Synthesis and ion responsiveness of optically active polyacetylenes containing salicylidene Schiff-base moieties

Article abstract of DOI:10.1016/j.reactfunctpolym.2015.01.003

Acetylenic monomers containing salicylidene Schiff-base groups (1a and 1b) as well as Schiff-base and hydroxy groups (1c) were synthesized and polymerized with [(nbd)RhCl]₂/Et₃N catalyst to afford the corresponding polymers 2a-c with

Full text of DOI:10.1016/j.reactfunctpolym.2015.01.003

Accepted Manuscript
Synthesis and ion responsiveness of optically active polyacetylenes containing
salicylidene Schiff-base moieties
Chunyu Zhang, Yu Zhang, Hexin Zhang, Yanming Hu, Xuequan Zhang, Toshio
Masuda
PII:
S1381-5148(15)00005-X
DOI:
http://dx.doi.org/10.1016/j.reactfunctpolym.2015.01.003
REACT 3483
Reference:
Reactive & Functional Polymers
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Revised Date:
Accepted Date:
24 October 2014
13 January 2015
15 January 2015
Please cite this article as: C. Zhang, Y. Zhang, H. Zhang, Y. Hu, X. Zhang, T. Masuda, Synthesis and ion
responsiveness of optically active polyacetylenes containing salicylidene Schiff-base moieties, Reactive &
Functional Polymers (2015), doi: http://dx.doi.org/10.1016/j.reactfunctpolym.2015.01.003
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Synthesis and ion responsiveness of optically active polyacetylenes containing
salicylidene Schiff-base moieties
Chunyu Zhanga, Yu Zhangb, Hexin Zhanga, Yanming Hua,*, Xuequan Zhanga, Toshio
Masudac
a Key Laboratory of Synthetic Rubber, Changchun Institute of Applied Chemistry, Chinese
Academy of Sciences, Changchun 130022, China
b Department of Polymer Science and Engineering, School of Chemical Engineering, Dalian
University of Technology, Dalian 116024, China
c Research Center for Environmentally Friendly Materials Engineering, Muroran Institute of
Technology, 27-1 Mizumoto-cho, Muroran 050-8585, Japan
* Corresponding author: Yanming Hu
Tel.: +86 431 85262305; fax: +86 431 85262274.
E-mail address: ymhu@ciac.ac.cn
1

ABSTRACT
Acetylenic monomers containing salicylidene Schiff-base groups (1a and 1b) as well as
Schiff-base and hydroxy groups (1c) were synthesized and polymerized with
[(nbd)RhCl]2/Et3N catalyst to afford the corresponding polymers 2a-c with high molecular
weights (Mn = 2.6‒7.2 × 105) in high yields (75–97%). Polarimetric, circular dichroism (CD),
and UV-vis spectroscopic analyses indicated that the polymers formed helical structures with
a predominantly one-handed screw sense. The addition of metal ions to salicylidene
Schiff-base-containing polymers 2a and 2b produced insoluble polymer/metal complexes
through ionic cross-linking as a result of salicylaldimine-metal ion complexation. Polymers
2b and 2c underwent a helix-coil transition upon the addition of HSO4¯, whereas these
polymers did not exhibit responsiveness to other anions, such as F¯, Cl¯, and Br¯.
Keywords: Conjugated polymer; Polyacetylene; Helix; Stimuli-responsive; Polymerization
2

1. Introduction
The development of novel artificial helical polymers continues to be a topic of
considerable interest and importance in the area of macromolecular science from both
fundamental and application-oriented perspectives [1-6]. Over the past decades, tremendous
strides have been made in the field of synthetic helical polymer chemistry, and a variety of
helical polymers have been successfully synthesized not only to mimic biological helices but
also for their potential applications in chiral recognition, asymmetric catalysis, chemical
sensors, and so forth [7‒10]. Among these polymers, conjugated helical polymers, such as
polyisocyanides, polysilanes, and polyacetylenes, are of great interest and are intensively
studied because of their unique functions resulting from their helical structures and
conjugated main chains.
As a class of typical π-conjugated polymers, polyacetylene and its derivatives exhibit
interesting chemical and physical properties [11-13]. Substituted polyacetylenes can form
helical structures with a predominantly one-handed screw sense through the introduction of
appropriate chiral substituents into the side chain or through the helix-sense-selective
polymerization of achiral monomers [14–22]. Polyacetylene derivatives adopt a dynamic
helical conformation due to the relatively low energy barriers for helix reversal [3]. These
derivatives can undergo helix/random coil transitions and/or helix inversions in response to
external stimuli, such as temperature, light, and change of medium conditions, including
polarity and pH, which is attractive in a wide variety of fields, including life sciences,
pharmacy, and chemical engineering. Although various helical polyacetylenes have been
reported, sophisticated studies are still being performed to design and tailor desired polymer
3

properties.
Salicylidene Schiff bases, which are an important and versatile class of ligands, have
attracted considerable attention because of their facile preparation via salicylaldehyde-amine
condensation, easy modification of their steric and electronic properties, and high binding
affinity toward various metal ions [23-25]. Various salicylidene Schiff-base/metal complexes
have been synthesized and have found potential applications in optic materials, chemical
sensors, biological probes, and efficient catalysts for organic reactions [26-29]. However,
compared with the extensively studied low-molecular-weight systems, the synthesis and
applications of salicylidene Schiff-base-containing polymers are quite limited. Lu and
coworkers prepared “light-controllable” fluorescent polystyrene micelles via
salicylaldimine-Zn2+ complexation [30]. Theato and coworkers prepared thermo- and
light-responsive polyacrylamides that contained different amounts of salicylideneaniline
chromophores [31]. Cai and coworkers reported the synthesis of metal-functionalized
polymer micelles through Co2+-salicylaldimine coordination [32]. The above-mentioned
salicylidene Schiff-base-containing polymers were synthesized through the side-chain
modification of polymers via aldehyde-amine condensation. In contrast, the direct
polymerization of salicylidene Schiff-base-containing monomers is a simple and
straightforward route for the synthesis of well-defined polymers with salicylidene Schiff-base
pendant
groups.
We
recently
reported
that
(S)-
and
(R)-N-(4-ethynylbenzylidene)-1-phenylethanamine, which are Schiff-base-functionalized
acetylenic monomers, polymerize with [(nbd)RhCl]2/Et3N catalyst to afford helical
polyacetylenes [33]. Thus, we can potentially prepare novel functional helical polyacetylenes
4

bearing salicylidene Schiff-base groups through direct polymerization of the corresponding
monomers, which could exhibit interesting properties as a result of the combination of the
unique characteristics of the salicylidene Schiff base and the higher-order structure of the
polyacetylene backbone.
The present study focuses on the synthesis and polymerization of novel acetylenic
monomers containing salicylidene Schiff-base moieties (1a and 1b) as well as a monomer
containing both Schiff-base and hydroxy groups (1c) for comparison (Scheme 1). The
secondary structures of the resulting polymers were investigated in detail, and their
responsiveness to metal ions and tetra-n-butylammonium hydrogen sulfate was examined.
(insert Scheme 1 here)
2. Experimental section
2.1. Measurements
1H and 13C NMR spectra were recorded on a Varian Unity-400 spectrometer. IR spectra
were recorded on a BRUKER Vertex-70 spectrophotometer. The number- and
weight-averaged molecular weights (Mn and Mw) of the polymers were determined using a gel
permeation chromatograph equipped with a Waters 515 HPLC pump and a Waters 2414
differential refractometer using THF as the eluent at a flow rate of 1.0 mL/min and calibrated
with polystyrene standards. Elemental analysis of the monomers was performed at the
Analytical Center of Dalian University of Technology. Specific rotations ([α]D) were
measured using a JASCO DIP-1000 digital polarimeter. CD and UV-vis spectra were
recorded on a JASCO J-810 spectropolarimeter.
2.2. Materials
5

THF, which was used as the polymerization solvent, was distilled over sodium prior to
use. Triethylamine was distilled and dried over potassium hydroxide. 4-Bromobenzaldehyde
(Aladdin Co.), 5-bromosalicylaldehyde (J & K), (R)-1-phenylethanamine (Aldrich),
(R)-2-phenylglycinol
(Aladdin
Co.),
trimethylsilylacetylene
(Acros),
bis(triphenylphosphine)palladium(II) dichloride (Aldrich), and [(nbd)RhCl]2 (Aldrich) were
used as received. Other solvents, such as methanol, toluene, and CHCl3, were of high purity
and
were
used
without
further
purification.
4-Ethylnylbenzaldehyde
and
5-ethynylsalicylaldehyde were synthesized following methods reported in the literature
[34,35].
2.3. Monomer synthesis
2.3.1. (R)-4-Ethynyl-2-((1-phenylethylimino)methyl)phenol (1a)
A 100-mL three-necked flask was equipped with a three-way stopcock and a magnetic
stirring bar. (R)-1-Phenylethanamine (0.61 g, 5 mmol) and 5-ethynylsalicyclaldehyde (0.73 g,
5 mmol) were dissolved in toluene (60 mL). The reaction mixture was heated at reflux
temperature for 10 h. The generated water was separated using a Dean-Stark apparatus. Then,
toluene in the reaction mixture was removed by evaporation, and the crude product was
purified by recrystallization from ethanol to afford bright yellow crystals in 55% yield; [α]D =
1
+23° (c = 0.2 g/dL, CHCl3, room temperature). H NMR (400 MHz, CDCl3): δ 13.8 (s, 1H,
≡C),
OH), 8.31 (s, 1H, CH=N), 7.42–6.88 (m, 8H, ArH), 4.54 (q, 1H, N-CH), 2.97 (s, 1H, HC
1.61 (m, 3H, CH3). 13C NMR (100 MHz, CDCl3): δ 162.8 (CH=N), 162.0, 143.5, 136.1, 135.5,
128.9, 127.6, 126.5 118.7, 117.6, 112.3, 83.3, 75.9, 68.4, 24.9. IR (cm-1, CHCl3): 3278, 3107,
2927, 1630 (CH=N), 1583, 1485, 1396, 1289, 973, 830, 770, 701. Anal. Calcd for C17H15NO:
6

C, 81.90; H, 6.06; N, 5.62. Found: C, 81.78; H, 6.21; N, 5.87.
2.3.2. (R)-4-Ethynyl-2-((2-hydroxy-1-phenylethylimino)methyl)phenol (1b)
This monomer was prepared using the same method as for monomer 1a but with
(R)-2-phenylglycinol rather than (R)-1-phenylethanamine to afford orange crystals in 50%
1
yield; [α]D = +9° (c = 0.1 g/dL, CHCl3, room temperature). H NMR (400 MHz, CDCl3): δ
8.40 (s, 1H, CH=N), 7.44–6.90 (m, 8H, ArH), 4.47 (t, 1H, N-CH), 3.91 (m, 2H, CH2OH), 2.99
(s, 1H, HC≡C). 13C NMR (100 MHz, CDCl3): δ 158.7 (CH=N), 145.1, 136.8, 132.4, 128.6,
128.3, 127.1, 126.8, 124.3, 83.5, 79.0, 70.0, 25.0. IR (cm-1, CHCl3): 3287, 3061, 2925, 2867,
1633 (CH=N), 1586, 1487, 1383, 1287, 1068, 893, 830, 760, 700. Anal. Calcd for C17H15NO2:
C, 76.96; H, 5.70; N, 5.28. Found: C, 76.73; H, 5.65; N, 5.47.
2.3.3. (R)-N-(4-Ethynylbenzylidene)-2-phenylglycinol (1c)
This monomer was prepared using the same method as for monomer 1a but with
(R)-2-phenylglycinol and 4-ethynylbenzaldehyde rather than (R)-1-phenylethanamineand
5-ethynylsalicylaldehyde to afford light yellow crystals in 54% yield; [α]D = +125o (c = 0.1
1
g/dL, CHCl3, room temperature). H NMR (400 MHz, CDCl3): δ 8.30 (s, 1H, CH=N),
7.69–7.29 (m, 9H, ArH), 4.50 (t, 1H, N-CH), 3.98 (m, 2H, CH2-O), 3.22 (s, 1H, HC≡C). 13C
NMR (100 MHz, CDCl3): δ 162.2 (CH=N), 140.6, 135.9, 132.4, 129.0, 128.8, 127.7, 126.9,
126.6, 126.3, 124.7, 83.4, 79.4, 67.8, 62.4. IR (cm-1, CHCl3): 3286, 3062, 3029, 2923, 2868,
1641 (CH=N), 1604, 1493, 1452, 1383, 839, 759, 701. Anal. Calcd for C17H15NO: C, 81.90;
H, 6.06; N, 5.62. Found: C, 81.60; H, 5.99; N, 5.55.
(insert Scheme 2 here)
2.4. Polymerization
7

The polymerizations were conducted in a glass tube equipped with a three-way stopcock
under dry nitrogen. [(nbd)RhCl]2 and Et3N were added to a monomer solution in THF under
nitrogen, and the resulting solution ([M]0 = 0.5 mol/L, [Rh]/[M]0 = 100, [Et3N]/[Rh] = 50) was
maintained at 30 °C for 4 h. The formed polymers were isolated by precipitation into a large
amount of n-hexane and dried to a constant weight under reduced pressure; the polymer yields
were gravimetrically determined.
2.5. Spectroscopic data of the polymers
2a: 1H NMR (400 MHz, CDCl3): δ 8.01 (br, 1H, CH=N), 7.57–6.65 (br, 9H, ArH), 5.81
(br, 1H, HC=C), 4.28 (br, 1H, NCH), 2.95–2.79 (br, 2H, CH2OH). IR (cm-1, CHCl3): 3501,
3111, 2955, 2927, 2863, 1632 (HC=N), 1558, 1489, 1456, 1395, 822, 760, 697. 2b: 1H NMR
(400 MHz, CDCl3): δ 8.40 (br, 1H, CH=N), 7.56–6.63 (br, 8H, ArH), 5.61 (br, 1H, HC=C),
4.48 (br, 1H, NCH), 3.91–3.74 (br, 2H, CH2OH). IR (cm-1, CHCl3): 3426, 3257, 3030，2949,
1
2871, 1631 (HC=N), 1586, 1489, 1442, 1373, 1105, 1062, 827, 783, 698. 2c: H NMR (400
MHz, CDCl3): δ 8.11 (br, 1H, CH=N), 7.57–7.05 (br, 9H, Ar), 5.78 (br, 1H, HC=C), 4.51 (br,
1H, NCH), 4.07‒4.3 (br, 2H, CH2OH). IR (cm-1, CHCl3): 3383, 3060, 3027, 2923, 2863, 1640
(HC=N), 1602, 1562, 1492, 1452, 1384, 826, 760, 701.
2.6. Preparation of polymer/metal ion complexes
The polymer/metal ion complexes were prepared by adding metal acetate to the polymer
solutions. Copper acetate, zinc acetate, and chromium acetate were used as metal acetate
hydrates. A detailed procedure is as follows: 2a (49.8 mg, 0.2 mmol in terms of repeat unit)
was placed in a flask and completely dissolved in THF (10 mL). A solution of copper acetate
[Cu(CH3COO)2·H2O, 20 mg, 0.1 mmol] in ethanol (3 mL) was added dropwise, and the
8

resulting mixture was stirred overnight at room temperature. During that time, the color of the
suspension changed from orange to brown, and a large amount of solid precipitated from the
solution. The precipitate was filtered and repeatedly washed with THF and methanol, and it
was dried to constant weight under reduced pressure.
3. Results and discussion
3.1 Monomer synthesis and polymerization
Acetylenic monomers 1a-c were synthesized via the salicylaldehyde-amine condensation
reaction according to Scheme 2. The structures of the monomers were identified by 1H NMR,
13C NMR, IR spectroscopy and elemental analysis.
Rhodium catalysts can efficiently polymerize various monosubstituted acetylenes to
afford polymers with high molecular weights and stereoregularity even though the monomers
possess polar and functional groups [36-39]. Thus, the polymerizations of monomers 1a-c
were conducted with [(nbd)RhCl]2/Et3N catalyst in THF, and the results are summarized in
Table 1. The corresponding polymers 2a-c with fairly high molecular weights (Mn = 2.6‒7.2 ×
105) were obtained in high yields (75‒96%). All of the polymers were soluble in common
organic solvents, such as CHCl3, CH2Cl2, THF, and DMF. The polymer structures were
1
examined using IR and H NMR spectroscopy. The monomers exhibited an absorption band
at approximately 3280 cm-1 assignable to the ≡C–H stretching vibration, which disappeared in
the IR spectra of the polymers. However, the absorption band due to HC=N at approximately
1640 cm-1 remained intact in the polymers. These results indicate that the polymerization
occurs to form polymers composed of alternating single and double bonds and with no change
in the Schiff-base group in the resulting polymers. However, we could not determine the
9

cis-contents of polymers from the integration ratio of cis-vinyl proton and the other proton
1
signals due to the broadness of the peaks in the H NMR spectra. Because the polymerization
of acetylenic monomers with Rh-based catalysts generally affords cis-rich polyacetylenes, it
is assumed that the geometric structure of 2a-c is also the same. This was further confirmed
by laser Raman analysis (Fig. S1), in which intense peaks at 1556 cm-1 (C=C stretching) and
1340 cm-1 (C-C stretching) attributable to the cis-polyacetylene structure were observed.
(insert Table 1 here)
3.2 Chiroptical properties of the polymers
The chiroptical properties of the polymers were examined by polarimetry, CD, and
UV-vis spectroscopy. As shown in Table 1, the polymers exhibited [α]D values 5‒20 times
larger than those of the corresponding monomers, suggesting that the polymers adopt helical
structures with a predominantly one-handed screw sense in CHCl3. This result was further
confirmed by the CD and UV-vis spectra of the obtained polymers measured in CHCl3 at
20 °C (Fig. 1). The monomer exhibited stronger Cotton effects at 300‒370 nm than its
corresponding polymer, and a similar result was observed in a previous study [40]. The
polymers exhibited split-type intense Cotton effects at approximately 330 and 390 nm.
Although the optical configuration of 1a was inverted to those of 1b and 1c, the polymers
exhibited helical structures with the same screw senses. These results might be due to the
presence of –CH2OH groups in the cases of 2b and 2c, thereby influencing their chiroptical
properties. In addition, whereas monomer 1a exhibited a strong UV absorption only in the
range of 300‒370 nm, the polymers showed strong UV absorptions over the wide range of
280‒500 nm. These results suggest that the chiral Schiff-base groups induced the Cotton
10

effects at approximately 330 nm and that the polyacetylene main chain induced the ones
approximately 385 nm. Thus, it is concluded that the CD signals of 2a–c arise from not only
the configurational chirality of the Schiff-base groups but also from the conformational one
based on the higher-order structures of the polyene backbone.
(insert Fig. 1 here)
Fig. 2 presents the CD and UV-vis spectra of the polymers measured in various solvents.
2a showed similar CD signals in both nonpolar and polar solvents, indicating that the helical
structure of the polymers originates from steric effects. 2b and 2c exhibited similar results,
but the solvent effects were somewhat larger. Although the reason is not yet clear, these
results might be due to the presence of –CH2OH groups, leading to more sensitive solvent
effects. A certain change in Cotton effects with solvents suggests that the helix of the present
polymers is dynamic.
(insert Fig. 2 here)
Fig. 3 shows the effects of temperature on the CD and UV-vis spectra of the polymers. In
the cases of 2a and 2b, the intensities of the Cotton effect were only slightly decreased by
increasing the temperature from 0 to 80 °C. The present temperature dependence of the helix
and the slight decrease in UV-vis absorption might be due to randomization of the chain
conformation activated by thermal perturbation. Additionally, the temperature effect on the
CD and UV-vis spectra of 2a and 2b was smaller than that of 2c. The higher thermal stability
of the helicity of 2a and 2b might be due to the formation of a six-membered pseudo-aromatic
ring via the hydrogen bond of O‒H···N, which forms between the hydroxy group of the
phenol ring and the nitrogen atom of imine, leading to a larger steric effect [41]. In addition,
11

in all cases, the CD and UV–vis spectral changes were reversible with increasing and
decreasing temperature. Similar results were observed in the cases of other helical
polyacetylene derivatives [3, 32-44]
(insert Fig. 3 here)
3.3 Responsiveness of 2a to metal ions
Polymers that contain coordinative groups in their main and side chains can coordinate
with metal ions to form functional polymer/metal complexes that exhibit interesting
properties. For example, (R,R)-salen/salan-based polymers could be used as fluorescence
sensors for Zn2+detection [45], and a Schiff-base-anchored polystyrene/Cr3+ complex
exhibited good microbial ability [46]. In the present study, the complexation of 2a with
various metal ions was investigated. Upon the addition of Cu2+ ions to a THF solution of 2a, a
precipitate formed in the system, suggesting that intra- and inter-molecular cross-linking
reactions occurred, and as gravimetrically determined, a quantitative conversion concerning
complexation was attained. The resulting product was insoluble in CHCl3, CH2Cl2, THF, and
DMF, in which 2a exhibited good solubility. Similar results were observed in the cases of 2b
and 2c and other metal cations such as Zn2+ and Cr3+. It is known that low-molecular-weight
salicylidene Schiff-base derivatives can coordinate with metal ions through bidentate bonding
to form bis-complexes, that is, one metal ion coordinates with two salicylaldimine ligands
[47-50]. According to the IR spectra (Fig. 4), the absorption peak of the imine C=N moiety of
2a appears at 1619 cm-1 after the addition of Cu2+ ions, which is clearly red-shifted compared
to that of 2a (1630 cm-1), indicating that the nitrogen atom of the imine coordinates to the
Cu2+ ion. Furthermore, the weak peak at 527 cm-1 assignable to ν(Cu‒O) suggests that the
12

hydroxy groups are involved in the formation of the polymer/metal complex [51]. Therefore,
the cross-links in the present study were likely generated by the formation of a metal-ligand
complex, as proposed in Fig. 5. Although the resulting polymer/metal complexes were
insoluble, they might serve as potential heterogeneous catalysts for asymmetric catalysis, and
this study is currently in progress.
(insert Fig. 4 and Fig. 5 here)
3.4 Responsiveness of 2c to anions
Fig. 6 shows the changes in the CD and UV-vis spectra upon the addition of
tetra-n-butylammonium hydrogen sulfate (n-Bu4N+HSO4¯) to a solution of 2c in THF. The
CD signals at 330 nm and 390 nm gradually decreased with increasing amount of
n-Bu4N+HSO4¯, and they completely disappeared upon the addition of 1.0 equivalent of
HSO4¯. This result indicates that 2c underwent a helix-coil transition. In contrast, other anions
such as F¯, Cl¯, and Br¯ did not result in detectable changes in the CD spectra. A similar result
was observed in the case of 2b (Fig. S2), whereas 2a did not exhibit responsiveness to HSO4¯.
1
Due to the broad peaks of the polymer in the 1H NMR spectra, we measured H NMR spectra
using (R)-2-(benzylideneamino)-2-phenylethanol as a model compound in the absence and
presence of n-Bu4N+HSO4¯. As shown in Fig. S3 in the Supporting Information, the peak
intensity of the hydroxy proton of the model compound decreased and finally disappeared
with increasing amounts of n-Bu4N+HSO4¯. Although the detailed mechanism of this
transition is not clear, it is hypothesized that the formation of hydrogen bonds between the
-
pendent groups of the polymer and HSO4 changes the shape and bulkiness of the side groups
[52], leading to a helix-coil transition.
13

(insert Fig. 6 here)
4. Conclusion
In the present study, we have demonstrated the synthesis and polymerization of novel
optically active, substituted acetylenic monomers containing both Schiff-base and hydroxy
groups using [(nbd)RhCl]2/Et3N catalyst. The produced polymers exhibited optical rotations
that were 5‒20 times larger than those of the corresponding monomers and intense CD signals
at the absorption region of the conjugated polyacetylene backbone, indicating that they form
predominantly one-handed helical structures. Polymers 2a and 2b containing salicylidene
Schiff-base moieties afforded cross-linking polymer/metal complexes through
salicylaldimine-metal ion complexation. Taking the advantage of the optical activity and
insolubility of these polymer complexes, they are promising as heterogeneous asymmetric
catalysts. Polymers 2b and 2c exhibited a helix-coil transition upon the addition of HSO4¯,
whereas no detectable CD signal changes were observed in the cases of F¯, Cl¯, and Br¯ ions.
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17

Captions for schemes and figures
Scheme 1. Synthesis of poly(phenylacetylene) derivatives 2a-c.
Scheme 2. Synthesis of monomers 1a-c.
Fig. 1. CD and UV-vis spectra of 1a and 2a-c measured in CHCl3 at 20 °C (c = 0.05 mg/mL).
Fig. 2. CD and UV-vis spectra of 2a-c measured in various solvents at 20 °C (c = 0.05
mg/mL).
Fig. 3. CD and UV-vis spectra of 2a-c measured in CHCl3 at various temperatures (c = 0.05
mg/mL).
Fig. 4. IR spectra of 2a and 2a/Cu2+ complex
Fig. 5. Schematic drawing of 2a/metal ion complex formed by the coordination of metal ionto
2a.
Fig. 6. CD and UV-vis spectra of 2c upon addition of HSO4¯ measured in THF at 20 °C (c =
0.05 mg/mL).
18

Scheme 1. Synthesis of poly(phenylacetylene) derivatives 2a-c.

Scheme 2. Synthesis of monomers 1a-c.

Fig. 1. CD and UV-vis spectra of 1a and 2a-c measured in CHCl3 at 20 °C (c = 0.05
mg/mL).

Fig. 2. CD and UV-vis spectra of 2a-c measured in various solvents at 20 °C (c = 0.05 mg/mL).

Fig. 3. CD and UV-vis spectra of 2a-c measured in CHCl3 at various temperatures (c = 0.05 mg/mL).

Fig. 4. IR spectra of 2a and 2a/Cu2+ complex

Fig. 5. Schematic drawing of 2a/metal ion complex formed by the coordination of
metal ion to 2a.

Fig. 6. CD and UV-vis spectra of 2c upon addition of HSO4ˉ measured in THF at
20 °C (c = 0.05 mg/mL).

Table 1
Polymerization of monomers 1a-c.a
d
[α]D (deg)
c
Monomer
Yieldb (%)
Mn× 10-5c
3.3
Mw/Mn
1.1
Monomer
+23
Polymer
+291
80
75
96
1a
1b
1c
2.6
1.1
+9
+197
7.2
1.2
+125
+718
a Polymerization conditions: in THF at 30 °C for 4 h, [M]0 = 0.5 mol/L, [M]0/[Rh] = 100.
b n-Hexane-insoluble part.
c Determined by GPC using THF as eluent with a polystyrene calibration.
d Measured by polarimetry at 20 °C, c = 0.20 g/dL in CHCl3.