Preparation and properties of two new soluble carbazole-containing functional polyacetylenes

Article abstract of DOI:10.1016/j.cclet.2011.05.008

Two new functional polyacetylenes bearing carbazole group as pendant, poly{3-[(4-ethynylstyryl)-N-butyl] carbazole}(P1) and poly{3-[4-(prop-2-ynyloxy) phenyl-N-butyl]carbazole}(P2), were prepared using [Rh(nbd)Cl] ₂-Et₃N as catalyst.

Full text of DOI:10.1016/j.cclet.2011.05.008

Available online at www.sciencedirect.com
Chinese Chemical Letters 22 (2011) 1017–1020
www.elsevier.com/locate/cclet
Preparation and properties of two new soluble
carbazole-containing functional polyacetylenes
*
Wei Ju Zhu, Zhen Yu Wu, Ji Ming Song, Cun Li
School of Chemistry and Chemical Engineering, Anhui University, Hefei 230039, China
Received 16 February 2011
Available online 25 June 2011
Abstract
Two new functional polyacetylenes bearing carbazole group as pendant, poly{3-[(4-ethynylstyryl)-N-butyl] carbazole}(P1) and
poly{3-[4-(prop-2-ynyloxy)phenyl-N-butyl]carbazole}(P2), were prepared using [Rh(nbd)Cl]2-Et3N as catalyst. The polymers
were soluble in common organic solvents such as CHCl3 and THF. Their structures and properties were characterized and evaluated
with FTIR, 1H NMR, UV, TGA, GPC, and CV, respectively. The results show that the polymers possess high thermal stability and
well hole-injection property.
# 2011 Cun Li. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Polyacetylene; CV; Hole-injection; Carbazole; Thermal stability
Polymers containing carbazole moieties in the main or side chains have attracted much attention because of their
unique properties such as photoconductivity, photorefractivity, and electroluminescence, and used as hole-transport
and blue emission materials for photoelectronic devices [1–4]. Much effort has been done to synthesize polymers
carrying carbazole in the main and side chains, poly-(carbazole) consisting of carbazolylene main chains exhibit
different properties each other according to the position of linkage [5–8]. Namely, 3, 6-linked poly(carbazole)
undergoes redox reaction via stable cation radical species [9,10]. Polyacetylenes (PAs) possess alternating double
bonds along the main chain, and many functional PAs with unique optical-electrical properties and high thermal
stability have been reported [11–14]. However, PAs with long p-electron conjugated carbazole pendent were little
investigated [6,15].
In this paper, we report the synthesis and polymerization of two novel acetylene monomers, 3-[(4-ethynylstyryl)-
N-butyl]carbazole (compound 3) and 3-[4-(prop-2-ynyloxy)phenyl-N-butyl] (compound 6), which are substituted
with 4-ethynylstyryl and 4-(prop-2-ynyloxy)phenyl group at 3-position of carbazole, and then their p-bridge is
extended to conjugated styryl units. It is expected that incorporation of carbazole moieties into PA leads to the
development of novel functional polymers on the basis of synergistic effect of carbazole units and PA main chain
conjugation. The thermal stability and electron affinity of two novel soluble carbazole-containing PAs were
investigated in detail.
* Corresponding author.
E-mail address: cunliahu@yahoo.com.cn (C. Li).
1001-8417/$ – see front matter # 2011 Cun Li. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2011.05.008

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W.J. Zhu et al. / Chinese Chemical Letters 22 (2011) 1017–1020
1. Experimental
The synthetic route is described in Scheme 1. The synthesis of compound 2 and 3 are similar to Refs. [14,16]. The
crude product of 3 was purified by column chromatography (Al2O3, ethyl acetate: petroleum ether = 1:20 as eluent)
and pale orange resultant product was obtained in 47.6% yield. FTIR (KBr, cmÀ1) 3315 (s, BB C–H), 2954, 2928, 2862
(m, C–H), 2104 (w, CBBC), 1593, 1504, 1471 (s and vs, Ar), 821 (s, Ar). 1H NMR (400 MHz, CDCl3): d 8.25 (s, 1H, 4-
H), 8.15 (d, 1H, 5-H), 7.69 (d, 1H, 1-H), 7.55–7.48 (m, 5H, 6,7,8,13-H), 7.43 (t, 2H, 12-H), 7.36 (d, 1H, J = 16.00 Hz,
10-H), 7.26 (d, 1H, 2-H), 7.14 (d, 1H, J = 16.40 Hz, 11-H), 4.34 (t, 2H, N–CH2–), 3.15 (s, 1H, BBC–H), 1.95–1.83 (m,
2H, –CH2–), 1.43 (m, 2H, –CH2–), 0.98 (t, 3H, CH3–). Anal. Calcd. for C26H23N: C 89.36, H 6.63, N 4.01. Found: C
89.27, H 6.66, N 3.97.
To obtain intermediate 4, 1.0 g (4 mmol) compound 1 was dissolved in 20 mL CH3OH, then 0.12 g (3 mmol)
NaBH4 was added slowly under stirring and the mixture was refluxed overnight. After the completion of the reaction,
the mixture was washed with distilled water. Ether was added to the mixture, the organic phase was dried over MgSO4.
After the removal of the solvent with a rotary evaporator, the residue was purified by recrystallized from ethanol.
0.88 g of white solid 4 was obtained in 86.6% yield. The synthesis of intermediate 5 and resultant monomer 6 are
similar to our previous work [16]. The crude product of 6 was purified by column chromatography (Al2O3, ethyl
acetate: petroleum ether = 1:10 as eluent) and white crystal resultant product was obtained in 65.4% yield. FTIR (KBr,
cmÀ1) 3288 (s, BBC–H), 2958, 2869 (m, C–H), 2127 (w, CBBC), 1599, 1508, 1471 (s and vs, Ar), 808 (s, Ar). 1H NMR
(400 MHz, CDCl3): d 8.23 (s, 1H, 4-H), 8.15(d, 1H, 5-H), 7.67 (d, 1H, 1-H), 7.54–7.39 (m, 5H, 6,7,8,12-H), 7.27 (d,
1H, 2-H), 7.23 (d, 1H, J = 15.60 Hz, 10-H), 7.13 (d, 1H, J = 16.40 Hz, 11-H), 7.02 (d, 2H, 13-H), 4.75 (s, 2H, –OCH2–
), 4.33 (t, 2H, –NCH2–), 2.57 (s, 1H, BBC–H), 1.89 (m, 2H, –CH2–), 1.42 (m, 2H, –CH2–), 0.98 (t, 3H, CH3–). Anal.
Calcd. for C27H25NO: C 85.45, H 6.64, N 3.69, O 4.22. Found: C 85.43, H 6.68, N 3.65, O 4.24.
The polymerization reaction was performed as following: a baked 20-mL Schlenk tube with a side arm was added
1.0 mmol of the monomer. The tube was evacuated under vacuum and then flushed with dry nitrogen three times
through the side arm. 3 mL of dioxane was injected into the tube to dissolve the monomer. The catalyst solution was
prepared in another tube by dissolving 4.6 mg (0.01 mmol) [Rh(nbd)Cl]2 and 2.02 mg (0.02 mmol) Et3N in 2 mL of
dioxane, which was transferred to the monomer solution using a hypodermic syringe. The reaction mixture was stirred
at 60 8C under nitrogen for 6 h. The mixture was then diluted with 5 mL of dioxane and added dropwise to 200 mL of
methanol under stirring. The precipitate was centrifuged and redissolved in THF. The THF solution was added
dropwise into 200 mL of methanol to precipitate the polymer. The dissolution–precipitation process was repeated
three times, and the finally isolated precipitant was dried under vacuum to a constant weight. P1: Brown red powder,
yield: 65.2%. GPC: Mw = 1.86 Â 104, Mw/Mn = 1.23. FTIR (KBr, cmÀ1) 3023 (w, C–H), 2927, 2872 (m, C–H), 1596,
[(Scheme_1)TD$FIG]
[
]
*
*
C
C
H
n
14
Br
6
13
C
CH
12
11
CHO
a
10
2
5
4
g
b
c
7
N
8
N
1
N
C4H9
C4H9
C4H9
3
P1
1
2
N
C4H9
14
15
13
g
OCH2C CH
12
11
PPh3+I-
CH2OH
e
10
d
4
5
[
*
C
H
C
*
]
6
n
1
f
C4H9
7
CH2O
2
N
N
N
8
N
1
C4H9
C4H9
4
C4H9
P2
6
5
Scheme 1. The synthesis routes of monomer and polymerization: (a) 4-Bromobenzyl(triphenyl)phosphonium bromide, NaOH, CH2Cl2; (b) CuI,
PdCl2(PPh3)2, riethylamine, DMF; (c) toluene, KOH; (d) NaBH4, methanol; (e) KI, HAc, PPh3, CHCl3; (f) 4-(prop-2-ynyloxy)benzaldehyde, NaOH,
CH2Cl2; (g) [Rh(nbd)Cl]2, triethylamine, 1, 4-dioxane.

[(Fig._1)TD$FIG]
W.J. Zhu et al. / Chinese Chemical Letters 22 (2011) 1017–1020
1019
1.2
1.0
P1
P2
0.8
0.6
0.4
0.2
0.0
250
300
350
400
450
500
550
Wavelength(nm)
Fig. 1. UV–vis absorption spectra of P1 and P2 in THF solution.
1471 (s and vs, Ar), 818(s, Ar). 1H NMR(400 MHz, CDCl3): d 0.99 (br., 3H, CH3), 1.44 (br., 2H, CH2CH3), 1.90 (br., 2H,
CH2CH2), 4.37 (br., 2H, NCH2), 6.22, 6.94 (br., Ar–H and trans C–H), 7.36–8.18 (br., Ar–H). P2: Gray solid, yield: 72%.
GPC: Mw = 2.05 Â 104, Mw/Mn = 1.18. FTIR (KBr, cmÀ1): 3022 (w, C–H), 2926, 2869 (m, C–H), 1600, 1507 (s and vs,
Ar), 816(s, Ar). 1H NMR(400 MHz, CDCl3):d 0.97(br., 3H, CH3), 1.42(br., 2H, CH2CH3), 1.87(br., 2H, CH2CH2), 4.31
(br., 2H, NCH2), 5.15 (br., 2H, OCH2), 6.54, 6.75 (br., Ar–H and trans C–H), 7.01–8.21 (br., Ar–H).
2. Results and discussion
The electronic absorption spectra of polymers in THF are shown in Fig. 1. P1 has two absorption peaks at 304 and
346 nm, corresponding the p–p* transitions of the phenyl and carbazole chromophore, respectively. Compared with
P1, P2 exhibits the absorption peak at 300 and 332 nm, which significantly blue-shifts when the pendant of the
carbazole-chromophoric segment varies, hinting that P1 has larger p electron delocalization effect than P2. This fact
means the extension of conjugation length upon transformation from the P2 to P1.
The thermal stability of the resulting polymers was evaluated by thermogravimetric analysis (TGA) under nitrogen
atmosphere. As shown in Fig. 2, the carbazole-containing polyacetylenes exhibit high thermal stability. When 3-
position of carbazole was substituted by different groups, the resulting polymers showed Td (defined as the temperature
of 5% weight loss) at 266 and 242 8C for P1 and P2, which are much higher than that for PPA (225 8C). Thus, the
incorporation of the carbazole groups to polyacetylenes endowed the polymers with better thermal stability. It may be
due to the ‘‘jacket effect’’ of the carbazole pendants. Similar phenomenon is also found by our previous work [11–14].
Cyclic voltammetry (CV) was employed to investigate the redox potentials, and then to estimate the HOMO and
LUMO energy levels of polymers according to the well-known semi-empirical method [17,18]. CV measurements
[(Fig._2)TD$FIG]
110
100
90
P1
P2
80
70
60
50
40
100
200
300
400
500
600
Temperature (0C)
Fig. 2. TGA thermograms of polymers measured under nitrogen.

[(Fig._3)TD$FIG]
1020
W.J. Zhu et al. / Chinese Chemical Letters 22 (2011) 1017–1020
0.008
P1
0.006
P2
0.004
0.002
0.000
-0.002
-0.004
-0.006
-0.008
-0.010
-0.012
0.4
0.6
0.8
1.0
1.2
1.4
1.6
Potential(V)
Fig. 3. Cyclic voltammogram of P1 and P2 in a 0.1 mol/L (n-Bu)4NClO4/acetonitrile solution. Scan rate: 50 mV/s.
were carried out at a scan rate of 50 mV/s on a LK98C electrochemical analyzer with a three electrode system
(platinum was used as working electrode and as counter electrode, and Ag/AgCl reference electrode) (in a 0.1 mol/L
(n-Bu)4NClO4/acetonitrile solution). The HOMO and LUMO energy levels of P1 and P2 obtained by CVanalysis are
shown in Fig. 3. The onset potentials of P1 and P2 appear at À0.71 and À1.07 V, respectively. The onset potentials can
be utilized to estimate the HOMO energy levels. The HOMO energy levels of P1 and P2 are À5.11 and À5.47 eV,
respectively. This attributes to the fact that P1 has larger p-electron conjugation owing to the direct linkage of
carbazole into PA main chain. The HOMO of P1 is higher than P2, meaning that the hole can be better injected into P1.
The high-lying HOMO energy level suggests that the polymers may find potential application for hole injection in
organic light-emitting diode (OLED).
In conclusion, two new functional PAs bearing different carbazole group as pendant were successfully synthesized
and their CV properties and thermal stability were evaluated. The results show that the polymers possess high thermal
stability and well hole injection properties. This work provides a new method for preparing soluble functional PAwith
good hole injection performance and high thermal stability.
Acknowledgments
This research was financially supported by the National Natural Science Fund of China (No. 21071002/B0111) and
the Natural Science Fund of Anhui Province (No. 11040606M33).
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