Effects of substitution and terminal groups for liquid-crystallinity enhanced luminescence of disubstituted polyacetylenes carrying chromophoric terphenyl pendants

Article abstract of DOI:10.1007/s11426-010-3166-1

Liquid-crystalline and light-emitting poly(2-alkyne)s containing terphenyl cores with hexamethyleneoxy spacers, and cyano or n-propoxy tails - [CH₃C=C(CH₂)₆O-terphenyl-R] _n ^-, where R=CN, CH3PA6CN, R=OCH₂CH ₂CH₃, CH3PA6OPr, were synthesized. The effects of the substitution and terminal groups on the properties, especially the mesomorphic and optical properties of the polymers, were investigated. The disubstituted acetylene monomers (CH3A6CN, CH3A6OPr) were prepared through multistep reaction routes and were polymerized by WCl₆-Ph₄Sn in good yields (up to 82%). All the monomers and CH3PA6CN exhibited the enantiotropic SmA phase with a monolayer arrangement at elevated temperatures, whereas CH3PA6OPr formed a bilayer SmAd packing arrangement. Upon excitation at 330 nm, strong UV and blue emission peaks at 362 and 411 nm were observed in CH3PA6OPr and CH3PA6CN, respectively. The luminescent properties of CH3PA6CN and CH3PA6OPr have been improved by introducing the methyl substituted group, and the quantum yield of the polymer with cyano tail CH3PA6CN (Φ = 74%) was found to be higher than that of CH3PA6OPr (Φ = 60%). Compared to polyacetylene parents, both CH3PA6OPr and CH3PA6CN showed a narrower energy gap. This demonstrated that the electrical conductivities of polyacetylenes could be enhanced by attaching appropriate pendants to the conjugated polyene backbones.

Full text of DOI:10.1007/s11426-010-3166-1

SCIENCE CHINA
Chemistry
June 2010 Vol.53 No.6: 1302–1315
doi: 10.1007/s11426-010-3166-1
• ARTICLES •
Effects of substitution and terminal groups for liquid-crystallinity
enhanced luminescence of disubstituted polyacetylenes carrying
chromophoric terphenyl pendants
ZHOU Dan, CHEN YiWang*, CHEN Lie*, LI Fan, NIE HuaRong & YAO Kai
Institute of Polymers/Department of Chemistry, Nanchang University, Nanchang 330031, China
Received January 9, 2010; accepted March 4, 2010
Liquid-crystalline and light-emitting poly(2-alkyne)s containing terphenyl cores with hexamethyleneoxy spacers, and cyano or
n-propoxy tails [CH3C=C(CH2)6O-terphenyl-R]n, where R=CN, CH3PA6CN, R=OCH2CH2CH3, CH3PA6OPr, were
synthesized. The effects of the substitution and terminal groups on the properties, especially the mesomorphic and optical
properties of the polymers, were investigated. The disubstituted acetylene monomers (CH3A6CN, CH3A6OPr) were pre-
pared through multistep reaction routes and were polymerized by WCl6-Ph4Sn in good yields (up to 82%). All the monomers
and CH3PA6CN exhibited the enantiotropic SmA phase with a monolayer arrangement at elevated temperatures, whereas
CH3PA6OPr formed a bilayer SmAd packing arrangement. Upon excitation at 330 nm, strong UV and blue emission peaks at
362 and 411 nm were observed in CH3PA6OPr and CH3PA6CN, respectively. The luminescent properties of CH3PA6CN
and CH3PA6OPr have been improved by introducing the methyl substituted group, and the quantum yield of the polymer
with cyano tail CH3PA6CN ( = 74%) was found to be higher than that of CH3PA6OPr ( = 60%). Compared to polyacety-
lene parents, both CH3PA6OPr and CH3PA6CN showed a narrower energy gap. This demonstrated that the electrical con-
ductivities of polyacetylenes could be enhanced by attaching appropriate pendants to the conjugated polyene backbones.
disubstituted polyacetylenes, liquid crystallinity, phase transition, photoluminescence
didates as high-performance engineering materials. Inspired
1 Introduction
by these prospects, a variety of LC conjugated polymers
have been widely investigated because they are of both
theoretical and practical interest [9–11]. In particular, a
large number of monosubstituted polyacetylenes (PAs) and
some disubstituted PAs containing LC groups in their side
chains have been considered with growing interest due to
their excellent properties and their optical and electrical
properties are expected to be controlled by the molecular
orientation of the LC side chain [12–16].
Despite the fascinating functionalities, monosubstituted
polyacetylenes, however, still suffer from the instability
problem during storage, especially when they were in the
solution state. The polymers could be readily oxidized when
the solutions are exposed to air without the protection of
nitrogen [13]. This has seriously restricted the scope of their
Conjugated polymers are quintessential materials for the
“plastic electronics” revolution and have been extensively
studied for their potential applications in light-emitting di-
odes, electrochemical cells, field effect transistors, lasers,
and photovoltaic cells [1–6]. Liquid crystalline (LC) mate-
rials play a significant role in the modern optical display
systems and show a variety of characteristic properties in
the application of electric and magnetic fields [7, 8]. Combi-
nation of the anisotropic properties of liquid crystals with
conjugated polymers’ properties may endow new materials
with novel functional properties, which are promising can-
*Corresponding author (email: ywchen@ncu.edu.cn; chenlienc@163.com)
© Science China Press and Springer-Verlag Berlin Heidelberg 2010
chem.scichina.com
www.springerlink.com

ZHOU Dan, et al. Sci China Chem June (2010) Vol.53 No.6
1303
potential technological applications. In sharp contrast to
monosubstituted PAs, disubstituted PAs possess many ad-
vantages: high thermal stability, good film forming, me-
chanically strong and excellent luminescence [17–19]. Ter-
phenyl is not only an efficient chromophore but also a good
mesogenic core. It has been widely employed in construct-
ing low molecular mass gelators and optically helical poly-
mers [20–22]. Melding of optically active terphenyl
mesogenic cores with electronically active PAs at the mo-
lecular level may endow liquid crystalline polyacetylenes
(LCPAs) with both optical and electronic activities. The
spontaneous orientation and luminescent property of the
terphenyl mesogens might result in polymers with excellent
photoelectric properties. Attachment of the chromophoric
and mesogenic terphenyl pendants onto the disubstituted
polyacetylene backbones may further enhance their fluo-
rescence quantum yields through the energy transfer from
the pendant to the backbone.
In our previous work, we synthesized a group of mono-
substituted PAs containing terphenyl mesogenic pendants
and found that the polymer with one methylene spacer was
nonmesomorphic, while the polymer with six methylene
units showed good mesomorphism and better luminescence
property (Chart 1) [23]. In other words, the long spacer is
good for both mesomorphism and luminescence of PAs
bearing terphenyl pendants. Although it is challenging to
synthesize and even polymerize disubstituted PAs. At-
tracted by the potential of generating new functional poly-
mers with enhanced emissions, good mesomorphic and ex-
cellent heat stable properties, we decided to extend our in-
vestigations and take the challenge to design and synthesize
disubstituted PAs containing terphenyl pendants with six
methylene spacers and different terminal groups. We found
that structural variations exhibit much influence on the liq-
uid crystallinity behaviors and the optical properties of the
polymers CH3PA6CN and CH3PA6OPr. The luminescence
and thermal stabilities of CH3PA6CN and CH3PA6OPr
were better than those of monosubstituted PAs with ter-
phenyl mesogenic pendants.
(2.2 M in hexane, packaged under argon in resealable), and
tetrakis(triphenylphosphine)palladium(0) were purchased
from Alfa Aasar. Trimethyl borate, 4-bromobenzonitrile,
sodium acetylide, and 1,6-dibromehexane were purchased
from Aldrich, and used as received. 4-Iodophenol (Aladdin),
1-bromopropane (Aladdin), and CH3I were prepared in our
laboratory. Tetrahydrofuran (THF) was dried over sodium
and then distilled under nitrogen. Other chemicals were
obtained from Shanghai Reagent Co. Ltd., and used as re-
ceived.
2.2 Methods
The infrared (IR) spectra were recorded on a Shimadzu IR-
Prestige-21 Fourier transform infrared (FTIR) spectropho-
tometer by drop-casting sample solutions on KBr substrates.
The nuclear magnetic resonance (NMR) spectra were col-
lected on a Bruker ARX 400 NMR and Bruker AV 600
NMR spectrometer with deuterated chloroform or THF or
DMSO as the solvent and with tetramethylsilane (= 0) as
the internal standard. Thermogravimetric analysis (TGA)
was performed on a TA Q600 SDT for thermogravimetry at
a heating rate of 10 °C/min under nitrogen with a sample
size of 8–10 mg. Texture observations by polarizing optical
microscopy (POM) were carried out with a Nikon E600POL
polarizing optical microscope equipped with an Instec HS
400 heating and cooling stage. Differential scanning calo-
rimetry (DSC) was used to determine phase-transition tem-
peratures on a SHIMADZU DSC-60 differential scanning
calorimeter with a constant heating/cooling rate of 10 °C/min.
The X-ray diffraction (XRD) study of the samples was car-
ried out on a Bruker D8 Focus X-ray diffractometer operat-
ing at 30 kV and 20 mA with a copper target (= 1.54 Å)
and at a scanning rate of 1°/min. The UV spectra of the
samples were recorded on a Hitachi UV-2300 spectropho-
tometer. Fluorescence measurement for photoluminescence
(PL) of the polymers was carried out on a Shimadzu
RF-5301 PC with a xenon lamp as the light source. The gel
permeation chromatography (GPC), i.e., size-exclusion
chromatography (SEC) analysis, was conducted with a
Breeze Waters system equipped with a Rheodyne injector, a
1515 Isocratic pump and a Waters 2414 differential refrac-
tometer using polystyrenes as the standard and tetrahydro-
furan (THF) as the eluent at a flow rate of 1.0 mL/min and
40 °C through a Styragel column set, Styragel HT3 and
HT4 (19 mm × 300 mm, 103 + 104 Å), to separate molecular
weight (MW) ranging from 102 to 106. Electrochemical
measurements were made carried out in a standard three-
electrode cell by an electrochemical analyzer (CH Instru-
ments, Model CHI660C) using Ag/AgCl, platinum and
platinum wires as the reference, working electrode and
counter electrode, respectively, with a solution of a polymer
(103 M) and Tetra-n-butylammonium Tetrafluoroborate
(0.1 M) in THF. Elemental analyses (EA) were character-
ized by means of elemental analysis with Vario Elementar
Chart 1
2 Experimental
2.1 Materials
4-Bromo-4′-hydroxybiphenyl, WCl6, Ph4Sn, n-butyllithium

1304
ZHOU Dan, et al. Sci China Chem June (2010) Vol.53 No.6
III. The mass spectra were recorded on a Finnigan TSQ
7000 triple quadrupole mass spectrometer operating in a
chemical ionization (CI) mode using methane as carrier gas.
CDCl3, ppm):  3.42 (t, 2H, CH2Br), 2.20 (m, 2H, HC≡CCH2),
1.95 (t, 1H, HC≡), 1.87 (m, 2H, CH2CH2Br), 1.43–1.54 (m,
6H, CH2).
9-Bromo-2-nonyne
2.3 Synthesis of the monomers
The n-BuLi (2.2 M in n-hexane; 5.0 mL, 11.0 mmol) was
added slowly to a solution of 8-bromo-1-octyne (1.89 g,
9.98 mmol) in THF (20 mL) at 78 °C under nitrogen, and
the resulting solution was stirred at the same temperature
for 1 h. A solution of CH3I (1.52 mL, 25.2 mmol) in THF
(20 mL) was slowly added to the solution at 78 °C, and the
resulting mixture was subsequently warmed to room tem-
perature and stirred overnight. The formed solid was filtered,
and the solution was concentrated by rotary evaporator.
Vacuum distillation yielded 1.42 g of colorless oily product
The synthesis and structures of the monomers are outlined
in Scheme 1.
1
(100–102 °C/130 Pa). Yield: 69.8 %. H NMR (400 MHz,
CDCl3, ppm):  3.37 (t, 2H, CH2Br), 2.22 (t, 2H, CH3C≡
CCH2), 1.82 (m, 2H, CH2CH2Br), 1.78 (t, 3H, CH3C≡C),
1.47–1.40 (m, 2H, C≡CCH2CH2), 1.26–1.16 (m, 4H,
CH2CH2CH2CH2Br).
4-Iodo-n-propoxybenzene
A mixture of 4-iodophenol 44.00 g (0.20 mol), K2CO3
(46.00 g, 0.33 mol) and acetone 200 mL were was added in
a 500 mL flask. 40.50 g 1-Bromopropane (0.33 mol) was
added dropwise to the stirred refluxing mixture. The stirred
solution was heated under reflux for 24 h. The potassium
carbonate was filtered off, water was added to the filtrate
and the product was extracted two times with diethyl ether.
The combined ethereal extracts were washed with water,
5% sodium hydroxide, and dried with anhydrous MgS04.
Vacuum distillation yielded 40.90 g of light-yellow oily
1
product (80–82 °C/40 Pa). Yield: 78.0 %. H NMR (400
MHz, CDCl3, ppm):  7.50 (d, 2H, Ar-H, J = 8.4 Hz), 6.68
(d, 2H, Ar-H, J = 8.0 Hz), 3.84 (t, 2H, OCH2), 1.80 (m, 2H,
CH2CH3), 1.02 (t, 3H, CH2CH3).
4-n-Propoxyphenylboronic acid
1.90 g 4-Iodo-n-propoxybenzene (0.0072 mol) and 21 mL
of anhydrous THF were added in a 250 mL two-neck flask
equipped with a dropping funnel, thermometer, and nitrogen
inlet-outlet. The solution was cooled to 78 C with liquid
nitrogen and ethanol. 5.50 mL n-butyllithium (2.2 M in
hexane) was added dropwise over 0.5 h to the stirring mix-
ture, with the temperature maintained below 78 C.
B(OCH3)3 (1.86 mL) in 5.20 mL of anhydrous THF was
added dropwise to the stirring mixture, with the temperature
maintained below 78 C. The reaction mixture was subse-
quently warmed to room temperature and stirred overnight.
The dilute HCl (8.20 mL) was added over a period of
20 min, and the mixture was stirred for 1 h. The solution
was extracted two times with EtOAc and the combined or-
ganic layer was dried over MgSO4 and filtered, and the fil-
trate was concentrated in vacuum. The crude solid was puri-
Scheme
1
Illustration of procedures for synthesis of CH3A6CN,
CH3A6OPr, CH3PA6CN and CH3PA6OPr.
8-Bromo-1-octyne
To a two-necked 250 mL flask equipped with a nitrogen
inlet, a pressure-equalized dropping funnel, and a magnet
stirrer were added 30 mL of DMF and 1, 6-dibromohexane
(65 g, 0.27 mol). The mixture was heated to 40 °C, and a
solution of sodium acetylide (22 g, 18 wt% in xylene,
0.08 mol) was added slowly over a period of 20 min. After
the reaction mixture was refluxed for 24 h. The formed
solid was filtered, and the solvent was evaporated. Vacuum
distillation yielded 9.95 g of colorless oily product (60–62
°C/88 Pa). Yield: 66.0%. IR (KBr cm1):  3301 (≡CH),
2116 (C≡C), 637 (≡CH bending). 1H NMR (400 MHz,

ZHOU Dan, et al. Sci China Chem June (2010) Vol.53 No.6
1305
hexane). Yield: 52.1 % (white powder). IR (KBr, cm1): 
2230 (C≡N), 3351 (OH). H NMR (400 MHz, CDCl3,
ppm):  7.73 (d, 4H, Ar-H, J = 8.0 Hz), 7.65 (d, 4H, Ar-H, J
= 6.4 Hz), 7.53 (d, 2H, Ar-H, J=6.8 Hz), 6.93 (d, 2H, Ar-H,
J = 8.4 Hz ), 4.91 (s, 1H, OH).
fied by recrystallization from water to yield a white powder
0.59 g (yield 50.0 %), which was used in the next step
without further purification and characterization.
1
4-Hydroxy-4′-n-propoxy-p-terphenyl
4-Bromo-4′-hydroxybiphenyl (1.64 g, 6.58 mmol), Pd(PPh3)4
(0.19 g), 1 M Na2CO3 (9 mL) and toluene (12 mL) were
added to a 100 mL three-neck flask under nitrogen atmos-
phere. 4-n-Propoxyphenylboronic acid (2.70 g, 16.45 mmol
dissolved in 18 mL 95% ethanol) was added dropwise over
1 h at 80 C. The reaction mixture was stirred at the same
temperature overnight. The mixture was cooled to room
temperature and diluted with chloroform and water to form
two phases. The organic layer was separated, dried over
MgSO4, and filtered and the solvent was distilled with a
rotary evaporator. The resulting product was purified by
column chromatography (silica gel, dichloromethane/hexane)
to yield 1.03 g (51.3%) of white powder. IR (KBr, cm1): 
1351 (CH3), 3371 (-OH). 1H NMR (400 MHz, CDCl3, ppm):
 7.65 (d, 4H, Ar-H, J = 8.0 Hz), 7.62 (d, 2H, Ar-H, J=6.4
Hz), 7.46 (d, 2H, Ar-H, J = 6.4 Hz), 7.32 (d, 2H, Ar-H, J =
4.4 Hz ), 6.83 (d, 2H, Ar-H, J = 8.4 Hz), 4.91 (s, 1H, OH),
3.96 (t, 2H, OCH2, J = 4.4 Hz ), 1.76 (m, 2H, OCH2CH2, J=
4.4 Hz ), 0.96 (t, 3H, OCH2CH2CH3, J = 6.4 Hz ).
9-[(4′-n-Propoxy-4-terphenyl)oxy]-2-nonyne
A Schlenk flask was charged with 1.52 g 4-hydroxy-4′-n-
propoxy-p-terphenyl (0.0050 mol), 1.52 g 9-bromo-2-nonyne
(0.0075 mol), 1.12 g anhydrous potassium carbonate (0.012
mol), KI (0.083 g, 0.5 mmol) and 75 mL acetone. The mix-
ture was refluxed at 75 C for 24 h under nitrogen atmos-
phere. After the mixture was cooled to room temperature,
the solution was filtered off, and the filtrate was evaporated.
The crude product was purified by column chromatography
(silica gel, dichloromethane/hexane) to yield 1.52 g of pale
yellow solid (yield: 71.2%, mp 182–184 C). IR (KBr,
cm1):  2070 (C≡C). 1H NMR (400 MHz, CDCl3, ppm): 
7.60 (d, 4H, Ar-H, J = 5.2 Hz), 7.56 (d, 4H, Ar-H, J = 8.0
Hz), 6.98 (d, 4H, Ar-H, J = 6.4 Hz), 4.02 (m, 4H, OCH2),
1.85–1.78 (t, 5H, CH2C≡CCH3), 1.51–1.28 (m, 6H,
OCH2CH2, CH2CH2C≡CCH3), 1.08–1.04 (m, 4H, OCH2-
CH2CH2CH2), 0.89 (t,3H, OCH2CH2CH3). 13C NMR (400
MHz, CDCl3, ppm):  158.81 (aromatic carbon linked to
OCH2), 139.21 (terphenyl core carbons), 133.20 (terphenyl
core carbons), 128.25 (aromatic carbon meta to OCH2 and
terphenyl core carbons), 127.97 (aromatic carbon para to
OCH2), 114.92 (aromatic carbon orth to OCH2). MS (CI):
m/e 425.1 [(M+), calcd 426. Anal. calcd for C30H34O2: C,
84.51; H, 7.98. Found: C, 84.62; H, 8.02.
4-Cyanophenylboronic acid
1.82 g 4-Bromobenzene carbonitrile (0.010 mol) and 100 mL
of anhydrous THF were added in a 250 mL two-neck flask
equipped with a dropping funnel, thermometer, and nitrogen
inlet-outlet. The solution was cooled to 78 C with liquid
nitrogen and ethanol. 21.10 mL n-BuLi (2.2 M in hexane)
was added dropwise over 0.5 h to the stirring mixture, with
the temperature maintained below 78 C. B(OCH3)3 (7.44
mL) in 21.00 mL of anhydrous THF was added slowly to
the stirring mixture, with the temperature maintained below
78 C. The reaction mixture was subsequently warmed to
room temperature and stirred overnight. 40.20 mL dilute
HCl was added dropwise, and the mixture was stirred for
1 h. The solution was extracted two times with Et2O,
washed with water, dried over MgSO4 and filtered, and the
solvent was evaporated to yield a white powder. The pow-
der was dissolved in THF, precipitated in hexane, and fil-
tered to yield 1.36 g white powder (yield 75.1%), which
was used in the next step without further purification and
characterization.
9-[(4'-Cyano-4-terphenyl)oxy]-2-nonyne
This compound was prepared using a method similar to that
described for 9-[(4′-n-propoxy-4-terphenyl)oxy]-2-nonyne.
Quantity used: 2.71 g 4-hydroxy-4′-cyano-p-terphenyl
(0.010 mol), 3.04 g 9-bromo-2-nonyne (0.015 mol), 2.04 g
anhydrous potassium carbonate (0.024 mol), KI (0.163 g,
1.0 mmol) and 130 mL acetone. Yellow solid: 2.78 g (yield
70.8%, mp 156–157 C). IR (KBr, cm1):  2229 (C≡C,
1
C≡N). H NMR (400 MHz, THF, ppm):  7.76 (d, 4H,
Ar-H, J = 5.6 Hz), 7.65 (d, 4H, Ar-H, J = 8.4Hz), 7.51 (d,
2H, Ar-H, J = 6.4 Hz), 6.89 (d, 2H, Ar-H, J = 6.4 Hz), 3.91
(t, 2H, OCH2), 1.70–1.60 (t, 5H, CH2C≡CCH3), 1.40 (m,
2H, OCH2CH2), 1.26–1.18 (m, 6H, OCH2CH2CH2CH2,
CH2CH2C≡CCH3). 13C NMR (400 MHz, THF, ppm): 
158.92 (aromatic carbon linked to OCH2), 144.45 (aromatic
carbon para to CN), 137.52 (terphenyl core carbons), 132.06
(aromatic carbons ortho to CN), 127.24–126.42 (aromatic
carbons meta and para to OCH2, aromatic carbons meta to
CN and terphenyl core carbons), 122.10 (C≡N), 119.12
(aromatic carbon ortho to OCH2), 114.25 (aromatic carbon
linked to CN). MS (CI): m/e 391.8 [(M+), calcd 393. Anal.
calcd for C28H27ON: C, 85.50; H, 6.87. Found: C, 85.39; H,
6.79.
4-Hydroxy-4′-cyano-p-terphenyl
This compound was obtained using a method similar to that
described for 4-hydroxy-4′-n-propoxy-p-terphenyl. Quantity
used: 4-bromo-4′-hydroxybiphenyl (1.64 g, 6.58 mmol),
Pd(PPh3)4 (0.19 g), 1 M Na2CO3 (9 mL), toluene (12 mL)
and 4-cyanophenylboronic acid (1.34 g, 0.0085 mol dissolved
in 9 mL 95% ethanol). The resulting product was purified
by column chromatography (silica gel, dichloromethane/

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ZHOU Dan, et al. Sci China Chem June (2010) Vol.53 No.6
2.4 Polymerization and characterization
132.05 (aromatic carbons ortho to CN), 126.90–126.42
(aromatic carbons meta to OCH2, aromatic carbons meta to
CN and terphenyl core carbons), 118.13 (C≡N and
C=CCH3), 115.32 (aromatic carbon ortho to OCH2). Anal.
calcd for (C28H27ON)n: C, 85.50; H, 6.87. Found: C, 85.61;
H, 6.92.
All of the polymerization reactions and manipulations were
carried out under nitrogen using Schlenk techniques in a
vacuum line system or an inert atmosphere glovebox (vac-
uum atmospheres), except for the purification of the poly-
mers, which was carried out in an open atmosphere. A typi-
cal experimental procedure for the polymerization of
CH3A6OPr was as follows.
3 Results and discussion
3.1 Synthesis of the monomers
In the sidearm, 339.0 mg CH3A6OPr (0.8 mmol) was
added in a baked 20 mL Schlenk tube with a stopcock. The
tube was evacuated under vacuum and flushed with dry
nitrogen three times through the sidearm. Freshly distilled
THF (2 mL) was injected into the tube to dissolve the
monomer. The catalyst solution was prepared in another
tube by dissolving 16.0 mg of tungsten (VI) chloride and
17.5 mg of tetraphenyltin in 2 mL of THF. The two tubes
were aged at 60 °C for 15 min and the monomer solution
was transferred to the catalyst solution using a hypodermic
syringe. The reaction mixture was stirred at 60 °C under
nitrogen for 24 h. The solution was then cooled to room
temperature, diluted with 5 mL of chloroform, and added
dropwise to 500 mL of acetone through a cotton filter under
stirring. The precipitate was allowed to stand overnight,
which was then filtered with a Gooch crucible. The polymer
was washed with acetone and dried in a vacuum oven to a
constant weight.
Scheme 1 illustrates the synthetic routes for the monomers
CH3A6CN and CH3A6OPr. CH3A6OPr was synthesized
as follows. First, 4-iodo-n-propoxybenzene was prepared by
the reaction of 4-iodophenol with the corresponding
1-bromopropane using K2CO3 as a catalyst. 4-n-propoxy-
phenylboronic acid was obtained by 4-iodo-n-propoxyben-
zene, n-BuLi (2.2 M in hexane) and B(OCH3)3 in 50.0%
yield. 4-Hydroxy-4′-n-propoxy-p-terphenyl was prepared
between 4-bromo-4′-hydroxybiphenyl and 4-n-propoxy-
phenylboronic acid using tetrakis(triphenylphosphine)pal-
ladium (0) as the catalyst by the Suzuki coupling reaction.
8-Bromo-1-octyne was prepared by the etherification of
1,6-dibromohexane with sodium acetylide in DMF. 9-Bromo-
2-nonyne was also obtained by the etherification reaction.
4-Hydroxy-4′-n-propoxy-p-terphenyl was transformed to
CH3A6OPr 9-[(4′-n-propoxy-4-terphenyl)oxy]-2-nonyne
by the etherification reaction with 9-bromo-2-nonyne in the
presence of a mixture of K2CO3, KI and acetone. CH3A6CN
was prepared using a procedure similar to that described for
CH3A6OPr. The intermediates and the final monomers
were confirmed by FT, IR, and NMR. All the ter-
phenyl-containing hexyloxy spacer monomers showed good
solubility in common solvents such as CHCl3, CH2Cl2, THF,
and DMSO. An IR spectrum of CH3A6OPr and its corre-
sponding polymer is shown in Figure 1 as an example. A
peak at about 2070 cm1 associated with C≡C stretching
vibrations was observed in CH3A6OPr, which disappeared
CH3PA6OPr
1
White powder: yield 82.5%. H NMR (400 MHz, THF,
ppm):  7.50 (d, 4H, Ar-H, J = 5.6 Hz), 7.44 (d, 4H, Ar-H,
J=7.2Hz), 6.86–6.69 (d, 4H, Ar-H, J=6.4 Hz), 3.90 (m, 4H,
OCH2), 1.71–1.62 (t, 5H, CH2C=CCH3), 1.40 (m, 6H,
OCH2CH2, CH2CH2C CCH3), 1.22–1.18 (m, 4H, OCH2-
=
CH2CH2CH2), 0.95 (t, 3H, OCH2CH2CH3). 13C NMR (400
MHz, THF, ppm):  158.51–157.02 (aromatic carbon linked
to OCH2), 138.95 (terphenyl core carbons), 132.56–131.34
(terphenyl core carbons and CH3C=C), 127.05 (aromatic
carbon meta to OCH2 and terphenyl core carbons), 126.07–
125.98 (aromatic carbon para to OCH2 and CH3C=C),
115.06–114.18 (aromatic carbon orth to OCH2). Anal. calcd
for (C30H34O2)n: C, 84.51; H, 7.98. Found: C, 84.47; H,
7.90.
CH3PA6CN
White powder: yield 83.4 %. IR (KBr, cm1):  2230
(C≡N). 1H NMR (400 MHz, DMSO, ppm):  7.82–7.78 (d,
4H, Ar-H, J = 8.0 Hz), 7.67–7.64 (d, 4H, Ar-H, J=6.4 Hz),
7.62 (d, 2H, Ar-H, J = 6.4 Hz), 7.02 (d, 2H, Ar-H, J = 8.4
Hz), 4.01 (t, 2H, OCH2), 1.76–1.72 (t, 5H, CH2C=CCH3),
1.46–1.42 (m, 2H,OCH2CH2), 1.24 (m, 6H, OCH2CH2CH2-
CH2CH2). 13C NMR (600 MHz, THF, ppm):  154.48
(aromatic carbon linked to OCH2), 141.02 (aromatic carbon
para to CN), 135.15 (terphenyl core carbons and CH3C=C),
Figure 1 IR spectra of (a) CH3A6OPr and (b) CH3PA6OPr.

ZHOU Dan, et al. Sci China Chem June (2010) Vol.53 No.6
1307
in the IR profile of CH3PA6OPr. The disappearance of the
acetylene absorption band in the spectrum of CH3PA6OPr
indicates that the triple bonds have been transformed to the
polyene double bonds.
average molecular weight Mw = 8200 and number-average
molecular weight Mn = 7300 for CH3PA6OPr; Mw = 8600
and Mn = 7400 for CH3PA6CN).
3.3 Structural characterization
3.2 Synthesis of the polymers
The intermediates, monomers and the final purified poly-
merization products gave satisfactory spectroscopic data
corresponding to their expected molecular structures (see
Experimental Section for details). CH3A6OPr exhibited a
weak absorption at 2070 cm1 which is assignable to the
C≡C stretching vibrations and completely vanished in the
spectrum of its polymer (Figure 1(b)). The disappearance of
the acetylene absorption band in the spectrum of CH3PA6OPr
implies that the triple bonds have been transformed to the
polyene double bonds after polymerization. Figures 2 and 3
Transition-metal compounds TaCl5 and NbCl5 are the most
widely used catalysts for the polymerization of disubstituted
acetylenes [24]. However, because of the “toxic” interac-
tions of the ester and ether functional groups with the tran-
sition metal mixtures, these transition-metal catalysts are
often found to be ineffective for the polymerization of sub-
stituted acetylene monomers containing polar functional
groups, such as ester and ether units [25–26].
The polar cyano functional group is known to be “toxic”
to the classical metathesis catalysts for acetylene polymeri-
zation [27–30]. Therefore, it is challenging to polymerize
disubstituted acetylenes containing polar functional groups.
However, Tang et al. found that the transition metal ini-
tiator WCl6-Ph4Sn could be an effective catalyst for the po-
lymerization of substituted acetylenes with polar cyano
groups or ester units [13, 14, 31–33]. We thus attempted to
polymerize CH3A6OPr in the presence of WCl6-Ph4Sn at
60 °C for 24 h, using THF as the solvent, which yielded a
polymer with a moderate molecular weight in > 80% yield.
CH3A6CN was also polymerized under similar conditions.
The polyacetylenes CH3PA6OPr and CH3PA6CN polym-
erized by WCl6-Ph4Sn showed narrow polydispersities with
moderate molecular weights (shown in Table 1) (weight-
1
depict the H NMR spectra of CH3A6OPr (in CDCl3-d),
CH3PA6OPr (in THF-d6), CH3A6CN (in THF-d6) and
CH3PA6CN (in DMSO-d6). All the resonance peaks could
be well assigned and no other unexpected signals are ob-
1
served in the H NMR spectra of the polymers and mono-
mers, demonstrating that the molecular structures of the
polymers are indeed CH3PA6OPr and CH3PA6CN (shown
in Chart 1). The structures of the monomers and the corre-
sponding polymers were further characterized by 13C NMR
(Figures 4 and 5). While the acetylenic carbon atoms of
CH3A6OPr resonate at  75.1 and 67.9. These peaks were
totally absent in the spectrum of CH3PA6OPr. Because of
the transformation of the acetylenic triple bonds to the ole-
finic double bonds by the acetylene polymerization, the
resonance peaks of the acetylenic methyl carbons (CH3C≡C)
at  6.79 and the propargyl carbon (≡CCH2) at  19.2 all
vanished (Figure 4). As in CH3PA6CN, after polymeriza-
tion the resonant peaks of acetylene carbon atoms centered
at  75.0 and 65.2 ppm disappeared completely. The peaks
Table 1 Molecular weights of the polymers
Polymers
CH3PA6OPr
CH3PA6CN
Mn
7300
7400
Mw
8200
8600
MWD a)
1.12
DP b)
17.1
18.8
1.16
a) MWD, molecular weight distribution; b) DP, degree of polymerization
calculated by Mn/mru (mru, molecular weight of the molecular repeat unit).
Figure 2 1H NMR spectra of (A) CH3A6OPr (in CDCl3-d), and (B) its polymers CH3PA6OPr (in THF-d6).

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ZHOU Dan, et al. Sci China Chem June (2010) Vol.53 No.6
Figure 3 1H NMR spectra of (A) CH3A6CN (in THF-d6), and (B) its polymers CH3PA6CN (in DMSO-d6).
Figure 4 13C NMR spectra of CH3A6OPr (in CDCl3-d), and its polymers CH3PA6OPr (in THF-d6).
Figure 5 13C NMR spectra of CH3A6CN (in THF-d), and its polymers CH3PA6CN (in THF-d6).

ZHOU Dan, et al. Sci China Chem June (2010) Vol.53 No.6
1309
at  6.54 and 18.5, which are assignable to acetylenic
methyl carbons and the propargyl carbon in CH3A6CN,
vanished in the figure of CH3PA6CN (Figure 5). However,
the absorptions of the olefinic carbons of the polyene back-
bone in CH3PA6OPr and CH3PA6CN cannot be readily
observed owing to their overlapping with those of the ter-
phenyl carbons. The NMR and IR results discussed above
are enough to demonstrate that the acetylene triple bond has
been consumed by the polymerization reaction.
3.4 Thermal stability and liquid crystallinity
As shown in Figure 6, all the polymers possess good ther-
mal stability. CH3PA6CN and CH3PA6OPr showed a 5%
weight loss at 336 and 316 C, respectively. The combina-
tion of terphenyl pendants with the polyacetylene backbone
has apparently enhanced the resistance of the polymer to
thermolysis, which is ascribed to that the terphenyl pendants
may have well wrapped the polyacetylene backbones plus
the additional shielding effect contributed by the methyl
directly linked to the polyene backbone, thus protecting
them from the attack by the degradative species.
Figure 7 shows the POM microphotographs of the me-
somorphic textures of the monomers and their polymers
CH3PA6OPr and CH3PA6CN. All the monomers and
polymers exhibited enantiotropic liquid-crystalline optical
anisotropy. When CH3A6OPr is cooled from the isotropic
state to 210 °C, many anisotropic entities are formed but
their development into the focal conic texture of SmA phase
is very difficult. Upon cooling CH3A6CN to 198 °C, ani-
sotropic entities with birefringent textures were formed, but
the exact nature of the mesophase is also problematic to
identify. With the aid of X-ray diffraction (XRD) measure-
ments, the textures of CH3A6OPr and CH3A6CN are as-
signable to SmA (discussed later). Upon cooling CH3PA6OPr
from the isotropic state, many small bâtonnets started to
emerge from the dark background. The bâtonnets grew to
Figure 7 Mesomorphic textures observed upon cooling (a) CH3A6OPr
to 210 °C, (b) CH3A6CN to 198 °C, (c) CH3PA6OPr to 235 °C, (d)
CH3PA6CN to 238 °C from their isotropic melts.
bigger larger domains when the polymer was fur ther cooled,
resulting in the formation of a typical focal conic fan texture
of SmA phase. The cousin polymer CH3PA6CN with dif-
ferent tails shows focal-conic fan smectic phase (Figure
7(d)). Small optically anisotropic entities emerged from the
dark background of the isotropic liquid when the CH3PA6CN
was cooled to the anisotropic state, suggesting that
CH3PA6CN was better packed than its homologous
monomer CH3A6CN. The polymer chain plays a construc-
tive role in the alignment and packing of the mesogenic
pendants [12, 34].
Differential scanning calorimetry (DSC) measurements
were carried out to evaluate the thermal transition tempera-
tures. Figure 8 shows the DSC thermograms of monomers
and polymers under nitrogen during the first cooling and the
second heating scans at a rate of 10 °C/min. The isotropiza-
tion transition and melting temperature of CH3A6OPr in
the first cooling curve were observed at 227.4 and 185.1 °C,
respectively. The associated k-SmA and SmA-i transitions
were discovered at 196.1 and 231.4 °C, respectively. The
thermogram recorded in the first cooling scan of CH3PA6OPr
displays a sharp exothermic peak associated with the i-SmA
transition at 240.3 °C, and a strong exothermic peak ap-
peared at 225.3 °C associated with the SmA-g transition. In
the second heating profile, two transitions were found at
230.3 and 251.3 °C. CH3PA6CN enters the SmA
mesophase from its isotropic state at 256.7 °C and the
mesophase is stable in a wide temperature range over 86.6
°C. The corresponding g-SmA and SmA-i transitions are
detected at 175.1 and 279.5 °C in the second heating profile.
The DSC thermogram of CH3A6CN exhibits two broad
endothermic peaks at 157.1 and 250.6 °C in the second heat-
ing cycle, and the i-SmA and SmA-k transitions are de-
tected at 229.6 °C and 155.6 °C, respectively. The polymer
Figure 6 TGA thermograms of CH3PA6CN and CH3PA6OPr recorded
under nitrogen at a heating rate of 10 °C/min.

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ZHOU Dan, et al. Sci China Chem June (2010) Vol.53 No.6
Figure 8 DSC thermograms of mesomorphic monomers and polymers recorded under nitrogen during the (a and c) first cooling and (b and d) second
heating scans at a scan rate of 10 °C/min.
with polar cyano tail CH3PA6CN undergoes an enanti-
otropic SmA transition over a wide temperature range
(103 °C), but its counterpart with less polar n-propoxy tails
CH3PA6OPr goes through enantiotropic SmAd transition
in a much narrower temperature range (21 °C), which may
be attributed to the former with polar cyano stabilizing the
ordering of the mesogenic groups.
In order to gain more information on the mesomorphic
structures and molecular packing arrangements in the me-
somorphic phases of the monomers and polymers, the XRD
thermograms of the monomers and polymers are shown in
Figure 9. The monomer CH3A6CN shows an XRD pattern
consisting of two broad low-angle peaks and several high
angle peaks. The broad peak in the low angle indicates that
CH3A6CN was not well packed in the mesophase, which
was in agreement with the broadness of its transition peaks
Figure 9 X-ray diffraction patterns of the mesogenic polyacetylenes and
monomers quenched with liquid nitrogen from their liquid crystalline states.
(Figure 8(d)) and the difficulty in growing the anisotropic
fine textures into large-size textures upon further cooling
(cf., Figure 7(b)). The broad low angel centered at 2 =
reflections at low and high angles. The d spacing derived
from the low-angle (2 = 2.68°) peak is 32.97 Å, which is
close to the calculated mesogenic length for the repeat unit
of CH3A6OPr at its most extended conformation (32.34 Å).
The peak at high angle 2 = 19.90° gives an average dis-
tance (d5) of 4.46 Å (Table 2) associated with the lateral
packing arrangement of the pendants. The CH3A6OPr
3.34° gives a spacing d1 = 26.46 Å, which is shorter than the
fully extended molecular length of the monomer unit (l =
30.39 Å), but close to that of the unit containing the
cyanoterphenyl and (CH2)4O groups. According to
Tang’s study [12], the CH3A6CN forms a monolayer SmA
structure. The diffractogram of CH3A6OPr exhibits strong

ZHOU Dan, et al. Sci China Chem June (2010) Vol.53 No.6
1311
Table 2 X-ray diffraction analysis data of CH3A6CN, CH3PA6CN, CH3A6OPr and CH3PA6OPr a)
Compounds
CH3A6CN
T (°C)
195
d1 (Å)
26.46
18.04
32.97
35.77
d2 (Å)
18.15
8.33
d3 (Å)
4.33
d4 (Å)
d5 (Å)
l (Å) b)
30.39
26.76
32.34
28.71
Ratio (d1/l)
0.87
Phase
SmA
SmA
SmA
SmAd
CH3PA6CN
CH3A6OPr
CH3PA6OPr
236
4.35
0.67
208
26.46
25.11
11.78
13.08
5.92
5.96
4.467
4.48
1.02
234
1.25
a) The mesophases in the liquid crystalline states at given temperatures were frozen by rapid freezing with liquid nitrogen. b) Calculated from molecular
length of monomers in their fully extended conformations.
shows a monolayer structure of the SmA phase. CH3PA6OPr
shows a sharp reflection in the low-angle region (2=2.47°)
corresponding to a layer spacing of 35.77 Å, which is in
considerable excess of the molecular length (28.71 Å). The
mesophase in CH3PA6OPr thus involves a bilayer SmAd
packing arrangement, in which the n-propoxy tails are in-
terdigitated in an antiparallel fashion (shown in Figure 10).
The mesogen pendant of CH3PA6OPr was packed so
regularly that a very steep reflection at 2 = 6.75° (d3 =
13.08 Å) was detected. It may be associated with the order-
ing of the terphenyl cores (d = 11.78 Å), because its ho-
mogenous monomer CH3A6OPr has a similar peak at 2=
7.50° (d3 = 11.78 Å). However, the polymer with cyano tail
CH3PA6CN displays Bragg reflections at low and high
angles. The intense reflection at the low angle 2 = 4.89° is
associated with a layer spacing of d1 = 18.04 Å, which is
shorter than the molecular length (26.76 Å). The mesophase
in CH3PA6CN thus involves a monolayer packing arrange-
ment. The molecular structures for polymers CH3PA6OPr
and CH3PA6CN are almost identical, except for that the
former and latter have n-propoxy and cyano tails, respec-
tively. This seemingly subtle structural difference exhibits
much influence on the layer structures and the arrangements
of mesogenic packing in liquid crystalline polyacetylenes,
with the former ordered in a bilayer structure in an inter-
digitated fashion, namely, interdigitated smectic A phase
(SmAd), while the latter packs in a monolayer structure.
Figure 11 UV spectra of THF solutions of the monomers and the
mesogenic polyacetylenes.
no absorptions were detected in the long wavelength region.
Polymers CH3PA6OPr and CH3PA6CN absorb UV light
strongly at 320 and 322 nm, indicating that the absorptions
are ascribed to the mesogen pendants. However, the polyene
backbone absorptions of the polymers CH3PA6OPr and
CH3PA6CN are not strong. Tang reported that the polyene
backbone absorptions of polymers [CH3C=C(CH2)mOCO-
biphenyl-O(CH2)6CH3]n, m = 4,9 were very weak [32].
This suggests that the UV absorptions of CH3PA6OPr and
CH3PA6CN are consistent with those of Tang’s. The low
absorptivity of the polyacetylenes main chain in the UV
spectra may be due to the steric effect of the bulky methyl
group directly linked to the polyene backbone, which twists
the double bonds and reduces the effective conjugation
length along the main chain. The attachment of mesogenic
and chromophoric pendants to the polyacetylene backbone
may enhance their quantum yields and find unique techno-
logical applications [35]. We thus investigated the fluores-
cence properties of the polymers and monomers in THF
solutions and the polymer films at different temperatures
(Figure 12). When CH3A6OPr and CH3A6CN are photo-
excited at 330 nm, they emit strong UV light at 361and 410
nm. The UV light emitting bands of their corresponding
polymers CH3PA6OPr and CH3PA6CN are shifted to the
longer regions with the higher intensity than those of the
monomers CH3A6OPr and CH3A6CN. It suggests that the
UV light emission originated from the polyene backbone
and the terphenyl mesogen pendants. The fluorescence
3.5 Electronic absorption and photoluminescence
The UV spectra of the monomers and polymers are given in
Figure 11. CH3A6OPr and CH3A6CN exhibit strong K-band
of the terphenyl mesogen pendants at 308 and 319 nm and
Figure 10 Smectic layer structure of CH3PA6OPr.

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ZHOU Dan, et al. Sci China Chem June (2010) Vol.53 No.6
Figure 12 Photoluminescence spectra of (a) the monomers and the mesogenic polyacetylenes in THF solutions (0.05 mM) and (b) the polymers frozen
with liquid nitrogen from their liquid crystalline state and its solid thin films at room temperature.
quantum of the famous highly luminescent disubstituted
polyacetylene poly(1-phenyl-1-octyne) {PPO; [(C6H5)C=
C(C6H13)]n} was 43 % when its polyene backbone was
photoexcited at 355 nm. Compared to the well-known lu-
minescent polymer PPO, both CH3PA6OPr and CH3PA6CN
show higher photoluminescence quantum yields when in-
duced at 330 nm. By using quinine sulfate dihydrate as the
reference, the emission efficiency of CH3PA6CN was cal-
culated to be 74 %, which is much higher than that of
CH3PA6OPr (60 %) by the 330 nm excitation. The fluo-
rescence quantum yield of CH3PA6CN is slightly higher
than that of the polymer [CH3C=C(CH2)4OCO-biphenyl-
O(CH2)6CH3]n (69%) reported by Tang [32]. The quan-
tum yields of CH3PA6CN and CH3PA6OPr are much
higher than those of their associated monosubstituted poly-
acetylenes [HC=C(CH2)6O-terphenyl-R]n, where R=CN
(64%) and R=OCH2CH2CH3 (49%), demonstrating that the
fluorescent quantum efficiencies were enhanced by the at-
tachment of the methyl group to the monosubstituted
polyene backbone. The photoluminescence spectrum of
CH3PA6CN was found to have a red shift of 49 nm with
higher intensity than that of CH3PA6OPr. It may be be-
cause the terphenyl chromophore pendant of CH3PA6CN
was well polarized by the push-pull interaction of the elec-
tron-donating hexamethyleneoxy and the electron-accepting
cyano. Figure 12(b) shows the photoluminescence (PL)
spectra of CH3PA6OPr and CH3PA6CN films frozen
from their liquid crystalline state. The PL spectra of
CH3PA6OPr and CH3PA6CN films at room temperature
are also given in the same figure for comparison. Upon
photoexcitation at 330 nm, the UV light emitting bands of
CH3PA6OPr and CH3PA6CN films frozen from their
liquid crystalline state at 235 C with liquid nitrogen were
stronger and red-shifted compared with their homogenous
films at room temperature. This may be because the poly-
mers CH3PA6OPr and CH3PA6CN form ordered smectic
phase at 235 C, making the backbone more coplanar with a
better conjugation, thus resulting in the observed hyper-
chromic effects. Figure 13 shows the fluorescence photo
graphs of the monomers and polymers excited by irradiation
of UV light of 330 nm, and the pure THF is also given for
the purpose of comparison. All the polymers emitted in-
tensely than their monomers. Compared with CH3PA6OPr,
the emission intensity of CH3PA6CN is much stronger. It
is in accordance with the results of photoluminescence.
3.6 Electrochemical properties
The electrochemical activities of CH3PA6OPr and
CH3PA6CN were analyzed by cyclic voltammetry (CV) in
a standard three-electrode cell with a platinum wire counter
electrode and an Ag/AgCl reference electrode (Figure 14).
The oxidation process corresponds to the removal of
charges from the HOMO energy level whereas the reduction
cycle corresponds to the electron addition to the LUMO
energy level. The oxidation and reduction of CH3PA6OPr
and CH3PA6CN showed irreversible waves in all four
cases. Irreversible oxidation of the polymers (Figure 14(c)
and (d) ) occurred at 1.19 and 1.24 V for CH3PA6CN and
CH3PA6OPr, respectively. The first reduction peaks of
CH3PA6CN and CH3PA6OPr were observed at 0.24 and
0.51 V (vs. Ag/Ag+) (shown in Table 3). The electro-
chemical energy gap (HOMO-LUMO) of the polymers
were calculated from the difference in the onsets of the first
Figure 13 The photographs of blue fluorescence of the polymers and
monomers in the THF solution and pure THF (right), excited by irradiation
of UV light of 330 nm.

ZHOU Dan, et al. Sci China Chem June (2010) Vol.53 No.6
1313
Figure 14 Cyclic voltammograms of polymers (a, c) CH3PA6CN and (b, d) CH3PA6OPr measured at a scan rate of 0.1 V/s, vs. Ag/Ag+ in a (C4H9)4
NBF4 solution.
Table 3 Electrochemical data for polymers a)
Polymers
E1red (V)
0.24 d)
0.51 d)
E2red (V)
1.75 d)
1.36 d)
E1ox (V)
1.19
HOMO (eV) b)
5.50
LUMO (eV) b)
4.23
Eg (eV) c)
1.27
CH3PA6CN
CH3PA6OPr
1.24
5.54
4.14
1.40
a) Experimental conditions are the same as those given in Figure 14. b) HOMO and LUMO values are calculated from the onset of the first peak of the
corresponding redox wave, ELUMO/HOMO = Eonset (red/ox) + 4.4 eV. c) Eg is the LUMO-HOMO energy gap. d) Irreversible peak.
oxidation and reduction peaks. The onset oxidation and re-
duction potentials were determined by the intersection of
the two tangents drawn at the rising current and background
charging current of the CV’s. The onset reduction potential
of the CH3PA6CN was 0.17 V, and the corresponding
onset potential of the oxidation was 1.10 V (vs. Ag/Ag+).
The onset reduction and oxidation of CH3PA6OPr were at
0.26 and 1.14 V. The HOMO and LUMO energy levels
were calculated from the following equation [36–37]:
a narrower electrochemical energy gap. It indicates that the
electrical conductivities of polyacetylenes were enhanced
by introducing the mesogen pendants onto the polyacety-
lenes backbone.
4 Conclusions
In this work, a group of disubstituted acetylene monomers
bearing chromophoric and mesogenic terphenyl pendants
with different tails were designed and synthesized. The
monomers were polymerized by WCl6-Ph4Sn in high yields
( 82%). The structural variations on the properties of the
monomers and polymers were investigated. All the poly-
mers are thermally stable, irrespective of the type of the
tails. The monomers and polymers are all enantiotropic liq-
uid crystalline. The polymers show better developed meso-
morphic textures than their associated monomers. This
ELUMO/HOMO = Eonset (red/ ox) + 4.4 eV
Using the equation, the electrochemical energy gaps (Eg)
of CH3PA6OPr and CH3PA6CN were calculated to be
1.40 and 1.27 eV, respectively. An interesting comparison is
the electrochemical value of the HOMO-LUMO gap with
respect to the optical energy band gap of unsubstituted
polyacetylene 1.50 eV (825 nm). Compared to unsubstituted
polyacetylene, both CH3PA6OPr and CH3PA6CN showed

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ZHOU Dan, et al. Sci China Chem June (2010) Vol.53 No.6
tion: Synthesis of chiral polythiophene derivatives from achiral
monomers in a cholesteric liquid crystal. Macromolecules, 2007, 4(5):
1377–1385
demonstrates that the polyacetylene backbone plays an ac-
tive role in the alignment and packing of the mesogenic
pendants. LC temperature range (∆T) for the polymer with
polar cyano tail CH3PA6CN is approximately five times
wider than that for the polymer with less polar n-propoxy
tail CH3PA6OPr. The terminal groups in the structures of
CH3PA6CN and CH3PA6OPr result in a big change in the
mesogenic packing: The mesostructure of the former in-
volves a monolayer arrangement, while the mesophase of
the latter is associated with a bilayer mesogenic alignment.
The disubstituted polyacetylenes CH3PA6CN and
CH3PA6OPr emitted more strongly than those of their
counterpart monosubstituted polyacetylenes, and their quan-
tum yields were enhanced by attaching the methyl substitu-
tion. Both CH3PA6CN and CH3PA6OPr emit UV light with
high efficiency (≥60%) upon excitation at 330 nm. Polymer
CH3PA6CN is a better fluorophore than CH3PA6OPr be-
cause of the push-pull interaction by the electron-donating
and the electron-accepting groups of the former. The band
gap calculations of the polymers CH3PA6OPr and
CH3PA6CN were lower than that of unsubstituted polya-
cetylene, showing that the conductivities of polyacetylenes
could be increased by the attachment of mesogen pendants
onto the polyacetylenes backbone.
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This work was supported by the National Natural Science Foundation of
China (50773029 & 50902067), the Natural Science Foundation of Jiangxi
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