Host-Guest complexation-triggered chiroptical change of poly(phenylacetylene)s bearing binaphthocrown ether moieties on the main chain

Article abstract of DOI:10.1002/pola.23881

Diacetylene monomers with respective lengths of the oxyethylene chains were cyclopolymerized with a rhodium catalyst to produce novel poly(phenylacetylene) s bearing a different cavity size of the chiral crown ether in the repeating units (2a-c), In the c

Full text of DOI:10.1002/pola.23881

Host–Guest Complexation-Triggered Chiroptical Change of
Poly(phenylacetylene)s Bearing Binaphthocrown Ether Moieties
on the Main Chain
RYOSUKE SAKAI, TAKAFUMI YONEKAWA, ISSEI OTSUKA, RYOHEI KAKUCHI, TOSHIFUMI SATOH, TOYOJI KAKUCHI
Division of Biotechnology and Macromolecular Chemistry, Graduate School of Engineering, Hokkaido University,
Sapporo 060-8628, Japan
Received 15 October 2009; accepted 13 December 2009
DOI: 10.1002/pola.23881
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: Diacetylene monomers with respective lengths of
the oxyethylene chains were cyclopolymerized with a rhodium
catalyst to produce novel poly(phenylacetylene)s bearing a dif-
ferent cavity size of the chiral crown ether in the repeating
units (2a–c). In the circular dichroism spectra of the resulting
polymers, characteristic Cotton effects were observed in the
range from 350 to 500 nm corresponding to the absorption of
the conjugated polymer backbone, indicating that the polymers
possessed a helical structure with an excess single screw
sense induced by the covalently bonded binaphthyl units. The
host–guest complexation of 2a–c with achiral guests produced
a chiroptical change based on the fluctuation in the main chain
conformation. The behavior of the complexation-induced
chiroptical change was essentially dictated by the cavity size
of the binaphthocrown ether units. Additionally, a chirality-
responsive helicity change was observed in the case of the
complexation of 2a–c with chiral guests, which also depended
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on the crown ether size. 2010 Wiley Periodicals, Inc. J Polym
Sci Part A: Polym Chem 48: 1197–1206, 2010
KEYWORDS: chiral; conjugated polymers; cyclopolymerization;
host–guest systems; polyacetylenes
INTRODUCTION The one-handed helical polymer has been
one of the major research subjects of polymer science due to
its unique conformational chirality and its tremendous
potentials for a wide variety of applications, such as enan-
tiomer separation, chiral catalysis, and chirality sensing.1–5
Thus, a number of helical polymers have been designed and
synthesized to realize the desired properties, functions, and
applications. In particular, the helical polymer capable of
responding to a specific molecular recognition event has
been recently become important based on the increasing
demand to develop smart and intelligent polymer inspired
by biological macromolecules.6–8 Through a number of so-
phisticated investigations, the molecular design of the bind-
ing sites has been found to be essential for the realization of
the desired stimuli-responsive helicity change.9–38 Thus, the
novel and unprecedented molecular design of the interaction
site has the significant potential to expand the limit and
scope in the field of stimuli-responsive helical polymers.
induced into the main chain via the host–guest complexation
with chiral guest molecules.43–45 Interesting to note is that
the polymer showed an exceptional sensitivity probably due
to the strong binding affinity between the aza-18-crown-6
host and the employed chiral guests. They further achieved
an enantiomer-selective helicity inversion accompanied by a
visible color change for poly(phenylacetylene) bearing b-
cyclodextrin pendants.46,47 In this case, the chirality of b-
cyclodextrin is essential for such a selectivity. We reported
the metal cation-induced helix inversion of a poly(phenylace-
tylene) grafted with a polycarbohydrate ionophore, which is
caused by the conformational change in the pendant iono-
phore on complexation with the given cation.48,49 The helix
inversion was clarified to only occur in the presence of cati-
ons with cationic radii greater than 1.16 Å.
We have also reported the helicity inductions of poly(phenyl
isocyanate) and poly(phenylacetylene) with achiral crown
ethers on their main chains, which were prepared using the
cyclopolymerization technique.50,51 These polymers were
revealed to form a one-handed helical structure via the
host–guest complexation with a chiral guest molecule. Con-
sidering that host units are generally designed as side chains
for other stimuli-responsive helical polymers, these examples
provided a novel and valuable insight into the complexation-
induced helicity change. Therefore, these successful results
The host–guest complex formation has been clarified to be
an ideal candidate among the various types of molecular
interactions, because a specific molecular binding is basically
realizable by the rational molecular design of the host
unit.39–42 For example, Yashima et al. reported the helicity
induction of poly(phenylacetylene) bearing aza-18-crown-6
pendants, in which a one-handed helical structure was
Correspondence to: T. Kakuchi (E-mail: kakuchi@poly-bm.eng.hokudai.ac.jp)
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Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 1197–1206 (2010) 2010 Wiley Periodicals, Inc.
CHIROPTICAL CHANGE OF POLY(PHENYLACETYLENE)S, SAKAI ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
C6H5)Bꢀ(C6H5)3] (Rh(nbd)BPh4) was prepared in accordance
with a previous report.57 The perchloric acid (HClO4) salts of
amines, amino acids, and amino ester were prepared accord-
ing to a previous report.58
Instruments
1
The H and 13C NMR spectra were recorded using JEOL JNM-
EX270 and JEOL JNM-A400II instruments. The laser Raman
spectra were recorded using a JASCO NRS-1000. Elemental
analysis was conducted using a Yanaco CHN corder MT-6
(Center for Instrumental Analysis, Hokkaido University). The
SEC was performed at 40 ꢁC using a Jasco GPC-900 system
equipped two Shodex KF-804L columns (column size, 8 mm
ꢂ 300 mm; bead size, 7 lm; exclusion limit, 4 ꢂ 105) and a
Waters Ultrastyragel column (column size, 7.8 mm ꢂ 300
mm; bead size, 7 lm; exclusion limit, 1 ꢂ 107) in tetrahydro-
furan (THF) at the flow rate of 0.8 mL minꢀ1. The number-
average molecular weight (Mn) and polydispersity (Mw/Mn)
of the polymers were calculated on the basis of a polysty-
rene calibration. CD spectra were measured in a 1 mm path
length using a JASCO J-720 spectropolarimeter. Preparation
of the polymerization solution was carried out in an
MBRAUN stainless steel glove box equipped with a gas puri-
fication system (molecular sieves and copper catalyst) under
dry argon atmosphere (H2O, O2 < 1 ppm).
SCHEME 1 Synthesis of poly(phenylacetylene)s with binaphtyl-
based chiral crown ether on the main chain.
inspired us to further fabricate a helical polymer bearing chi-
ral crown cavities on the main chain. To realize a high level
of main chain regulation, the binaphthyl group emerges as a
leading candidate of the chiral source at the cyclic repeating
units because of the significant performance that has been
proved in many fields of chiral chemistry, such as chiral rec-
ognition, asymmetric catalyst, chiral polymer, and chiral
supramolecule.52–55 The atropisomeric structure of the
binaphthyl group is expected to directly regulate the main
chain conformation through the asymmetric twisting of the
crown cavity, thus providing the one-handed helical confor-
mation. Given such a novel molecular design, of significant
interest is to evaluate the helicity change based on the host–
guest complexation with various guests.
2-[2-(4-Iodophenoxy)ethoxy]ethanol (3a)
To a stirred suspension of 4-iodophenol (25 g, 0.12 mol), po-
tassium carbonate (63 g, 0.46 mol), and potassium iodide
(13 g, 78 mmol) in DMF (200 mL) was slowly added ethyl-
ene glycol mono-b-chloroethylether (16 g, 0.13 mol), and the
reaction mixture was stirred at 75 ꢁC for 3 days. The reac-
tion mixture was filtered and then the filtrate was evapo-
rated under reduced pressure. The residue was dissolved in
dichloromethane (200 mL), and then washed with 1 N NaOH
(3 ꢂ 100 mL), 2 N HCl (3 ꢂ 100 mL), and water (3 ꢂ 100
mL). The organic layer was dried with anhydrous MgSO4 and
evaporated to give 3a. Yield: 25 g (71%). Characterization
for this compound has been reported previously.59
We now report the syntheses of poly(phenylacetylene)s with
binaphthocrown ethers on the main chain (2a–c) and the
chiroptical properties of the resulting polymers. Diacetylene
monomers with the respective lengths of the oxyethylene
chains (1a–c) have been designed and cyclopolymerized to
produce poly(phenylacetylene)s bearing a different cavity
size of the chiral crown ether in the repeating units (Scheme
1). The polymer structure was characterized by the size
1
2-[2-(2-(4-Iodophenoxy)ethoxy)ethoxy]ethanol (3b)
The same procedure as that for 3a was applied to 4-iodo-
phenol (25 g, 0.12 mol), potassium carbonate (63 g, 0.46
mol), potassium iodide (13 g, 78 mmol), and 2-[2-(2-chloro-
ethoxy)ethoxy]ethanol (23 g, 0.14 mol) in DMF (200 mL).
Yield: 32 g (80%).
exclusion chromatography (SEC), H NMR, Raman, and circu-
lar dichoism (CD) measurements. The chiroptical change in
2a–c through the host–guest complexation with achial and
chiral guests was also investigated with a focus on the varia-
tion in the cavity size of the crown ether.
1H NMR (CDCl3): d 7.54 (d, J ¼ 9.0 Hz, 2H, Ar), 6.70 (d, J ¼
8.9 Hz, 2H, Ar), 4.10 (t, J ¼ 4.8 Hz, 2H, AOCH2A), 3.85 (t, J
¼ 4.8 Hz, 2H, AOCH2A), 3.75–3.61 (m, 8H, AOCH2A). 13C
NMR (CDCl3): d 158.57, 138.16, 117.02, 83.00 (Ar), 72.44,
70.81, 70.32, 69.57, 67.44, 61.72 (AOCH2A). Anal. Calcd. for
EXPERIMENTAL
Materials
(Trimethylsilyl)acetylene was kindly supplied from the Shi-
netsu Chemical Co. (Tokyo, Japan). All other chemicals were
purchased from commercial sources and used without fur-
ther purification unless otherwise noted. Piperidine
(>98.0%) was purchased from the Kanto Chemicals Co. and
used after distillation over CaH2. Triphenylphosphine was
obtained from Kanto Chemicals Co. and used after recrystal-
lization from dichloromethane/diethyl ether. 2-[2-(2-(2-
Chloroethoxy)ethoxy)ethoxy]ethanol was synthesized by a
previously reported method.56 Rhþ(2,5-norbornadiene)[(g6-
C12H17IO4 (352.17): C, 40.93; H, 4.87. Found: C, 40.89; H,
4.78.
2-[2-(2-(2-(4-Iodophenoxy)ethoxy)ethoxy)
ethoxy]ethanol (3c)
The same procedure as that for 3a was applied to 4-iodo-
phenol (25 g, 0.12 mol), potassium carbonate (63 g, 0.46
mol), potassium iodide (13 g, 78 mmol), and 2-[2-(2-(2-
1198
INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

ARTICLE
chloroethoxy)ethoxy)ethoxy]ethanol (28 g, 0.13 mol) in DMF
(200 mL). Yield: 43 g (95%).
mmol), p-toluenesulfonyl chloride (20 g, 0.11 mol), 180 mL
of toluene, and 130 mL of 7.5 N NaOH aqueous solution.
Yield: 33 g (66%).
1H NMR (CDCl3): d 7.60 (d, J ¼ 9.0 Hz, 2H, Ar), 6.82 (d, J ¼
9.0 Hz, 2H, Ar), 4.13 (t, J ¼ 4.8 Hz, 2H, AOCH2A), 3.81 (t, J
¼ 4.8 Hz, 2H, AOCH2A), 3.66–3.50 (m, 12H, AOCH2A). 13C
NMR (CDCl3): d 158.45, 138.12, 117.07, 83.02 (Ar), 72.29,
70.44, 70.19, 70.10, 69.83, 69.39, 67.44, 61.05 (AOCH2A).
Anal. Calcd for C14H21IO5 (396.22): C, 42.44; H, 5.34. Found:
C, 42.59; H, 5.34.
1H NMR (CDCl3): d 7.78 (d, J ¼ 8.4 Hz, 2H, Ar), 7.52 (d, J ¼
8.9 Hz, 2H, Ar), 7.33 (d, J ¼ 8.5 Hz, 2H, Ar), 6.69 (d, J ¼ 8.9
Hz, 2H, Ar), 4.14 (t, J ¼ 4.8 Hz, 2H, AOCH2A), 4.08 (t, J ¼
4.8 Hz, 2H, AOCH2A), 3.83 (t, J ¼ 4.8 Hz, 2H, AOCH2A),
3.71–3.58 (m, 10H, AOCH2A), 2.43 (s, 3H, ACH3). 13C NMR
(CDCl3): d 158.61, 144.70, 138.06, 132.92, 129.74, 127.86,
116.98, 82.79 (Ar), 70.71, 70.65, 70.55, 70.45, 69.50, 69.16,
68.58, 67.45 (AOCH2A), 21.53 (ACH3). Anal. Calcd. for
2-[2-(4-Iodophenoxy)ethoxy]ethyl 4-toluenesulfonate
(4a)
C21H27IO7S (550.40): C, 45.83; H, 4.94; S, 5.83. Found: C,
To a stirred mixture of 3a (25 g, 82 mmol), benzyltriethy-
lammonium chloride (0.50 g, 2.2 mmol) in toluene (170 mL)
was added 7.5 N NaOH aqueous solution (130 mL). To the
biphase system was slowly added a solution of p-toluenesꢁul-
fonyl chloride (19 g, 98 mmol) in toluene (100 mL) at 0 C.
After vigorously stirring overnight at room temperature, the
organic layer was separated and the aqueous layer was
extracted by toluene (3 ꢂ 100 mL). The combined organic
layer was washed with 1 N HCl (2 ꢂ 100 mL) and water (3
ꢂ 100 mL), and then dried with anhydrous MgSO4. The tolu-
ene solution was evaporated to give 4a as a solid, which
was used in the next step without further purification. Yield:
36 g (96%).
45.52; H, 4.81; S, 5.79.
(R)-2,20-Bis[2-(2-(4-iodophenoxy)ethoxy)ethoxy]-1,10-
binaphthyl (5a)
To a mixture of (R)-(þ)-1,10-bi-2-naphthol (11 g, 37 mmol)
and NaOH (4.8 g, 0.12 mol) in DMSO (50 mL) was added a
solution of 4a (35 g, 76 mmol) in DMSO (80 mL). The reac-
tion mixture was stirred at 80 ꢁC for 24 h. After solvent
was removed under reduced pressure, the residue was dis-
solved in water (150 mL) and then the organics was
extracted with chloroform (200 mL). The chloroform solu-
tion was washed with brine (2 ꢂ 100 mL), and then dried
with anhydrous MgSO4. After evaporation, the crude prod-
uct was purified by column chromatography on silica gel
with hexane/ethyl acetate (6/4, v/v) to give 5a as a syrup.
Yield: 17 g (70%).
1H NMR (CDCl3): d 7.77 (d, J ¼ 8.4 Hz, 2H, Ar), 7.53 (d, J ¼
9.1 Hz, 2H, Ar), 7.29 (d, J ¼ 8.5 Hz, 2H, Ar), 6.65 (d, J ¼ 8.9
Hz, 2H, Ar), 4.18 (t, J ¼ 4.8 Hz, 2H, AOCH2A), 3.99 (t, J ¼
4.7 Hz, 2H, AOCH2A), 3.77–3.72 (m, 4H, AOCH2A), 2.41 (s,
3H, ACH3). 13C NMR (CDCl3): d 158.45, 144.74, 138.08,
132.82. 129.72, 127.82, 116.93, 82.94 (Ar), 69.60, 69.11,
68.78, 67.38 (AOCH2A), 21.53 (ACH3). Anal. Calcd. for
1H NMR (CDCl3): d 7.90 (d, J ¼ 8.9 Hz, 2H, Ar), 7.83 (d, J ¼
8.0 Hz, 2H, Ar), 7.50 (d, J ¼ 8.9 Hz, 4H, Ar), 7.38 (d, J ¼ 8.9
Hz, 2H, Ar), 7.34–7.14 (m, 6H, Ar), 6.55 (d, J ¼ 8.9 Hz, 4H,
Ar), 4.14–4.05 (m, 4H, AOCH2A), 3.53–3.48 (m, 8H,
AOCH2A), 3.28–3.11 (m, 4H, AOCH2A). 13C NMR (CDCl3): d
158.58, 154.19, 138.04, 134.04, 129.34, 129.25, 127.79,
126.33, 125.46, 123.71, 120.43, 116.93, 115.41, 82.74 (Ar),
70.02, 69.61, 69.39, 67.15 (AOCH2A). Anal. Calcd. for
C17H19IO5S (462.30): C, 44.17; H, 4.14; S, 6.94. Found: C,
43.89; H, 4.11; S, 7.06.
2-[2-(2-(4-Iodophenoxy)ethoxy)ethoxy]ethyl
4-toluenesulfonate (4b)
C40H36I2O6 (866.52): C, 55.44; H, 4.19. Found: C, 55.98; H,
The same procedure as that for 4a was applied to 3b (32 g,
91 mmol), benzyltriethylammonium chloride (0.55 g, 2.4
mmol), p-toluenesulfonyl chloride (20 g, 0.11 mol), 180 mL
of toluene, and 130 mL of 7.5 N NaOH aqueous solution.
Yield: 45 g (98%).
4.29.
(R)-2,20-Bis[2-(2-(2-(4-iodophenoxy)ethoxy)ethoxy)
ethoxy]-1,10-binaphthyl (5b)
The same procedure as that for 5a was applied to 4b (25 g,
50 mmol), (R)-(þ)-1,10-bi-2-naphthol (7.3 g, 25 mmol), NaOH
(3.7 g, 93 mmol) in DMSO (90 mL). Yield: 11 g (47%).
1H NMR (CDCl3): d 7.76 (d, J ¼ 8.2 Hz, 2H, Ar), 7.49 (d, J ¼
8.8 Hz, 2H, Ar), 7.29 (d, J ¼ 8.2 Hz, 2H, Ar), 6.66 (d, J ¼ 8.8
Hz, 2H, Ar), 4.13 (t, J ¼ 4.7 Hz, 2H, AOCH2A), 4.02 (t, J ¼
4.7 Hz, 2H, AOCH2A), 3.76 (t, J ¼ 4.6 Hz, 2H, AOCH2A),
3.66–3.56 (m, 6H, AOCH2A), 2.38 (s, 3H, ACH3). 13C NMR
(CDCl3): d 158.34, 144.47, 137.77, 132.58, 129.52, 127.53,
116.75, 82.55 (Ar), 70.32, 69.21, 69.00, 68.28, 67.16
(AOCH2A), 21.29 (ACH3). Anal. Calcd. for C19H23IO6S
(506.35): C, 45.07; H, 4.58; S, 6.33. Found: C, 44.97; H, 4.53;
S, 6.51.
1H NMR (CDCl3): d 7.89 (d, J ¼ 9.0 Hz, 2H, Ar), 7.82 (d, J ¼
8.1 Hz, 2H, Ar), 7.51 (d, J ¼ 8.9 Hz, 4H, Ar), 7.39 (d, J ¼ 9.0
Hz, 2H, Ar), 7.32–7.12 (m, 6H, Ar), 6.63 (d, J ¼ 9.0 Hz, 4H,
Ar), 4.08 (t, J ¼ 5.0 Hz, 4H, AOCH2A), 3.94 (t, J ¼ 4.9 Hz,
4H, AOCH2A), 3.61 (t, J ¼ 4.8 Hz, 4H, AOCH2A), 3.45 (t, J ¼
4.8 Hz, 4H, AOCH2A), 3.25 (t, J ¼ 4.5 Hz, 4H, AOCH2A),
3.19–3.05 (m, 4H, AOCH2A). 13C NMR (CDCl3): d 158.59,
154.21, 138.06, 133.99, 129.28, 129.15, 127.73, 126.19,
125.42, 123.60, 120.39, 116.95, 115.55, 82.79 (Ar), 70.52,
70.43, 69.78, 69.55, 69.24, 67.33 (AOCH2A). Anal. Calcd. for
2-[2-(2-(2-(4-Iodophenoxy)ethoxy)ethoxy)ethoxy]ethyl
4-toluenesulfonate (4c)
The same procedure as that for 4a was applied to 3c (36 g,
91 mmol), benzyltriethylammonium chloride (0.55 g, 2.4
C
4.65.
44H44I2O8 (954.62): C, 55.36; H, 4.65. Found: C, 55.01; H,
CHIROPTICAL CHANGE OF POLY(PHENYLACETYLENE)S, SAKAI ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
(R)-2,20-Bis[2-(2-(2-(2-(4-iodophenoxy)ethoxy)ethoxy)
ethoxy)ethoxy]-1,10-binaphthyl (5c)
(AOCH2A), 0.03 (ACH3). Anal. Calcd. for C54H62O8Si2
(895.24): C, 72.45; H, 6.98. Found: C, 71.81; H, 7.27.
The same procedure as that for 5a was applied to 4c (22 g,
39 mmol), (R)-(þ)-1,10-bi-2-naphthol (5.2 g, 18 mmol), and
NaOH (2.5 g, 64 mmol) in DMSO (65 mL). Yield: 15 g (78%).
(R)-2,20-Bis[2-(2-(2-(2-(4-((trimethylsilyl)ethynyl)phe-
noxy)ethoxy)ethoxy)ethoxy)ethoxy]-1,10-binaphthyl (6c)
The same procedure as that for 6a was applied to 5c (12 g,
11 mmol), triphenylphosphine (0.37 g, 1.4 mmol), bis(triphe-
nylphosphine)palladium(II) dichloride (0.36 g, 0.52 mmol),
copper(I) iodide (91 mg, 0.48 mmol), and (trimethylsilyl)ace-
tylene (10 mL, 71 mmol) in dry piperidine (110 mL). Yield:
11 g (93%).
1H NMR (CDCl3): d 7.91 (d, J ¼ 9.0 Hz, 2H, Ar), 7.83 (d, J ¼
8.0 Hz, 2H, Ar), 7.51 (d, J ¼ 9.1 Hz, 4H, Ar), 7.40 (d, J ¼ 9.1
Hz, 2H, Ar), 7.33–7.12 (m, 6H, Ar), 6.66 (d, J ¼ 8.9 Hz, 4H,
Ar), 4.09–4.01 (m, 8H, AOCH2A), 3.76 (t, J ¼ 4.8 Hz, 4H,
AOCH2A), 3.60 (t, J ¼ 4.8 Hz, 4H, AOCH2A), 3.49–3.42 (m,
8H, AOCH2A), 3.23-3.05 (m, 8H, AOCH2A). 13C NMR
(CDCl3): d 158.61, 154.24, 138.09, 134.00, 129.31, 129.18,
127.74, 126.20, 125.43, 123.61, 120.44, 116.98, 115.62,
82.84 (Ar), 70.66, 70.41, 70.35, 70.31, 69.80, 69.52, 69.47,
67.44 (AOCH2A). Anal. Calcd. for C48H52I2O10 (1042.73): C,
55.29; H, 5.03. Found: C, 54.81; H, 5.06.
1H NMR (CDCl3): d 7.89 (d, J ¼ 9.1 Hz, 2H, Ar), 7.81 (d, J ¼
8.1 Hz, 2H, Ar), 7.40–7.12 (m, 12H, Ar), 6.79 (d, J ¼ 8.6 Hz,
4H, Ar), 4.08–4.02 (m, 8H, AOCH2A), 3.75 (t, J ¼ 4.8 Hz, 4H,
AOCH2A), 3.58 (t, J ¼ 4.8 Hz, 4H, AOCH2A), 3.48-3.40 (m,
8H, AOCH2A), 3.20 (t, J ¼ 4.6 Hz, 4H, AOCH2A), 3.18-3.05
(m, 4H, AOCH2A), 0.24 (s, 18H, ACH3). 13C NMR (CDCl3): d
158.90, 154.25, 134.02, 133.39, 129.33, 129.20, 127.77,
126.22, 125.45, 123.63, 120.45, 115.62, 115.34, 114.39 (Ar),
105.13 (ArACBCASiMe3), 92.43 (ArACBCASiMe3), 70.69,
70.43, 70.37, 70.34, 69.83, 69.53, 69.51, 67.34 (AOCH2A),
0.03 (ACH3). Anal. Calcd. for C58H70O10Si2 (983.34): C,
70.84; H, 7.18. Found: C, 70.58; H, 7.29.
(R)-2,20-Bis[2-(2-(4-((trimethylsilyl)ethynyl)phenoxy)
ethoxy)ethoxy]-1,10-binaphthyl (6a)
To a mixture of 5a (17 g, 19 mmol), triphenylphosphine
(0.56 g, 2.1 mmol), bis(triphenylphosphine)palladium(II)
dichloride (0.59 g, 0.83 mmol), and copper(I) iodide (0.12 g,
0.64 mmol) in dry piperidine (160 mL) was added (trime-
thylsilyl)acetylene (11 mL, 78 mmol) under argon atmos-
phere. After stirring at r.t. for four days, the reaction mixture
was filtered and evaporated. The residue was purified by col-
umn chromatography on silica gel with hexane/ethyl acetate
(6.5/3.5, v/v) to give 6a as a glassy solid. Yield: 15 g (97%).
(R)-2,20-Bis[2-(2-(4-ethynylphenoxy)ethoxy)ethoxy]-1,10-
binaphthyl (1a)
To a solution of 6a (0.10 g, 0.13 mmol) in the mixed solvent
of methanol (5 mL) and THF (5 mL) was slowly added 1 N
KOH (5 mL). After stirring for 18 h at room temperature, the
reaction mixture was neutralized with saturated NH4Cl and
extracted with dichloromethane (3 ꢂ 30 mL), and then dried
over anhydrous MgSO4. After evaporation, the residue was
purified by column chromatography on silica gel with hex-
ane/dichloromethane/ethyl acetate (6.5/2/1.5, v/v/v) to
give 1a as a syrup. Yield: 0.070 g (85%).
1H NMR (CDCl3): d 7.90 (d, J ¼ 9.0 Hz, 2H, Ar), 7.83 (d, J ¼
8.0 Hz, 2H, Ar), 7.40–7.15 (m, 12H, Ar), 6.67 (d, J ¼ 8.8 Hz,
4H, Ar), 4.15–4.06 (m, 4H, AOCH2A), 3.56–3.51 (m, 8H,
AOCH2A), 3.29–3.12 (m, 4H, AOCH2A), 0.24 (s, 18H, ACH3).
13C NMR (CDCl3): d 158.90, 154.23, 134.08, 133.34, 129.38,
129.28, 127.82, 126.34, 125.49, 123.74, 120.47, 115.44,
115.27, 114.37 (Ar), 105.19 (ArAC¼¼CASiMe3), 92.43
(ArAC¼¼CASiMe3), 70.06, 69.64, 69.44, 67.07 (AOCH2A),
0.06 (ACH3). Anal. Calcd. for C50H54O6Si2 (807.13): C, 74.40;
H, 6.74. Found: C, 73.87; H, 6.64.
1H NMR (CDCl3): d 7.89 (d, J ¼ 9.0 Hz, 2H, Ar), 7.82 (d, J ¼
8.1 Hz, 2H, Ar), 7.40–7.35 (m, 6H, Ar), 7.33–7.15 (m, 6H, Ar),
6.69 (d, J ¼ 8.9 Hz, 4H, Ar), 4.14–4.05 (m, 4H, AOCH2A),
3.58–3.48 (m, 8H, AOCH2A), 3.29–3.12 (m, 4H, AOCH2A),
2.98 (s, 2H, CBCAH). 13C NMR (CDCl3): d 159.05, 154.18,
134.02, 133.41, 129.32, 129.24, 127.78, 126.31, 125.43,
123.69, 120.40, 115.39, 114.45, 114.12 (Ar), 83.62
(ArACBCAH), 75.82 (ArACBCAH), 69.99, 69.58, 69.36,
67.07 (AOCH2A). Anal. Calcd. for C44H38O6 (662.77): C,
79.74; H, 5.78. Found: C, 79.48; H, 6.05.
(R)-2,20-Bis[2-(2-(2-(4-((trimethylsilyl)ethynyl)phenoxy)
ethoxy)ethoxy)ethoxy]-1,10-binaphthyl (6b)
The same procedure as that for 6a was applied to 5b (11 g,
12 mmol), triphenylphosphine (0.37 g, 1.4 mmol), bis(triphe-
nylphosphine)palladium(II) dichloride (0.36 g, 0.52 mmol),
copper(I) iodide (91 mg, 0.48 mmol), and (trimethylsilyl)ace-
tylene (10 mL, 71 mmol) in dry piperidine (120 mL). Yield:
9.9 g (95%).
(R)-2,20-Bis[2-(2-(2-(4-ethynylphenoxy)ethoxy)ethoxy)
ethoxy]-1,10-binaphthyl (1b)
The same procedure as that for 1a was applied to 6b (6.0 g,
6.7 mmol), 1 N KOH (230 mL), 150 mL of methanol, and
150 mL of THF. Yield: 3.8 g (76%).
1H NMR (CDCl3): d 7.89 (d, J ¼ 9.1 Hz, 2H, Ar), 7.82 (d, J ¼
8.0 Hz, 2H, Ar), 7.41–7.12 (m, 12H, Ar), 6.78 (d, J ¼ 8.5 Hz,
4H, Ar), 4.08 (t, J ¼ 4.8 Hz, 4H, AOCH2A), 3.97 (t, J ¼ 4.8
Hz, 4H, AOCH2A), 3.62 (t, J ¼ 4.8 Hz, 4H, AOCH2A), 3.46 (t,
J ¼ 4.8 Hz, 4H, AOCH2A), 3.25 (t, J ¼ 4.5 Hz, 4H, AOCH2A),
3.21–3.05 (m, 4H, AOCH2A), 0.24 (s, 18H, ACH3). 13C
NMR (CDCl3): d 158.90, 154.25, 134.03, 133.38, 129.33,
129.19, 127.76, 126.22, 125.45, 123.62, 120.44, 115.58,
115.33, 114.38 (Ar), 105.15 (ArACBCASiMe3), 92.43
(ArACBCASiMe3), 70.55, 70.46, 69.84, 69.58, 69.29, 67.27
1H NMR (CDCl3): d 7.90 (d, J ¼ 9.0 Hz, 2H, Ar), 7.82 (d, J ¼
8.0 Hz, 2H, Ar), 7.41–7.37 (m, 6H, Ar), 7.32–7.13 (m, 6H, Ar),
6.80 (d, J ¼ 8.9 Hz, 4H, Ar), 4.11–4.05 (m, 4H, AOCH2A),
3.98 (t, J ¼ 4.8 Hz, 4H, AOCH2A), 3.63 (t, J ¼ 4.9 Hz, 4H,
AOCH2A), 3.49–3.43 (m, 4H, AOCH2A), 3.25 (t, J ¼ 4.5 Hz,
4H, AOCH2A), 3.18–3.06 (m, 4H, AOCH2A), 2.99 (s, 2H,
CBCAH). 13C NMR (CDCl3):
d 159.05, 154.20, 133.98,
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ARTICLE
SCHEME 2 Synthesis of diacetylene monomers (1a–c).
133.44, 129.27, 129.15, 127.72, 126.18, 125.40, 123.58,
120.37, 115.52, 114.46, 114.17 (Ar), 83.55 (ArACBCAH),
75.83 (ArACBCAH), 70.49, 70.42, 69.78, 69.53, 69.23, 67.24
(AOCH2A). Anal. Calcd. for C48H46O8 (750.87): C, 76.78; H,
6.17. Found: C, 76.16; H, 6.31.
tered and then poured into a large amount of methanol. The
precipitate was purified by reprecipitation with chloroform/
methanol and then dried under reduced pressure to give 2b
as a yellow powder. Yield: 0.22 g (73%). Mn ¼ 1.5 ꢂ 104,
Mw/Mn ¼ 3.13. 1H NMR (CDCl3): d 8.21–6.05 (br, 20H, Ar),
5.97–5.58 (br, 2H, ¼¼CHA), 4.71–2.83 (br, 24H, AOCH2A).
(R)-2,20-Bis[2-(2-(2-(2-(4-ethynylphenoxy)ethoxy)
ethoxy)ethoxy)ethoxy]-1,10-binaphthyl (1c)
The same procedure as that for 1a was applied to 6c (3.6 g,
3.6 mmol), 1 N KOH (120 mL), 90 mL of methanol, and 90
mL of THF. Yield: 2.2 g (73%).
RESULTS AND DISCUSSION
Synthesis of Poly(phenylacetylene) Bearing
Binaphthocrown Ether on the Main Chain
The synthetic procedure of a series of a,x-diacetylene mono-
mers with a (R)-1,10-binaphthyl moiety (1a–c) is illustrated
in Scheme 2. 4-Iodophenol was coupled with the Cl-bearing
oligoethyleneglycohols using K2CO3 to afford mono-modified
oligoethyleneglycohols with a 4-iodophenyl group, which
have the respective chain lengths (3a–c). Subsequently, 3a–c
were reacted with p-toluenesulfonyl chloride (TsCl) using the
phase-transfer technique to give the tosylated compounds
4a–c, followed by the coupling reaction with (R)-1,10-bi-2-
naphthol under a basic condition (NaOH) in DMSO to pro-
vide 5a–c. The intermediates 5a–c were then converted to
the corresponding precursors 6a–c through the Sonogashira
coupling reaction with (trimethylsilyl)acetylene (TMSA) using
the Pd(0)/Cu(I) catalyst system in piperidine. Finally, 6a–c
were treated with KOH aq. in THF/MeOH for deprotecting
the trimethylsilyl groups, producing the targeted atropiso-
meric diacetylene monomers 1a–c, which were assigned by
the 1H and 13C NMR measurements and elemental analysis.
These monomers 1a–c consist of a (R)-1,10-binaphthyl unit
as the chiral source at the center of the molecules, two poly-
merizable ethynyl groups at both chain ends, and two oxy-
ethylene chains between the acetylene and binaphthyl func-
tionalities. The structural difference in each monomer is only
the length of the oxyethylene chains, which essentially
1H NMR (CDCl3): d 7.91 (d, J ¼ 9.0 Hz, 2H, Ar), 7.83 (d, J ¼
8.1 Hz, 2H, Ar), 7.41–7.38 (m, 6H, Ar), 7.32–7.13 (m, 6H, Ar),
6.83 (d, J ¼ 9.0 Hz, 4H, Ar), 4.09–4.06 (m, 8H, AOCH2A),
3.78 (t, J ¼ 4.8 Hz, 4H, AOCH2A), 3.61 (t, J ¼ 4.8 Hz, 4H,
AOCH2A), 3.49–3.41 (m, 8H, AOCH2A), 3.21 (t, J ¼ 4.6 Hz,
4H, AOCH2A), 3.17–3.05 (m, 4H, AOCH2A), 2.99 (s, 2H,
CBCAH). 13C NMR (CDCl3):
d 159.11, 154.26, 134.02,
133.51, 129.33, 129.20, 127.77, 126.22, 125.46, 123.63,
120.45, 115.62, 114.52, 114.24 (Ar), 83.60 (ArACBCAH),
75.82 (ArACBCAH), 70.69, 70.43, 70.37, 70.34, 69.83,
69.53, 69.50, 67.38 (AOCH2A). Anal. Calcd. for C52H54O10
(838.98): C, 74.44; H, 6.49. Found: C, 74.19; H, 6.71.
Polymerization
The polymerizations of 1a–c were carried out in a dry flask
under an argon atmosphere. An example of the procedure is
described below. In a glovebox (under moisture- and oxygen-
free argon atmosphere, H2O, O2 < 1 ppm), Rh(nbd)BPh4 (2.0
mg, 4.0 lmol) was weighed into a flask and dissolved in dry
chloroform (18.5 mL). To the solution was added a solution
of 1b in dry chloroform (0.27 mmol Lꢀ1, 1.5 mL, 0.40
mmol). After stirring at 30 ꢁC for 24 h, triphenylphosphine
(6.3 mg, 24 lmol) was added to the reaction mixture to
quench the polymerization reaction. The solution was fil-
CHIROPTICAL CHANGE OF POLY(PHENYLACETYLENE)S, SAKAI ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
Raman measurements. Figure 1(b) shows the 1H NMR spec-
trum of the product resulting from the cyclopolymerization
of 1a. The signal due to the main chain protons appeared at
5.7 ppm along with those due to the aromatic protons and
oxyethylene chains, while the signals at 3.0 ppm due to the
ethynyl protons completely disappeared. Thus, the polymer-
ization was found to proceed via a cyclopolymerization
mechanism and the extent of the cyclization was ꢃ100%.
Based on these results, the polymer synthesized from 1a
were assignable to poly(phenylacetylene) bearing the
binaphtyl-based chiral crown ether on the backbone, 2a. The
1H NMR analysis generally provides us with detailed infor-
mation about the stereoregularity of the polyacetylene deriv-
atives, which was an important element for forming a stable
helical structure.11 Unfortunately, we could not estimate the
a
TABLE 1 Cyclopolymerizations of 1a–c Using Rh(nbd)BPh4
Mn ꢂ 10ꢀ4b
Mw/Mn
b
Polymer
Yield (%)
2a
2b
2c
a
70
73
60
1.0
1.5
3.5
2.49
3.13
3.53
[M]/[I] ¼ 100; [M] ¼ 0.02 mol Lꢀ1 time, 24 h; solvent, CHCl3; tempera-
ture, 30 ꢁC.
b
Determined by SEC in THF using polystyrene standards.
dictates the size of the chiral crown ether in the repeating
units.
We previously reported that a,x-diacetylene monomers
bearing the oligooxyethylene chain were successfully cyclo-
polymerized using Rh(nbd)BPh4 under a highly dilute condi-
tion, such as 0.02 mol Lꢀ1, to afford polymers without gela-
tion.51 Thus, this established condition was applied to the
cyclopolymerizations of 1a–c (Scheme 1). The polymeriza-
tion results are listed in Table 1. The cyclopolymerizations of
1a–c using Rh(nbd)BPh4 in chloroform at 30 ꢁC homogene-
ously proceeded to give the gel-free polymers in the yield of
60–73%, which had a good solubility in organic solvents
such as chloroform, DMF, and THF. The Mns of the products
resulted from 1a, 1b, and 1c were determined to be 1.0 ꢂ
105, 1.5 ꢂ 105, and 3.5 ꢂ 105, respectively.
1
stereoregularity of 2a from the H NMR spectrum due to the
broadening of the main chain protons and the overlapping of
some aromatic protons. Hence, we performed a laser Raman
measurement, which is a versatile method to directly deter-
mine the stereoregularity of the polyacetylenes.60 The laser
Raman spectrum of 2a showed characteristic peaks at 1544
and 1341 cmꢀ1, which were assigned to the C¼¼C and CAC
vibrations in the cis-polyacetylenes (Fig. 2). In contrast, no
distinct peaks due to the trans structure were observed in
this spectrum, indicating that 2a had a highly stereoregular
cis structure. Similar results were also obtained for the 1H
NMR and the laser Raman analyses of the products resulting
from the cyclopolymerizations of 1b and 1c, and thus these
products were assigned to 2b and 2c, respectively. Conse-
quently, the cyclopolymerization of the diacetylene mono-
mers with the (R)-1,10-binaphthyl moiety (1a–c) was shown
to be a very useful strategy to synthesize a series of poly
(phenylacetylene)s bearing the binaphthocrown ether as the
repeating units. Note that a significantly large-membered
cyclic structure could be precisely synthesized as the
To assign the microstructure of the constitutional units in
the resulting products, we performed 1H NMR and laser
FIGURE 1 1H NMR spectra of 1a (upper) and 2a (lower) in
FIGURE 2 Laser Raman spectrum of 2a in the solid state.
CDCl3.
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ARTICLE
mer structure is definitely novel type in the field of the heli-
cal polymer chemistry, thus inspiring us to investigate
whether the chiroptical change of the polymers occurs in
response to the host-guest complex formation between the
helically arraying chiral crown ethers and both chiral and
achiral guest molecules.
Chiroptical Change Based on the Host–Guest
Complexation
To investigate the chiroptical change of 2a–c based on the
host–guest complexation with an achiral guest, the CD meas-
urements of 2a–c were carried out in the presence of achiral
ammonium perchlorate, 7, 8, 9, and 10 as shown in Chart 1.
The addition of any achiral guests led to almost no signifi-
cant change in the CD intensity and the pattern of 2a [Fig.
4(a)]. This suggests that the main chain conformation of 2a
is essentially unchangeable by the addition of any guest mol-
ecules, though the slight change in the CD intensity implies
that the complexation actually occurs. Such behavior of 2a
should be ascribed to the rigid cyclic structure stably con-
structed by the axial chirality of the binaphthyl units. Thus,
the host–guest complexation appears to be not strong
enough to influence the original helical structure of 2a. In
sharp contrast, the CD spectrum of 2b notably changed by
adding every achiral guest, as shown in Figure 4(b). The pos-
itive effect in the CD intensity is explainable by the enhance-
ment of the chiral translation from the binaphthyl unit to the
polymer backbone via the host–guest complexation. In par-
ticular, the CD intensity of 2b in the presence of 10 was esti-
mated to be þ1.0 ꢂ 104 deg cm2 dmolꢀ1, which was nearly
three times greater than that of 2b without any guests. A
similar but negative effect was observed in the case of 2c
[Fig. 4(c)]. The CD intensity of 2c decreased by the addition
of the achiral guests and reached almost half of the original
one. This indicates that the influence of the host–guest com-
plexation is antagonistic to the chirality regulation based on
the binaphtyl unit, leading to the destabilization of the origi-
nal helical structure.
FIGURE 3 CD and absorption spectra of 2a–c in CHCl3/acetoni-
trile (2/1, v/v) at 25 ꢁC. Concentrations of 2a, 2b, and 2c were
1.5, 1.3, and 1.2 mM, respectively.
repeating units without any undesirable gelation, that is, 29-,
35-, and 41-membered ones for 2a, 2b, and 2c, respectively.
To our knowledge, the 41-membered ring is the largest
cyclic structure produced by the cyclopolymerization
process.
Chiroptical Properties of the Polymers
The pendant binaphthyl moiety has a potential to endow the
main chain with a one-handed helical structure. Hence, the
chiroptical properties of the polymers 2a–c were investi-
gated by CD measurements. Figure 3 shows the CD and
absorption spectra of 2a–c in chloroform/acetonitrile (2/1,
v/v). Every resulting polymer showed a positive Cotton
effect in the range from 350 to 500 nm corresponding to the
absorption of the conjugated polymer backbone. This result
obviously indicates that these polymers possess a helical
structure with an excess single screw sense induced by the
covalently bonded (R)-1,10-binaphthyl units. It is worth not-
ing that the main chain helical structure is directly regulated
by the binaphthyl-based atropisomeric structure through the
cyclic structure of the monomeric units.
Considering the chirality of the binaphthocrown ether, of
great interest is to investigate the helicity change triggered
by the host–guest complexation with chiral guest molecules
as well as achiral ones. Figure 5(a) shows the effect of chiral
guests on the CD spectrum of 2a. Every chiral guest appa-
rently did not influence the original helical structure of 2a
regardless of the chirality of the guest. On the other hand,
the helicity change depending on the chirality of the guest
was observed for 2b [Fig. 5(b)]. The CD spectrum of 2b in
the presence of D-Pgly HClO4 showed a more intense Cotton
Among these polymers, 2a showed a notably high CD inten-
sity in comparison to those of 2b and 2c. This should be at-
tributable to the distance between the main chain and chiral
units. A more interesting result is that these polymers
formed relatively stable helical structures, though the main
chains of these polymers connect with the binaphthyl units
through the long flexible chains, that is, the oxyethylene
chains consisting of the six bonds for 2a, the nine bonds for
2b, and the 12-bonds for 2c. Such a long-range chirality
transfer should be caused by the direct regulation based on
the cyclic structure in the repeating units and the axial
asymmetry of the binaphthyl units.
All the aforementioned characterizations revealed that the
polymers possessed one-handed helical backbone, which was
surrounded by their chiral crown ether moieties. Such poly-
CHART 1 Structures of achiral guest molecules.
CHIROPTICAL CHANGE OF POLY(PHENYLACETYLENE)S, SAKAI ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 4 Changes in the CD and absorption spectra of (a) 2a, (b) 2b, and (c) 2c in CHCl3/acetonitrile (2/1, v/v) at 25 ꢁC on the addi-
tion of achiral guests (50 equiv.). The concentrations of 2a, 2b, and 2c were 1.5, 1.3, and 1.2 mM, respectively.
effect than the original one, whereas almost no change was
observed in the CD spectrum of the 2b/L-Pgly HClO4 system.
This result clearly indicates the chirality-responsive fluctua-
tion in the helical structure of 2b. However, for the other
amino acid derivatives, such as Phe HClO4 and Leu HClO4,
neither enantiomer produced similar changes in the CD spec-
tra. This may indicate that 2b possesses a substrate specific-
ity along with the enantiomer-selectivity in the conformation
change, which is probably due to the strictly built-up crown
cavity of 2b. The polymer 2c also showed a chiral recogni-
tion property toward Pgly HClO4. The addition of L-Pgly
HClO4 did not bring about a significant change in the CD
spectrum [Fig. 5(c)]. On the contrary, the CD spectrum of 2c
changed in the negative direction by the addition of D-Pgly
HClO4. Moreover, a similar decrease in the CD intensity was
observed for Phe HClO4 and Leu HClO4 regardless of their
chirality. For this substrate specificity, only L-Pgly HClO4
seemed to be an inappropriate guest to produce the chiropti-
cal change. Therefore, the substrate specificity of 2c was
found to be lower than that of 2b.
complexation-induced chiroptical change was clarified to
drastically vary among polymers (2a–c). Given the similarity
in the polymer structure of 2a–c, it is obvious that the cavity
size of the binaphthyl-based crown ether essentially dictates
the behavior of the complexation-induced fluctuation in the
main chain conformation of 2a–c.
CONCLUSIONS
We demonstrated the synthesis and chiroptical property of
poly(phenylacetylene)s bearing the binaphthocrown ether on
the main chain. The cyclopolymerizations of the diacetylene
monomers afforded the targeted polymers (2a–c), in which
the cavity sizes of the chiral crown ether units were
designed to be different from each other. The CD analysis
revealed that the polymers possessed a helical structure
with an excess single screw sense induced by the covalently
bonded binaphthyl units. The host–guest complexation of
2a–c with both the achiral and chiral guests brought about a
chiroptical change based on the fluctuation in the main chain
conformation. For this complexation-induced chiroptical
change, each polymer exhibited a specific behavior, which
was considered to be essentially dictated by the cavity size
Through all the experiments regarding the host–guest com-
plexation of 2a–c with both the achiral and chiral guests, the
FIGURE 5 Changes in the CD and absorption spectra of (a) 2a, (b) 2b, and (c) 2c in CHCl3/acetonitrile (2/1, v/v) at 25 ꢁC on the addi-
tion of chiral guests (50 equiv.). The concentrations of 2a, 2b, and 2c were 1.5, 1.3, and 1.2 mM, respectively.
1204
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ARTICLE
21 Sanda, F.; Terada, K.; Masuda, T. Macromolecules 2005, 38,
of the binaphthocrown ether units. Considering the novelty
in the polymer structure of 2a–c, the presented results may
contribute to the further design of helical polymers and
binaphthyl-based chiral compounds. Chiral discrimination
using 2a–c is currently being investigated and will be
reported in due course.
8149–8154.
22 Hasegawa, T.; Morino, K.; Tanaka, Y.; Katagiri, H.; Furusho,
Y.; Yashima, E. Macromolecules 2006, 39, 482–488.
23 Sakai, R.; Otsuka, I.; Satoh, T.; Kakuchi, R.; Kaga, H.; Kaku-
chi, T. J Polym Sci Part A: Polym Chem 2006, 44, 325–334.
The authors thank T. Masuda and T. Tago (Graduate School of
Engineering, Hokkaido University) for their help in the laser
Raman measurements. The authors also gratefully acknowl-
edge the Global COE Program (Catalysis as the Basis for Innova-
tion in Materials Science) of the Ministry of Education, Culture,
Sports, Science and Technology for the financial support.
24 Sakai, R.; Otsuka, I.; Satoh, T.; Kakuchi, R.; Kaga, H.; Kaku-
chi, T. Macromolecules 2006, 39, 4032–4037.
25 Maeda, K.; Morioka, K.; Yashima, E. Macromolecules 2007,
40, 1349–1352.
26 Maeda, K.; Tsukui, H.; Matsushita, Y.; Yashima, E. Macro-
molecules 2007, 40, 7721–7726.
27 Kakuchi, R.; Nagata, S.; Sakai, R.; Otsuka, I.; Nakade, H.;
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