Synthesis of highly luminescent organoboron polymers connected by bifunctional 8-aminoquinolate linkers

Article abstract of DOI:10.1002/pola.24153

New organoboron aminoquinolate-based polymers linked by π-conjugated bridge were prepared by SonogashiraHagihara coupling of organoboron aminoquinolate-based bisiodo monomers bearing biphenyl or bithiophene moiety with 1,4-diethynylbenzene derivatives. Te

Full text of DOI:10.1002/pola.24153

Synthesis of Highly Luminescent Organoboron Polymers Connected by
Bifunctional 8-Aminoquinolate Linkers
YUICHIRO TOKORO, ATSUSHI NAGAI, YOSHIKI CHUJO
Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku,
Kyoto 615-8510, Japan
Received 13 April 2010; accepted 24 May 2010
DOI: 10.1002/pola.24153
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: New organoboron aminoquinolate-based polymers
linked by p-conjugated bridge were prepared by Sonogashira–
Hagihara coupling of organoboron aminoquinolate-based
bisiodo monomers bearing biphenyl or bithiophene moiety with
1,4-diethynylbenzene derivatives. Tetracoordination states of bo-
ron atoms in the obtained polymers were confirmed by 11B NMR
spectroscopy, and they were also characterized by 1H NMR and IR
spectroscopies and size-exclusion chromatography. Their optical
properties were studied by UV–vis absorption and photolumines-
cence spectroscopies. In the region above 400 nm, the polymers
prepared from 1,4-diethynyl-2,5-dioctyloxybenzene showed
bathochromic shifts when compared with those prepared from
1.4-diethynyl-2-perfluorooctyl-5-trifluoromethylbenzene. The
polymers with biphenyl moiety showed higher absolute fluores-
cence quantum yields (UF ¼ 0.28 and 0.65), whereas those with
bithiophene moiety led to decreasing of the low quantum yields
(UF ¼ 0.19 and 0.00). The density-functional theory (DFT) and
time-dependent–DFT calculations of model compounds corre-
sponding to the polymers were in good agreement with the
results from UV–vis properties. The calculations revealed that the
electronic structure of the polymer with bithiophene moiety is dif-
ferent from that with biphenyl moiety, and predicted the electron
transfer from the bithiophene moiety to the p-extended quinoline
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moiety in transition state. 2010 Wiley Periodicals, Inc. J Polym
Sci Part A: Polym Chem 48: 3693–3701, 2010
KEYWORDS: fluorescence; heteroatom-containing polymer; poly-
condensation
INTRODUCTION For a few decades, conjugated polymers
have received much attention because of their extensive
applications to electronic and photonic devices such as poly-
meric light-emitting diodes,1 plastic lasers,2 nonlinear optical
materials,3 and polymer-based photovoltaic cells.4 The poly-
mers have an advantage of low cost device fabrication via
solution processing methods, including dip coating, spin cast-
ing, and ink-jet printing, when compared with inorganic or
low molecular weight counterparts.5 To control the physical
properties of conjugated polymers from the view point of
the molecular scale, various aromatic moieties and side
chains have been incorporated into them.6–8 One of the
interesting approaches is an introduction of functional dyes
into the conjugated polymer backbone.9–12 This method
allows for increasing not only of the diversity of emission
maxima available in the dyes, which were incorporated into
the conjugated linkers, but also of stability of the dyes.
the high emission quantum yields. They showed, however,
lower molar absorption coefficient corresponding to the
HOMO (highest occupied molecular orbital)-LUMO (lowest
unoccupied molecular orbital) transition relative to typical p-
conjugated molecules. This weak point has been improved
by the synthesis of organoboron quinolate-containing conju-
gated polymers, in which p-phenylene-ethynylene units were
embedded to boron atoms in the polymer backbones.18,19
These polymers gave strong green fluorescence, and an effi-
cient energy migration from conjugated linkers with high
molar absorption coefficient to boron quinolate moieties was
observed. However, the linkage between boron atom and
two p-phenylene-ethynylene moieties in the polymers pre-
vented the phenylene-ethynylene linkers from p-conjugating
to boron quinolate cores. Therefore, these polymers did not
obviously change the absorption and emission maxima of bo-
ron quinolate moiety. Generally, the control of absorption
and emission wavelength is as important as improvement of
the molar absorption coefficient toward the application of
actual device fabrication. Embedding the quinolato ligands in
various main chains of conjugated polymers accomplished
the efficient control by through-bond interaction between
quinolato moiety and p-conjugated bridge. There are two
types of polymer architecture fit for that qualification: (i)
Many fluorescent organoboron dyes have been used as
chemical probes, photosensitizers, and optical sensing due to
high emission quantum yields.13–15 Among them, organo-
boron quinolates such as 8-hydroxyquinoline biphenylboron
(BPh2q)16 turned out to be attractive as an alternative to
tris(8-hydroxyquinoline)aluminum (Alq3)17 for organic light-
emitting diodes because of their good thermal stabilities and
Correspondence to: Y. Chujo (E-mail: chujo@chujo.synchem.kyoto-u.ac.jp)
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Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 3693–3701 (2010) 2010 Wiley Periodicals, Inc.
SYNTHESIS OF LUMINESCENT ORGANOBORON POLYMERS, TOKORO, NAGAI, AND CHUJO
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
both the boron centers and the quinolato ligands are embed-
ded in the main chain20 and (ii) quinolate group is part of
the polymer backbone with diphenylboron moieties as a
pendant group.21 The majority of polymers prepared by this
procedure represented less emission quantum yield than
BPh2q. However, we have previously reported organoboron
8-aminoquinolate–connected polymers with red-shifts of the
emission maxima and higher absolute quantum yields when
compared with BPh2q.22 Herein, we report the synthesis and
characterization of novel organoboron 8-aminoquinolate–
connected polymers and discuss the relationship between
the optical property and the structure of the polymer back-
bone in detail.
stirred at room temperature for 20 h. The mixture was
transferred to a separating funnel and washed with aqueous
NaHCO3. The organic layer was dried over MgSO4, and the
solvent was removed under vacuum. Recrystallization from
hexane gave a brown solid in 86% yield (7.52 g, 17.16
mmol).
1H NMR (CDCl3): d ¼ 9.81 (s, 1H, ANHACOA), 8.77 (d, J ¼
4.1 Hz, 1H, Ar-H), 8.57 (d, J ¼ 8.3 Hz, 1H, Ar-H), 8.37 (d, J ¼
8.6 Hz, 1H, Ar-H), 8.07 (d, J ¼ 8.3 Hz, 1H, Ar-H), 7.53 (dd, J
¼
8.3, 4.2 Hz, 1H, Ar-H), 2.55 (t,
J
¼
7.6 Hz, 2H,
ACOACH2A), 1.81 (m, 2H, COACH2ACH2A), 1.43–1.26 (m,
14H, ACH2A), 0.87 (t, J ¼ 6.6 Hz, 1H, ACH3) ppm. 11B NMR
(CDCl3): d ¼ 7.13 ppm. 13C NMR (CDCl3): d ¼ 171.98
(>C¼¼O), 148.64 (Ar), 140.72 (Ar), 138.94 (Ar), 138.30 (Ar),
135.47 (Ar), 129.55 (Ar), 123.09 (Ar), 117.76 (Ar), 88.98
(Ar-I), 38.28, 31.87, 29.56, 29.48, 29.38, 29.27, 25.57, 22.66.
EXPERIMENTAL
General Procedures
1H (400 MHz), 13C (100 MHz), and 11B (128 MHz) NMR
spectra were recorded on a JEOL JNM-EX400 spectrometer.
1H and 13C NMR spectra used tetramethylsilane as an inter-
nal standard, 11B NMR spectra were referenced externally to
BF3OEt2 (sealed capillary) in CDCl3. The number-average
molecular weights (Mn) and molecular weight distribution
[weight-average molecular weight/number-average molecu-
lar weight (Mw/Mn)] values of all polymers were estimated
4,40-Bis(phenylbromoboryl)-biphenyl (3P)
Trimethyl(phenyl)tin (4.78 mL, 26.3 mmol) was added to a
solution of 4,40-bis(dibromoboryl)biphenyl (6.49 g, 13.2
mmol) in toluene (263 mL), and the mixture was stirred for
14 h. All volatile components were removed under a high
vacuum, and the solid was washed with hexane to give a
crude product (3.96 g), which was used without further
purification.
by size-exclusion chromatography (SEC) with
a TOSOH
G3000HXI system equipped with three consecutive polysty-
rene gel columns [TOSOH gels: a-4000, a-3000, and a-2500]
and ultraviolet detector at 40 ꢀC. The system was operated
at a flow rate of 1.0 mL/min, with tetrahydrofuran (THF) as
an eluent. Polystyrene standards were employed for calibra-
tion. UV–vis spectra were recorded on a Shimadzu UV-3600
spectrophotometer. Fluorescence emission spectra were
recorded on a HORIBA JOBIN YVON Fluoromax-4 spectro-
fluorometer. FTIR spectra were obtained using a SHIMADZU
IRPrestige-21 infrared spectrometer. Elemental analysis was
performed at the Microanalytical Center of Kyoto University.
All reactions were performed under nitrogen or argon
atmosphere.
Monomer (4P)
The crude product 3P (0.746 g), N-(5-iodo-8-quinolyl)unde-
canamide (1.75 g, 4.00 mmol), and triethylamine (0.43 mL,
3.1 mmol) were dissolved in toluene (30 mL). After the reac-
tion mixture was refluxed for 12 h, the solvent was removed
by rotary evaporation. The residue was treated with water,
followed by extraction with diethyl ether, drying over MgSO4,
and removal of the solvent under vacuum. The crude prod-
ucts were purified by silica gel (neutral) column chromatog-
raphy eluted with hexane/dichloromethane. Recrystallization
from hexane/dichloromethane gave a yellow solid in 50%
yield (0.918 g, 0.763 mmol).
1H NMR (CDCl3): d ¼ 8.77 (d, J ¼ 8.3 Hz, 2H, Ar-H), 8.47 (m,
4H, Ar-H), 8.23 (d, J ¼ 8.3 Hz, 1H, Ar-H), 7.63 (dd, J ¼ 8.4,
5.3 Hz, 2H, Ar-H), 7.52–7.44 (m, 12H, Ar-H), 7.28–7.25 (m,
6H, Ar-H), 2.18 (t, J ¼ 7.6 Hz, 4H, ACOACH2A), 1.23 (br, 8H,
ACH2A), 1.15 (br, 8H, ACH2A), 1.09 (br, 8H, ACH2A), 0.96
(br, 8H, ACH2A), 0.83 (m, 6H, ACH3) ppm. 11B NMR
(CDCl3): d ¼ 6.74 ppm. 13C NMR (CDCl3): d ¼ 177.48
(>C¼¼O), 143.16 (Ar), 142.91 (Ar), 142.61 (Ar), 140.18 (Ar),
139.91 (Ar), 138.30 (Ar), 133.84 (Ar), 133.40 (Ar), 129.61
(Ar), 127.87 (Ar), 127.25 (Ar), 126.39 (Ar), 123.58 (Ar),
120.21 (Ar), 81.71 (Ar-I), 38.45 (ACOACH2A), 31.84, 29.49,
29.38, 29.32, 29.24, 29.08, 25.20, 22.65, 14.11 (ACH3). IR
(KBr): m ¼ 3069, 3048, 3013, 2926, 2855, 1647 (C¼¼O),
1574 (Ar-H), 1503, 1462, 1433, 1387, 1308, 1207, 1190,
1148, 1107, 1057, 1043, 1003, 961, 878, 841, 818, 781, 739,
High-resolution mass spectra (HRMS) were obtained on a
JEOL JMSSX102A spectrometer for electron ionization (EI)
method and on a JEOL JMSHX110A for fast atom bombard-
ment (FAB) method.
Preparation of the Compounds
5-Iodo-8-aminoquinoline,22 4,40-bis(dibromoboryl)biphenyl,23
2,20-bis(dibromoboryl)bithiophene,23
1,4-diethynyl-2,5-dio-
ctyloxybenzene,24 and 1.4-diethynyl-2-perfluorooctyl-5-tri-
fluoromethylbenzene25 were prepared according to the liter-
ature. THF and triethylamine (Et3N) were purified using a
two-column solid-state purification system (Glasscontour
System, Joerg Meyer, Irvine, CA). Other reagents were com-
mercially available and used as received.
N-(5-Iodo-8-quinolyl)undecanamide (2)
5-Iodo-8-aminoquinoline (5.40 g, 20.0 mmol) and undeca-
noyl chloride (4.62 mL, 21.0 mmol) were dissolved in
dichloromethane (90 mL), followed by addition of triethyl-
amine (2.93 mL, 21.0 mmol). The resulting mixture was
708, 665, 644 cmꢁ1
60H70B2I2N4O2: 1202.3774; found: 1202.3813 [M]þ. Anal.
.
HRMS (FABþ): m/z: Calcd. for
C
Calcd. for C60H70B2I2N4O2: C, 63.91; H, 5.87; N, 4.66. Found:
C, 63.47; H, 5.81; N, 4.60.
3694
INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

ARTICLE
2,20-Bis(phenylbromoboryl)-5,50-bithiophene (3T)
ACH2A), 1.34 (4H, ACH2A), 1.22–1.08 (36H, ACH2A), 0.96
(8H, ACH2A), 0.81 (12H, ACH3) ppm. 11B NMR (CDCl3): d ¼
2.93 ppm. 13C NMR (CDCl3): d ¼ 177.57 (>C¼¼O), 153.62
(Ar), 142.28 (Ar), 139.92 (Ar), 137.60 (Ar), 133.94 (Ar),
133.44 (Ar), 128.21 (Ar), 127.87 (Ar), 127.25 (Ar), 126,39
(Ar), 122.73 (Ar), 118.44 (Ar), 115.69 (Ar), 113.48 (Ar),
111.33 (Ar), 91.51 (ACBCA), 91.13 (ACBCA), 69.32
(AOCH2A), 38.53 (ACOACH2A), 31.87, 31.74, 29.51, 29.40,
29.25, 26.02, 25.28, 22.66, 22.60, 14.12 (ACH3), 14.06
(ACH3) ppm. IR (KBr): m ¼ 3069, 3049, 3010, 2930, 2909,
2845, 2197 (CBC), 1653 (C¼¼O), 1570 (Ar-H), 1499, 1476,
1431, 1395, 1373, 1310, 1273, 1215, 1190, 1144, 1067,
1001, 876, 847, 818, 783, 737, 706, 683, 654 cmꢁ1. Anal.
Calcd. for C90H106B2N4O4: C, 81.31; H, 8.04; N, 4.21. Found:
C, 79.38; H, 7.98; N, 4.03.
A solution of 2,20-bis(dibromoboryl)-5,50-bithiophene (1.50 g,
3.00 mmol) in toluene (90 mL) was cooled to ꢁ78 ꢀC and
then trimethyl(phenyl)tin was added. The reaction mixture
was slowly allowed to warm up to room temperature and
left stirring for 16 h. All volatile components were removed
under a high vacuum, and the solid was washed with CH2Cl2
and hexane to give a crude product (1.08 g), which was used
without further purification.
Monomer (4T)
The crude product 3T (0.750 g), N-(5-iodo-8-quinolyl)unde-
canamide (1.45 g, 3.30 mmol), and triethylamine (0.42 mL,
3.0 mmol) were dissolved in toluene (30 mL). After the reac-
tion mixture was refluxed for 12 h, water was added, fol-
lowed by extraction with ethyl ether, drying over MgSO4, and
removal of the solvent under vacuum. The crude products
were purified by silica gel (neutral) column chromatography
eluted with dichloromethane. Recrystallization from hexane/
dichloromethane gave a yellow solid in 47% yield (0.856 g,
0.705 mmol).
Polymer (6PF)
Similarly to the preparation of 6PO, polymer 6PF was pre-
pared from monomer 4P (0.144 g, 0.120 mmol) and 1.4-
diethynyl-2-perfluorooctyl-5-trifluoromethylbenzene (0.0735
g, 0.120 mmol) in 85% yield as a yellow solid; Mn ¼ 15,400.
1H NMR (CDCl3): d ¼ 8.73 (dd, J ¼ 8.3, 4.2 Hz, 2H, Ar-H),
8.49 (d, J ¼ 8.3 Hz, 2H, Ar-H), 8.42 (d, J ¼ 4.9 Hz, 2H, Ar-H),
8.23 (dd, J ¼ 8.4, 3.1 Hz, 2H, Ar-H), 7.64 (m, 2H, Ar-H), 7.54
(d, J ¼ 3.9 Hz, 4H, Ar-H), 7.26 (m, 6H, Ar-H), 7.08 (m, 4H,
Ar-H), 2.26 (m, 4H, ACOACH2A), 1.35–0.98 (br, 32H,
ACH2A), 0.85 (m, 6H, ACH3) ppm. 11B NMR (CDCl3): d ¼
4.40 ppm. 13C NMR (CDCl3): d ¼ 177.31 (>C¼¼O), 143.37
(Ar), 142.57 (Ar), 142.41 (Ar), 140.63 (Ar), 130.18 (Ar),
137.73 (Ar), 133.02 (Ar), 132.81 (Ar), 132.49 (Ar), 132.24
(Ar), 129.61 (Ar), 127.95 (Ar), 127.61 (Ar), 124.18 (Ar),
123.94 (Ar), 123.66 (Ar), 123.45 (Ar), 120.22 (Ar), 81.93
(Ar-I), 38.27 (ACOACH2A), 31.85, 29.48, 29.36, 29.25,
29.07, 25.18, 22.65, 14.12 (ACH3). IR (KBr): m ¼ 3071, 3049,
3005, 2924, 2852, 1653 (C¼¼O), 1591, 1574 (Ar-H), 1501,
1460, 1433, 1412, 1387, 1371, 1308, 1283, 1211, 1148,
1103, 1057, 1043, 961, 885, 841, 804, 781, 725, 706, 669,
648 cmꢁ1. HRMS (FABþ): m/z: Calcd. for C60H60B2I2N6O4:
1214.2903; found: 1214.2869 [M]þ. Anal. Calcd. for
1H NMR (CDCl3): d ¼ 8.98 (2H, Ar-H), 8.80 (2H, Ar-H), 8.52
(2H, Ar-H), 8.09 (3H, Ar-H), 7.98 (1H, Ar-H), 7.71 (1H, Ar-H),
7.64 (1H, Ar-H), 7.52 (12H, Ar-H), 7.28 (4H, Ar-H), 7.24 (1H,
Ar-H), 7.09 (1H, Ar-H), 2.22 (4H, ACOACH2A), 1.24–1.08
(24H, ACH2A), 0.96 (8H, ACH2A), 0.83 (6H, ACH3) ppm.
11B NMR (CDCl3): d ¼ 5.18 ppm. IR (KBr): m ¼ 3071, 3049,
3011, 2928, 2855, 2203 (CBC), 1663 (C¼¼O), 1614, 1572
(Ar-H), 1499, 1476, 1433, 1395, 1379, 1310, 1240, 1213,
1202, 1148, 1117, 1088, 1053, 1016, 1003, 978, 878, 851,
820, 783, 737, 706, 677, 656 cmꢁ1
83H72B2F20N4O2: C, 63.94; H, 4.65; N, 3.59. Found: C, 63.13;
. Anal. Calcd. for
C
H, 4.62; N, 3.56.
Polymer (6TO)
Similarly to the preparation of 6PO, polymer 6TO was pre-
pared from monomer 4T (0.122 g, 0.100 mmol) and 1,4-
diethynyl-2,5-dioctyloxybenzene (0.0383 g, 0.100 mmol) in
88% yield as a red solid; Mn ¼ 27,900.
C60H66B2I2N4O2S2: C, 59.32; H, 5.48; N, 4.61. Found: C,
59.12; H, 5.35; N, 4.53.
1H NMR (CDCl3): d ¼ 8.98 (2H, Ar-H), 8.80 (2H, Ar-H), 8.52
(2H, Ar-H), 8.09 (3H, Ar-H), 7.98 (1H, Ar-H), 7.71 (1H, Ar-H),
7.64 (1H, Ar-H), 7.52 (12H, Ar-H), 7.28 (4H, Ar-H), 7.24 (1H,
Ar-H), 7.09 (1H, Ar-H), 2.22 (4H, ACOACH2A), 1.24–1.08
(24H, ACH2A), 0.96 (8H, ACH2A), 0.83 (6H, ACH3) ppm.
11B NMR (CDCl3): d ¼ 2.15 ppm. 13C NMR (CDCl3): d ¼
177.40 (>C¼¼O), 153.63 (Ar), 148.21 (Ar), 145.55 (Ar),
141.81 (Ar), 140.50 (Ar), 140.24 (Ar), 139.09 (Ar), 137.08
(Ar), 135.93 (Ar), 134.55 (Ar), 132.97 (Ar), 132.39 (Ar),
128.22 (Ar), 127.96 (Ar), 127.61 (Ar), 124.14 (Ar), 122.71
(Ar), 118.45 (Ar), 115.75 (Ar), 113.50 (Ar), 111.52 (Ar),
91.61 (ACBCA), 91.04 (ACBCA), 69.33 (AOCH2A), 38.36
(ACOACH2A), 31.88, 31.74, 29.58, 29.51, 29.40, 29.32,
29.26, 29.11, 26.02, 25.26, 22.68, 22.60, 14.14 (ACH3), 14.07
(ACH3). IR (KBr): m ¼ 3070, 3051, 3005, 2924, 2853, 2199
(CBC), 1653 (C¼¼O), 1570 (Ar-H), 1499, 1468, 1431, 1395,
1375, 1312, 1271, 1217, 1190, 1146, 1113, 1067, 1051,
Polymer (6PO)
A typical procedure is shown as follows: triethylamine (0.70
mL) was added to a solution of 4 (0.168 g, 0.14 mmol), 1,4-
diethynyl-2,5-dioctyloxybenzene (0.054 g, 0.140 mmol),
Pd(PPh3)4 (8.10 mg, 7.00 lmol), CuI (1.30 mg, 7.00 lmol) in
THF (1.40 mL) at room temperature. After the mixture was
stirred at 40 ꢀC for 48 h, a small amount of CHCl3 was
added and poured into a large excess of methanol to precipi-
tate the polymer. The polymer was purified by repeated pre-
cipitations from a small amount of CHCl3 into a large excess
of methanol and hexane, respectively, to give a red solid in
91% yield (0.169 g, 0.127 mmol); Mn ¼ 34,000.
1H NMR (CDCl3): d ¼ 8.96 (4H, Ar-H), 8.49 (2H, Ar-H), 8.00
(2H, Ar-H), 7.59 (2H, Ar-H), 7.51 (12H, Ar-H), 7.28 (4H, Ar-
H), 7.24 (2H, Ar-H), 7.09 (2H, Ar-H), 4.10 (4H, AOCH2A),
2.21 (4H, ACOACH2A), 1.90 (4H, ACH2A), 1.53 (4H,
1024, 912, 885, 849, 804, 783, 758, 739, 704, 655 cmꢁ1
.
SYNTHESIS OF LUMINESCENT ORGANOBORON POLYMERS, TOKORO, NAGAI, AND CHUJO
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME 1 Synthesis of ligand 2.
Anal. Calcd. for C86H102B2N4O4S2: C, 77.00; H, 7.66; N, 4.18.
Found: C, 75.67; H, 7.41; N, 4.00.
(Ar), 123.55 (Ar), 120.19 (Ar), 81.65 (Ar-I), 38.41
(ACOACH2A), 31.88, 29.50, 29.37, 29.27, 29.03, 25.16,
22.66, 14.11 (ACH3) ppm. IR (KBr): m ¼ 3071, 3048, 3005,
2924, 2853, 1645 (C¼¼O), 1576 (Ar-H), 1504, 1460, 1433,
1412, 1387, 1368, 1337, 1308, 1227, 1209, 1190, 1146,
1113, 1055, 1043, 961, 895, 878, 835, 781, 741, 704, 642
cmꢁ1. HRMS (EI): m/z: Calcd. for C32H36BIN2O: 602.1965;
found: 602.1955 [M]þ. Anal. Calcd. for C32H36BIN2O: C,
63.81; H, 6.02; N, 4.65. Found: C, 63.63; H, 5.98; N, 4.69.
Polymer (6TF)
Similarly to the preparation of 6PO, polymer 6TF was pre-
pared from monomer 4T (0.146 g, 0.120 mmol) and 1.4-
diethynyl-2-perfluorooctyl-5-trifluoromethylbenzene (0.0735
g, 0.120 mmol) in 89% yield as a yellow solid; Mn ¼ 12,600.
1H NMR (CDCl3): d ¼ 8.94 (2H, Ar-H), 8.83–8.74 (2H, Ar-H),
8.49 (2H, Ar-H), 8.11–7.98 (4H, Ar-H), 7.72–7.55 (6H, Ar-H),
7.28 (6H, Ar-H), 7.10 (4H, Ar-H), 2.30 (4H, ACOACH2A),
1.16–1.10 (24H, ACH2A), 1.00 (8H, ACH2A), 0.84 (6H,
ACH3) ppm. 11B NMR (CDCl3): d ¼ 3.52 ppm. IR (KBr): m ¼
3073, 3051, 2926, 2855, 2203 (CBC), 1663 (C¼¼O), 1570
(Ar-H), 1501, 1474, 1433, 1395, 1379, 1312, 1240, 1213,
1200, 1170, 1146, 1117, 1070, 1053, 910, 851, 810, 783,
743, 704, 656 cmꢁ1. Anal. Calcd. for C83H72B2F20N4O2: C,
63.94; H, 4.65; N, 3.59. Found: C, 63.13; H, 4.62; N, 3.56.
Model Compound (8)
Triethylamine (2.0 mL) was added to a solution of N-(5-
iodo-8-quinolyl)-N-(diphenylboryl)undecanamide (0.482 g,
0.800 mmol), 1,4-diethynyl-2,5-dioctyloxybenzene (0.153 g,
0.400 mmol), Pd(PPh3)4 (23.1 mg, 20.0 lmol), CuI (3.80 mg,
20.0 lmol) in THF (4.0 mL) at room temperature. After the
mixture was stirred at 40 ꢀC for 24 h, the solvent was
removed under vacuum. The crude was precipitated from a
small amount of CHCl3 into a large excess of methanol twice.
The precipitate was purified by recrystallization from hex-
ane/dichloromethane to give a red solid in 68% (0.359 g,
0.273 mmol).
N-(5-Iodo-8-quinolyl)-N-(diphenylboryl)undecanamide (7)
Triphenylborane (0.969 g, 4.00 mmol) and N-(8-quinolyl)un-
decanamide (1.75 g, 4.00 mmol) were dissolved in toluene
(24 mL). After the reaction mixture was refluxed for 12 h,
the solvent was removed under vacuum. The crude product
was purified by precipitation from a small amount of CH2Cl2
into a large excess of hexane, followed by precipitation from
a small amount of CHCl3 into a large excess of methanol to
give a yellow solid in 57% yield (1.37 g, 2.27 mmol).
1H NMR (CDCl3): d ¼ 9.01 (d, J ¼ 8.4 Hz, 2H, Ar-H), 8.95 (d,
J ¼ 8.0 Hz, 2H, Ar-H), 8.48 (d, J ¼ 4.4 Hz, 2H, Ar-H), 8.00 (d,
J ¼ 8.4 Hz, 2H, Ar-H), 7.61 (dd, J ¼ 8.0, 5.6 Hz, 2H, Ar-H),
7.49 (m, 8H, Ar-H), 7.29 (m, 10H, Ar-H), 7.10 (s, 2H, Ar-H),
4.11 (t, J ¼ 6.8 Hz, 4H, AOCH2A), 2.19 (t, J ¼ 7.6 Hz, 4H,
ACOACH2A), 1.93 (m, 4H, ACH2A), 1.53 (m, 4H, ACH2A),
1.36 (m, 4H, ACH2A), 1.23–1.12 (m, 36H, ACH2A), 0.97 (m,
8H, ACH2A), 0.87 (t, J ¼ 7.2 Hz, 12H, ACH3), 0.82 (t, J ¼ 6.8
Hz, 6H, ACH3) ppm. 11B NMR (CDCl3): d ¼ 6.26 ppm. 13C
NMR (CDCl3): d ¼ 177.56 (>C¼¼O), 153.64 (Ar), 142.33 (Ar),
140.05 (Ar), 138.78 (Ar), 137.60 (Ar), 135.93 (Ar), 133.46
(Ar), 128.19 (Ar), 127.84 (Ar), 127.19 (Ar), 122.72 (Ar),
118.38 (Ar), 115.80 (Ar), 113.54 (Ar), 111.28 (Ar), 91.47
(ACBCA), 91.11 (ACBCA), 69.37 (AOCH2A), 38.48
(ACOACH2A), 31.89, 31.73, 29.57, 29.51, 29.40, 29.28,
1H NMR (CDCl3): d ¼ 8.76 (d, J ¼ 8.4 Hz, 1H, Ar-H), 8.48 (d,
J ¼ 8.4 Hz, 1H, Ar-H), 8.44 (d, J ¼ 4.8 Hz, 1H, Ar-H), 8.23 (d,
J ¼ 8.4 Hz, 1H, Ar-H), 7.63 (dd, J ¼ 8.4, 5.2 Hz, 1H, Ar-H),
7.45 (m, 4H, Ar-H), 7.29–7.25 (m, 6H, Ar-H), 2.16 (t, J ¼ 7.6
Hz, 2H, ACOACH2A), 1.26–1.09 (m, 12H, ACH2A), 0.96 (m,
4H, ACH2A), 0.87 (t, J ¼ 8.0 Hz, ACH3) ppm. 11B NMR
(CDCl3): d ¼ 6.45 ppm. 13C NMR (CDCl3): d ¼ 177.47
(>C¼¼O), 143.12 (Ar), 142.94 (Ar), 142.59 (Ar), 140.15 (Ar),
138.30 (Ar), 133.41 (Ar), 129.58 (Ar), 127.84 (Ar), 127.21
SCHEME 2 Synthesis of mono-
mers.
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SCHEME 3 Synthesis of polymers.
29.24, 29.06, 26.03, 25.23, 22.67, 22.58, 14.11 (ACH3), 14.03
(ACH3) ppm. IR (KBr): m ¼ 3071, 3049, 3005, 2924, 2853,
2201 (ACBCA), 1653 (C¼¼O), 1570 (Ar-H), 1499, 1476,
1429, 1395, 1377, 1312, 1275, 1217, 1190, 1144, 1051, 877,
847, 820, 785, 760, 739, 704, 644 cmꢁ1. HRMS (FABþ): m/
z: Calcd. for C90H108B2N4O4: 1330.8557; found: 1330.8547
[M]þ. Anal. Calcd. for C90H108B2N4O4: C, 81.19; H, 8.18; N,
4.21. Found: C, 81.12; H, 8.18; N, 4.23.
to the upfield relative to that of 4P. The basic structures of
4P and 4T were also characterized by 1H NMR, 13C NMR,
ELEM ANAL, and mass spectroscopies. Connecting of the amino-
quinolate generates a stereogenic center at boron. However,
the stereoconformation might be not significantly responsi-
ble for emission behavior, so that the stereoisomers were
not separated here.20,26 Sonogashira–Hagihara coupling poly-
merizations of 4P or 4T were conducted with 1,4-diethynyl-
2,5-dioctyloxybenzene24 or 1,4-diethynyl-2-(perfluorooctyl)-
5-(trifluoromethyl)benzene25 in the presence of Pd(PPh3)4
and CuI in the mixed solvent of THF and triethylamine
RESULTS AND DISCUSSION
ꢀ
Synthesis
(Et3N) at 40 C for 48 h (Scheme 3). The obtained polymers
Initially, the ligand N-(5-iodo-8-quinolyl)undecanamide (2)
was synthesized from 8-aminoquinoline as a starting com-
pound according to Scheme 1. The other precursors for orga-
noboron monomers, 4,40-bis(phenylbromoboryl)biphenyl 3P
and bithiophene 3T were obtained via tin–boron exchange
from 4,40-bis(dibromoboryl)biphenyl23 and 2,20-bis(dibromo-
boryl)thiophene23 on reaction with trimethyl(phenyl)tin. 3P
and 3T were not absolutely purified due to their high reac-
tivities. The reaction of these bis(phehylbromoboryl)-func-
tionalized compounds with the ligand 2 produced organo-
boron aminoquinolate-based monomers 4P and 4T bearing
bisiodo groups as yellow powders (Scheme 2). These mono-
mers possess good solubility in various organic solvents due
to the long alkyl chains attached by amide linkages. The tet-
racoordination state of the boron atoms in 4P and 4T was
6PO and 6TO were collected as red solids, while 6PF and
6TF were collected as yellow solids. The polymers were
soluble in THF, CH2Cl2, and CHCl3. The 11B NMR spectra of
the obtained polymers were observed at dB ¼ 5.18–2.15
ppm assignable to the tetracoordination state of the boron
atoms in each polymer, indicating that the polymerization
proceeded without any damage to the structure in the orga-
noboron quinolate moiety. The IR spectra of the polymers
showed the weak absorption peaks at 2203–2197 cmꢁ1 and
the strong absorption peaks at 1663–1653 cmꢁ1, which are
attributable to stretching of the CBC bond and the C¼¼O
confirmed by the 11B NMR spectroscopy in CDCl3 [4P: dB
¼
6.74 ppm, 4T: dB ¼ 4.40 ppm]. Strong electron-donating na-
ture of the bithiophene unit moved chemical shift dB of 4T
TABLE 1 Polymerization Results
Yielda (%)
Mn
Mw
Mw/Mn
DPc
b
b
b
Polymer
6PO
6PF
6TO
6TF
a
91
85
88
89
34,000
15,400
28,000
12,600
100,300
29,800
102,000
23,200
3.0
1.9
3.7
1.8
25.6
9.9
20.9
8.0
Isolated yields after reprecipitation.
b
c
Estimated by SEC based on polystyrene standards in THF.
Degree of polymerization estimated by number-average molecular
weight.
SCHEME 4 Synthesis of model 8.
SYNTHESIS OF LUMINESCENT ORGANOBORON POLYMERS, TOKORO, NAGAI, AND CHUJO
3697

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 3 UV–Vis spectra of polymers and model compounds
in film state.
FIGURE 1 UV–Vis spectra of polymers and model compounds
in CHCl3 (1.0 ꢂ 10ꢁ5 M).
and photoluminescence experiments. Figure 1 illustrates UV–
vis absorption spectra of the polymers and the model com-
pound in CHCl3 solution (c ¼ 1.0 ꢂ 10ꢁ5 M). The spectra of
the polymer 6PO and its model compound 8 overlapped in
the region of the wavelength between 300 and 550 nm, obvi-
ously indicating that the polymer 6PO consists of the scaf-
fold of the model compound 8, and their absorption bands
in this region were probably assigned to the absorption of
the unit composed of two quinoline rings and diethynylben-
zene (qAr2q unit). In the region of the wavelength above
400 nm, the polymers having the same side chain at Ar2 give
the same absorption peaks. The absorption bands of the
polymers with octyloxy group (6PO and 6TO) were batho-
chromically shifted in comparison with those of the polymers
with perfluoroalkyl group (6PF and 6TF). This would mean
that the absorption maximum of the polymer with any Ar1
unit depends on Ar2 unit, i.e., the diethynyl-functionalized
monomer in Scheme 3, and the bathochromic shift is related
to the electron-donating nature of Ar2 unit in that region. All
the polymers and the model compounds strongly absorb the
visible light at longer wavelength in comparison with typical
organoboron quinolates and aminoquinolates, meaning
bond, respectively. Table 1 summarizes the polymerization
results. The number-average molecular weights (Mn) and the
molecular weight distributions (Mw/Mn) of the polymers,
measured by SEC in THF toward polystyrene standards,
were 12,600–34,000 and 1.4–3.0, respectively. The low reac-
tivity of the monomer 5F with electronegative substituent
for Sonogashira–Hagihara coupling resulted in the low mo-
lecular weight polymers 6PF and 6TF when compared with
the polymers 6PO and 6TO. To evaluate the optical proper-
ties of the polymers, a model compound (8) for the polymer
6PO was also prepared from boron aminoquinolate bearing
mono-iodo group (7) and 1,4-diethynyl-2,5-dioctyloxyben-
zene under the similar condition to the polymerization
(Scheme 4). After the purification by the reprecipitation, the
model compound 8 was collected as a solid, which is similar
color to the polymer 6PO.
Optical Properties
The optical properties of the obtained polymers and the
model compound were investigated by UV–vis absorption
FIGURE 2 Normalized emission spectra of polymers and model
compounds in CHCl3 (1.0 ꢂ 10ꢁ5 M).
FIGURE 4 Normalized emission spectra of polymers and model
compounds in film state.
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TABLE 2 UV–Vis Absorption and Photoluminescence Properties in Solution State
kabs,max (nm)a
e (Mꢁ1 cmꢁ1 b
)
Ex (nm)c
kem,max (nm)d
UF
e
Compound
6PO
6PF
6TO
6TF
8
272, 356, 376, 471
273, 389, 457
35,800
53,800
33,900
54,000
35,200
471
457
471
455
470
555
519
558
531
550
0.28
0.65
0.19
0.00
0.29
263, 353, 471
271, 331, 388, 455
268, 356, 376, 470
a
d
e
Absorption maxima: CHCl3 (1.0 ꢂ 10ꢁ5 M).
Fluorescence maxima: CHCl3 (1.0 ꢂ 10ꢁ5 M).
b
c
Molar extinction coefficients at the longest absorption maxima.
Excited wavelength.
Absolute quantum yield.
coplanarity and extended p-conjugation of quinoline rings
through Ar2 unit.
indicating that repulsion between highly electronegative
surfaces of perfluoroalkyl chains inhibits the stabilization by
the stacking of p-conjugated main chain. In the normalized
fluorescence spectra, the film state disappears in the differ-
ence between the polymers with biphenyl moiety and those
with bithiophene moiety as shown in the solution state (Fig.
2). This is probably due to no solvation of the transition
state from charge transfer in the film of 6TO and 6TF
(Tables 2 and 3).
Emission spectra of the polymers and the model compound
in CHCl3 solution (c ¼ 1.0 ꢂ 10ꢁ5 M) are represented in Fig-
ure 2. All the emission data given here were obtained after
exciting at the longest wavelength of the absorption peaks,
i.e., absorption maxima corresponding to qAr2q unit. The
emission bands of the polymers with octyloxy group (6PO
and 6TO) were red-shifted in comparison with those with
perfluoroalkyl group (6PF and 6TF). Moreover, the spectrum
of the polymer 6PO coincided with that of the model com-
pound (8). Based on these results, it can be concluded that
the polymers emit the light from qAr2q unit, and its wave-
length is mainly controlled by electron-donating Ar2 unit like
the visible light absorption of the polymers. In the case that
the polymers have the same Ar2 group, the emission band of
the polymer with bithiophene moiety (6TO or 6TF)
appeared in the region of longer wavelength than that with
biphenyl moiety (6PO or 6PF). On the contrary, Ar1 unit
shifted the emission band while that had no relation with
the absorption band in the region above 400 nm. This would
mean that Ar1 affects the electronic structure of qAr2q unit
not in the ground state but in the excited state. Absolute flu-
orescence quantum yields (UF) of the polymers and the
model compound in CHCl3 were measured by integrating
sphere method. The quantum yields of the polymers with
bithiophene moiety (6TO, 6TF) were lower than those with
biphenyl moiety (6PO or 6PF), and especially, the polymer
with strong electron-withdrawing substituent (6TF) gave UF
¼ 0.00. It seems to be that electron-donating ability of the
bithiophene moiety is very strong, so that electron transfer
from bithiophene moiety to quinoline ring leads to decreas-
ing of the quantum yield.
Molecular Orbital Calculations
To further understand the nature of optical properties, we
have carried out theoretical calculation for model com-
pounds 9PO and 9TF using density-functional theory (DFT)
method at the B3LYP/6-31G(d), and also using time-depend-
ent–DFT (TD-DFT) at the B3LYP/6-31G(d,p).27 Figure 5(A,B)
exhibit HOMO and LUMO of 9PO and 9TF, respectively, and
the molecular orbitals around frontier orbitals separate well
into qAr2q and Ar1 units. The HOMO and LUMO of 9PO are
located predominantly on qAr2q unit, and the oscillator
strength (f) mainly responsible for HOMO–LUMO transition
of 9PO was large (f ¼ 1.1089). These results indicate that
the p-conjugation is extended through Ar2 moiety, and that
the HOMO–LUMO transition at qAr2q unit results in the
absorption band of the polymer 6PO ꢃ470 nm as mentioned
above. In contrast, the HOMO of 9TF is localized on bithio-
phene moiety, and the LUMO is on qAr2q unit. TD-DFT
TABLE 3 UV–Vis Absorption and Photoluminescence Properties
in Film State
Compound
kabs,max (nm)a
Ex (nm)b
kem,max (nm)c
UV–vis absorption and photoluminescence experiments in
spin-coated film state were also carried out (Figs. 3 and 4).
All the polymers and the model compound in film state
showed bathochromic shift of the absorption and photolumi-
nescence spectra (7–29 nm) when compared with those in
solution state due to intermolecular stacking interaction of
p-conjugated main chain. Moreover, the polymers with per-
fluoroalkyl chains (6PF and 6TF) represented smaller batho-
chromic shift than those with alkoxy chains (6PO and 6TO),
6PO
6PF
6TO
6TF
8
369, 489
467
489
467
490
468
497
580
537
586
538
579
362, 490
468
367, 497
a
Absorption maxima.
Excited wavelength.
Fluorescence maxima.
b
c
SYNTHESIS OF LUMINESCENT ORGANOBORON POLYMERS, TOKORO, NAGAI, AND CHUJO
3699

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 5 Molecular orbital diagrams for the HOMO and LUMO of (A) 9PO and (B) 9TF (B3LYP/6-31G(d)// B3LYP/6-31G(d)).
REFERENCES AND NOTES
calculation revealed that HOMO–LUMO transition hardly
occurs (f ꢃ 0.01), whereas transition from HOMO-2 on
qAr2q unit to LUMO easily occurs (f ¼ 1.5044) correspond-
ing to the absorption band of the polymer 6TF ꢃ455 nm
(Fig. 1). The order of the oscillator strength was consistent
with that of the molar extinction coefficient. From the result
of 9TF, it can be said that the electron transition from
HOMO-2 to LUMO provides a hole at HOMO-2 on qAr2q unit
and that an electron localized on the bithiophene moiety
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state leading to the nonradiative relaxation.
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