Hyperbranched polytriazoles with high molecular compressibility: Aggregation-induced emission and superamplified explosive detection

Article abstract of DOI:10.1039/c0jm04100a

Hyperbranched polytriazoles with spring-like architectures exhibit the feature of aggregation-induced emission (AIE) due to the high compressibility of polymer spheres from solution to aggregate. Thanks to their AIE effect, the polymer nanoaggregates can

Full text of DOI:10.1039/c0jm04100a

www.rsc.org/materials
Volume 21 | Number 12 | 28 March 2011 | Pages 3973–4704
ISSN 0959-9428
COMMUNICATION
Anjun Qin and Ben Zhong Tang et al.
Hyperbranched polytriazoles with high molecular compressibility:
aggregation-induced emission and superamplified explosive detection

Dynamic Article Links <
C
Journal of
Materials Chemistry
Cite this: J. Mater. Chem., 2011, 21, 4056
www.rsc.org/materials
COMMUNICATION
Hyperbranched polytriazoles with high molecular compressibility:
aggregation-induced emission and superamplified explosive detection†
a
a
b
c
a
Jian Wang, Ju Mei, Wangzhang Yuan, Ping Lu, Anjun Qin, Jingzhi Sun,a Yuguang Mac
*
ab
*
and Ben Zhong Tang
Received 26th November 2010, Accepted 18th January 2011
DOI: 10.1039/c0jm04100a
expensive equipment and complicated processes, which are not well
suited to the manufacture of large-area, flat-panel devices. Whereas
high molecular weight polymers can surmount these disadvantages
because they can form films readily by simple processing techniques
such as spin-coating, static casting and ink printing etc.
Hyperbranched polytriazoles with spring-like architectures exhibit
the feature of aggregation-induced emission (AIE) due to the high
compressibility of polymer spheres from solution to aggregate.
Thanks to their AIE effect, the polymer nanoaggregates can detect
explosives with superamplification effect.
The AIE features have been developed in polymers with linear
structures by incorporating the easy-to-prepare and ready-to-func-
tionalize TPE moieties in our group,7 but it remains a challenge in the
hyperbranched polymer system. Due to their remarkable features,
such as one-pot synthesis, high solubility, low viscosity, three-
dimensional (3D) structure and multiple end groups etc, hyper-
branched polymers have drawn growing attention.8 We have tried to
prepare the hyperbranched polymers with AIE features but polymers
obtained mostly feature aggregation-enhance emission (AEE) char-
acteristics, that is, the polymers are emissive in solution.9
Development of efficient solid-state luminescent materials is of great
importance for practical application in diverse areas, such as organic
light-emitting diodes, organic solid-state lasers, and organic fluores-
cent sensors etc.1 The thorny problem encountered is that the emis-
sion of traditional fluorophores is strong in solution but weakened or
nonemissive in condensed phases, such as thin films or aggregates,
that is, these fluorophores suffer from the aggregation-caused
quenching (ACQ).2 Various chemical, physical, and engineering
approaches have been taken to prevent fluorophore aggregation and
to alleviate the notorious ACQ effect, but met with limited success.3
Exactly opposite to ACQ effect, we recently discovered a unique
phenomenon of aggregation-induced emission (AIE): a series of
propeller-shaped molecules such as tetraphenylethene (TPE) and
hexaphenylsilole (HPS) as well as their derivatives are nonemissive
when molecularly dissolved, but induced to emit efficiently by
aggregate formation.4 Restriction of intramolecular rotation (RIR) of
their multiple phenyl rotors in the aggregates has been proven
theoretically and experimentally as the main cause for AIE effect.5,6
Attracted by the exotic prospects, our and other groups have been
actively involved in the exploration of new AIE systems.5,6 A large
number of AIE active low molecular weight luminogens have been
developed for diverse applications such as in fluorescent sensors and
bioprobes, stimuli-responsive nanomaterials, and active layers in
efficient organic light-emitting diodes.3 For practical applications,
these luminogens have to be fabricated into solid films using
We first polycyclotrimerized the AIE-active 1,1-diethynylsilole
moieties to produce hyperbranched poly(1,1-silole) in 2003.10
Surprisingly, the obtained polymer is AIE-inactive. The rigid and
crowded architectures of the polymer have already restricted the
intramolecular rotation of the phenyl rotors of silole even in solution,
making the polymer emissive. The size and volume of polymer is,
however, scarcely changed in aggregate state due to its rigid structure,
and the fluorescence intensity is almost identical to that in solution
aMoE Key Laboratory of Macromolecular Synthesis and
Functionalization, Department of Polymer Science and Engineering,
Zhejiang University, Hangzhou, 310027, China. E-mail: qinaj@zju.edu.
cn; tangbenz@ust.hk; Fax: (+852) 2358–1594
bDepartment of Chemistry, The Hong Kong University of Science &
Technology, Clear Water Bay, Kowloon, Hong Kong, China
cState Key Laboratory of Supramolecular Structure and Materials, Jilin
University, Changchun, 130012, China
Fig. 1 Illustration of the size/volume changes of hyperbranched poly-
mers in solution and aggregate states. The spheres are symbolized as
hyperbranched polymers.
† Electronic supplementary information (ESI) available: Experimental
details and characterization data and spectra for the monomers, model
compound and polymers. See DOI: 10.1039/c0jm04100a
4056 | J. Mater. Chem., 2011, 21, 4056–4059
This journal is ª The Royal Society of Chemistry 2011

(Fig. 1a). Altering the ethynyl groups from 1,1- to 2,5-positions in
silole moieties, the yielded hyperbranched poly(2,5-silole)s are
AEE-active.9a Though the obtained polymers are relatively ‘‘softer’’
and possess larger free volume and lower steric hindrance than the
poly(1,1-silole), the polymers are still emissive in solution because the
rotation of the phenyl rotors of siloles is still partially restricted.
Adding nonsolvents into their molecularly dissolved solutions
intensified the emission due to the aggregate formation, demon-
strating an AEE phenomenon. The aAIE, which is defined as the ratio
of the quantum yields or emission intensities of an AIE luminogen in
aggregate and solution states,11 is calculated to be only 3–5.
Introducing a flexible node such as silicon atom into the hyper-
branched poly(silylenephenylene)s has enabled the polymers with
much free volume and to shrink slightly in the aggregate state, but the
obtained polymers still feature AEE characteristics with aAIE of 3.3
(Fig. 1b).9b,9c If such hyperbranched polymers are employed as fluo-
rescent chemosensors in solution state, the background fluorescence
will decrease the signal to noise ratio, which will lower the sensitivity
of the detection. It thus will be nice if the hyperbranched polymer is
nonemissive in solution but emits intensely in aggregate state, that is,
the polymer is AIE-active.
characterization of their structures using ‘‘wet’’ spectroscopic tech-
niques. To facilitate the structure characterization, model compound
1
11 was also synthesized (Scheme S3, ESI†). By comparing the H
NMR spectra of hb-P1a and its monomers (1a and 2) as well as 11
in DMSO-d6 (Fig. S1, ESI†), we found that all the peaks of the
polymer are unambiguously assigned corresponding to its expected
molecular structure. Satisfactory analysis data were also obtained for
hb-P1b (Fig. S2, ESI†). As can be seen from the thermogravimeteric
analysis curves shown in Fig. S3 in the ESI†, hb-P1a and hb-P1b
are thermally stable with 5% of their weights loss at temperatures of
378 and 366 ꢀC, respectively. The detailed synthetic procedures
and characterization data for monomers and polymers are given in
the ESI†.
The TPE moiety is AIE active. Will such feature be preserved in
the TPE-containing hyperbranched polymers with flexible spacers?
We thus investigated the photoluminescence (PL) behaviours of
hb-P1a and hb-P1b in solution and aggregate states. Excitingly, the
PL spectra of polymers are almost flat lines parallel to the abscissa in
THF solution, manifesting that they are virtually nonluminescent
when molecularly dissolved in their good solvent. The emission
peaked at 490 nm is, however, continuously intensified with gradual
addition of water (Fig. 2a, and Fig. S4 in the ESI†). Such PL
behaviours are the typical AIE processes, indicative of hb-P1a and
hb-P1b are AIE-active.
On the basis of aforementioned efforts, we envisage that if spring-
like flexible spacers are introduced into hyperbranched architectures,
the obtained polymers will have considerably extended conformation
in solution but be tightly compressed in aggregate state, which will be
promising for possession of the AIE feature according to the RIR
mechanism (Fig. 1c).
The trajectories in the quantum yields (FF) of hb-P1a and hb-P1b
in the aqueous mixtures further confirm their AIE characteristics
(Fig. 2b). The FF values of hb-P1a and hb-P1b are both negligible
(0.11 and 0.14%, respectively) in pure solvents and remain almost
unchanged until ca. 40% of water is added. The highest FF values of
hb-P1a and hb-P1b are recorded at water fractions (fw) of 90%, which
reach 38.31 and 32.25, respectively. The aAIE of hb-P1a and hb-P1b
are thus calculated to be 348.3 and 230.4, which are two orders higher
than our aforementioned polymers and even better than the famous
AIE luminogens of TPE and HPS (220).5f The encouraged results of
hyperbranched polytriazoles prompted us to further investigate their
emission in the solid states. The FF values of the spin-coated films of
hb-P1a and hb-P1b are both measured to be 100% by integrating
sphere. Of the reported hyperbranched polymers, the highest FF
values are for hb-P1a and hb-P1b, indicating their bright prospects for
application in polymeric light-emitting diodes.13
With this idea in mind, we designed triazides 1a and 1b with
varying space lengths for the purpose of investigating their effects on
the AIE feature when they are integrated into hyperbranched struc-
tures by the well-established copper(I)-catalyzed click polymerizations
with diyne (Scheme 1).12 Due to its simple preparation procedure,
easy modification, and high aAIE value (61),11 TPE derivative of diyne
2 was designed as the comonomer for the preparation of hyper-
branched polytriazoles.3 The triazides 1a and 1b and diyne 2 were
synthesized according to our previous published procedures (Schemes
S1 and S2, ESI†). Cu(ꢀPPh3)3Br-mediated click polymerizations of 1
and 2 in DMF at 60 C for 5–7 h, readily furnish 1,4-regioregular
hyperbranched polytriazoles hb-P1a and hb-P1b with satisfactory
molecular weights (Mw up to 12400) in high yields (up to 88.3%) (see
Table S1, ESI†).
hb-P1a and hb-P1b are soluble in common organic solvents such
as THF, dichloromethane, chloroform etc, which enable the
Fig. 2 PL spectra of (a) hb-P1a in THF/water mixtures with different
fractions of water. lex ¼ 333 nm. Polymer concentration: 10 mM. (b)
Variation in quantum yield (FF) of hb-P1a and hb-P1b with water frac-
tion (fw) in THF/water mixture. The FF values were estimated using
quinine sulfate in 0.1 N H2SO4 (FF ¼ 54.6%) as standard. Inset shows the
fluorescent images of hb-P1a solution in THF and THF/water mixture
(fw ¼ 90%).
Scheme 1 Preparation of hyperbranched polytriazoles.
This journal is ª The Royal Society of Chemistry 2011
J. Mater. Chem., 2011, 21, 4056–4059 | 4057

The unprecedented AIE feature of hb-P1a and hb-P1b could be
attributed to their innovative spring-like architectures with flexible
spacers. When molecularly dissolved in good solvents, the alkyl
chains (spring) of the hyperbranched polymers are probably fully
stretched, endowing the polymers a bulky sphere with considerable
cavities. The large free volumes enable the phenyl rings of the TPE
units to rotate freely, making the polymers nonemissive. When large
amount of water was added, the solvating power of the aqueous
mixtures become worse, causing the flexible and hydrophobic poly-
mer branches agglomerated and the bulky spheres compressed to
smaller ones. The reduced cavities within the spheres greatly restricted
the intramolecular rotation of phenyl rings, which effectively blocks
the non-radiative energy dissipation channels, populates the radiative
decay of the excitons and then turns the emission of polymers on. It is
also deduced from the aAIE values of hb-P1a and hb-P1b that the
longer the alkyl spacers, the higher the compression ratio. The Bru-
nauer–Emmet–Teller (BET) surface area of 5.8 m2gꢁ1 of hb-P1a are
negligibly low compared to other hyperbranched polymers (>1000
m2gꢁ1),14 suggesting the polymer is tightly compressed with almost no
cavities in the solid state (Fig. S5, ESI†). Thus, the AIE-active hb-P1a
and hb-P1b could be potentially regarded as organic ‘‘quantum dots’’
with low cytotoxity in the solid state.
Fig. 3 (a) PL spectra of hb-P1a in THF/water mixture (1 : 9 v/v) con-
taining different amounts of PA. Concentration of hb-P1a: 10 mM; lex
¼
333 nm. (b) Stern–Volmer plots of I0/I versus [PA] in THF/water with
fw ¼ 90% and [TNT] in THF/methanol with fm ¼ 90%. Inset: enlarged
plot of I0/I versus [PA]. [Q] represents the concentration of PA and TNT;
I ¼ peak intensity and I0 ¼ peak intensity at [Q] ¼ 0 mM.
knowledge, there is little literature to account for the intrinsic reason.
We tried to account for this phenomenon by investigating the UV
spectra of PA and TNT as well as the PL spectrum of hb-P1a. The
obvious spectral overlap of the absorption of PA and emission of the
polymer in the range of 390 to 500 nm reveals that the energy transfer
from the excited state of the hb-P1a to the ground state of PA will be
the main quenching pathway.7a,15a This mechanism, however, cannot
be applied to explain the quenching effect of TNT because there is no
spectral overlap between the absorption of TNT and the emission of
polymer (Fig. 4a).
The flexible alkyl chains (spring) enable hb-P1a and hb-P1b to
possess good filming abilities and high optical transparency in their
film states (Fig. S6, ESI†). The light transmittances of hb-P1a and
hb-P1b reach 99% at wavelengths as short as 437 and 420 nm for their
thin films with thickness of 24.1 and 20.0 nm, respectively, making
them promising for photonic applications.
Further investigating the UV spectra of the mixtures of explosives
with hb-P1a, we found a tail in the mixture of hb-P1a and TNT
(Fig. 4b, and Fig. S8 in the ESI†) which is probably ascribed to their
interaction, which may facilitate the charge transfer between
them.17a,18 Cyclic voltammetry measurement of hb-P1a further
substantiates the conclusion (Fig. S9, ESI†): the higher energy of
lowest unoccupied molecular orbital (LUMO, ꢁ3.28 eV) of the
polymer facilitates the electron to jump to the lower one of TNT
(ꢁ3.7 eV).15a,19
The intriguing AIE effect of hb-P1a and hb-P1b prompted us to
explore their potential applications as chemosensors. Although they
are free from the noise of fluorescence background in their solution
state, the high sensitivity of the polymer aggregates will be more
attractive because it can decrease the sensing limitation.7b,9b Detection
of explosives is of great importance and receiving extensive interest
because of its homeland security and anti-terrorism implications.15
Picric acid (PA) and 2,4,6-trinitrotoluene (TNT) are employed as
model explosives among the nitroaromatic compounds. We prepared
the polymer aggregates in THF/water and THF/methanol mixtures
with water or methanol fraction (fm) of 90% in according to the
different solubility of PA and TNT, respectively. Importantly, the
emissions in the THF/water and THF/methanol mixtures are both
efficient with no peaks shift, suggesting that the solvent imparts little
effect on the polymer aggregate emission.
The above experimental results indicate that the main quenching
mechanism for PA is the energy transfer, whereas, that for TNT is the
charge transfer. It is well known that the energy transfer is a long-
range process and the charge transfer is a short-range one.20 In the
Upon addition of the explosives into the aggregates suspended in
the mixture solvents, for example, the emission intensities of hb-P1a
decrease progressively but with no change in spectral profiles (Fig. 3a,
and Fig. S7 in the ESI†). When the concentration of PA and TNT are
below 0.09 and 1.0 mM, the Stern–Volmer plots of hb-P1a are linear
and give quenching constants of 56484 and 704 Mꢁ1, respectively
(Fig. 3b). Afterwards, both plots bend upward, indicative of super-
amplified quenching effect.9b,16 The unique phenomenon could be
attributed to the 3-dimensional topological structures of the aggre-
gates that generate more small cavities, which enable the small
explosive molecules to enter through electrostatic interactions and
offer more diffusion channels for the excitons to migrate, allowing
them to be more quickly annihilated by the explosive quenchers.
From Fig. 3b, we also notice that the quenching of the emission of
polymer aggregates is more sensitive to PA than TNT. Although
a similar phenomenon was observed previously,17 to the best of our
Fig. 4 (a) Normalized absorption spectra of TNT and PA, as well as the
PL spectrum of hb-P1a in THF/methanol (fm ¼ 90%) and THF/water
(fw ¼ 90%). (b) Absorption spectra of TNT, hb-P1a and their mixture in
THF/methanol (fm ¼ 90%). Inset: enlarged UV spectra of TNT, hb-P1a
and their mixture in the range of 380–700 nm. [TNT]: 90 mM, [hb-P1a]: 10
mM.
4058 | J. Mater. Chem., 2011, 21, 4056–4059
This journal is ª The Royal Society of Chemistry 2011

Y. Dong, S. Lo, I. D. Williams, D. Zhu and B. Z. Tang, Chem.
Mater., 2003, 15, 1535.
polymer aggregates, PA can interact with the fluorophores
surrounding it, but TNT can only quench the emission of the fluo-
rophores that have interaction with it. Thus, quenching the emission
of polymer aggregates is more sensitive to PA than TNT.
6 (a) C.-T. Lai and J.-L. Hong, J. Phys. Chem. B, 2010, 114, 10302; (b)
K. Y. Pu and B. Liu, Adv. Funct. Mater., 2009, 19, 277; (c) L. Liu,
G. Zhang, J. Xiang, D. Zhang and D. Zhu, Org. Lett., 2008, 10,
4581; (d) L. Qian, J. Zhi, B. Tong, F. Yang, W. Zhao and Y. Dong,
Prog. Chem., 2008, 20, 673; (e) Y. Liu, X. Tao, F. Wang, X. Dang,
D. Zou, Y. Ren and M. Jiang, J. Phys. Chem. C, 2008, 112, 3975;
(f) Q. Peng, Y. Yi, Z. Shuai and J. Shao, J. Am. Chem. Soc., 2007,
129, 9333; (g) H. C. Yeh, S. J. Yeh and C. T. Chen, Chem.
Commun., 2003, 2632; (h) B. K. An, S. K. Kwon, S. D. Jung and
S. Y. Park, J. Am. Chem. Soc., 2002, 124, 14410; (i) Y. Jiang,
Y. Wang, J. Hua, J. Tang, B. Li, S. Qian and H. Tian, Chem.
Commun., 2010, 46, 4689; (j) Z. Xie, B. Yang, W. Xie, L. Liu,
F. Shen, H. Wang, X. Yang, Z. Wang, Y. Li, M. Hanif, G. Yang,
L. Ye and Y. Ma, J. Phys. Chem. B, 2006, 110, 20993.
7 (a) A. Qin, J. W. Y. Lam, L. Tang, C. K. W. Jim, H. Zhao, J. Sun and
B. Z. Tang, Macromolecules, 2009, 42, 1421; (b) A. Qin, L. Tang,
J. W. Y. Lam, C. K. W. Jim, Y. Yu, H. Zhao, J. Sun and
B. Z. Tang, Adv. Funct. Mater., 2009, 19, 1891.
8 (a) B. Voit and A. Lederer, Chem. Rev., 2009, 109, 5924; (b)
€
M. Haubler, A. Qin and B. Z. Tang, Polymer, 2007, 48, 6181; (c)
C. Gao and D. Yan, Prog. Polym. Sci., 2004, 29, 183.
9 (a) J. Liu, Y. Zhong, J. W. Y. Lam, P. Lu, Y. Hong, Y. Yu, Y. Yue,
M. Faisal, H. H. Y. Sung, I. D. Williams, K. S. Wong and B. Z. Tang,
Macromolecules, 2010, 43, 4921; (b) J. Liu, Y. Zhong, P. Lu, Y. Hong,
J. W. Y. Lam, M. Faisal, Y. Yu, K. S. Wong and B. Z. Tang, Polym.
Chem., 2010, 1, 426; (c) P. Lu, J. W. Y. Lam, J. Liu, C. K. W. Jim,
W. Yuan, N. Xie, Y. Zhong, Q. Hu, K. S. Wong, K. K. L. Cheuk
and B. Z. Tang, Macromol. Rapid Commun., 2010, 31, 834.
10 J. Chen, H. Peng, C. C. W. Law, Y. Dong, J. W. Y. Lam,
I. D. Williams and B. Z. Tang, Macromolecules, 2003, 36, 4319.
11 Z. Zhao, S. Chen, X. Shen, M. Faisal, Y. Yu, P. Lu, J. W. Y. Lam,
H. S. Kwok and B. Z. Tang, Chem. Commun., 2010, 46, 686.
In summary, by taking advantage of the innovative spring-like
architectures, we have synthesized AIE-active hyperbranched poly-
triazoles by the well-established Cu(PPh3)3Br-mediated triazide-diyne
click polymerization. The aAIE values (up to 348.3) of hyperbranched
polytriazoles are larger than those of many AIE luminogens, such as
TPE and HPS. Thanks to the high compression ratio of the polymers
from solution to solid states, the intramolecular rotation of phenyl
rings was greatly restricted and efficient light emission in aggregate
(FF up to 38.31) and solid state (FF ¼ 100%) was obtained. The
polymers are soluble and thermally stable, and possess good film-
forming ability. Using the novel AIE effect, the polymers can act as
chemosensors for the superamplified detection of explosives in their
aggregate states. The main mechanism for the detection of PA is
ascribed to the energy transfer, and that for TNT is the charge
transfer. The concept of spring-like polymeric structures is of great
value in terms of guiding future molecular engineering endeavors in
designing hyperbranched polymers with AIE characteristics. The
possibility of using these AIE-active hyperbranched polymers for
other high-tech applications is currently under exploration in our
laboratories.
Acknowledgements
12 (a) A. Qin, J. W. Y. Lam and B. Z. Tang, Chem. Soc. Rev., 2010, 39,
2522; (b) A. Qin, J. W. Y. Lam and B. Z. Tang, Macromolecules, 2010,
43, 8693; (c) A. Qin, J. W. Y. Lam, C. K. W. Jim, L. Zhang, J. Yan,
This work is partially supported by the National Natural Science
Foundation of China (20634020, 50703033, 20974098), the Ministry
of Science and Technology of China (2009CB623605), the University
Grants Committee of Hong Kong (AoE/P-03/08), the Research
Grants Council of Hong Kong (603509, 601608, 602707, and ITS/
168/09). A.J.Q. and B.Z.T acknowledge the supports from the
Fundamental Research Funds for the Central Universities
(2010KYJD005), and the Cao Guangbiao Foundation of Zhejiang
University, respectively.
€
M. Haussler, J. Liu, Y. Dong, D. Liang, E. Chen, G. Jia and
B. Z. Tang, Macromolecules, 2008, 41, 3808; (d) V. V. Rostovtsev,
L. G. Green, V. V. Fokin and K. B. Sharpless, Angew. Chem., Int.
Ed., 2002, 41, 2596; (e) C. W. Tornøe, C. Christensen and
M. Meldal, J. Org. Chem., 2002, 67, 3057.
13 (a) Z. Xie, S. J. Yoon and S. Y. Park, Adv. Funct. Mater., 2010, 20,
1638; (b) Q. Peng, L. Yan, D. Chen, F. Wang, P. Wang and
D. Zou, J. Polym. Sci., Part A: Polym. Chem., 2007, 45, 5296; (c)
X. Liu, C. He, X. Hao, L. Tan, Y. Li and K. S. Ong,
Macromolecules, 2004, 37, 5965; (d) Q. He, H. Huang, Q. Sun,
H. Lin, J. Yang and F. Bai, Polym. Adv. Technol., 2004, 15, 43.
14 (a) N. B. McKeown and P. M. Budd, Macromolecules, 2010, 43,
5163; (b) J. X. Jiang, A. Trewin, F. Su, C. D. Wood, H. Niu,
J. T. A. Jones, Y. Z. Khimyak and A. I. Cooper, Macromolecules,
2009, 42, 2658.
Notes and References
1 M. Shimizu and T. Hiyama, Chem.–Asian J., 2010, 5, 1516.
2 J. B. Birks, Photophysics of Aromatic Molecules, Wiley, London,
1970.
3 Y. Hong, J. W. Y. Lam and B. Z. Tang, Chem. Commun., 2009, 4332.
4 (a) J. Luo, Z. Xie, J. W. Y. Lam, L. Cheng, H. Chen, C. Qiu,
H. S. Kwok, X. Zhan, Y. Liu, D. Zhu and B. Z. Tang, Chem.
Commun., 2001, 1740; (b) J. Liu, J. W. Y. Lam and B. Z. Tang,
Chem. Rev., 2009, 109, 5799.
5 (a) Y. Liu, Y. Tang, N. N. Barashkov, I. S. Irgibaeva, J. W. Y. Lam,
R. Hu, D. Birimzhanova, Y. Yu and B. Z. Tang, J. Am. Chem. Soc.,
2010, 132, 13951; (b) Z. Zhao, Z. Wang, P. Lu, C. Y. K. Chan, D. Liu,
J. W. Y. Lam, H. H. Y. Sung, I. D. Williams, Y. Ma and B. Z. Tang,
Angew. Chem., Int. Ed., 2009, 48, 7608; (c) A. Qin, J. W. Y. Lam,
M. Faisal, C. K. W. Jim, L. Tang, J. Sun, H. H. Y. Sung,
I. D. Williams and B. Z. Tang, Appl. Phys. Lett., 2009, 94, 253308;
15 (a) S. W. Thomas III, G. D. Joly and T. M. Swager, Chem. Rev., 2007,
107, 1339; (b) S. J. Toal and W. C. Trogler, J. Mater. Chem., 2006, 16,
2871.
16 D. Zhao and T. M. Swager, Macromolecules, 2005, 38, 9377.
17 (a) H. Sohn, M. J. Sailor, D. Magde and W. C. Trogler, J. Am. Chem.
Soc., 2003, 125, 3821; (b) T. H. Kim, H. J. Kim, C. G. Kwak,
W. H. Park and T. S. Lee, J. Polym. Sci., Part A: Polym. Chem.,
2006, 44, 2059.
18 (a) S. W. Thomas III, J. P. Amara, R. E. Bjork and T. M. Swager,
Chem. Commun., 2005, 4572; (b) R. Tu, B. Liu, Z. Wang, D. Gao,
F. Wang, Q. Fang and Z. Zhang, Anal. Chem., 2008, 80, 3458; (c)
Y. H. Lee, H. Liu, J. Y. Lee, S. H. Kim, S. K. Kim, J. L. Sessler,
Y. Kim and J. S. Kim, Chem.–Eur. J., 2010, 16, 5895.
€
(d) Z. Li, Y. Q. Dong, J. W. Y. Lam, J. Sun, A. Qin, M. Haubler,
Y. P. Dong, H. H. Y. Sung, I. D. Williams, H. S. Kwok and
B. Z. Tang, Adv. Funct. Mater., 2009, 19, 905; (e) G. Yu, S. Yin,
Y. Liu, J. Chen, X. Xu, X. Sun, D. Ma, X. Zhan, Q. Peng,
Z. Shuai, B. Z. Tang, D. Zhu, W. Fang and Y. Luo, J. Am. Chem.
Soc., 2005, 127, 6335; (f) J. Chen, C. W. Law, J. W. Y. Lam,
19 (a) J.-S. Yang and T. M. Swager, J. Am. Chem. Soc., 1998, 120, 11864;
ꢀ
(b) J. L. Bredas, R. Silbey, D. S. Boudreaux and R. R. Chance, J. Am.
Chem. Soc., 1983, 105, 6555.
20 B. Valeur, Molecular Fluorescence: Principle and Applications, Wiley-
VCH, Weinheim, 2002.
This journal is ª The Royal Society of Chemistry 2011
J. Mater. Chem., 2011, 21, 4056–4059 | 4059