Salen-based chiral fluorescence polymer sensor for enantioselective recognition of α-hydroxyl carboxylic acids

Article abstract of DOI:10.1021/jo3005233

(R,R)-Salen-based chiral polymer P-1 was synthesized by the polymerization of 5,5′-((2,5-dibutoxy-1,4-phenylene)bis(ethyne-2,1-diyl))bis(2-hydroxy-3- (piperidin-1-ylmethyl) benzaldehyde (M-1) with (1R,2R)-cyclohexane-1,2-diamine (M-2) via nucleophilic addition- elimination reaction, and (R,R)-salan-based polymer P-2 could be obtained by the reduction reaction of P-1 with NaBH ₄. (R,R)-Salen-based chiral polymer P-1 can exhibit greater fluorescence enhancement response toward (l)-α-hydroxyl carboxylic acids, and the value of enantiomeric fluorescence difference ratio (ef) can reach as high as 8.41 for mandelic acid and 6.55 for lactic acid. On the contrary, (R,R)-salan-based chiral polymer P-2 shows obvious fluorescence quenching response toward α-hydroxyl carboxylic acids. Most importantly, (R,R)-salen-based polymer P-1 can display bright blue fluorescence color change in the presence of (l)-α-hydroxyl carboxylic acids under a commercially available UV lamp, which can be clearly observed by the naked eyes.

Full text of DOI:10.1021/jo3005233

Article
pubs.acs.org/joc
Salen-Based Chiral Fluorescence Polymer Sensor for Enantioselective
Recognition of α-Hydroxyl Carboxylic Acids
Fengyan Song,† Guo Wei,† Lu Wang,† Jiemin Jiao,† Yixiang Cheng,*,† and Chengjian Zhu*,‡
†Key Laboratory of Mesoscopic Chemistry of MOE, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing
210093, China
‡State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing
210093, China
S
* Supporting Information
ABSTRACT: (R,R)-Salen-based chiral polymer P-1 was synthesized by the polymer-
ization of 5,5′-((2,5-dibutoxy-1,4-phenylene)bis(ethyne-2,1-diyl))bis(2-hydroxy-3-(pi-
peridin-1-ylmethyl) benzaldehyde (M-1) with (1R,2R)-cyclohexane-1,2-diamine (M-2)
via nucleophilic addition− elimination reaction, and (R,R)-salan-based polymer P-2
could be obtained by the reduction reaction of P-1 with NaBH4. (R,R)-Salen-based chiral
polymer P-1 can exhibit greater fluorescence enhancement response toward (L)-α-
hydroxyl carboxylic acids, and the value of enantiomeric fluorescence difference ratio (ef)
can reach as high as 8.41 for mandelic acid and 6.55 for lactic acid. On the contrary,
(R,R)-salan-based chiral polymer P-2 shows obvious fluorescence quenching response
toward α-hydroxyl carboxylic acids. Most importantly, (R,R)-salen-based polymer P-1
can display bright blue fluorescence color change in the presence of (L)-α-hydroxyl
carboxylic acids under a commercially available UV lamp, which can be clearly observed
by the naked eyes.
possible cooperative effects of multiple chiral units. In
particular, they can make use of the high sensitivity of
conjugated polymers to external structural perturbations and
to electron density changes of the conjugated polymer
backbone, when they interact and form complexes with
analytes.7,8 Swager reported that the delocalizable π-electronic
conjugated “molecular wire” polymer can greatly amplify the
fluorescence response signal due to facile energy migration
along the polymer backbone upon light excitations.7a,b
Moreover, these chiral fluorescence polymers can be system-
atically modified by the introduction of the different functional
groups based on steric and electronic property at well-defined
molecular level.
Optically active 1,2-diaminocyclohexane is one of the most
important C2 symmetric compounds. The chiral salen/salan-
based ligands have been extensively used in asymmetric
catalysis because of the potentially tetradentate N2O2 donor
with metal ions.9 Recently, these molecules are getting
increasing attention in chiral recognition area. In our previous
work, we first reported salen-based and salan-based chiral
polymers as fluorescence sensors for enantioselective recog-
nition of phenylglycinol.8b In this paper, we further designed
(R,R)-salen-based and salan-based chiral fluorescence polymers
by introduction of the piperidyl group as the side chain of the
conjugated polymer backbone to systematically adjust the
microenvironment of (R,R)-salen/salan moieties and improve
INTRODUCTION
■
More and more attention has been paid to highly selective and
sensitive fluorescence sensors for enantioselective recognition
because chiral molecular recognition is one of the most
fundamental and significant processes in nature systems. Chiral
recognition has great potential applications in analytical,
biological, and clinical biochemical environments, and it also
effectively provides a real-time analytical tool for chiral
compound assay.1 Using chiral fluorescence-based sensors can
not only greatly facilitate rapid determination of enantiomeric
composition of chiral compounds, but also allow a rapid
screening of high-throughput catalysts for their asymmetric
synthesis.2 In the past several years, there has been a growing
interest in the enantioselective recognition of α-hydroxycarbox-
ylic acids due to their biological significance and synthetic
utility.1c,3,4 Pu and co-workers developed several highly
enantioselective fluorescence sensors bearing the scaffold of
BINOL-amino alcohol for α-hydroxycarboxylic acids, α-amino
acid, and their derivatives.3d,e,5 Zhao also reported that
enantioselective recognition of mandelic acid could be detected
by using the boronic acid-based chiral fluorescence sensors via
the relay mechanism of the D-PET effect.4b,f,i
Although there have been some reports on enantioselective
recognition of chiral hydroxycarboxylic acids, most of them are
based on chiral small molecules,3,4 and fluorescent polymer-
based sensors are very few.6 Chiral polymers used as
fluorescence-based sensors for enantioselective recognition of
chiral molecules offer several advantages over small molecule
sensors, such as fluorescence efficiency enhancement and
Received: March 15, 2012
Published: April 29, 2012
© 2012 American Chemical Society
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Scheme 1. Synthesis Procedures of M-1, the Chiral Polymer Sensors P-1 and P-2
Table 1. GPC, Thermal Properties, and Fluorescence Quantum Yields of P-1 and P-2
a
a
a
b
c
20
yield (%)
[α]D (c 0.2, THF)
Mw (g/mol)
Mn (g/mol)
PDI (Mw/Mn)
Td (°C)
fluorescence quantum yield
P-1
P-2
72
83
+316.0
+57.0
13040
14080
4800
8800
2.72
1.60
400
380
0.087
0.30
a
Molecular weight was determined by gel permeation chromatography (GPC) with Waters-244 HPLC pump, and THF was used as solvent and
b
c
relative to polystyrene standards. Temperature at 5% weight loss estimated using TGA under N2. The fluorescence quantum yields of P-1 and P-2
were determined using quinine bisulfate in 0.05 M H2SO4 solution as the standard.
enantioselective recognition effect of α-hydroxyl carboxylic
acids. The results show that (R,R)-salen-based chiral
fluorescence polymer can exhibit great fluorescence enhance-
ment response toward (L)-α-hydroxyl carboxylic acids. More
importantly, (R,R)-salen-based chiral polymer can display
bright blue fluorescence color change in the presence of (L)-
α-hydroxyl carboxylic acids under a commercially available UV
lamp, which can be clearly observed by the naked eye. To the
best of our knowledge, this is the first example of the polymer-
based fluorescence sensor for enantioselective recognition of α-
hydroxyl carboxylic acids.
Supporting Information, Figure S6). (R,R)-Salen/salan moieties
of P-1 and P-2 as the chiral sites can orient a well-defined
spatial arrangement in the regular polymer main chain
backbones. Furthermore, (R,R)-salen/salan moieties modified
by two piperidyl groups can effectively activate and improve the
building block microenvironment of (R,R)-salen or salan
receptors, while the chiral polymer hosts interact with chiral
guests.
Both P-1 and P-2 can dissolve in common organic solvents,
such as toluene, CH2Cl2 and THF, which can be attributed to
the nonplanarity of the polymer backbone and the flexible n-
butoxy substitutents on phenyl units as side chains of the
polymers. gel permeation chromatography (GPC), thermal
properties, and quantum yields of P-1 and P-2 are showed in
Table 1. According to Table 1, GPC results of both P-1 and P-
2 show moderate molecular weights. But the molecular weight
of P-1 is higher than P-2, which could be attributed to the
changes of conformational mobility. TGA of P-1 and P-2 were
carried out under a N2 atmosphere at a heating rate of 10 °C/
min (see Supporting Information, Figure S1). The result shows
that P-1 and P-2 have high thermal stability without loss weight
before 380 °C and tend to complete decomposition at 700 °C.
Therefore, the two polymers can provide a desirable thermal
property for practical application as fluorescence sensors. The
CD spectra of P-1 and P-2 have been investigated in THF
solution (see Figure 3). The molecular ellipticities of P-1 are as
follows: [θ]λ(max) = +2.83 × 105 (245.8 nm), −2.15 × 105
(265.4 nm), +1.27 × 105 (322.4 nm), −5.98 × 104 (347.6 nm),
+3.28 × 105 (384.0 nm); and P-2: +4.33 × 104 (384.0 nm).
The fluorescence spectra of P-1 and P-2 were carried out in a
mixed solution of toluene and DME (v/v, 0.4%). The (R,R)-
salen-based chiral polymer P-1 host shows a weak fluorescence
emission with lower fluorescence quantum yield of 0.087 at 465
nm on excitation at 420 nm due to the strong and ordered
intramolecular hydrogen bonding between imine and hydroxyl
RESULTS AND DISCUSSION
■
The synthesis procedures of M-1 and chiral polymer sensors P-
1 and P-2 are outlined in Scheme 1. 1,4-Dibutoxy-2,5-
diethynylbenzene was synthesized according to the reported
literature.8f 5-Bromo-2-hydroxy-3-(piperidin-1-ylmethyl)-
benzaldehyde could be synthesized by Mannich reaction from
the starting material 5-bromosalicylaldehyde in 77% yield.10
The monomer M-1, 5,5′-((2,5-dibutoxy-1,4-phenylene)bis-
(ethyne-2,1-diyl))bis(2-hydroxy-3-(piperidin-1-ylmethyl)-ben-
zaldehyde, could be synthesized by the reaction of 1,4-dibutoxy-
2,5-diethynylbenzene with 5-bromo-2-hydroxy-3-(piperidin-1-
ylmethyl)-benzaldehyde via a typical Pd-catalyzed Sonogashira
cross-coupling reaction. (R,R)-Salen-based polymer P-1 was
synthesized by the polymerization of M-1 with (1R,2R)-
cyclohexane-1,2-diamine (M-2) in 72% yield. (R,R)-Salan-
based polymer P-2 could be obtained by reduction of P-1 with
NaBH4 in 83% yield. P-1 and P-2 were further purified by
MeOH and collected as yellow and gray solids, respectively. As
evident from 1H NMR spectra of the polymers P-1 and P-2, P-
1 has one well-resolved peak at 8.29 ppm corresponding to the
imine group adjacent to the phenyl (CHN). But 8.29
ppm in 1H NMR spectra of the polymer P-2 disappears, which
indicates the complete reduction of imine group of P-1 (see
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of phenol, which leads to nonradiative transition. But the (R,R)-
salan-based chiral polymer P-2 can show a strong fluorescence
emission with higher fluorescence quantum yield of 0.30 at 465
nm on excitation at 385 nm, which may be attributed to the
weak and disordered intramolecular hydrogen bonding between
hydroxyl of phenol and amine or piperidyl. Figure 1 shows the
fluorescence spectra of the chiral polymer P-1 (1.0 × 10−5 mol/
L corresponding to salen-based unit) upon addition of (L)- or
(D)-mandelic acid (1.0 × 10−2 mol/L in toluene, 10% v/v
DME). Obvious fluorescence enhancement response could be
observed as demonstrated in Figure 1a, on the contrary, (D)-
mandelic acid (MA) has little effect on the fluorescence
intensity of P-1 under the same condition (Figure 1b). In
addition, in the spectra of P-1, a new shoulder peak at 440 nm
can be observed upon addition of MA. As the molar ratio of
(L)-MA increases from 1 to 15, the fluorescence intensities of
P-1 also appear to have gradual enhancement and reach as high
as 8.79-fold, compared to 2.59-fold of (D)-MA (Figure 1c). The
selective recognition effect on the guest of the chiral molecular
isomers is related to the enantiomeric fluorescence difference
ratio, ef [ef = (IL − I0)/(ID − I0)]. I0 represents the fluorescence
emission intensity in the absence of the chiral substrate. IL and
ID are the fluorescence intensities in the presence of (L)-
substrate and (D)-substrate, respectively.3k The value of ef is
8.41 for P-1, which indicates that this polymer can exhibit
highly enantioselective response toward (L)-MA. The reason
may be attributed to an inherent chiral recognition based on
the steric repulsion of (R,R)-salen precursor for (L)-MA. The
building block of (R,R)-salen receptor modified by the piperidyl
groups can well fit for the formation of a more stable complex
of R−L complex as compared to the R−D diastereomeric
complex. Interestingly, the fluorescent color of P-1 solution
turns bright blue upon the addition of (L)-MA, which can be
clearly observed by the naked eyes (Figure 1c, inset). In this
experiment, the fluorescence image of a solution of the polymer
(5 × 10−5 mol/L) plus 15.0 equiv of MA were excited by a
commercially available UV lamp (λ = 365 nm). Meanwhile, we
also found that free-P-1 solution appears to have the similar
fluorescent color to (D)-MA-polymer.
In a set of comparable experiments, we also studied the
fluorescence response behavior of polymer P-2 on (D)- and (L)-
MA. As is evident from Figure 2, the interesting results show
that both (L)- or (D)-MA can lead to gradual and obvious
fluorescence quenching of salan-based chiral polymer P-2 as the
molar ratio increase of the guest MA. Fluorescence quenching
ratios of P-2 are 60.6% for (D)-MA and 83.4% for (L)-MA, the
1:30 molar ratio addition of MA, respectively. The obvious
fluorescence enhancement of P-1 with MA can be attributed to
the suppressed photoinduced-electron-transfer (PET) quench-
ing11 when the protons of MA interact with the nitrogen atoms
of imine moieties in the salen-based chiral polymer main chain
through the intramolecular hydrogen bond.12 On complexation,
the lone pair of electrons on the nitrogen atom is no longer
available for PET, leading to the fluorescence enhancement.8b,c
Compared to the rigid and helical chain backbone structure of
salen-based polymer P-1, the chain backbone of the salan-based
polymer P-2 becomes flexible and twisted, and the intra-
molecular hydrogen bond is in disorder. It is evident from CD
spectra of P-1 and P-2 (Figure 3) that the rigid and stable chain
configuration of salen-based polymer P-1 appears to have
strong positive and negative Cotton effect since the (R,R)-salen
moieties can orient a well-defined spatial arrangement in the
regular polymer backbone. On the contrary, salan-based
polymer P-2 appears to have almost no Cotton effect at
short wavelengths in the CD spectra. It may be attributed to the
chiral salan-based repeating unit in the disordered state and the
irregular chain backbone. It can be further demonstrated by
specific rotation values from the great difference of two chiral
polymers (Table 1). While the flexible salen-based polymer P-2
reacts with the guest MA, formation of the unstable complex
will produce a relaxation channel for the excited state to decay.
Figure 1. Fluorescence spectra of P-1 (1.0 × 10−5 mol/L
corresponding to salen moiety in toluene, 0.4% v/v DME) with
increasing amounts of (L)-MA (a) and (D)-MA (b) (0, 1, 3, 5, 8, 10,
15, 30, 60, 100 × 10−5 mol/L, 1.0 × 10−2 mol/L in toluene, 10% v/v
DME). (c) Fluorescence enhancement of P-1 (1.0 × 10−5 mol/L)
with (D)- and (L)-MA (λem = 465 nm; λex = 420 nm) (inset: left, P-1;
middle, P-1 + (D)-MA; right, P-1 + (L)-MA).
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treated with 2-acetoxy-2-phenylacetic acid or methyl 2-hydroxy-
2-phenylacetate (1.0 × 10−2 mol/L in toluene, 5% v/v DME),
P-1 displays a little fluorescence enhancement response, but
almost no enantioselective effect can be observed (see
Supporting Information, Figures S2 and S3). These studies
demonstrate that both the carboxylic acid group and the
hydroxyl group of MA play important role in the
enantioselective recognition of salen-based chiral fluorescence
sensor. Inspired by the preliminary results, we further
investigated the enantioselectivity of P-1 toward other α-
hydroxyl carboxylic acids, such as lactic acid and tartaic acid. As
is evident from Figure 4, the chiral polymer sensor can exhibit
obvious enantioselective response toward (L)-lactic acid, and
the value of ef is 6.55 at 1:20 molar ratio. While using (D)-/(L)-
tartaic acid as guest molecules, no obvious fluorescence
enhancement responses on the enantioselectivity of tartaic
acid were observed (see Supporting Information Figure S4).
CONCLUSION
■
In summary, two novel chiral fluorescence polymers incorpo-
rating functional (R,R)-salen/salan moieties were designed.
And (R,R)-salen-based chiral polymer can exhibit a greater
fluorescence “turn-on” response toward (L)-α-hydroxyl carbox-
ylic acids and appear bright blue fluorescence color change
under a commercially available UV lamp, which can be clearly
observed by the naked eyes. The value of enantiomeric
fluorescence difference ratio (ef) can reach as high as 8.41 for
mandelic acid and 6.55 for lactic acid. On the contrary, (R,R)-
salan-based chiral polymer shows an obvious fluorescence
“turn-off” response toward α-hydroxyl carboxylic acids.
Figure 2. (a) Fluorescence spectra of P-2 (1.0 × 10−5 mol/L
corresponding to salan moiety in toluene, 0.4% v/v DME) with and
without (D)- and (L)-MA (1.0 × 10−2 mol/L in toluene, 10% v/v
DME) at 1:30 molar ratio. (b) Fluorescence enhancement of P-2 (1.0
× 10−5 mol/L) with (D)- and (L)-MA (λem = 465 nm; λex = 385 nm).
EXPERIMENTAL SECTION
■
5-Bromo-2-hydroxy-3-(piperidin-1-ylmethyl)benzaldehyde.
Piperidine (2.0 mL, 20 mmol) was added to a solution of
paraformaldehyde (0.6 g, 20 mmol) dissolved in HAc (30 mL) and
stirred for 12 h at room temperature. Then 5-bromo-2-hydrox-
ybenzaldehyde (4.02 g, 20 mmol) was added, and the mixture was
heated at reflux for 24 h. After cooling to rt, the mixture was brought
to pH ∼ 8 with saturated Na2CO3, extracted with CHCl3, dried over
anhydrous Na2SO4, and concentrated. The crude product was purified
by silica gel column chromatography (ethyl acetate/petroleum ether,
2:1, v/v) to yield 4.61 g (77%) of the product as a pale yellow solid
1
after removal of the solvent: mp 70 °C (dec.); H NMR (300 MHz,
CDCl3) δ 10.36 (s, 1H), 7.78 (d, J = 2.1 Hz, 1H), 7.32 (d, J = 2.1 Hz,
1H), 3.72 (s, 2H), 2.58 (br, 4H), 1.73 −1.65 (m, 4H), 1.55 (br, 2H);
13C NMR (75 MHz, CDCl3) δ 189.2, 161.3, 136.7, 129.7, 125.4, 124.4,
110.7, 60.6, 53.7, 25.5, 23.5; ESI-MS 298.17; FT-IR (KBr, cm−1) 3417,
2935, 2864, 1674, 1594, 1448, 1385, 1238, 1110, 989. Anal. Calcd for
C48H59N4O3: C, 77.91; H, 8.01; N, 7.57. Found: C, 76.59; H, 7.69; N,
7.80. Anal. Calcd for C13H16BrNO2: C, 52.36; H, 5.41; N, 4.70. Found:
C, 52.29; H, 5.41; N, 4.80.
5,5′-((2,5-Dibutoxy-1,4-phenylene)bis(ethyne-2,1-diyl))bis-
(2-hydroxy-3-(piperidin-1-ylmethyl)benzaldehyde. 1,4-Dibu-
toxy-2,5-diethynylbenzene could be synthesized from hydroquinone
by a four-step reaction according to reported literature.8f The mixture
of 1,4-dibutoxy-2,5-diethynylbenzene (0.87 g, 3.2 mmol), 5-bromo-2-
hydroxy-3-(piperidin-1-ylmethyl)benzaldehyde (2.01 g, 6.7 mmol),
Pd(PPh3)2Cl2 (121.2 mg, 0.17 mmol), and CuI (33.1 mg, 0.17 mmol)
was dissolved in 50 mL of anhydrous Et3N. The reaction mixture was
stirred for 24 h at 70 °C under N2. 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/
triethylamine, 1:1, v/v) and then dichloromethane as eluent on a
short plug of silica gel. The solvent was removed and then washed by
ethyl acetate to afford 5,5′-((2,5-dibutoxy-1,4-phenylene)bis(ethyne-
2,1-diyl))bis(2-hydroxy-3-(piperidin-1-ylme-thyl)benzaldehyde (M-1)
Figure 3. CD spectra of P-1 and P-2 (1.0 × 10−4 mol/L in THF).
As a result, the initial excitation leads to formation of an
exciton, which can rapidly migrate between isoenergetic sites
along the π-electronic conjugated system to a low energy
acceptor site, which blocks the radiative decay and activates the
nonradiative path.7d,13
To further understand the fluorescence response behavior of
the interaction mechanism between host P-1 and guest MA, we
studied the fluorescence change of P-1 in the presence of the
derivatives of MA by esterified protection of either the acid
group or the hydroxyl group (Scheme 2). Whether P-1 was
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Scheme 2. Chiral Guests Used in the Enantioselective Recognitions with the P-1 and P-2
1
as a yellow powder (975 mg, 43%): mp > 300 °C; H NMR (300 M
Hz, CDCl3) δ 10.41 (s, 2H), 7.87 (s, 2H), 7.40 (s, 2H), 6.99(s, 2H),
4.05 (t, J = 6.6 Hz, 4H), 3.76 (s, 4H), 2.60 (br, 8H), 1.88−1.53 (m,
20H), 1.04 (t, J = 7.5 Hz, 6H); 13C NMR (75 MHz, CDCl3) δ 189.9,
162.4, 153.4, 137.0, 131.2, 123.4, 123.1, 116.8, 113.8, 113.7, 93.8, 85.0,
69.3, 60.8, 53.7, 31.3, 25.5, 23.6, 19.2, 13.9; ESI-MS 705.33; FT-IR
(KBr, cm−1) 3422, 2931, 2857, 2360, 1671, 1603, 1465, 1383, 1208,
1113. Anal. Calcd for C44H52N2O6: C, 74.97; H, 7.44; N, 3.97. Found:
C, 75.18; H, 7.42; N, 3.80.
Chiral Polymer Sensor P-1. A mixture of M-1 (705.0 mg, 1.0
mmol) and (1R,2R)-cyclohexane-1,2-diamine (114.2 mg, 1.0 mmol)
was dissolved in THF (60 mL) and kept refluxing for 12 h. The
solvent was removed under reduced pressure, the residue was
dissolved in a small quantity of THF, and 100 mL of methanol was
added to precipitate the polymer. A yellow solid was filtered off and
washed with methanol several times. Further purification could be
conducted by dissolving the polymer in CH2Cl2 to precipitate in
methanol again. The polymer was dried under vacuum at room
25
temperature for 24 h. The final yield was 72% (563.2 mg): [α]D
=
1
+316.0 (c 0.2, THF); Mw = 13040, Mn = 4800, PDI = 2.72; H NMR
(300 MHz, CDCl3) δ 8.29 (s, 2H), 7.52 (s, 2H), 7.34 (s, 2H), 6.96 (s,
2H), 4.02 (t, J = 6.3 Hz, 4H), 3.66−3.53 (m, 4H), 3.36 (br, 2H), 2.50
(br, 8H), 1.85−1.44 (m), 1.00 (t, J = 6.9 Hz, 6H); FT-IR (KBr, cm−1)
3418, 2926, 2857, 2200, 1625, 1497, 1456, 1380, 1266, 1197, 1021,
852. Anal. Calcd for C48H59N4O3: C, 77.91; H, 8.04; N, 7.57. Found:
C, 77.59; H, 7.69; N, 7.80.
Chiral Polymer Sensor P-2. Polymer P-1 (200 mg) was dissolved
in the mixed solvents of 10 mL of THF and 10 mL of MeOH, and
then 80 mg NaBH4 was added in batches to the above solution. The
reaction mixture was stirred at room temperature for 2 h, and 10 mL
of water was added to stop the reduction reaction. The mixture was
extracted with CH2Cl2 (3 × 20 mL). The combined organic layers
were dried with anhydrous Na2SO4 and evaporated under reduced
25
pressure to afford P-2 as a gray powder (167 mg, 83% yield): [α]D
=
1
+57.0 (c 0.2, THF); GPC Mw = 14080; Mn = 8800; PDI = 1.60; H
NMR (300 Hz, CDCl3) δ = 7.33 (s, 2H), 7.12 (s, 2H), 6.97 (s, 2H),
4.02 (s, 4H), 3.92−3.74 (m, 4H), 3.60 (s, 4H), 2.47−2.34 (m, 8H +
2H), 2.11 (s, 4H), 1.82−1.27 (m), 1.00 (s, 6H); FT-IR (KBr, cm−1)
3424, 2925, 2358, 1601, 1463, 1381, 1194, 1107, 854. Anal. Calcd for
C48H63N4O3: C, 77.48; H, 8.53; N, 7.53. Found: C, 77.36; H, 8.58; N,
7.03.
ASSOCIATED CONTENT
■
S
* Supporting Information
1
Fluorescence and data mentioned in above paragraphs and H
and 13C NMR spectra of all new compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.
Figure 4. Fluorescence spectra of P-1 (1.0 × 10−5 mol/L in toluene,
0.4% v/v DME) with increasing amounts of (L)-LA (a) and (D)-LA
(b) (0, 1, 3, 5, 8, 10, 15, 20, 30, 40 × 10−5 mol/L, 1.0 × 10−2 mol/L in
toluene, 5% v/v DME). (c) Fluorescence enhancement of P-1 (1.0 ×
10−5 mol/L) with (D)- and (L)-LA (λem = 465 nm; λex = 420 nm).
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: yxcheng@nju.edu.cn; cjzhu@nju.edu.cn.
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(8) For selected examples, see: (a) Song, F. Y.; Ma, X.; Hou, J. L.;
Huang, X. B.; Cheng, Y. X.; Zhu, C. J. Polymer 2011, 52, 6029. (b) Xu,
Y.; Zheng, L. F.; Huang, X. B.; Cheng Y. X. Zhu, C. J. Polymer 2010,
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We gratefully acknowledge the National Natural Science
Foundation of China (No. 21074054, 51173078, 21172106),
National Basic Research Program of China (2010CB923303),
and Zhejiang Provincial Natural Science Foundation (No.
Y4110141) for their financial support.
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