Strict size specificity in colorimetric anion detection based on poly(phenylacetylene) receptor bearing second generation lysine dendrons

Article abstract of DOI:10.1021/ma200710r

Poly(phenylacetylene) bearing second generation lysine dendrons through urea groups (poly-2) was demonstrated to be a superior anion receptor possessing strict size specificity in colorimetric anion detection. On the basis of the comparison of the colorim

Full text of DOI:10.1021/ma200710r

ARTICLE
pubs.acs.org/Macromolecules
Strict Size Specificity in Colorimetric Anion Detection Based on
Poly(phenylacetylene) Receptor Bearing Second Generation Lysine
Dendrons
Ryosuke Sakai,†,§ Naoya Sakai,† Toshifumi Satoh,† Wen Li,‡ Afang Zhang,‡ and Toyoji Kakuchi*,†
†Division of Biotechnology and Macromolecular Chemistry, Graduate School of Engineering, Hokkaido University, Sapporo 060-8628,
Japan
‡Department of Polymer Materials, Shanghai University, Shanghai 201800, China
S Supporting Information
b
ABSTRACT: Poly(phenylacetylene) bearing second genera-
tion lysine dendrons through urea groups (poly-2) was demon-
strated to be a superior anion receptor possessing strict size
specificity in colorimetric anion detection. On the basis of the
comparison of the colorimetric response behavior between
poly-2 and poly-1, which is poly(phenylacetylene) bearing first
generation lysine dendrons, the size of the pendant dendron was
implied to dictate the selectivity in the colorimetric anion
1
detection. Various instrumental analyses including H NMR,
light scattering, and viscosity measurements concluded that the conjugation of the bulky G2 dendrons in the vicinity of the urea
receptors plays a crucial role in imparting the strict size specificity in the anion-sensing ability of poly-2.
’ INTRODUCTION
The detailed investigations suggested that the observed colori-
metric response was dictated by the anion size. For these
polymers, the polymer backbone probably acts as a scaffold for
the three-dimensional organization of the multiple urea binding
sites, which might impart a size-selective anion-binding ability
based on the steric hindrance.40ꢀ49 Although such a receptor
design that leverages a macromolecular scaffold might be one of
the successful examples for size-specific anion detection, further
improvement in the anion selectivity is still desired to realize a
reliable and sophisticated anion sensor.
For the enhancement and adjustment of the size specificity in
anion recognition, one of the rational approaches should be the
fine-tuning of the steric factor in the vicinity of the binding sites.
For the modulation of such a steric factor, the dendron emerges
as an ideal candidate for the bulky substituent capable of spatially
regulating the receptor environment because significant perfor-
mance has already been proven in a wide variety of chemistry
fields including supramolecular chemistry.50ꢀ53 In fact, dendro-
nized polymers, which are linear polymers bearing dendrons at
each repeating unit on the polymer chain, often exhibit a unique
behavior due to the three-dimensional bulkiness of the pendant
dendrons.54ꢀ76 Therefore, the conjugation of bulky dendrons in
the vicinity of the urea groups on the poly(phenylacetylene)
receptor is highly expected to influence the selectivity in colori-
metric anion detection.
The fabrication of a reliable, robust, and efficient anion sensor
has been increasingly in demand because anions are significant
analytes in diverse fields including environmental, industrial,
biological, and medical uses.1,2 For such sensory materials, the
design and construction of synthetic receptors with selective
anion detection ability is highly required.3ꢀ19 However, the
realization of such selective and specific anion binding has been
recognized as a remarkably challenging task because of the
diversity in the chemical and physical properties of anions, which
includes basicity, size, and shape. Therefore, considerable effort has
been devoted recently to exploring the rational design of receptor
molecules for any target anions, which led to developing several
effective strategies for selective anion detection, e.g., the fine-tuning
of binding site, utilization of macrocyclic receptor molecules, and
three-dimensional arrangement of multiple binding sites.20ꢀ36
For example, Beer and colleague have succeeded in selective
luminescent sensing of hydrogensulfate by using a rhenium-
(I)ꢀbipyridyl-based rotaxane, in which the unique interlocked
structural cavity plays an important role in the selectivity.21 Flood
et al. have realized selective recognition of Clꢀ and Brꢀ for a series of
macrocyclic [34]triazolophane receptors, in which the fixed size
of the central cavity provides a means for the selective recognition.26
Sessler and co-workers have reported that a pyrrolyl-based
triazolophane bearing both CH and NH donor groups exhibits
a preferential binding ability for pyrophosphate anions.34
We previously reported the colorimetric anion detection
based on urea-functionalized poly(phenylacetylene)s, in which
the color change was dependent on the anions employed.37ꢀ39
Received: March 28, 2011
Revised:
April 27, 2011
Published: May 12, 2011
r
2011 American Chemical Society
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|

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ARTICLE
Scheme 1. Synthesis of Poly(phenylacetylene) Bearing G2 Lysine Dendrons (Poly-2)
We have now designed poly(phenylacetylene) bearing second
generation lysine dendrons through a urea group (poly-2) as a
novel anion receptor with colorimetric detection ability
(Scheme 1). The morphology of poly-2 in solution was deter-
mined by the NMR, static light scattering, and viscosity measure-
ments. Circular dichroism (CD) and UVꢀvis analyses in the
presence of a series of anions were carried out to clarify the
specificity in the colorimetric anion sensing of poly-2. This result
was compared with those for poly(phenylacetylene) featuring first
generation lysine dendrons (poly-1) and urea-deficient poly-
(phenylacetylene) (poly-11), providing insight into the strict size
specificity in the colorimetric anion detection of poly-2.
exclusion limit, 4 ꢁ 105; bead size, 7 μm), a DAWN 8 multiangle laser
light scattering (MALLS) detector (Wyatt Technology, Santa Barbara,
CA), a Viscostar viscosity detector (Wyatt Technology), and an
Optilab rEX refractive index detector (Wyatt Technology). The
MarkꢀHouwinkꢀSakurada constant (R) was estimated by ASTRA
5.1.6.0 software (Wyatt Technology).
Synthesis of 4. A solution of methanesulfonyl chloride (MsCl)
(2.41 g, 21.4 mmol) in 10 mL of dichloromethane (DCM) was added
dropwise to a mixture of 3 (3.5 g, 10.5 mmol) and triethylamine (TEA)
(5.33 g, 52.7 mmol) in DCM (120 mL) at ꢀ10 °C. After stirring for 2 h,
MeOH was added to quench the reaction. After washing with pure
water, the organic phase was dried over MgSO4 and then evaporated.
The residue was purified by column chromatography on silica gel with
hexane/ethyl acetate (2/1, v/v) to give 4 as a colorless oil. Yield: 2.5 g
’ EXPERIMENTAL SECTION
1
(58%). H NMR (CDCl3): δ (ppm) = 1.31ꢀ1.62 (m, 24H, CH2 þ
CH3), 3.05ꢀ3.17 (m, 5H, CH2 þ CH3), 3.82ꢀ3.84 (m, 1H, CH2),
4.16ꢀ4.30 (m, 2H, CH2 þ CH), 4.64ꢀ4.80 (br, 2H, NH). HRMS
(ESI): m/z calcd for C17H34N2O7S [M þ H]þ: 411.2159. Found:
411.2161.
Materials. All chemicals were purchased from commercial sources
and used without further purification unless otherwise noted. Bis-Boc-
lysinol (3),77 4-ethynylbenzoic acid,78 and Rhþ(2,5-norbornadiene)-
[(η6-C6H5)Bꢀ(C6H5)3] (Rh(nbd)BPh4)79 were prepared in accor-
dance with previous reports.
Synthesis of 5. A mixture of 4 (2.50 g, 6.09 mmol) and NaN3
(1.19 g, 18.27 mmol) in DMF (30 mL) was stirred overnight at 55 °C.
After evaporation, the residue was dissolved in DCM and washed with
brine. The organic phase was dried over MgSO4, and the solvent then
evaporated. The residue was purified by column chromatography on
silica gel with hexane/ethyl acetate (6/1, v/v) to give 5 as a colorless oil.
Yield: 1.7 g (78%). 1H NMR (CDCl3): δ (ppm) = 1.37ꢀ1.48 (m, 24H,
CH2 þ CH3), 3.09ꢀ3.11 (m, 2H, CH2), 3.32ꢀ3.41 (m, 2H, CH2), 3.68
(m, 1H, CH), 4.58ꢀ4.61 (d, 2H, NH). 13C NMR (CDCl3): δ (ppm) =
23.03, 23.36, 27.30, 27.81, 28.76, 28.82, 30.21, 31.97, 32.29, 40.49, 50.60,
55.23, 79.52, 80.07, 155.80, 156.48. HRMS (ESI): m/z calcd for
C16H31N5O4Na [M þ Na]þ: 380.2268. Found: 380.2265.
Instruments. The 1H and 13C NMR spectra were recorded using a
JEOL JNM-A400II and JEOL JNM-EX270 instruments. Size exclusion
chromatography (SEC) was performed at 40 °C using a Jasco high-
performance liquid chromatography (HPLC) system (PU-980 Intelli-
gent HPLC pump, CO-965 Column oven, RI-930 Intelligent RI
detector, and Shodex DEGAS KT-16) equipped with a Shodex Asahipak
GF-310 HQ column (linear, 7.6 mm ꢁ 300 mm; pore size, 20 nm; bead
size, 5 μm; exclusion limit, 4 ꢁ 104) and a Shodex Asahipak GF-7 M HQ
column (linear, 7.6 mm ꢁ 300 mm; pore size, 20 nm; bead size, 9 μm;
exclusion limit, 4 ꢁ 107) in DMF containing lithium chloride (0.01 M)
at a flow rate of 0.4 mL minꢀ1. The number-average molecular weight
(Mn) and polydispersity (Mw/Mn) of the polymer were calculated on
the basis of polystyrene calibration. The specific rotations were mea-
sured in THF using a Jasco DIP 1000 digital polarimeter with a Na lamp
(wavelength, 589 nm). A circular dichroism (CD) spectrum was
obtained using a JASCO J-720 spectropolarimeter equipped with a
Jasco ETC-505T temperature controller. The melting points were
measured by the differential scanning calorimetry (DSC) analysis using
a Bruker AXS DSC 3100 SA under a nitrogen atmosphere. The absolute
molecular weight and viscosity of polymer samples were determined by
SEC in THF at 40 °C using an Agilent 1100 series instrument equipped
with two Shodex KF-804 L columns (linear, 8.0 mm ꢁ 300 mm;
Synthesis of 6. To a solution of 5 (1.60 g, 4.48 mmol) in THF
(40 mL) was added 25% HCl(aq) (10 mL) at 0 °C, and the reaction
mixture was stirred for 26 h at room temperature. The solvent was
1
removed in vacuo to give 6 as a colorless oil. Yield: 1.00 g (97%). H
NMR (CD3OD): δ (ppm) = 1.34ꢀ1.53 (m, 2H, CH2), 1.67ꢀ1.74 (m,
4H, CH2), 2.94ꢀ2.97 (m, 2H, CH2), 3.56ꢀ3.60 (m, 1H, CH2),
3.61ꢀ3.3.65 (m, 1H, CH2), 3.77ꢀ3.81 (dd, 1H, CH). 13C NMR
(CD3OD): δ (ppm) = 23.03, 23.36, 27.30, 27.81, 28.76, 28.82, 30.21,
31.97, 32.29, 34.90, 40.49, 50.60, 55.23, 79.52, 80.07, 155.80, 156.48.
HRMS (ESI): m/z calcd for C6H16N5 [M þ H]þ: 158.1400. Found:
158.1397.
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Synthesis of 7. To a mixture of 6 (1.0 g, 4.34 mmol) and
diisopropylethylamine (DIPEA) (5.6 g, 43.0 mmol) in DMF (25 mL)
was slowly added a solution of Boc-Lys(Boc)-ONp (9) (5.07 g,
10.9 mmol) in DCM (40 mL) at ꢀ15 °C. After stirring overnight, the
reaction mixture was washed with brine, and then the organic phase was
dried over MgSO4. After evaporation, the residue was purified by
column chromatography on silica gel with hexane/ethyl acetate (1/1
Synthesis of G1 Monomer (1). To a solution of 4-ethynylaniline
(309 mg, 2.64 mmol) in DCM (14.0 mL) was added CDI (485 mg,
2.99 mmol). After stirring at room temperature for 18 h, a solution of 10
(683 mg, 2.06 mmol) in DCM (11.0 mL) was then added to the reaction
mixture, which was further stirred at room temperature for 22 h. The
solution was removed under reduced pressure. The residue was purified
by column chromatography on silica gel with DCM/ethyl acetate (1/1,
v/v) to give 1 as a white solid. Yield: 737 mg (75.3%); mp =123 °C.
1
and 1/2, v/v) to give 7. Yield: 3.20 g (91%). H NMR (CDCl3): δ
1
(ppm) = 1.24ꢀ1.52 (m, 50 H, CH2 þ CH3), 1.57ꢀ1.74 (m, 4H, CH2),
3.08ꢀ3.10 (m, 4H, CH2), 3.30ꢀ3.39 (m, 2H, CH2), 3.91 (br, 1H, CH),
4.08ꢀ4.10 (m, 1H, CH), 4.24ꢀ4.25 (m, 1H, CH), 4.77 (br, 2H, NH),
5.59 (br, 1H, NH), 5.91 (br, 1H, NH), 7.01 (br, 1H, NH), 7.10 (br, 1H,
NH). 13C NMR (CDCl3): δ (ppm) = 21.60, 22.96, 23.11, 28.53, 28.55,
28.59, 29.60, 29.81, 30.61, 31.04, 31.56, 32.73, 36.60, 37.80, 40.37, 48.87,
54.14, 54.60, 54.93, 79.12, 80.01, 80.09, 156.22, 156.42, 156.63, 162.67,
173.40, 173.69. HRMS (ESI): m/z calcd for C38H71N9O10Na [M þ
Na]þ: 836.5216. Found: 836.5211.
[R]D = ꢀ4.12°. H NMR (CDCl3): δ (ppm) = 1.43ꢀ1.48 (m, 24H,
CH2 þ CH3), 3.01 (s, 1H, CtCH), 3.10 (m, 2H, CH2), 3.28 (m, 2H,
CH2), 3.57 (br, 1H, CH), 4.73 (s, 1H, NH), 5.13 (s, 1H, NH), 5.94 (s,
1H, NH), 7.38 (m, 4H, aromatic), 7.77 (s, 1H, NH). 13C NMR
(CDCl3): δ (ppm) = 22.49, 28.34, 28.43, 29.85, 31.62, 39.65, 44.08,
51.65, 79.36, 79.55, 83.74, 115.52, 118.55, 132.87, 140.09, 156.23,
156.61. HRMS (ESI): m/z calcd for C25H38N4O5Na [M þ Na]þ:
497.2740. Found: 497.2744. Anal. calcd for C25H38N4O5: C, 63.27; H,
8.07; N, 11.81. Found: C, 63.31; H, 8.02; N, 11.72.
Synthesis of G2-NH2 (8). A mixture of 7 (3.10 g, 3.81 mmol) and
PPh3 (1.50 g, 5.72 mmol) in THF (120 mL) and water (20 mL) was
stirred overnight at 50 °C. After evaporation of THF, DCM was added to
dissolve the organic compounds. The organic phase was separated,
further washed with water, and dried over MgSO4. After evaporation, the
residue was purified by column chromatography on silica gel with
DCM/MeOH (15/1 and 10/1, v/v) to give 8 as a colorless form. Yield:
Synthesis of Monomer 11. To a mixture of 3 (292 mg,
0.878 mmol), 4-ethynylbenzoic acid (191 mg, 1.31 mmol), and
4-(dimethylamino)pyridinium p-toluenesulfonate (DPTS) (106 mg,
0.361 mmol) in DCM (5.0 mL) was added N,N0-diisopropylcarbodiimide
(DIC) (170 mg, 1.35 mmol) under a N2 atmosphere. The reaction
mixture was stirred for 40 h at room temperature and was then filtered.
The filtrate was evaporated, and the residue was purified by column
chromatography on silica gel with hexane/ethyl acetate (3/2, v/v)
to give 11 as a white powder. Yield: 253 mg (62.6%); mp =105 °C.
[R]D = ꢀ10.9°. 1H NMR (CDCl3): δ = 1.35ꢀ1.65 (m, 24H, CH2 þ
CH3), 3.12 (m, 2H, CH2), 3.25 (s, 1H, CtCH), 4.00 (m, 1H, CH2),
4.30 (m, 2H, CH2 þ CH), 4.62 (br, 2H, NH), 7.55 (d, J = 8.5 Hz, 2H,
aromatic), 7.99 (d, J = 8.6 Hz, 2H, aromatic). 13C NMR (CDCl3): δ =
22.92, 28.32, 28.41, 29.79, 31.47, 40.12, 49.50, 67.16, 77.20, 79.56, 80.15,
82.74, 126.90, 129.56, 129.88, 132.08, 155.55, 156.03, 165.78. HRMS
(ESI): m/z calcd for C25H36N2O6Na [M þ Na]þ: 483.2471. Found:
1
2.60 g (86%). H NMR (CD3OD): δ (ppm) = 1.24ꢀ1.51 (m, 50 H,
CH2 þ CH3), 1.64ꢀ1.84 (m, 4H, CH2), 2.73ꢀ2.77 (m, 2H, CH2),
3.09ꢀ3.36 (m, 5H, CH2), 3.39ꢀ3.40 (m, 1H, CH2), 3.73 (br, 1H,
CH2), 3.84 (br, 1H, CH), 4.10ꢀ4.13 (m, 2H, CH), 4.78 (br, 1H, NH),
4.91 (br, 1H, NH), 5.68 (br, 1H, NH), 5.76 (br, 1H, NH), 6.88 (br, 1H,
NH), 6.96 (br, 1H, NH). 13C NMR (CD3OD): δ (ppm) = 21.43, 23.27,
28.80, 28.86, 29.91, 29.99, 31.50, 32.41, 38.54, 40.53, 54.61, 54.96, 79.41,
80.25, 156.68, 171.53, 173.51. HRMS (ESI): m/z calcd for C38H73N7-
O10Na [M þ Na]þ: 810.5311. Found: 810.5323.
483.2502. Anal. calcd for C25H36N2O6 1/5H2O: C, 64.69; H, 7.90; N,
Synthesis of G2 Monomer (2). To a solution of 4-ethynylaniline
(112 mg, 951 μmol) in DCM (5.0 mL) was added 1,10-carbonyldiimi-
dazole (CDI) (175 mg, 1.08 mmol). After stirring at room temperature
for 18 h, a solution of 8 (596 mg, 756 μmol) in DCM (4.0 mL) was
added to the reaction mixture, which was further stirred at room
temperature for 22 h. The solution was removed under reduced
pressure. The residue was purified by column chromatography on silica
gel with DCM/MeOH (27/2, v/v) to give 2 as a pale yellow solid. Yield:
621 mg (87.6%); mp =107 °C. [R]D = ꢀ45.7°. 1H NMR (CDCl3): δ
(ppm) 1.22ꢀ1.57 (m, 50 H, CH2 þ CH3), 1.58ꢀ1.85 (m, 4H, CH2),
3.00 (s, 1H, CtCH), 2.90ꢀ3.46 (m, 8H, CH2), 3.89 (m, 1H, CHꢀ),
4.12 (br, 2H, CH), 4.77 (br, 1H, NH), 5.13 (br, 1H, NH), 5.77ꢀ5.97
(br, 3H, ꢀNH), 6.86ꢀ7.10 (br, 2H, NH), 7.38 (m, 4H, aromatic), 8.20
(s, 1H, NH). 13C NMR (CDCl3): δ (ppm) 21.65, 22.81, 28.31, 28.35,
28.42, 28.47, 31.87, 37.97, 40.08, 43.70, 48.59, 54.37, 54.84, 83.88, 79.10,
79.80, 115.07, 118.07, 132.82, 140.44, 155.90, 156.05, 173.36, 173.57.
HRMS (ESI): m/z calcd for C47H78N8O11Na [M þ Na]þ: 953.5688.
3
6.04. Found: C, 64.67; H, 7.96; N, 6.10.
Polymerization of 1. The polymerization of 1 was carried out in a
dry Schlenk flask under an argon atmosphere. Rh(nbd)BPh4 (6.3 mg,
12 μmol) was added to a Schlenk flask with a stirring bar and was
evacuated for 15 min. Monomer 1 (294 mg, 619 μmol) was placed in
another flask and dissolved in dry THF (21.0 mL). The monomer
solution was sparged with argon for 10 min and then transferred via a
cannula to the Schlenk flask loaded with Rh(I) catalyst. The reaction
mixture was stirred at room temperature for 24 h. PPh3 (19.9 mg, 75.8 μmol)
was then added to the reaction mixture to terminate the polymeriza-
tion reaction. The solution was concentrated and then poured into a
large amount of diethyl ether. The precipitate was purified by repreci-
pitation with THF/diethyl ether and was then dried under reduced
pressure to give poly-1 as a green powder. Yield: 263 mg (89.4%). Mn =
2.0 ꢁ 105, Mw/Mn = 3.4.
Polymerization of 2. The same procedure as that for the poly-
merization of 1 was applied to the polymerization of 2, in which
Rh(nbd)BPh4 (5.6 mg, 11 μmol), 2 (500 mg, 530 μmol), dry THF
(18.0 mL), and PPh3 (18.0 mg, 67.0 μmol) were used to give poly-2 as a
brown solid. Yield: 470 mg (93.0%). Mn = 2.5 ꢁ 105, Mw/Mn = 9.0.
Polymerization of 11. The same procedure as that for the
polymerization of 1 was applied to the polymerization of 11, in which
Rh(nbd)BPh4 (2.3 mg, 4.47 μmol), 11 (103 mg, 224 μmol), dry THF
(7.2 mL), and PPh3 (6.9 mg, 26.3 μmol) were used to give poly-11 as a
yellow solid. Yield: 92.5 mg (89.8%). Mn = 7.4 ꢁ 104, Mw/Mn = 3.1.
Typical Experimental Procedure for CD and Absorption
Measurements. All CD and UVꢀvis absorption measurements were
performed in dry THF. The concentrations of poly-1, poly-2, and poly-
11, which were calculated on the basis of the monomer units, were
1.0 mM for all measurements. A typical experimental procedure is
Found: 953.5681. Anal. calcd for C47H78N8O11 3/4H2O: C, 59.76; H,
3
8.48; N, 11.86. Found: C, 59.87; H, 8.58; N, 11.83.
Synthesis of G1-NH2 (10). A mixture of 5 (1.80 g, 5.04 mmol) and
PPh3 (1.98 g, 7.55 mmol) in THF (50 mL) and water (10 mL) was
stirred overnight at 50 °C. After evaporation, the residue was dissolved in
DCM and washed with brine. The organic phase was dried over MgSO4.
The residue was purified by column chromatography on silica gel with
DCM/MeOH (10/1, v/v) to give 10 as a pale yellow oil. Yield: 1.42 g
(85%). 1H NMR (CDCl3): δ (ppm) = 1.43ꢀ1.48 (m, 22H, CH2þCH3),
1.83ꢀ1.99 (m, NH2), 2.10ꢀ2.16 (m, 2H, CH2), 2.64ꢀ2.77 (m, 2H, CH2),
3.07ꢀ3.11 (m, 2H, CH), 3.53 (br, 1H, CH), 4.71ꢀ4.80 (m, 2H, NH).
13C NMR (CDCl3): δ (ppm) = 23.45, 25.89, 28.82, 30.20, 32.78, 40.58,
46.25, 52.94, 53.82, 68.33, 79.38, 79.57, 156.51, 156.58. HRMS (ESI):
m/z calcd for C16H34N3O4 [M þ H]þ: 332.2544. Found: 332.2550.
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Scheme 2. Synthesis of Phenylacetylene Monomer Featuring G2 Lysine Dendron and Urea Receptor (2)
described as follows: Stock solutions of poly-2 (2.0 mM) and tetra-n-
butylammonium acetate (TBAA) (50 mM) in THF were prepared in
flasks equipped with stopcocks. The poly-2 solution (1 mL) and the
TBAA solution (0.8 mL) were transferred to a vial, and the resulting
mixture was then diluted with dry THF (0.2 mL) to give the sample
solution, in which the [monomer units of poly-2] and
[TBAA]/[monomer units of poly-2] were adjusted to 1.0 mM and 20,
respectively. The CD and UVꢀvis absorption spectra of the resulting
sample solution were measured in a quartz cell with a 1.0 mm path length
at 25 °C.
’ RESULTS AND DISCUSSION
Synthesis of Poly(phenylacetylene) Bearing Lysine-Based
Dendron. The synthetic procedure for the phenylacetylene
Figure 1. 1H NMR spectra of (a) 2 and (b) poly-2 in THF-d8 at
monomer with a second generation lysine dendron and a urea
group (2) is illustrated in Scheme 2. Boc-protected lysinol (3)
was treated with MsCl, followed by the substitution reaction with
NaN3 to afford core unit (5). The deprotection of 5 using 25%
HCl(aq) in THF provided the corresponding HCl salt (6).
Compound 6 was reacted with Boc-Lys(Boc)-ONp (9) to
produce azide-functionalized second generation lysine dendron
(7), which was further converted to the corresponding amine (8)
through a Staudinger reaction with PPh3. Finally, the precursor 8
was reacted with 4-ethynylaniline and CDI to yield target G2
monomer (2).
ambient temperature.
dendron protons of poly-2, while no signal was observed at
3.26 ppm where the acetylene proton appeared for that of
monomer 2 (Figure 1). It is important to note that signals
corresponding to the main chain and aromatic protons were
extremely broadened under any analysis conditions. This phe-
nomenon is ascribable to the low mobility of the polymer
backbone probably due to the dendronized structure. Given
the tendency that poly(phenylacetylene) brushes show no main
chain signals in their 1H NMR spectra,80ꢀ84 the G2 dendron on
poly-2 is bulky enough to provide significant influence on the
whole polymer structure and conformation of poly-2.
The polymerization of 2 was carried out using Rh(nbd)BPh4
in dry THF at ambient temperature for 24 h to produce
dendronized poly(phenylacetylene) (poly-2) in 93% yield
(Scheme 1). By the size exclusion chromatography (SEC)
In order to further provide information on the morphology of
measurement, the number-average molecular weight (Mn,SEC
)
poly-2 in solution, the absolute molecular weight (Mw,MALLS)
and molecular weight distribution (Mw/Mn) of poly-2 were
and viscosity were determined by SEC equipped with a multi-
angle laser light scattering (MALLS) detector and viscosity
detector. The resulting Mw,MALLS value was 1.6 ꢁ 106, which
1
determined to be 2.5 ꢁ 105 and 9.0, respectively. The H
NMR spectrum of poly-2 displayed the signals due to the
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Figure 2. MarkꢀHouwink plots of poly-2 in THF.
was much higher than that determined by the above SEC
measurement. In addition, the inherent viscosity ([η]) was
estimated to be 50 mL gꢀ1. These values are the averaged value
of the entire polymer chain of poly-2. Because the detectors
are connected to the SEC in this instrument, the dependences of
the Mw,MALLS and [η] values of each polymer chain could also be
obtained, which allows a more detailed discussion of the mor-
phology of poly-2.
Figure 3. (a) CD (upper) and absorption (lower) spectra and (b)
photograph of poly-2 in the presence of TBA salts of a series of
anions in THF at 25 °C ([monomer units of poly-2] = 1.0 mM,
[anion]/[monomer units of poly-2] = 20).
The relationship between the intrinsic viscosity and the
molecular weight is described by the MarkꢀHouwinkꢀSakurada
equation as follows:
½ηꢂ ¼ KMR
Cotton effect was observed at a wavelength shorter than 300 nm,
whereas it should be due to the chirality of the lysine dendron
itself. Although the very small positive Cotton effect at 330 nm
might be due to the main chain chirality, poly-2 was not found to
form a one-handed helical structure regardless of the side chain
chirality derived from the lysine dendron.86
where K and R are the MarkꢀHouwink constant and exponent,
respectively. Based on the results of the light scattering and
viscosity measurements, the MarkꢀHauwink plots, double-loga-
rithmic plots of [η] versus Mw,MALLS of poly-2, were prepared
(Figure 2). The plots displayed linearity with a slope of 1.25,
which is identical with the R value of poly-2. The R value is a
particularly important value, which is known to be closely related
to the polymer morphology in solution. In general, conventional
linear polymers with a random coil conformation possess R
values ranging from 0.5 to 0.8. On the other hand, R values larger
than 1.0 are obtained for elongated rod polymers. Therefore, the
observed large R value of 1.25 strongly suggests that poly-2
possesses an elongated rodlike conformation in THF, which
should be ascribed to the huge G2 dendron pendants. Compre-
hensively considering the morphology of poly-2 in THF, the
elongated poly(phenylacetylene) backbone is certain to be
densely covered with a number of the bulky lysine dendrons.
Note that the urea functionalities in poly-2 as the anion receptor
units are also located medial to the whole polymer chain, leading
to a unique size specificity in anion recognition.
Colorimetric Anion Detection. To evaluate the anion-
sensing ability of poly-2, circular dichroism (CD) and UVꢀvis
measurements were performed in the presence of tetra-n-butyl-
ammonium (TBA) salts of a series of anions in THF, as shown in
Figure 3. Although poly-2 possesses a π-conjugated system in the
main chain structure, no absorption was observed in the visible
range, leading to a colorless solution. Considering the brown
color of poly-2 in the solid state, the conjugation length of the
main chain, which is susceptible to the polymer conformation,
should be very short in solution probably due to the bulkiness of
the G2 dendron and intramolecular hydrogen bonding between
the urea groups.85 In the CD spectrum of poly-2, a negative
Upon the addition of CH3CO2ꢀ, the colorless polymer
solution immediately turned to a red solution, indicating an
acetate recognition property of poly-2. As shown in Figure 3a, a
new absorbance with a maximum at 512 nm was developed by
the CH3CO2ꢀ addition.ꢀ87 On the other hand, the CD spectrum
of the poly-2/CH3CO2 system showed an intense split-type
Cotton effect in the range from 340 to 630 nm, indicating that a
biased one-handed helical structure was induced in the backbone
of poly-2 by the CH3CO2ꢀ addition. Given that the absorption
change was accompanied by a drastic CD change, the observed
color change was found to be attributable to the extension of the
main chain conjugation length based on the conformation
change in the polymer main chain.
ꢀ
Large bathochromic shifts similar to the case with CH3CO2
were observed for the addition of Fꢀ and Clꢀ, thus providing red
solutions (Figure 3).87 The accompanying CD change indicated
that the colorimetric response is based on the conformational
change in poly-2. However, the CD spectrum of poly-2 in the
presence of Fꢀ exhibited a weak negative Cotton effect at
500 nm, which was different from those observed with
CH3CO2ꢀ and Clꢀ. The Fꢀ recognition of poly-2 may producꢀe
a different helical conformation from those driven by CH3CO2
and Clꢀ. In contrast to the above three anions, Brꢀ, NO3ꢀ, N3
,
ꢀ
and ClO4ꢀ apparently caused no essential changes in both their
CD and absorption spectra, though slightly pale yellow solutions
were obtained in the cases with NO3 and N3ꢀ. These results
ꢀ
suggested that poly-2 possesses a strict selectivity in the colori-
metric anion detection.
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Scheme 3. Synthesis of Poly(phenylacetylene) Bearing G1 Lysine Dendrons (Poly-1)
Figure 5. 1H NMR spectra of 2 in the presence of (a) 0, (b) 0.5, (c) 1.0,
(d) 2.0, (e) 3.0, (f) 4.0, (g) 5.0, and (h) 10 equiv of TBAA in THF-d8.
Closed circles show the signals due to the urea protons.
response was basically due to the conformational change in the
polymer main chain of poly-1.87 In sharp contrast to poly-2, poly-
1 exhibited obvious colorimetric responses to N3ꢀ, NO3ꢀ, and
Brꢀ. Given that the structural difference between poly-1 and
poly-2 is only the generation of the lysine dendron, the size of the
pendant dendron might play an important role in governing the
selectivity in the colorimetric anion detection for these macro-
molecular receptors.
Figure 4. (a) CD (upper) and absorption (lower) spectra and (b)
photograph of poly-1 in the presence of TBA salts of a series of
anions in THF at 25 °C ([monomer units of poly-1] = 1.0 mM,
[anion]/[monomer units of poly-1] = 10).
Although a number of urea-based receptor molecules have
been clarified to possess an anion-responsive property, the
observed anion selectivity in the color change was
unprecedented.18,88 Considering that the most characteristic
feature of poly-2 is a dendronized structure, such unusual
selectivity in the colorimetric response might be caused by the
bulky dendron side groups. Thus, we synthesized a control
polymer with first generation lysine dendrons (poly-1) to
compare its anion detection ability with that of poly-2. According
to the synthetic procedure summarized in Scheme 3, poly-1 was
successfully prepared. The CD and UVꢀvis measurements of
poly-1 were then conducted in the presence of TBA salts of a
series of anions in THF (Figure 4). Poly-1 itself afforded an
almost colorless solution similar to the case of poly-2. Upon the
addition of anions except for ClO4ꢀ, the colorless solution
immediately turned to colored solutions dependent on the
anions. These anions brought about clear changes in both CD
and UVꢀvis spectra, indicating that the observed colorimetric
In order to provide further insight into the selectivity in the
colorimetric anion detection, we next focused on the clarification
of the detailed mechanism of the anion recognition event. In
anion recognition chemistry, a color change of a urea receptor
molecule has been known to be based on a complex formation
with an anion or anion-induced deprotonation.88ꢀ91 To eluci-
date the anion recognition mode of poly-2, we performed a 1H
NMR titration experiment on monomer 2 with CH3CO2ꢀ, in
which 2 was used as a model compound of poly-2 because the
1
highly broadened signals in the H NMR spectrum of poly-2
were expected to provide no useful information. With the
addition of CH3CO2ꢀ, a downfield shift was observed in the
signals due to the urea protons of 2 (Figure 5). This downfield
shift of the urea protons indicates the establishment oꢀf a92hydrogen
bond interaction between urea groups and CH3CO2
. Further-
more, as well as urea protons, those of the amide and carbamate
of 2 in the range from 8.3 to 5.7 ppm also shifted to the downfield
region with the CH3CO2ꢀ addition. These results indicate that
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Scheme 4. Synthesis of Urea-Deficient Poly(phenylacetylene) Bearing G1 Lysine Dendrons (Poly-11)
Figure 6. CD (upper) and absorption (lower) spectra of poly-11 in the
presence and absence of tetra-n-butylammonium acetate (TBAA) in
THF at 25 °C ([monomer units of poly-11]
[TBAA]/[monomer units of poly-11] = 20).
= 1.0 mM,
all the urea, amide, and carbamate groups on poly-2 participate in
the anion binding.
Here a question arises. Is the urea group unnecessary for the
colorimetric anion detection? To exclude this possibility, a urea-
deficient polymer, poly(phenylacetylene) bearing first genera-
tion dendrons through ester linkages (poly-11), was prepared as
a suitable model compound for clarifying the importance of the
urea receptor unit in the colorimetric anion detection
(Scheme 4). The CD and UVꢀvis measurementsꢀof poly-11
were carried out in the presence of CH3CO2 in THF
(Figure 6). In sharp contrast to poly-1 and poly-2, no essential
change was observed in the spectra of poly-11. On the basis of
these observations, the complex formation between the urea
group and the anion is clarified to play a crucial role in the
colorimetric anion detection of poly-1 and poly-2. Although
the amide and carbamate groups on the polymers might facilitate
the anion binding event, such interactions do not contribute to
the color change of the polymers.
We finally focused on the elucidation of the selectivity in the
colorimetric response of poly-1 and poly-2. For anion recogni-
tion based on urea receptors, the color change is generally
dictated by the basicity of the anions,18,88 which increases in the
order of ClO4ꢀ < Brꢀ ≈ NO3ꢀ < Clꢀ < N3ꢀ < CH3CO2ꢀ < Fꢀ.93
However, neither poly-1 nor poly-2 showed a colorimetric response
well correlated with the basicity of the anions. Therefore, other
Figure 7. Relationship between the ionic radius of the employed anion
and the apparent red shift (Δλ) observed in the UVꢀvis absorption
spectra of (a) poly-1 and (b) poly-2.
factors should be involved in the anion detection events of both
poly-1 and poly-2.
Figure 7 shows the relationship between the ionic radius94,95
of the employed anion and the apparent red shift (Δλ) observed
in the UVꢀvis absorption spectra of poly-1 and poly-2.96 The
plots for poly-1 indicated a tendency for a smaller anion to
provide a larger red shift in the absorption spectrum. In addition,
a more clear-cut effect of the anion size on the colorimetric
response was observed in the plots for poly-2. Therefore, it is no
wonder that the steric factor of the pendant dendron participates
in this colorimetric response as one of the prime elements
dictating the selectivity of the anion detection. Particularly for
poly-2, the steric hindrance of the bulky G2 dendron would
highly restrict the interaction itself of the larger anions with the
urea group and/or the complexation-triggered conformational
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change in the polymer chain, thus realizing the unprecedentedly
strict size-specific anion detection. Although some effective
methods for size-specific anion detection have already been
established, such strict size specificity has never been achieved.
(5) Gale, P. A.; Quesada, R. Coord. Chem. Rev. 2006,
250, 3219–3244.
(6) Anzenbacher, P., Jr.; Nishiyabu, R.; Palacios, M. A. Coord. Chem.
Rev. 2006, 250, 2929–2938.
(7) Davis, A. P. Coord. Chem. Rev. 2006, 250, 2939–2951.
(8) Katayev, E. A.; Ustynyuk, Y. A.; Sessler, J. L. Coord. Chem. Rev.
2006, 250, 3004–3037.
’ CONCLUSIONS
(9) Gale, P. A. Chem. Commun. 2008, 4525–4540.
(10) Schmidtchen, F. P. Chem. Soc. Rev. 2010, 39, 3916–3935.
(11) Kubik, S. Chem. Soc. Rev. 2010, 39, 3648–3663.
(12) Kim, S.-K.; Sessler, J. L. Chem. Soc. Rev. 2010, 39, 3784–3809.
(13) Juwarker, H.; Jeong, K.-S. Chem. Soc. Rev. 2010, 39, 3664–3674.
(14) Joyce, L. A.; Shabbir, S. H.; Anslyn, E. V. Chem. Soc. Rev. 2010,
39, 3621–3632.
(15) Custelcean, R. Chem. Soc. Rev. 2010, 39, 3675–3685.
(16) Cavallo, G.; Metrangolo, P.; Pilati, T.; Resnati, G.; Sansotera,
M.; Terraneo, G. Chem. Soc. Rev. 2010, 39, 3772–3783.
(17) Brotherhood, P. R.; Davis, A. P. Chem. Soc. Rev. 2010,
39, 3633–3647.
We demonstrated the size-selective colorimetric anion sensing
based on poly(phenylacetylene) bearing second generation
lysine dendrons through a urea group. On the basis of various
experiments and instrumental analyses, the conjugation of the
bulky G2 dendrons in the vicinity of the urea receptors was
clarified to impart the strict size selectivity to the dendronized
polymer. Although there are several ways to enhance selectivity
in anion recognition, the present approach that leverages a
macromolecular receptor densely covered with variable sizes of
pendants is a novel method for realizing highly specific anion
recognition. It is important to note that the practical colorimetric
anion detection was also accomplished in this system, in which
the adoption of poly(phenylacetylene) enabled the imparting of
the optical output ability. Given the novelty and significant
performance in this examination, we believe that the demon-
strated size-specific anion detection based on the dendronized
poly(phenylacetylene) receptor will contribute to the future
design of reliable and sophisticated anion sensor materials.
(18) Amendola, V.; Fabbrizzi, L.; Mosca, L. Chem. Soc. Rev. 2010,
39, 3889–3915.
(19) Gale, P. A. Chem. Commun. 2011, 47, 82–86.
(20) Beer, P. D.; Gale, P. A. Angew. Chem., Int. Ed. 2001,
40, 486–516.
(21) Curiel, D.; Beer, P. D. Chem. Commun. 2005, 1909–1911.
(22) Panda, P. K.; Lee, C.-H. J. Org. Chem. 2005, 70, 3148–3156.
(23) Cormode, D. P.; Murray, S. S.; Cowley, A. R.; Beer, P. D. Dalton
Trans. 2006, 5135–5140.
(24) Gale, P. A. Acc. Chem. Res. 2006, 39, 465–475.
(25) Singh, N.; Jang, D. O. Org. Lett. 2007, 9, 1991–1994.
(26) Li, Y.; Flood, A. H. J. Am. Chem. Soc. 2008, 130, 12111–12122.
(27) Bazzicalupi, C.; Bencini, A.; Biagini, S.; Faggi, E.; Meini, S.;
Giorgi, C.; Spepi, A.; Valtancoli, B. J. Org. Chem. 2009, 74, 7349–7363.
(28) Goswami, S.; Hazra, A.; Chakrabarty, R.; Fun, H.-K. Org. Lett.
2009, 11, 4350–4353.
(29) Mateus, P.; Delgado, R.; Brandao, P.; Carvalho, S.; Felix, V. Org.
Biomol. Chem. 2009, 7, 4661–4673.
(30) Mullen, K. M.; Mercurio, J.; Serpell, C. J.; Beer, P. D. Angew.
Chem., Int. Ed. 2009, 48, 4781ꢀ4784, S4781/4781-S4781/4788.
(31) Amendola, V.; Bergamaschi, G.; Boiocchi, M.; Fabbrizzi, L.;
Milani, M. Chem.—Eur. J. 2010, 16, 4368–4380.
’ ASSOCIATED CONTENT
S
Supporting Information. CD and absorption spectra of
b
poly-1 and poly-2 in the presence of increasing amounts of
anions and the resulting titration curves. This material is available
free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*Tel þ81 11 706 6602; Fax þ81 11 706 6602; e-mail kakuchi@
poly-bm.eng.hokudai.ac.jp.
(32) Mendy, J. S.; Pilate, M. L.; Horne, T.; Day, V. W.; Hossain,
M. A. Chem. Commun. 2010, 46, 6084–6086.
Present Addresses
§Department of Materials Chemistry, Asahikawa National Col-
lege of Technology, Asahikawa 071-8142, Japan.
(33) Sarwar, M. G.; Dragisic, B.; Sagoo, S.; Taylor, M. S. Angew.
Chem., Int. Ed. 2010, 49, 1674ꢀ1677, S1674/1671ꢀS1674/1618.
(34) Sessler, J. L.; Cai, J.; Gong, H.-Y.; Yang, X.; Arambula, J. F.; Hay,
B. P. J. Am. Chem. Soc. 2010, 132, 14058–14060.
(35) Kondo, S.-i.; Nagamine, M.; Karasawa, S.; Ishihara, M.; Unno,
M.; Yano, Y. Tetrahedron 2011, 67, 943–950.
’ ACKNOWLEDGMENT
(36) Young, P. G.; Clegg, J. K.; Bhadbhade, M.; Jolliffe, K. A. Chem.
Commun. 2011, 47, 463–465.
(37) Kakuchi, R.; Nagata, S.; Sakai, R.; Otsuka, I.; Nakade, H.; Satoh,
T.; Kakuchi, T. Chem.—Eur. J. 2008, 14, 10259–10266.
(38) Kakuchi, R.; Tago, Y.; Sakai, R.; Satoh, T.; Kakuchi, T. Macro-
molecules 2009, 42, 4430–4435.
(39) Sakai, R.; Okade, S.; Barasa, E. B.; Kakuchi, R.; Ziabka, M.;
Umeda, S.; Tsuda, K.; Satoh, T.; Kakuchi, T. Macromolecules 2010,
43, 7406–7411.
We gratefully acknowledge the Global COE Program
(Catalysis as the Basis for Innovation in Materials Science) of
the Ministry of Education, Culture, Sports, Science and Tech-
nology, Japan for the financial support. A.Z. thanks the financial
support from National Natural Science Foundation of China
(No. 21034004), Science and Technology Commission of
Shanghai (No. 10520500300), and National Science Foundation
of Switzerland (Nos. 200021-113690 and 200020-121817).
(40) Okamoto, Y.; Nakano, T. Chem. Rev. 1994, 94, 349–372.
(41) McQuade, D. T.; Pullen, A. E.; Swager, T. M. Chem. Rev. 2000,
100, 2537–2574.
’ REFERENCES
(1) Sessler, J. L.; Gale, P. A.; Cho, W. S. Anion Receptor Chemistry;
Royal Society of Chemistry: Cambridge, U.K., 2006.
(2) Caltagirone, C.; Gale, P. A. Chem. Soc. Rev. 2009, 38, 520–563.
(3) Martinez-Manez, R.; Sancenon, F. Chem. Rev. 2003,
103, 4419–4476.
(42) Hill, D. J.; Mio, M. J.; Prince, R. B.; Hughes, T. S.; Moore, J. S.
Chem. Rev. 2001, 101, 3893–4012.
(43) Nakano, T.; Okamoto, Y. Chem. Rev. 2001, 101, 4013–4038.
(44) Cornelissen, J. J. L. M.; Rowan, A. E.; Nolte, R. J. M.;
Sommerdijk, N. A. J. M. Chem. Rev. 2001, 101, 4039–4070.
(45) Thomas, S. W.; Joly, G. D.; Swager, T. M. Chem. Rev. 2007,
107, 1339–1386.
(4) Gunnlaugsson, T.; Glynn, M.; Tocci, G. M.; Kruger, P. E.;
Pfeffer, F. M. Coord. Chem. Rev. 2006, 250, 3094–3117.
4256
dx.doi.org/10.1021/ma200710r |Macromolecules 2011, 44, 4249–4257

Macromolecules
ARTICLE
(46) Yashima, E.; Maeda, K.; Nishimura, T. Chem.—Eur. J. 2004,
10, 42–51.
(83) Zhang, W.; Shiotsuki, M.; Masuda, T.; Kumaki, J.; Yashima, E.
Macromolecules 2007, 40, 178–185.
(47) Yashima, E.; Maeda, K. Macromolecules 2008, 41, 3–12.
(48) Furusho, Y.; Yashima, E. J. Polym. Sci., Part A: Polym. Chem.
2009, 47, 5195–5207.
(49) Yashima, E.; Maeda, K.; Iida, H.; Furusho, Y.; Nagai, K. Chem.
Rev. 2009, 109, 6102–6211.
(50) Grayson, S. M.; Frechet, J. M. J. Chem. Rev. 2001,
101, 3819–3867.
(51) Carlmark, A.; Hawker, C.; Hult, A.; Malkoch, M. Chem. Soc. Rev.
2009, 38, 352–362.
(84) Otsuka, I.; Sakai, R.; Kakuchi, R.; Satoh, T.; Kakuchi, T. Eur.
Polym. J. 2008, 44, 2971–2979.
(85) A similar hypsochromic effect probably due to intramolecular
hydrogen bonding was also observed for previously reported poly-
(phenylacetylene)s with urea pendants, though a colorless solution
has never been obtained. See refs 37ꢀ39.
(86) Similar polymers also showed no obvious Cotton effect prob-
ably due to the structural feature including urea functionalities. See refs
37 and 38.
(52) Rosen, B. M.; Wilson, C. J.; Wilson, D. A.; Peterca, M.; Imam,
M. R.; Percec, V. Chem. Rev. 2009, 109, 6275–6540.
(53) Tomalia, D. A. Soft Matter 2010, 6, 456–474.
(54) Zhang, A.; Shu, L.; Bo, Z.; Schluter, A. D. Macromol. Chem. Phys.
2003, 204, 328–339.
(87) The spectral changes in CD and absorption in the presence of
increasing amounts of anions and the resulting titration curves are
shown in the Supporting Information.
(88) Amendola, V.; Esteban-Gomez, D.; Fabbrizzi, L.; Licchelli, M.
Acc. Chem. Res. 2006, 39, 343–353.
(55) Zhang, A.; Zhang, B.; Waechtersbach, E.; Schmidt, M.;
Schlueter, A. D. Chem.—Eur. J. 2003, 9, 6083–6092.
(56) Frauenrath, H. Prog. Polym. Sci. 2005, 30, 325–384.
(57) Mynar, J. L.; Choi, T.-L.; Yoshida, M.; Kim, V.; Hawker, C. J.;
Frechet, J. M. J. Chem. Commun. 2005, 5169–5171.
(58) Lee, C. C.; Frechet, J. M. J. Macromolecules 2006, 39, 476–481.
(59) Percec, V.; Aqad, E.; Peterca, M.; Rudick, J. G.; Lemon, L.;
Ronda, J. C.; De, B. B.; Heiney, P. A.; Meijer, E. W. J. Am. Chem. Soc.
2006, 128, 16365–16372.
(89) Gomez, D. E.; Fabbrizzi, L.; Licchelli, M.; Monzani, E. Org.
Biomol. Chem. 2005, 3, 1495–1500.
(90) Jose, D. A.; Kumar, D. K.; Ganguly, B.; Das, A. Tetrahedron Lett.
2005, 46, 5343–5346.
(91) Gale, P. A. Acc. Chem. Res. 2006, 39, 465–475.
(92) Boiocchi, M.; Del Boca, L.; Gomez, D. E.; Fabbrizzi, L.;
Licchelli, M.; Monzani, E. J. Am. Chem. Soc. 2004, 126, 16507–16514.
(93) The acidꢀbase equilibrium constants in DMSO were used as
an alternative.
(60) Marcos, M.; Martin-Rapun, R.; Omenat, A.; Serrano, J. L. Chem.
Soc. Rev. 2007, 36, 1889–1901.
(94) We used the thermochemical radii for anionic guests because
the anions, except for halide, did not possess ionic radii.
(95) Bianchi, A.; Bowman-James, K.; Garcia-Espana, E. Supramole-
cular Chemistry of Anions; Wiley-VCH: New York, 1997.
(96) Because a maximum absorption wavelength could not be
determined for poly-1 and poly-2, the Δλ value was defined as a red
shift from 340 nm for poly-1 and 350 nm for poly-2. Although the
estimated Δλ value does not mean an exact red shift, it is sufficient to
discuss the colorimetric response.
(61) Rajaram, S.; Choi, T.-L.; Rolandi, M.; Frꢀechet, J. M. J. J. Am.
Chem. Soc. 2007, 129, 9619–9621.
(62) Rudick, J. G.; Percec, V. New J. Chem. 2007, 31, 1083–1096.
(63) Xiong, X.; Chen, Y.; Feng, S.; Wang, W. Macromolecules 2007,
40, 9084–9093.
(64) Zhu, B.; Han, Y.; Sun, M.; Bo, Z. Macromolecules 2007,
40, 4494–4500.
(65) Li, W.; Zhang, A.; Feldman, K.; Walde, P.; Schlueter, A. D.
Macromolecules 2008, 41, 3659–3667.
(66) Li, W.; Zhang, A.; Schluter, A. D. Chem. Commun.
2008, 5523–5525.
(67) Peterca, M.; Percec, V.; Imam, M. R.; Leowanawat, P.;
Morimitsu, K.; Heiney, P. A. J. Am. Chem. Soc. 2008, 130, 14840–14852.
(68) Rudick, J. G.; Percec, V. Acc. Chem. Res. 2008, 41, 1641–1652.
(69) Zhang, A. Macromol. Rapid Commun. 2008, 29, 839–845.
(70) Zhang, A.; Rodriguez-Ropero, F.; Zanuy, D.; Alemin, C.;
Meijer, E. W.; Schluter, A. D. Chem.—Eur. J. 2008, 14, 6924–6934.
(71) Das, J.; Frechet, J. M. J.; Chakraborty, A. K. J. Phys. Chem. B
2009, 113, 13768–13775.
(72) Efthymiopoulos, P.; Vlahos, C.; Kosmas, M. Macromolecules
2009, 42, 1362–1369.
(73) Chen, Y.; Xiong, X. Chem. Commun. 2010, 46, 5049–5060.
(74) Junk, M. J. N.; Li, W.; Schlueter, A. D.; Wegner, G.; Spiess,
H. W.; Zhang, A.; Hinderberger, D. Angew. Chem., Int. Ed. 2010,
49, 5683–5687.
(75) Popa, I.; Zhang, B.; Maroni, P.; Schlueter, A. D.; Borkovec, M.
Angew. Chem., Int. Ed. 2010, 49, 4250–4253.
(76) Qin, C.-J.; Wu, X.-F.; Tong, H.; Wang, L.-X. J. Mater. Chem.
2010, 20, 7957–7964.
(77) Loukas, V.; Noula, C.; Kokotos, G. J. Pept. Sci. 2003,
9, 312–319.
(78) Yashima, E.; Matsushima, T.; Okamoto, Y. J. Am. Chem. Soc.
1997, 119, 6345–6359.
(79) Kishimoto, Y.; Itou, M.; Miyatake, T.; Ikariya, T.; Noyori, R.
Macromolecules 2002, 28, 6662–6666.
(80) Maeda, K.; Kamiya, N.; Yashima, E. Chem.—Eur. J. 2004,
10, 4000–4010.
(81) Otsuka, I.; Sakai, R.; Satoh, T.; Kakuchi, R.; Kaga, H.; Kakuchi,
T. J. Polym. Sci., Part A: Polym. Chem. 2005, 43, 5855–5863.
(82) Zhang, W.; Shiotsuki, M.; Masuda, T. Macromolecules 2007,
40, 1421–1428.
4257
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