An efficient fluorescent sensor for redox active species based on novel poly(aryl ether) containing electroactive pendant

Article abstract of DOI:10.1039/c1jm13422a

We describe the synthesis of a novel poly(aryl ether), containing pendant oligoaniline and anthracene moieties (PAE-p-OA), and both side chains present in equal amounts. Structures were confirmed spectroscopically via nuclear magnetic resonance (NMR), mor

Full text of DOI:10.1039/c1jm13422a

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PAPER
An efficient fluorescent sensor for redox active species based on novel poly
(aryl ether) containing electroactive pendant
a
c
a
a
b
a
Danming Chao,ab Xiaoteng Jia, Fuquan Bai, Hongtao Liu, Lili Cui, Erik B. Berda and Ce Wang
*
*
Received 19th July 2011, Accepted 1st November 2011
DOI: 10.1039/c1jm13422a
We describe the synthesis of a novel poly(aryl ether), containing pendant oligoaniline and anthracene
moieties (PAE-p-OA), and both side chains present in equal amounts. Structures were confirmed
spectroscopically via nuclear magnetic resonance (NMR), morphological data ascertained via X-ray
diffraction (XRD), and thermal stability probed via thermogravimetric analysis (TGA).
Electrochemical and photophysical properties were also investigated using cyclic voltammetry and
UV-Vis and fluorescence spectroscopy. This material exhibits an interesting fluorescent response to
redox active species. When PAE-p-OA is in the reduced state, oxidative materials interact with the
oligoaniline side chains resulting in a progression from leucoemeraldine base (LEB) to the emeraldine
base (EB). The resulting change in molecular conformation of the oliganiline unit increases its
propensity for interaction with the anthracene side chain (corroborated by molecular modeling),
leading to decreased fluorescence via quenching and thus ‘‘turn off’’ fluorescence sensing. When
PAE-p-OA is in the oxidized state, reduction of the oligoaniline from the EB to the LEB via interaction
with a reductive species delivers ‘‘turn on’’ fluorescence sensing via decreased interaction between the
oligoaniline and anthracene side chains, again due to a change in the molecular conformation of
oligoaniline.
methods, which demand rapid, convenient and low cost detec-
tion for the redox active species.
Introduction
Redox active species are widely found in our environment,
species such as Fe3+, Mn4+, S2ꢀ in the earth and soil,1,2 Cl2, ClOꢀ,
As3+ in drinking water,3,4 H2O2, NO, O2_ꢀ in living organisms.5
Due to their toxicity, reactivity and/or importance, it is desirable
to develop efficient means for detecting the presence of such types
of materials. Traditional analytical methods used for detection of
these materials are atomic absorption spectroscopy, inductively
coupled plasma mass spectrometry, spectrophotometric analysis
and electrochemical schemes, which depend on the specificity of
each analyte.6,7 Although accurate and sensitive analysis is
supplied by these methods, they require complicated procedures,
rigorous experimental conditions, and sophisticated equipment.
It is therefore increasingly of interest to develop new analysis
Fluorescent sensors based on conjugated polymers have
attracted great academic and commercial interest in the fields of
biological, chemical, food and environmental science8–15 due to
their real-time detection, high sensitivity, and good stability.16,17
Until now, few fluorescent polymer sensors exclusively for
detection of redox active species have been reported.18,19 Due to
their novelty and effectiveness, there is a need for fluorescent
sensors to detect redox active species.
We have recently reported the preparation and properties of
an unconjugated copolymer with oligoaniline and anthracene
groups in the main chain.20 An interesting feature of this
copolymer is an observed decrease in the fluorescence intensity
with the oxidation of oligoaniline from leucoemeraldine base
(LEB) to emeraldine base (EB). Taking advantage of the
reversible redox properties of oligoaniline, we surmised that an
oligoaniline unit and a fluorophore unit introduced into the
same polymer chain would provide a material that would be
useful as a fluorescent sensor for redox active species. Herein,
we describe a dual fluorescent sensor system based on a poly
(aryl ether) containing pendant oligoaniline and anthracene
moieties (PAE-p-OA), which can detect oxidative materials via
‘‘turn–off’’ fluorescence and reductive materials by ‘‘turn–on’’
fluorescence.
aAlan G. MacDiarmid Institute, College of Chemistry, Jilin University,
Changchun, 130012, P.R. China. E-mail: cwang@jlu.edu.cn; Fax: +86-
431-85168292; Tel: +86-431-85168292
bDepartment of Chemistry and Materials Science Program, University of
New Hampshire, Durham, NH, 03824, USA. E-mail: Erik.Berda@unh.
edu; Fax: +603-862-4278; Tel: +603-862-1762
cState Key Laboratory of Theoretical and Computational Chemistry,
Institute of Theoretical Chemistry, Jilin University, Changchun, 130023,
P.R. China
3028 | J. Mater. Chem., 2012, 22, 3028–3034
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d ¼ 10.51 (s, 1H, due to –CONH–), d ¼ 7.80 (s, 1H, due to –
NH–), d ¼ 7.77 (s, 1H, due to –NH–), d ¼ 7.65 (s, 1H, due to
–NH–), d ¼ 7.56 (t, 1H, due to Ar–H), d ¼ 7.48 (d, 2H, due to Ar–
H), d ¼ 7.23 (t, 2H, due to Ar–H), d ¼ 7.14 (t, 2H, due to Ar–H),
d ¼ 6.96 (m, 12H, due to Ar–H), d ¼ 6.68(t, 1H, due to Ar–H).
Experimental
Materials
2,6-Difluorobenzoyl chloride, N-phenyl-p-phenylenediamine
and 2-aminoanthracene were purchased from Aldrich. 4,40-Iso-
propylidene diphenol were purchased from Shanghai Chemical
ꢁ
Synthesis of 2,6-difluorobenzoyl anthracene
Factory. K2CO3 was dried at 110 C for 24 h before used. All
other reagents were obtained from commercial sources and used
as received without further purification. Distilled and deionized
water was used.
A solution of 0.8828 g (5 mmol) 2,6-difluorobenzoyl chloride in
15 mL of dry tetrahydrofuran (THF) was added dropwise over
a period of 2 h to a stirring mixture of 2-aminoanthracene
(0.9662 g, 5 mmol) and triethylamine (2 mL) in 15 mL of THF.
The reaction, carried out in an atmosphere of dry nitrogen to
avoid oxidation of 2-aminoanthracene, proceeded readily at
room temperature, with the formation of a grey solution.
Following the addition of the solution of 2,6-difluorobenzoyl
chloride, the resulting solution was stirred for 1 h. Then the
solvent was removed at reduced pressure to give grey crude
product which was washed with methylene chloride two times,
filtered and dried under dynamic vacuum at 45 ꢁC for 24 h. The
white powder was obtained in 91% yield.
Measurement
Mass spectroscopy (MS) was performed on an AXIMA-CFR
laser desorption ionization flying time spectrometer
(COMPACT). Fourier-transform infrared spectra (FTIR)
measurements were recorded on a BRUKER VECTOR 22
Spectrometer by averaging 128 scans at a solution of 4 cmꢀ1 in the
range of 4000–400 cmꢀ1. The nuclear magnetic resonance spectra
(NMR) of 2,6-difluorobenzoyl aniline tetramer, 2,6-difluor-
obenzoyl anthracene and PAE-p-OA in deuterated dimethyl
sulfoxide (DMSO) were run on a BRUKER-500 spectrometer to
determine the chemical structure and tetramethylsilane was used
as the internal standard. The number-average molecular weight
(Mn), weight-average molecular weight (Mw), and molecular
weight distribution of PAE-p-OA were measured with a gel
permeation chromatography (GPC) instrument equipped with
a Shimadzu GPC-802D gel column and SPD-M10AVP detector
with N,N0-dimethylformamide as an eluent at a flow rate of 1 mL
minꢀ1. Calibration was accomplished with monodispersed poly-
styrene (PS) standards. X-ray powder diffraction (XRD) patterns
of PAE-p-OA were recorded on a Siemens D5005 diffractometer
using Cu-Ka radiation. A Perkin-Elmer PYRIS 1 TGA was used
to investigate the thermal stability of PAE-p-OA in the tempera-
ture range from 100 ꢁC to 700 ꢁC at a rate of 10.0 ꢁC minꢀ1 under
nitrogen protection. The cyclic voltammetry (CV) was performed
with a CHI 660A Electrochemical Workstation (CH Instruments,
USA) in a conventional three-electrode cell, by using PAE-p-OA
thin films cast from DMAc solutions onto a g-c electrode. The film
was cycled at 1.0 M H2SO4 aqueous solution in the range from
0 mV to + 1000 mV. UV-Vis spectra were performed on UV-2501
PC Spectrometer (SHIMADZU). Fluorescene spectra were
investigated on a fluorometer of SPEXF212 model (SPEX). The
individual fluorescence values given in the text are the average of
three measurements. The geometry structures of the model
molecules were fully optimized by B3LYP (Becke’s three param-
eter functional and the Lee–Yang–Parr functional) method21–23
with the 6-31G* basis set. All of the calculations were carried out
with Gaussian 09 software package24 on an IBM server.
MALDI-TOF-MS: m/z calculated for C21H13F2NO ¼ 333.3.
Found 332.6. FTIR (KBr, cmꢀ1): 3249 (s, nNH), 1655 (vs, nC ¼ O),
1591(vs, nC ¼ C of benzenoid rings), 1313 (s, nC–N), 1010(s, dCF),
1
889 (m, dCH), 739 (m, dCH). H NMR (d6-DMSO): d ¼ 11.09
(s, 1H, due to –CONH–), d ¼ 8.67 (s, 1H, due to Ar–H on
anthracene), d ¼ 8.55 (s, 2H, due to Ar–H on anthracene), d ¼
8.11 (m, 3H, due to Ar–H on anthracene), d ¼ 7.63 (m, 2H, due
to Ar–H), d ¼ 7.51 (m, 2H, due to Ar–H on anthracene), d ¼ 7.31
(t, 2H, due to Ar–H adjacent to Ar–F).
Synthesis of poly(aryl ether) containing pendant oligoaniline and
anthracene moieties (PAE-p-OA)
A typical synthesis procedure of polymer was as follows. A
mixture of NMP (20 mL), toluene (10 mL), anhydrous potassium
carbonate (0.8354 g), 2,6-difluorobenzoyl aniline tetramer
(1.520 g, 3 mmol), 2,6-difluorobenzoyl anthracene (1.000 g,
3 mmol), and 4,40-isopropylidene diphenol (1.370 g, 6 mmol)
were added to a 100 mL three-necked round-bottom flask and
heated to reflux under nitrogen with magnetic stirring for 2 h to
remove the water by azeotropic distillation with toluene, and the
toluene was then removed. The mixture was heated to reflux for
8 h to ensure the completion of the reaction. The solution was
cooled to room temperature and poured into 200 mL water,
which yielded a pearl blue precipitate. The precipitate was
washed with water and ethanol several times, filtered and dried
under dynamic vacuum at 40 ꢁC for 30 h. Yield: 87%.
Results and discussion
Synthesis of 2,6-difluorobenzoyl aniline tetramer
Synthesis and characterization of PAE-p-OA
The synthesis of 2,6-difluorobenzoyl aniline tetramer was con-
ducted according to the literature.25
The synthetic procedure for PAE-p-OA is depicted in Scheme 1.
The polymerization proceeded by K2CO3-mediated nucleophilic
aromatic polycondensation using 4,40-isopropylidene diphenol as
bisphenol monomer. The ratio of oligoaniline to anthracene is
about 0.5 : 0.5. The reaction temperature was first controlled at
140 ꢁC to remove the waterꢁby azeotropic distillation with toluene,
and then increased to 200 C to accomplish the polymerization.
MALDI-TOF-MS: m/z calculated for C31H24F2N4O ¼ 506.5.
Found 506.6. FTIR (KBr, cmꢀ1): 3369 (s, nNH), 3299 (s, nNH),
1657 (vs, nC ¼ O), 1600(s, nC ¼ C of benzenoid rings), 1525 (vs,
nC ¼ C of benzenoid rings), 1303 (s, nC–N), 1008(m, dCF), 817
1
(m, dCH), 746 (m, dCH), 692 (m, dCH). H NMR (d6-DMSO):
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Scheme 1 Synthesis of fluorescent PAE-p-OA.
The chemical structure of PAE-p-OA was confirmed by FTIR, 1H
NMR spectroscopy, GPC and XRD. FTIR spectra of PAE-p-OA
showed the characteristic absorption bonds around 3397 cmꢀ1
corresponding to N–H stretching vibration, around 2973 cmꢀ1
based on C–H stretching vibration of methyl groups and around
1633 cmꢀ1 due to C]O stretching vibration in aryl carbonyl
groups. The vibration at around 1603 cmꢀ1 and 1508 cmꢀ1 is
attributed to the stretching vibration of C]C in the benzene rings,
and the peak at 1232 cmꢀ1 can be assigned to the stretching
vibration of C–O–C of the aryl ether linkages. The bands at
1298 cmꢀ1(nC–N), 827 cmꢀ1(dCH), and 746cmꢀ1(dCH), based on the
structure ofoligoanilineand anthracene, were alsofound. Inthe 1H
NMR spectra of PAE-p-OA, the signals at d ¼ 10.87 and 10.24 are
assigned to proton of –CONH– from 2,6-difluorobenzoyl chloride
and 2,6-difluorobenzoyl aniline tetramer, the integral area ratio of
thetwopeaksisabout1, whichindicatethattheoligoanilinehasthe
same quantities with anthracene in the polymer chain. The signals
at d ¼ 7.90 ppm is attributed to the –NH– of the oligoaniline and
the signals around d ¼ 1.57ppm are ascribedto the methyl protons.
Furthermore, aromatic protons appeared at d ¼ 8.50–8.10 and d ¼
7.56–6.45. All of the 1H NMR signals support the proposed
molecular structure of PAE-p-OA. The number average molecular
weight (Mn) and the polydispersity index of PAE-p-OA, obtained
by GPC, are 33800 and 1.79. Moreover, PAE-p-OA exhibited
outstanding solubility in polar solvents such as THF, NMP,
DMAc, and DMSO due to the bulky pendant groups, which
impede the interchain entanglement to some extent.
corresponding to the decomposition of main chain. 5% and 10%
weigꢁht loss temperatures of the obtained polymer are 394 ꢁC and
445 C, respectively. It indicates that the obtained polymer has
good thermal stability and higher degradation temperature
compared with usual polyaniline materials,26 which will benefit
the useful life of optoelectronic devices.
Electrochemical activity
Fig. 3 shows the cyclic voltammetry of PAE-p-OA using Ag/Ag+
as the reference electrode with a scan rate of 50 mV sꢀ1. The
DMAc solution of PAE-p-OA was cast on the g-c working
electrode and was evaporated to form a thin solid film. Under
these conditions, the cyclic voltammetry of PAE-p-OA shows
two pairs of redox current peaks at 340 mV/210 mV, and 525 mV/
430 mV, which were respectively assigned to the transformation
of the LEB/EB, and the EB/PNB. Compared with conventional
polyaniline,27 the shift of the redox current peaks in the cyclic
voltammogram of PAE-p-OA was observed, which suggests that
the chemical structure plays an important role in the electro-
chemical behavior.
Photophysical properties
Photophysical properties of parent aniline tetramer, 2-amino-
anthracene and PAE-p-OA were characterized by UV-Vis
spectra and fluorescence emission spectra (Fig. 4). In the UV-Vis
spectra, parent aniline tetramer, 2-aminoanthracene and PAE-p-
OA in the DMAc are peaked at 325, 278 and 319 nm,
The wide-angle XRD patterns of PAE-p-OA (Fig. 1) shows
a broad peak, which is characteristic of the diffraction by
amorphous polymer. This is mainly due to the fact that the bulky
pendant oligoaniline and anthracene groups decrease the inter-
chain hydrogen bonding and p–p interactions and disturb the
close packing and regularity of the polymer chains. The amor-
phous structure is a basic requirement for spin-coated polymer
films, which are usually used in optoelectronic devices. Aggre-
gation and microcrystallization would greatly affect the forma-
tion of large-scale continuous film.
Thermal properties
The thermal properties of PAE-p-OA were evaluated by TGA
(Fig. 2). A single stage mass loss beginning at 330 ꢁC is observed
Fig. 1 The wide-angle XRD patterns of PAE-p-OA.
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Fig. 4 UV-Vis spectra and fluorescence emission spectra of PAE-p-OA,
Fig. 2 TGA thermograms of PAE-p-OA in N2.
parent aniline tetramer and 2-aminoanthracene in DMAc.
much attention compared with other conjugated polymers, due
to the low fluorescent essence and quenching by the quinoid units
in the oxidized states. The design described here uses this char-
acteristic as an advantage: if its emission quenching degree can be
modulated by oxidative degree of oligoaniline, then a fluorescent
response to redox active species should be possible.
The responsive properties of PAE-p-OA to redox active
species was investigated by UV-Vis and fluorescence spectros-
copy in a DMAc (containing 3 vol% H2O) solution at a polymer
repeat unit concentration of 1.0 ꢂ 10ꢀ5 M. Firstly, we investi-
gated its sensor properties for oxidative materials. The titrations
Fig. 3 Cyclic voltammograms of PAE-p-OA with a scan rate of
50 mV sꢀ1
2ꢀ
were carried out by adding 1.0 ꢂ 10ꢀ3 M oxidative S2O8 ions
.
DMAc (containing 3 vol% H2O) solution into PAE-p-OA solu-
tion with 20 min stirring at room temperature. Because of the
large differences between the two concentrations, the change of
polymer concentration after titration could be ignored. On
respectively, associated with p–p* transition in the conjugated
structure. 2-Aminoanthracene shows characteristic absorption
bands at 320, 337 and 355 nm. PAE-p-OA displays characteristic
absorption between 390 and 470 nm. In the fluorescence spectra,
parent aniline tetramer shows blue fluorescence at 440 nm
derived from benzenoid unites. Moreover, 2-aminoanthracene
and PAE-p-OA showed green emission with maximum at 502
and 512 nm, and anthracene units should be the main chromo-
phore in the polymer chain because of the low fluorescent essence
of the oligoaniline.28,29
2ꢀ
adding of S2O8 ions (0.00–1.00 eq), the absorbance band at
319 nm in UV-Vis spectra (Fig. 5a), associated with p–p* tran-
sition of conjugated structure of PAE-p-OA, decreased in
intensity and underwent a blue shift. Meanwhile, a new band
appeared at 585 nm and continually increased in intensity, which
is assigned to exciton-type transition between the HOMO orbital
of the benzoid ring and the LUMO orbital of the quinoid ring in
oligoaniline groups. The formation of new band at 585 nm is
2ꢀ
attributed to the oxidation of S2O8 ions leading to trans-
Sensing properties
formation of oligoaniline from leucoemeraldine base (LEB) to
2ꢀ
emeraldine base (EB). With further addition of S2O8 ions
Though polyaniline and its oligomers have been extensively
studied, their photoluminescence properties have not drawn
(1.00–2.00 eq), all the absorption peaks decreased as the
Fig. 5 (a) UV-Vis spectra and (b) fluorescence emission spectra of leucoemeraldine base PAE-p-OA ([PAE-p-OA] ¼ 1.0 ꢂ 10ꢀ5 M in repeat units in
2ꢀ
DMAc solution (containing 3 vol% H2O)) and those in the presence of different amounts of S2O8 ions; excitation wavelength 310 nm. Inset of the
graph illustrates the plot of the fluorescence intensity I512 against varing S2O82ꢀ concentration.
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An extensive survey of materials suggests that PAE-p-OA
is also responsive to other redox active species (Fig. 7), such as
Fe3+, hydrazine and so on, and the extent of fluorescene
quenching/enhancing is almost the same as that of S2O82ꢀ/S2ꢀ
.
But the time for fluorescene quenching/enhancing by different
types of redox materials is in the range of 20–30 min due to the
unique redox behavior of each species. These results indicate that
this dual sensor has an excellent universality for redox active
species. Moreover, in Fig. 7, some ‘neutral’ redox inactive species
such as Na+, K+ and Mg2+ cause no fluorescene quenching/
enhancing of PAE-p-OA.
Fig. 6 Fluorescence emission spectra of emeraldine base PAE-p-OA
([PAE-p-OA] ¼ 1.0 ꢂ 10ꢀ5 M in DMAc solution (containing 3 vol%
H2O)) and those in the presence of different amounts of S2ꢀ ions; exci-
tation wavelength 310 nm.
To evaluate the sensitivity of this sensing system, a fluores-
2ꢀ
cence sensing test to S2O8 ions at the low concentration was
achieved. In Fig. 8, by adjusting the parameters of the fluo-
rometer, PAE-p-OA has a acceptable respond to the redox active
species even when the polymer repeat unit concentration is 1.0 ꢂ
10ꢀ8 M. But the spectrum shape is not very good because of the
low concentration. This detection limit is moderate for fluores-
cence sensors.
oligoaniline fully converted to the pernigraniline base (PNB).
During the oxidative process, the green solution gradually turned
to dark blue and finally purple. Fig. 5b displays the changes to
2ꢀ
the emission spectra of PAE-p-OA with S2O8 ions concentra-
2ꢀ
tion and it can be seen that with the increase of S2O8 ions
concentration, the fluorescence intensity of the emission
maximum at 512 nm underwent a reduction and reached to 62%
after the addition of 1.00 eq S2O82ꢀ. It is clear that no new
Dual sensing mechanism for redox active species
These results lead us to propose the principle for emission
quenching/enhancing with redox active species. Because of its
unconjugated structure, the energy transfer between anthracene
and oligoaniline could not proceed within the polymer chain. A
possible mechanism for this dual sensor can be expressed with the
2ꢀ
emitting species were generated by the oxidation of S2O8 ions
since the spectrum shape does not change. In addition, no
significant change was observed in the emission spectra after
adding more S2O82ꢀ ions (1.00–2.00 eq) during transformation of
oligoanilline from EB to PNB. The inset of Fig. 5b is the plot of
fluorescence intensity I512 vs. S2O82ꢀ concentration and it reveals
2ꢀ
that fluorescence intensity decreases linearly as the S2O8
concentration increases at low concentrations (0.00–1.00 eq).
Based on the reversible redox property of polyaniline, we
reasoned that PAE-p-OA in EB might be used as a sensor to
detect reductive materials. In order to test this hypothesis, we
oxidized PAE-p-OA into EB at first, and then the toxic S2ꢀ ion
was chosen as the reductive reagent. The fluorescence emission
spectroscopy in Fig. 6 revealed a fluorescence enhancement
without any change to the spectrum shape after the addition of
S2ꢀ ions. In conclusion, the reversibility of this redox property
could bring an excellent reutilization, because the oxidative state
of PAE-p-OA could be easily modulated by chemical and elec-
trochemical methods.
Fig. 8 Fluorescence emission spectra of leucoemeraldine base (LEB)
and emeraldine base (EB) PAE-p-OA ([PAE-p-OA] ¼ 1.0 ꢂ 10ꢀ8 M in
DMAc solution (containing 3 vol% H2O)); excitation wavelength 310 nm.
Fig. 7 Fluorescence emission spectra of leucoemeraldine base or emeraldine base PAE-p-OA ([PAE-p-OA] ¼ 1.0 ꢂ 10ꢀ5 M in DMAc solution
(containing 3 vol% H2O)), and those in the presence of different amounts and different kind of materials, such as Fe3+, N2H4, Mg2+, Na+, K+; excitation
wavelength 310 nm.
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Fig. 9 Description of the dual sensing mechanism, based on a redox-induced conformational change of oligoaniline and a resultant fluorescence change
of PAE-p-OA.
aid of the molecular conformation (Fig. 9). Upon oxidation of
oligoaniline from LEB to EB, the molecular conformation of
oligoaniline plane becomes flatter due to the formation of C]N
double bonds, which leads to compact p-stacking of anthracene
and oligoaniline. Energy migration can then occur between the
two conjugated planes. Moreover, the quinoid rings in the oli-
goaniline have a very short-lived excited state and show no
observable fluorescence (nonradiative decay), they then act as
excitation traps and quench fluorescence, which make the sensor
in the ‘off’ state. When the oligoaniline is reduced from EB to
LEB, the non-radiative decay pathway is eliminated, resulting in
the sensor to be in the ‘on’ state. In addition, the approach to
redox active species detection has several advantages compared
with universal fluorescence sensors. The sensory scheme is based
on the redox reaction between the analyte and oligoaniline,
instead of the coordination and/or supramolecular action, which
avoids the matching difficulty between receptor and analyte.
Also, the reversibility of redox property will bring an excellent
reutilization, because the oxidative state of polymer could be
modulated easily by chemical and electrochemical methods.
Given the universality and reutilization, this kind of fluorescence
sensor would be a competent supplement for fluorescence
detecting.
between the oligoaniline and anthracene side groups, again due
to a change in the molecular conformation of the oligoaniline.
This disclosure represents the beginning of our work in this area.
Future studies will aim to increase the scope of this design, such
that it can be applied as a rapid, inexpensive, and effective way to
evaluate soil and water quality in remote or impoverished areas
where more sophisticate methods are unavailable.
Acknowledgements
This work has been supported in part by the National Natural
Science Foundation of China (No. 21104024 and 50973038), and
the National 973 Project (No. S2009061009). We acknowledge
funding from the Nanoscale Science & Engineering Center for
High-Rate Nanomanufacturing (Grant NSF EEC 0832785). We
are extremely grateful to Dr Fangfei Li from Jilin University for
constructive comments and discussions.
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Conclusion
We describe the synthesis of a novel poly(aryl ether) containing
oligoaniline and anthracene side chains, both present in equal
amounts. This material exhibits an interesting fluorescent
response to redox active species. The anthracene part is used as
a fluorophore and the oligoaniline acts a receptor to redox
species. When PAE-p-OA is in a reduced state, oxidative mate-
rials interact with the oligoaniline side chains resulting in
a progression from leucoemeraldine base (LEB) to the emer-
aldine base (EB). The resulting change in molecular conforma-
tion of the oliganiline unit increases its propensity for interaction
with the anthracene side chain, leading to decreased fluorescence
via quenching and thus ‘‘turn off’’ fluorescence sensing. When
PAE-p-OA is in the oxidized state, reduction of the oligoaniline
from the EB to the LEB via interaction with a reductive species
delivers ‘‘turn on’’ fluorescence sensing via decreased interaction
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J. Mater. Chem., 2012, 22, 3028–3034 | 3033

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