Initiator-lightened polymers: Preparation of end-functionalized polymers by ATRP and their intramolecular charge transfer and aggregation-induced emission

Article abstract of DOI:10.1039/c2cc35266d

A simple strategy to prepare AIE polymers is invented using an AIE initiator for atom transfer radical polymerization. The dual photoresponse by intramolecular charge-transfer and luminogen aggregation of the initiator is well-realized and even enlarged after polymerization, due to the linkage of polymer chains.

Full text of DOI:10.1039/c2cc35266d

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ARTICLE TYPE
Initiator-lightened Polymers : preparation of end-functionalized
polymers by ATRP and their intramolecular charge transfer and
aggregation-induced emission
Pei-Yang Gua, Cai-Jian Lua, Fei-Long Yea, Jian-Feng Gea, Qing-Feng Xu*a, Zhi-Jun Hua, Na-Jun Lia,
5
Jian-Mei Lu,*a
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
after polymerization was studied.
A simple strategy to prepare AIE polymers is invented using
an AIE initiator for atom transfer radical polymerization.
10 The dual photoresponse by intramolecular charge-transfer
and luminogen aggregation of the initiator is well-realized
and even enlarged after polymerization, due to the linkage of
polymer chains.
In the present research, we designed and synthesized an
50 intramolecular charge transfer (ICT) and an AIE dual active
initiator, TPPꢀNI (Fig. 1a). This molecule originated from a
pyrazoline chromophore; it possesses an electron donor
(dimethylamino),
and
an
electron
acceptor
(l,8ꢀ
naphthalimide). The DFT calculation showed that the
55 distortion angle of the naphthalimide and pyrazole rings
reached 58º (see Fig. 1b). Such a structure could hamper the
effective πꢀπ stacking between the dye molecules, a process
that enables the molecules to efficiently emit in the condensed
phase. The photoluminescence (PL) of TPPꢀNI was quenched
60 in DMF solution, but was recovered by the following method:
using poor polar solvent, such as toluene; and producing
nanoaggregation.
Molecules equipped with aggregationꢀinduced emission (AIE)
15 have gained serious attention because of potential applications
in optoelectronic devices, chemosensors, and bioprobes.1aꢀ1g
Tang’s group and others have successfully designed and
synthesized various small AIE active molecules, such as
2aꢀb
TPE1e,
and HPS.2c Fabrication of small AIEꢀequipped
20 molecule for practical applications, however, remains a
challenge, largely because of the reliance on expensive
equipment and complicated processes for fabrication. In light
of those problems, high molecular weight polymers have been
considered as candidates. High molecular weight polymers
25 possess highꢀquality film, and can be prepared using simple
processing techniques, such as spinꢀcoating. Until now, few
AIEꢀactive polymers have been developed; most cases have
been developed by introducing a monomer with AIE moiety
into the main or side chain.2aꢀb, 2d However, it is difficult to
30 confirm the exact number of AIE moiety in the copolymer
chain. If a single chromophore anchored on a polymer chain,
as well as its AIE effect, could be preserved, it would be an
extremely interesting method with which to obtain an AIE
active polymer. A pertinent question thus becomes how to
35 effectively realize the design of such a process. Further, the
question of whether a single chromophoric unit in a polymer
chain could induce sufficient changes in the properties of the
polymer remains important. One efficient existing method
involves the use of controlled radical polymerization
40 techniques, such as atom transfer radical polymerization
(ATRP) and reversible additionꢀfragmentation chain transfer
(RAFT) technologies.3aꢀ3cATRP, which was first proposed by
Matyjaszewski and Sawamoto, etc., has emerged as a feasible
Figure 1 (a) Formula of TPPꢀNI; (b) Optimized groundꢀstate geometry of
65 initiator with B3LYP/6ꢀ31G* in gas phase; (c) Scheme of synthetic
routine of polymers.
When TPPꢀNI was used as an ATRP initiator, the regular
monomers, such as styrene (St), methyl methacrylate (MMA),
and 2ꢀhydroxyethyl methacrylate (HEMA) (with different
70 hydrophilic properties) could be respectively polymerized in a
moderate condition. These αꢀend functionalized polymers (PS,
technique
for
obtaining
wellꢀdefined
polymers.4aꢀb
45 Considering the above information, in this study, an AIE
active initiator was introduced at the end of a polymer chain;
subsequently, its impact on the AIE effect both before and
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about 60 %, λem was red shifted, the intensity ratio (I/I0)
but tended to aggregate when water or ethanol was added. 60 reached a maximum value of 13, and the fluorescent quantum
PMMA, and PHEMA) were well dissolved in DMF solution,
Interestingly, the molecules were almost nonemissive in pure
DMF solution; yet an abrupt increase of PL intensity and
quantum yield was observed when the polymer chains
aggregated. The emission intensity was stronger than that in
yield (QY) was 1.4 % (Fig. 3a).
The PS emission was studied using a DMF/ethanol mixture.
The weak emission band of PS in DMF solution was at about
545 nm; this was blue shifted by about 30 nm in comparison
5
the respective DMF solution by the following, according to 65 to the weak emission band of the initiator. This could likely
solution: PS in DMF/ethanol mixture, 155ꢀfold; PMMA in
DMF/water mixture, 65ꢀfold; and PHEMA in DMF/water
10 mixture, 10ꢀfold. Further, the PL intensity of PHEMA
dramatically enhanced with the increased acidification of the
be attributed to different intramolecular and intermolecular
interactions in the polymer chains. With the addition of
ethanol into the DMF solution, the emission band of PSa was
slightly blue shifted, and intensity increased gradually after 50
solution; specifically, PL intensity was about 7ꢀfold higher 70 % ethanol content was reached. The highest intensity was
than it was in DMF/water. We thus attempted to elucidate the
AIE mechanism differences herein.
15 The existence of ICT was confirmed by measuring the
absorption and emission spectra of the initiator and PS in
reached in 99 % ethanol, a value that was 155ꢀfold higher (ΦF
= 19 %) than that in the pure DMF (ΦF < 1 %). The emission
intensities of PSb and PSc were 98ꢀfold (ΦF = 15 %) and 72ꢀ
fold (ΦF = 13 %) larger than those in pure DMF, respectively
three different polar solvents (DMF, THF, and toluene). In the 75 (Fig. 3b). Additionally, normal PS with BABrP doped in
DMF solution of the initiator, there are two prominent bands
at 330 nm and 475 nm, which can be ascribed to a localized
20 aromatic πꢀπ* transition, and an ICT character of l, 8ꢀ
naphthalimide, respectively. When the polarity of the solvent
could not achieve the AIE effect, because the BABrP still
dissolved in ethanol when PS aggregated. It may be explained
that the chromophore anchored at the end of polymers was
easily twisted in the best emissive form by a rigid matrix.
decreased, an ICT character blueꢀshift was observed (460 nm 80 Moreover, the QY of PSa was the highest, although AIE
and 451 nm in THF and toluene, respectively). Initiator
emission was almost quenched in DMF (549 nm), was
25 moderate in THF (525 nm), and was highest in toluene (507
nm) (Fig. 2a). The obvious increase in the stokes’ shift with
fluorphore content was the lowest due to its largest Mw. It
may be proposed that the stronger wrapping of polymer chains
not only protected the initiator from solvent to avoid
quenching, but that it also amplified the AIE effect. Therefore,
the increasing polarity of solvents (2,449 cmꢀ1 in toluene, 85 the emission amplification of polymers was mainly ascribed to
2,691 cmꢀ1 in THF, and 2,838 cmꢀ1 in DMF) further verified
the ICT character of the excited state in our system.
30 Generally, ICT states can be effectively stabilized in polar
media such as DMF and water, and this is not benefitial to
emission in our system.54ꢀb These phenomena were observed
in PS solution, indicating that polymer ICT was wellꢀ
preserved. Using different solvents, we could turn on the
35 emission of the TPPꢀNI molecule and its endꢀfunctionalized
polymers.
two
facts
that
the
aggregated
polymer
protected initiator from solvent to avoid quenching and made
it in an emissive configuration.
We also studied the initiator and polymers AIE effect in a
DMF/water (ethanol) mixture; the absorption spectra of the
initiators have been presented and discussed in detail in the
40 supporting information.
The absorption behaviors were similar for the three PS with
different molecular weights (see Fig. S4ꢀ3, S4ꢀ4, and S4ꢀ5).
The absorption spectra of PSa with various fractions of
ethanol have been shown in Fig. 2b. With added ethanol, the
45 light scattering effect of the nanoaggregates could be observed
gradually.6 The polymer chain formed different sizes of
nanoparticles in accordance with different ethanol volumes
added (Fig. S7ꢀ2). Specifically, with increased ethanol
content, smaller nanoparticles were obtained accordingly.
50 The absorption pattern of PMMA was similar to that of PS,
but the aggregate degree was relatively lower (Fig. 2c).
However, the absorption pattern of PHEMA was different;
light scattering was not observed, even when the water
content was increased to 80 % (Fig. 2d). This was likely due
55 to the strong interaction between PHEMA and polar solvents
and the fact that its aggregation degree was the lowest.
Compared to that of DMF solution, the effect of water on
initiator emission was obvious. When the water fraction was
90 Figure 2 (a) Absorption and emission spectra of initiator in different
solvents; (b) Absorption spectra of PSa with the composition of the
DMF/ethanol mixture; (c) Absorption spectra of PMMA with the
composition of the DMF/water mixture; (d) Absorption spectra of
PHEMA with the composition of the DMF/water mixture.
95 It should be noted that PS films prepared by spinꢀcoating were
highly emissive under UV light irradiation. In particular, the
QYs of PS films were unexpectedly high, and increased as
molecular weight increased (PSa was 48 %, PSb was 42 %,
and PSc was 35 %). This interesting result may make them
100 good candidates for optical chips.
The PMMA showed similar AIE effects compared to those of
2
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PS. However, the AIE amplification effect in PMMA was 45 fold) (Fig. 3d). PHEMA could be applied in an oral drugꢀ
weaker than it was in PS because the polarity of PMMA is
stronger than that of PS, and the wrapping of the fluorphore is
less effective.
delivery system, both as an optical sensor and as a
supplemental carrier to encase the hydrophobic drug
molecules effectively in the stomach.
5
The AIE phenomenon was much weaker in the PHEMA
In summary, an AIEꢀactive initiator is introduced to the
system. When water content was increased to 90 %, the 50 terminal of a polymer chain and enables the regular polymers
intensity was only 10ꢀfold higher than it was in the DMF
solution; it exhibited a weak emission at 570 nm, which was
similar to that of the initiator. This was because the polar
10 PHEMA chain could not easily hamper initiator ICT, and
obvious emission quenching was thus observed.
to emit dramatically. Although the AIE effect of this small
molecule is not distinctive, the obvious amplification of
polymers emission is observed. It should partly attributed to
the wrapping and coiling of flexible hydrophobic chains. The
55 AIE effect is originated from initiator TPPꢀNI, but amplified
through polymer chains or tuned by polarity of the polymer
side chains. The prepared polymers exhibit not only the AIE
effect of the terminal group but also the property of the
polymer chains, such as easy fabrication. In particular, the
The pressing question of how to recover the emission
remains. When sulfuric acid was added into the DMF
solution,
a gradual increase of emission intensity was
15 observed; it reached a maximum when the pH value was about
1. However, only a slight enhancement of emission intensity 60 PHEMA shows a pHꢀoptical sensitive phenomenon, which is
could be observed in similar PS and PMMA systems,
respectively (see Fig. S4ꢀ10). We tentatively propose the
following reasons for the AIE mechanism observed in
20 PHEMA: (i) although the dimethylamino (DMA) group in
not obvious in both small molecules and regular polymers
without such a fluorphore. We believe that such a method is
promising in preparation of AIE polymers and studying the
morphology of classical polymers using fluorescence.
TPPꢀNI is a wellꢀknown pH sensor in solution, TPPꢀNI itself 65 Acknowledgements The authors graciously thank Prof. Qingꢀ
could not dissolve in water, and the pH effect was nearly
unobservable; (ii) because the polarities of PS and PMMA
nanoparticles are low, there are few DMA groups anchored on
25 the particle surface, and the enhancement of emission is
Hua Xu (National University of Singapore) for such beneficial
discussion. The authors also thank the Chinese Natural
Science Foundation (21071105 and 21176164), the 863 Major
Project (SQ2009AA06XK1482331), PAPD and the Project of
limited; and (iii) hydrogen bonds between HEMA’s hydroxyl 70 Science and Technology of Suzhou (SYG201114).
group and the water molecule are destroyed in acid solution,
Notes and references
and thereafter the polymer aggregates. However, the polarity
of PHEMA causes the exposure of more dimethylamino
Department of polymer science, College of Chemistry, Chemical
30 groups on the surface, and the effect of the pH value is
75
Engineering and Materials Science, Soochow University, Suzhou,
China 215123.
amplified.
Eꢀmail: lujm@suda.edu.cn, xuqingfeng@suda.edu.cn; Fax: +86 (0) 512ꢀ
65880367; Tel: +86 (0)512ꢀ6588 0368
†Electronic Supplementary Information (ESI) available: Experimental
80 section. See DOI: 10.1039/b000000x/
1(a) M. M. Cai, Z. Q. Gao, X. H. Zhou, X. P. Wang, S. F. Chen, Y. Z.
Zhao, Y. Qian, N. E. Shi, B. X. Mi, L. H. Xie and W. Huang, Phys.
Chem. Chem. Phys., 2012, 14, 5289; (b) Z. Q. Guo, W. H. Zhu and
H. Tian, Chem. Commun., 2012, 48, 6073; (c) J. A. Ho, H. C. Chang
85
90
95
and W. T. Su, Anal. Chem. 2012, 84, 3246; (d) T. Y. Han, X. Feng,
B. Tong, J. B. Shi, L. Chen, J. G. Zhi and Y. P. Dong, Chem.
Commun., 2012, 48, 416; (e) C. H. Li, T. Wu, C. Y. Hong, G. Q.
Zhang and S. Y. Liu, Angew. Chem. Int. Ed. 2012, 51, 455; (f) V.
Bhalla, V. Vij, A. Dhir and M. Kumar, Chem. Eur. J. 2012, 18, 3765;
(g) S. Kim, Q. D. Zheng, G. S. He, D. J. Bharali, H. E. Pudavar, A.
Baev and P. N. Prasad, Adv. Funct. Mater. 2006, 16, 2317.
2 (a) L. Tang, J. K. Jin, A. Qin, W. Z. Yuan, Y. Mao, J. Mei, J. Z. Sun
and B. Z. Tang, Chem. Commun., 2009, 4974; (b) A. J. Qin, L. Tang,
J. W. Y. Lam, C. K. W. Jim, Y. Yu, H. Zhao, J. Z. Sun and B. Z.
Tang, Adv. Funct. Mater. 2009, 19, 1891; (c) Y. N. Hong, J. W. Y.
Lam and B. Z. Tang, Chem. Soc. Rev., 2011,40, 5361.(review); (d) H.
G. Lu, F. Y. Su, Q. Mei, X. F. Zhou, Y. Q. Tian, W. J. Tian, R. H.
Johnson and D. R. Meldrum, J. Polym. Sci. Part A: Polym. Chem.,
2012, 50, 890.
Figure 3 (a) Change in the relative PL intensity (I/I0) of initiator in the
DMF/water mixture. I0 = PL intensity in DMF solution. Concentration: 25
35 uM; excitation wavelength: 467 nm; (b) Change in QYs of PS in the
DMF/ethanol mixture; (c) Change in emission intensity of PHEMA in
DMF at different pH values; (d) Emission spectra of PHEMA in DMF, 100 3 (a) P. Theato, Angew. Chem. Int. Ed., 2011, 50, 5804; (b) S. Nojima, Y.
DMF/water mixture, and SGJ solution, respectively.
Ohguma, K. I. Kadena, T. Ishizone, Y. Iwasaki, K.Yamaguchi,
Macromolecules 2010, 43, 3916; (c) P. Y. Gu, C. J. Lu, Q. F. Xu, G.
J. Ye, W. Q. Chen, X. M. Duan, L. H. Wang and J. M. Lu, J. Polym.
Sci. Part A: Polym. Chem., 2012, 50, 480.
These characteristic differences of PHEMA make it more
40 attractive for future practical applications. We have utilized
PHEMA as a PL sensor in simulated gastric juice (SGJ)
solution. The λem of PHEMA in SGJ solution was blue
shifted by almost 10 nm, but the intensity was much higher
than those in the DMF (70ꢀfold) and DMF/water mixtures (7ꢀ
105 4 (a) J. Qiu and K. Matyjaszewski, Macromolecules 1997, 30, 5643; (b)
J. Ueda, M. Atsuyaman, M. Kamigaito and M. Sawamoto,
Macromolecules 1998, 31, 557.
This journal is © The Royal Society of Chemistry [year]
Journal Name, [year], [vol], 00–00 | 3

ChemComm
Page 4 of 4
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5 (a)C. J. Fahrni, L. C. Yang, D. G. VanDerveer, J. Am. Chem. Soc.,
2003, 125, 3799; (b) J. Cody, S. Mandal, L. C. Yang, C. Fahrni, J.
Am. Chem. Soc., 2008, 130, 13023.
6 Y. Liu, S. M. Chen, J. W. Y. Lam, P. Lu, R. T. K. KwoK, F. Mahtab, H.
S. Kwok and B. Z. Tang, Chem. Mater., 2011, 23, 2536.
5
4
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