Synthesis of Polyacetylenes Having Pendant Carbazole Groups and Their Photo- and Electroluminescence Properties

Article abstract of DOI:10.1021/ma035972g

Novel carbazole-containing polymers, i.e., poly(3,6-di-tert-butyl-N-(p- ethynylphenyl)carbazole) [poly(t-Bu₂CzPA)] and poly(N-(p- ethynylbenzoyl)carbazole) [poly(CzCOPA)] were synthesized by the polymerization of the corresponding carbazole-con

Full text of DOI:10.1021/ma035972g

Macromolecules 2004, 37, 2703-2708
2703
Synthesis of Polyacetylenes Having Pendant Carbazole Groups and
Their Photo- and Electroluminescence Properties
F u m io Sa n d a ,*,† Ta k a fu m i Na k a i,† Nor ih isa Koba ya sh i,‡ a n d Tosh io Ma su d a *,†
Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University,
Kyoto 615-8510, J apan and Department of Information and Image Sciences, Chiba University,
Chiba 263-8522, J apan
Received December 22, 2003; Revised Manuscript Received February 6, 2004
ABSTRACT: Novel carbazole-containing polymers, i.e., poly(3,6-di-tert-butyl-N-(p-ethynylphenyl)carba-
zole) [poly(t-Bu2CzPA)] and poly(N-(p-ethynylbenzoyl)carbazole) [poly(CzCOPA)] were synthesized by the
polymerization of the corresponding carbazole-containing acetylene monomers using [(norbornadiene)-
RhCl]2-Et3N, WCl6-n-Bu4Sn, and WCl4 catalysts. The UV-vis absorption band edge wavelengths of
the polymers obtained by the polymerization with W catalysts were longer than those of the Rh-based
polymers. The photoluminescence quantum yield of the W-based poly(t-Bu2CzPA) was 55%, while that of
the Rh-based one was as low as 3.6%. The photocurrent of poly(t-Bu2CzPA) was 40-50 times higher
than the dark current. Poly(t-Bu2CzPA) in conjunction with iridium complexes exhibited electrolumi-
nescence (13-18 cd/m2).
Sch em e 1
In tr od u ction
Carbazole is a well-known hole-transporting and
electroluminescent unit. Polymers containing carbazole
moieties in the main chain or side chain have attracted
much attention because of their unique properties,
which allow various photonic applications such as
photoconductive, electroluminescent, and photorefrac-
tive materials.1 Meanwhile, polyacetylene derivatives
exhibit unique characteristics such as semiconductivity,
high gas permeability, helix inversion, and nonlinear
optical properties.2 It is expected that incorporation of
carbazole moieties into polyacetylene will lead to the
development of novel functional polymers based on
synergistic actions of carbazole and main chain conjuga-
tion.
Tang et al. synthesized several polyacetylenes carry-
ing carbazole chromophores which show photolumines-
cence and photoconductivity.3 Advincula et al. also
synthesized a series of carbazole-substituted poly(phen-
ylacetylene)s and examined the cross-linking reaction
by electrochemical oxidation.4 The redox potential de-
creases with increasing length of the alkyl chain. Tabata
et al. synthesized several poly(N-alkyl-3-ethynylcarba-
zole) derivatives to find that the resulting polymers take
a pseudohexagonal columnar structure in the solid
phase.5 We previously synthesized poly(N-carbazoly-
lacetylene), which shows a third-order susceptibility of
18 × 10-12 esu, two orders larger than that of poly-
(phenylacetylene).6 We also synthesized poly(3-(N-car-
bazolyl)-1-propyne), but the polymer obtained is in-
soluble in any solvents.7 On the other hand, poly(1-(p-
N-carbazolylphenyl)-2-phenylacetylene) is partly soluble
in toluene and chloroform and the polymer film shows
photoconductivity and redox activity.8 More recently, we
synthesized poly(9-(4-ethynylphenyl)carbazole) [poly(p-
CzPA)] with Rh and W catalysts.9 Poly(p-CzPA) ob-
tained by WCl6-n-Bu4Sn-catalyzed polymerization ex-
hibited UV-vis absorption apparently at a longer
wavelength than the MoCl5-n-Bu4Sn-based counterpart
did. Poly(p-CzPA) is expected to show unique properties
based on the conjugated structure of polyacetylene main
chain and carbazolylphenyl side chain. Unfortunately,
however, poly(p-CzPA) is poorly soluble in organic
solvents and the strength of the film is insufficient to
elucidate the photo- and electroluminescence properties.
This article deals with the synthesis of novel solvent-
soluble poly(p-CzPA) derivatives, poly(3,6-di-tert-butyl-
N-(p-ethynylphenyl)carbazole) [poly(t-Bu2CzPA)] and
poly(N-(p-ethynylbenzoyl)carbazole) [poly(CzCOPA)]
(Scheme 1), and characterization of the polymers to
obtain information on their possibility as photo- and
electroluminescence materials.
Exp er im en ta l Section
Mea su r em en ts. 1H (400 MHz) and 13C (100 MHz) NMR
spectra were recorded on a J EOL EX-400 spectrometer using
tetramethylsilane as an internal standard. IR, UV-vis, and
fluorescence spectra were measured on Shimadzu FTIR-8100,
J ASCO V-550, and J ASCO FP750 spectrophotometers, respec-
tively. Melting points (mp) were measured by a Yanaco micro
melting point apparatus. Elemental analysis was carried out
at the Kyoto University Elemental Analysis Center. The
number- and weight-average molecular weights (Mn and Mw)
of polymers were determined by gel permeation chromatog-
* Corresponding authors. Phone: +81-75-383-2589. Fax:
+81-75-383-2590. E-mail: sanda@adv.polym.kyoto-u.ac.jp and
masuda@adv.polym.kyoto-u.ac.jp.
† Kyoto University.
‡ Chiba University.
10.1021/ma035972g CCC: $27.50 © 2004 American Chemical Society
Published on Web 03/26/2004

2704 Sanda et al.
Macromolecules, Vol. 37, No. 8, 2004
raphy (GPC) on a J ASCO GULLIVER system (PU-980, CO-
965, RI-930, and UV-1570) equipped with polystyrene gel
columns (Shodex columns K804, K805, and J 806) using
tetrahydrofuran (THF) as an eluent at a flow rate of 1.0 mL/
min, calibrated by polystyrene standards at 40 °C. Thermal
gravimetric analysis (TGA) was carried out with a Perkin-
Elmer TGA-7.
Sch em e 2
Eva lu a tion of P h otocon d u ctivity. A 2 wt % solution of
poly(t-Bu2CzPA) in THF was cast on an ITO electrode and then
dried for 6 h in vacuo to prepare a thin film with a thickness
of 2 µm. Au was vacuum-evaporated to prepare a counter
electrode for the ITO electrode. The relationships between
current (I) and applied voltage (V) for the ITO/poly(t-Bu2CzPA)
film/Au cells (effective electrode area 0.24 cm2) were measured
at room temperature under reduced pressure of 10-2 Torr in
the dark and under photoillumination (2.5 mW/m2) with a Xe
lamp using a thermoabsorption filter. Mobility was measured
by conventional time-of-flight (TOF) techniques. The cell was
placed in a cryostat, and the pressure was reduced below ca.
10-2 Torr. A N2 gas laser (NDC J S-1000L. 337 nm pulse, pulse
duration of 5 ns, max light intensity of 5 mJ ) was irradiated
on a positively biased ITO electrode. The transient photocur-
rent signal was monitored using a digital storage oscilloscope
(Tektronix TDS3012).
E va lu a t ion of E lect r olu m in escen ce. On
a
glass
substrate with a patterned ITO electrode, a hole buffer layer
of poly(ethylenedioxythiophene)/polystyrenesulfonic acid
(PEDOT/PSS) was formed by spin-coating method, and sub-
sequently a light-emitting layer was formed by spin-coating a
solution of poly(t-Bu2CzPA), 2-(4-tert-butylphenyl)-5-(4-biphen-
ylyl)-1,3,4-oxadiazole (PBD), and an Ir complex (weight ratio
60:32:8) in toluene. The thicknesses of each layer were 80 nm.
Then 20-nm-thick calcium and 150-nm-thick aluminum as a
cathode were deposited by high-vacuum thermal evaporation,
and current density-voltage-luminance characteristics were
measured.
Ma ter ia ls. Unless otherwise stated, reagents were com-
mercially obtained and used without further purification. 3,6-
Di-tert-butyl-N-(p-ethynylphenyl)carbazole was synthesized
according to the literature.10 The solvents for polymerization
were purified before use by the standard methods. Iridium-
(III) tris(2-(4′-tert-butylphenyl)pyridinato),11 [Ir(t-Buppy)3], and
iridium(III) bis(2-(2′-benzothienyl)pyridinato-N,C3′)(acetyl-
acetonate),12 [Ir(btp)2(acac)], were prepared according to the
literature. PBD and PEDOT/PSS (Baytron P CH8000) were
purchased from Dojindo Molecular Technologies, Inc. and H.
C. Starck-V TECH Ltd., respectively.
and concentrated to obtain crude N-(p-trimethylsilylethynyl-
benzoyl)carbazole (10.4 g, 28.3 mmol, 89%). n-Bu4NF (1.0 M
in THF, 21 mL) was added to N-(p-trimethylsilylethynylben-
zoyl)carbazole (8.6 g, 23.4 mmol) in THF (340 mL) at 0 °C,
and the resulting mixture was stirred at that temperature for
5 min. HCl (1 M) was added to the mixture, and the resulting
mixture was extracted with ether. The organic layer was
washed with aq NaCl and water subsequently, dried over
anhydrous Na2SO4, and concentrated by rotary evaporation
to obtain solid. It was purified by silica gel column chroma-
tography eluted with n-hexane/ethyl acetate ) 40/1 (volume
ratio) and recrystallization from ethyl acetate and benzene
subsequently to obtain a white solid. Yield 1.6 g (5.4 mmol,
17%). Mp 178.0-179.8 °C. 1H NMR (δ, DMSO-d6): 4.50 (s, 1H,
-C≡H), 7.38-7.40 (m, 6H, Ar), 7.67-7.74, (m, 4H, Ar), 8.20-
8.21 (m, 2H, Ar). 13C NMR (δ, DMSO-d6): 82.8, 84.0 (C≡CH),
115.5, 120.6, 123.9, 125.7, 125.8, 127.2, 129.2, 132.5, 135.6,
138.6 (Ph), 168.4 (CdO). IR (cm-1, KBr): 3272 (C≡CH), 1674
(CdO), 1605, 1489, 1478, 1453, 1443, 1406, 1362, 1343, 1327,
1304, 1233, 1217, 1183, 1075, 949, 872, 845, 760, 750, 723,
710, 691, 648, 639, 629, 615, 590, 565, 531, and 421. Anal.
Calcd for C21H13NO: C, 85.40; H, 4.44; N, 4.74. Found: C,
85.72; H, 4.50; N, 4.57.
N-(p-Iod oben zoyl)ca r ba zole. A solution of lithium bis-
(trimethylsilyl)amide in THF (29%, 33 mL, 56 mmol) was
added to a solution of carbazole (9.3 g, 56 mmol) in THF (120
mL) at -78 °C. The reaction mixture was warmed to room
temperature and stirred for 2 h. It was again cooled to -78
°C, and a solution of p-iodobenzoyl chloride (15 g, 56 mmol) in
THF (30 mL) was added to the mixture. The resulting mixture
was stirred at that temperature for 1 h, and then it was stirred
at room temperature overnight. The solvent was distilled off
by rotary evaporation, and 1 M HCl was added to the residue.
The mixture was extracted with ethyl acetate, and the organic
layer was washed with water and aq NaCl. It was dried over
anhydrous MgSO4, and the solvent was distilled off by rotary
evaporation. The residual mass was purified by silica gel
column chromatography eluted with n-hexane/ethyl acetate,
P olym er iza tion . All polymerizations were carried out in
a
glass tube equipped with a three-way stopcock under
nitrogen. The polymerization mixture was poured into a large
amount of methanol or ether to precipitate a polymer. It was
separated from the supernatant by filtration and dried under
reduced pressure.
Sp ectr oscop ic Da ta of th e P olym er s. Poly(t-Bu2CzPA):
1H NMR (400 MHz, δ in ppm, C6D6) 0.6-1.6 (18H, br, -CH3),
5.8-8.2 (11H, br, Ar and CHdC<), 4.71 (1H, br s, -CHdC<),
7.02 (2H, br s, Ar), 7.40 (4H, br s, Ar). IR (KBr, cm-1) 2961,
1509, 1364, 810. Poly(CzCOPA): 1H NMR (400 MHz, δ in ppm,
1,4-dioxane) 6.4-8.2 (br). IR (KBr, cm-1) 1676, 1445, 1327,
1302, 754, 723.
followed by recrystallization. Yield 12.8 g (32 mmol, 58%). 13
C
Molecu la r Mech a n ics (MM) Ca lcu la tion . All calcula-
tions were carried out with Wavefunction, Inc., Spartan ‘04
Windows.
NMR (δ, DMSO-d6): 100.7, 115.5, 120.6, 123.8, 125.7, 127.2,
130.8, 134.9, 138.2, 138.6, 168.6 (CdO).
N-(p-Eth yn ylben zoyl)ca r ba zole (CzCOP A). A mixture
of N-(p-iodobenzoyl)carbazole (12.6 g, 31.7 mmol), (trimethyl-
silyl)acetylene (5.3 mL, 37.5 mmol), PdCl2(PPh3)2 (665 mg, 0.95
mmol), PPh3 (993 mg, 3.80 mmol), CuI (1.08 g, 5.70 mmol),
Et3N (150 mL), and pyridine (150 mL) was stirred at room
temperature overnight. Et3N and pyridine were removed from
the reaction mixture by evaporation. Ether and ethyl acetate
were added to the resulting mass, and insoluble solid was
filtered off. The filtrate was washed with 1 M HCl and aq
NaCl. The organic layer was dried with anhydrous Na2SO4
Resu lts a n d Discu ssion
Mon om er Syn th esis. Scheme 2 illustrates the syn-
thetic routes for the novel N-(p-ethynylbenzoyl)carbazole
monomer, CzCOPA. It was synthesized by the reaction
of p-iodobenzoyl chloride with carbazole anion prepared
with lithium bis(trimethylsilyl)amide as a base, followed
by Sonogashira coupling with (trimethylsilyl)acetylene

Macromolecules, Vol. 37, No. 8, 2004
Synthesis of Polyacetylenes 2705
Ta ble 1. P olym er iza tion of t-Bu 2CzP A a n d CzCOP Aa
polymer
c
run
monomer
catalyst-cocatalyst
solvent
time (h) yieldb (%) Mn × 10-3c Mw/Mn
color
yellow
brown
yellow-brown
yellow
red
red
red
orange
1
2
3
4
5
6
7
8
t-Bu2CzPA [(nbd)RhCl]2-Et3N toluene
t-Bu2CzPA WCl6-n-Bu4Sn
3
24
3
99
94
94
212
3
2.3
2.3
1.5
1.7
1.4
1.8
1.6
1.6
toluene
CzCOPA
CzCOPA
CzCOPA
CzCOPA
CzCOPA
CzCOPA
[(nbd)RhCl]2-Et3N toluened
[(nbd)RhCl]2-Et3N THF
WCl6-n-Bu4Sn
WCl6-n-Bu4Sn
WCl6-n-Bu4Sn
WCl4
156
240
23
10
44
5
3
100
13
33
13
10
toluene
anisole
1,4-dioxane
24
24
24
24
benzene/methyl acetate (1/1, v/v)d
a
b
Polymerization conditions; [M]0 ) 0.2 M, [Rh] ) 2.0 mM, [W] ) 10 mM, [cocatalyst]/[catalyst] ) 2.0, at 30 °C. Methanol- or ether-
insoluble part. c THF-soluble part, determined by GPC (THF, PSt). [M]0 ) 0.1 M.
Ta ble 2. Solu bility of P oly(t-Bu 2CzP A) a n d P oly(CzCOP A)a
solvent
ether
d
polymerb
C6H6
toluene
anisole
CHCl3
THF
1,4-dioxane
MeOH
poly(t-Bu2CzPA) (Rh)
poly(t-Bu2CzPA) (W)
poly(CzCOPA) (Rh)
poly(CzCOPA) (W)
+++
+++
+
+++
++
+
+
+++
++
++
+++
-
+++
+++
++
+
-
-
+
-
+++
+++
+++
++
+
+++
+++
+
+
+++
-
+++
a
b
+++: soluble. ++: partly insoluble. +: partly soluble. -: insoluble. Rh and W in parentheses mean the catalyst used in the
polymerization to obtain the polymer.
and desilylation using n-Bu4NF. The reaction of carba-
zole with the acyl chloride in the absence of lithium bis-
(trimethylsilyl)amide resulted in recovery of carbazole,
presumably due to the low nucleophilicity of carbazole.
should be caused by the difference of main chain
structures (cis and trans) and conjugated lengths be-
tween the polymers.
Table 2 summarizes the solubility of the polymers in
several organic solvents. Poly(t-Bu2CzPA) was soluble
in most of the solvents, irrespective of the catalyst used
in the polymerization. The solubility of poly(t-Bu2CzPA)
was apparently good compared to that of the previously
reported corresponding polymer without the tert-butyl
group, i.e., the polymer without tert-butyl groups ob-
tained by the polymerization with W catalyst was
soluble in benzene, toluene, CHCl3, and THF, but the
polymer obtained by polymerization with Rh catalyst
was insoluble in these solvents, probably due to the
difference of the cis-trans configuration of the poly-
acetylene main chains based on the catalysts used.9
Aggregation between the inter- and/or intramolecular
chains or formation of a molecular assemble also may
be the reason for this insolubility. On the other hand,
poly(CzCOPA) was highly soluble in polar solvents such
as anisole, THF, and 1,4-dioxane but was not in non-
polar solvents such as benzene and toluene. The differ-
ence in solubility according to the catalysts used is not
as large in the present polymers.
P olym er Str u ctu r e. The polymer structures were
examined by 1H NMR and IR spectroscopies. It has been
reported that Rh catalysts predominantly afford poly-
acetylenes with cis structure, while W catalysts afford
trans-rich polyacetylenes.2 Unfortunately, however, the
1H NMR signals of poly(t-Bu2CzPA) and poly(CzCOPA)
appeared very broadly, and the signal assignable to the
olefinic proton in the polyacetylene main chain coalesced
with aromatic proton signals, which makes it impossible
to determine the cis/trans ratio of the main chain. The
IR spectra of the polymers obtained by the polymeriza-
tion with Rh and W catalysts exhibited almost the same
1
The structure was confirmed by H and 13C NMR, IR,
and elemental analysis.
P olym er iza tion . Table 1 summarizes the conditions
and results of the polymerization of the carbazole-
containing novel acetylene monomers, catalyzed by
[(nbd)RhCl]2-Et3N, WCl6-n-Bu4Sn, and WCl4 in tolu-
ene, THF, anisole, 1,4-dioxane, cyclohexane, and benzene/
methyl acetate (1/1, v/v) at 30 °C for 3-24 h. In the first
stage of the polymerization of CzCOPA in toluene, the
reaction mixture became heterogeneous due to precipi-
tation of the polymer formed (runs 3 and 5). Otherwise,
the polymerization proceeded homogeneously. The cor-
responding polymers with Mn ranging from 3 000 to
240 000 were obtained in 10% quantitative yield.
[(nbd)RhCl]2-Et3N, developed by Tabata et al.,13 gave
polymers with higher Mn in higher yields than W
catalysts did. In our previous paper,9 the Rh complex
catalyst also afforded the polymer of the phenylacety-
lene monomer carrying carbazole (p-CzPA) in a higher
yield than the W catalyst did. On the contrary, Rh
catalysts cannot polymerize disubstituted acetylenes,
although W catalysts can. The difference of activities
between Rh and W catalysts should be based on the
difference of polymerization mechanisms, i.e., Rh-
catalyzed polymerization of acetylene monomers pro-
ceeds via an insertion mechanism, while a W-catalyzed
one proceeds via a metathesis mechanism. Vohlidal et
al.14 and we15 reported that use of oxygen-atom-contain-
ing solvents, especially 1,4-dioxane, is effective in phen-
ylacetylene polymerization with W catalysts to obtain
high-molecular-weight poly(phenylacetylene). In the
polymerization of CzCOPA, employment of anisole (run
6) and 1,4-dioxane (run 7) was effective to increase the
polymer yield and Mn compared to that of toluene (run
5). Benzene/methyl acetate mixed solvent was also
examined in the polymerization with WCl4, but this
system was not operative to increase the polymer yield
and Mn (run 8). The color of the polymers obtained by
polymerization with the Rh catalyst was yellow-brown,
while that with the W catalysts was red-brown. This
patterns. No absorption peaks of ν
and νC≡C were
≡C-H
observed around 3270 and 2120 cm-1, respectively,
which confirms polymerization of the acetylene group.
Otherwise, the IR spectroscopic patterns of the polymers
were similar to those of the corresponding monomers.
P olym er P r op er ties. Figure 1 depicts the UV-vis
spectra of poly(t-Bu2CzPA) and poly(CzCOPA). Both of
the polymers exhibited absorption peaks at a longer

2706 Sanda et al.
Macromolecules, Vol. 37, No. 8, 2004
F igu r e 2. UV-vis and fluorescence spectra of poly(t-Bu2-
CzPA) obtained by the polymerization with (A) Rh and (B) W
catalysts measured in THF (c ) 5.3 × 10-6 mol/L, excited at
335 nm). The photographs are the appearance of the sample
solutions. Samples: runs 1 and 2 in Table 1.
F igu r e 1. UV-vis spectra of (A) poly(t-Bu2CzPA) and
(B) poly(CzCOPA) obtained by the polymerization with Rh
and W catalysts. The spectra of poly(t-Bu2CzPA) and poly-
(CzCOPA) were measured in THF and 1,4-dioxane, respec-
tively. Samples: runs 1, 2, 3, and 5 in Table 1.
wavelength than did the corresponding monomers,
which is due to conjugation of the polyacetylene main
chain. The polymers obtained by the W-catalyzed po-
lymerization exhibited an UV-vis absorption band edge
at a longer wavelength (640-700 nm) than the Rh-based
ones (510-530 nm), which indicates the former poly-
mers have a main chain conjugation longer than those
of the latter.
Figure 2 shows fluorescence spectra of poly(t-Bu2-
CzPA) obtained by the polymerization using Rh and W
catalysts, along with photographs of the polymer solu-
tion emitting luminescence, whose maximum wave-
length was observed at 410 nm upon excitation at 335
nm. It is noteworthy that the fluorescence quantum
yield of the Rh-based polymer was only 3.6%, while that
of the W-based one was as large as 55%. The monomers
exhibited fluorescence at 370 nm when they were
excited in a manner similar to the polymers. The
polymers showed luminescence at wavelengths as much
as 40 nm longer than the monomers.
Figure 3 shows the excitation spectrum of W-based
poly(t-Bu2CzPA) along with the UV-vis absorption
spectra of poly(t-Bu2CzPA) and the monomer. Both the
absorption and excitation spectra of the polymer were
red-shifted compared to the absorption spectrum of the
monomer. It is likely that the excitation spectrum of
poly(t-Bu2CzPA) is not based on the interaction between
the polyacetylene main chain and carbazole side chain
but on an excimer formed between the carbazole side
chains, because the spectroscopic pattern of the excita-
tion spectrum was similar to that of carbazole. Figure
4 illustrates the molecular modeling of octamers of
t-Bu2CzPA having cis-trans and trans-trans main
F igu r e 3. Absorption and excitation (emission 411 nm)
spectra of W-based poly(t-Bu2CzPA) measured in THF.
chains, which were optimized by molecular mechanics
calculation. In the cis-trans geometry, the length
between the carbazole side chains ranged from 4.5 to
4.7 Å. Meanwhile, in the trans-trans structure, it
ranged from 5.0 to 5.5 Å. Although the main chain
structures of the polymers in the present work are not
clear, one can assume that cis-trans-rich and trans-
trans-rich poly(t-Bu2CzPA) were obtained by the po-
lymerization with Rh and W catalysts, respectively.2 It
is therefore reasonable that W-based poly(t-Bu2CzPA)
exhibited large photoluminescence presumably based on
the excimer of the side chain carbazoles, because the
distance between the carbazole side chains is short
enough, as demonstrated by molecular modeling. The
trans-trans structure is apparently more sterically
unfavorable than the cis-trans one. It therefore seems
that the lower molecular weights of the W-based poly-

Macromolecules, Vol. 37, No. 8, 2004
Synthesis of Polyacetylenes 2707
F igu r e 6. Double-logarithmic plots of the transient photo-
current of poly(t-Bu2CzPA) under an electric field of 2.5 × 106
V/cm at room temperature. Polymer sample: run 1 in Table
1.
F igu r e 4. Geometries of cis-trans and trans-trans octamers
of t-Bu2CzPA optimized by MM. Hydrogen atoms are omitted
for simplification.
F igu r e 5. Relationships between current and voltage applied
to ITO/poly(t-Bu2CzPA)/Au cells (effective electrode area 0.24
cm2, thickness 2 µm) measured at room temperature under
reduced pressure of 10-2 Torr. (b) Without photoirradiation.
(9) Under photoirradiation (2.5 mW/m2) with a Xe lamp using
a thermoabsorption filter. Polymer sample: run 1 in Table 1.
F igu r e 7. Relationships between luminance and voltage
applied to poly(t-Bu2CzPA) (60 wt %), PBD (32 wt %), Ir(btp)3-
(acac), or Ir(t-Buppy)3 (8 wt %). Polymer sample: run 1 in
Table 1.
mers than those of the Rh-based ones are due to the
steric factors.
Bu2CzPA) bulk. Transient time was, therefore, esti-
mated from the intersection of the asymptotes to the
plateau and tail of a log t - log I of the transient signal
as shown in Figure 6. The mobility was calculated to
be ca. 3 × 10-6 cm2/V s. The mobility of PVCz has been
reported to be ca. 10-6 cm2/V s under an electric field of
4 × 105 V/cm.18 Poly(t-Bu2CzPA) showed lower mobility
when the 1 order higher electric field of the present
measurement was taken into account. Bulky t-Bu
groups may work positively for solubility and process-
ability but negatively for carrier transport by hindering
the carrier transport pathways. On the other hand, the
high conductivity in poly(t-Bu2CzPA) in comparison with
PVCz can be explained by the larger number of charge
carriers. It is assumed that the electronic interaction
between the π-conjugation system of the poly(t-Bu2-
CzPA) main chain and that of the side chain carbazole
group through the phenylene unit is effective for carrier
generation but is not extended enough to stimulate
charge carrier transport.
Figure 5 depicts the I-V curve of an ITO/poly(t-Bu2-
CzPA)/Au cell. The current was 40-50 times higher
under photoillumination than without. This proves that
poly(t-Bu2CzPA) exhibits photoconductivity. The dark
conductivity of poly(t-Bu2CzPA) was calculated to be ca.
3 × 10-16 S/cm under an electric field of 104-105 V/cm.
This value is 1 order higher than that of poly(vinylcar-
bazole) (PVCz),16 presumably due to π-conjugation of the
poly(t-Bu2CzPA) main chain. It has been reported that
the photocurrent/dark current ratio of PVCz is less than
100.17 This value depends on several factors, including
light intensity, illumination wavelength, and electric
field. It is impossible to directly compare the photocon-
ductivity of poly(t-Bu2CzPA) with that of PVCz. How-
ever, the results in Figure 5 clearly indicate that the
designed polymer works as an optoelectronic functional
polymer. Figure 6 depicts double-logarithmic plots of the
transient photocurrent of poly(t-Bu2CzPA) under an
electric field of 2.5 × 106 V/cm at room temperature. It
should be noted that the transient signal of poly(t-Bu2-
CzPA) represented dispersive character as seen in the
inset (double linear plots) of Figure 6. This is due to
the presence of multiple trapping levels in the poly(t-
Figure 7 depicts the electroluminescence properties
of poly(t-Bu2CzPA) doped with Ir(btp)3(acac) or Ir(t-
Buppy)3 using PBD as an electron-transporting agent.
The device started emitting luminescence when 20-25
V was applied to the electrode. The luminance maxi-

2708 Sanda et al.
Macromolecules, Vol. 37, No. 8, 2004
sity for their helpful discussion. The authors are grateful
to Mr. Motoaki Kamachi at Showa Denko Co. for the
measurement of the electroluminescence properties of
the polymers.
Refer en ces a n d Notes
(1) For reviews, see: (a) Kippelen, B.; Golemme, A.; Hendrickx,
E.; Wang, J . F.; Marder, S. R.; Peyghambarian, N. Photore-
fractive Polymers and Polymer-Dispersed Liquid Crystals. In
Field Responsive Polymers: Electroresponsive, Photorespon-
sive, and Responsive Polymers in Chemistry and Biology;
Khan, I. M., Harrison, J . S., Eds.; ACS Symposium Series
726; American Chemical Society: Washington, D.C., 1999; p
204. (b) Wang, Y. Z.; Epstein, A. J . Acc. Chem. Res. 1999,
32, 217. (c) Kippelen, B.; Meerholz, K.; Peyghambarian, N.
An Introduction to Photorefractive Polymers. In Nonlinear
Optics of Organic Molecules and Polymers; Nalwa, H. S.,
Miyata, S., Eds.; CRC: Boca Raton, FL, 1997; p 465.
(2) For reviews, see: (a) Nagai, K.; Masuda, T.; Nakagawa, T.;
Freeman, B. D.; Pinnau, I. Prog. Polym. Sci. 2001, 26, 721.
(b) Masuda, T. Acetylenic Polymers. In Polymeric Material
Encyclopedia; Salamone, J . C., Ed.; CRC Press: New York,
1996; Vol. 1, p 32.
(3) (a) Xie, Z. L.; Lam, J . W. Y.; Qiu, C. F.; Wong, M.; Kwok, H.
S.; Tang, B. Z. Polym. Mater. Sci. Eng. 2003, 89, 416. (b) Xie,
Z. L.; Lam, J . W. Y.; Qiu, C. F.; Man, W.; Kwok, H. S.; Tang,
B. Z. Polym. Mater. Sci. Eng. 2003, 88, 410. (c) Xie, Z. L.;
Lam, J . W. Y.; Chen, J .; Dong, Y. P.; Qiu, C. F.; Man, W.;
Kwok, H. S.; Tang, B. Z. ACS Polym. Prepr. 2002, 43 (1), 411.
(d) Lee, P. P. S.; Cheuk, K. K. L.; Dong, Y. P.; Chau, F. S.
W.; Tang, B. Z. Polym. Mater. Sci. Eng. 2001, 84, 637. (e)
Dong, Y. P.; Lam, J . W. Y.; Lee, P. P. S.; Tang, B. Z. Polym.
Mater. Sci. Eng. 2001, 84, 616. (f) Lee, P. P. S.; Dong, Y. P.;
Cheuk, K. K. L.; Chau, F. S. W.; Tang, B. Z. ACS Polym.
Prepr. 2001, 42 (1), 502. (g) Tang, B. Z.; Chen, H. Z.; Xu, R.
S.; Lam, J . W. Y.; Cheuk, K. K. L.; Wong, H. N. C.; Wang, M.
Chem. Mater. 2000, 12, 213. (h) Pui-Sze Lee, P.; Geng, Y.;
Kwok, H. S.; Tang, B. Z. Thin Solid Films 2000, 363, 149.
(4) Onishi, K.; Advincula, R. C.; Abdul Karim, S. M.; Nakai, T.;
Masuda, T. ACS Polym. Prepr. 2002, 43 (1), 171.
F igu r e 8. TGA curves of poly(t-Bu2CzPA) and poly(CzCOPA)
obtained by the polymerization with Rh and W catalysts
measured in nitrogen with a heating rate of 10 °C/min.
mum was 13-18 cd/m2. The electroluminescence ef-
ficiency was low compared to those of PVCz and poly(4-
(9-carbzolylstyrene)).19 The lower electroluminescence
efficiency of the carbazole-containing polyacetylene than
the carbazole-containing vinyl polymers may be due to
quenching of the luminescence of the Ir complexes by
the polyacetylene main chain. The high light-emitting
voltage of the device is possibly due to the lower charge
carrier mobility of poly(t-Bu2CzPA) than that of PVCz.
Figure 8 depicts the TGA traces of the polymers
measured under nitrogen. The weight loss began around
200 °C and continued gradually up to 700 °C. In the
early stage of the TGA measurement, the W-based
polymers lost their weight faster than Rh-based poly-
mers. Considering that the former polymers have a
predominantly trans-trans structure, it seems that the
main chain fission takes place more rapidly due to the
steric repulsion between polymer side chains larger than
the latter ones, as shown in Figure 4.
(5) Fukushima, T.; Sone, T.; Tabata, M.; Sadahiro, Y. IUPAC
World Polymer Congress 2002, Beijing, China, Preprints p
167.
(6) Sata, T.; Nomura, R.; Wada, T.; Sasabe, H.; Masuda, T. J .
Polym. Sci., Part A: Polym. Chem. 1998, 36, 2489.
(7) Nakano, M.; Masuda, T.; Higashimura, T. Polym. Bull. 1995,
34, 191.
Su m m a r y
In this article we demonstrated the synthesis of novel
carbazole-containing polyacetylenes, poly(t-Bu2CzPA)
and poly(CzCOPA). Both the polymers obtained by the
polymerization using W catalysts exhibited UV-vis
absorption band edges at longer wavelengths than the
Rh-based ones. It seems that the W-based polymers
have main chain conjugation longer than the Rh-based
counterparts. Poly(t-Bu2CzPA) showed conductivity 1
order higher than that of PVCz, probably due to the
larger number of charge carriers. The current of poly-
(t-Bu2CzPA) under photoirradiation was 40-50 times
higher than that in the dark. It was confirmed that it
works as an optoelectronic functional polymer. The
electron mobility of poly(t-Bu2CzPA) was lower than
that of PVCz. The hindrance of carrier transport path-
ways by the bulky t-Bu group may be responsible for
this result. Poly(t-Bu2CzPA) doped with Ir(btp)3(acac)
or Ir(t-Buppy)3 emitted luminescence when 20-25 V
was applied.
(8) Tachimori, H.; Masuda, T. J . Polym. Sci., Part A: Polym.
Chem. 1995, 33, 2079.
(9) Sanda, F.; Kawaguchi, T.; Masuda, T.; Kobayashi, N. Mac-
romolecules 2003, 36, 2224.
(10) Zhu, Z.; Moore, J . S. J . Org. Chem. 2000, 65, 116.
(11) Zhu, W.; Liu, C.; Su, L.; Yang, W.; Yuan, M.; Cao, Y. J . Mater.
Chem. 2003, 13, 50.
(12) Lamansky, S.; Djurovich, P.; Murphy, D.; Abdel-Razzaq, F.;
Lee, H. E.; Adachi, C.; Burrows, P. E.; Forrest, S. R.;
Thompson, M. E. J . Am. Chem. Soc. 2001, 123, 4304.
(13) Tabata, M.; Yang, W.; Yokota, K. Polym. J . 1990, 22, 1105.
(14) Sedlacek, J .; Pacovska, M.; Vohlidal, J .; Grubisic-Gallot, Z.;
Zigon, M. Macromol. Chem. Phys. 1995, 196, 1705.
(15) Masuda, T.; Takahashi, T.; Yamamoto, K.; Higashimura, T.
J . Polym. Sci., Polym. Chem. Ed. 1982, 20, 2603.
(16) Okamoto, K.; Kusabayashi, S.; Mikawa, H. Bull. Chem. Soc.
J pn. 1973, 46, 1953.
(17) Okamoto, K.; Kusabayashi, S.; Mikawa, H. Bull. Chem. Soc.
J pn. 1973, 46, 2324.
(18) Yoshida, M.; Ayano, M.; Kobayashi, N. J . Polym. Sci., Part
B: Polym. Phys. 2000, 38, 362.
(19) The devices similarly formulated from PVCz and poly(4-(9-
carbzolylstyrene)) using Ir(t-Buppy)3 as a dopant started
emitting luminescence at 5-6 V, and the luminance maxima
were 4020 and 6290 cd/m2, respectively.
Ack n ow led gm en t. The authors thank Professor
Shinzaburo Ito and Dr. Hideo Ohkita at Kyoto Univer-
MA035972G