Novel polyphenylenes containing phenol-substituted oxadiazole moieties as fluorescent chemosensors for fluoride ion

Article abstract of DOI:10.1021/ma049027j

Novel phenyl-based conjugated polymers with different content of 2,5-bis(2-hydroxyphenyl)-1,3,4-oxadiazole (1) or 2-(2-hydroxyphenyl)-5-phenyl-1, 3,4-oxadiazole (2) units in the main chain were synthesized through Suzuki coupling. The measurements of sens

Full text of DOI:10.1021/ma049027j

2148
Macromolecules 2005, 38, 2148-2153
Novel Polyphenylenes Containing Phenol-Substituted Oxadiazole
Moieties as Fluorescent Chemosensors for Fluoride Ion
Gang Zhou, Yanxiang Cheng, Lixiang Wang,* Xiabin Jing, and Fosong Wang
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry,
Chinese Academy of Sciences, Changchun 130022, P. R. China
Received May 18, 2004; Revised Manuscript Received September 1, 2004
ABSTRACT: Novel phenyl-based conjugated polymers with different content of 2,5-bis(2-hydroxyphenyl)-
1,3,4-oxadiazole (1) or 2-(2-hydroxyphenyl)-5-phenyl-1,3,4-oxadiazole (2) units in the main chain were
synthesized through Suzuki coupling. The measurements of sensing behavior to various anions, i.e., F-,
Cl-, Br-, I-, BF4-, PF6-, and H2PO4-, reveal that the polymers are highly sensitive and selective F-
sensory materials, and the sensitivity is much higher than that of small molecules 1 and 2. The best
performance was observed with polymer P3 containing 40 mol % oxadiazole unit 1. A 380-fold fluorescence
quenching occurred upon adding F- into P3 chloroform solution, with only 6-fold reduction of emission
-
by using H2PO4 instead. Addition of other anions caused almost no change in emission spectra. The
sensitivity of the polymers to F- decreases with increasing solvent polarity. Like molecules 1 and 2,
these polymers can also be used as colorimetric sensors for F- and H2PO4
.
-
Chart 1
Introduction
Fluorescent conjugated polymers (CPs) have been
widely explored as highly sensitive chemosensors.1-3
A
key advantage of sensors based on CPs over those using
small molecules4-7 is that the former ones exhibit
transport collective properties and are very sensitive to
minor perturbations. In CP-based sensors, only frac-
tional binding of analyte can cause an amplified signal
due to delocalization of exciton along the conjugated
chain. Poly(p-phenylene)s,8 poly(p-phenylene ethyn-
ylene)s,9 poly(p-phenylene vinylene)s,10 polythiophenes,11
polyfluorenes12 with receptor groups, e.g., crown ethers,13
pyridine derivatives,14 and ionic groups15 in the side
chain or main chain have been successfully used for
sensing ions and biological species. Anion sensing is one
of current research interest in chemosensors because
of their importance in biological monitoring and envi-
ronmental assays. However, while many fluorescent
conjugated polymers for sensing metal ions were
demonstrated,16-19 few examples have been reported for
sensing anions.8,20 Among all anion sensors, those for
fluoride ion are of particular importance in revealing a
number of biological processes, disease states, and
environmental pollutions.21 Several approaches have
been developed based on small molecules for sensing
fluoride ion.22-28 Recently, we reported two organic
small molecules, 1 and 2 (Chart 1), as fluorescent
chemosensors for phosphate and fluoride ions based on
hydrogen-bonding and electrostatic interactions be-
tween receptors and analytes.29 Both 1 and 2 show high
phosphate/chloride and fluoride/chloride selectivity. In
particular, compound 1 can even distinguish phosphate
from fluoride. Herein, we designed and synthesized
novel conjugated polymers with 1 or 2 units in the main
chain for combining their selectivity with high sensitiv-
ity of polymeric systems.
1. They were synthesized following Scheme 1. Monomers
3 and 4, which include one and two methoxyl groups,
respectively, were synthesized from commercially avail-
able starting materials. Their copolymerization with 1,4-
diborate-2,5-dibutoxybenzene and 2,7-dibromo-9,9-di-
octylfluorene through Suzuki coupling30 followed with
demethylation31 afforded target polymers P1-P10. The
feed ratio of comonomers was adjusted to control the
content of oxadiazole moieties in the polymers. The
structures of polymers were verified with 1H NMR,
FTIR, GPC, and elemental analysis. The actual content
of the oxadiazole moiety was calculated from the inte-
gration of the peaks at δ ) 8.30 and 3.88-4.01 ppm in
1H NMR spectra of the polymers, which are attributed
to the o-phenyl proton at the oxadiazole unit and the
methylene proton close to the oxygen atom in the
dibutoxybenzene unit, respectively. As seen in Table 1,
the actual composition of the copolymers is almost
consistent with the feed ratio. Molecular weight and
polydispersity of polymers before demethylation are
listed in Table 1. The complete demethylation of the
polymers was confirmed by the appearance of a 1H NMR
Results and Discussion
Synthesis and Structure Characterization. Struc-
tures of polymers in current work are depicted in Chart
signal at 10.2 ppm and an IR peak at 3259 cm-1
characteristics of a phenol group, and the disappearance
,
* Corresponding author: e-mail lixiang@ciac.jl.cn; Fax 0086-
431-5685653.
10.1021/ma049027j CCC: $30.25 © 2005 American Chemical Society
Published on Web 02/11/2005

Macromolecules, Vol. 38, No. 6, 2005
Novel Polyphenylenes 2149
Scheme 1. Synthesis of Polymers P1-P10a
Table 2. Stern-Volmer Constants (Ksv) Value of Polymers
for Different Anionsa
-
polymer
Ksv[F-]a
Ksv[H2PO4
]
Ksv[Cl-]
P2
P3
P4
P6
P7
P8
4.25 × 105
7.11 × 105
1.78 × 105
2.49 × 105
3.57 × 105
6.25 × 104
3.71 × 104
9.58 × 104
9.97 × 103
7.61 × 104
1.71 × 105
1.74 × 104
<1 × 103
<1 × 103
<1 × 103
<1 × 103
<1 × 103
<1 × 103
a All errors are (15%. Anions used in this assay were in the
form of their tetrabutylammonium salts.
in common organic solvents, such as chloroform (CHCl3)
and tetrahydrofuran (THF).
Optical Properties. Absorption and fluorescence
spectra of all polymers have the similar features with
maximum various in the range of 349-356 and 398-
440 nm, respectively, depending on the content of
oxadiazole moieties (as seen in the Supporting Informa-
tion). In contrast to model compounds 1 and 2 in which
long wavelength emission attributed to excited-state
intramolecular proton transfer (ESIPT) was observed,29
all polymers exhibit a featureless emission band inde-
pendent of excitation wavelength from conjugated back-
bone, The absence of ESIPT emission in polymers is
probably due to different excited-state structure of
polymers from those of compounds 1 and 2. The pho-
toluminescence quantum yield is greatly affected by the
content of oxadiazole moieties and decreases from 0.74
for P1 to 0.01 for P5 and P9 (Table 1). The decreased
quantum yield with the increasing oxadiazole content
is probably due to low photoluminescence quantum yield
of 1 and 2, as reported by Doroshenko et al.33 Moreover,
the photoluminescence quantum yield of the polymers
is weakly solvent dependent; for example, that of P3 in
methylene chloride, chloroform, ethyl acetate, THF, and
DMF is 0.28, 0.23, 0.20, 0.19, and 0.13, respectively. The
measurements of sensing properties were concentrated
on P2-P4 and P6-P8 in the following sections because
of very low photoluminescence quantum yield of P5 and
P9 and the absence of oxadiazole moieties in P1.
Sensing Properties. The sensing capability of P2-
P4 and P6-P8 to different anions was characterized
in 5 µM chloroform solutions. The Stern-Volmer con-
stants (Ksv) for F-, H2PO4-, and Cl- are listed in Table
2. All polymers show the lowest Ksv for Cl- owing to
their weak hydrogen-bond-forming ability. In contrast
to compounds 1 and 2,29 all these polymers show higher
Ksv for F- than that for H2PO4-. Furthermore, polymers
P2-P4 with units 1 have higher Ksv for F- and lower
Ksv for H2PO4-, respectively, compared with P6-P8.
a (a) Br2, CH3COOH, dark, 0 °C, 10 h; (b) SOCl2, 60 °C, 4 h;
(c) NH2NH2HCl, Et3N, CHCl3, 70 °C, 12 h; (d) p-BrPh-
COONHNH2, Et3N, CHCl3, 70 °C, 12 h; (e) POCl3, 80 °C, 5 h;
(f) Pd(PPh3)4, K2CO3, THF/H2O, 80 °C, 72 h; (g) CH2Cl2, BBr3,
-78 °C, 24 h.
Table 1. Weight-Average Molecular Weight (Mw),
Polydispersity (PDI), UV-Vis Absorption/Fluorescence
Maximum, and Photoluminescence Quantum Yield in
Chloroform Solution with Concentration of 5 × 10-6
M
(Repeat Unit)
λmax,abs
λmax,PL
(nm)
a
b
c
d
polymer Xf
Xc
Mw
PDIc (nm)
ΦPL
The Ksv value for both F- and H2PO4 increased from
-
P1
P2
P3
P4
P5
P6
P7
P8
P9
P10
0.00 0.00 34 010 1.51
0.20 0.20 40 823 1.76 300, 355 417
0.40 0.39 43 521 1.93 298, 353 398, 422 (she) 0.23
372 416, 440 (she) 0.74
0.44
P2 and P6 to P3 and P7 and then decreased with
further increasing oxadiazole moieties. The increased
sensitivity at low content of oxadiazole moieties is due
to the increased number of binding site.34 The decreased
sensitivity at high content of oxadiazole moieties is
probably attributed to the lower quantum yield of the
polymers along with their lower molecular weight.
Figure 1 reveals fluorescence emission response pro-
files of polymers P2-P4 and P6-P8 upon addition of
different anions with the concentration of 10-3 M. While
almost no emission quenching is observed upon addition
of Cl-, Br-, I-, BF4-, and PF6-, all these polymers are
active to F- and H2PO4- and have the highest sensitiv-
ity to F-. Polymers P2-P4, which have two phenol
groups in each oxadiazole unit, exhibit higher sensitivity
to F- and lower sensitivity to H2PO4-, respectively,
0.60 0.58 8 502 1.37 296, 349 440
1.00 1.00 13 100 1.42 294 423
0.09
0.01
0.37
0.20
0.05
0.01
0.20 0.21 41 198 1.56 299, 356 417
0.40 0.39 35 281 1.53 296, 351 434
0.60 0.55 11 569 1.73 295, 350 427
1.00 1.00 13 480 1.58
15 521 1.37
295 425
356 418, 436 (she) 0.17
a The feed ratio of oxadiazole units. b The content of oxadiazole
units as calculated from 1H NMR spectra. c The values measured
before demethylation with GPC using polystyrene as standard.
d Solution fluorescence quantum yield measured relative to 9,10-
diphenylanthracene (10-5 M).32 e Shoulder peak.
of the proton signal of methoxyl groups in 1H NMR
spectra at 4.1 ppm. All polymers have good solubility

2150 Zhou et al.
Macromolecules, Vol. 38, No. 6, 2005
Figure 3. Fluorescence spectra of P10 upon addition of F-
-
and H2PO4
.
Figure 1. Fluorescence emission response profiles of polymers
P2-P4 and P6-P8 upon addition of various anions.
sor.35,36 Titration of P3 with other halide ions and BF4
,
-
-
PF6 did not cause obvious change of fluorescence
spectra, and the addition of H2PO4- only led to a 6-fold
reduction in emission intensity, indicating that P3 has
very high selectivity and sensitivity to F- over other
anions. The fact that P3 shows the most efficient
fluorescence quenching and highest binding affinity to
fluoride ion than other anions is actually not surprising
because of the smaller size, higher charge density, and
higher electron affinity of F-,37 which enables it to be a
strong hydrogen-bonding acceptor and be able to easily
interact with phenolic group, OH.38
The anion-binding properties of P7 in CHCl3 are
similar to those of P3. An over 80-fold quenching is
observed upon addition of 10-3 M F- while other halide
brings almost no change of the emission intensity. The
significantly different sensitivity between P3 and P7
for F- is due to the different number of receptor in each
repeat unit. Notably, it demonstrated a selective 11-fold
quenching upon addition of excess H2PO4-, exhibiting
different behavior from polymer P3.
Figure 2. Fluorescence spectra of P3 (5 µM) in chloroform
upon titration with F-. The Stern-Volmer plots are shown as
inset, and the plots show τ0/τ independent of F- concentration.
From above discussion, unlike compounds 1 and 2,
which have higher selectivity to phosphate ion, polymers
P2-P4 and P6-P8 have much higher selectivity to
fluoride ion over phosphate ion. This difference can be
explained as follows: It is well-known that polymer
chain can form a coil in solution depending on the
surrounding environment.39 Consequently, it will be
much more difficult for large anions such as H2PO4- to
access the hydroxyl group than a smaller anion F-
because of steric hindrance. For small molecules like 1
and 2, this concept is not applicable, and both F- and
compared with P6-P8 with one phenol group in each
oxadiazole unit. The best performance was observed
with P3 containing 40 mol % oxadiazole unit. In
particular, the strongest emission quenching with ad-
dition of F- accompanied by low sensitivity to H2PO4
-
indicates P3 is a highly sensitive and selective F-
sensory material. The dependence of quenching effect
on the content of oxadiazole moieties is in the same
trend with that of Ksv.
Figure 2 displays the fluorescence spectra upon ti-
tration of polymer P3 (5 µM in CHCl3) with F-. Upon
addition of F-, emission intensity decreased dramati-
cally with an emission red shift up to 15 nm and
fluorescence quenching up to 380-fold. In contrast, only
around 3-fold reduction of emission intensity was ob-
served for compound 1.29 The much higher sensitivity
of P3 than that of compound 1 is consistent with
amplification effect of conjugated polymers. As shown
in the inset of Figure 2, polymer P3 displays a linear
Stern-Volmer relationship with the addition of F-.
Additionally, the lifetime of P3 is almost independent
-
H2PO4 ions can access the hydroxyl group easily. On
the other hand, from a previous report, compound 1 can
form a stable dimer with H2PO4- through two hydrogen
bonds to efficiently quench the emission.29 Therefore,
polymers P6-P8 have a higher sensitivity to phosphate
ion than P2-P4, as revealed in Table 2 and Figure 1.
The hydrogen-bonding ability of both receptor and
analyte molecules is one of the main factors affecting
sensing behavior of materials.24-27,40 To evaluate the
importance of oxadiazole group, we also synthesized P10
without oxadiazole moieties for comparison. Below 1-fold
fluorescence quenching along with 50-70 nm red shift
of F- concentrations. With F- concentration of 0, 10-5
,
and 10-3 M, it is 0.16, 0.14, and 0.15 ns, respectively.
The association constant Ka determined to be 6.09 ×
105 M-1 is close to Ksv (7.11 × 105). These indicate that
a static quenching process instead of a dynamic quench-
ing process is dominant in this polymer chemosen-
for both F- and H2PO4 was observed (Figure 3). It is
-
believed that electron-withdrawing effects will render
the phenolic proton more acidic and lead to higher anion
binding affinities.27 This indicates that oxadiazole moi-

Macromolecules, Vol. 38, No. 6, 2005
Novel Polyphenylenes 2151
chemosensors.6 Figure 5 shows a photograph of chloro-
form solutions of polymer P3 (5 µM) containing excess
-
amount (10-3 M) of certain anions (Cl-, Br-, I-, BF4
,
PF6-, H2PO4-, and F-). The solutions remain colorless
upon addition of all the above anions, except for F- and
H2PO4-, whereby the solutions turn dark-brown and
yellowish, respectively. These color changes are caused
by the changes of absorption spectra as revealed in
Figure 6. Addition of Cl- into the solution of P3 caused
Figure 4. Fluorescence emission response profiles of P3 in
different solvents.
eties are crucial in current system for achieving high
sensitivity.
It is well-known that intramolecular charge transfer
(ICT) can cause a bathochromic shift of the emission
with increasing solvent polarity.41 The presence of ICT
in current polymers is confirmed by the red-shifted
photoluminescence with increasing solvent polarity, as
seen in the Supporting Information. Our studies also
show that solvent properties can greatly change the
nature of the quenching effects.42 In the current system,
the sensitivity of the polymers to F- decreases with
increased solvent polarity. As an example shown in
Figure 4, polymer P3 exhibits the highest sensitivity
to F- in methylene chloride. Upon addition of F- with
the concentration of 10-3 M, a 430-fold emission quench-
ing was observed in methylene chloride, while the
emission in methanol was only quenched 50 times. This
difference should be attributed to the different confor-
mations of polymer chains in different solvents and the
solvent polarity related charge-transfer interaction.40
Moreover, in protonic solvents, hydrogen-bonding in-
teractions between binding site and analyte are greatly
influenced by the competition between the solvent
molecules and fluoride ion.26 The aggregation of the
polymer in DMF and methanol is probably another
factor to reduce the sensitivity, as revealed by the low
photoluminescence quantum yield of P3 in DMF (0.13)
and its poor solubility in methanol. The sensitivity of
P3 to H2PO4- slightly decreased with increasing solvent
polarity. A 3.3-fold emission quenching was observed
in DMF, corresponding to 6.8-fold quenching in meth-
ylene chloride.
Figure 6. Absorption spectra of P3 (5 µM) in chloroform upon
addition of anions with the concentration of 10-4 M.
almost no changes of absorption spectra. While F- and
H2PO4- were added, a long-wavelength absorption band
around 462 nm appeared along with a reduction of the
main absorption band around 375 nm. These absorption
changes indicate the appearance of the hydrogen-
bonding complex26 and originated from that enhanced
electron cloud density on phenol oxygen, which strength-
ens the intramolecular charge transfer (ICT) effect
between the 1,3,4-oxadiazole electron-withdrawing group
and the OH electron-donating group.26,38,43,44
Conclusion
Novel conjugated polymers with oxadiazole units
carrying phenol groups in the main chain as both
colorimetric and fluorescent chemosensors for fluoride
ion have been designed and synthesized. Key observa-
tions are recapitulated as follows:
-
(1) All polymers are active to F- and H2PO4 with
much higher sensitivity to F-, while almost no change
of emission upon adding anions Cl-, Br-, I-, BF4-, and
PF6- is observed. Polymers containing oxadiazole units
Similar to model compounds 1 and 2, polymers P2-
P4 and P6-P8 can also be used as colorimetric
Figure 5. Color changes of P3 (5 µM) in chloroform upon addition of no anion, Cl-, Br-, I-, BF4-, PF6-, H2PO4-, and F- (from
left to right) with the concentration of 10-4 M.

2152 Zhou et al.
Macromolecules, Vol. 38, No. 6, 2005
rus oxychloride was removed, and the residue was recrystal-
lized from ethanol/chloroform to give pure product as white
crystal (5.6, 68%). 1H NMR (CDCl3) δ (ppm): 8.11 (s, 1H), 7.96
(d, 2H), 7.79 (d, 2H), 7.61 (d, 1H), 7.02 (d, 1H), 3.96 (s, 3H).
General Procedure of Polymerization with P3 as an
Example. To a flask containing 2,7-dibromo-9,9-dioctylfluo-
rene (0.164 g, 0.300 mmol), 1,4-diborate-2,5-dibutoxybenzene
(0.155 g, 0.500 mmol), 2,5-bis(5-bromo-2-methoxyphenyl)-
[1,3,4]oxadiazole (0.0881 g, 0.200 mmol), and tetrakis(tri-
phenylphosphine)palladium(0) (20 mg) was added 3 mL of 2
M aqueous potassium carbonate and 4 mL of tetrahydrofuran
under argon. The mixture was stirred at 80 °C for 72 h. The
mixture was then poured into methanol. The precipitate was
collected by filtration, dried, and then dissolved in dichlo-
romethane. The solution was washed with water and dried
over anhydrous Na2SO4. After removing most of the solvent,
the residue was poured into methanol to give fiberlike polymer.
The polymer was further purified by a Soxhlet extraction in
acetone for 24 h. The reprecipitation procedure in dichlo-
romethane/methanol was then repeated for several times. The
final product, a light-yellow fiber, was obtained after drying
in a vacuum with a yield of 0.136 g (48%). 1H NMR (CDCl3) δ
(ppm): 8.31-3.93 (m, Ar-H), 4.15 (s, OCH3), 4.05-3.97 (m,
OCH2), 2.03-1.10 (m, CH2), 0.99-0.79 (m, CH3). IR (CaF2),
cm-1: 2957 (sh), 2928 (s), 2856 (m), 1612 (w), 1511 (w), 1463
(s), 1379 (m), 1259 (sh), 1205 (m), 1069 (m), 1027 (m), 979 (w),
869 (w), 822 (w), 757 (w). Anal. Calcd for C189H246N4O16: C,
80.25; H, 8.70; N, 1.98. Found: C, 80.50; H, 8.39; N, 1.53.
General Procedure of Demethylation with P3 as an
Example. Into a mixture of 0.101 g of polymer and 30 mL of
dichloromethane was dropwise added boron tribromide at -78
°C. The mixture was allowed to warm to room temperature
and stirred for one more day and then poured into 100 mL of
water. The mixture was extracted with dichloromethane (3 ×
100 mL). The dichloromethane extracts were combined, washed
with brine, and dried over anhydrous Na2SO4. After the solvent
was evaporated to around 5 mL, the residue was poured into
hexane to give the product (0.0413 g, 40%) as an orange
with two phenol groups, i.e., P2-P4, have higher
sensitivity to F- and lower sensitivity to H2PO4
,
-
respectively, than P6-P8, which contain oxadiazole
units with only one phenol group.
(2) The polymer with optimized content of 2,5-bis(2-
hydroxyphenyl)-1,3,4-oxadiazole (1), i.e., P3 with 40 mol
% oxadiazole unit, exhibits the best performance as a
fluoride ion sensor. A 380-fold fluorescence quenching
occurred upon adding F- into P3 chloroform solution
-
while H2PO4 could only cause 6-fold reduction.
(3) The sensitivity of the polymers to F- decreases
with increasing solvent polarity. The polymer P3 shows
the highest sensitivity in methylene chloride and lowest
sensitivity in methanol with 430-fold and 50-fold fluo-
rescence quenching, respectively.
(4) The polymers can also be used as colorimetric
-
sensors to F- and H2PO4 without response to other
anions.
Experimental Section
Material Synthesis. All chemicals and reagents were used
as received from commercial sources without further purifica-
tion. Solvents for chemical synthesis were purified according
to standard procedures. All chemical reactions were carried
out under an inert atmosphere. Intermediates 2,7-dibromo-
9,9-dioctyl-9H-fluorene and 1,4-diborate-2,5-dibutoxybenzene
were synthesized as previously described.30
4-Bromo-2-methoxybenzoic Acid. Into a solution of
2-methoxybenzoic acid (15.2 g, 0.10 mol) in 100 mL of acetic
acid was slowly added bromine (24 g, 0.15 mol) in 50 mL of
acetic acid. After 10 h, the mixture was poured into 300 mL
of water. The precipitate was filtered and recrystallized from
ethanol to give the product as a white crystal (21.2 g, 92%).
1H NMR (CDCl3 ) δ (ppm): 11.29 (s, 1H), 8.30 (s, 1H), 7.91 (d,
1H), 6.99 (d, 1H), 4.09 (s, 3H).
5-Bromo-2-methoxybenzoyl Chloride. A mixture of 4-bro-
mo-2-methoxybenzoic acid (23 g, 0.10 mol) and thionyl chloride
(100 mL) was refluxed for 5 h. Excess thionyl chloride was
removed by distillation under vacuum. The residue was
recrystallized from hexane to give the product as a white
needlelike crystal (18.8 g, 76%). 1H NMR (CDCl3) δ (ppm): 8.17
(s, 1H), 7.66 (d, 1H), 6.90 (d, 1H), 3.92 (s, 3H).
1
powder. H NMR (CDCl3) δ (ppm): 10.01 (s, OH), 8.31-3.93
(m, Ar-H), 4.05-3.97 (m, OCH2), 2.03-1.10 (m, CH2), 0.99-
0.79 (m, CH3). IR (CaF2), cm-1: 3560 (w), 3259 (br), 2957 (m),
2928 (s), 1628 (w), 1591 (w), 1540 (w), 1495 (w), 1464 (s), 1270
(m), 1233 (m), 1199 (m), 1065 (w), 1025 (w), 823 (w), 734 (w).
Anal. Calcd for C185H238N4O16: C, 80.14; H, 8.59; N, 2.02.
Found: C, 80.47; H, 8.43; N, 1.61.
Characterizations and Measurements. 1H NMR spectra
were collected using Varian HG-300 (300 MHz) or HG-400 (400
MHz) spectrometer with chloroform-d as solvent and tetra-
methylsilane as the internal standard. The elemental analysis
was performed on a Bio-Rad elemental analysis system. Gel
permeation chromatography (GPC) analysis was conducted on
a Waters 510 system using polystyrene as standard and THF
as eluent. IR spectra were obtained on Bio-Rad FTS 135
spectrometer by dispersing samples in KBr matrix. Fluores-
cence spectra were obtained on a Perkin-Elmer LS 50B
luminescence spectrometer with xenon discharge lamp excita-
tion. UV/vis measurements were carried out on a Perkin-Elmer
Lambda 35 UV/vis spectrophotometer. Fluorescence lifetimes
were obtained on FL920 fluorescence lifetime spectrometer
with a nF900 flash lamp (Edinburgh Instruments).
1,2-Bis(5-bromo-2-methoxy)benzoylhydrazine. Into a
mixture of hydrazine hydrochloride (3.4 g, 0.49 mol), triethyl-
amine (20 mL), and chloroform (80 mL) was slowly added
5-bromo-2-methoxybenzoyl chloride (12.4 g, 0.10 mol) in 50 mL
of chloroform. The mixture had been refluxed for 10 h before
filtration. The solid was washed with methanol three times
and recrystallized from ethanol to afford the product (5.6 g,
53%). 1H NMR (CDCl3) δ (ppm): 8.15 (s, 2H), 7.61 (d, 2H),
6.99 (d, 1H), 3.95 (s, 6H).
1-(5-Bromo-2-methoxy)benzoyl-2-(4-bromobenzoyl)hy-
drazine. Into a solution of 4-bromobenzoic acid hydrazide
(10.7 g, 0.05 mol), triethylamine (20 mL), and chloroform (80
mL) was slowly added 5-bromo-2-methoxybenzoyl chloride (6.2
g, 0.05 mol) in 50 mL of chloroform. The mixture had been
refluxed for 10 h before filtration. The solid was washed with
methanol three times and recrystallized from ethanol to afford
1
the product (7.0 g, 61%). H NMR (CDCl3) δ (ppm): 8.14 (s,
Acknowledgment. We thank Mrs. Rong Hua for
performing the GPC experiments. This work was sup-
ported by the NSFC (29725410; 29992530 and 20174042)
and 973 Project (2002CB613X02).
1H), 8.00 (d, 2H), 7.81 (d, 2H), 7.71 (d, 1H), 6.99 (d, 1H), 3.94
(s, 3H).
2,5-Bis(5-bromo-2-methoxyphenyl)-[1,3,4]oxadiazole (3).
A mixture of 1,2-bis(5-bromo-2-methoxy)benzoylhydrazine (9.2
g, 0.02 mol) and 30 mL of phosphorus oxychloride was refluxed
for 6 h. Excess phosphorus oxychloride was removed, and the
residue was recrystallized from ethanol/chloroform to give pure
product as a white crystal (6.4 g, 74%). 1H NMR (CDCl3) δ
(ppm): 8.13 (s, 2H), 7.61 (d, 2H), 6.97 (d, 2H), 4.00 (s, 6H).
2-(5-Bromo-2-methoxyphenyl)-5-(4-bromophenyl)-[1,3,4]-
oxadiazole (4). A mixture of 1-(5-bromo-2-methoxy)benzoyl-
2-(4-bromobenzoyl)hydrazine (8.6 g, 0.02 mol) and 30 mL of
phosphorus oxychloride was refluxed for 6 h. Excess phospho-
Supporting Information Available: Detailed UV-vis
absorption and photoluminescence spectra in dilute solution
upon titration. This material is available free of charge via
the Internet at http://pubs.acs.org.
References and Notes
(1) McQuade, D. T.; Pullen, A. E.; Swager, T. M. Chem. Rev.
2000, 100, 2537-2574.

Macromolecules, Vol. 38, No. 6, 2005
Novel Polyphenylenes 2153
(2) Chen, L.; McBranch, D. W.; Wang, H. L.; Helgeson, R.; Wudl,
F.; Whitten, D. G. Proc. Natl. Acad. Sci. U.S.A. 1999, 96,
12287-12292.
(24) Black, C. B.; Andrioletti, B.; Try, A. C.; Ruiperez, C.; Sessler,
J. L. J. Am. Chem. Soc. 1999, 121, 10438-10439.
(25) Jurs´ıkova´, K.; Sessler, J. L. J. Am. Chem. Soc. 2000, 122,
(3) Swager, T. M. Acc. Chem. Res. 1998, 31, 201-207.
(4) de Silva, A. P.; Gunaratne, H. Q. N.; Gunnlaugsson, T.;
Huxley, A. J. M.; McCoy, C. P.; Rademacher, J. T.; Rice, T.
E. Chem. Rev. 1997, 97, 1515-1566.
9350-9351.
(26) Lee, K. H.; Lee, H.; Lee, D. H.; Hong, J. Tetrahedron Lett.
2001, 42, 5447-5449.
(27) Mizuno, T.; Wei, W. H.; Eller, L. R.; Sessler, J. L. J. Am.
(5) Beer, P. D.; Gale, P. A. Angew. Chem., Int. Ed. 2001, 40, 486-
516.
Chem. Soc. 2002, 124, 1134-1135.
(28) Kubo, Y.; Yamamoto, M.; Ikeda, M.; Takeuchi, M.; Shinkai,
S.; Yamaguchi, S.; Tamao, K. Angew. Chem., Int. Ed. 2003,
42, 2036-2040.
(6) Martinez-Manez, R. Sancenon, F. Chem. Rev. 2003, 103,
4419-4476.
(7) Prodi, L.; Bolletta, F.; Montalti, M.; Zaccheroni, N. Coord.
Chem. Rev. 2000, 205, 59-83.
(29) Tong, H.; Zhou. G.; Wang, L.; Jing, X.; Wang, F.; Zhang, J.
Tetrahedron Lett. 2003, 44, 131-134.
(8) Harrison, B. S.; Ramey, M. B.; Reynolds, J. R.; Schanze, K.
S. J. Am. Chem. Soc. 2000, 122, 8561-8562.
(9) Yang, J. S.; Swager, T. M. J. Am. Chem. Soc. 1998, 120,
11864-11873.
(30) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457-2483.
(31) Ma, H.; Jen, A. K. Y.; Wu, J.; Wu, X.; Liu, S.; Shu, C.; Dalton,
L. R.; Marder, S. R.; Thayumanavan, S. Chem. Mater. 1999,
11, 2218-2225.
(10) Fan, C.; Plaxco, K. W.; Heeger, A. J. J. Am. Chem. Soc. 2002,
124, 5642-5643.
(32) Demas, J. N.; Crosby, G. A. J. Phys. Chem. 1971, 75, 991-
(11) McCullough, R. D.; Ewbank, P. C.; Loewe, R. S. J. Am. Chem.
Soc. 1997, 119, 633-634.
1024.
(33) Doroshenko, A. D.; Posokhov, E. A.; Verezubova, A. A.;
(12) Gaylord, B. S.; Heeger, A. J.; Bazan, G. C. J. Am. Chem. Soc.
2003, 125, 896-900.
Ptyagina, L. M. J. Phys. Org. Chem. 2000, 13, 253-265.
(34) Wosnick, J. H.; Swager, T. M. Curr. Opin. Chem. Biol. 2000,
(13) Kim, J.; McQuade, D. T.; McHugh, S. K.; Swager, T. M.
Angew. Chem. 2000, 112, 4026-4030.
4, 715-720.
(35) Lakowicz, J. R. Principles of Fluorescence Spectroscopy;
(14) Kimura, M.; Horai, T.; Hanabusa, K.; Shirai, H. Adv. Mater.
1998, 10, 459-462.
Plenum Press: New York, 1986.
(36) Zhou, Q.; Swager, T. M. J. Am. Chem. Soc. 1995, 117, 12593-
(15) Chen, L.; McBranch, D. W.; Wang, H. L.; Helgeson, R.; Wudl,
F.; Whitten, D. G. Proc. Natl. Acad. Sci. U.S.A. 1999, 96,
12287-12292.
12602.
(37) Zhang, X.; Guo L.; Wu, F.; Jiang, Y. Org. Lett. 2003, 5, 2667-
(16) Wang, B.; Wasielewski, M. R. J. Am. Chem. Soc. 1997, 119,
12-21.
2670.
(38) Lee, D. H.; Lee, K. H.; Hong, J. Org. Lett. 2001, 3, 5-8.
(17) Crawford, K. B.; Goldfinger, M. B.; Swager, T. M. J. Am.
Chem. Soc. 1998, 120, 5187-5192.
(39) Tadd, E. H.; Bradley, J.; Tannenbaum, R. Langmuir 2002,
18, 2378-2384.
(18) Zhang, Y.; Murphy, C. B.; Jones, W. E. Macromolecules 2002,
35, 630-636.
(40) Miyaji, H.; Sessler, J. L. Angew. Chem., Int. Ed. 2001, 40,
154-157.
(19) Liu, B.; Yu, W. L.; Pei, J.; Liu, S. Y.; Lai, Y. H.; Huang, W.
Macromolecules 2001, 34, 7932-7940.
(41) Nguyen, T.; Doan, V.; Schwartz, B. J. J. Chem. Phys. 1999,
110, 4068-4078.
(20) Tong, H.; Wang, L.; Jing, X.; Wang, F. Macromolecules 2003,
36, 2584-2586.
(42) Aquino, A. J. A.; Tunega, D.; Haberhauer, G.; Gerzabek, M.
H.; Lischka, H. J. Phys. Chem. A 2002, 106, 1862-1871.
(21) Tomich, J. M.; Wallace, D.; Henderson, K.; Mitchell, K. E.;
Radke, G.; Brandt, R.; Ambler, C. A.; Scott, A. J.; Grantham,
J.; Sullivan, L.; Iwamoto, T. Biophys. J. 1998, 74, 256-267.
(22) Shionoya, M.; Furuta, H.; Lynch, V.; Harriman, A.; Sessler,
J. L. J. Am. Chem. Soc. 1992, 114, 5714-5722.
(23) Cooper, C. R.; Spencer, N.; James, T. D. Chem. Commun.
1998, 1365-1366.
(43) Diwu, Z.; Lu, Y.; Zhang, C.; Klaubert, D. H.; Haugland, R. P.
Photochem. Photobiol. 1997, 66, 424-427.
(44) DiCesare, N.; Lakowicz, J. R. Chem. Commum. 2001,
2022-2023.
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