dendrimers were not satisfied, then improved properties of
optical transparency and stability were meaningless. To eval-
uate the NLO activity of these dendrimers, their poled thin-
films were prepared. The most convenient technique to
study the second-order NLO activity is 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 re-
ported in our previous papers.[6–8,10] From the experimental
data, the d33 values of the dendrimers were calculated at a
fundamental wavelength of 1064 nm (Table 4). To check the
reproducibility, we repeated the measurements at least three
times and almost got the same results. However, during the
poling procedure, the thin films of G4-S-GL were always
Figure 4. 2D NMR spectra of G3-S-GL in CDCl3. A) H,H-COSY;
B) C,H-COSY).
Table 4. NLO results of dendrimers.
[c]
[d]
Te[a]
[8C]
ls[b]
[mm]
d33
[pmVꢀ1
d33 (1)
[pmVꢀ1
]
F[e]
N[f]
G
G
]
U
G1-S
G2-S
G3-S
G4-S
70
0.27
0.24
0.25
0.19
0.21
0.27
0.18
0.22
52
72
14
20
29
33
38
29
38
51
0.11
0.18
0.20
0.23
0.31
0.19
0.29
0.33
0.467
0.567
0.604
0.620
0.627
0.490
0.578
0.609
120
130
140
165
65
103
117
133
107
136
181
G5-S
Figure 5. UV/Vis spectra of THF solutions of dendrimers G1-S to G5-S
G1-S-GL
G2-S-GL
G3-S-GL
(0.02 mgmLꢀ1).
125
130
[a] The best poling temperature. [b] Film thickness. [c] Second harmonic
generation (SHG) coefficient. [d] The nonresonant d33 values calculated
by using the approximate two-level model. [e] Order parameter F=1ꢀ
A1A0ꢀ1, A1 and A0 are the absorbance of the polymer film after and
before poling, respectively.[f] The loading density of the effective chromo-
phore moieties.
tures (Tg) of the dendrimers were also investigated by using
differential scanning calorimetry (DSC), with the results
summarized in Table 3. Similar to G1 to G5 and G1-TPA to
G3-TPA, the growth of the NLO dendrimers in this paper
also resulted in the increase of Tg values. Due to the special
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Nonlinear Optical Dendrimers
FULL PAPER
broken by the DC electric field, and therefore, its d33 value
was not obtained. The reason for this is unclear at present.
Similar to our previous case on the nitro-chromophore-
based dendrimers, the d33 values increased from G1-S
(52 pmVꢀ1) to G5-S (133 pmVꢀ1), accompanied with the in-
creasing loading density of the chromophore moieties, and
the higher the generation of dendrons, the higher the d33
values. Due to the more ideal 3D branched topological
structure, the dendrimers demonstrated much higher d33
values than the normal ones. In particular, the high genera-
tion dendrimer G3-S-GL, its d33 value was up to 181 pmVꢀ1,
which should be, to the best of our knowledge, the highest
value so far for polymers containing the sulfonyl-based chro-
mophore moieties. Compared with the nitro-chromophore-
based dendrimers (the d33 value of G5 was 193.1 pmVꢀ1,
whereas it was 246.0 pmVꢀ1 for G3-TPA), it seems that the
NLO coefficients of the sulfonyl-chromophore-based den-
drimers possessed no advantage. However, this was not the
case, and it may be due to the different resonant enhance-
ment effects at 532 nm (double the frequency of the
1064 nm fundamental wavelength) of these two types of
dendrimers, for their different optical transparency.[14]
Therefore, by using the approximate two-level model, we
calculated their nonresonant d33 values, and the results were
summarized in Table 4 (d33(1) values). Because of the much
better optical transparency of the sulfonyl-chromophore-
based dendrimers, their d33(1) values were still very high. For
example, the d33(1) value of G5-S was 38 pmVꢀ1, and the
d33(1) value of G3-S-GL was even up to 51 pmVꢀ1, higher
than their corresponding nitro-chromophore-based counter-
parts (the d33(1) value of G5 is 34 pmVꢀ1, whereas it is
43 pmVꢀ1 for G3-TPA). Considering that the d33 value of
the same NLO polymer could be different when measured
by different methods or different testing systems, even at
different times, and the d33(1) value was calculated by the
approximate two-level model, it was not so convincing to
say “the NLO coefficients of these sulfonyl-chromophore-
based dendrimers were higher than their corresponding
nitro-chromophore-based ones”. However, at least, we
could draw a conclusion: the NLO coefficients of these sul-
fonyl-chromophore-based dendrimers were at least on the
same level to their corresponding nitro-chromophore-based
counterparts.
Figure 6. Decay curves of the SHG coefficients of dendrimers as a func-
tion of the temperature.
monitored as the poled films were heated from 40 to 1608C
in air at a rate of 48Cminꢀ1. Figure 6 displays the decay of
the SHG coefficient of G3-S to G5-S and G3-S-GL as a
function of temperature. As expected, all of them demon-
strated higher stability than the nitro-chromophore-based
dendrimers. For example, the onset temperatures for decays
(Tonset) in the d33 values of G5-S was up to 1238C, whereas
only 1078C for G5. And this should be ascribed to the spe-
cial main-chain structure of the sulfonyl-based chromophore
moieties in these dendrimers as mentioned above.
Conclusion
By using a combination of divergent and convergent ap-
proaches, two series of the sulfonyl-chromophore-based
high-generation NLO dendrimers, G1-S to G5-S and G1-S-
GL to G4-S-GL, were successfully obtained through the
powerful “click-chemistry” reaction. Compared with the cor-
responding nitro-chromophore-based dendrimers, there
were at least two advantages of these sulfonyl-chromo-
phore-based analogues: much better optical transparency
derived from the lower m value of the sulfonyl chromophore
and the much higher stability from the special main-chain
structure of the sulfonyl-chromophore moieties in these den-
drimers. Meanwhile, thanks to the perfect three-dimensional
(3D) spatial isolation from the highly branched structure,
large NLO coefficients were still achieved, and the d33 value
for G3-S-GL of 181 pmVꢀ1, to the best of our knowledge,
should be the highest one so far reported for the polymers
containing the sulfonyl-chromophore moieties.
To further explore the alignment of the chromophore
moieties in these dendrimers, we measured their order pa-
rameter (F; Table 4 and Figure S75–S82). By using the rela-
tion of F=1ꢀA1A0ꢀ1, the F values of the dendrimers were
calculated, with the results listed in Table 4. The trend of
the F values was the same as the d33 values of dendrimers,
confirming that higher generation and increasingly 3D
branched topological structure, led to the better alignment
of the chromophore moieties under the poling process, and
thus to better NLO performance.
Experimental Section
To further confirm the better stability of these dendrimers
than the nitro-chromophore-based ones, the depoling ex-
periments of poled films of these dendrimers were conduct-
ed, in which the real-time decays of their SHG signals were
Materials and instrumentation: Tetrahydrofuran (THF) was dried over
and distilled from a K/Na alloy under an atmosphere of dry nitrogen.
N,N-Dimethylform amide (DMF) was dried over and distilled from CaH2
Chem. Eur. J. 2013, 00, 0 – 0
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C. Li, Z. Li et al.
under an atmosphere of dry nitrogen. Compound S1, S2, and S3 have
been already prepared in our previous work.[7a,b] N,N,N,N,N-Pentamethyl-
diethylenetriamine (PMDETA) and 1,3,5-tris(bromomethyl)benzene (S4)
was purchased from Alfa Aesar. All other reagents were used as re-
ceived.
16.84, 21.38, 22.27, 23.42, 46.82, 49.39, 50.81, 54.60, 54.85, 61.46, 70.11,
81.60, 85.37, 111.59, 122.52, 125.67, 128.13, 128.66, 129.22, 132.90, 138.11,
143.78, 145.84, 149.16, 150.69, 155.71, 166.03 ppm; IR (KBr): n˜ =3289
(CꢁCH), 1716 (C=O), 1316, 1132 cmꢀ1 (-SO2-); MALDI-TOF MS: m/z
calcd (%) for C91H89N15O14S3: 1734.6 [M+Na]+; found: 1734.1.
1H and 13C NMR spectra were measured on a Varian Mercury300, Varian
Mercury600 or Bruker ARX 400 spectrometer. H,H COSY and
C,H COSY spectra of high generation dendrimers were measured on a
600 MHz Bruker Avance III NMR Spectrometer with a CryOProbe. The
Fourier transform infrared (FTIR) spectra were recorded on a Perkin-
Synthesis of dendrimer G2-S: The procedure was similar to the synthesis
ꢁ
of dendrimer G1-S but using dendrimer G1- -S (450.0 mg, 0.263 mmol)
and S1 (27.7 mg, 0.119 mmol). The crude product was purified by column
chromatography on silica gel using THF/chloroform (1:1, v/v) as eluent
to afford orange solid G2-S (291.2 mg, 66.9%). 1H NMR (400 MHz,
CDCl3, 298 K): d=2.08 (m, -CH2-), 2.77 (m, -CH2C-), 3.15 (s, br, -SCH2-
), 3.62 (s, br, -NCH2-), 3.73 (s, br, -NCH2-), 3.94 (t, J=8.0 Hz, -NCH2-),
4.35 (s, br, -NCH2-), 4.43 (s, br, -NCH2-), 4.59 (t, J=8.0 Hz, -COOCH2-),
6.60 (d, J=8.0 Hz, ArH), 6.71 (d, J=8.0 Hz, ArH), 6.79 (s, ArH), 6.96 (d,
J=8.0 Hz, ArH), 7.13 (s, C=CH), 7.40 (m, ArH), 7.56 (m, ArH), 7.9–
8.1 ppm (m, ArH); 13C NMR (100 MHz, CDCl3, 298 K): d=22.64, 23.78,
47.26, 47.61, 49.85, 55.24, 61.80, 78.26, 109.99, 110.01, 111.99, 115.86,
122.92, 126.06, 129.05, 133.30, 138.54, 144.28, 147.96, 150.99, 156.19,
166.48 ppm; IR (KBr), n˜ =1716 (C=O), 1316, 1131 cmꢀ1 (-SO2-);
MALDI-TOF MS: m/z calcd for C192H191N37O28S6: 3680 [M+Na]+;
found: 3679; elemental analysis calcd (%) for C192H191N37O28S6: C 63.06,
H 5.26, N 14.17; found: C 62.41, H 5.34, N 13.91.
ACHTUNGTRENNUNG
Elmer-2 spectrometer in the region of 3000–400 cmꢀ1. UV/Visible spectra
were obtained using a Shimadzu UV-2550 spectrometer. Matrix-assisted
laser desorption ionization time-of-flight mass spectra (MALDI-TOF
MS) were measured on a Voyager-DE-STR MALDI-TOF mass spec-
trometer (ABI, American) equipped with a 337 nm nitrogen laser and a
1.2 m linear flight path in positive ion mode. Elemental analyses (EA)
were performed by a CARLOERBA-1106 micro-elemental analyzer. Gel
permeation chromatography (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. Polystyrene 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 NETZSCH STA449C thermal ana-
lyzer at a heating rate of 108Cminꢀ1 in nitrogen at a flow rate of
50 cm3 minꢀ1 for thermogravimetric analysis (TGA). The thermal transi-
tions of the polymers were investigated using a METTLER differential
scanning calorimeter DSC822e under nitrogen at a scanning rate of
108Cminꢀ1. The thermometer for measurement of the melting point was
uncorrected. The thickness of the films was measured with an Ambios
Technology XP-2 profilometer.
ꢁ
Synthesis of dendrimer G2- -S: The procedure was similar to the synthe-
ꢁ
sis of dendrimer G1- -S but using diazonium salt S2 (64.4 mg,
0.20 mmol) and dendrimer G2-S (182.9 mg, 0.050 mmol). The reaction
time was 5 days. The crude product was purified by column chromatogra-
phy on silica gel using THF/chloroform (1:1, v/v) as eluent to afford
orange solid G2- -S (143.2 mg, 73.6%). 1H NMR (400 MHz, CDCl3,
ꢁ
ꢁ
298 K), d (TMS, ppm): 2.08 (m, -CH2- and C CH), 2.80 (m, -CH2C-),
3.15 (m, -SCH2-), 3.73 (s, br, -NCH2-), 3.94 (m, -NCH2-), 4.43 (s, br,
-NCH2-), 4.59 (t, J=8.0 Hz, -COOCH2-), 6.69 (d, J=8.0 Hz, ArH), 6.97
(d, J=8.0 Hz, ArH), 7.22 (s, C=CH), 7.41 (m, ArH), 7.56 (m, ArH), 7.9–
8.1 ppm (m, ArH); 13C NMR (100 MHz, CDCl3, 298 K): d=17.24, 21.75,
23.46, 29.22, 33.32, 45.18, 47.26, 49.83, 55.25, 61.83, 67.28, 67.59, 70.40,
80.48, 98.34, 101.77, 107.90, 110.00, 111.99, 122.55, 122.91, 124.77, 126.06,
129.61, 133.30, 138.51, 144.24, 146.26, 149.42, 151.02, 156.16, 166.48 ppm;
ꢁ
Synthesis of dendrimer G1-S: Chromophore G0- -S (823.3 mg,
1.32 mmol), N,N-bis(2-azidoethyl)aniline (S1) (138.8 mg, 0.60 mmol),
CuSO4·5H2O (10 mol%), NaHCO3 (20 mol%), and ascorbic acid
(20 mol%) were dissolved in THF (24 mL)/H2O (6 mL) under nitrogen
in a Schlenk flask. After the mixture was stirred at 25–308C under nitro-
gen atmosphere for 3 h, the reaction was terminated by the addition of
water, and then extracted with chloroform, and washed with brine. The
organic layer was dried over anhydrous magnesium sulfate and purified
by column chromatography using ethyl acetate/chloroform (2:1, v/v) as
eluent to afford an orange solid G1-S (840.8 mg, 94.8%). 1H NMR
(300 MHz, CDCl3, 298 K): d=2.08 (m, 4H, -CH2-), 2.80 (t, J=6.3 Hz,
4H, -CH2C-), 3.15 (t, J=6.9 Hz, 4H, -SCH2-), 3.63 (s, br, 4H, -NCH2-),
3.95 (s, br, 8H, -NCH2-), 4.35 (s, br, 4H, -NCH2-),4.59 (s, br, 8H,
-COOCH2-), 6.62 (d, J=7.5 Hz, 2H, ArH), 6.81 (t, J=8.1 Hz, 1H, ArH),
6.97 (d, J=7.5 Hz, 4H, ArH), 7.14 (s, 2H, C=CH), 7.25 (m, 2H, ArH),
7.40 (m, 8H, ArH), 7.56 (m, 4H, ArH), 7.9–8.10 ppm (m, 20H, ArH);
13C NMR (75 MHz, CDCl3, 298 K): d=22.47, 23.64, 47.21, 49.61, 51.34,
55.08, 61.60, 111.78, 112.79, 118.37, 122.10, 122.68, 125.84, 128.30, 128.85,
129.41, 129.66, 133.07, 138.39, 144.05, 145.53, 145.78, 150.77, 155.94,
166.23 ppm; IR (KBr): n˜ =1711 (C=O), 1316, 1130 cmꢀ1 (-SO2-);
MALDI-TOF MS m/z calcd for (C80H79N13O12S2): 1501.7 [M+Na]+;
found: 1501.5; elemental analysis calcd (%) for C80H79N13O12S2: C 64.98,
H 5.38, N 12.31; found: C 64.58, H 5.61, N, 12.35.
IR (KBr): n˜ =3286 (C CH), 1716 (C=O), 1316, 1132 cmꢀ1 (-SO2-);
ꢁ
MALDI-TOF MS: m/z calcd for C203H201N39O30S7: 3914 [M+Na]+;
found: 3914.
Synthesis of dendrimer G1-4Cl-S: The procedure was similar to the syn-
thesis of dendrimer G1-S but using chromophore S3 (497.6 mg,
1.10 mmol) and N,N-bis(2-azidoethyl)aniline (S1; 115.6 mg, 0.50 mmol).
The crude product was purified by column chromatography on silica gel
using pure acetate as eluent to afford orange solid G1-4Cl-S (514.1 mg,
90.5%). 1H NMR (300 MHz, CDCl3, 298 K), d=2.08 (m, 4H, -CH2-),
2.81 (br, s, 4H, -CH2C-), 3.16 (br, s, 4H, -SCH2-), 3.64 (br, s, 4H, -NCH2-
), 3.72 (br, s, 8H, -CH2Cl-), 3.86 (br, s, 8H, -NCH2-), 4.35 (br, s, 4H,
-NCH2-), 6.63 (d, J=7.2 Hz, 2H, ArH), 6.79 (d, J=7.2 Hz, 5H, ArH),
7.15 (s, 2H, C=CH), 7.80–8.00 ppm (m, 14H, ArH); 13C NMR (75 MHz,
CDCl3, 298 K): d=22.52, 23.67, 40.11, 47.24, 51.49, 53.28, 55.13, 111.52,
112.79, 118.49, 122.21, 122.85, 125.97, 128.97, 129.81, 138.59, 144.31,
145.87, 149.45, 155.90 ppm; IR (KBr): n˜ =1316, 1131 cmꢀ1 (-SO2-);
MALDI-TOF MS: m/z calcd for C52H59N13O4S2Cl4: 1159.0 [M+Na]+;
found: 1158.5.
ꢁ
Synthesis of dendrimer G1- -S: Diazonium salt S2 (241.6 mg, 0.75 mmol)
and dendrimer G1-S (739.0 mg, 0.50 mmol) were dissolved in DMF
(10 mL)/THF (5 mL) at 08C. The reaction mixture was stirred for 40 h at
08C, then treated with H2O and extracted with CHCl3, washed with
brine. The organic layer was dried over anhydrous sodium sulfate. After
removal the organic solvent, the crude product was purified by column
chromatography on silica gel using ethyl acetate/chloroform (2:1, v/v) as
Synthesis of dendrimer G1-4N3-S: A Schlenk flask was charged with
compound G1-4Cl-S (284 mg, 0.25 mmol), NaN3 (130 mg, 2.0 mmol) and
DMF (2.5 mL). The reaction was allowed to stir at 808C for 12 h and
then the solution was poured into a large amount of water. The precipi-
tate was collected and washed several times with water and methanol/
water (1:1) and then dried under vacuum to afford orange solid (275 mg,
94.6%). 1H NMR (300 MHz, CDCl3, 298 K): d=2.07 (m, 4H, -CH2-),
2.80 (br, s, 4H, -CH2C-), 3.16 (t, J=7.8 Hz, 4H, -SCH2-), 3.60 (br, s, 8H,
-CH2N3-), 3.69 (br, s, 4H, -NCH2-), 4.35 (br, s, 4H, -NCH2-), 6.62 (d, J=
8.1 Hz, 2H, ArH), 6.81 (d, J=8.1 Hz, 5H, ArH), 7.16 (s, 2H, C=CH),
7.80–8.00 ppm (m, 14H, ArH); 13C NMR (75 MHz, CDCl3, 298 K): d=
22.26, 23.41, 46.91, 48.26, 50.15, 51.00, 54.82, 111.44, 112.30, 117.89,
121.95, 122.50, 125.62, 128.65, 129.39, 138.18, 143.80, 145.30, 145.51,
149.59, 155.60 ppm; IR (KBr): n˜ =2097 (-N3), 1316, 1131 cmꢀ1 (-SO2-);
eluent to afford orange solid G1- -S (670.4 mg, 78.3%). 1H NMR
ꢁ
ꢁ
(300 MHz, CDCl3, 298 K): d=1.96 (m, 3H, -CH2- and C CH), 2.10 (m,
2H, -CH2-), 2.33 (s, br, 2H, -CH2-), 2.83 (t, 4H, -CH2-), 3.15 (t, 4H,
-SCH2-), 3.27 (t, J=6.9 Hz, 2H, -SCH2-), 3.74 (br, s, 4H, -NCH2-), 3.96
(br, s, 8H, -NCH2-), 4.44 (s, br, 4H, -NCH2-), 4.59 (s, br, 8H, -COOACTHNUTRGNECUNG H2-
), 6.73 (d, J=8.4 Hz, 2H, ArH), 6.98 (d, J=9.0 Hz, 4H, ArH), 7.23 (s,
2H, C=CH), 7.43 (t, J=7.8 Hz, 8H, ArH), 7.54 (t, J=6.3 Hz, 8H, ArH),
7.9–8.1 ppm (m, 20H, ArH); 13C NMR (75 MHz, CDCl3, 298 K): d=
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Nonlinear Optical Dendrimers
FULL PAPER
MALDI-TOF MS: m/z calcd for C52H59N25O4S2: 1184.5 [M+Na]+;
found: 1184.7.
obtained as orange powder (70.0 mg, 89.7%). 1H NMR (300 MHz,
CDCl3, 298 K): d=1.6–2.2 (-CH2-), 2.7–2.9 (-CH2C- and -CH2-), 3.1–3.4
(-SCH2-), 3.6–4.0 (-NCH2-), 4.3–4.8 (-OCH2- and -COOCH2-), 6.4–6.8
(ArH), 6.9–7.0 (ArH), 7.2–7.6 (ArH and C=CH), 7.8–8.3 ppm (ArH);
13C NMR (150 MHz, CDCl3, 298 K): d=22.88, 24.01, 50.03, 55.46, 62.03,
112.14, 123.13, 126.29, 128.72, 129.27, 129.82, 133.52, 138.63, 144.37,
146.43, 151.15, 156.30, 166.68 ppm; IR (KBr): n˜ =1716 (C=O), 1316,
Synthesis of dendrimer G2-8Cl-S: The procedure was similar to the syn-
thesis of dendrimer G1-S, but using chromophore S3 (199.1 mg,
0.44 mmol) and G1–4N3-S (116.2 mg, 0.10 mmol). The crude product was
purified by column chromatography on silica gel by using THF/chloro-
form (1:1) as eluent to afford orange solid G2-8Cl-S (276.0 mg, 92.9%).
1H NMR (300 MHz, CDCl3, 298 K): d=1.6–1.9 (-CH2-), 2.0–2.2 (-CH2-),
2.79 (br, s, -CH2C-), 3.14 (br, s, -SCH2-), 3.62 (br, s, -NCH2-), 3.71 (br, s,
-NCH2-), 3.86 (br, s, -CH2Cl-), 3.94 (br, s, -NCH2-), 4.36 (br, s, -NCH2-),
4.43 (br, s, -NCH2-), 6.62 (br, s, ArH), 6.76 (d, J=7.8 Hz, ArH), 6.79 (d,
J=8.4 Hz, ArH), 7.15 (s, C=CH), 7.8–8.1 ppm (ArH); 13C NMR
(75 MHz, CDCl3, 298 K): d=22.54, 23.67, 27.69, 40.21, 47.09, 51.13, 53.25,
55.12, 68.44, 107.54, 111.62, 112.83, 122.41, 122.87, 125.98, 128.95, 129.80,
138.60, 144.32, 146.12, 149.62, 155.90 ppm; IR (KBr): n˜ =1316, 1131 cmꢀ1
(-SO2-); MALDI-TOF MS: m/z calcd for C136H151Cl8N37O12S6: 2994 [M+
Na]+; found: m/z 2993.
1130 cmꢀ1 (-SO2-); elemental analysis calcd (%) for C1760H1759N373O252S62
C 61.89, H 5.19, N 15.30; found: C 61.50, H 5.44, N 15.02.
:
Synthesis of core G0-3N3: 1,3,5-Tris(bromomethyl)benzene (S4) (1.78 g,
5.0 mmol) and NaN3 (1.95 g, 30.0 mmol) were dissolved in DMF (25 mL).
The reaction was stirred for 12 h at 808C, then treated with H2O and ex-
tracted with CHCl3, 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
petroleum ether/chloroform (1:2, v/v) as eluent to afford colorless oil G0-
3N3 (1.17 g, 95.9%). 1H NMR (300 MHz, CDCl3, 298 K): d=4.38 (s, 6H,
-CH2-), 7.24 ppm (s, 3H, -ArH-); 13C NMR (75 MHz, CDCl3, 298 K): d=
53.89, 127.11, 136.62 ppm.
Synthesis of dendrimer G2-8N3-S: The procedure was similar as the syn-
thesis of dendrimer G1-4N3-S but using G2-8Cl-S (178.0 mg, 0.060 mmol)
and NaN3 (62.4 mg, 0.96 mmol). The crude product was purified by
column chromatography on silica gel using THF/chloroform (1:1) as
eluent to afford orange solid G2-8N3-S (127.6 mg, 66.4%). 1H NMR
(300 MHz, CDCl3, 298 K): d=1.4–1.6 (-CH2-), 2.08 (s, br, -CH2-), 2.81
(br, s, -CH2C-), 3.14 (br, s, -SCH2-), 3.59 (br, s, -CH2N3-), 3.71 (br, s,
-NCH2-), 4.34 (br, s, -NCH2-), 4.44 (br, s, -NCH2-), 6.63 (br, s, ArH), 6.72
(br, s, ArH), 6.81 (d, J=8.7 Hz, ArH), 7.14 (s, C=CH), 7.8–8.1 ppm
(ArH); 13C NMR (75 MHz, CDCl3, 298 K): d=22.50, 23.67, 47.27, 48.63,
50.53, 55.13, 111.81, 112.93, 122.80, 125.93, 128.91, 138.53, 144.22, 145.81,
146.09, 149.22, 149.89, 155.94 ppm; IR (KBr): n˜ =2096 (-N3), 1316,
1130 cmꢀ1 (-SO2-); MALDI-TOF MS: m/z calcd for C136H151N61O12S6:
3047 [M+Na]+; found: 3045.
Synthesis of dendrimer G1-6Cl-S-GL: The procedure was similar to the
synthesis of dendrimer G1–4Cl-S, but using chromophore S4 (497.6 g,
1.1 mmol) and G0-3N3 (81.1 mg, 0.33 mmol). The crude product was puri-
fied by column chromatography using pure ethyl acetate as eluent to
1
afford orange solid G1-6Cl-S-GL (447.9 mg, 84.0%). H NMR (300 MHz,
CDCl3, 298 K): d=2.12 (m, 6H, -CH2-), 2.83 (t, J=6.0 Hz, 6H, -CH2C-),
3.19 (t, J=6.0 Hz, 6H, -SCH2-), 3.71 (t, J=6.0 Hz, 12H, -NCH2-), 3.85 (t,
J=6.0 Hz, 12H, -CH2Cl), 5.44 (s, 6H, -NCH2-), 6.79 (d, J=8.7 Hz, 6H,
ArH), 7.09 (s, 3H, C=CH), 7.31 (s, 3H, ArH), 7.9–8.0 ppm (m, 18H,
ArH); 13C NMR (75 MHz, CDCl3, 298 K): d=22.21, 23.59, 40.07, 52.97,
55.02, 67.24, 107.53, 111.43, 121.48, 122.63, 125.77, 127.19, 128.76, 136.64,
138.42, 144.08, 146.16, 149.48, 155.64 ppm; IR (KBr): n˜ =1316, 1131 cmꢀ1
(-SO2-); MALDI-TOF MS: m/z calcd for C72H78Cl6N18O6S3: 1623.4 [M+
Na]+; found: 1623.0.
General procedure for the synthesis of G3-S, G4-S, and G5-S: A mixture
of G2-8N3-S (1.00 equiv), different end-capped dendrons (9.00 equiv),
and CuBr (8.00 equiv) were dissolved in DMF (0.02m-N3) under nitrogen
Synthesis of dendrimer G1-6N3-S-GL: The procedure was similar to the
synthesis of dendrimer G1-4N3-S, but using compound G0-6Cl-S-GL
(360.0 mg, 0.225 mmol), NaN3 (175.5 mg, 2.7 mmol). G1-6N3-S-GL was
obtained as orange solid (298.2 mg, 80.8%). 1H NMR (300 MHz, CDCl3,
298 K): d=2.12 (s, br, 6H, -CH2-), 2.84 (s, br, 6H, -CH2C-), 3.20 (s, br,
6H, -SCH2-), 3.59 (s, br, 12H, -CH2Cl), 3.71 (s, br, 12H, -NCH2-), 5.43 (s,
6H, -NCH2-), 6.81 (d, J=8.1 Hz, 6H, ArH), 7.08 (s, 3H, C=CH), 7.30 (s,
3H, ArH), 7.9–8.0 ppm (m, 18H, ArH); 13C NMR (75 MHz, CDCl3,
298 K): d=22.41, 23.81, 48.66, 50.59, 53.07, 55.22, 111.78, 121.46, 122.80,
125.92, 127.26, 128.94, 126.86, 138.56, 144.28, 146.43, 149.80, 155.94 ppm;
IR (KBr): n˜ =2097 (-N3), 1316, 1131 cmꢀ1 (-SO2-); MALDI-TOF MS:
m/z calcd for C72H78N36O6S3: 1673 [M]+; found: 1674.
in
a Schlenk flask, then N,N,N,N,N-pentamethyldiethylenetriamine
(PMDETA) (8.00 equiv) was added. After the mixture was stirred at 25–
308C for 6 h, the reaction was stopped by addition of water. The precipi-
tate was purified by repeating precipitations of their THF or CHCl3 solu-
tions into ethyl acetate or acetone, and then filtered and washed with lots
of ethyl acetate or acetone, dried in vacuum at 408C to a constant
weight.
G3-S: According to the general procedure using compound G2-8N3-S
ꢁ
(30.2 mg, 0.010 mmol) and G0- -S (56.1 mg, 0.090 mmol). G3-S was ob-
tained as orange powder (66.0 mg, 82.4%). 1H NMR (300 MHz, CDCl3,
298 K): d=1.6–1.9 (-CH2-), 2.0–2.2 (-CH2-), 2.7–2.9 (-CH2C- and -CH2-),
3.1–3.3 (-SCH2-), 3.6–3.8 (-NCH2-), 3.8–4.0 (-NCH2-), 4.3–4.5 (-OCH2-),
4.5–4.7 (-COOCH2-), 6.6–6.8 (ArH), 6.9–7.0 (ArH), 7.2–7.6 (ArH and C=
CH), 7.8–8.1 ppm (ArH); 13C NMR (150 MHz, CDCl3, 298 K): d=22.67,
23.84, 47.29, 49.86, 51.25, 55.27, 61.83, 111.95, 122.96, 126.11, 128.56,
129.10, 129.65, 133.35, 138.46, 144.22, 150.96, 156.17, 166.51 ppm; IR
(KBr): n˜ =1316, 1716 (C=O), 1130 cmꢀ1 (-SO2-); MALDI-TOF MS: m/z
calcd for C416H415N65O60S14: 8036 [M+Na]+; found: 8038; elemental anal-
ysis calcd (%) for C416H415N65O60S14: C 62.35; H 5.22; N 14.86; found: C
62.04; H 5.88; N 14.68.
Synthesis of dendrimer G1-S-GL: The procedure was similar to the syn-
ꢁ
thesis of dendrimer G1-S, but using chromophore G0- -S (102.9 mg,
0.165 mmol) and G0-3N3 (12.2 mg, 0.050 mmol). The crude product was
purified by column chromatography using pure ethyl acetate as eluent to
afford orange solid G1-S-GL (98.2 mg, 92.9%). 1H NMR (400 MHz,
CDCl3, 298 K): d=1.63 (s, br, -CH2-), 2.15 (m, -CH2-), 2.84 (t, J=8.0 Hz,
-CH2C-), 3.20 (t, J=8.0 Hz, -SCH2-), 3.93 (m, -NCH2-), 4.58 (t, J=8.0 Hz,
-COOCH2-), 5.44 (s, -NCH2-), 6.71 (d, J=8.0 Hz, ArH), 7.02 (s, C=CH),
7.40 (m, ArH), 7.52 (m, ArH), 7.8–8.0 ppm (m, ArH); 13C NMR
(100 MHz, CDCl3, 298 K): d=13.73, 19.18, 22.54, 23.94, 30.57, 49.84,
53.21, 55.35, 61.81, 65.56, 112.00, 121.62, 112.00, 121.62, 122.90, 126.06,
127.41, 128.50, 128.84, 129.07, ꢁ19.63, 130.62, 136.21, 138.31, 145.84, 150/
99, 166.46 ppm; IR (KBr): n˜ =1711 (C=O), 1316, 1130 cmꢀ1 (-SO2-);
MALDI-TOF MS: m/z calcd for C114H108N18O18S3: 2135.7 [M+Na]+;
found: 2135.4; elemental analysis calcd (%) for C114H108N18O18S3: C
64.76, H 5.15, N 11.92; found: C 64.22, H 4.99, N 12.21.
G4-S: According to the general procedure using compound G2-8N3-S
ꢁ
(18.1 mg, 0.006 mmol) and G1- -S (92.5 mg, 0.054 mmol). G4-S was ob-
tained as orange powder (78.1 mg, 78.0%). 1H NMR (300 MHz, CDCl3,
298 K): d=1.6–1.9 (-CH2-), 2.0–2.2 (-CH2-), 2.6–2.9 (-CH2C- and -CH2-),
3.0–3.3 (-SCH2-), 3.6–3.8 (-NCH2-), 3.8–4.0 (-NCH2-), 4.3–4.5 (-OCH2-),
4.5–4.7 (-COOCH2-), 6.5–6.8 (ArH), 6.9–7.0 (ArH), 7.2–7.6 (ArH and C=
CH), 7.8–8.1 ppm (ArH); 13C NMR (150 MHz, CDCl3, 298 K) d=22.86,
24.00, 47.44, 50.04, 51.44 55.44, 62.02, 122.14, 122.79, 123.14, 126.29,
128.73, 129.27, 129.82, 133.53, 138.65, 144.40, 146.45, 151.15, 156.34,
166.69 ppm; IR (KBr): n˜ =1716 (C=O), 1316, 1130 cmꢀ1 (-SO2-); elemen-
tal analysis calcd (%) for C864H863N181O124S30: C 62.03, H 5.20, N 15.16;
found: C 61.06, H 5.87, N 14.75.
General procedure for the synthesis of G2-S-GL, G3-S-GL and G4-S-
GL: A mixture of G1-6N3-S-GL (1.00 equiv), different end-capped den-
drons (7.00 equiv), and CuBr (3.00 equiv) were dissolved in DMF
(0.02m-N3) under nitrogen in a Schlenk flask, then N,N,N,N,N-penta-
ACHUTNGRENmNUG ethACHUTNGTRENyNGUN ldiethylenetriamine (PMDETA) (3.00 equiv) was added. After the
G5-S: According to the general procedure using compound G2-8N3-N
mixture was stirred at 25–308C for 6 h, the reaction was terminated by
ꢁ
(6.91 mg, 0.00228 mmol) and G2- -S (80.0 mg, 0.0206 mmol). G5-S was
addition of water. The precipitate was purified by repeating precipita-
Chem. Eur. J. 2013, 00, 0 – 0
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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C. Li, Z. Li et al.
tions of their THF or CHCl3 solutions into ethyl acetate or acetone, and
then filtered and washed with lots of ethyl acetate or acetone, dried in
vacuum at 408C to a constant weight.
Acknowledgements
We are grateful to the National Science Foundation of China (no.
21034006 and 21075134), and the Doctoral Fund of Ministry of Education
of China (20090141110043) for financial support.
G2-S-GL: According to the general procedure using compound G1-6N3-
ꢁ
S-GL (32.8 mg, 0.020 mmol) and G0- -S (87.3 mg, 0.14 mmol). G2-Ph-
GL was obtained as orange powder (86.4 mg, 80.3%). 1H NMR
(300 MHz, CDCl3, 298 K): d=1.62 (s, br, -CH2-), 2.80 (s, br, -CH2C-),
3.16 (s, br, -SCH2-), 3.73 (s, br, -NCH2-), 3.95 (s, br, -NCH2-), 4.34 (s, br,
-NCH2-), 4.58 (s, br, -COOCH2-), 5.40 (s, -NCH2-), 6.72 (s, br, ArH), 6.97
(d, J=8.7 Hz, ArH), 7.05 (s, C=CH), 7.42 (s, br, ArH), 7.56 (s, br, ArH),
7.8–8.1 ppm (m, ArH); 13C NMR (75 MHz, CDCl3, 298 K): d=22.60,
23.71, 29.61, 47.16, 49.77, 51.23, 53.09, 55.18, 61.71, 111.88, 121.53, 122.41,
122.84, 125.99, 127.25, 128.43, 129.00, 129.54, 133.24, 138.42, 144.17,
144.58, 146.21, 149.13, 150.85, 156.09, 166.39 ppm; IR (KBr): n˜ =1710
(C=O), 1316, 1131 cmꢀ1 (-SO2-); MALDI-TOF MS: m/z calcd for
C282H276N54O42S9: 5405 [M+Na]+; found: 5406; elemental analysis calcd
for C282H276N54O42S9: C 62.93, H 5.17, N 14.05; found: C 62.54, H 5.23, N
14.37.
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G3-S-GL: According to the general procedure using compound G1-6N3-
ꢁ
S-GL (16.4 mg, 0.010 mmol) and G1- -S (113.1 mg, 0.066 mmol). G3-Ph-
GL was obtained as orange powder (82.1 mg, 68.9%). 1H NMR
(300 MHz, CDCl3, 298 K): d=1.6–2.4 (-CH2-), 2.76 (s, br, -CH2C-), 3.14
(s, br, -SCH2-), 3.71 (s, br, -NCH2-), 3.93 (s, br, -NCH2-), 4.43 (s, br,
-NCH2-), 4.55 (s, br, -COOCH2-), 5.33 (s, -NCH2-), 6.69 (s, br, ArH), 6.96
(s, br, ArH), 7.2–7.6 (ArH and C=CH), 7.7–8.2 ppm (ArH); 13C NMR
(150 MHz, CDCl3, 298 K): d=22.86, 24.01, 50.06, 55.46, 62.02, 112.15,
123.14, 126.30, 128.73, 129.28, 129.84, 133.54, 138.67, 144.42, 146.38,
151.15, 156.34, 166.69 ppm; IR (KBr): n˜ =1711 (C=O), 1316, 1131 cmꢀ1
(-SO2-); MALDI-TOF MS: m/z calcd for C618H612N126O90S21: 11954 [M+
Na]+; found: 11941; elemental analysis calcd (%) for C618H612N126O90S21:
C 62.28, H 5.18, N 14.81; found: C 62.77, H 5.29, N 14.44.
G4-S-GL: According to the general procedure using compound G1-6N3-
ꢁ
S-GL (5.1 mg, 0.0032 mmol) and G2- -S (80.0 mg, 0.0206 mmol). G4-Ph-
GL was obtained as orange powder (65.7 mg, 84.4%). 1H NMR
(300 MHz, CDCl3, 298 K): d=1.68 (s, br, -CH2-), 2.74 (s, br, -CH2C-),
3.13 (s, br, -SCH2-), 3.70 (s, br, -NCH2-), 3.91 (s, br, -NCH2-), 4.42 (s, br,
-NCH2-), 4.54 (s, br, -COOCH2-), 5.35 (s, -NCH2-), 6.79 (s, br, ArH), 6.94
(s, br, ArH), 7.2–7.6 (ArH and C=CH), 7.7–8.1 ppm (ArH); 13C NMR
(150 MHz, CDCl3, 298 K): d=22.87, 24.02, 29.93, 47.46, 50.08, 55.49,
62.02, 112.20, 123.12, 126.26, 128.71, 129.26, 129.82, 133.50, 138.79, 144.47,
146.44, 151.21, 156.35, 166.65 ppm; IR (KBr): n˜ =1710 (C=O), 1316,
1131 cmꢀ1 (-SO2-); elemental analysis calcd (%) for C1290H1284N270O186S45
C 62.00, H 5.18, N 15.13; found: C 62.93, H 5.53, N 15.44.
:
Preparation of polymer thin-films: The dendrimers were dissolved in
THF (concentration ꢂ3 wt%), and the solutions were filtered through
syringe filters. The dendrimer films were spin coated onto indium-tin-
oxide (ITO)-coated glass substrates, which were cleaned by DMF, ace-
tone, distilled water, and THF sequentially in an ultrasonic bath before
use. Residual solvent was removed by heating the films in a vacuum oven
at 408C.
NLO measurement of poled films: 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 opti-
cal windows and three needle electrodes.[15] The films were kept at 458 to
the incident beam and poled inside the oven, and the SHG intensity was
monitored simultaneously. Poling conditions were as follows: tempera-
ture, different for each polymer (Table 4); 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.
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Received: October 6, 2012
Revised: February 15, 2013
Published online: && &&, 2013
Chem. Eur. J. 2013, 00, 0 – 0
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C. Li, Z. Li et al.
Dendrimers
W. Wu, G. Xu, C. Li,* G. Yu, Y. Liu,
C. Ye, J. Qin, Z. Li* ......... &&&& — &&&&
From Nitro- to Sulfonyl-Based Chro-
mophores: Improvement of the
Comprehensive Performance of
Nonlinear Optical Dendrimers
Branching out: Through the combina-
tion of a divergent and convergent
approach, by using the powerful
“click-chemistry” reaction, two new
series of sulfonyl-chromophore-based
high-generation nonlinear optical
(NLO) dendrimers were conveniently
prepared in satisfactory yields (see
figure). These dendrimers exhibited
large second harmonic generation
coefficient (d33) values, as well as out-
standing optical transparencies and
NLO stabilities, simultaneously.
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These are not the final page numbers!