Synthesis and fluorescent properties of a chiral conjugated polymer based on (S)-2,2′-binaphtho-20-crown-6

Article abstract of DOI:10.1246/bcsj.81.1116

Linear conjugated polymer was obtained by the polymerization of 2,3-dibutoxy-1,4-diethynylnaphthalene (M-l) and (S)-5,5′-dibromo-6, 6′-dibutyl-2,2′-binaphtho-20-crown-6 (S-M-2) via Pd-catalyzed Sonogashira reaction. The conjugated polymer shows strong green-blue fluorescence due to the extended Π-electronic structure between the chiral repeating unit (S)-6,6′-dibutyl-2,2′-binaphtho-20-crown-6 and the conjugated linker 2,3-dibutoxynaphthyl group via acetylene bridge. The responsive properties of the chiral polymer on K⁺, Pb²⁺, Hg²⁺, and As^III were investigated by fluorescent spectra. The results show that Hg²⁺ and As^III can cause effective fluorescent quenching of the polymer, whereas, K⁺ and Pb²⁺ do not produce obvious changes in the polymer fluorescence. The obvious fluorescent influence shows that the 2,2′-binaphtho-20-crown-6 moiety plays an important role in fluorescent recognition for Hg²⁺ and As^III due to the effective photoinduced electron transfer (PET) and charge transfer (PCT) between the conjugated polymer backbone and receptor species.

Full text of DOI:10.1246/bcsj.81.1116

1
116 Bull. Chem. Soc. Jpn. Vol. 81, No. 9, 1116–1124 (2008)
ꢁ 2008 The Chemical Society of Japan
Synthesis and Fluorescent Properties of a Chiral Conjugated Polymer
0
Based on (S)-2,2 -Binaphtho-20-crown-6
1
ꢀ2
1
1;2
1
ꢀ1
Hui Huang, Qian Miao, Yixiong Kang, Xiaobo Huang, Jinqian Xu, and Yixiang Cheng
1
Key Lab of Mesoscopic Chemistry of MOE, School of Chemistry and Chemical Engineering,
Nanjing University, Nanjing 210093, P. R. China
2
College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou 325027, P. R. China
Received February 8, 2008; E-mail: yxcheng@nju.edu.cn
Linear conjugated polymer was obtained by the polymerization of 2,3-dibutoxy-1,4-diethynylnaphthalene (M-1)
0
0
0
and (S)-5,5 -dibromo-6,6 -dibutyl-2,2 -binaphtho-20-crown-6 (S-M-2) via Pd-catalyzed Sonogashira reaction. The con-
jugated polymer shows strong green-blue fluorescence due to the extended ꢀ-electronic structure between the chiral re-
peating unit (S)-6,6 -dibutyl-2,2 -binaphtho-20-crown-6 and the conjugated linker 2,3-dibutoxynaphthyl group via acet-
0
0
ylene bridge. The responsive properties of the chiral polymer on K , Pb , Hg , and AsIII were investigated by fluo-
þ
2þ
2þ
rescent spectra. The results show that Hg and AsIII can cause effective fluorescent quenching of the polymer, whereas,
2
þ
þ
2þ
K
and Pb do not produce obvious changes in the polymer fluorescence. The obvious fluorescent influence shows that
the 2,2 -binaphtho-20-crown-6 moiety plays an important role in fluorescent recognition for Hg and AsIII due to the
effective photoinduced electron transfer (PET) and charge transfer (PCT) between the conjugated polymer backbone and
receptor species.
0
2þ
0
Optically active 1,1 -bi-2-naphthol (BINOL) and its deriva-
aration of chiral amines or ꢁ-amino acids by chiral HPLC,
and as useful chiral ligands in highly selective chiral lumines-
tives have attracted particular interest because their versatile
backbone can be systematically modified by the introduction
of functional groups based on steric and electronic proper-
0
0
cent sensors. Shinbo et al. employed 3,3 -dibenzo-2,2 -binaph-
tho-20-crown-6 as chromatographic packing for the separation
of racemic amino acids. The results indicate that the chiral
crown ether-coating packing is very powerful for the optical
resolution of a variety of amino acids and optically active
amines.38 The Japanese company Daicel has successfully used
the chromatographically stable phase Crownpak CR (+)ꢀ and
CR (ꢁ)ꢀ for the resolution of amino acids and compounds
with a primary amino group with an asymmetric center. But
1
–11
ties.
In the last decade, Pu and other research groups report-
0
ed a series of chiral polymers based on (R)- or (S)-1,1 -bi-2-
naphthol as the starting material. These rigid and regular chiral
binaphthyl-based polymers exhibit excellent fluorescent mate-
rials with good fluorescence quantum efficiencies and repre-
sent a new generation of materials for potential applications
in areas such as fluorescent sensors in chiral molecule recogni-
tion, electro-optical materials.3
,4,12–23
According to the report-
ed literature, the skeletal structure of BINOL can be selective-
linear chiral polymers incorporating a 2,2 -binaphtho-20-
0
0
crown-6 moiety at 5,5 -positions of conjugated polybinaph-
thyls have not been reported so far. In this paper, we report
the synthesis and fluorescent properties of a linear conjugated
0
0
ly halogenated at the 3,3 - or 6,6 -positions of binaphthyl, lead-
4–29
ing to a variety of binaphthyl derivatives.2
have been few reports on the halogenation of BINOL at the
But so far there
0
0
polymer incorporating optically active 6,6 -dibutyl-2,2 -bi-
naphtho-20-crown-6. The conjugated polymer shows strong
green-blue fluorescence with high PL efficiency. Based on
the responsive fluorescent properties of the chiral polymer,
0
5
,5 -positions except that our group reported the facile synthe-
0
0
0
sis of 5,5 -dibromo-6,6 -dialkyl-1,1 -bi-2-naphthol, and Pirkle
and Schreiner described the synthesis and chiral resolution
0
0
0
0
þ 2þ 2þ 2þ
III
III
of racemic 5,5 -dibromo-6,6 ,7,7 -tetramethyl-1,1 -bi-2-naph-
3
K , Pb , Hg , and As , Hg and As cause effective
2þ
0–34
þ
thol.
cifically brominated at 5,5 -positions under mild conditions
Based on our current study, (S)-BINOL can be spe-
0
fluorescent quenching of the polymer, whereas K and Pb
do not produce obvious change in polymer fluorescence or
UV–vis absorption spectra. The obvious fluorescence changes
0
to afford a pure product in an excellent yield when 6,6 -posi-
0
0
0
tions are occupied by n-butyl groups. 5,5 -Dibromo-6,6 -
0
show that the 2,2 -binaphtho-20-crown-6 moiety in the poly-
mer main chain backbone plays an important role in fluores-
dialkyl-1,1 -bi-2-naphthol can further be used as an entry into
a wide range of other derivatives by strategic placement of
substituents at the well-defined molecular level.
2þ
III
cent recognition for Hg and As due to effective photoin-
duced electron transfer and charge transfer between the conju-
gated polymer backbone and receptor species.
Polybinaphthyl hosts developed for molecular recognition
purposes are mainly focused on crown ethers and cyclic
amides. (R)- or (S)-2,2 -binaphtho-20-crown-6 and its deriva-
tives used in molecular recognition devices have been exten-
sively studied by Cram et al.3
ethers have been recognized as efficient selectors for the sep-
0
Results and Discussion
Syntheses and Features of Monomers and the Chiral
Polymer. 2,3-Dibutoxy-1,4-diethynylnaphthalene (M-1)
was obtained via Pd-catalyzed Sonogashira reaction from the
5–37
BINOL-derived chiral crown
Published on the web September 11, 2008; doi:10.1246/bcsj.81.1116

H. Huang et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 9 (2008) 1117
Br
Br
1) H-C C-TMS
Pd(PPh ) /CuI
3
4
OH
OH
OBu-n
OBu-n
OBu-n
OBu-n
OBu-n
n-BuBr
Br2
Et3N
K CO3
AcOH
2
2)NaOH
27%
OBu-n
M-1
Br
Br
OH NaH
n-Bu
) n-BuLi
1
2
OH Br2
OH
O
O
O
OH Br2
OH -78oC
) n-BuBr
) HCl
3.4%
OH MOMCl
O
3
9
99%
Br
Br
Br
n-Bu
Br
Br
Br
Br
n-Bu
n-Bu
n-Bu
OH ClCH CH OH
n-Bu
O
O
OHTsO(CH2CH2O)3Ts
OH
NaH
0%
O
O
2
2
O
O
OH
K CO3
2
O
O
7
61%
n-Bu
n-Bu
Br
S-M-2
Scheme 1. Synthesis procedures of M-1 and S-M-2.
starting material 1,4-dibromo-2,3-dibutoxynaphthalene, which
was synthesized according to the literature (Scheme 1).39
Sonogashira coupling is one of the most important C–C cou-
n-Bu
Bu-n n-BuO
OBu-n
n
Pd(PPh ) /CuI
pling reactions in synthetic organic chemistry.4
0–44
Normally
3 4
M-1 + S-M-2
toluene/Et N
3
the reactivity order of organic halides for Sonogashira cou-
pling is vinyl iodide ꢂ vinyl triflate > vinyl bromide > vinyl
chloride > aryl iodide > aryl bromide ꢃ aryl chloride, and
employs Pd(PPh3)4 > Pd(PPh3)2Cl2 > Pd(AcO)2 as catalyst.
Herein, we chose Pd(PPh3)4 as a catalyst and CuI as a cocata-
lyst. Even at high temperature and long reaction time, M-1 was
obtained in a low yield due to the enhanced electron density of
butoxy group at the 2,3-positions of naphthalene.
O
O
O
O
O
O
Scheme 2. Synthesis procedure of the chiral polymer.
0
55
1,1 -binaphthyl was used as a starting material. Herein,
0
0
0
0
The chiral monomer (S)-5,5 -dibromo-6,6 -dibutyl-2,2 -
binaphtho-20-crown-6 (S-M-2) was prepared from starting
(R)-BINOL can be specifically brominated at 5,5 -positions
at low temperature to directly afford a pure product in an ex-
material (S)-BINOL as in the reported literature,3
which was different from the traditional synthesis routes by
1,45
cellent yield of 99% when the 6,6 -positions are occupied by n-
butyl groups. Starting from the BINOL derivatives brominated
0
3
5,36,46,47
0
Cram (Scheme 1).
Triethylene glycol ditosylate
at the 5,5 -positions, we can further design and synthesize a
[
TsO(CH2CH2O)3Ts] was synthesized according to the litera-
series of novel binaphthyl-based chiral ligands by strategic
placement of substituents within the framework of a given
BINOL derivative. In this paper, a chiral conjugated polymer
was obtained by the polymerization of 2,3-dibutoxy-1,4-di-
4
8
ture. In all cases, the hydroxy group of (S)-BINOL was first
transformed to an ether with 2-chloroethanol, and then the
2
pling with Ts(OCH2CH2)3OTs in an overall yield of 44%. Op-
tically active 1,1 -bi-2-naphthol (BINOL) derivatives have of-
0
,2 -binaphtho-20-crown-6 can be directly obtained by cou-
0
0
ethynylnaphthalene (M-1) with (S)-5,5 -dibromo-6,6 -di-
0
0
butyl-2,2 -binaphtho-20-crown-6 (S-M-2) via Pd-catalyzed
ten been used as the starting materials for the preparation of
conjugated polymers that have a chiral main-chain configura-
tion. But so far there have been very few reports on halogen-
Sonogashira reaction (Scheme 2). Sonogashira cross coupling
was carried out in toluene solution in the presence of Pd(PPh3)4
(5 mol %), CuI (20 mol %), and n-BuNH2 under a N2 atmo-
0
30,31
ꢄ
ation of BINOL at the 5,5 -positions.
0
Based on Lin et
0
sphere at 80 C. The resulting polymer was obtained in
4
9–51
52
al.
1
and Pu et al., with (S)-6,6 -dichloro-2,2 -diethoxy-
,1 -binaphthyl was chosen as the starting material, bromina-
moderate yield. The molecular weight was determined by gel
permeation chromatography (GPC): Mw ¼ 6030, Mn ¼ 4200,
PDI ¼ 1:44. The GPC result indicates that the polymer shows
moderate molecular weight. The alkyl group and crown ether
substituents on the naphthyl ring side chains of the polymer
not only modify the electronic properties and conjugated struc-
ture of the linear polymer, but also improve solubility dramat-
ically in common organic solvents. The chiral conjugated poly-
mer exhibits strong green-blue fluorescence with high PL effi-
ciency due to the extended ꢀ-electronic structure between the
chiral repeating unit and the conjugated unit via ethynyl linker,
0
0
ꢄ
tion occurred at the 4,4 -positions in CH2Cl2 at ꢁ78 C with
0
1
6
0 equiv of bromine to afford a pure product 4,4 -dibromo-
0
0
0
,6 -dichloro-2,2 -diethoxy-1,1 -binaphthyl in a very high
yield of 98%. And according to Chan et al., the bromination
0
ꢄ
0
occurred at the 6,6 -positions at ꢁ78 C when 4,4 -dibromo-
53,54
BINOL was chosen as the starting material.
0
Pu et al. also
0
0
reported preparation of (R)- or (S)-4,4 ,6,6 -tetrabromo-2,2 -di-
0
hexyloxy-1,1 -binaphthyl in AcOH at room temperature with
0
1
0 equiv of bromine when optically pure 2,2 -dihexyloxy-

1
118 Bull. Chem. Soc. Jpn. Vol. 81, No. 9 (2008)
A Fluorescent Chemosensor of a Chiral Conjugated Polymer
which improves the electron-transporting properties of the
chiral conjugated polymer within the conjugated polymer
backbone. Furthermore, this kind of ethynyl bridge can reduce
steric hindrance between backbone rings and groups, and also
has a beneficial effect on the corresponding polymer stability.
The polymer is an air stable solid with brown color and
shows good solubility in THF, CH2Cl2, CHCl3, and DMF
temperature (Tg). Thermogravimetric analysis (TGA) of the
polymer was carried out under a N2 atmosphere at a heating
ꢄ
ꢁ1
rate of 10 C min . According to Figure 1, the polymer shows
ꢄ
high thermal stability, there is no weight loss before 250 C.
An apparently one-step degradation was observed at tempera-
ꢄ
ture ranging from 280 to 675 C. The polymer tends toward
ꢄ
complete decomposition at 720 C. A total loss of about 46%
ꢄ
0
due to attachment of the flexible butoxy and 6,6 -dibutyl-
0
is observed when heated to 720 C.
Optical Properties. Figures 2 and 3 illustrate the UV–vis
absorption and fluorescent spectra of 2,3-dibutoxy-1,4-dieth-
2,2 -binaphtho-20-crown-6 group substitutents in the side of
the chiral polymer. The polymer does not show glass-transition
0
0
0
ynylnaphthalene (M-1), (S)-5,5 -dibromo-6,6 -dibutyl-2,2 -bi-
naphtho-20-crown-6 (S-M-2), and the chiral polymer. Optical
data of M-1, S-M-2, and the polymer are summarized in
Table 1. UV–vis spectra of the polymer are similar in THF,
CH2Cl2, acetone, and DMF. It can be concluded that solvent
has no effect on the conjugation structure of the chain back-
bone. Compared to M-1 and S-M-2, UV–vis absorption spec-
trum of the chiral polymer displays a large red shift. UV ab-
sorption maxima ꢂmax of M-1 and S-M-2 appear at 240 and
100
9
8
7
6
0
0
0
0
243 nm, respectively. The absorption maxima ꢂmax of the
polymer appears in a broad region from 375 to 500 nm, which
shows that a large red shift can be ascribed to the effective
ꢀ
chain.
ꢀ
–ꢀ -conjugated segment in the polybinaphthyl main
1
00
200
300
Temperature / C
Figure 1. TGA curve of the chiral polymer.
400
500
600
700
15,20,56,57
o
The polymer emits green-blue light under ultraviolet light
(254 or 365 nm) or sunlight even at low concentration
2
1
1
0
0
0
.0
.6
.2
.8
.4
.0
2
1
1
0
0
.0
.6
.2
.8
.4
M-1
S-M-2 (CH
Polymer (CH
Polymer (THF)
Polymer (Acetone)
Polymer (DMF)
(CH
2
Cl
Cl
Cl
2
)
)
)
M-1
S-M-2 (CH
Polymer (CH
Polymer (THF)
Polymer (Acetone)
Polymer (DMF)
(CH
2
Cl
Cl
Cl
2
)
)
)
2
2
2
2
2
2
2
2
0.0
250
300
350
400
450
500
350 400 450 500 550 600 650 700 750
Wavelength /nm
Wavelength /nm
Figure 2. UV–vis spectra of M-1, S-M-2, and the chiral
polymer.
Figure 3. Fluorescent spectra of M-1, S-M-2, and the
chiral polymer.
Table 1. Optical Properties of M-1, S-M-2, and the Chiral Polymer
PL (ꢂmax)/nm
UV–vis (ꢂmax)/nm
Stokes shift/nme)
ꢀPLf)
ꢂ
ex
ꢂ
em
M-1a)
S-M-2
Polymer
Polymer
Polymer
Polymer
243, 323
240
434
434
434
403
360
366
366
366
366
454
382
494, 526(sh)
497, 529(sh)
494, 526(sh)
494, 527(sh)
a)
a)
b)
c)
d)
60
63
60
60
0.61
434
a) Determined in CH2Cl2 solution. b) Determined in THF solution. c) Determined in acetone solution.
d) Determined in DMF solution. e) Stokes shift = PL ꢂmax (nm) ꢁ UV–vis ꢂmax (nm). f) These val-
ꢁ
5
ꢁ1
ꢁ1
ues were estimated by using a quinine sulfate solution (ca. 1:1 ꢅ 10 mol L ) in 0.5 mol L H2SO4
(
ꢀf ¼ 55%) as a standard.

H. Huang et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 9 (2008) 1119
Table 2. CD Spectra Data of S-M-2 and the Chiral Polymer
[
ꢃ] (ꢂmax in nm)
5
S-M-2 ꢅ 10 (CH2Cl2)
ꢁ3:69 (229.5), +5.47 (242.2)
5
Polymer ꢅ 10 (CH2Cl2)
ꢁ14:35 (223.0), +10.23 (250.6), ꢁ2:03 (327.3)
ꢁ14:01 (222.4), +9.84 (250.6), ꢁ2:00 (327.3)
5
Polymer ꢅ 10 (THF)
Table 3. The Quenching Ratios of Metal Ions to the Chiral
Polymer
1
000000
S-M-2 (CH
Polymer (CH
Polymer (THF)
2
Cl
Cl
2
)
2
2)
500000
nPolymer:nion
1
:1
1:2
1:5
1:10
1:20
1:50
0
þ
2
K
Pb
4.29
3.01
4.82
3.87
5.16
4.94
6.08
7.95
5.89
5.72
12.66
9.32
7.63
3.31
19.76
14.23
6.81
5.55
29.22
21.97
7.93
7.45
58.13
44.96
þ
þ
2
-
500000
Hg
III
As
-
-
1000000
1500000
Responsive Fluorescence Properties of the Chiral Poly-
mer towards Metal Ions. Most fluorescent chemosensors
for cations are composed of a cation recognition unit (iono-
phore) together with a fluorogenic unit (fluorophore) and are
called fluoroionophores. An effective fluorescence chemosen-
sor must convert the event of cation recognition by the iono-
225
250
275
300
325
350
Wavelength /nm
Figure 4. CD spectra of S-M-2 and the chiral polymer.
4
ꢁ1
(
1:0 ꢅ 10ꢁ mol L ). According to Figure 3, the maximum
phore into an easily monitored and highly sensitive optical
61–67
F
fluorescent wavelengths ꢂ max of M-1 and S-M-2 show photo-
luminescent bands at 454 and 382 nm in CH2Cl2, respectively.
The chiral conjugated polymer shows two bands at 494 and
signal from the fluorophore.
Fluorescent conjugated poly-
mers have several advantages over small molecule sensors due
to enhancements associated with electronic communication
between receptors along the polymer backbone, processability,
and ease of structural modification.68
Conjugated polymers incorporating molecular recognition
moieties can show high sensitivity of fluorescent chemosen-
sors to external structural perturbations and to electron density
changes within the conjugated polymer main backbone when
they interact with metal ions to form complexes. One effective
group of fluorescent chemosensors for alkali metal, alkaline
5
3
ꢂ
26 nm in CH2Cl2, acetone and DMF. But the polymer shows
nm of red shift in THF, and the fluorescent wavelengths
F
max appear at 497 and 529 nm. The PL efficiency (ꢀPL) of
the polymer is 0.61. The polymer shows strong fluorescence
with high PL efficiency due to the extended ꢀ-electronic struc-
ture between the chiral repeating unit and the conjugated linker
5
8,59
via ethynyl linker.
The greatly enhanced fluorescence of
0
0
the conjugated polymer incorporating 6,6 -dibutyl-2,2 -binaph-
tho-20-crown-6 moiety is expected to have potential applica-
tion in polarized light-emitting materials and fluorescent
sensors for the sensitive detection of various metal ions and
enantiomeric recognition of chiral amines, chiral amino acids,
and amino esters.
earth metal, and heavy metal ions involves chromophores hav-
ing covalently linked crown ether substituents.6
9–74
These sen-
sors are known to form complexes with various metal cations.
Fluorescent sensing often involves changes in luminescence
via PET, PCT, and excimer formation after the crown ether co-
25
0
CD Spectra. The specific rotation value (½ꢁꢆ ) of S-M-2
ordinates the analyte. In this paper, 2,2 -binaphtho-20-crown-6
D
is ꢁ56:1 (c 0.25, CH2Cl2), and of the conjugated polymer is
substituents can orient in a well-defined spatial arrangement in
the main chain backbone of linear conjugated polymer. Based
on the size of the metal ion and crown ether cavity, we chose
the conjugated polymer as fluorescent chemosensor for the rec-
ꢁ
170:6 (c 0.17, THF). Both S-M-2 and the chiral conjugated
polymer exhibit intense CD signals with negative and positive
Cotton effects in their CD spectra (Figure 4). CD spectral data
1
1
þ
2þ
2þ
III
of S-M-2 and polymer are listed in Table 2. The La and Bb
band intensity and position of the polymer are similar in
CH2Cl2 and THF. But the La and Bb band intensity and po-
sition of the polymer are different from that of S-M-2. CD in-
tensity of the polymer is stronger than that of S-M-2. More-
ognition of K , Pb , Hg , and As . These cations or groups
can fit well into the 20-crown-6 cavity to form the correspond-
ing polymer complexes, which may lead to optical signal
changes of the polymer.
1
1
The responsive fluorescent changes of a conjugated polymer
2þ
III
1
0
þ
over, the La bands of the CD spectrum of the polymer show
1
incorporating (S)-2,2 -binaphtho-20-crown-6 on K , Pb ,
2þ
about 5 nm of red shift compared to S-M-2, and Bb bands of
Hg , and As have been investigated. The concentration of
ꢁ1
ꢁ5
the CD spectrum of the polymer show about 7 nm of blue shift
relative to S-M-2. The chiral polymer exhibits a weaker Cotton
effect at about 327 nm. The chiral conjugated polymer adopts a
linear backbone configuration due to the main chain backbone
the polymer was fixed at 4:6 ꢅ 10 mol L corresponding
0
to 2,2 -binaphtho-20-crown-6 receptor moiety in THF. Aque-
ous nitrate or acetate salts were used at a concentration of
4:3 ꢅ 10ꢁ mol L . The influences of metal ions on the
fluorescent emission response of the polymer are shown
in Table 3. As is evident from Figures 5 and 6, an effective
fluorescence quenching can be detected upon the various molar
2
ꢁ1
0
0
30
at 5,5 -positions of 1,1 -binaphthyl, which has a chain back-
0
0
bone similar to the chiral polymer at the 4,4 -positions of 1,1 -
0
6
binaphthyl.

1
120 Bull. Chem. Soc. Jpn. Vol. 81, No. 9 (2008)
A Fluorescent Chemosensor of a Chiral Conjugated Polymer
6
6
nPolymer:nK
+
a
2
Pb
+
5
4
3
2
1
0
1:0
1
1
1
1
1
1
:1
:2
:5
:10
:20
:50
5
4
3
2
+
K
III
As
2
+
Hg
4
50
475
500
525
550
575
600
Wavelength /nm
0
5
10 15 20 25 30 35 40 45 50
[Metal ion] / [Polymer]
6
5
4
3
2
1
0
nPolymer:nPb2+
1:0
b
Figure 6. The fluorescent quenching effect of the polymer
þ
1:1
on K , Pb , Hg , and AsIII.
2þ
2þ
1:2
1
1
1
1
:5
ratio additions of Hg2 and AsIII from 1:1 to 1:50, whereas,
þ
:10
:20
:50
þ
2þ
there is no obvious fluorescence change for K and Pb . It
can also be seen that the emission wavelengths of the metal–
polymer complexes do not show an obvious difference from
metal-free polymer at the maximum fluorescent wavelengths
F
max. But the polymer complexes display a new emission
wavelength at 468 nm, and its intensity is gradually enhanced
with the increase of Hg or As solution concentration. The
emission intensities of the complexes were significantly
quenched by the addition of Hg and As (50 equiv) with
a reduction of ca. 45% and 58%, respectively. Fluorescence
ꢂ
4
50
475
500
525
550
575
600
2þ
III
Wavelength /nm
2þ
III
1
0
c
nPolymer:nHg2+
2þ
III
1
1
1
1
1
1
1
:0
:1
:2
:5
:10
:20
:50
changes of the chiral polymer in response to Hg and As
8
6
4
2
0
can be regarded as effective intramolecular photoinduced elec-
tron transfer (PET) and photoinduced charge transfer (PCT)
along the extended ꢀ-conjugated structure after the crown
ether group coordinates with the metal ions.
UV–vis absorption spectra changes of the conjugated poly-
2þ
þ
2þ
III
mer in response to K , Pb , Hg , and As are shown in
Figure 7. According to Figures 7a and 7b, UV–vis spectra of
þ
the polymer exhibit nearly no change upon addition of K
or Pb . On the contrary, UV–vis absorption spectra of the
2
þ
4
50
475
500
525
550
575
600
2þ
polymer exhibit obvious changes upon addition of Hg or
III
Wavelength /nm
As (Figures 7c and 7d). The UV–vis absorption intensities
2
þ
III
8
6
4
2
0
of the polymer in response to Hg and As show a pro-
nounced increase upon molar ratio additions from 1:5 to
1:20, but the absorption positions are similar to the free-metal
polymer. The 434 nm absorption wavelength arising from the
conjugated structure of the polymer backbone exhibits slight
enhancement. Moreover, the absorption intensity of the poly-
mer at about 228 nm which is regarded as the absorption band
of the naphthyl group exhibits dramatic enhancement with the
nPolymer:n
AsIII
d
1
:0
1:1
:2
:5
:10
:20
:50
1
1
1
1
1
2
þ
III
increase of Hg or As concentration.
Conclusion
Linear conjugated polymer were obtained by the polymer-
ization of 2,3-dibutoxy-1,4-diethynylnaphthalene and (S)-
4
50
475
500
525
550
575
600
Wavelength /nm
0 0 0
5
,5 -dibromo-6,6 -dibutyl-2,2 -binaphtho-20-crown-6 via Pd-
Figure 5. Fluorescent titration curves of the chiral polymer
2þ
catalyzed Sonogashira reaction. The conjugated polymer
shows strong green-blue fluorescence due to the extended ꢀ-
electronic structure between the chiral repeating unit (S)-
þ
2þ
(c), and AsIII (d) (ꢂex ¼
on K (a), Pb
66 nm).
(b), Hg
3

H. Huang et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 9 (2008) 1121
0
0
6
,6 -dibutyl-2,2 -binaphtho-20-crown-6 and the conjugated
a
Polymer
1
1
0
0
.6
.2
.8
.4
linker 2,3-dibutoxynaphthyl group via ethynyl bridge. Based
on the responsive fluorescent properties of the chiral polymer
+
Polymer--K (1:5)
+
Polymer--K (1:20)
þ
2þ
2þ
III
2þ
III
to K , Pb , Hg , and As , Hg and As cause effective
2þ
þ
fluorescent quenching of the polymer, whereas, Pb and K
do not produce obvious change of the polymer fluorescence
and absorption spectra. The obvious fluorescence influence
0
shows that the 2,2 -binaphtho-20-crown-6 moiety plays an im-
2þ
III
portant role in fluorescent recognition for Hg and As due
to the effective photoinduced electron transfer and charge
transfer between the conjugated polymer backbone and recep-
tor species.
2
50
300
350
400
450
500
Wavelength /nm
Experimental
13
1
General Methods.
H and C NMR spectra measurements
b
Polymer
1
1
0
0
.6
.2
.8
.4
(all in CDCl3) were recorded on a 300-Bruker spectrometer with
TMS as an internal standard. FTIR spectra were recorded on a
Nexus 870 FTIR spectrometer. UV–vis spectra were obtained with
a Perkin-Elmer Lambda 25 spectrometer. DSC-TGA was per-
formed on a Perkin-Elmer Pyris-1 instrument under a N2 atmo-
sphere. Fluorescent spectra were obtained with a 48000 DSCF
spectrometer. Mass spectrometry (MS) was determined on a Mi-
cromass GCT. C, H, and N elemental analyses were performed
on an Elementar Vario MICRO analyzer. The circular dichroism
Polymer--Pb2+ (1:5)
Polymer--Pb2+ (1:20)
(
CD) spectrum was determined with a JASCO J-810 spectropo-
larimeter. Molecular weight was determined by gel permeation
chromatography (GPC) relative to polystyrene standards with a
Waters-244 HPLC pump and THF was used as solvent. All sol-
2
50
300
350
400
450
500
Wavelength /nm
vents and reagents were commercially available A.R. grade. (S)-
0
3
2
2
2
1
1
0
0
.2
.8
.4
.0
.6
.2
.8
.4
1
,1 -Bi-2-naphthol (BINOL) were purchased from Aldrich and
c
Polymer
used directly without purification. All reactions were performed
under a N2 atmosphere using Schlenk tube techniques. THF and
Et3N were purified by distillation from sodium in the presence
of benzophenone. CH2Cl2 and CH3CN were distilled from P2O5.
Metal Ion Titration. Each metal ion titration experiment was
started with 3.0 mL of polymer in THF solution with known con-
Polymer--Hg2+ (1:5)
Polymer--Hg2+ (1:20)
ꢁ
5
ꢁ1
centration (4:6 ꢅ 10 mol L ). Aqueous nitrate or acetate salts
ꢁ
2
ꢁ1
(
4:3 ꢅ 10 mol L ) were used for the titration. Polymer com-
plexes were produced by adding aliquots of a solution of the se-
lected analyte to a THF solution of the chiral polymer (3.0 mL).
The mixture was stirred constantly during the titration. Steady-
state fluorescence spectra were monitored 15 min after addition
of aqueous analyte to the polymer solution. Distilled water was
monitored as a blank.
2
50
300
350
400
450
500
Wavelength /nm
3
2
2
2
1
1
0
0
.2
.8
.4
.0
.6
.2
.8
.4
Synthesis of 2,3-Dibutoxy-1,4-diethynylnaphthalene (M-1)
Polymer
Polymer--As (1:5)
Polymer--As (1:20)
(
4
0
Scheme 1).
1,4-Dibromo-2,3-dibutoxynaphthalene (2.13 g,
.9 mmol), Pd(PPh3)4 (283 mg, 0.25 mmol), and CuI (186.6 mg,
.98 mmol) were mixed and dissolved in 20 mL of n-BuNH2,
d
III
III
and trimethylsilylethyne (1.44 g, 13.8 mmol) was added via sy-
ringe to the above solution. The reaction mixture was stirred
and refluxed for 72 h. After the mixture was cooled to room tem-
perature, the solution was filtered through a short column of silica
gel with ethyl acetate as eluent. After removal of solvent, the
crude product 1,4-di(trimethylsilylethynyl)-2,3-dibutoxynaphtha-
lene was dissolved in 100 mL of a mixed solvents of THF–MeOH
(
4:1 v/v). The solution was bubbled with N2 for 10 min, and aque-
ous NaOH (0.78 g and 1 mL water) was added to the above solu-
tion. The mixture was stirred for 2 h at room temperature and then
the solvent was removed under reduced pressure. The residual sol-
id was extracted with CH2Cl2 (2 ꢅ 100 mL) and washed with sat-
urated brine twice. The combined organic layers were dried over
2
50
300
350
400
450
500
Wavelength /nm
þ
2þ
Figure 7. UV–vis spectra of the polymer on K (a), Pb
b), Hg2 (c), and AsIII (d).
þ
(

1
122 Bull. Chem. Soc. Jpn. Vol. 81, No. 9 (2008)
A Fluorescent Chemosensor of a Chiral Conjugated Polymer
anhydrous Na2SO4. After the solvent was removed under reduced
pressure, the crude product was purified on a silica column using
petroleum ether as the eluent to afford a brown viscous product in
32.7, 23.0, 14.3. ESI-MS: 554.4 m=z (M þ 1). Anal. Calcd for
C28H28Br2O2: C, 60.45; H, 5.07%. Found: C, 60.41; H, 5.11%.
ꢁ1
FTIR (KBr, cm ): 3530.2, 3027.4, 2956.5, 2928.9, 1597.9,
1567.3, 1467.1, 1367.7, 1248.7, 1212.0, 1154.1, 1132.9, 970.7,
819.2.
1
a yield of 27% (0.42 g). H NMR (300 MHz, CDCl3): ꢄ 8.26 (dd,
2
H, J ¼ 6:6, 3.3 Hz), 7.53 (dd, 2H, J ¼ 6:6, 3.3 Hz), 4.23 (t, 4H,
0 0 0
J ¼ 6:6 Hz), 3.75 (s, 2H), 1.89–1.80 (m, 4H), 1.64–1.51 (m, 4H),
Synthesis of (S)-5,5 -Dibromo-6,6 -dibutyl-2,2 -di(2-hy-
1
3
0 0
droxyethoxy)-1,1 -binaphthyl: A mixture of (S)-5,5 -dibromo-
1.00 (t, 6H, J ¼ 7:2 Hz). C NMR (CDCl3): ꢄ 155.1, 131.3,
126.8, 126.2, 114.8, 88.0, 78.1, 74.9, 32.8, 19.6, 14.3. GC-MS:
320 m=z (M).
0
0
6,6 -dibutyl-1,1 -bi-2-naphthol (2.0 g, 3.6 mmol), ClCH2CH2OH
(1.16 g, 14.4 mmol), and K2CO3 (6.0 g, 43.2 mmol) in 23 mL of
0
0
0
ꢄ
Synthesis of (S)-5,5 -Dibromo-6,6 -dibutyl-2,2 -binaphtho-
0
DMF was stirred at 130 C for 24 h. The mixture was poured into
ꢁ1
2
tyl-1,1 -bi-2-naphthol:
0-crown-6 (S-M-2) (Scheme 1). Synthesis of (S)-6,6 -Dibu-
0
100 mL of aqueous NaOH (1 mol L ) and the crude product pre-
0
0
(S)-6,6 -Dibromo-2,2 -di(methoxy-
methoxy)-1,1 -binaphthyl (2.0 g, 3.8 mmol) was dissolved in
cipitated. The solid was filtered and dissolved with CH2Cl2, and
the solution was washed with water to pH 7. The crude product
was purified on a silica column with a mixed solvent of petroleum
ether and ethyl acetate (2:1, v/v) as eluent to afford a pale yellow
0
3
0.0 mL of anhydrous THF. 3.8 mL of n-BuLi (9.5 mmol, 2.5
ꢄ
ꢁ1
mol L in hexane) was added by syringe injection at ꢁ78 C un-
der a N2 atmosphere. After the reaction mixture was stirred for
ꢄ
25
D
viscous product in a yield of 61% (1.4 g). Mp: 53–55 C. ½ꢁꢆ
¼
1
1
0 min, n-C4H9Br (2.1 g, 15.2 mmol) was added to the above solu-
ꢁ8:8 (c 0.80, THF). H NMR (300 MHz, CDCl3): ꢄ 8.50 (d, 2H,
J ¼ 9:6 Hz), 7.51 (d, 2H, J ¼ 9:6 Hz), 7.10 (d, 2H, J ¼ 8:7 Hz),
6.97 (d, 2H, J ¼ 8:7 Hz), 4.28–4.22 (m, 2H), 4.09–4.03 (m, 2H),
3.65–3.60 (m, 4H), 2.91 (t, 4H, J ¼ 7:2 Hz), 2.18 (s, 2H), 1.67–
1.59 (m, 4H), 1.46–1.39 (m, 4H), 0.96 (t, 6H, J ¼ 7:2 Hz).
ꢄ
tion at ꢁ78 C under a N2 atmosphere. The reaction mixture was
gradually warmed to room temperature and stirred overnight. The
mixture was extracted with ethyl acetate (2 ꢅ 50 mL). The com-
bined organic layers were washed with water and brine, and then
dried over anhydrous Na2SO4. After removal of solvent under re-
duced pressure, the crude product was purified by column chroma-
tography (petroleum ether/ethyl acetate) (30:1 v/v) to afford a
colorless viscous product (0.93 g, 51% yield). The product was
dissolved in 10 mL of THF. A mixture of 10 mL of methanol
and 15 mL of hydrochloric acid (12 mol L ) was added to the
above solution, and the mixed solution was stirred at room tem-
perature for 12 h. After removal of all solvents under reduced
pressure, the residue was extracted with ethyl acetate
13
C NMR (CDCl3): ꢄ 178.0, 169.4, 159.7, 155.1, 130.8, 120.5,
75.5, 72.0, 68.2, 67.4, 63.3, 62.9, 62.5, 58.5, 53.4, 38.4. FTIR
(KBr, cm 1): 3386.1, 2953.9, 2927.2, 2859.4, 1613.8, 1591.6,
1556.6, 1477.2, 1465.4, 1455.1, 1344.9, 1317.3, 1261.4, 1212.6,
1145.0, 1088.9, 1048.3, 990.1, 973.1, 896.9, 807.6. Anal. Calcd
for C32H36Br2O4: C, 59.64; H, 5.63%. Found: C, 59.60; H, 5.70%.
ꢁ
ꢁ
1
0
0
0
Synthesis of (S)-5,5 -Dibromo-6,6 -dibutyl-2,2 -binaphtho-
20-crown-6 (S-M-2): A solution of NaH (0.42 g, 17.5 mmol)
0
0
0
0
and (S)-5,5 -dibromo-6,6 -dibutyl-2,2 -di(2-hydroxyethoxy)-1,1 -
binaphthyl (1.13 g, 1.75 mmol) in 20 mL of THF was stirred and
kept refluxing under a N2 atmosphere. A solution of
(
2
2 ꢅ 30 mL). The combined organic layers were washed with
ꢁ
1
mol L NaHCO3 solution and brine twice, and then dried over
anhydrous Na2SO4. The crude product was purified by column
chromatography on silica gel using the mixed solvents of petro-
leum ether/ethyl acetate (20:1 v/v) to afford a white solid product
TsO(CH2CH2O)3Ts (0.88 g, 1.93 mmol in 5 mL of THF) was
added dropwise. The mixture was refluxed for 24 h. After being
cooled to room temperature and filtered, the resulting solution
was evaporated to remove solvent under reduced pressure, and
the residue was extracted with CH2Cl2 (2 ꢅ 40 mL). The solution
was washed with brine three times and dried over anhydrous
Na2SO4, and then the solvent was evaporated under reduced pres-
sure to give a brown product. The crude product was purified on a
silica column with mixed solvents of petroleum ether and ethyl
acetate (2:1, v/v) as eluent to afford a colorless viscous product
ꢄ
25
in a yield of 93.4% (0.71 g). Mp: 72–74 C. ½ꢁꢆ ¼ ꢁ82:9 (c
D
0
.31, CH2Cl2). 1H NMR (300 MHz, CDCl3): ꢄ 7.92 (d, 2H,
J ¼ 9:0 Hz), 7.69 (s, 2H), 7.36 (d, 2H, J ¼ 9:0 Hz), 7.19 (d, 2H,
J ¼ 8:4 Hz), 7.12 (d, 2H, J ¼ 8:4 Hz), 5.01 (s, 2H), 2.76 (t, 4H,
J ¼ 7:8 Hz), 1.74–1.64 (m, 4H), 1.49–1.36 (m, 4H), 0.97 (t, 6H,
13
J ¼ 7:2 Hz). C NMR (CDCl3): ꢄ 152.5, 139.0, 132.1, 131.2,
1
FTIR (KBr, cm ): 3503.4, 3421.9, 2950.1, 2921.8, 1598.1,
30.0, 129.4, 127.3, 124.6, 118.0, 111.3, 35.9, 33.9, 22.8, 14.4.
ꢁ
1
25
in a yield of 70% (0.93 g). ½ꢁꢆ ¼ ꢁ56:1 (c 0.25, CH2Cl2).
D
1
1
8
507.3, 1474.1, 1363.7, 1214.1, 1142.6, 1124.5, 952.2, 880.6,
27.1.
H NMR (300 MHz, CDCl3): ꢄ 8.45 (d, 2H, J ¼ 9:3 Hz), 7.53
(d, 2H, J ¼ 9:3 Hz), 7.06 (d, 2H, J ¼ 8:7 Hz), 6.98 (d, 2H, J ¼
8:7 Hz), 4.22–4.18 (m, 2H), 4.08–4.05 (m, 2H), 3.66–3.41 (m,
12H), 3.40–3.39 (m, 4H), 2.91 (t, 4H, J ¼ 7:5 Hz), 1.67–1.59
0
0
0
Synthesis of (S)-5,5 -Dibromo-6,6 -dibutyl-1,1 -bi-2-naph-
thol: 0.14 mL of bromine (2.8 mmol in 5 mL of CH2Cl2) was
0
0
13
slowly added to a solution of (S)-6,6 -dibutyl-1,1 -bi-2-naphthol
ꢄ
(m, 4H), 1.46–1.39 (m, 4H), 0.95 (t, 6H, J ¼ 7:2 Hz). C NMR
(
0.52 g, 1.33 mmol) in CH2Cl2 (10 mL) at ꢁ78 C over 1 h. The
(CDCl3): ꢄ 154.8, 138.4, 134.1, 129.2, 129.0, 128.7, 125.2,
123.9, 120.6, 117.1, 71.3, 71.0, 70.9, 70.1, 70.0, 37.3, 32.7,
23.0, 14.3. Anal. Calcd for C38H46Br2O6: C, 60.17; H, 6.11%.
Found: C, 59.11; H, 6.15%.
solution was stirred overnight and gradually warmed to room tem-
perature. The reaction was quenched with 15 mL of saturated
NaHSO3 solution. The mixture was extracted with CH2Cl2
(
2 ꢅ 30 mL). The combined organic layers were washed with wa-
Synthesis of Polymer (Scheme 2).
A mixture of M-1
ter and saturated brine, and then dried over anhydrous Na2SO4.
After removal of solvent, a pure solid product was directly ob-
tained in a yield of 99% (0.73 g) without further purification.
(106.3 mg, 0.332 mmol) and S-M-2 (251.6 mg, 0.332 mmol) was
dissolved in 7 mL of toluene, and then Pd(PPh3)4 (19.2 mg,
0.017 mmol), CuI (12.7 mg, 0.067 mmol), and 3 mL of n-BuNH2
were added to the above solution. The solution was stirred and
Mp: 48–50 C. ½ꢁꢆ ¼ ꢁ13:3 (c 0.23, CH2Cl2). 1H NMR
ꢄ
25
D
ꢄ
(
9
300 MHz, CDCl3): ꢄ 8.52 (d, 2H, J ¼ 9:0 Hz), 7.46 (d, 2H, J ¼
heated at 80 C for 72 h under a N2 atmosphere. After phenylacet-
:6 Hz), 7.17 (d, 2H, J ¼ 8:4 Hz), 7.01 (d, 2H, J ¼ 8:7 Hz), 5.04
ylene (3.6 mL, 0.033 mmol) was added to the above solution, the
solution was kept refluxing for an additional 2 h. Then bromoben-
zene (7 mL, 0.067 mmol) was added to the mixture, the solution
continued to be refluxed for another 2 h. After the mixture was
(
s, 2H), 2.93–2.92 (m, 4H), 1.67–1.62 (m, 4H), 1.49–1.42 (m,
4
1
H), 0.99–0.94 (m, 6H). 13C NMR (CDCl3): ꢄ 153.1, 139.1,
33.4, 131.5, 130.2, 128.9, 124.6, 124.0, 119.2, 111.3, 37.3,

H. Huang et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 9 (2008) 1123
cooled down to room temperature, the mixture was filtered
through a silica gel column into methanol (50 mL) to precipitate
out the brown crude polymer. The crude polymer was obtained
by centrifuge and washed with methanol several times. The poly-
mer was dried in vacuo and collected in a yield of 35.2%
24 P. J. Cox, W. Wang, V. Snieckus, Tetrahedron Lett. 1992,
33, 2253.
25 G. D. Y. Sogah, D. J. Cram, J. Am. Chem. Soc. 1979, 101,
3035.
26 A. Minatti, K. H. D o¨ tz, Tetrahedron: Asymmetry 2005, 16,
3256.
27 Y. J. Xu, G. C. Clarkson, G. Docherty, C. L. North,
G. Woodward, M. Wills, J. Org. Chem. 2005, 70, 8079.
28 M. Shi, L. H. Chen, C. Q. Li, J. Am. Chem. Soc. 2005, 127,
3790.
(
1
126 mg). GPC analysis result: Mw ¼ 6030, Mn ¼ 4200, PDI ¼
2
D
5
1
:44. ½ꢁꢆ ¼ ꢁ170:6 (c 0.17, THF). H NMR (300 MHz, CDCl3):
ꢄ 8.44–8.41 (m, 2H), 7.53–7.50 (m, 4H), 7.05–7.02 (m, 2H), 6.97–
.95 (m, 2H), 4.32–4.31 (m, 4H), 3.60–3.47 (m, 16H), 3.39–3.37
m, 4H), 2.89–2.88 (m, 4H), 0.93 (t, J ¼ 7:2 Hz, 6H). FTIR (KBr,
6
(
ꢁ1
cm ): 3245.4, 2961.4, 2928.8, 2869.8, 1615.4, 1593.7, 1561.0,
29 R. Zimmer, L. Schefzig, A. Peritz, V. Dekaris, H. U.
Reissig, Synthesis 2004, 9, 1439.
30 Y. Liu, L. L. Zong, L. F. Zheng, L. L. Wu, Y. X. Cheng,
Polymer 2007, 48, 6799.
1
8
463.2, 1422.3, 1349.8, 1261.7, 1217.3, 1096.6, 1022.9, 863.9,
02.0, 759.6. Anal. Calcd for C60H68O8: C, 78.57; H, 7.47%.
Found: C, 77.14; H, 7.89%.
3
1
L. L. Wu, L. F. Zheng, L. L. Zong, J. Q. Xu, Y. X. Cheng,
Tetrahedron 2008, 64, 2651.
32 Y. Liu, Q. Miao, S. W. Zhang, X. B. Huang, L. F. Zheng,
Y. X. Cheng, Macromol. Chem. Phys. 2008, 209, 685.
This work was supported by the National Natural Science
Foundation of China (Nos. 20474028 and 20774042), and
Zhejiang Provincial Natural Science Foundation of China
3
3
S. W. Zhang, Y. Liu, H. Huang, L. F. Zheng, L. L. Wu,
Y. X. Cheng, Synlett 2008, 853.
W. H. Pirkle, J. L. Schreiner, J. Org. Chem. 1981, 46,
(No. Y406068).
3
4
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