In situ Cu(II)-containing chiral polymer complex sensor for enantioselective recognition of phenylglycinol

Article abstract of DOI:10.1016/j.polymer.2012.10.047

A chiral polymer P1 was synthesized by the polymerization of 2,5-dibutoxy-1,4-di(benzaldehyde)-1,4-diethynylbenzene (M-1) with (R,R)-1,2-diaminocyclohexane (M-2) via Schiff's base formation, and the chiral polymer P2 could be obtained by the reduction reaction of P1 with NaBH ₄. P2 can serve as a "turn-off" fluorescent sensor toward Cu²⁺ and Ni²⁺. The in situ generated Cu(II)-containing polymer complex of P2 (Cu(II)-P2) can exhibit remarkable "turn-on" fluorescence enhancement response and considerable enantioselectivity toward unmodified phenylglycinol via a ligand displacement mechanism. More importantly, (R,R)-Cu(II)-P2 solution can turn on bright blue fluorescence color change again upon addition of l-phenylglycinol under a commercially available UV lamp, which can be clearly observed by the naked eyes for direct visual discrimination at low concentration. The simple, rapid and sensitive benign process makes this protocol promising for recognition of phenylglycinol enantiomers.

Full text of DOI:10.1016/j.polymer.2012.10.047

Polymer 53 (2012) 6033e6038
Contents lists available at SciVerse ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
In situ Cu(II)-containing chiral polymer complex sensor for enantioselective
recognition of phenylglycinol
Lu Wang, Fengyan Song, Jiali Hou, Junfeng Li, Yixiang Cheng , Chengjian Zhu*
*
Key Lab of Mesoscopic Chemistry of MOE, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 13 June 2012
Received in revised form
A chiral polymer P1 was synthesized by the polymerization of 2,5-dibutoxy-1,4-di(benzaldehyde)-1,4-
diethynylbenzene (M-1) with (R,R)-1,2-diaminocyclohexane (M-2) via Schiff’s base formation, and the
4
chiral polymer P2 could be obtained by the reduction reaction of P1 with NaBH . P2 can serve as a “turn-
14 October 2012
2þ
2þ
off” fluorescent sensor toward Cu and Ni . The in situ generated Cu(II)-containing polymer complex of
P2 (Cu(II)-P2) can exhibit remarkable “turn-on” fluorescence enhancement response and considerable
enantioselectivity toward unmodified phenylglycinol via a ligand displacement mechanism. More
importantly, (R,R)-Cu(II)-P2 solution can turn on bright blue fluorescence color change again upon
Accepted 24 October 2012
Available online 1 November 2012
Keywords:
Enantioselective recognition
Phenylglycinol
addition of L-phenylglycinol under a commercially available UV lamp, which can be clearly observed by
the naked eyes for direct visual discrimination at low concentration. The simple, rapid and sensitive
benign process makes this protocol promising for recognition of phenylglycinol enantiomers.
Ó 2012 Elsevier Ltd. All rights reserved.
Cu(II)-containing polymer complex
1. Introduction
sensing properties, such as quenching or emission red/blue shift,
which can be attributed to electron density variations [27].
As chiral stereogenic carbon atoms are abundant in natural
products, such as amino acids, sugar, amine alcohols and
hydroxyl carboxylic acids, chiral enantioselective recognition
Moreover, while different chiral enantiomer guest were added to
the metal ion containing host, the mixture can usually appear
obvious color change or form some complex precipitates due to
the competitive binding to metal ion between host and guest,
which could be clearly observed by the naked eyes. This kind
direct visual detection can offer a very simple and rapid method
for chiral enantiomer discrimination. Encouraged by the brilliant
achievements of Anslyn’s [28,29], Wolf’s [26,30], Pu’s [31], and
Feng’s previous works [32e34], recently, our group reported the
in situ generated perazamacrocycle-Cu(II) complex as chiral
florescence sensor and successfully realized enantioselective
a
-
plays an important role in many fields of science and technology
[
1e7]. Besides, studies on chiral recognition can contribute to the
understanding of living systems on molecular level. Recently,
more and more attentions have been paid on enantioselective
recognition of chiral molecules using fluorescence sensors such as
chiral macrocycles [8e11], dendrimers [12e15] and oligomers
[
16,17]. The progresses of these chiral enantiomers recognition
have been generally achieved through intermolecular non-
covalent interaction such as hydrogen bonding between the
recognition towards unmodified
a-amino acids in protic solution
fluorescence sensors and the chiral molecules [18e25].
A
[35]. To the best of our knowledge, most of the works on metal
ion containing complexes as chiral fluorescence sensors are
focused on chiral small molecules, however, almost no report on
polymer complex sensors. Compared to chiral small organic
molecules, polymer-based chiral sensors exhibit important
advantages. They are highly sensitive to minor external structural
perturbations or to electron density changes within the polymer
backbone in the presence of analytes [36e41]. Moreover, these
chiral fluorescence-based polymers can also be systematically
modified by the introduction of different functional groups with
steric and electronic properties, which can greatly improve both
the binding ability and recognition selectivity for specific analytes
[42e44]. Inspired by these impressive progresses on metal ion
remaining drawback of this approach is the limited sensitivity
due to relatively low association constants between the sensors
and the chiral hydrogen bond donating substrates [26]. Therefore,
the design and development of a novel approach for the highly
enantioselective recognition of chiral molecules and the rapid
determination of their enantiomeric composition is highly desir-
able. After coordination with metal ions, the fluorescence sensors
usually exhibit fluorescence changes and show distinguishing
*
Corresponding authors.
E-mail address: yxcheng@nju.edu.cn (Y. Cheng).
0
032-3861/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.polymer.2012.10.047

6034
L. Wang et al. / Polymer 53 (2012) 6033e6038
0
containing fluorescence sensors, we continued our interest in
polymer-based fluorescence sensor [45e51] and designed a novel
chiral polymer P2, which can serve as a “turn-off” fluorescent
2.3. Synthesis of 4,4 -((2,5-dibutoxy-1,4-phenylene)bis(ethyne-2,1-
diyl))dibenzaldehyde (M-1)
sensor toward Cu2
þ
and Ni
2þ
.
Interestingly, the in situ
The mixture of 1,4-dibutoxy-2,5-diiodobenzene 1 (474.1 mg,
1.0 mmol), 4-ethynyl- benzaldehyde 2 (390.1 mg, 3.0 mmol),
Pd(PPh ) Cl (70.6 mg, 0.1 mmol), and CuI (37.5 mg, 0.2 mmol)
3 2 2
was dissolved in the mixed solvents of THF (10 mL) and Et
(30 mL). The reaction mixture was heated to 80 C overnight
generated Cu(II)-containing polymer complex of P2 (Cu(II)-P2)
can exhibit remarkable “turn-on” fluorescence enhancement
behavior and considerable enantioselectivity toward unmodified
phenylglycinol.
3
N
ꢀ
2
under N atmosphere. After cooling to room temperature, the
solvent was removed by a rotary evaporator. The residue was
purified by flash chromatography on silica gel (ethyl acetate/
petroleum ether, 1:3, v/v). The solvent was removed to afford M-1
2
. Experimental part
2.1. Instruments and materials
ꢀ
1
as a bright yellow powder (242 mg, 51%). Mp: 150e152 C.
NMR (300 MHz, CDCl
H
3
)
d
10.03 (s, 2H), 7.88 (d, J ¼ 8.2 Hz, 4H), 7.68
NMR spectra were obtained using a 300-Bruker spectrometer
(
(
d, J ¼ 8.1 Hz, 4H), 7.05 (s, 2H), 4.06 (t, J ¼ 6.4 Hz, 4H), 1.91e1.81
1
13
3
00 MHz for H NMR and 75 MHz for C NMR and reported as
m, 4H), 1.59 (dd, J ¼ 15.0, 7.3 Hz, 4H), 1.02 (t, J ¼ 7.4 Hz, 6H).
parts per million (ppm) from the internal standard TMS. FT-IR
spectra were taken on a Nexus 870 FT-IR spectrometer. Fluores-
cence spectra were obtained from an RF-5301PC spectrometer.
Specific rotation was determined with a Ruololph Research
Analytical Autopol IV-T/V. Electrospray ionization mass spectra
13
3
C NMR (75 MHz, CDCl ) d191.42, 153.86, 135.42, 132.04, 129.62,
116.82, 113.90, 94.26, 90.00, 77.22, 69.30, 31.31, 19.27, 13.90. TOF-
MS: m/z: 478.1.
(
ESI-MS) were measured on a Thermo Finnigan LCQ Fleet system
2.4. Synthesis of P1
and time-of-flight mass spectrometry (TOF-MS) was determined on
a Micromass GCT. C, H, N of elemental analyses were performed on
an Elemental Vario MICRO analyzer. The gel permeation chroma-
tography (GPC) analysis of the polymers was conducted on a Shi-
madzu 10 Å with THF as the eluent and polystyrene as the standard.
The data were analyzed by using the software package provided by
Shimadzu Instruments. Thermogravimetric analyses (TGA) were
performed on a PerkineElmer Pyris-1 instrument under N atmo-
2
sphere. Circular dichroism (CD) spectra were carried out on
a JACSCO J-810 Circular Dichroism Spectrophotometer. All solvents
A mixture of M-1 (100.0 mg, 0.19 mmol) and (R,R)-1,2-
diaminocyclohexane (M-2, 21.0 mg, 0.19 mmol) was dissolved
ꢀ
in 2 mL of CHCl
3
. The solution was stirred at 40 C for 4 h.
2
0 mL of methanol was added to precipitate the yellow solid P1.
The resulting P1 was filtrated and washed with methanol
several times and dried in the yield of 85% (90.0 mg). GPC
2
5
results: M
w
¼ 21,170; M
n
¼ 7170; PDI ¼ 2.9. ½
a
ꢃ
¼ ꢂ435.0 (c
D
1
0
(
1
(
.20, THF). H NMR (300 Hz, CDCl
m, ArH), 7.49e7.44 (m, ArH), 6.97 (s, ArH), 4.03e3.98 (t, CH
.89e1.76 (m, CH ), 1.61e1.49(m, CH ), 1.03e0.96 (m, CH ). FT-IR
KBr, cm ): 3416, 2928, 2858, 1697, 1636, 1502, 1382, 1273,
3
)
d
8.17 (s, HC ¼ N), 7.62e7.57
2
O),
3
and reagents were commercially available A.R. grade. THF and Et N
were purified by distillation from sodium in the presence of
benzophenone.
2
2
3
ꢂ1
1
208, 830.
2.2. Synthesis of 4-ethynylbenzaldehyde 2
2.5. Synthesis of P2
1
,4-Diiodo-2,5-dibutoxybenzene 1 could be synthesized from
0
.1 g P1 was dissolved in the mixed solvents of 10 mL THF
hydroquinone according to the reported procedures [52]. Tri-
methylsilylacetylene (19.4 mL, 135.9 mmol) was added to
mixture of 4-bromobenzaldehyde (5.0 g, 27.18 mmol),
Pd(PPh
in Et
After cooling to room temperature, the resulting ammonium salt
was filtered off, and the solvent was removed by rotary evapo-
ration. The residue was purified by silica gel column chroma-
tography with petroleum ether as eluent to afford 4-
(trimethylsilyl)ethynyl)benzaldehyde as a yellow powder after
removal of the solvent (4.0 g, 74%). H NMR (300 MHz, CDCl )
3
and 10 mL MeOH, and then NaBH (500 mg) was added in
4
batches to the above solution. The reaction mixture was stirred
at room temperature until the yellow color turn light. The
solution was stirred for another 30 min, and 10 mL water was
added to stop the reduction reaction. The mixture was extracted
with CH
dried with anhydrous Na
pressure to afford polymer P2 as a yellow solid (0.08 g, 86%).
GPC: M
THF). H NMR (300 Hz, CDCl
m, ArH), 7.04e6.99 (m, ArH), 4.02e3.97 (m, NH), 3.75e3.67
m, CH
a
3
)
2
Cl
2
(950 mg, 1.36 mmol) and CuI (520 mg, 2.72 mmol)
ꢀ
3
N (60 mL). The mixture was stirred overnight at 40 C.
2
Cl
2
(3 ꢁ 20 mL). The combined organic layers were
2
SO and evaporated under reduced
4
25
w
¼ 21,400; M
n
¼ 7230; PDI ¼ 2.6. ½
a
ꢃ
D
¼ þ10.0 (c 0.20,
(
1
3
)
d
7.52e7.49 (m, ArH), 7.33e7.31
1
(
(
CH
d
0
10.00 (s, 1H), 7.82 (d, J ¼ 8.5 Hz, 2H), 7.60 (d, J ¼ 8.2 Hz, 2H),
.27 (s, 9H).
-((Trimethylsilyl)ethynyl)benzaldehyde (2.0 g, 10.0 mmol) and
KOH (561 mg, 10.0 mmol) were dissolved in the mixed solvents of
CH Cl (10 mL) and MeOH (5 mL). The mixture was stirred at room
temperature for 6 h, and then the solvent was concentrated under
reduced pressure. H O (20 mL) and CH Cl (20 mL) were added to
the obtained residue to afford a two-phase solution. The aqueous
layer was extracted with CH Cl
(2 ꢁ 20 mL), and the combined
organic layers were washed with H O, and then dried over MgSO
2
O), 2.42 (br, CH
2
N), 1.82e1.26 (m, CH
2
), 0.90e0.89 (m,
ꢂ1
3
). FT-IR (KBr, cm ): 3552, 3414, 2928, 2868, 1618, 1412, 1213,
4
8
17, 617.
2
2
2.6. Fluorescence measurements
2
2
2
The concentrations of the stock solution of metal salts (nitrate)
ꢂ2
2
2
and the unmodified amino alcohols are 1.0 ꢁ 10 mol/L in H
2
O and
ꢂ2
2
4
.
1.0 ꢁ 10 mol/L in THF, respectively. Initially each experiment was
The solution was filtered, and the solvent was removed by rotary
evaporation to give a light yellow powder identified as 4-
ethynylbenzaldehyde 2 (1.17 g, 90%). H NMR (300 MHz, CDCl
started with a 3.0 mL polymer with a known concentration
ꢂ5
(1.0 ꢁ 10 mol/L corresponding to (R,R)-cyclohexane moiety in
1
3
)
THF). The adding amount of each experiment example of metal salt
and unmodified amino alcohols is shown on the figure
interpretation.
d
10.01 (s,1H), 7.86-7.81 (m, 2H), 7.63 (d, J ¼ 8.2 Hz, 2H), 3.32 (s,1H).
ꢂ
ESI-MS: m/z: 129.17 [M ꢂ H] .

L. Wang et al. / Polymer 53 (2012) 6033e6038
6035
3
. Results and discussion
100
3
.1. Synthesis and structure feature of the polymers P1 and P2
P1
P2
80
60
40
20
Chiral small molecules 3 and 4 could be synthesized according
to the reported procedures [53]. The synthetic routes of the two
chiral polymers P1 and P2 are illustrated in Scheme 1. The mono-
mer M-1, 4,4 -((2,5-dibutoxy-1,4-phenylene)bis(ethyne-2,1-diyl))
dibenzaldehyde, was prepared according to the reported proce-
dures [47], and then reacted with 1,2-diaminocyclohexane (M-2) to
afford the corresponding chiral polymer P1 as a yellow solid in
0
8
5.0% yield. P2 could be obtained by the reduction reaction of P1
1
4
with NaBH in 85.3% yield. As evident from H NMR spectra of the
polymers P1 and P2, P1 has one well-resolved peak at 8.17 ppm
corresponding to the imine group adjacent to the phenyl (eCH]
Ne). But 8.17 ppm in H NMR spectra of the polymer P2
100
200
300
400
500
600
700
o
Temperature ( C)
1
completely disappears, which indicates the complete reduction of
imine group of P1 (Fig. S18). (R,R)-1,2-diaminocyclohexane moiety
of P1 and P2 as a chiral site and ligand can orient a well-defined
spatial arrangement in the regular polymer main chain backbone.
GPC results of both P1 and P2 show moderate molecular weights.
Both the chiral polymers P1 and P2 are air stable solids and have
good solubility in common organic solvents, such as toluene, THF,
Fig. 1. TGA curves of the chiral polymers P1 and P2.
with high fluorescence quantum yield of 0.77 and 0.54, respec-
tively. The fluorescence response behavior of P1 and P2
ꢂ5
(
1.0 ꢁ 10 mol/L corresponding to cyclohexane moiety in THF) on
various metal ions have been investigated by fluorescence spectra
with the excitation at 381 nm and 371 nm, respectively. It was
found that P1 has no obvious response to the addition of metal
ions (Fig. 2a). As is evident from Fig. 2b, almost no fluorescence
3 2 2
CHCl and CH Cl , which can be attributed to the nonplanarity of
the twisted polymer backbone and the flexible n-butoxy group
substituents. In addition, the ethynyl linker can reduce steric
hindrance between phenyl groups and also have a beneficial
influence on the stability of the resulting chiral polymers. TGA
results of P1 and P2 suggest that the chiral polymers have high
þ
3þ
2þ
response can be observed upon the addition of Ag , Al , Ba
,
2þ
2þ
3þ
2þ
3þ
þ
2þ
2þ
þ
2þ
4þ
Ca , Cd , Cr , Fe , K , Mg , Mn , Na , Zn , Zr at 1:1 M
ratio. But Cu ions can lead to almost complete quenching of P2.
Fig. 2c illustrates the fluorescence titration of chiral polymer P2
ꢀ
ꢀ
thermal stability without loss weight before 420 C and 380 C,
respectively (Fig. 1). Therefore, the resulting chiral polymers P1 and
P2 can provide a desirable thermal property for practical applica-
tion as a fluorescence sensor.
2þ
2þ
towards Cu . The quenching ratios (
h
) of P2 on Cu
can be
0
is the
calculated according to equation:
h
¼ 1ꢂI/I . Herein, I
0
fluorescent emission intensity in the absence of the quencher, and
I is the fluorescent emission intensity in the presence of the
quencher. As a result, the fluorescence quenching ratio of P2 is
.2. The selective recognition of the polymer sensors of P2 on Cu2
þ
2þ
3
0.913 upon 1:1 M ratio addition of the Cu salt solution. The
quenching efficiency of P2 is related to the Stern-volmer constant,
The fluorescence spectra of P1 and P2 were carried out in
a solution of THF. Both P1 and P2 can emit the strong fluorescence
K
SV, and is determined by monitoring measurable changes in the
fluorescence spectra via the Stern-volmer equation:
Scheme 1. Synthesis procedures of 3, 4, M-1, P1 and P2.

6036
L. Wang et al. / Polymer 53 (2012) 6033e6038
I
0
/I ¼ 1 þ KSV[Q], herein, [Q] is the quencher concentration.
2
þ
Average lg KSV of the polymer P2 on Cu is 6.245. The fluores-
cence curve of P2 with Cu
quenching value I
concentration change from 0.1 to 1.0 ꢁ 10 mol/L, indicating that
the polymer sensor can form a 1:1 Cu(II)-containing polymer
complex called Cu(II)-P2 (Fig. 2c). Moreover, the bright blue color
of the polymer sensor disappears under a commercially available
UV lamp after upon addition of Cu . Meanwhile, it could be also
observed that Ni ions can lead to obvious quenching of P2.
2
þ
reveals that the fluorescent
a
2þ
1000
0
/I exhibited a good linear response to the Cu
ꢂ5
8
6
4
2
00
00
00
00
0
2þ
2
þ
3
.3. CD spectra of 3, 4, P1, P2 and Cu(II)-P2
The CD spectra of 3, 4, P1, P2 and Cu(II)-P2 are shown in Fig. 3
ꢂ5
(1.0 ꢁ 10 mol/L in THF). It can be observed that there is great
difference between chiral small molecules and two chiral polymers.
Both the chiral molecule 3 and the chiral polymer P1 exhibit strong
CD signals with negative and positive Cotton effects at short
wavelengths in their CD spectra. It can also be found that P1 has
strong negative Cotton effect at wavelengths of 331 nm, which can
be regarded as the extended conjugated structure in the repeating
unit and a high rigidity of polymer backbone [47,54e57]. P1
appears the strongest Cotton effect in the long wavelength centered
at about 395 nm, which is attributed to significant chiral amplifi-
cation arisen from the helical conformation backbone of chiral
conjugated polymer chain [45,58,59,61]. In this paper the resulting
chiral polymer P1 can adopt a stable helical configuration since the
+
3+
2+
2+
2+
3+
2+
3+
+
2+
2+
+
2+
4+
2+
Blank Ag Al Ba Ca Cd Cr Cu Fe K Mg Mn Na Ni Zr Zn
b
5
00
00
00
00
00
0
4
3
2
1
(R,R)-Schiff base moieties can orient a welledefined spatial
arrangement in the regular and rigid polymer backbone, that is,
each unit in the chiral polymer P1 acts independently with an
organized helical chain structure. A helix is highly regular structure
in which all bonds that form the helix have the same configuration
(either R or S) [55,60e62]. Takeishi pointed out that the main
chains composed of rigid segments are twisted to one-direction by
the chiral molecule linker and an ordered structure of the main
chain backbone can adopt the stable helical configuration [63].
Yashima thought the generation of a helical structure should result
in significant chiral amplification [62]. On the contrary, chiral small
molecule 4, chiral polymer P2 and the corresponding polymer
complex Cu(II)-P2 appear almost no Cotton effect in their CD
spectra. It could be contributed to the reason that the chiral moiety
+
3+
2+
2+
2+
3+
2+
3+
+
2+
2+
+
2+
4+
2+
Blank Ag Al Ba Ca Cd Cr Cu Fe K Mg Mn Na Ni Zr Zn
c
3
3
2
2
1
1
50
350
300
250
2
+
Cu
(R,R)-1,2-diaminocyclohexane is no longer available for the conju-
00
50
00
50
00
gated system [64]. It can be demonstrated by their specific rotation
2
1
1
00
50
00
2
5
values (Table 1). ½
a
ꢃ
of chiral small molecules 3 and 4 are ꢂ258.62
25
D
(c 0.23, THF) and ꢂ86.15 (c 0.26, THF). And ½
a
ꢃ
of the chiral
D
50
polymers P1 and P2 are ꢂ435.0 (c 0.20, THF) and þ10.0 (c 0.20,
2
5
THF), respectively. Compared with 4 and P1, ½
a
ꢃ
of P2 shows
0
.0
0.2
0.4
0.6
0.8
1.0
1.2
D
Cu x10 mol/L
Chiral small molecules 3
1000000
Chiral small molecules 4
P1
50
P2
500000
Cu(II)-P2
0
0
380 400 420 440 460 480 500 520 540 560 580
Wavelength (nm)
-500000
ꢂ5
Fig. 2. (a) Fluorescence responses of P1 (1.0 ꢁ 10 mol/L in THF,
l
ex ¼ 381 nm); (b)
-
1000000
ꢂ5
P2 (1.0 ꢁ 10 mol/L in THF,
l
ex ¼ 371 nm) to 1:1 M ratio of various metal ions; (c)
ꢂ5
Fluorescence spectra of P2 (1.0 ꢁ 10 mol/L in THF,
l
ex ¼ 371 nm) in the presence of
2þ
-1500000
increasing amount of Cu . The inset features the dependence of the intensity emission
at 422 nm on the concentration of Cu2 (insert: the photo of the fluorescence color of
polymer sensor P2 (1) and Cu(II)-P2 (2)).
þ
250
300
350
400
450
500
Wavelength(nm)
Fig. 3. CD spectra of 3, 4, P1, P2 and Cu(II)-P2 (1.0 ꢁ 10ꢂ5 mol/L in THF).

L. Wang et al. / Polymer 53 (2012) 6033e6038
6037
Table 1
25
a
½
a
ꢃ
and CD data of 3, 4, P1 and P2.
D
150
3
4
P1
P2
2
5
½
a
ꢃ
(THF)
ꢂ258.62 (c 0.23) ꢂ86.15 ꢂ435.0 (c 0.20) þ10.0 (c 0.20)
c 0.26)
D
(
Cu(II)-P2
5
[
q
] ꢁ 10
þ12.91 (234.5)
e
þ2.32 (248.5)
þ2.32 (299.5)
ꢂ4.20 (331.0)
ꢂ6.98 (395.0)
þ2.71 (234.5)
Cu(II)-P2 +
Cu(II)-P2 +
L
-phenylglycinol
(
l
max in nm) ꢂ16.18 (255.5)
100
D
-phenylglycinol
50
opposite specific rotation signal, indicating the chiral repeating unit
2
5
in the disordered state and the flexible chain backbone. ½
a
ꢃ
of P1
D
is much larger than its corresponding chiral small molecule 3,
which can be attributed to the counteracting result of the repeating
chiral unit upon the formation of helical chiral polymer configu-
ration [65e70].
0
400
450
500
550
Wavelength (nm)
3.4. Fluorescence recognition of the polymer complex Cu(II)-P2 on
D
- or -phenylglycinol
L
b
In this paper we further investigated the fluorescence response
behaviors of chiral polymer sensor towards phenylglycinol by using
P1 and P2. Almost no fluorescence response changes and enan-
tioselectivities can be observed by adding phenylglycinol enantio-
mers (Figs. S3 and S4). Interestingly, while using in situ generated
5
4
3
2
1
1
:1 Cu(II)-containing polymer complex Cu(II)-P2 as a fluorescence
senor, remarkable difference in fluorescent enhancement
a
response behaviors between these two enantiomers could be
detected as demonstrated in Fig. 4. The fluorescence spectra of
ꢂ5
Cu(II)-P2 (1.0 ꢁ 10 mol/L in THF) were carried out by addition of
L-phenylglycinol
ꢂ3
L
- or
Fig. 4a,
rescent intensity of Cu(II)-P2.
fluorescence enhancement response of Cu(II)-P2, but its influence
shows lower than that of -isomer. It can also be found that the
D
-phenylglycinol (2.0 ꢁ 10 mol/L in THF). As is evident from
D-phenylglycinol
L
-phenylglycinol can lead to a large increase on the fluo-
D
-isomer can also lead to the obvious
L
0
100
200
300
400
500
600
700
fluorescent emission wavelengths do not show an obvious differ-
ence between guest-free sensor and guest-sensor. More impor-
tantly, Cu(II)-P2 solution can turn on bright blue fluorescence color
-
5
[
phenylglycinol] x 10 mol/L
ꢂ5
change again upon addition of
L-phenylglycinol under a commer-
Fig. 4. (a) Fluorescence spectra of Cu(II)-P2 (1.0 ꢁ 10 mol/L in THF,
l
ex ¼ 371 nm)
ꢂ3
with D- or L-phenylglycinol (2.0 ꢁ 10 mol/L in THF) and (b) plots of (I/I
0
) vs. phe-
cially available UV lamp, which can be clearly observed by the
naked eyes for direct visual discrimination at low concentration
nylglycinol concentration during the titration of Cu(II)-P2 with D- or L-phenylglycinol
(
l
ex ¼ 371 nm, em ¼ 422 nm). (insert: the photo of the fluorescence color changes of
l
(Fig. 4a). The obvious fluorescence enhancement of Cu(II)-P2 with
Cu(II)-P2 complex sensor (1), Cu(II)-P2 þ D-phenylglycinol (2) and Cu(II)-P2 þ L-
phenylglycinol (3), [D- or L-phenylglycinol]: [Cu(II)-P2] ¼ 150: 1).
phenylglycinol can be attributed to a ligand displacement mecha-
nism [45e51]. As chelating ligands, amino alcohols are highly
associable with many metal ions. Thus, they probably are able to
associate with Cu(II) and displace the fluorescence polymer P2
from Cu(II)-P2, which may conduce to the fluorescence recovery of
P2 quenched by Cu(II) as shown on Scheme 2.
Herein, the interaction of Cu(II)-P2 with phenylglycinol was
studied at a much broader concentration range. In regard to the
fluorescence signal changes of this chiral polymer sensor on
phenylglycinol, the fluorescence intensities appear gradual
In a set of comparable experiments, we also studied the inter-
action of (R,R)-Cu(II)-P2 sensor with other amino alcohols
including phenylalaninol, alaninol and valinol (Scheme 3), almost
no enantioselective recognition effect could be detected even the
obvious fluorescence enhancement responses can be observed
enhancement upon addition of
glycinol in the range from 1:10 to 1:700 M ratios (Fig. S5). The
enantiomeric fluorescence difference ratio ef [ef¼(I ꢂI )/(I ꢂI )] in
this case is 2.90 at 1:150 M ratio, which indicates that (R,R)-Cu(II)-
P2 can exhibit considerable enantioselective response towards
L-phenylglycinol and D-phenyl-
L
0
D
0
L-
phenylglycinol. The reason may be attributed to an inherent chiral
recognition based on the steric repulsion of (R,R)-Cu(II)-P2
precursor for
generated 1:1 (R,R)-Cu(II)-P2 is controlled by the flexible CeN
bond and can well fit for the insert of guest molecule -phenyl-
L-phenylglycinol. The building block of in situ
L
glycinol to coordinate with Cu(II) and displace the fluorescence
polymer P2.
Scheme 2. Proposed mechanism of ligand displacement process.

6038
L. Wang et al. / Polymer 53 (2012) 6033e6038
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4
. Conclusions
We designed and synthesized a versatile chiral polymer P2 as
a “turn-off” fluorescence sensor for Cu(II), and the in situ generated
R,R)-Cu(II)-P2 can exhibit remarkable “turn-on” fluorescent
enhancement response and considerable enantioselectivities
toward -phenylglycinol via a ligand displace mechanism. This
(
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We gratefully acknowledge the National Natural Science Foun-
dation of China (No. 21074054, 51173078, 21172106), National Basic
Research Program of China (2010CB923303) and Zhejiang Provin-
cial Natural Science Foundation (No. Y4110141) for their financial
support.
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Appendix A. Supplementary data
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1
Supplementary data related to this article can be found at http://
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