Light-driven and aggregation-induced emission from side-chain azoindazole polymers

Article abstract of DOI:10.1002/pola.24947

The well-defined azoindazole-containing homopolymer, poly(6-{6-[(4- dimethylamino) phenylazo]-indazole}-hexyl methacrylate) (PDHMA), and amphiphilic diblock copolymer, poly({6-[6-(4-dimethylamino)phenylazo]-indazole}-hexyl methacrylate)-b-poly(2-(dimethyl

Full text of DOI:10.1002/pola.24947

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ARTICLE
Light-Driven and Aggregation-Induced Emission from Side-Chain
Azoindazole Polymers
Ying Li,1 Nianchen Zhou,1,2 Wei Zhang,1 Feng Zhang,1 Jian Zhu,1 Zhengbiao Zhang,1
Zhenping Cheng,1 Yingfeng Tu,1 Xiulin Zhu1
1Jiangsu Key Laboratory of Advanced Functional Polymer Design and Application, Department of Polymer Science and
Engineering, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123,
People’s Republic of China
2Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Soochow University, Suzhou, 215123, Jiangsu,
People’s Republic of China
Correspondence to: N. Zhou (E-mail: nczhou@suda.edu.cn) or X. Zhu (E-mail: xlzhu@suda.edu.cn)
Received 22 May 2011; accepted 11 August 2011; published online 9 September 2011
DOI: 10.1002/pola.24947
ABSTRACT: The well-defined azoindazole-containing homopoly-
mer, poly(6-{6-[(4-dimethylamino) phenylazo]-indazole}-hexyl
methacrylate) (PDHMA), and amphiphilic diblock copolymer,
poly({6-[6-(4-dimethylamino)phenylazo]-indazole}-hexyl methac-
rylate)-b-poly(2-(dimethylamino)ethylmethacrylate) (PDHMAm-
b-PDMAEMAn), were successfully prepared via reversible
addition-fragmentation chain transfer polymerization tech-
nique. The homopolymer and amphiphilic diblock copolymer
in CH2Cl2 exhibited intense fluorescence emission accompa-
nied by trans–cis photoisomerization of azoindazole group
under UV irradiation. The experiment results indicated that the
intense fluorescence emission may be attributed to an inhibi-
tion of photoinduced electron transfer of the cis form of azoin-
dazole. On the other hand, the intense fluorescence emission
of amphiphilic diblock copolymers in water-tetrahydrofuran
mixture was observed, which increased with the volume ratio
of water in the mixed solvent. The self-aggregation behaviors
of three amphiphilic diblock copolymers were examined by
transmission electron microscopy, laser light scattering, and
UV–vis spectra. The restriction of intramolecular rotation of the
azoindazole groups in aggregates was considered as the main
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cause of aggregation-induced fluorescence emission.
2011
Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49:
4911–4920, 2011
KEYWORDS: aggregation-induced emission; azo polymers; light-
driven emission; reversible addition-fragmentation chain trans-
fer; self-assembly
INTRODUCTION It is well-known that azobenzene com-
pounds are one of the frequently used photoresponsive
materials in many fields,1 such as optical data storage,2 liq-
uid crystal displays,3 photoinduced bending,4 optical switch-
ing,5 and holographic surface relief gratings,6 because of the
unique trans–cis–trans isomerization behavior of the azoben-
zene chromophores. Normally, azobenzene compounds are
nonfluorescent because main nonradiative relaxation process
of the azobenzene group inhibits its fluorescence property.
However, there were a few exceptions.7–14 Some of the possi-
ble reasons for unusual fluorescent behaviors of these azo-
benzene compounds were mostly attributed to the light-
driven7–10 and aggregation-induced emission (AIE).11–14 The
mechanisms of emission are generally accepted to be origins
of an inhibition of photoinduced electron transfer (PET),7,9
the restriction effects on nonradiative relaxation process of
the trans–cis isomerization of azobenzene groups and so
on.12–14 Up to now, the real reasons of fluorescence emission
of the azobenzene chromophore were not yet clearly
understood.
Attempts to fine-tune the fluorescence properties of azoben-
zene derivatives have been received extensive attentions.
Zacharias et al.7 and Smitha and Asha9 reported the fluores-
cent enhancement accompanied by isomerization from non-
aggregated azobenzene solution bearing fluorophores, and
the inhibiting PET was origin of enhanced luminescence as
the nonplanar geometry in the cis isomer of the azobenzene
group. Tang and coworkers15 reported a series of silole mol-
ecules to be nonluminescent in the solution state but emis-
sive in the aggregated state, and put forward that AIE due to
the restriction of the intramolecular rotation. Han et al.8
found the light-driven intense fluorescence emission from
azobenzene derivatives with a dual hydrophobic–hydrophilic
characters in dichloromethane. Subsequently, our group also
reported that azoindazole end-functionalized polystyrene
showed intense fluorescence emission resulted from the
Additional Supporting Information may be found in the online version of this article.
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SCHEME 1 The synthetic routes of monomer (DHMA), homopolymer (PDHMA) and amphiphilic diblock copolymer (PDHMAm-b-
PDMAEMAn).
photoinduced aggregation.14 Bo and Zhao13 reported that the
amphiphilic diblock copolymer composed of a hydrophilic
quaternized poly(4-vinyl pyridine) (QP4VP) and a hydropho-
bic liquid crystalline polymethacrylate bearing azobenzene
groups (PAzoMA) was nonfluorescent in N,N-dimethylforma-
mide (DMF) but became emissive as a result of the micelliza-
tion on addition of water.
philic diblock copolymer in CH2Cl2 under UV irradiation
showed the intense fluorescent emission. Furthermore, the
amphiphilic diblock copolymer in water-tetrahydrofuran
(THF) mixture also exhibited the intense aggregation-induced
fluorescence emission. This is the first report of both light-
driven and aggregation-induced emission from side-chain
azoindazole-containing polymers.
Most of the azobenzene-containing polymers were prepared
via free radical polymerization method, but these polymers
had uncontrolled molecular weights and molecular weight
distributions.16 Fortunately, the recent advances in controlled
‘‘living’’ radical polymerization facilitated the synthesis of
functional polymers with predetermined chemical composi-
tions. Among these methods, atom transfer radical polymer-
ization (ATRP),17 nitroxide-mediated radical polymeriza-
tion,18 reversible addition-fragmentation chain transfer
(RAFT)19 polymerization, and single-electron transfer medi-
ated living radical polymerization20 were mainly used. The
both ATRP21 and RAFT6a,22 techniques were reported to be
used to synthesize the well-defined azobenzene-containing
polymers. Compared with ATRP system, RAFT polymeriza-
tion can be conducted in the absence of metal catalysts. On
the other hand, poly(2-(dimethylamino ethyl)methacrylate)
(PDMAEMA) is a hydrophilic polymer block investigated
widely, and amphiphilic diblock copolymers containing
PDMAEMA exhibited good self-assembly behaviors.23
EXPERIMENTAL
Materials
Unless otherwise specified, all chemicals were purchased
from Shanghai Chemical Reagent, Shanghai, China. 2,20-Azobi-
s(isobutyronitrile) (AIBN, 98%) was recrystallized twice
from ethanol before use. THF and dichloromethane were
dried and distilled before use. 2-(Dimethylamino) ethyl
methacrylate (DMAEMA) (Acros, 99.5%) was distilled under
vacuum before use. 6-Aminoindazole (Alfa Aesar, 98%), 6-
choloro-1-hydroxyhexane (Alfa Aesar, 98%), and isobutylyl
chloride (Acros, 98%) were used as received. 2-Cyanoprop-
2-yl-1-dithionaphthalate (CPDN) and 6-(4-(dimethylamino)-
phenylazo)-1H-indazole (DMPI; Scheme 1) were synthesized
according to the method described in the literature.10
Synthesis of 6-{6-[(4-Dimethylamino)phenylazo]-
indazole}-hexan-1-ol
DMPI (5.3 g, 20 mmol) was dissolved in 50 mL of DMF in a
100-mL round-bottom flask. Anhydrous sodium hydroxide
(1.6 g, 40 mmol) and a catalytic amount of potassium iodide
were added. After the mixture was stirred for 5 h at 80 ꢀC,
1-chloro-6-hydroxyhexane (2.7 g, 20 mmol) was added drop-
wise to the mixture. The above mixture reacted for 24 h at
80 ꢀC, and then it was poured into 1 L of deionized water.
The precipitate was collected by filtration and purified by
silica gel chromatography with a mixture of petroleum ether-
Herein, we designed and prepared azoindazole-containing side
chain homopolymer, poly(6-{6-[(4-dimethylamino) phenylazo]-
indazole}-hexyl methacrylate) (PDHMA), and amphiphilic
diblock copolymer, poly({6-[6-(4-dimethylamino)phenylazo]-
indazole}-hexyl methacrylate)-b-poly(2-(dimethylamino)ethyl-
methacrylate) (PDHMAm-b-PDMAEMAn), via RAFT polymeriza-
tion technique. Interestingly, both homopolymer and amphi-
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ethyl acetate (1:2, v/v) as eluent to obtain 4.3 g (yield: 60%)
of red solid.
Synthesis of Poly[6-(4-phenylazophenoxy)
hexylmethacrylate]-b-Poly[(2-dimethylamino) ethyl
methacrylate)] (PDHMAm-b-PDMAEMAn))
Anal. Calcd. for C21H27N5O: C, 69.01%; H, 7.45%; N, 19.16%.
Found: C, 69.21%; H, 7.44%; N, 19.43%. 1H NMR (CDCl3, d
in ppm): 1.27–1.39 (m, 6H, ACH2CH2CH2A), 1.85–1.88 (m,
2H, ACH2A), 3.07 (s, 6H, AN(CH3)2), 3.33–3.36 (t, 2H,
ACH2Aindazole), 3.38 (s, 1H, AOH), 4.46–4.50 (t, 2H,
ACH2AOH), 6.85–6.87 (d, 2H, phenyl), 7.62–7.64 (m, 1H,
phenyl), 7.81–7.85 (m, 3H, indazole), 8.07–8.11 (d, 2H,
indazole) (spectrum was provided in Supporting Information
Fig. S1).
The PDHMAm-b-PDMAEMAn was prepared with a similar
procedures of RAFT polymerization of DHMA, except that
PDHMA was used as the macro-RAFT agent ([DMAE-
MA]0:[AIBN]0:[macro-RAFT]0 ¼ 500:1:3). THF and petroleum
ether were used as the solvent and the precipitator, respec-
tively. The obtained three amphiphilic diblock copolymers
were as follows: PDHMA33-b-PDMAEMA57 (called as P57),
PDHMA31-b-PDMAEMA100 (called as P100), and PDHMA31-b-
PDMAEMA148 (called as P148).
Preparation of the Aggregates in Mixed Solvents
The amphiphilic diblock copolymer (PDHMAm-b-PDMAE-
MAn)s (2.00 mg) was first dissolved in dry THF at a concen-
tration of 1.0 mg/mL. Then, the solution was filtered through
0.22 lm pore size filter. The mixtures of copolymers with
different fractions of water-THF were obtained by adding dif-
ferent volumes of Milli-Q water into above solution under
stirring.
Synthesis of {6-[6-(4-Dimethylamino)phenylazo]-
indazole}-hexyl Methacrylate (DHMA)
Triethylamine (10 mL, 50 mmol) was added to a solution
of 6-{6-[(4-Dimethylamino)phenylazo]-indazole}-hexan-1-ol
(DMPIH) (7.3 g 20 mmol) in 50 mL of dry THF. The solution
was stirred in an ice bath, and methacryloyl chloride (4.5
mL, 50 mmol) in dry THF (100 mL) was added dropwise
under an argon atmosphere. Then, the mixture was stirred
overnight at room temperature. The solution was filtered,
and the solvent was removed in vacuum. The obtained crude
product was purified by silica gel chromatography with a
mixture of petroleum ether-ethyl acetate (10:1, v/v) as elu-
ent. The obtained crude product was purified by recrystalli-
zation from ethanol to give 7.4 g (yield: 85%) of red crystal.
Characterization
The number-average molecular weight (Mn(GPC)) and polydis-
persity index value (PDI ¼ Mw/Mn) of the polymers were
determined with a Waters 1515 gel permeation chromatog-
raphy (GPC) equipped with a refractive index detector, with
HR1, HR3, and HR4 columns with a molecular weight range
of 100–500,000 and calibrated with poly(methyl methacry-
late) as the standard sample. THF was used as the eluent at
Anal. Calcd for C25H31N5O2: C, 69.26%; H, 7.21%; N, 16.15%.
Found: C, 68.68%; H, 7.86%; N, 16.18%. 1H NMR (CDCl3, d
in ppm): 1.41–1.42 (m, 4H, ACH2CH2A), 1.62–1.68 (m, 2H,
ACH2A), 1.92 (d, 1H, ACH3), 1.96–2.03 (m, 2H, ACH2A),
3.10 (s, 6H, AN(CH3)2, 4.10–4.13 (t, 2H, ACH2-indazole),
4.43–4.47 (t, 2H, ACH2OCO), 5.52 (s, 1H, AC¼¼CH2), 6.07 (s,
1H, AC¼¼CH2), 6.77–6.79 (d, 2H, phenyl), 7.75 (s, 2H, phe-
nyl), 7.87 (s, 1H, indazole), 7.91–7.93 (d, 2H, indazole), 8.00
(s, 1H, indazole) (spectrum was provided in Supporting
Information Fig. S2).
ꢀ
a flow rate of 1.0 mL/min at 30 C. Proton nuclear magnetic
resonance (1H NMR) spectra were recorded on a Varian
Inova 400 MHz NMR instrument with deuterium dichlorome-
thane (CD2Cl2) or deuterium chloroform (CDCl3) as the sol-
vent and tetramethylsilane (TMS) as the internal standard.
The UV–vis absorption spectra of the polymers in dichloro-
methane solutions were determined on a Shimadzu-RF540
spectrophotometer. The fluorescent spectra were obtained
on a PerkinElmer LS-50B fluorescence spectrophotometer
with CH2Cl2 or THF as solvent at room temperature. The
quantum yields of the copolymers (P57) in THF and water-
THF mixture were determined using quinine sulfate in 0.5 M
H2SO4 solutions with a quantum yield of 0.546 as the refer-
ence compound, respectively. The initial concentration of
copolymers in THF was 1.0 mg/mL, and the volume fraction
of water in water-THF mixture was 34%. The experiments
were repeated three times and the final values of the quan-
tum yields were reported as the average within a deviation
of 60.01. The size of micelles were determined using laser
light scattering (LLS). The micellar solutions were filtered
through a 0.45 lm syringe filter before measurements. The
LLS experiments were conducted using a Brookhaven Instru-
ment coupled with a BI-200SM goniometer, a BI-9000AT cor-
relator, and a BI-APD for photon counting. Both the scatter-
ing intensity and hydrodynamic diameter were measured at
Synthesis of Poly(6-{6-[(4-dimethylamino) phenylazo]-
indazole}-hexyl methacrylate)
The typical procedures for the preparation of PDHMA are
as following: a master batch of DHMA (0.82 g, 2.00
mmol), AIBN (1.64 mg, 0.02 mmol), and CPDN (8.14 mg,
0.06 mmol) was dissolved in 1.5 mL of toluene in one
ampule. The contents were purged with argon for 10 min
to eliminate the oxygen. Then, the ampules were flame
sealed and placed in an oil bath held by a thermostat at
60 ꢀC to polymerize. At designed time interval, the tube
was cooled in ice water and then opened. The polymer
were purified by precipitating twice from THF to methanol
and dried in a vacuum oven overnight at 50 ꢀC. The con-
version of polymerization was determined gravimetrically.
The other homopolymers with different molecular weights
were obtained by changing molar ratio between monomer
and CPDN or reaction time with the similar procedures
above.
ꢀ
a scattering angle of 90ꢀ at 20 C. Transmission electron mi-
croscopy (TEM) was recorded on Tecnai G2-20 TEM at a
120 kV accelerating voltage.
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extension experiment in anisole solution at 70 ꢀC using
PDHMA as the macro-RAFT agent, AIBN as the initiator, and
DMAEMA as the second monomer. Three amphiphilic block
copolymers (called as P57, P100, and P148, respectively)
with different ratio of PDHMA/PDMAEMA were obtained as
shown in Table 1 (entries 4–6). The GPC elution curves (C–E
in Fig. 1) of three amphiphilic block copolymers (P57, P100,
and P148) also showed that the well-controlled copolymers
were successfully obtained.
The typical 1H NMR spectra of the homopolymer PDHMA22
and amphiphilic block copolymer PDHMA33-b-PDMAEMA57
1
in CDCl3 were given in Figure 2. Compared with the H NMR
spectrum of PDHMA22, the appearance of typical peaks of
DMAEMA units (h, i, and j) confirmed the successful prepara-
tion of the amphiphilic block copolymer PDHMA33-b-
PDMAEMA57. The polymerization degrees (DP) of PDMAEMA
blocks were calculated from the recorded 1H NMR spectra
by comparing the relative integration values of the methyl-
ene protons (h) adjacent to nitrogen atom of PDMAEMA
block at d ¼ 2.56 ppm and methyl protons (d) adjacent to
nitrogen atom of PDHMA block at d ¼ 2.90 ppm, molecular
weight of macro-RAFT agent are known, which was shown
in Table 1 (entries 4–6). As can be seen from Table 1
(entries 4–6), the DP of PDMAEMA is 57 for PDHMA33-b-
PDMAEMA57 (P57), 100 for PDHMA31-b-PDMAEMA100
(P100), and 148 for PDHMA31-b-PDMAEMA148 (P148),
respectively.
FIGURE 1 The GPC curves of homopolymers and coplymers.
(A): PDHMA31 (Mn(GPC) ¼ 13,850 g/mol, Mw/Mn ¼ 1.19); (B):
PDHMA33 (Mn(GPC)
¼
14,700 g/mol, Mw/Mn
¼
1.26); (C):
PDHMA33-b-PDMAEMA57 (Mn(GPC) ¼ 18,250 g/mol, Mw/Mn
¼
1.43); (D): PDHMA31-b-PDMAEMA100 (Mn(GPC) ¼ 21,520 g/mol,
Mw/Mn ¼ 1.41); and (E): PDHMA31-b-PDMAEMA148 (Mn(GPC)
26,620 g/mol, Mw/Mn ¼ 1.47).
¼
RESULTS AND DISCUSSION
Preparation and Characterization of Homopolymer
(PDHMA) and Amphiphilic Copolymers (PDHMAm-b-
PDMAEMAn)
The general synthetic routes of the homopolymer, PDHMA,
and amphiphilic diblock copolymer, PDHMAm-b-PDMAEMAn,
are presented in Scheme 1. First, homopolymer (PDHMA)
was synthesized via RAFT polymerization of DHMA in tolu-
ene solution at 60 ꢀC using CPDN as the RAFT agent and
AIBN as the initiator. The polymerization results of three
homopolymers (PDHMA22, PDHMA31, and PDHMA33) were
given in Table 1 (entries 1–3) and in Figure 1 (A and B), and
Supporting Information Figure S3. The GPC elution curves
(Fig. 1(A and B) and Supporting Information Fig. S3) of three
homopolymers exhibited narrow and symmetric shapes with
relatively narrow molecular weight distributions (Mw/Mn),
which confirmed the successful preparation of the well-con-
trolled PDHMAs. The amphiphilic block copolymers,
PDHMAm-b-PDMAEMAn, were then prepared via RAFT chain-
Light-Driven Fluorescence Emission
Although indazole is a well-known fluorescent chromophore
group, the CH2Cl2 solutions of monomer (DHMA) and its
polymers (PDHMA, PDHMAm-b-PDMAEMAn) were virtually
nonfluorescent. The reason is that the fluorescent emissions
of DHMA and its polymers were quenched by azo group af-
ter indazole was coupled with phenyl azo group. However,
the intense fluorescent emission was found from the non-
fluorescent CH2Cl2 solutions of monomer (data not shown
here) and its polymers after continuous 365 nm light irradia-
tion. Here, we focused on investigating the fluorescent
behaviors of homopolymer and copolymers accompanied by
trans–cis photoisomerization of azoindazole group.
TABLE 1 Macromolecular Characteristics of Homopolymer (PDHMA) and Amphiphilic Block
Copolymers (PDHMAm-b-PDMAEMAn)
[Monomer]0/
Time
(h)
Mn(GPC)
Entry
[AIBN]0/[CPDN]0
(g/mol)
Mw/Mn
m
n
PDHMA22
100/1/3
200/1/3
200/1/3
500/1/3
500/1/3
500/1/3
12
2
9650
13,850
14,700
18,250
21,520
26,620
1.17
1.20
1.26
1.43
1.41
1.47
22
31
33
33
31
31
-
-
-
PDHMA31
PDHMA33
3
PDHMA33-b-PDMAEMA57 (P57)
PDHMA31-b-PDMAEMA100 (P100)
PDHMA31-b-PDMAEMA148 (P148)
3.5
3.5
4.0
57
100
148
m, polymerization degree (DP) of PDHMA; n, DP of PDMAEMA; Mn(GPC), number-average molecular weight
measures by GPC using PMMA as the standard; Mw/Mn, molecular weight distribution measured by GPC;
AIBN, 2,20-azobisisobutyronitrile; CPDN, 2-cyanoprop-2-yl-1-dithionaphthalate; PDHMA, poly(6-{6-[(4-dimethy-
lamino) phenylazo]-indazole}-hexyl methacrylate); PDMAEMA, poly(2-(dimethylamino)ethylmethacrylate).
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FIGURE 2 1H NMR spectra of homopolymer (PDHMA22) and copolymer (PDHMA33-b-PDMAEMA57) in CDCl3 with TMS as internal stand-
ard. (A): PDHMA22 (Mn(GPC) ¼ 9650 g/mol, Mw/Mn ¼ 1.17) and (B) PDHMA33-b-PDMAEMA57 (Mn(GPC) ¼ 18,250 g/mol, Mw/Mn ¼ 1.43).
Homopolymer PDHMA in CH2Cl2 was irradiated with 365 nm
light at room temperature for different time until the photo-
stationary state was reached. The UV–vis spectra of PDHMA
in CH2Cl2 were recorded as shown in Figure 3(a). In Figure
3(a), the absorption intensity of the intense p–p* transition
band related to trans-azoindazole at about 420 nm decreased,
and the absorption intensity of the n–p* transition band
related to cis-azoindazole at about 550 nm gradually
increased with irradiation time. The process of trans-to-cis
photoisomerization of azoindazole in PDHMA chain needed
170 min irradiation to reach its photostationary equilibrium.
Meanwhile, the fluorescence emission of PDHMA in CH2Cl2
under irradiation with 365 nm light was also investigated.
Figure 3(b) presented the fluorescent spectra of PDHMA in
CH2Cl2 with different irradiation time using 365 nm light. The
fluorescent intensity of PDHMA solution in CH2Cl2 centered at
620 nm (kex ¼ 550 nm) increased with the irradiation time.
and the results were shown in Figure 4(b). After 3 days re-
covery of cis-to-trans isomerization in the dark, the absorption
of the trans-azoindazole at about 420 nm increased, and the
absorption of the cis-azoindazole at about 550 nm obviously
decreased. After continuous 10 days recovery of cis-to-trans
isomerization in the dark, the absorption of the trans-azoinda-
zole increased to the initial value before UV irradiation, and
the absorption of the cis-azoindazole reduced to a very low
value. Until continuous 15 days recovery of cis-to-trans isom-
erization in the dark, the absorption of the cis- and trans-
azoindazole almost remain unchanged because of the achieve-
ment of its equilibrium state. The UV–vis absorption of
PDHMA22 in CH2Cl2 accompanied by recovery of cis-to-trans
isomerization in the dark are basically consistent with corre-
sponding fluorescence emission, which was fully proved that
the fluorescence emission was originated from the cis configu-
ration of azoindazole group in PDHMA chain.
The fluorescence emission of PDHMA22 in CH2Cl2 accompa-
nied by recovery of cis-to-trans isomerization in the dark
were also investigated as given in Figure 4. Interestingly, the
fluorescent intensity of PDHMA in CH2Cl2 was found
decreased to 1/10 of original value at the trans-to-cis photo-
stationary state after the recovery of 15 days in the dark, as
shown in Figure 4(a). The corresponding UV–vis absorption of
PDHMA22 in CH2Cl2 with a time in the dark was also studied,
It is worth noting that UV irradiation for a long time may
cause decomposition of polymer chain. Thus, the PDHMA in
deuterated CH2Cl2 before and after UV irradiation was char-
1
acterized by H NMR spectra as given in Supporting Informa-
tion Figure S4. Supporting Information Figure S4 shows that
no obvious difference was detected after 170 min UV irradia-
tion, which implied that no decomposition reaction occurred
during the UV irradiation process.
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aggregates were found, which indicated that the fluorescence
emission of homopolymer and copolymers after the 365 nm
light irradiation were not due to the aggregation. According
to the literature reported,9 the fluorescence emission of
PDHMA and its copolymers accompanied by trans-to-cis pho-
toisomerization may be explained by the mechanism of inhi-
bition of PET. The nonplanar bent-shaped cis form of azoin-
dazole obstructs the effective conjugation of lone pair of
electrons on azo group with the pi electrons in indazole
group, which causes the fluorescence emission.
Aggregation-Induced Fluorescence Emission
AIE of azobenzene-containing polymers were also
reported.11–14 The fluorescent behaviors of amphiphilic
diblock copolymers in mixture of water-THF were studied.
Most interestingly, the copolymers (P57, P100, and P148)
showed the intense fluorescence emission at about 540 nm
(kex ¼ 495 nm) when the water (poor solvent) was added
into the THF solution of the copolymers, respectively. The
FIGURE 3 UV–vis spectra (a) and fluorescence emission spectra
(b) (kex ¼ 550 nm) of PDHMA22 (Mn(GPC) ¼ 9650 g/mol and Mw/
Mn ¼ 1.17) in CH2Cl2 as a function of irradiation time with 365-
nm light at ambient temperature. The concentration of polymer
solution was 2.2 ꢁ 10ꢂ2 mg/mL.
Similarly, the UV–vis spectra of three copolymers PDHMAm-b-
PDMAEMAn (P57, P100, and P148) in CH2Cl2 were also
recorded before and after UV irradiation under the same con-
dition of homopolymer PDHMA as shown in Supporting Infor-
mation Figure S5. The change of UV–vis spectra of P57, P100,
and P148 were similar to that of homopolymer. However, it is
interesting to find that the absorption peaks for P57 and
P100 centered at about 550 nm became detectable after 60
min irradiation with 365 nm light, but 90 min for P148. This
phenomenon explained that long PDMAEMA block chains in
copolymers hinder the photoisomerization of the azoindazole
group.9 On the other hand, the fluorescence emission of three
copolymers centered at 620 nm (the inset part in Supporting
Information Fig. S5) also increased with the irradiation time,
which is similar to that of homopolymer PDHMA. However,
the fluorescent intensity of three copolymers are lower than
that of homopolymer PDHMA after the same irradiation time,
which may be attributed to that the concentrations of azoin-
dazole in copolymers were lower than that of homopolymer
PDHMA as shown in Supporting Information Table S1.
FIGURE 4 Fluorescence emission spectra (kex ¼ 550 nm) (a) and
UV–vis spectra (b) of PDHMA22 (Mn(GPC) ¼ 9650 g/mol, Mw/Mn
¼
1.17) in CH2Cl2 as a function of recovery time in the dark. (A) UV-
irradiation for 170 min (at the trans-to-cis photostationary state);
(B) 3 days recovery in the dark; (C) 10 days recovery in the dark;
and (D) 15 days recovery in the dark. The concentration of poly-
mer solution was 2.2 ꢁ 10ꢂ2 mg/mL. [Color figure can be viewed
in the online issue, which is available at wileyonlinelibrary.com.]
The solutions of homopolymer and copolymers after UV light
irradiation were examined by LLS and TEM to confirm
the origin of the fluorescence emission. As a result, no
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FIGURE 5 The fluorescence emission spectra (kex ¼ 495 nm) of copolymers on addition of water into THF solution of three copoly-
mers, P57 (a), P100 (b), and P148 (c). Changes of maximum values of fluorescence emission of three copolymers as water fraction
in water/THF mixture (d). The initial concentrations of copolymers in THF were 1.0 mg/mL. [Color figure can be viewed in the
online issue, which is available at wileyonlinelibrary.com.]
fluorescent intensities of three copolymers are gradually
increased with the increasing water content in the mixture
as presented in Figure 5(a–c). The fluorescent emissions of
P57 and P100 were centered at 540 nm, before and after
the addition of water [Fig. 5(a) and (b)], but the fluorescence
emission of P148 centered at 540 nm had a subtle blue shift
(about 7 nm) when the water content increased from 29 to
50% in Figure 5(c). The changes of maximum value of fluo-
rescent emission of three copolymers as a function of water
fraction were given in Figure 5(d). For P57, the fluorescence
emission was significantly enhanced by 480-fold when the
water content increased from 13 to 34%, and no obvious
enhancement was observed with further addition of water to
about 50%. The quantum yield of P57 in THF (the initial
concentration was 1.0 mg/mL) was determined to be about
1.05 ꢁ 10ꢂ5. The quantum yield of the micellar solution was
enhanced to about 2.36 ꢁ 10ꢂ3 after addition of 34% (v/v)
water in water-THF mixture.
FIGURE 6 TEM images of P57 (a), P100 (b), and P148 (c) in water/THF mixture (50% volume fraction of water). The inset part of
TEM images of (a), (b), and (c) is the photographs of P57, P100, and P148 in water/THF mixture (50% volume fraction of water),
respectively. The initial concentrations of three copolymers in THF were 1.0 mg/mL.
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ined by TEM as shown in Figure 6. The aggregates with
vesicle structures of three copolymers were found. The forma-
tion of the vesicles was attributed to the aggregate formation
for the hydrophobic PDHMA block in the mixtures. The aggre-
gates sizes in diameter is ꢃ500–1,200 nm for P57 [Fig. 6(a)],
200–360 nm for P100 [Fig. 6(b)], and 120–180 nm for P148
[Fig. 6(c)]. The aggregates sizes decreased in the following
order, P57 > P100 > P148, which demonstrated that the
aggregation became weak along with the increase of
PDMAEMA chain length. The turbidities of copolymers in
water-THF mixture (50% volume fraction of water) also
became weak with the increase of PDMAEMA chain length as
shown in Figure 6 (the inset part). The sizes of three copoly-
mers aggregates in water-THF mixture were further moni-
tored by LLS; TEM image only showed aggregates morphology
of copolymers in dry state. The hydrodynamic diameter distri-
butions for three copolymers were shown in Figure 7. The
26% water content (v/v) in water-THF mixture was chosen to
measure the aggregates size of P57 because of the high tur-
bidity of P57 in the mixed solvent when the water content in
mixture solvent exceeds 26%. The 50% water content (v/v)
in water-THF mixture was used to investigate aggregate sizes
of other two copolymers. It can be seen in Figure 7 that an
average diameter of 2240 nm for P57, 430 nm for P100, and
FIGURE 7 The hydrodynamic diameter distribution of the aggre-
gates of three copolymers in water/THF mixture: P57 (a) at 26%
water content (v/v) in water/THF mixture; P100 (b) and P148 (c)
at 50% water content (v/v) in the mixture solvent. The initial
concentrations of three copolymers in THF were 1.0 mg/mL.
Compared to P57 under the same conditions, the relatively
weak enhancement of other two copolymers was obtained. The
fluorescence enhancement of P100 showed only 100-fold when
the water content increased from 12 to ꢃ36%. 60-fold enhance-
ment for P148 was obtained when the water content increased
from 19 to 41%. The possible reason was that the different
chain lengths of PDMAEMAs influenced the aggregation behav-
iors of corresponding copolymers in the mixed solvent.14a,23
FIGURE 8 (a) Changes of maximum values of fluorescence
emission (kex ¼ 495 nm) of copolymer P57 as a function of
water in water/THF mixture and (b) The hydrodynamic diame-
ter distribution of P57 with 50% water content (v/v) in water/
THF mixture. The initial concentration of polymer in THF was
2.2 ꢁ 10ꢂ2 mg/mL.
To investigate the relationship between self-assembly behav-
iors and the fluorescence emission, the aggregate morpholo-
gies of three copolymers (THF/water ¼ 1/1, v/v) were exam-
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light, as shown in Supporting Information; Figure S6(a). The
fluorescence emission had a slight decrease after UV irradia-
tion prolonged to 100 min for the trans-to-cis photoisomeri-
zation. After subsequent visible light (550 nm) irradiation
for 190 min for the reverse of cis-to-trans photoisomeriza-
tion, the fluorescence emission raised a little again.
The aggregate size of copolymers should be very important for
its fluorescence emission,8,10 so the change of aggregates size
of copolymers in THF-water mixture on irradiation was meas-
ured as shown in Supporting Information Figure S6(b). The
hydrodynamic diameter distributions of aggregates size had a
slight decrease after UV irradiation and a slight increase again
after subsequent visible light irradiation. The bent shape of cis
form of azobenzene was more or less hydrophilic relative to
that of rod-shaped trans isomers, which can lead to the change
in the aggregate size of micelles or vesicles.13,24 The hydro-
philic–hydrophobic balance of copolymers in THF-water mix-
ture was affected by the change of cis and trans forms of
azoindazole moieties; however, a severe confinement of the
aggregation structure may hinder the isomerization of azoinda-
zole. Thus, with a smaller size change, the aggregation and low
sensitivity of fluorescence emission on irradiation with differ-
ent wavelength light were observed in current system.
FIGURE 9 UV–vis spectra of three copolymers in THF before
and after addition of water (50% water content (v/v) in water/
THF mixture). A–C: before addition of water; a–c: after addition
of water. P57: (A), (a); P100: (B) (b); P148 (C), (c). The initial
concentrations of all the copolymers in THF were 0.10 mg/mL.
[Color figure can be viewed in the online issue, which is avail-
able at wileyonlinelibrary.com.]
520 nm for P148 was obtained, respectively. The average
diameters of three copolymers were all higher than those of
the dried samples obtained by TEM, which were attributed to
the dry shrinking of the samples in dry state.
UV–vis spectra of P57, P100, and P148 in THF solution (0.1
mg/mL) before and after addition of water (50%, v/v) were
shown in Figure 9. Compared to the corresponding copoly-
mer solutions in THF, the position of maximum absorption
of three copolymers had bathochromic shift on addition of
water. For example, the red shift of P57 was about 7 nm
(from 419 to 426 nm). The results showed that the type of
aggregation morphology of copolymer was the J-aggregation
in mixed solvent.8,25 The bulky indazole group in side chain
may tend to form the head-to-tail intermolecular interac-
tions, which resulted in the formation of J-aggregation.
The initial concentration of the copolymer in THF had an
obvious effect on its self-assembly and fluorescent emission
behavior. In case of P57, both the intensity of fluorescent
emission and the average diameter at initial concentration of
0.22 mg/mL (Fig. 8) were lower than those of 1.0 mg/mL as
shown in Figures 5(a) and 7(a). Interestingly, the fluorescent
emission disappeared when the initial concentration of P57
in THF was decreased to 2.2 ꢁ 10ꢂ2 mg/mL. The reason
was that the aggregation became weaker at the relatively
lower initial concentration of copolymer.
Aggregation-induced unusual fluorescence emission in this
work allowed us to consider the restriction of intramolecular
rotation (RIR) in the aggregates as the possible mechanism.15
First, the azoindazole group in solution is easy to undergo the
trans-to-cis photoisomerization process, which serves as a
nonradiative relaxation channel for the excited azoindazole to
return to their ground state. However, when this nonradiative
relaxation channel was restricted by packing the azoindazole
moieties into aggregates, the radiative process, such as the flu-
orescent emission was induced. Second, the conformation of
bulky pendant azoindazole groups in the aggregates can be
severely twisted by RIR, so the effective conjugation of p-elec-
tron pair on azoindazole group is disastrously jeopardized,
which causes fluorescence emission. The exact reason of un-
usual intense fluorescence emission induced by the aggrega-
tion in this work needs further investigation.
On the basis of above results, the relatively higher initial con-
centration of copolymer in THF, such as 1.0 mg/mL of copoly-
mer P57, was in favor of the formation of aggregates with big-
ger sizes, and induced stronger fluorescence emission
compared with those at relatively lower concentrations. How-
ever, it was noticeable that when the initial concentration of co-
polymer P57 in THF was higher than 1.0 mg/mL, any further
fluorescence emission cannot be observed, which was due to
the concentration quenching of fluorescence emission. The fur-
ther experiment work is being in progress in our laboratory.
The fluorescence emission (kex ¼ 475 nm) of P57 in THF-
water mixture (THF-water ¼ 1/1, v/v) for the trans-to-cis
and the reverse of cis-to-trans isomerization of azoindazole
moieties were investigated before and after UV (365 nm)
irradiation, after subsequent visible light (550 nm) irradia-
tion, respectively. The initial concentration of P57 in THF
was 2.2 ꢁ 10ꢂ1 mg/mL. The fluorescence emission of micel-
lar solution of copolymers in THF-water mixture showed a
smaller sensitivity for both the irradiation of UV and visible
CONCLUSIONS
In summary, we have successfully synthesized the azoinda-
zole-containing homopolymer and diblock amphiphilic
copolymers via RAFT technique. The unusual fluorescence
emissions of these polymers were observed from trans-to-cis
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miche, L.; Nakatani, K. Chem Mater 2006, 18, 1261–1267; (c)
Wang, D. R.; Ye, G.; Zhu, Y.; Wang, X. G. Macromolecules
2009, 42, 2651–2657; (d) Kulikovska, Q.; Goldenberg, L. M.; Kuli-
kovsky, L.; Stumpe, J. Chem Mater 2008, 20, 3528–3534.
photoisomerization and self-assembly or aggregation. The
light-driven fluorescence emission accompanying by trans-to-
cis photoisomerization was attributed to an inhibition of PET
of cis form. The aggregation-induced emission phenomenon
may be due to the RIR mechanisms. The intensity of fluores-
cence emission increased with the aggregates size. The
unusal light-driven and aggregation-induced intense fluores-
cence emission of the well-defined homopolymer and diblock
amphiphilic copolymers containing pendent azoindazole
groups will expand versatility of azobenzene compounds for
the applications in biomaterials and optical materials.
7 Zacharias, P. S.; Ameerunisha, S.; Korupoju, S. R. J Chem
Soc Perkin Trans 1998, 2, 2055–2059.
8 (a) Han, M.; Hara, M.
J Am Chem Soc 2005, 127,
10951–10955; (b) Han, M. R.; Hirayama, Y.; Hara, M. Chem
Mater 2006, 18, 2784–2786.
9 Smitha, P.; Asha, S. K. J Phys Chem B 2007, 111, 6364–6373.
10 Ma, F.; Zhou, N. C.; Zhu, J.; Zhang, W.; Fan, L. J.; Zhu, X. L.
Eur Polym J 2009, 45, 2131–2137.
The financial support from the National Natural Science
Foundation of China (Nos. 20874069, 50803044, 20974071,
20904036, 21074080, 21074082 and 21104052), the Special-
ized Research Fund for the Doctoral Program of Higher Educa-
11 Shimomura, M.; Kunitake, T. J Am Chem Soc 1987, 109,
5175–5183.
12 Tsuda, K.; Dol, G. C.; Gensch, T.; Hofkens, J.; Latterini, L.;
Weener, J. W.; Meijer, E. W.; Schryver, F. C.; J Am Chem Soc
2000, 122, 3445–3452.
tion
contract
grant
(Nos.
200802850005
and
13 Bo, Q.; Zhao, Y. Langmuir 2007, 23, 5746–5751.
20103201110005), the Applied and Fundamental Research
Project (Industrial Part) of Suzhou Science and Technology
(SYG201026), the open project from Jiangsu Key Laboratory for
Carbon-Based Functional Materials & Devices (SUDA-JSCFMD-
09-02), the Qing Lan Project, the Program of Innovative
Research Team of Soochow University, and a Project Funded by
the Priority Academic Program Development of Jiangsu Higher
Education Institutions (PAPD) is gratefully acknowledged.
14 (a) Xu, J.; Zhang, W.; Zhou, N. C.; Zhu, J.; Cheng, Z. P.; Xu,
Y.; Zhu, X. L. J Polym Sci A: Polym Chem 2008, 46, 5652–5662;
(b) Xiang, Y.; Xue, X. Q.; Zhu, J.; Zhang, Z. B.; Zhang, W.;
Zhou, N. C.; Zhu, X. L. Polym Chem 2010, 1, 1453–1457.
15 (a) Luo, J. D.; Xie, Z. L.; Lam, J. W. Y.; Cheng, L.; Chen, H. Y.;
Qiu, C. F.; Kwok, H. S.; Zhan, X. W.; Liu, Y. Q.; Zhu, D. B.; Tang,
B. Z. Chem Commun 2001, 18, 1740–1741; (b) Hong, Y. N.; Lam,
J. W. Y.; Tang, B. Z. Chem Commun 2009, 29, 4332–4353.
16 (a) Saminathan, M.; Pillai, C. Macromol Chem Phys 2000, 201,
2475–2483; (b) Ho, M. S.; Natansohn, A.; Rochon, P. Macromole-
cules 1995, 28, 6124–6127; (c) Meng, X.; Natansohn, A.; Rochon,
P. Polymer 1997, 38, 2677–2682; (d) Chen, J. P.; Gao, C. J.;
Wang, Z. Y. J Polym Sci A: Polym Chem 1997, 35, 9–16; (e) Lam-
beth, R. H.; Moore, J. S. Macromolecules 2007, 40, 1838–1842.
REFERENCES AND NOTES
1 (a) Kumar, G. S.; Neckers, D. C. Chem Rev 1989, 89,
1915–1925; (b) Brown, D., Natansohn, A.; Rochon, P. Macromo-
lecules 1995, 28, 6116–6123; (c) Ziker, S. J.; Bieringer, T.;
Haarer, S.; Stein, R. S.; Van Egmond, J. W.; Kostromine, S. G.
Adv Mater 1998, 10, 855–859; (d) Natansohn, A.; Rochon, P.
Chem Rev 2002, 102, 4139–4175; (e) Delaire, J. A.; Nakatani, K.;
Chem Rev 2000, 100, 1817–1845; (f) Barrett, C. J.; Mamiya, J.;
Yagerc, K. G.; Ikeda, T. Soft Mater 2007, 3, 1249–1261; (g) Zhao,
Y.; He, J. Soft Mater 2009, 5, 2686–2693.
17 (a) Matyjaszewski, K.; Xia, J. H. Chem Rev 2001, 101,
2921–2990; (b) Kamigaito, M.; Ando, T.; Sawamoto, M. Chem
Rev 2001, 101, 3689–3745.
18 Hawker, C. J.; Bosman, A. W.; Harth, E. Chem Rev 2001,
101, 3661–3688.
19 Moad, G.; Rizzardo, E.; Thang, S. H. Aust J Chem 2005, 58,
379–410.
2 (a) Pedersen, T. G.; Johansen, P. M.; Pedersen, H. C. J Opt A:
Pure Appl Opt 2000, 2, 272–278; (b) Rasmussen, P. H.; Ramanu-
jam, P. S.; Hvilsted, S.; Berg, R. H. J Am Chem Soc 1999, 121,
4738–4743.
20 Percec, V.; Guliashvili, T.; Ladislaw, J. S.; Wistrand, A.;
Stjerndahl, A.; Sienkowska, M. J.; Monteiro, M. J.; Sahoo, S. J
Am Chem Soc 2006, 128, 14156–14165.
3 (a) Hore, D.; Natansohn, A.; Rochon, P.; J Phys Chem B 2003,
107, 2197–2204; (b) Cui, L.; Zhao, Y. Chem Mater 2004, 16,
2076–2082; (c) Acierno, D.; Amendola, E.; Bugatti, V.; Concilio,
S.; Giorgini, L.; Iannelli, P.; Piotto, S. P. Macromolecules 2004,
37, 6418–6423; (d) Han, Y. K.; Dufour, B.; Wu, W.; Kowalewski,
T.; Matyjaszewski, K. Macromolecules 2004, 37, 9355–9365; (e)
Yu, H. F.; Naka, Y.; Shishido, A.; Ikeda, T. Macromolecules
2008, 41, 7959–7966; (f) Han, D. H.; Tong, X.; Zhao, Y.; Zhao, Y.
Angew Chem Int Ed 2010, 49, 9162–9165.
21 (a) Tian, Y. Q.; Watanabe, K.; Kong, X. X.; Abe, J.; Iyoda, T.
Macromolecules 2002, 35, 3739–3747; (b) He, X. H.; Yan, D.Y.
Macromol Rapid Commun 2004, 25, 949–953; (c) Cui, L.; Zhao, Y.;
Yavrian, A.; Galstian, T. Macromolecules 2003, 36, 8246–8252.
22 Yu, L. P.; Zhang, Z. B.; Chen, X. R.; Zhang, W.; Wu, J. H.;
Cheng, Z. P.; Zhu, J.; Zhu, X. L. J Polym Sci A: Polym Chem
2008, 46, 682–691.
23 (a) You, Y. Z.; Zhou, Q. H.; Manickam, D. S.; Wan, L.; Mao,
G. Z.; Oupicky, D. Macromolecules 2007, 40, 8617–8624; (b)
Bougard, F.; Jeusette, M.; Mespouille, L.; Dubois, P.; Lazzaroni,
R. Langmuir 2007, 23, 2339–2345; (c) Mao, J.; Ni, P.; Mai, Y.;
Yan, D. Langmuir 2007, 23, 5127–5134.
4 (a) Yu, Y. L.; Nakano, M.; Ikeda, T. Nature 2003, 425, 145; (b)
Kondo, M.; Yu, Y. L.; Ikeda, T. Angew Chem Int Ed 2006, 45,
1378–1382; (c) Cheng, F. T.; Yin, R. Y.; Zhang, Y. Y.; Yen, C. C.; Yu,
Y. L.; Soft Mater 2010, 6, 3447–3449; (d) Cheng, F. T.; Zhang, Y. Y.;
Yin, R. Y.; Yu, Y. L. J Mater Chem 2010, 20, 4888–4896.
24 Zhao, Y. and Ikeda, T. Smart Light-Responsive Materials:
Azobenzene-Containing Polymers and Liquid Crystal, Wiley:
New Jersey, 2009, pp. 215–239.
5 Chen, X. B.; Zhang, Y. H.; Liu, B. J.; Zhang, J. J.; Wang, H.;
Zhang, W. Y.; Chen, Q. D.; Pei, S. H.; Jiang, Z. H. J Mater Chem
2008, 18, 5019–5026.
25 (a) Jelly, E. E. Nature 1936, 138, 1009–1010; (b) Jelly, E. E.
Nature 1937, 139, 631–632; (c) Scheibe, G. Angew Chem Int Ed
1936, 49, 563–563; (d) Scheibe, G. Angew Chem Int Ed 1937, 50,
51–51; (e) Kasha, M. Photochem Photobiol 1964, 3, 317–331; (f)
Kasha, M.; Rawls, H. Pure Appl Chem 1965, 11, 371–392.
6 (a) Zhang, Y. Y.; Cheng, Z. P.; Chen, X. R.; Zhang, W.; Wu, J.
H.; Zhu, J.; Zhu, X. L. Macromolecules 2007, 40, 4809–4817; (b)
Ishow, E.; Lebon, B.; He, Y. N.; Wang, X. G.; Bouteiller, L.; Gal-
4920
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