The first soluble conjugated poly(2,6-anthrylene): Synthesis and properties

Article abstract of DOI:10.1039/b713463k

The first soluble conjugated poly(2,6-anthrylene) with 9,10-diphenyl- anthracene as the repeating unit is reported; photophysical studies reveal that this polymer represents a novel well-conjugated system. The Royal Society of Chemistry.

Full text of DOI:10.1039/b713463k

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The first soluble conjugated poly(2,6-anthrylene): synthesis and
propertiesw
Weibin Cui, Yubo Wu, Hongkun Tian, Yanhou Geng* and Fosong Wang
Received (in Cambridge, UK) 3rd September 2007, Accepted 4th December 2007
First published as an Advance Article on the web 18th December 2007
DOI: 10.1039/b713463k
The first soluble conjugated poly(2,6-anthrylene) with 9,10-
diphenyl-anthracene as the repeating unit is reported; photophy-
sical studies reveal that this polymer represents a novel
well-conjugated system.
jugated oligo(2,6-anthrylene)s through introducing alkynyl
substituents at 9 and 10 positions of anthracene units.16
However, their solubility decreases dramatically with increas-
ing repeating unit up to 5. Consequently, synthesis of soluble
poly(2,6-anthrylene) was not successful. In the current paper,
we report the synthesis and properties of the first solution
processable poly(2,6-anthrylene), i.e. poly[9,10-bis(p-dodecyl-
phenyl)anthracen-2,6-diyl] (PBPA), through introduction of
one pair of p-dodecylphenyl groups at the 9 and 10 positions
of the anthracene units. Photophysical studies of this polymer
and its oligomeric model compounds reveal that extending the
molecular length along the 2 and 6 positions of anthracene
does endow the molecules with better conjugation.
Conjugated polymers are of current interest due to their
intriguing optoelectronic properties and advantageous low-
cost solution processing, and as a result they have been
intensively studied in a variety of optoelectronic applications.1
These applications in turn encourage the incessant exploration
of conjugated polymers with new structures. Anthracene is a
very important aromatic unit during the development of
organic optoelectronics. For instance, organic electrolumines-
cence was first demonstrated from its single crystals.2 Due to
its promising light-emitting properties and charge carrier
transport properties, anthracene has been widely used as a
building block for conjugated small molecules, oligomers and
polymers with promising optoelectronic properties.3–8 Several
groups have reported oligomers and polymers composed of
9,10-linked anthracene derivatives.9–11 Ladder-type conju-
gated polymers containing 9,10-diaryl-anthracene and
naphthylene have also been reported by Zheng and Scherf,
The chemical structure and the synthesis of the polymer
PBPA are depicted in Scheme 1. The repeating unit, dipheny-
lanthracene, is a well-known blue light-emitting unit with high
photoluminescence (PL) quantum yield and high mobility for
both electrons and holes.17 To synthesize the polymer,
p-bromododecylbenzene was first treated with n-BuLi. Then
2,6-dibromoanthraquinone was reacted with the resulting
p-dodecylphenyllithium followed by reduction with KI–NaH2-
PO2 to afford 2,6-dibromo-9,10-bis(p-dodecylphenyl)anthra-
cene (2) in a yield of 40% over two steps. The polymer PBPA
was finally synthesized by means of a typical Yamamoto
coupling reaction in a yield of 60% as a light-yellow fiber
after purification by Soxhlet extraction and repetitive precipi-
tation. The polymer is soluble in chloroform and chloroben-
zene with the solubility 410 mg mLꢀ1. The number-average
molecular weight (Mn) and polydispersity (PDI) are 3.85 ꢁ 104
g molꢀ1 and 2.54, respectively, measured by means of gel-
permeation chromatography (GPC) corresponding to a poly-
styrene standard. This Mn value might be overestimated as
respectively.12 Mullen et al. reported the synthesis and proper-
¨
ties of oligo(9,10-anthrylene)s and poly(p-phenylene-alt-9,10-
anthrylene)s.9,10 In this case, the main chain of the oligomers
and polymers is strongly twisted because of the high steric
hindrance. For example, the dihedral angle between neighbor-
ing repeating units in 9,90-bianthryl is up to 81.51.13 Thereby
the conjugation of these molecules is severely limited. Extend-
ing the molecular length along the 2 and 6 positions of
anthracene should enable elimination of the detrimental effect
of steric hindrance on molecular conjugation. However, to
date only a few poly(2,6-anthrylene)s and oligo(2,6-anthry-
lene)s, which are insoluble in common organic solvents, have
been reported.14,15 Hodge et al. synthesized the first poly(2,6-
anthrylene) via a precursor approach.14 Oligo(2,6-anthrylene)s
up to trimers were demonstrated by Ito et al., and were used in
fabrication of organic thin-film transistors (OTFTs) by va-
cuum deposition technique.15 We recently also reported the
synthesis and properties of the first solution processable con-
State Key Laboratory of Polymer Physics and Chemistry, Changchun
Institute of Applied Chemistry, Chinese Academy of Sciences,
Changchun 130022, Graduate School of Chinese Academy of Sciences,
Beijing 100039, P.R. China. E-mail: yhgeng@ciac.jl.cn;
Fax: +86-431-85685653
w Electronic supplementary information (ESI) available: Complete
synthetic and experimental data. See DOI: 10.1039/b713463k
Scheme 1 Synthesis of the polymer PBPA.
Chem. Commun., 2008, 1017–1019 | 1017
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observed in other conjugated polymers.18 Thermogravimetric
analysis (TGA) measurements reveal that PBPA is highly
stable with a decomposition temperature of 353 1C (5 wt%
weight loss) in a N2 atmosphere. Neither a glass transition nor
crystal melting or a liquid crystalline–isotropic transition was
observed in the temperature range of 25–300 1C by means of
both differential scanning calorimetry (DSC) and polarizing
optical microscopy (POM).
The polymer PBPA exhibits similar optical properties to
ladder-type P3 in ref. 12a. Displayed in Fig. 1 are UV-Vis
absorption and PL spectra of PBPA in chloroform solution
(10ꢀ5 M of repeating unit) and in the film state. In dilute
solution, PBPA exhibits an absorption maximum of 462 nm,
corresponding to the p–p* transition of the conjugated back-
bone. This polymer emits bluish green PL with a maximum of
482 nm and a quantum yield of 0.53 (Measured in chloroform
with quinine as a standard19). Only a 20 nm Stokes shift and
the well-resolved absorption spectrum indicate that the poly-
mer backbone is fairly rigid. From the dilute solution to the
film, both absorption and PL spectra display a small red-shift
of 5 nm. This indicates that there is almost no conformation
change of the polymer backbone from solution to film state.
Meanwhile, no any new peak corresponding to aggregation
was observed, probably ascribed to that the twist phenyl
groups in diphenylanthracene unit can suppress the close
packing of the polymer chain. As known from the reference,
there is an internal rotation of the phenyl ring by B701 from
the plane of anthracene.20
Fig. 2 Structures of the oligomers OA-n.
In a similar trend, the PL maximum of OA-n is red-shifted
from 418 nm for OA-1 to 458 nm for OA-2 and 467 nm
for OA-3.
The electrochemical properties of OA-1, OA-2 and OA-3
were characterized in methylene chloride in a three-electrode
electrochemical cell with Bu4NPF6 (0.1 M) and Ag/AgCl as
the electrolyte and reference electrode, respectively. All oligo-
mers exhibit one or several reversible redox processes at
positive potential, and the number of redox waves is related
to the number of repeating units. As depicted in Fig. 4, the
oligomers OA-1, OA-2 and OA-3 exhibit one redox couple at
(1.23 V, 1.11 V), two redox couples at (1.15 V, 1.03 V) and
(1.40 V, 1.28 V), and three redox couples at (1.09 V, 0.99 V),
(1.26 V, 1.16 V) and (1.47 V, 1.37 V), respectively. With
increasing molecular length, the first oxidation potential de-
creases gradually, indicating an easier oxidation process.
Meanwhile, the potential difference between the first and
second oxidation processes also decreases in the order of
OA-2 (250 mV) and OA-3 (170 mV). All these features are
typical behaviors of conjugated p-systems, such as oligophe-
nylenes,21 oligo(phenylenevinylene)s,22 oligo-thiophenes,23
and oligo(fluorene-co-bithiophene)s.24 In contrast, the first
To fully understand the structure–property correlation of
the current conjugated system, oligo[9,10-di(p-tolyl)anthra-
cen-2,6-diyl]s (OA-n, Fig. 2) with number of repeating units
n = 1–3 have been synthesized (ESIw). As shown in Fig. 3,
with increasing number of repeating units, the absorption
maximum is red-shifted from 397 nm for OA-1 to 419 nm
for OA-2 and then to 439 nm for OA-3. Introduction of one
more unit results in a red shift of 22 and 20 nm for OA-1 to
OA-2 and OA-2 to OA-3, respectively. Moreover, there is still
a 23 nm red-shift from OA-3 to the polymer PBPA. In
contrast, the absorption of oligo(9,10-anthrylene)s from the
dimer to the trimer is only red-shifted around 10 nm.9b This
indicates that extending the molecular length along the 2 and 6
positions does endow the molecules with better conjugation.
Fig. 1 Solution (10ꢀ5 M of the repeating unit in chloroform) and film
UV-Vis absorption (left hand peaks) and PL (right hand peaks)
spectra of PBPA.
Fig. 3 UV-Vis absorption and PL spectra of OA-n in chloroform
with the concentration of 10ꢀ5 M.
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and C.-F. Shu, Chem. Mater., 2004, 16, 930; (c) Y.-H. Kim, H.-C.
Jeong, S.-H. Kim, K. Yang and S.-K. Kwon, Adv. Funct. Mater.,
2005, 15, 1799.
5 (a) M.-X. Yu, J.-P. Duan, C.-H. Lin, C.-H. Cheng and Y.-T. Tao,
Chem. Mater., 2002, 14, 3958; (b) K. Danel, T.-H. Huang, J.-T.
Lin, Y.-T. Tao and C.-H. Chuen, Chem. Mater., 2002, 14, 3860; (c)
T.-H. Huang, J. T. Lin, Y.-T. Tao and C.-H. Chuen, Chem.
Mater., 2003, 15, 4854.
6 S. W. Cha, S.-H. Choi, K. Kim and J.-I. Jin, J. Mater. Chem.,
2003, 13, 1900.
7 (a) S. Ando, J.-I. Nishida, E. Fujiwara, H. Tada, Y. Inoue, S.
Tokito and Y. Yamashita, Chem. Mater., 2005, 17, 1261; (b) H.
Meng, F. Sun, M. B. Goldfinger, G. D. Jaycox, Z. Li, W. J.
Marshall and G. S. Blackman, J. Am. Chem. Soc., 2005, 127, 2406;
(c) J.-H. Park, D. S. Chung, J.-W. Park, T. Ahn, H. Kong, Y. K.
Jung, J. Lee, C. E. Park, S.-K. Kwon and H.-K. Shim, Org. Lett.,
2007, 9, 2573.
8 (a) G. Klarner, M. H. Davey, W.-D. Chen, J. C. Scott and R. D.
¨
Miller, Adv. Mater., 1998, 10, 993; (b) D. Marsitzky, J. C. Scott, J.-
Fig. 4 Cyclic voltammograms of the OA-1, OA-2 and OA-3 at a scan
rate of 50 mV sꢀ1
P. Chen, V. Y. Lee, R. D. Miller, S. Setayesh and K. Mullen, Adv.
¨
.
Mater., 2001, 13, 1096; (c) J. Ohshita, S. Kangai, Y. Tada, H.
Yoshida, K. Sakamaki, A. Kunai and Y. Kunugai, J. Organomet.
Chem., 2007, 692, 1020.
oxidation potential of oligo(9,10-anthrylene)s is almost the
same from 9,90-bianthryl to 20,30-dihexyl-9,10-trisanthrylene.9a
From the onset oxidation potentials, the highest occupied
molecular orbital (HOMO) energy levels of oligomers
OA-1,OA-2 and OA-3 were estimated to be ꢀ5.49, ꢀ5.41
and ꢀ5.37 eV, respectively. A satisfactory cyclic voltammo-
gram of polymer PBPA could not be obtained in methylene
chloride due to its low solubility. However, its HOMO energy
level should be higher than ꢀ5.37 eV.
9 (a) M. Baumgarten, U. Muller, A. Bohnen and K. Mullen, Angew.
¨
¨
Chem., Int. Ed. Engl., 1992, 31, 448; (b) U. Muller, M. Adam and
¨
K. Mullen, Chem. Ber., 1994, 127, 437; (c) S. Heun, H. Bassler, U.
¨
Muller and K. Mullen, J. Phys. Chem., 1994, 98, 7355.
¨
¨
¨
10 (a) C. Yang, J. Jacob and K. Mullen, Macromolecules, 2006, 39,
¨
5696; (b) C. Yang, J. Jacob and K. Mullen, Macromol. Chem.
Phys., 2006, 207, 1107.
¨
11 (a) T. Kaneko, T. Matsubara and T. Aoki, Chem. Mater., 2002, 14,
3898; (b) L. S. Park, Y. S. Han, J. S. Hwang and S. D. Kim, J.
Polym. Sci., Part A: Polym. Chem., 2000, 38, 3173; (c) S. Zheng
and J. Shi, Chem. Mater., 2001, 13, 4405; (d) S. Zheng and J. Shi,
Polym. Mater. Sci. Eng., 2001, 84, 337.
In summary, we have successfully synthesized the first
soluble conjugated poly(2,6-anthrylene) and its oligomeric
model compounds with 9,10-diphenylanthracene as the re-
peating unit. Photophysical studies confirm that they represent
a novel well-conjugated system. Further investigation of their
optoelectronic properties is under the way.
12 (a) S. Zheng and J. Shi, Polym. Prepr., 2002, 43, 599; (b) B. S.
Nehls, S. Fuldner, E. Preis, T. Farrell and U. Scherf, Macromole-
¨
cules, 2005, 38, 687.
13 H.-D. Becker, V. Langer, J. Sieler and H.-C. Becker, J. Org.
Chem., 1992, 57, 1883.
14 P. Hodge, G. A. Power and M. A. Rabjohns, Chem. Commun.,
1997, 73.
15 K. Ito, T. Suzuki, Y. Sakamoto, D. Kubota, Y. Inoue, F. Sato and
S. Tokito, Angew. Chem., Int. Ed., 2003, 42, 1159.
16 W. Cui, X. Zhang, X. Jiang, H. Tian, D. Yan, Y. H. Geng, X. Jing
and F. Wang, Org. Lett., 2006, 8, 785.
This work is supported by NSFC (Nos. 20423003, 20674083
and 20521415), and Science Fund for Creative Research
Groups of NSFC (20621401).
17 (a) R. Bezman and L. R. Faulkner, J. Am. Chem. Soc., 1972, 94,
6317; (b) A. K. Tripathi, M. Heinrich, T. Siegrist and J. Pflaum,
Adv. Mater., 2007, 19, 2097.
18 M. Grell, D. D. C. Bradley, X. Long, T. Chamberlain, M.
Inbasekaran, E. P. Woo and M. Soliman, Acta Polym., 1998, 49,
439.
19 D. F. Eaton, Pure Appl. Chem., 1988, 60, 1107.
20 J. M. Adams and S. Ramdas, Acta Crystallogr., Sect. B: Struct.
Crystallogr. Cryst. Chem., 1979, 35, 679.
Notes and references
1 (a) R. H. Friend, R. W. Gymer, A. B. Holmes, J. H. Burroughes,
R. N. Marks, C. Taliani, D. D. C. Bradley, D. A. Dos Santos, J. L.
´
Bredas, M. Logdlund and W. R. Salaneck, Nature, 1999, 397, 121;
¨
(b) A. Kraft, A. C. Grimsdale and A. B. Holmes, Angew. Chem.,
Int. Ed., 1998, 37, 402; (c) H. Sirringhaus, Adv. Mater., 2005, 17,
2411; (d) S. Gunes, H. Neugebauer and N. S. Sariciftci, Chem.
¨
Rev., 2007, 107, 1324.
2 M. Sano, M. Pope and H. Kallmann, J. Chem. Phys., 1965, 43,
2920.
21 A. Bohnen, W. Heitz, K. Mullen, H.-J. Ra
¨
der and R. Schenk,
¨
Makromol. Chem., 1991, 192, 1679.
3 (a) J. M. Shi and C. W. Tang, Appl. Phys. Lett., 2002, 80, 3201; (b)
Y. Kan, L. Wang, L. Duan, Y. Hu, G. Wu and Y. Qiu, Appl. Phys.
Lett., 2004, 84, 1513.
4 (a) Y.-H. Kim, D.-C. Shin, S.-H. Kim, C.-H. Ko, H.-S. Yu, Y.-S.
Chae and S.-K. Kwon, Adv. Mater., 2001, 13, 1690; (b) W.-J. Shen,
R. Dodda, C.-C. Wu, F.-I. Wu, T.-H. Liu, H.-H. Chen, C. H. Chen
22 R. Schenk, H. Gregorius, K. Meerholz, J. Heinze and K. Mullen,
¨
J. Am. Chem. Soc., 1991, 113, 2634.
23 T. Kirschbaum, R. Azumi, E. Mena-Osteritz and P. Bauerle, New
J. Chem., 1999, 23, 241.
¨
24 X. Zhang, Y. Qu, L. Bu, H. Tian, J. Zhang, L. Wang, Y. H. Geng
and F. Wang, Chem.–Eur. J., 2007, 13, 6238.
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