High-generation second-order nonlinear optical (NLO) dendrimers: Convenient synthesis by click chemistry and the increasing trend of nlo effects

Article abstract of DOI:10.1002/anie.200906946

(Figure Presented) Click it in: Forth and fifth generation dendrimers (see structure), bearing 30 and 62 azobenzene chromophore moiet-ies, respectively, are conveniently pre-pared in satisfactory yields through a combination of divergent and convergent approaches by using the powerful Sharpless click reaction.

Full text of DOI:10.1002/anie.200906946

Angewandte
Chemie
DOI: 10.1002/anie.200906946
Dendrimers
High-Generation Second-Order Nonlinear Optical (NLO)
Dendrimers: Convenient Synthesis by Click Chemistry and the
Increasing Trend of NLO Effects**
Zhong’an Li, Wenbo Wu, Qianqian Li, Gui Yu, Li Xiao, Yunqi Liu, Cheng Ye, Jingui Qin, and
Zhen Li*
Dendrimers are defect-free and perfect monodisperse macro-
molecules with a regular and highly three-dimensional
branched structure, which can bring out many special proper-
ties: nanometer size, globular shape, multivalent character,
and modularity of the assembly. These characteristics make
them competitive candidates for applications in a variety of
fields including catalysis, biology, and materials science.[1–3]
Generally, highly branched dendrimers could be constructed
through a divergent (a growing pattern from a multivalent
core) or convergent (a dendron is grafted on to the core)
synthetic strategy.[1] However, the tedious multistep synthetic
protocols often make the preparation of dendrimers relatively
costly and involve some difficulties, such as the incomplete
reaction of the end groups in the divergent approach (leading
to the structural defects) and steric hindrance between the
reactive segments and core molecule (hampering the forma-
tion of high generations) in the convergent strategy.[2b]
Versatile methodologies to address these issues have now
rendered the synthesis of dendrimers more precise and
economical.[2c] As typical examples, through the combination
of the divergent and convergent approaches (a “double-
stage” method),[4] proposed by Frꢀchet and co-workers,[4a] the
synthetic efficiency could be raised rapidly; also, by the
utilization of the powerful CuI-catalyzed 1,3-dipolar cyclo-
addition reactions between azides and alkynes (the Sharpless
“click” reaction),[5] many divergently built-up dendrimers
were yielded after the pioneering work of Frꢀchet and co-
workers.[6–8] However, there are currently very few reports of
the use of “click chemistry” for both parts of a combined
divergent and convergent approach.
performance and cost improvements related to telecommu-
nications, computing, embedded network sensing, terahertz
wave generation and detection, and many other applica-
tions.[9,10] One major obstacle that hinders the rapid develop-
ment of this field is efficient translation of the large b values
of the organic chromophores into high macroscopic NLO
activities of polymers, because of the strong dipole–dipole
interactions among the chromophore moieties with donor–p-
acceptor structure in the polymeric system. This interaction
makes the poling-induced noncentrosymmetric alignment of
chromophore moieties (necessary for the materials to exhibit
the NLO effect) a daunting task during the poling process
under an electric field.[11] Fortunately, according to the
experimental results and theoretical analysis of Jen, Dalton,
and co-workers, the dendritic structure, present in dendrim-
ers, hyperbranched polymers, and dendronized polymers (in
which some isolation groups were bonded to the chromo-
phore moieties to decrease the interactions and increase the
poling efficiency by applying the site isolation principle), was
considered a very promising molecular topology for the next
generation of highly efficient NLO materials and expected to
meet the basic requirements of practical applications: large
macroscopic optical nonlinearity, high physical and chemical
stability, and good optical transparency.[12,13] On the basis of
their excellent work, and according to the concept of “suitable
isolation group” summarized from the experimental results of
our systematically research in the dendronized polymers,[14,15]
we recently designed a new convergent approach to NLO
dendrimers G1–G3 (Scheme S1 in the Supporting Informa-
tion).[16] These dendrimers not only confirmed our thoughts
on the formed triazole rings as the suitable isolation groups to
enhance the macroscopic NLO effect, but, more excitingly,
also demonstrated that accompanying the increased loading
density of the chromophore moieties was an increase in the
tested NLO effects. This result was really abnormal but very
important to solve the obstacle in the NLO field mentioned
above, and indicated that the frequently observed asymptotic
dependence of electrooptic activity on the chromophore
number density may be overcome through rational design.[17]
If the loading density of chromophore moieties in
dendrimers is further increased, much better NLO effects
should be achieved. Thus, we attempted to prepare high-
generation dendrimers as derivatives of G1–G3. However, in
this instance, the higher-generation dendrimers could not be
obtained easily in satisfactory yields through the convergent
method as G1–G3, because of steric effects and the difficulty
of chromatographic separation. To improve the synthetic
The development of organic second-order nonlinear
optical (NLO) materials is motivated by the promising of
[*] Z. Li,[+] W. Wu,[+] Q. Li, L. Xiao, Prof. J. Qin, Prof. Z. Li
Department of Chemistry, Wuhan University
Wuhan 430072 (China)
Fax: (+86)27-6875-6757
E-mail: lizhen@whu.edu.cn
Prof. G. Yu, Prof. Y. Liu, Prof. C. Ye
Institute of Chemistry, The Chinese Academy of Sciences
Beijing 100080 (China)
[+] These authors contributed equally to this manuscript.
[**] We are grateful to the National Science Foundation of China (no.
20674059, J0730426), the program of NCET, and Wuhan University
(5081002) for financial support.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.200906946.
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Communications
efficiency, a “double-stage” method was designed (Schemes 1
and 2), in which the core (G2–8N3, Scheme 1) was prepared
through a divergent approach through click chemistry, while
moieties, respectively, were conveniently prepared in good
yields. The success of the synthetic route should be ascribed to
the nearly perfect Sharpless “click chemistry”, as well as a
well-designed “double-stage” approach. The core (G2–8N3)
was synthesized through a divergent approach from AB2-type
ꢀ
ꢀ
the end-capped dendrons (G1- and G2- , Scheme S1) were
Scheme 2. Synthesis of dendrimers G4 and G5.
monomer G0–2Cl, which was crafted to contain two chlor-
oethyl groups and one terminal alkyne group. After the click
chemistry reaction between G0–2Cl and compound 3, the
first-generation dendrimer G1–4Cl was obtained easily in
75.7% yield. Then, G1–4N3 was produced in high yield
(99.0%) through the substitution of the chloride groups in
G1–4Cl. A click reaction between the azides of G1–4N3 and
the terminal alkyne in chromophore G0–2Cl gave the second-
generation dendrimer G2–8Cl, which could undergo a further
substitution reaction of the chloride groups to produce the
core G2–8N3 in high yield (96.3%). Therefore, it seemed that
by repeating click reaction and substitution reaction, high-
generation dendrimer G5 would be obtained. However,
unexpectedly, G3–16Cl could not be synthesized successfully,
although we tried several times, by using either CuSO4/
sodium ascorbate or CuBr/pentamethyldiethyltriamine
(PMDETA) as catalyst. Moreover, even though the prepara-
tion of G3–16Cl was successful, to synthesize the target
dendrimer (G5), there were still five steps required (Route 1
in Table 1), which was very tedious and some other problems
might be encountered.
Scheme 1. Synthesis of the core (G2–8N3) of the dendrimers.
obtained through a convergent approach also by click
chemistry. By the combination of divergent and convergent
approaches, as well as the usage of click chemistry, the whole
synthetic route was convenient and highly efficient. Excit-
ingly, accompanying the change in loading concentration of
the chromophore moieties from 0.520 in G3 to 0.537 in G4 to
0.544 in G5, the measured NLO coefficient values increased
from 122.7 (G3) to 177.0 (G4) to 193.1 pmVꢁ1 (G5), which
further confirmed that the frequently observed asymptotic
dependence of electrooptic activity on the chromophore
number density may be overcome through rational design. To
the best of our knowledge, the tested NLO effect
(193.1 pmVꢁ1) is the highest value reported so far for
simple azo chromophore moieties. Thus, the successful
examples might open up a new avenue to achieve further
good NLO polymers with even higher NLO effects by
utilizing other NLO chromophores with larger b values, and
the “double-stage” method coupled with “click chemistry”
could aid other scientists in the convenient preparation of
further high-generation dendrimers with perfect structures.
As shown in Schemes 1 and 2, high-generation dendrimers
G4 and G5, bearing 30 and 62 NLO azobenzene chromophore
On the other hand, we have prepared a series of NLO
dendrimers (G1–G3) through
a convergent approach
(Scheme S1 and Chart S1 in the Supporting Information). In
Table 1: Synthesis of G5. The number of the chromophore moieties in
the dendrimers is given in parentheses.
ꢀ
G0-
ꢀ
G1-
ꢀ
G2-
G0–2N3
G1–4N3
G2–8N3
G1(2)
G2(7)
G3(14)
G2(6)
G3(14)
G4(30)
G3(14)
G4(30)
G5(62)
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that synthetic route (convergent approach), we took advant-
age of the combination of click chemistry and azo coupling
reaction to make all the involved reactions conducted under
mild conditions, and there was no need to protect/deprotect
some functional groups or include the conversion of one
reactive group to another. In this route (Route 2 in Table 1),
G5 might also be obtained from G3 with only four steps
needed, which is relatively simple in comparison with
Route 1. However, as mentioned above, the higher-genera-
tion dendrimers could not be obtained easily in satisfactory
yields through the convergent method as for G1–G3, because
of steric effects and the difficulty of chromatographic
separation. The difficulty did not originate from the “click”
reaction, but rather the introduction of terminal alkyne group
by the azo coupling reaction. For example, in the synthesis of
dendrimers are thermally stable. Also, the growth of the NLO
dendrimers caused an increase in their glass transition
temperature (Tg). The Tg values of G4 and G5—117 and
1258C, respectively,—were higher than that of G3 (908C).
G4 and G5 were soluble in polar organic solvents, such as
chloroform, THF, DMF, and DMSO. Similar to G3, G4 and
G5 exhibited a good site-isolation effect in comparison with
free chromophore molecules and low-generation dendrimers,
revealing the fact that the exterior benzene moieties and the
interior triazole rings surrounding the azo chromophore
moieties play a key role in shielding them from the
solvatochromic effect (Figure S17 and Table S2 in the
Supporting Information). The maximum absorption wave-
lengths (lmax) of G4 and G5 were nearly the same as that of
G3 in solution; however, in solid films, G4 and G5 exhibited
blue-shifted maximum absorption (470 nm) relative to that of
G3 (480 nm), demonstrating the more perfect 3D structure of
G4 and G5. Thus, the enhanced effective site isolation
achieved in G4 and G5 directly decreases the strong
intermolecular dipole–dipole interactions among chromo-
phore moieties and greatly benefits the ordered noncentro-
symmetric alignment of the chromophore moieties during the
poling process. In addition, the blue-shifted absorption
maximum of dendrimers would result in wide optical trans-
parency windows and contribute to practical applications in
photonics fields.
ꢀ
G2- , the yield was not higher than 62.8%, even though the
azo coupling reaction was conducted for 80 h, whereas the
ꢀ
ꢀ
yields of G0- and G1- were 90.0 and 76.5%, respectively.
ꢀ
ꢀ
Thus, the yields of G3- and G4- in the next steps would be
much lower. Also, with an increase in generation of the
dendrimer, purification becomes much more difficult. There-
fore, Route 2 would be more expensive and difficult to
handle.
However, G5 could be obtained through Route 3
(Table 1), which is a combination of Routes 1 and 2, as a
ꢀ
product of the “click” reaction between G2–8N3 and G2- .
Thus, by using this “double-stage” approach, the number of
required synthetic steps could be decreased. The preparation
of G4 and G5 proceeded to completion in less than 6 h as
monitored by FTIR spectroscopy (disappearance of the peak
centered at 2096 cmꢁ1 associated with the azido groups). The
purification of G4 and G5 was very simple: repeated
precipitation of THF solutions into acetone, since G2–8N3,
G4 and G5 exhibit good film-forming ability, and their
poled films were prepared for the evaluation of their NLO
activities. A convenient technique to study the second-order
NLO activity was to investigate the second-harmonic gen-
eration (SHG) processes characterized by d33, an SHG
coefficient. The test procedure was similar to that we reported
previously,[18] and from the experimental data, their d33 values
were calculated at the 1064 nm fundamental wavelength
(Table 2).
ꢀ
ꢀ
G1- , and G2- are soluble in acetone. Satisfactory yields
were obtained (75.8% and 73.7%, respectively), thanks to the
powerful “click” reaction.
In our previous work, the d33 values increased from G1 to
G3 (Table 2), accompanying the increasing loading density of
the chromophore moieties. Here, upon the growth of NLO
dendrimers to the four (G4) and fifth generation (G5), the
loading density of chromophore moieties was increased
further still, and their NLO effects were enhanced accord-
ingly: accompanying the increase in loading concentration of
the chromophore moieties from 0.520 in G3 to 0.537 in G4, to
0.544 in G5, the measured NLO coefficient values increased
from 122.7 (G3) to 177.0 (G4), to 193.1 pmVꢁ1 (G5). These
values are very high relative to those of other reported NLO
polymers containing nitroazobenzene chromophores. These
encouraging results should be ascribed to the more perfect 3D
structure of G4 and G5 as discussed above. Furthermore, the
exterior benzene moieties and the interior triazole rings
played an important role in decreasing the interactions and
enhancing the poling efficiency, according to the concept of
“suitable isolation group”.[14,15] As there might be some
resonant enhancement due to the absorption of the chromo-
phore moieties at 532 nm, the NLO properties of dendrimers
should be smaller, as shown in Table 2 (d33(1)). Because of
their wide optical transparency window (the maximum
absorption wavelengths of their films were only around
470 nm), as well as their large d33 values, the d33(1) values of
The reaction products were characterized by spectroscop-
ic analysis, and all gave satisfactory data (some data listed in
Table S1) corresponding to their expected molecular struc-
tures (see Figure S1–S16 in the Supporting Information). The
degradation temperatures (Td) for G4 and G5 were around
262 and 2758C (Table 2), respectively, revealing that the
Table 2: Physical and NLO data of the dendrimers.
Td [8C][a] Tg [8C][b] d33 [pmVꢁ1 [c]
]
d33(1) [pmVꢁ1 [d]
]
F[e] N[f]
G1
G2
G3
G4
G5
300
295
278
262
275
56
76
90
117
125
100.0
108.1
122.7
177.0
193.1
13.4
14.2
18.2
31.3
34.1
0.20 0.402
0.18 0.488
0.25 0.520
0.27 0.537
0.31 0.544
[a] The 5% weight loss temperature of polymers detected by TGA
analyses under nitrogen at a heating rate of 108Cminꢁ1. [b] Glass
transition temperature of polymers detected by the DSC analyses under
argon at a heating rate of 108Cminꢁ1. [c] SHG coefficient. [d] The
nonresonant d33 values calculated by using the approximate two-level
model. [e] Order parameter F=1 A1/A0, where A1 and A0 are the
absorbance of the polymer film after and before corona poling,
respectively. [f] Loading density of the effective chromophore moieties.
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2765

Communications
G4 and G5 were still very high (31.3 and 34.1 pmVꢁ1), thus
linkable groups were introduced. Thus, it could be attribut-
able to the 3D macromolecule architecture, which might
suppress the relaxation of the ordered dipole alignment to
some extent. Thus, coupled with their large NLO effects and
improved optical transparency, G4 and G5 are promising
candidates for practical NLO applications.
making them attractive for potential optics applications.
It should be pointed out that although the loading density
of the chromophore moieties increased by only 0.017 from G3
to G4, the d33 value was enhanced by 55 pmVꢁ1, but only by
about 14 pmVꢁ1 from G2 to G3, despite the increase in
loading density of 0.032. From G4 to G5, the loading density
increased by only 0.007, but the d33 value was still enhanced by
16 pmVꢁ1. This result might indicate that after the loading
density of the chromophore moieties increased beyond a
critical point, the NLO effect would be enhanced dramatically
with further increases in loading density. While further
research is still needed, our results demonstrate that accom-
panying the increasing of the loading density of the chromo-
phore moieties, the tested NLO effects increase, indicating
that the frequently observed asymptotic dependence of
electrooptical activity on chromophore number density may
be overcome through rational design, in accordance with the
results and prediction of Sullivan, Robinson, Dalton, and co-
workers.[17] Thus, our results could provide some useful
information for the rational design of NLO materials with
better performance.
To further explore the alignment of the chromophore
moieties in these dendrimers, we measured their order
parameter (F, see Table 2 and Figure S18). The F values of
G4 and G5 were calculated (see footnote [e] in Table 2 for
equation) to be 0.27 and 0.31, respectively, confirming that the
alignment of the chromophore moieties in G4 and G5 upon
poling becomes easier than that in G3 (F = 0.25). Another
interesting phenomenon was that accompanying the enhance-
ment of d33 values, the best poling temperatures of G4 and G5
also increased relative to that of G3, indicating that better
temporal stabilities of the SHG signals could be realized.
Depoling experiments of G3–G5 were conducted,
whereby the real-time decays of the SHG signals were
monitored as the poled films were heated from 35 to 1408C
in air at a rate of 48Cminꢁ1. Figure 1 shows the decay of the
SHG coefficient of G3–G5 as a function of temperature. G3
decays at a temperature of only 708C, whereas the decay
temperatures of G4 and G5 increased to 100 and 1078C,
respectively. This result was unexpected, since no cross-
Received: December 9, 2009
Published online: March 9, 2010
Keywords: click chemistry · dendrimers · nonlinear optics
.
[1] a) J. M. J. Frꢀchet, Science 1994, 263, 1710 – 1715; b) S. M.
Grayson, J. M. J. Frꢀchet, Chem. Rev. 2001, 101, 3819 – 3867.
[2] a) F. Zeng, S. C. Zimmerman, Chem. Rev. 1997, 97, 1681 – 1712;
b) A. W. Bosman, H. M. Janssen, E. W. Meijer, Chem. Rev. 1999,
99, 1665 – 1688; c) A. J. Berresheim, M. Mꢁller, K. Mꢁllen,
Chem. Rev. 1999, 99, 1747 – 1787; d) S. C. Lo, P. L. Burn, Chem.
Rev. 2007, 107, 1097 – 1116; e) L. Crespo, G. Sanclimens, M.
Pons, E. Giralt, M. Royo, F. Albericio, Chem. Rev. 2005, 105,
1663 – 1681.
[3] a) B. Helms, E. W. Meijer, Science 2006, 313, 929 – 930; b) C.
Pitois, D. Wiesmann, M. Lindgren, A. Hult, Adv. Mater. 2001, 13,
1483 – 1487; c) M. R. Harpham, ꢂ. Sꢁzer, C.-Q. Ma, P. Bꢃuerle,
T. Goodson III, J. Am. Chem. Soc. 2009, 131, 973 – 979.
[4] a) K. L. Wooley, C. J. Hawker, J. M. J. Frꢀchet, J. Am. Chem.
Soc. 1991, 113, 4252 – 4261; b) T. M. Miller, T. X. Neenan, R.
Zayas, H. E. Bair, J. Am. Chem. Soc. 1992, 114, 1018 – 1025; c) J.-
L. Wang, J. Yan, Z. M. Tang, Q. Xiao, Y. Ma, J. Pei, J. Am. Chem.
Soc. 2008, 130, 9952 – 9962; d) Z. F. Xu, M. Kahr, K. L. Walker,
C. L. Wilkins, J. S. Moore, J. Am. Chem. Soc. 1994, 116, 4537 –
4550; e) H.-T. Chang, C.-T. Chen, T. Kondo, G. Siuzdak, K. B.
Sharpless, Angew. Chem. 1996, 108, 202 – 206; Angew. Chem. Int.
Ed. Engl. 1996, 35, 182 – 186.
[5] a) H. C. Kolb, M. G. Finn, K. B. Sharpless, Angew. Chem. 2001,
113, 2056 – 2075; Angew. Chem. Int. Ed. 2001, 40, 2004 – 2021;
b) V. V. Rostovtsev, L. G. Green, V. V. Fokin, K. B. Sharpless,
Angew. Chem. 2002, 114, 2708 – 2711; Angew. Chem. Int. Ed.
2002, 41, 2596 – 2599; c) M. Meldal, C. W. Tornøe, Chem. Rev.
2008, 108, 2952 – 3015.
[6] a) P. Wu, A. K. Feldman, A. K. Nugent, C. J. Hawker, A. Scheel,
B. Voit, J. Pyun, J. M. J. Frꢀchet, K. B. Sharpless, V. V. Fokin,
Angew. Chem. 2004, 116, 4018 – 4022; Angew. Chem. Int. Ed.
2004, 43, 3928 – 3932; b) C. Ornelas, J. R. Aranzaes, L. Salmon,
D. Astruc, Chem. Eur. J. 2008, 14, 50 – 64.
[7] a) X. Shen, H. Liu, Y. Li, S. Liu, Macromolecules 2008, 41, 2421 –
2425; b) M. R. Whittaker, C. N. Urbani, M. J. Monteiro, J. Am.
Chem. Soc. 2006, 128, 11360 – 11361; c) C. N. Urbani, C. A. Bell,
D. Lonsdale, M. R. Whittaker, M. J. Monteiro, Macromolecules
2008, 41, 76 – 86.
[8] a) J. A. Johnson, M. G. Finn, J. T. Koberstein, Macromol. Rapid
Commun. 2008, 29, 1052 – 1072; b) G. Franc, A. Kakkar, Chem.
Commun. 2008, 5267 – 5276.
[9] a) D. M. Burland, R. D. Miller, C. A. Walsh, Chem. Rev. 1994,
94, 31 – 75; b) Y. Bai, N. Song, J. P. Gao, X. Sun, X. Wang, G. Yu,
Z. Y. Wang, J. Am. Chem. Soc. 2005, 127, 2060 – 2061; c) T. J.
Marks, M. A. Ratner, Angew. Chem. 1995, 107, 167 – 187;
Angew. Chem. Int. Ed. Engl. 1995, 34, 155 – 173; d) D. Yu, A.
Gharavi, L. P. Yu, J. Am. Chem. Soc. 1995, 117, 11680 – 11686.
[10] a) S. R. Marder, B. Kippelen, A. K. Y. Jen, N. Peyghambarian,
Nature 1997, 388, 845 – 851; b) M. Lee, H. E. Katz, C. Erben,
D. M. Gill, P. Gopalan, J. D. Heber, D. J. McGee, Science 2002,
298, 1401 – 1403; c) Y. Shi, C. Zhang, H. Zhang, J. H. Bechtel,
L. R. Dalton, B. H. Robinson, W. H. Steier, L. R. Dalton,
Science 2000, 288, 119 – 122; d) C. V. Mclaughlin, M. Hayden,
Figure 1. Decay curves for the SHG coefficient d33 of G3–G5 as a
function of temperature.
2766 www.angewandte.org
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Angewandte
Chemie
B. Polishak, S. Huang, J. D. Luo, T.-D. Kim, A. K. Y. Jen, Appl.
Phys. Lett. 2008, 92, 151107.
[14] a) Z. Li, Z. Li, C. Di, Z. Zhu, Q. Li, Q. Zeng, K. Zhang, Y. Liu, C.
Ye, J. Qin, Macromolecules 2006, 39, 6951 – 6961; b) Q. Zeng, Z.
Li, Z. Li, C. Ye, J. Qin, B. Z. Tang, Macromolecules 2007, 40,
5634 – 5637; c) Q. Li, Z. Li, F. Zeng, W. Gong, Z. Li, Z. Zhu, Q.
Zeng, S. Yu, C. Ye, J. Qin, J. Phys. Chem. B 2007, 111, 508 – 514.
[15] a) Z. Li, Q. Zeng, Z. Li, S. Dong, Z. Zhu, Q. Li, C. Ye, C. Di, Y.
Liu, J. Qin, Macromolecules 2006, 39, 8544 – 8546; b) Q. Li, Z. Li,
C. Ye, J. Qin, J. Phys. Chem. B 2008, 112, 4928 – 4933.
[16] Z. Li, G. Yu, W. Wu, Y. Liu, C. Ye, J. Qin, Z. Li, Macromolecules
2009, 42, 3864 – 3868.
[17] P. A. Sullivan, H. Rommel, Y. Liao, B. C. Olbricht, A. J. P.
Akelaitis, K. A. Firestone, J-W. Kang, J. Luo, J. A. Davies, D. H.
Choi, B. E. Eichinger, P. J. Reid, A. Chen, A. K. Y. Jen, B. H.
Robinson, L. R. Dalton, J. Am. Chem. Soc. 2007, 129, 7523 –
7530.
[11] a) B. H. Robinson, L. R. Dalton, J. Phys. Chem. A 2000, 104,
4785 – 4795; b) B. H. Robinson, L. R. Dalton, H. W. Harper, A.
Ren, F. Wang, C. Zhang, G. Todorova, M. Lee, R. Aniszfeld, S.
Garner, A. Chen, W. H. Steier, S. Houbrecht, A. Persoons, I.
Ledoux, J. Zyss, A. K.-Y. Jen, Chem. Phys. 1999, 245, 35 – 50.
[12] a) M. J. Cho, D. H. Choia, P. A. Sullivan, A. J.-P. Akelaitis, L. R.
Dalton, Prog. Polym. Sci. 2008, 33, 1013 – 1058; b) Y. V. Per-
everzev, K. N. Gunnerson, O. V. Prezhdo, P. A. Sullivan, Y. Liao,
B. C. Olbricht, A. J. P. Akelaitis, A. K.-Y. Jen, L. R. Dalton, J.
Phys. Chem. C 2008, 112, 4355 – 4363.
[13] a) H. Ma, S. Liu, J. Luo, S. Suresh, L. Liu, S. H. Kang, M. Haller,
T. Sassa, L. R. Dalton, A. K. Y. Jen, Adv. Funct. Mater. 2002, 12,
565 – 574; b) W. Shi, J. Luo, S. Huang, X.-H. Zhou, T.-D. Kim, Y.-
J. Cheng, B. M. Polishak, T. R. Younkin, B. A. Block, A. K.-Y.
Jen, Chem. Mater. 2008, 20, 6372 – 6377.
[18] a) Z. Li, J. Qin, S. Li, C. Ye, J. Luo, Y. Cao, Macromolecules 2002,
35, 9232 – 9235; b) Z. Li, C. Huang, J. Hua, J. Qin, Z. Yang, C. Ye,
Macromolecules 2004, 37, 371 – 376.
Angew. Chem. Int. Ed. 2010, 49, 2763 –2767
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
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