Synthesis of pyrene-based planar conjugated polymers and the regioisomers by intramolecular cyclization

Article abstract of DOI:10.1002/cjoc.201400793

Several planar conjugated polymers and model compounds containing pyrene units are synthesized. The precursor polymers and model compounds are obtained through the Pd(0)-catalyzed Suzuki reaction, then the planar structure is formed through intramolecular

Full text of DOI:10.1002/cjoc.201400793

FULL PAPER
DOI: 10.1002/cjoc.201400793
Synthesis of Pyrene-based Planar Conjugated Polymers and
the Regioisomers by Intramolecular Cyclization
Xiaoyan Zhu, Yonggang Wu,* Lina Zhou, Yuan Wang, Hongchi Zhao,*
Baoxiang Gao, and Xinwu Ba
College of Chemistry and Environmental Science, Hebei University, Baoding, Hebei 071002, China
Several planar conjugated polymers and model compounds containing pyrene units are synthesized. The pre-
cursor polymers and model compounds are obtained through the Pd(0)-catalyzed Suzuki reaction, then the planar
structure is formed through intramolecular cyclization in the presence of acid. We investigate the regioisomers in
intramolecular cyclization reaction by using model compounds, suggesting that the syn- and anti-structures are
formed in ladder-type polymer LP1, and the syn-structure is more easily formed in LP3. The planar conjugated
polymers and model compounds show untypical features of ladder-type polymers, they display broad absorption
and blue or blue-green emission in solution, and interchain π-π stacking in film still occurs. Moreover, the new
polymers and model compounds are characterized by nuclear magnetic resonance (NMR) spectroscopy,
gel-permeation chromatography (GPC) and cyclic voltammetry (CV).
Keywords planar conjugated polymer, pyrene units, ladder-type polymer, regioisomers, defects
Introduction
develop new extended π-systems for organic optoelec-
tronics.[40-43] Its derivatives that are substituted at the 2-
and 7-positions are of particular interest because the few
examples known exhibit useful properties.[44,45] Ex-
tending the π-conjugated plane of pyrene by fusing at
the non-K-region is still an challenge for developing
new types of functional materials.[46] To achieve the
π-conjugated plane of pyrene, the ladder structure was
introduced in this issue. We direct our attention toward
ladderized polymers incorporating 2,7-pyrene units as
higher benzenoid building blocks, which will generate
unique electronic and optical properties. Ladder-type
polymers LP1, LP2 and LP3 are synthesized, and
contrary to the classical synthetic strategies of ladder-
type polymer, only one high yield cyclization step is
required to afford ladder structure. In the simple route
less structure defect remains.[47,48] In the previous report
of ladder few insight of the regioisomers in intramolecu-
lar cyclization reaction is brought. In the cyclization for
affording ladder-type polymers LP1, LP2 and LP3, the
expected syn- or anti-ring-closed isomer units will be
formed. Poriel and Müllen et al. had reported the
regioisomers in intramolecular cyclization reaction in
the presence of a Lewis acid.[49,50] Well characterized
smaller molecular units, however, are more suitable
than polymers for detailed structure-property relation-
ships studies, so a series of small molecular units were
synthesized and characterized for the polymer structure
studies in this paper.
Conjugated polymers are still widely studied in
fields of organic light emitting diodes, solar cell, and
sensor.[1-21] The special electronic and optical properties
are strictly determined by the structure of polymers.
More detail research and advances have increased the
demanding for polymers of well controlled structure.
Phenylene-based polymers are one of the most impor-
tant classes of conjugated materials for electronic
applications. An important member of the phenylene-
based conjugated polymer family, the all-carbon conju-
gated ladder-type polymer or graphite ribbon is reported
by Scherf, Müllen, and Swager et al.[22-25] The aromatic
ladder-type polymers possess a unique set of character-
istic properties due to their planar structure. The unique
rigid and planar structure not only enhances the conju-
gation, carrier mobility, and luminescence intensity,[26-31]
but also leads to the aggregation, bad solubility and
complicated synthesis.[32-35] In the past decade, number-
ous novel ladder-type polymers such as ladder-type
polymer with soluble side chain,[36,37] hyperbranched
ladder-type polymer[38] and the defectless ladder-type
polymer[39] have been synthesized to eliminate the
defects. All the efforts would endow the ladder-type
polymers better electronic and optical properties, even
promising for the future application.
Pyrene, which has been widely investigated for its
unique properties, is a promising building block to
*
E-mail: wuyonggang@hbu.edu.cn, zhc@hbu.edu.cn
Received November 24, 2014; accepted January 12, 2015; published online February 3, 2015.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc.201400793 or from the author.
Chin. J. Chem. 2015, 33, 431—440
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Zhu et al.
FULL PAPER
Experimental
ter removal of most of the solvent, the residue was pre-
cipitated in methanol and dried under vacuum to give
polymer P1 as white solid (70 mg, 96%). 1H NMR (600
MHz, CDCl3) δ: 8.77 (broad, 0.5H), 8.34－8.19 (broad,
3H), 7.81 (broad, 0.5H), 7.71－7.41 (broad, 4H), 7.34－
7.24 (broad, 2H), 7.11－7.04 (broad, 4H), 6.88－6.72
(broad, 4H), 5.91－5.64 (broad, 4H), 4.08 (broad, 1H),
3.71－3.35 (broad, 4H), 3.30－3.27 (broad, 3H), 2.71
(broad, 6H), 1.76 (broad, 8H), 1.41 (broad, 40H), 0.99
(broad, 12H). Anal. calcd for C82H96O6: C 83.63, H 8.22;
found C 82.98, H 8.01.
Materials and instruments
Reagents purchased from commercial suppliers were
tested for purity before use. Pyrene was purified before
use by crystallization from dichloromethane (DCM)/
methanol. Other commercial chemicals were used with-
out further purification. Tetrahydrofuran (THF), DCM
and toluene were dried and distilled by a standard pro-
cess before use. Pd(PPh3)4 was synthesized according to
published literature.[51] Pyrene-2,7-bis-(4,4,5,5-tetrameth-
yl-[1,3,2]dioxaborolane) (M1),[52] M2,[48] 2,5-dibromo-
1,4-di((4-octyloxy)phenylethynyl)benzene (M3),[24] 2,5-
dibromo-1,4-bis((4-hexadecyloxy)phenylethynyl)ben-
zene (M4),[24] 2-bromo-1-((4-octyloxy)phenylethynyl)-
benzene (5a),[53] 2-bromo-1-((4-hexadeyloxy)phenyleth-
ynyl)benzene (5b)[53] and 2-bromo-1-((3,5-di-tert-butyl)-
phenylethynyl)benzene (8)[53] were synthesized according
to published literature. The reactions were monitored by
thin layer chromatography (TLC) with silica gel 60
F254 (Merck, 0.2 mm). Column chromatography was
Synthesis and characterization of ladder-type
polymer LP1
P1 (35 mg) was dissolved in dry CH2Cl2 (30 mL),
and treated with BF3•OEt2 (2 mL, 30%). After stirring
for 1 h at room temperature, 10 mL of ethanol was
added to the mixture to destroy the catalyst. Water and
CH2Cl2 (200 mL) were added, the organic layer was
separated, washed with water three times, dried over
Na2SO4, and evaporated to dryness. The crude polymer
was precipitated from THF solution in methanol to give
ladder-type polymer LP1 as yellow solid (34 mg, 98%).
1H NMR (600 MHz, CDCl3) δ: 8.57－7.89 (broad, 3H),
7.65－7.35 (broad, 4H), 7.31－6.90 (broad, 5H), 7.81－
6.43 (broad, 8H), 4.09 (broad, 4H), 1.86 (broad, 4H),
1.57 (broad, 10H), 1.34 (m, 32H), 0.91 (broad, 12H),
0.57 (broad, 6H). Anal. calcd for C80H88O4: C 86.29, H
7.97; found C 85.98, H 7.51.
carried out on silica gel (200－300 mesh). H and 13C
1
NMR spectra were recorded on a Bruker AV600 spec-
trometer. The electrochemical behavior of compounds
was investigated by cyclic voltammetry (Holland, Ivium
Plus II) with a standard three-electrode electrochemical
cell in a 0.1 mol/L tetrabutyl ammonium tetrafluoro-
borate solution in CH2Cl2 at room temperature at
atmosphere with a scanning rate of 50 mV•s−1. A glassy
carbon working electrode, a Pt wire counter electrode,
and an Ag/AgNO3 (0.01 mol/L in CH3CN) reference
electrode were used. The experiments were calibrated
with the standard ferrocene/ferrocenium (Fc) redox
system and on the assumption that the energy level of
Fc is 4.8 eV below vacuum. The GPC measurements
were performed on Waters 515 system against poly-
styrene standards in THF. UV-visible absorption spectra
were obtained on a Shimadzu UV-visible spectrometer
model UV-2550. Fluorescence spectra were recorded on
a Shimadzu RF-5301PC fluorescence spectrophotometer.
Elemental analyses were performed on a Flash EA 1112
analyzer. MALDI-TOF analyses were obtained by using
Bruker Daltonics Inc Autoflex III. Thermal gravimetric
analysis (TGA) and differential scanning calorimetry
(DSC) measurements were performed on Perkin-Elmer
Pyris 6 TGA and Perkin-Elmer Diamond DSC instru-
ments, respectively, under a nitrogen atmosphere at a
heating rate of 10 ℃/min to record TGA and DSC
curves.
Synthesis and characterization of polymer P3
A mixture of M1 (33 mg, 0.072 mmol), M4 (66 mg,
0.072 mmol), NaHCO3 (0.26 g), THF (12 mL), toluene
(12 mL) and H2O (3 mL) was degassed, and Pd(PPh3)4
(5 mg, 0.0043 mmol) was added under a nitrogen
atmosphere. The mixture was heated at reflux and
stirred under nitrogen for 5 d. Water and CH2Cl2 (200
mL) were added, the organic layer was separated and
dried over Na2SO4. After removal of most of the solvent,
the residue was precipitated in methanol and dried under
vacuum to give polymer P3 as yellow solid (58 mg,
85%). 1H NMR (600 MHz, CDCl3) δ: 8.72－8.43
(broad, 2H), 8.18－7.71 (broad, 4H), 7.58－7.40 (broad,
4H), 7.28－7.03 (broad, 4H), 6.91－6.72 (broad, 4H),
3.97－3.87 (broad, 4H), 1.80－1.27 (broad, 56H), 0.87
(broad, 6H). Anal. calcd for C70H84: C 90.85, H 9.15;
found C 88.98, H 8.51.
Synthesis and characterization of ladder-type
polymer LP3
Synthesis and characterization of polymer P1
P3 (40 mg) was dissolved in dry CH2Cl2 (30 mL),
and treated with F3CCOOH (2 mL). After stirring for 3
h at room temperature, water and CH2Cl2 were added,
the organic layer was separated, washed with water
three times, dried over Na2SO4, and evaporated to
dryness. The crude polymer was precipitated from THF
solution in methanol to give ladder-type polymer LP3
as dark solid (38 mg, 95%). 1H NMR (600 MHz, CDCl3)
A mixture of M1 (30 mg, 0.062 mmol), M2 (70 mg,
0.062 mmol), NaHCO3 (0.26 g), THF (25 mL) and H2O
(3 mL) was degassed, and Pd(PPh3)4 (6 mg, 0.0052
mmol) was added under a nitrogen atmosphere. The
mixture was heated at reflux and stirred under nitrogen
for 4 d. Water and CH2Cl2 (200 mL) were added, the
organic layer was separated and dried over Na2SO4. Af-
432
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Chin. J. Chem. 2015, 33, 431—440

Synthesis of Pyrene-based Planar Conjugated Polymers and the Regioisomers
δ: 9.07－8.10 (broad, 6H), 7.80－7.30 (broad, 6H),
7.28－6.92 (broad, 4H), 4.10 (broad, 4H), 2.00－1.29
(broad, 56H), 0.87 (broad, 6H). Anal. calcd for C70H84:
C 90.85, H 9.15; found C 88.08, H 8.31.
[M＋]: 738.9, found 738.3.
1
Model compound 4: H NMR (600 MHz, CDCl3) δ:
8.53 (s, 2H), 8.04 (d, J＝9.6 Hz, 2H), 8.02 (d, J＝7.2
Hz, 2H), 7.97 (d, J＝9.6 Hz, 2H), 7.52 (d, J＝7.2 Hz,
2H), 7.42 (t, J＝7.2 Hz, 2H), 7.31－7.28 (m, 10H), 7.02
(d, J＝8.4 Hz, 8H), 2.28 (s, 12H); 13C NMR (150 MHz,
CDCl3) δ: 155.57, 145.23, 140.37, 139.96, 138.53,
136.09, 131.98, 129.00, 128.80, 128.38, 127.86, 127.40,
126.98, 125.82, 125.42, 124.67, 120.07, 116.97, 65.68,
20.90. MALDI-TOF calcd for C58H42 [M＋ ]: 738.9,
found 738.3.
Synthesis and characterization of 2,7-di(methylben-
zoate-2-yl)pyrene (2)
A mixture of M1 (0.52 g, 1.14 mmol), methyl
2-bromobenzoate (1) (0.62 g, 2.86 mmol), NaHCO3
(0.35 g), THF (40 mL) and H2O (7 mL) was degassed,
and Pd(PPh3)4 (30 mg, 0.026 mmol) was added under a
nitrogen atmosphere. The mixture was heated at reflux
and stirred under nitrogen for 24 h. Water and CH2Cl2
(200 mL) were added, the organic layer was separated
and dried over Na2SO4. After removal of the solvent,
the residue was chromatographically purified on silica
gel eluting with CH2Cl2/petroleum ether (1∶1, V∶V)
to afford 2 as a white solid (0.50 g, 94%). 1H NMR (600
MHz, CDCl3) δ: 8.18 (s, 4H), 8.13 (s, 4H), 7.98 (d, J＝
7.2 Hz, 2H), 7.08－7.64 (m, 4H), 7.54 (t, J＝7.2 Hz,
2H), 3.54 (s, 6H); 13C NMR (150 MHz, CDCl3) δ:
169.34, 142.66, 139.18, 131.58, 131.44, 131.36, 131.01,
129.99, 127.84, 127.41, 125.03, 123.72, 52.01. Anal.
calcd for C32H22O4: C 81.69, H 4.71; found C 81.58, H
4.70.
Synthesis and characterization of 2,7-di((4-octyloxy)-
phenylethynylphenyl)pyrene (6a) and 2,7-di((4-hexa-
deyloxy)phenylethynylphenyl)pyrene (6b)
A mixture of M1 (58 mg, 0.13 mmol), 2-bromo-1-
((4-octyloxy)phenylethynyl) benzene (5a) (0.10 g, 0.26
mmol), NaHCO3 (0.25 g), THF (25 mL) and H2O (4 mL)
was degassed, and Pd(PPh3)4 (14 mg, 0.013 mmol) was
added under a nitrogen atmosphere. The mixture was
heated at reflux and stirred under nitrogen for 24 h.
Water and CH2Cl2 (200 mL) were added, the organic
layer was separated and dried over Na2SO4. After
removal of the solvent, the residue was chromatographi-
cally purified on silica gel eluting with CH2Cl2/petro-
leum ether (1∶8, V∶V) to afford 6a as a yellow solid
Synthesis and characterization of model compounds
3 and 4
1
(45 mg, 45%). H NMR (600 MHz, CDCl3) δ: 8.57 (s,
2H), 8.19 (s, 2H), 7.77 (d, J＝7.8 Hz, 2H), 7.73 (d, J＝
7.8 Hz, 2H), 7.52 (t, J＝7.8 Hz, 2H), 7.45 (t, J＝7.8 Hz,
2H), 7.16 (d, J＝9.0 Hz, 4H), 6.71 (d, J＝9.0 Hz, 4H),
3.86 (t, J＝6.6 Hz, 4H), 1.72 (m, 4H), 1.40 (m, 4H),
1.32－1.25 (m, 16H), 0.89 (t, J＝6.6 Hz, 6H); 13C NMR
(150 MHz, CDCl3) δ: 159.15, 143.72, 138.44, 132.77,
130.98, 130.29, 128.29, 127.79, 127.26, 126.18, 123.95,
122.62, 115.12, 114.46, 92.69, 88.22, 68.01, 31.78,
29.31, 29.20, 29.14, 25.96, 22.63, 14.07. Anal. calcd for
C60H58O2: C 88.85, H 7.21; found C 88.83, H 7.18.
2-Bromo-1-((4-hexadeyloxy)phenylethynyl)benzene
(5b) (0.40 g, 0.81mmol) was used, 6b (0.15 g, 42%)
To a solution of 4-bromotoluene (3.20 g, 20 mmol)
in THF (30 mL) was added n-BuLi (13 mL, 20 mmol) at
−78 ℃ under nitrogen. The reaction was kept at −78
℃ for 1 h, a solution of 2 (0.44 g, 0.96 mmol) in THF
(10 mL) was added dropwise into the mixture at −78 ℃.
The reaction mixture was allowed to warm gradually to
room temperature, water and CH2Cl2 (200 mL) were
added, the organic layer was separated and dried over
Na2SO4. After removal of most of the solvent, the
residue was chromatographically purified on silica gel
eluting with CH2Cl2/petroleum ether (2∶1, V∶V) to
afford reduced product as a white solid (0.23 g, 31%).
The reduced product (0.23 g, 0.28 mmol) was dissolved
in dry CH2Cl2 (30 mL), and treated with BF3•OEt2 (2
mL, 30%). After stirring for 1 h at room temperature, 10
mL of ethanol was added to the mixture to destroy the
catalyst. Water and CH2Cl2 (200 mL) were added, the
organic layer was separated, washed with water three
times, dried over Na2SO4, and evaporated to dryness.
The residue was chromatographically purified on silica
gel eluting with CH2Cl2/petroleum ether (1∶8, V∶V)
to afford 3 (0.11 g, 52%) and 4 (0.037 g, 17%) as
yellow solid.
1
was obtained. H NMR (600 MHz, CDCl3) δ: 8.57 (s,
2H), 8.19 (s, 2H), 7.77 (d, J＝7.8 Hz, 2H), 7.73 (d, J＝
7.8 Hz, 2H), 7.52 (t, J＝7.8 Hz, 2H), 7.45 (t, J＝7.8 Hz,
2H), 7.16 (d, J＝9.0 Hz, 4H), 6.71 (d, J＝9.0 Hz, 4H),
3.86 (t, J＝6.6 Hz, 4H), 1.73 (m, 4H), 1.39 (m, 4H),
1.32－1.27 (m, 48H), 0.91 (t, J＝6.6 Hz, 6H); 13C NMR
(150 MHz, CDCl3) δ: 159.15, 143.71, 138.44, 132.77,
130.98, 130.29, 128.29, 127.80, 127.26, 126.19, 123.95,
122.62, 115.11, 114.45, 92.69, 88.22, 68.01, 31.94,
29.69, 29.57, 29.37, 29.15, 25.98, 22.70, 14.13. Anal.
calcd for C76H90O2: C 88.15, H 8.76; found C 88.13, H
8.74.
1
Model compound 3: H NMR (600 MHz, CDCl3) δ:
Synthesis and characterization of model compounds
7a and 7b
8.61 (s, 2H), 8.19 (s, 2H) , 8.04 (d, J＝7.2 Hz, 2H), 7.84
(s, 2H), 7.47 (d, J＝7.8 Hz, 2H), 7.43 (t, J＝7.8 Hz, 2H),
7.30 (t, J＝7.2 Hz, 2H), 7.22 (d, J＝8.4 Hz, 8H), 6.98 (d,
J＝8.4 Hz, 8H), 2.26 (s, 12H); 13C NMR (150 MHz,
CDCl3) δ: 131.24, 129.68, 129.02, 128.84, 128.35,
127.75, 127.39, 125.62, 125.36, 124.82, 120.09, 116.98,
65.52, 29.72, 20.92. MALDI-TOF calcd for C58H42
6a (45 mg, 0.055 mmol) was dissolved in dry
CH2Cl2 (30 mL), and treated with F3CCOOH (2 mL).
After stirring for 3 h at room temperature, water and
CH2Cl2 (200 mL) were added, the organic layer was
separated, washed with water three times, dried over
Chin. J. Chem. 2015, 33, 431—440
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Zhu et al.
FULL PAPER
Na2SO4, and evaporated to dryness. The residue was
chromatographically purified on silica gel eluting with
CH2Cl2/petroleum ether (1∶4, V∶V) to afford 7a as
yellow solid (44 mg, 98%). 1H NMR (600 MHz, CDCl3)
δ: 9.21 (s, 2H), 8.93 (d, J＝8.4 Hz, 2H), 7.99 (s, 2H),
7.97 (d, J＝7.2 Hz, 2H), 7.80 (s, 2H), 7.75 (t, J＝7.2 Hz,
2H), 7.73 (s, 2H), 7.69 (t, J＝7.2 Hz, 2H), 7.29 (d, J＝
8.4 Hz, 4H), 6.93 (d, J＝8.4 Hz, 4H), 4.08 (t, J＝6.6 Hz,
4H), 1.91 (m, 4H), 1.57 (m, 4H), 1.46－1.37 (m, 16H),
0.98 (t, J＝6.6 Hz, 6H); 13C NMR (150 MHz, CDCl3) δ:
158.43, 138.20, 137.42, 131.55, 130.50, 130.25, 129.94,
129.57, 128.58, 128.35, 127.60, 126.94, 126.52, 125.66,
125.49, 124.57, 123.22, 119.74, 114.82, 68.21, 31.96,
29.63, 29.57, 29.42, 26.25, 22.76, 14.19. MALDI-TOF
calcd for C60H58O2 [M＋]: 811.1, found 810.4.
(200 mL) were added, the organic layer was separated,
washed with water three times, dried over Na2SO4, and
evaporated to dryness. The residue was chromatographi-
cally purified on silica gel eluting with CH2Cl2/petro-
leum ether (1∶4, V∶V) to afford 10 (26 mg, 41%) and
11 (33 mg, 52%) as yellow solid.
Model compound 10: 1H NMR (600 MHz, CDCl3) δ:
9.47 (s, 2H), 9.10 (d, J＝8.4 Hz, 2H), 8.22 (s, 2H), 8.06
(d, J＝7.8 Hz, 2H), 7.95 (s, 2H), 7.82 (t, J＝7.2 Hz, 2H),
7.75 (t, J＝7.2 Hz, 2H), 7.58 (s, 2H), 7.46 (s, 2H), 7.28
(s, 4H), 1.30 (s, 36H); 13C NMR (150 MHz, CDCl3) δ:
151.39, 144.66, 139.75, 131.28, 130.57, 130.08, 129.55,
128.88, 128.34, 127.05, 126.66, 125.81, 125.76, 124.93,
123.36, 120.34, 119.89, 34.91, 31.51. MALDI-TOF
calcd for C60H58 [M＋]: 779.1, found 778.3.
6b (0.13 g, 0.12 mmol) was used, 7b (0.12 g, 96%)
Model compound 11: 1H NMR (600 MHz, CDCl3) δ:
9.49 (s, 2H), 9.05 (d, J＝8.4 Hz, 2H), 8.05 (d, J＝9.0
Hz, 4H), 7.97 (s, 2H), 7.92 (d, J＝9.0 Hz, 2H), 7.80 (t,
J＝7.2 Hz, 2H), 7.74 (t, J＝7.2 Hz, 2H), 7.62 (s, 2H),
7.47 (s, 4H), 1.42 (s, 36H); 13C NMR (150 MHz, CDCl3)
δ: 151.52, 144.79, 139.68, 131.34, 130.37, 130.11,
129.77, 129.39, 128.44, 128.27, 127.15, 126.73, 125.90,
125.36, 124.81, 123.59, 123.24, 120.72, 119.73, 35.05,
31.58, 29.70. MALDI-TOF calcd for C60H58 [M＋ ]:
779.1, found 778.3.
1
was obtained. H NMR (600 MHz, CDCl3) δ: 9.38 (s,
2H), 9.03 (d, J＝8.4 Hz, 2H) , 8.16 (s, 2H), 8.01 (d, J＝
7.2 Hz, 2H), 7.85 (s, 2H), 7.84 (s, 2H), 7.79 (t, J＝7.2
Hz, 2H), 7.72 (t, J＝7.2 Hz, 2H), 7.37 (d, J＝8.4 Hz,
4H), 6.98 (d, J＝8.4 Hz, 4H), 4.11 (t, J＝6.6 Hz, 4H),
1.91 (m, 4H), 1.58 (m, 4H), 1.47－1.29 (m, 48H), 0.91
(t, J＝6.6 Hz, 6H); 13C NMR (150 MHz, CDCl3) δ:
158.47, 138.27, 137.44, 131.59, 130.58, 130.36, 129.95,
129.66, 128.71, 128.39, 127.72, 127.00, 126.60, 125.75,
125.58, 124.69, 123.24, 119.77, 114.88, 68.22, 53.42,
31.95, 29.75, 29.68, 29.55, 29.39, 26.23, 22.71, 14.13.
MALDI-TOF calcd for C76H90O2 [M＋]: 1035.5, found
1034.4.
Results and Discussion
Synthesis and characterization of polymer
The synthetic route of planar conjugated polymers
LP1, LP2, and LP3 is shown in Scheme 1. The polym-
erizations of monomers M1 with M2 were carried out in
a biphasic mixture of aqueous NaHCO3 and THF with
freshly prepared Pd(PPh3)4 as the catalyst. Polymer P1
was obtained in yield 96% and facilely converted to
ladder-type polymer LP1 in yield of 98% by the treat-
ment with a catalytic amount of BF3•OEt2. Polymers P2
and P3 were easily precipitated from the reaction mix-
ture of THF/H2O, and difficultly dissolved in common
organic solvents such as THF, chloroform and di-
chloromethane. According the literature,[54] a modified
Suzuki polycondensation condition, THF-toluene (1∶1,
V∶V)/aqueous NaHCO3 with Pd(PPh3)4 as a catalyst
precursor was applied to the polymerizations of mono-
mers M1 with M3 and M4. Under the modified poly-
condensation condition, polymer P2 was obtained in
low yield 48%, polymer P3 with long side chain was
obtained in good yield 85%, and easily dissolved in
common organic solvents. Polymers P2 and P3 were
facilely converted to ladder-type polymers LP2 and
LP3 in yields of 95% and 96%, respectively, by the
treatment with a catalytic amount of F3CCOOH. The
ring closure reactions of polymers were brought out in
high efficiency, because the characteristic signals of the
methoxy group at δ 2.71 in the proton NMR spectra
(Supporting Information) of the polymer P1 and the
C≡C group at 2210 cm−1 in the IR spectra (shown in
Figure 1) of the polymer P3 completely disappeared.
Synthesis and characterization of 2,7-di((3,5-di-tert-
butyl)phenylethynyl)phenylpyrene (9)
A mixture of M1 (0.12 g, 0.26 mmol), 2-bromo-1-
((3,5-di-tert-butyl)phenylethynyl)benzene (8) (0.20 g,
0.54 mmol), NaHCO3 (0.25 g), THF (25 mL) and H2O
(4 mL) was degassed, and Pd(PPh3)4 (30 mg, 0.026
mmol) was added under a nitrogen atmosphere. The
mixture was heated at reflux and stirred under nitrogen
for 24 h. Water and CH2Cl2 (200 mL) was added, the
organic layer was separated and dried over Na2SO4.
After removal of the solvent, the residue was chromato-
graphically purified on silica gel eluting with CH2Cl2/
petroleum ether (1∶8, V∶V) to afford 9 as a yellow
solid (0.14 g, 71%). 1H NMR (600 MHz, CDCl3) δ: 8.59
(s, 2H), 8.20 (s, 2H), 7.82 (d, J＝7.8 Hz, 2H), 7.77 (d,
J＝7.8 Hz, 2H), 7.55 (t, J＝7.8 Hz, 2H), 7.47 (t, J＝7.8
Hz, 2H), 7.27 (s, 2H), 7.07 (s, 4H), 1.15 (s, 36H); 13C
NMR (150 MHz, CDCl3) δ: 150.69, 144.13, 138.40,
132.92, 131.01, 130.21, 128.43, 127.92, 127.26, 126.14,
125.57, 123.96, 122.62, 122.21, 93.73, 88.24, 34.59,
31.15. Anal. calcd for C60H58: C 92.50, H 7.50; found C
92.43, H 7.44.
Synthesis and characterization of model compounds
10 and 11
9 (63 mg, 0.081 mmol) was dissolved in dry CH2Cl2
(30 mL), and treated with F3CCOOH (2 mL). After
stirring for 3 h at room temperature, water and CH2Cl2
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Chin. J. Chem. 2015, 33, 431—440

Synthesis of Pyrene-based Planar Conjugated Polymers and the Regioisomers
Scheme 1 Synthesis of ladder-type copolymers
C8H17O
OC8H17
OC8H17
C8H17O
C
C
O
O
C
Br
BF3 . Et2O
CH2Cl2
O
O
O
O
Pd(PPh3)4
THF/H2O
B
B
+
Br
n
O
C
O
OC8H17
M1
C8H17O
OC8H17
P1
OC8H17
M2
C8H17O
OC8H17
H17C8O
C8H17O
OC8H17
OC8H17
n
n
LP1
C8H17O
OC8H17
R
R
O
B
O
O
O
Pd(PPh3)4
B
Br
Br
+
THF/toluene/H2O
n
P2 R = OC8H17
P3 R = OC16H33
M3 R = OC8H17
M4 R = OC16H33
M1
R
R
R R
CF3COOH
CH2Cl2
n
LP2 R = OC8H17
LP3 R = OC16H33
The number-average molecular weight ( M n ) and
weight-average molecular weight ( M w ) of polymer P1
were 27.1 and 54.8 kg•mol−1, respectively; the M n
and M w of the ladder-type polymer LP1 decreased to
Chin. J. Chem. 2015, 33, 431—440
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Zhu et al.
FULL PAPER
6b
P3
LP3
P1
LP1
P3
C
C
LP3
Standard Mn = 12000
6
8
10
12
14
16
4000 3500 3000 2500 2000 1500 1000
Wavenumber/cm-1
500
Retention time/min
Figure 1 IR spectra of compound 6b, polymers P3 and LP3.
Figure 2 GPC elution traces of polymers P1, LP1, P3, LP3 and
standard.
12.5 and 34.2 kg•mol−1, respectively, the decrease of
molecular weight observed by GPC after ring closure
indicated the smaller effective volume the boardlike
LP1 as opposed to the cylindrically shaped P1.[7] Poly-
mer P2 is partly soluble in THF and chloroform, poly-
mer P2 shows a lower M n of 4.9 kg•mol−1, and a
M w of 13.5 kg•mol−1. Polymer P3 can be soluble in
common solution such as THF and chloroform, the
M n and M w of polymer P3 are 25.1 and 67.5
kg•mol−1, respectively. After ring closure, the ladder-
type polymer LP2 shows a lower M n of 4.5 kg•mol−1,
and a M w of 11.5 kg•mol−1; the M n and M w of
the ladder-type polymer LP3 are 22.6 and 60.6 kg•mol−1,
respectively. Ladder-type polymers LP2 and LP3 have
similar structure, so only characterizations of P3 and
LP3 are list. The elution curves are shown in Figure 2.
TGA thermograms of the two polymers exhibit good
thermal stability up to 250 ℃. Weight loss (5%) starts
at 330 and 335 ℃ for LP1 and LP3 as shown in Figure
3. DSC analysis of the polymers shows neither a glass
transition process (Tg) nor other thermal processes from
30 to 300 ℃.
120
100
80
LP3
60
LP1
40
20
0
100
200
300
400
500
600
700
Temperature/oC
Figure 3 TGA traces of ladder polymer LP1 and LP3.
syn-product 3 shows a singlet of singlets at δ 8.19 and
7.84, these signals are assigned to the aromatic protons
at 4-, 5- and 9-, 10-positions in pyrene units, respec-
tively; the anti-product 4 shows a doublet of doublets
assigned to 4- and 5-positions protons at δ 8.04 and 7.97
with coupling constants of 9.6 Hz. The ring closure re-
action of model compounds 3 and 4 is similar to the
ladder-type polymer LP1, so we can get an insight into
the structure of LP1, mostly probably LP1 was formed
by syn- and anti-repeated units. To confirm the structure
of LP2 and LP3, a series of model compounds were
synthesized. Suzuki coupling of M1 with 5a and 5b
generated compounds 6a and 6b in yields 60% and 56%,
respectively. After ring closure reaction by the treatment
with a catalytic amount of F3CCOOH, model com-
pounds 7a and 7b were obtained in yields 45% and 42%,
respectively. Unexpectedly, only one kind of product
was observed in the ring closure reaction. The only
product 7a shows a singlet of singlets assigned to the 4-,
5- and 9-, 10-positions protons at δ 7.99 and 7.73, re-
spectively; the only product 7b shows a singlet of
singlets assigned to the 4-, 5- and 9-, 10-positions pro-
tons at δ 8.16 and 7.85. It is clear that 7a and 7b are
syn-products. To get a deep insight into the ring closure
Synthesis and characterization of model compounds
As described in Scheme 1, the intramolecular cycli-
zation of the precursor polymers P1, P2 and P3 will be
generated in two possible positions because of the rota-
tion of the main chain, so the ladder polymers LP1, LP2
and LP3 are formed by two regioisomers of the
syn-repeated units, syn- and anti-repeated units. But the
ratio and anti-units cannot be determined from NMR or
other spectroscopic methods. To more precisely assess
the intrinsic properties of ladder polymers LP1, LP2
and LP3, it is necessary to prepare model compounds,
as presented in Scheme 2. M1 and methyl 2-bromo-
benzoate (1) were transformed into compounds 2 in
yield 94%, addition of 4-methylphenyllithium gave the
corresponding alcohol compound, after ring closure
with BF3•OEt2, two kinds of model compounds 3 (syn-)
and 4 (anti-) were obtained in the ratio of 3∶1. The
regioisomers in intramolecular cyclization reaction can
1
be clearly identified by the H NMR spectrum, the
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Chin. J. Chem. 2015, 33, 431—440

Synthesis of Pyrene-based Planar Conjugated Polymers and the Regioisomers
Scheme 2 Synthesis of model compounds
O
O
O
O
Li
Pd(PPh3)4
THF/H2O
HO
Br
M1
+
THF
O
1
O
OH
2
H5
H4
.
BF3 Et2O
H4
H5
+
CH2Cl2
3
75%
H10
H9
25%
4
R
R
R
R
Pd(PPh3)4
THF/H2O
+
M1
CF3COOH
CH2Cl2
H4 H5
Br
5a R = OC8H17
5b R = OC16H33
6a R = OC8H17
6b R = OC16H33
>98%
H10 H9
R
7a R = OC8H17
7b R = OC16H33
Pd(PPh3)4
THF/H2O
H4
H5
CF3COOH
CH2Cl2
+
M1
+
Br
8
H10 H9
44%
10
9
H5
H4
11
56%
reaction, the compound 8 with large side group was
synthesized. After coupling with M1, compound 9 was
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437

Zhu et al.
FULL PAPER
obtained in yield 71%, the cyclization of 9 generated
two kinds of products syn-10 and anti-11 in the ratio
44∶56. Syn-10 shows a singlet of singlets assigned to
the 4-, 5- and 9-, 10-positions protons at δ 8.22 and 7.58,
respectively; anti-11 shows a doublet of doublets as-
signed to the 4- and 5-positions protons at δ 8.05 and
7.92, respectively. We conclude that the bulky side
group makes the anti-structure easily formed. This re-
sult also suggests that the polymers LP2 and LP3 con-
tain predominantly syn-ring closed isomers units. Planar
small organic molecules 7a and 7b have melting points
of 197 and 203 ℃, respectively, and no melting points
are observed for other planar small organic molecules.
the UV-Vis absorption spectra with unclear peaks. The
absorption band of ladder-type polymer LP1 is between
300 and 450 nm, the absorption band of ladder-type
polymer LP3 is between 350 and 600 nm. The emission
bands of polymer LP1 and LP3 are peaked at 447 and
508 nm, respectively, the emission peaks of the
ladder-type polymers LP1 and LP3 are red-shifted.
Usually the ladder-type polymers exhibit well-resolved
absorption and emission spectra, which is typical for a
rigid, planar, one-dimensional π-system,[39,55] but LP1
and LP3 are different in contrast to most stepladder-
type and ladder-type poly-p-phenylene-based polymers
(LPPPs). Müllen had reported that ladder-type polymers
containing 9,10-anthrylene also showed different ab-
sorption and emission in contrast to most ladder-type
polymers.[50] All the model compounds show different
UV and PL spectra from their precursor compounds,
and exhibit blue fluorescence in solution. The regioi-
somers 3 and 4 exhibit similar absorbance and emission
properties in solution. They have strong absorption
peaks between 300 and 380 nm, and weak double peaks
at 400 and 423 nm. The double peaks for 4 are nearly
invisible. Compounds 3 and 4 exhibit similar blue
photoluminescence maximum at 425 nm with two side-
bands at 450 and 477 nm. Model compounds 7a, 7b and
10 have similar π-conjugated backbone, and they show
nearly the same absorption band between 300 and 450
nm with peak at 429 nm. 7a and 7b show the same
emission band with peak at 460 nm. 10 shows PL
Optical properties
The optical properties of the novel ladder-type
polymers LP1, LP3 and their model compounds are
acquired in diluted dichloromethane solutions. The
UV-Vis absorption (UV) and photoluminescence (PL)
characteristics are shown in Figure 4. The UV and PL
spectra of the precursor polymers P1, P3 and the
ladder-type polymers LP1, LP3 in diluted dichloro-
methane solutions present a significant difference which
can be attributed to the change in the conformation. The
polymers P1 and P3 exhibit an absorption band in the
ultraviolet region with a maximum at 357 and 347 nm,
and a broad blue emission band with a maximum at 417
and 420 nm, respectively. After ring closure, the ladder-
type polymers LP1 and LP3 show a very broad band in
0.24
0.20
0.16
0.12
0.08
0.04
0.00
600
500
400
300
200
100
0
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
700
600
500
400
300
200
100
0
(a)
(b)
UV P3
PL P3
UV LP3
PL LP3
UV P1
PL P1
UV LP1
PL LP1
300 350 400 450 500 550 600 650 700
Wavelength/nm
300
350
400
450
500
550
Wavelength/nm
600
0.12
0.10
0.08
0.06
0.04
0.02
0.00
(c)
(d)
UV 10
PL 10
UV 11
PL 11
0.20
0.15
0.10
0.05
0.00
800
600
400
200
0
500
400
300
200
100
0
UV 3
PL 3
UV 4
PL 4
UV 7a
PL 7a
UV 7b
PL 7b
300
350
400
450
500
550
600
300
350
400
450
500
550
600
Wavelength/nm
Wavelength/nm
Figure 4 UV-Vis absorption and fluorescence spectra of polymers P1 and LP1 (a), P3 and LP3 (b), compounds 3 and 4 (c), compounds
7a, 7b, 10 and 11 (d) in dichloromethane solution at room temperature.
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Synthesis of Pyrene-based Planar Conjugated Polymers and the Regioisomers
maximum at 453 nm with two shoulder sidebands at
470 and 480 nm. The compund 11 shows different UV
and PL spectra to its regioisomers 10, it displays
red-shifted absorption and emission relative to its regio-
isomers 10. Compound 11 shows a broad absorption
band between 300 and 450 nm with a maximum
wavelength peak at 445 nm, and a main emission
peaked at 462 nm with a clear shoulder peak at 493 nm.
The difference of the UV and PL spectra can be
attributed that the syn-compond 11 has better π-conju-
gated system than its regioisomers 10. The PL quantum
yields (ΦF) of all polymers and model compounds in
toluene solution were measured with 9,10-diphenylanth-
racene as a reference standard (toluene, ΦF 0.9).[56] The
PL quantum yields of polymers LP1 and LP3 are 0.62
and 0.36, respectively; the PL quantum yields of model
compounds 3, 4, 7a, 7b, 10 and 11 are 0.12, 0.37, 0.35,
0.35, 0.32 and 0.49, respectively.
stacking in film still occurs in model compounds 7a, 7b,
10 and 11, as a result, the peaks and edges of absorption
become unclear, the compounds show red-shifted maxi-
mum peaked at 480, 520, 560 and 540 nm, respectively.
Electrochemical properties
The electrochemical behavior of ladder-type poly-
mers LP1, LP3 and model compounds 3, 4, 7a, 7b, 10
and 11 in CH2Cl2 solution are investigated by using
cyclic voltammetry. The cathodic wave was not ob-
served for polymers and model compounds within the
solvent limit. The onset of oxidation wave determined
with ferroceneas as the internal reference standard is
1.03 V. The energy levels of the HOMO and the band
gap (Egap) were estimated from the cyclic voltam-
mogram and the onset of the absorption spectra. The
LUMO level of polymers and compounds were
calculated according to the following equation: ELUMO
＝
Solid films of ladder-type polymers and model
compounds on quartz plates used for UV-Vis and
fluorescence are prepared by spin-coating from a 1%
THF solution at 1000 r/min. The results are shown in
Surpporting Information. The absorption and photo-
luminescence spectra of polymer LP1 are similar to
those in solution. The polymer LP1 shows 3 nm red-
shift both in the absorption and photoluminescence
spectra. The absorption and photoluminescence spectra
of compounds 3 and 4 in film are different from those in
solution, the peaks and edges of the absorption become
unclear. The self-absorption of 3 and 4 can be seen in
the photoluminescence spectra, the intensity of the 0-0
transition is greatly diminished. The absorption spec-
trum of ladder-type polymer LP3 is identical with that
in solution, but ladder-type polymer LP3 shows no
emission in film due to the aggregation. Interchain π-π
E
HOMO＋Egap. The CV curves are shown in Figure 5, the
result data are listed in Table 1. The oxidation peaks of
ladder-type polymer LP3 is not evident due to the
limited solubility in CH2Cl2, so the onset of oxidation
can not be achieved.
Conclusions
In summary several planar conjugated polymers and
model compounds containing pyrene units were synthe-
sized through the Pd(0)-catalyzed Suzuki reaction and
intramolecular cyclization reaction. The polymers and
model compounds did not show typical features of
ladder-type polymers, they display broad absorption and
lower fluorescence quantum yield in solution. The high
efficiency of the intramolecular cyclization reaction
leads to perfect structure and regioisomers, model com-
6.0x10-5
(b)
4.0x10-5
(a)
5.0x10-5
3.0x10-5
4.0x10-5
LP1
7a
LP3
3.0x10-5
2.0x10-5
7b
2.0x10-5
3
1.0x10-5
10
1.0x10-5
4
11
0.0
0.0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
E/V (Ag/Ag+)
E/V (Ag/Ag+)
Figure 5 The cyclic voltammograms of ladder-type polymers LP1 and LP3 (a), model compounds 3 and 4 (a), 7a, 7b, 10, and 11 (b) in
dichloromethane solution at a scan rate of 50 mV•s−1.
Table 1 HOMO and LUMO energies and band gap data of polymer LP1 and compounds 3, 4, 7a, 7b, 10 and 11
Compound
HOMO/eV
LUMO/eV
Band gap/eV
LP1
−5.41
3
4
7a
−5.39
−2.64
2.75
7b
10
−5.40
−2.65
2.75
11
−5.39
−2.49
2.90
−5.40
−2.48
2.92
−5.39
−2.64
2.75
−5.36
−2.72
2.67
−2.68
2.73
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439

Zhu et al.
FULL PAPER
2014, 32, 788.
pounds suggest that the syn- and anti-structures are
formed in ladder-type polymer LP1; and syn-structure
in ladder-type polymer LP3. The ladder-type polymer
LP1 and all model compounds show blue light-emitting
in solution, the ladder-type polymer LP3 shows
blue-green light-emitting in solution, and interchain π-π
stacking can be detected in film of all the polymers and
model compounds.
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This material is based on work supported by the
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Natural Science Foundation of Hebei Province of China
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and Training Program for Innovative Research Team
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