Synthesis of π-Conjugated polymers containing organoboron benzo[ h ]quinolate in the main chain

Article abstract of DOI:10.1021/ma100814v

A study was conducted to synthesize π-conjugated polymers containing organoboron benzo[h]quinolate in the main chain. cTetrahydrofuran (THF) and triethylamine (Et₃N) were purified using a two-column solid-state purification system. 10-Hydroxybe

Full text of DOI:10.1021/ma100814v

Macromolecules 2010, 43, 6229–6233 6229
DOI: 10.1021/ma100814v
Synthesis of π-Conjugated Polymers Containing Organoboron
Benzo[h]quinolate in the Main Chain
Yuichiro Tokoro, Atsushi Nagai, and Yoshiki Chujo*
Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku,
Kyoto 615-8510, Japan
Received April 14, 2010; Revised Manuscript Received June 19, 2010
Introduction
reasonable candidate for that aim, i.e., color change via the
extended π-conjugated system of Q-ligand. Herein, we wish to
Organoboron dyes have recently found widespread interest as
species with promising optical properties in various fields. They
have been used as chemical probes,1 photosensitizers,2 and
optical sensing3 due to high luminescent quantum yields, large
extinction coefficients, or two-photon absorption cross section.
Among them, organoboron quinolates such as 8-hydroxyquino-
linatediphenylboron (BPh2q)4 turned out to be attractive as an
alternative to tris(8-hydroxyquinolinate)aluminum (Alq3)5 for
organic light-emitting diodes (OLEDs) because of their good
thermal stabilities as well as the high emission quantum yields.
BPh2q and their derivatives emit intense light from a quinoline-
based intraligand charge transfer (ILCT) excited state.6 This
ILCT state is formed when the highest occupied molecular orbital
(HOMO) and the lowest unoccupied molecular orbital (LUMO)
are localized on the phenolate ring and on the pyridyl ring of
the quinoline ligand, respectively. Introduction into polymers by
covalent bonding is expected to be advantageous because of the
improved processability such as film formability, thermal stabi-
report novel synthesis of 10-hydroxybenzo[h]quinolinatediphenyl-
boron (1) and the incorporation of 1 into π-conjugated polymer
backbone and discuss their optical properties in comparison with
BPh2q.
Experimental Section
Measurements. 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
(TMS) as an internal standard; 11B NMR spectra were refer-
enced externally to BF3OEt2 (sealed capillary) in CDCl3. The
number-average molecular weight (Mn) and the molecular
weight distribution [weight-average molecular weight/number-
average molecular weight (Mw/Mn)] values of all polymers were
estimated by size-exclusion chromatography (SEC) with a TO-
SOH G3000HXI system equipped with three consecutive poly-
styrene gel columns [TOSOH gels: R-4000, R-3000, and R-2500]
and ultraviolet detector at 40 °C The system was operated at a
flow rate of 1.0 mL/min, with tetrahydrofuran as an eluent.
Polystyrene standards were employed for calibration. UV-vis
spectra were recorded on a Shimadzu UV-3600 spectrophoto-
meter. Fluorescence emission spectra were recorded on a HOR-
IBA JOBIN YVON Fluoromax-4 spectrofluorometer, and the
absolute quantum yield was calculated by the integrating sphere
method on the HORIBA JOBIN YVON Fluoromax-4 spectro-
fluorometer in chloroform. FT-IR spectra were obtained using a
SHIMADZU IRPrestige-21 infrared spectrometer. Thermogra-
vimetric analyses (TGA) were performed on a Seiko TG/DTA
6200 at a scan rate of 10 °C/min. X-ray crystallographic analysis
was carried out by a Rigaku R-AXIS RAPID-F graphite-
monochromated Mo KR radiation diffractometer with an imag-
ing plate. A symmetry related absorption correction was carried
out by using the program ABSCOR.13 The analysis was carried
out with direct methods (SHELX-9714 or SIR9715) using
Yadokari-XG.16 The program ORTEP317 was used to generate
the X-ray structural diagram. Elemental analysis was performed
at the Microanalytical Center of Kyoto University.
€
lity, and photostability, etc. Jakle et al. first reported the synthesis
of well-defined polymers incorporated into the polystyrene side
chain via multistage polymeric reaction of poly(4-dibromoboryl-
styrene),7 and Weck et al. also proposed the potentiality of
organoboron quinolate-functionalized polystyrene as the excel-
lent precursors for OLEDs.8
Recently, we have also prepared organoboron quinolate-con-
taining conjugated polymers, in which p-phenyleneethynylene
units were embedded to boron atoms in the polymer backbones.9
Those polymers gave strong green fluorescence, and an efficient
energy migration from conjugated linkers with high molar
absorption coefficient to boron quinolate moieties was observed.
Substituting groups on the Q-ligand moiety can change the
emission color of the polymers; i.e., polymers with methyl-
substituted organoboron quinolate polymers exhibited green-
blue or blue photoluminescence.10 Elements such as oxygen,
sulfur, and selenium also affect the emission wavelength of the
organoboron quinolate polymer.11 Increasing of atomic number
of the 16 group atom adjacent to the boron atom caused emission
shift to longer wavelength and decreasing of absolute quantum
yields for both the low-molecular-mass model compounds and
the polymers.
Materials. Tetrahydrofuran (THF) and triethylamine (Et3N)
were purified using a two-column solid-state purification system
(Glasscontour System, Joerg Meyer, Irvine, CA). 10-Hydroxy-
benzo[h]quinoline,18 1,4-diethynyl-2,5-dihexadecyloxybenzene,19
and 1,4-diethynyl-2-perfluorooctyl-5-trifluoromethylbenzene20
were prepared according to the literature.
Synthesis of 1. Triphenylborane (0.726 g, 3.00 mmol) and 10-
hydroxybenzo[h]quinoline (0.59 g, 3.00 mmol) were dissolved in
toluene (18 mL). After the reaction mixture was refluxed for
12 h, the mixture was allowed to stand for 1 day at -20 °C to
precipitate a product. The precipitate was collected by filtration
to give a yellow solid in 76% yield (0.82 g, 2.28 mmol). 1H NMR
Extension of π-conjugation is another important approach to
changing the emission color. 10-Hydroxybenzo[h]quinoline can
be regarded as a π-extended 8-hydroxyquinoline and shows
proton transfer emission resemblant to the emission from ILCT
state,12 so that 10-hydroxybenzo[h]quinolinatediphenylboron
and the benzo[h]quinoline-containing polymers seem to be a
*Corresponding author. E-mail: chujo@chujo.synchem.kyoto-u.ac.jp.
r 2010 American Chemical Society
Published on Web 07/02/2010
pubs.acs.org/Macromolecules

6230 Macromolecules, Vol. 43, No. 14, 2010
Note
(CDCl3, δ, ppm): 8.47 (m, 1H, Ar), 8.42 (m, 1H, Ar), 7.84 (dd,
J = 8.9, 4.8 Hz, 1H, Ar), 7.72-7.61 (m, 3H, Ar), 7.41 (d, J = 8.1
Hz, 1H, Ar), 7.33 (m, 5H, Ar), 7.24-7.15 (m, 6H, Ar). 11B NMR
(CDCl3, δ, ppm): 6.55. 13C NMR (CDCl3, δ, ppm): 157.81 (Ar),
143.21 (Ar), 140.58 (Ar), 139.78 (Ar) 134.78 (Ar), 133.11 (Ar),
132.82 (Ar), 130.74 (Ar), 127.32 (Ar), 126.58 (Ar), 126.34
(Ar), 123.25 (Ar), 120.74 (Ar), 117.67 (Ar), 116.98 (Ar), 115.26
(Ar). HRMS (EI) Calcd for C25H18BNO: m/z 359.1481. Found:
m/z 359.1478. Anal. Calcd for C25H18BNO: C, 83.59; H, 5.05; N,
3.90. Found: C, 83.48; H, 5.19; N, 3.77.
Synthesis of 2. 9.4 mL (1.6 M, 15 mmol) of n-BuLi was slowly
added to the solution of 1,4-diiodobenzene (4.95 g, 15.0 mmol)
in 75 mL of THF at -78 °C, and the mixture was stirred
at -78 °C for 1 h. BBr3 (0.48 mL, 5.0 mmol) was added to the
reaction mixture at -78 °C and then allowed to warm to room
temperature and refluxed for 12 h. 10-Hydroxybenzo[h]quino-
line (0.98 g, 5.00 mmol) dissolved in 15 mL of THF in another
flask was added to the reaction mixture and then refluxed for
6 h. The reaction mixture was concentrated under vacuum. The
remaining oil was diluted by a small amount of CHCl3, and the
solution was reprecipitated with 100 mL of methanol to give a
yellow solid. This solid was purified by dissolving in a small
amount of CH2Cl2 and reprecipitating with 100 mL of hexane to
obtain 2 in 53% yield (1.63 g, 2.67 mmol) as a yellow solid. 1H
NMR (CDCl3, δ, ppm): 8.47 (d, J = 7.8 Hz, 1H, Ar), 8.38 (d,
J = 4.4 Hz, 1H, Ar), 7.88 (d, J = 9.0 Hz, 1H, Ar), 7.74-7.65 (m,
3H, Ar), 7.52 (d, J = 8.1 Hz, 4H, Ar), 7.37 (dd, J = 7.8, 4.4 Hz,
2H, Ar), 7.00 (d, J = 8.0 Hz, 4H, Ar) . 11B NMR (CDCl3, δ,
ppm): 6.06. 13C NMR (CDCl3, δ, ppm): 157.25 (Ar), 142.80
(Ar), 140.40 (Ar), 140.18 (Ar) 136.44 (Ar), 135.06 (Ar), 134.75
(Ar), 133.00 (Ar), 130.93 (Ar), 126.49 (Ar), 123.30 (Ar), 120.93
(Ar), 118.10 (Ar), 116.94 (Ar), 115.05 (Ar), 93.26 (Ar-I).
HRMS (EI) Calcd for C25H16BI2NO: m/z 610.9414. Found:
m/z 610.9415. Anal. Calcd for C25H16BI2NO: C, 49.14; H, 2.64;
N, 2.29. Found: C, 48.99; H, 2.81; N, 2.29.
Figure 1. X-ray crystal structure of 1 with thermal ellipsoids drawn to
the 50% probability level.
Scheme 1. Synthesis of Model Compound
Synthesis of 4O. Monomer 2 (0.12 g, 0.20 mmol), 1,4-diethy-
nyl-2,5-dioctyloxybenzene (0.12 g, 0.20 mmol), CuI (1.9 mg,
0.01 mmol), and Pd(PPh3)4 (12.0 mg, 0.01 mmol) were dissolved
in 2.0 mL of THF and 1.0 mL of Et3N. After the mixture was
stirred at 40 °C for 48 h, a small amount of CHCl3 was added,
and the mixture was poured into a large excess of methanol to
precipitate the polymer. The polymer was purified by repeated
precipitations from a small amount of CHCl3 into a large excess
of methanol and hexane to give a yellow solid in 72% yield
(0.14 g, 0.14 mmol). Mn = 10 800 g/mol. 1H NMR (CDCl3, δ,
ppm): 8.46 (1H, Ar), 8.41 (1H, Ar), 7.87 (1H, Ar), 7.72-7.67
(4H, Ar), 7.42-7.36 (6H, Ar), 7.28-7.25 (4H, Ar), 6.93 (2H,
Ar), 3.96 (4H, -OCHH2-), 1.78 (4H, -CH2-), 1.58 (4H,
-CH2-), 1.47 (4H, -CH2-), 1.21 (44H, -CH2-), 0.86 (6H,
-CH3). 13C NMR (CDCl3, δ, ppm): 157.52 (Ar), 153.53 (Ar),
143.02 (Ar), 140.53 (Ar), 134.77 (Ar), 132.96 (Ar), 130.90
(Ar), 130.59 (Ar), 126.46 (Ar), 123.27 (Ar), 121.59 (Ar), 120.88
(Ar), 117.97 (Ar), 117.08 (Ar), 115.19 (Ar), 114.09 (Ar), 95.57
(-CtC-), 85.35 (-CtC-), 69.62 (-OCH2-), 31.93, 29.67,
29.60, 29.38, 29.34, 25.98, 22.70, 14.15. 11B NMR (CDCl3, δ,
ppm): 4.10. IR (KBr): ν = 3061 (Ar), 3017 (Ar), 2924, 2853,
2205 (CtC), 1923 (Ar), 1630 (Ar), 1597 (Ar), 1510, 1468, 1437,
1379, 1342, 1294, 1215, 1148, 1076, 1049, 970, 908, 889, 835,
721 cm-1. Anal. Calcd for C67H84BNO3: C, 83.63; H, 8.80; N,
1.46. Found: C, 81.01; H, 8.44; N, 1.46.
C44H18BF20NO: C, 54.63; H, 1.88; N, 1.45. Found: C, 53.98; H,
2.25; N, 1.39.
Results and Discussion
Synthesis of Model Compound 1. The reaction between 10-
hydroxybenzo[h]quinoline18 and triphenylborane in toluene
under reflux conditions afforded organoboron benzo[h]-
quinolate (1) as a yellow precipitate in the reaction mixture
at -20 °C (Scheme 1). This compound was stable under air
and showed high solubility in dichloromethane and chloro-
form. The tetracoordination state of the boron atoms in 1
was confirmed by the 11B NMR spectroscopy in CDCl3
(δB = 6.55 ppm), and the basic structure was also character-
ized by 1H NMR, 13C NMR, and EI mass spectroscopies and
by elemental analysis.
The crystallographically determined molecular structure
of 1 is shown in Figure 1. The chelate ring in 1 is six-
membered and puckered, differing from that in 8-hydroxy-
quinolate ligand, with planar five-membered ring. The sp3
orbital-hybridized boron centers of 1 appear as a slightly
distorted tetrahedral geometry with the dihedral angle
O(1)-B(1)-N(1) of 105.1° (Table 1), which is closer to an
ideal orientation of four sp3 orbitals than that of B(C2H5)2q
(97.0°, q = 8-hydroxyquinolate)4 and B(4-iodophenyl)2q
(99.9°).10 On the other hand, the angle C(23)-O(1)-B(1)
of 117.8° suggested large distortion around oxygen atom of 1
Synthesis of 4F. Similarly to the preparation of 4O, 4F was
prepared from monomer 2 (97.8 mg, 0.16 mmol) and 1.4-
diethynyl-2-perfluorooctyl-5-trifluoromethylbenzene (98.0 mg,
0.16 mmol) in 57% yield as a yellow solid. Mn = 6400 g/mol. 1H
NMR (CDCl3, δ, ppm): 8.51 (1H, Ar), 8.43 (1H, Ar), 7.89 (2H,
Ar), 7.79 (1H, Ar), 7.71 (4H, Ar), 7.40 (5H, Ar), 7.32 (3H, Ar),
7.28 (1H, Ar). 11B NMR (CDCl3, δ, ppm): 4.30. IR (KBr):
ν= 3065 (Ar), 3021 (Ar), 2216 (CtC), 1923 (Ar), 1802 (Ar),
1630 (Ar), 1597 (Ar), 1512, 1441, 1344, 1298, 1244, 1213, 1144,
1078, 1047, 1020, 970, 910, 889, 835, 721 cm-1. Anal. Calcd for

Note
Table 1. Selected Bond Lengths (A) and Angles (deg) for 1
Macromolecules, Vol. 43, No. 14, 2010 6231
˚
Table 2. Polymerization of Organoboron Quinolate-Based Mono-
mers and 1,4-Diethynylbenzene Derivativesa
B(1)-N(1)
B(1)-O(1)
O(1)-C(23)
C(23)-C(24)
C(24)-C(25)
N(1)-C(25)
B(1)-C(1)
B(1)-C(7)
1.635(4)
1.500(3)
1.358(3)
1.415(5)
1.441(4)
1.369(3)
1.602(4)
1.613(5)
O(1)-B(1)-N(1)
C(23)-O(1)-B(1)
O(1)-C(23)-C(24)
C(23)-C(24)-C(25)
N(1)-C(25)-C(24)
C(25)-N(1)-B(1)
105.1(2)
117.8(2)
120.6(3)
120.7(3)
118.7(2)
118.4(2)
yieldb
(%)
Mn
(g/mol)
Mw
(g/mol)
T5
(°C)e
c
c
c
d
polymer
Mw/Mn
DPn
4O
4F
72
57
10 800
6 400
25 500
16 200
2.4
2.5
11.2
6.6
298
368
a Conditions: Sonogashira-Hagihara couplings of organoboron qui-
nolate-based monomer (1 equiv) and 1,4-diethynylbenzene derivatives
(1 equiv) were carried out in the presence of Pd(PPh3)4 and CuI in the
mixed solvent (THF/NEt3 = 2/1) at 40 °C for 48 h. b Isolated yields after
precipitation. c Estimated by size-exclusion chromatography (SEC)
based on polystyrene standard in tetrahydrofuran (THF). dAverage
number of repeating units calculated from Mn and molecular weights of
repeating units. e Thermogravimetric analysis: heating rate 10 K/min
under air; values given for weight loss of 5%.
Scheme 2. Synthesis of Monomer
Table 3. UV-vis Absorption and Photoluminescence Data
e
compound
λ λ
abs,max/nma ε/M-1 cm-1 b Ex/nmc em,max/nmd ΦF
1
4O
4F
302, 420
314, 373
359, 375
3 600
39 000
47 700
420
373
375
513
513
509
0.10
0.16
0.18
a Absorption maxima: CHCl3 (1.0 Â 10-5 M). b Molar extinction
coefficients at the longest absorption maxima. c Excited wavelength.
d Fluorescence maxima: CHCl3 (1.0 Â 10-5 M). e Absolute quantum
yield.
Scheme 3. Synthesis of Polymers
indicating that the polymerization proceeded without any
damage to the structure in the organoboron quinolate
moiety. The IR spectra of the polymers showed the absorp-
tion peaks at 2205 cm-1 (for 4O) and 2216 cm-1 (for 4F),
which are attributable to stretching of the -CtC- bond in
the polymer backbone. Moreover, strong broad peaks as-
signable to the C-F stretching band were observed at
around 1200 cm-1 in the spectra of 4F. The number-average
molecular weights (Mn) and the molecular weight distribu-
tions (Mw/Mn) of 4O and 4F, measured by size-exclusion
chromatography (SEC) in THF, were 10 800 g/mol, 2.4 and
6400 g/mol, 2.5, respectively (Table 2). The degrees of poly-
merization (DPn) of 4O and 4F, estimated by Mn from SEC,
were 11.2 and 6.6, respectively. Thermal stabilities of the
polymers were examined by thermogravimetric analysis
(TGA) under air. The start of the thermal degradation under
air for the polymers 4O and 4F lies at 298 and 368 °C, where
5% weight loss was recorded. These data suggest that
the obtained polymers present similar thermal stability to
general poly(p-phenyleneethynylene)s21 and π-conjugated
polymers containing organoboron quinolates in the main
chain.11
Optical Properties. The optical properties of the obtained
polymers were investigated by UV-vis absorption and
photoluminescence in CHCl3 solution (1.0 Â 10-5 M) as
compared to those of model compounds. The results from
the absorption and emission spectra are summarized in
Table 3. The model compound 1 showed the weak absorp-
tion peaks at 302 and 420 nm arising from the benzo-
[h]quinolate ligand (Figure 2). These peaks stand on the
bathochromic side in comparison with those of BPh2q (264
and 395 nm). This means that the extension of π-conjugation
from quinolate to benzo[h]quinolate reduces the width be-
tween molecular orbitals and causes the bathochromic shift
of the absorption peaks. The polymers 4O and 4F exhibited
strong absorption bands in the region from 300 to 400 nm
like other π-conjugated polymers containing organoboron
quinolates in the main chain. Therefore, these bands can be
assignable to the π-conjugated linkers connecting the benzo-
[h]quinolate units with each other, and the electronic struc-
ture of the π-conjugated linker is also independent from that
of the benzo[h]quinolate.
as compared with that of B(C2H5)2q (111.8°).4 The average
˚
of B(1)-N(1) bond length of 1 (1.635 A) was almost identical
to that of B(C2H5)2q (1.636 A) and B(4-iodophenyl)2q
4
˚
10
(1.629 A), probably indicating that 10-hydroxybenzo[h]-
˚
quinolate possesses high chelating ability as well as 8-hydro-
xyquinolate.
Synthesis of Polymers. Organoboron benzo[h]quinolate-
based monomer 2 was prepared from 10-hydroxybenzo[h]-
quinoline according to Scheme 2. Compound 2 was obtained
as a yellow solid analogous to the model compound when the
compound was purified by reprecipitation from methanol
and hexane. The monomer was stable under air and soluble
in dichloromethane and chloroform. The tetracoordination
state of the boron atoms in 2 was confirmed by the 11B NMR
spectroscopy in CDCl3 (δB = 6.06 ppm), which is similar to
the model compound. Moreover, the structure of 2 was also
1
fully characterized by H NMR, 13C NMR, and EI mass
spectroscopies and by elemental analysis.
Scheme 3 and Table 2 summarize the conditions and
results for the polymerization of monomer 2 with 1,4-diethy-
nylbenzene derivatives 3O or 3F in the presence of a catalytic
amount of Pd(PPh3)4 and CuI in the mixed solvent of
tetrahydrofuran (THF) and triethylamine. The obtained
polymers 4O and 4F were collected as yellow solids, and
their yields were 72% and 57%, respectively. The 11B NMR
spectra of the obtained polymers were observed at δB = 4.10
ppm (for 4O) and 4.30 ppm (for 4F) assignable to the
tetracoordination state of the boron atoms in each polymer,

6232 Macromolecules, Vol. 43, No. 14, 2010
Note
Figure 2. UV-vis spectra of polymers and model compound in CHCl3
(1.0 Â 10-5 M).
Emission data were obtained after exciting at the longest
wavelength of the absorption peaks; i.e., absorption maxima
of the polymers and the model compound are corresponding
to phenyleneethynylene and benzo[h]quinoline, respectively
(Figure S1). The spectra of the polymers 4O and 4F coin-
cided with its model compound 1, implying that the polymers
emit light from the benzo[h]quinolate moiety, and the poly-
mer side chains are nonresponsive to the wavelength of the
emission. Although the emission bands of the organoboron
benzo[h]quinolates were bathochromically shifted as com-
pared with BPh2q, the Stokes shifts of the former are smaller
than that of the latter. In addition, full widths at half-
maximum (FWHMs) of the organoboron benzo[h]quino-
lates were narrower than that of BPh2q. From these results, it
can be said that the benzo[h]quinolate ligand disturbs the
nuclear reorientation and oscillation in the transition state.
The photoluminescence property of the model compound 1
in different solvents (THF, DMSO, DMF, and acetonitrile)
was also examined. Shifts of the absorption spectra and
fluorescence spectra depend on the nature of the solvent,
and the solvent polarity greatly affected the Stokes shift. The
change in the Stokes shift (Δν) was roughly proportional to
the orientational polarizability (Δf) of the solvent, obey-
ing the dipole interaction theory of Lippert and Mataga
(Figure S2).22 On the basis of this analysis, it can be con-
cluded that the excitation of the organoboron benzo[h]-
quinolate 1 causes ILCT like organoboron quinolate, lead-
ing to the charge-separated state. Fluorescence excitation
spectra of the polymers in CHCl3 (c=1.0 Â 10-5 M) dis-
played the similar shapes as the UV-vis absorption spectra;
i.e., the strong absorption at π-conjugated linkers in the main
chain is crucial in photoluminescence (Figure S3). This
suggests that the energy transfer from the π-conjugated
linkers to the benzo[h]quinolate ligands on the boron centers
occurs, followed by photoluminescence from the ligands.
Absolute fluorescence quantum yields (ΦF) of the polymers
and the model compound in CHCl3 were measured by the
integrating sphere method. The quantum yield of 1 (ΦF =
0.10) is lower than that of BPh2q (ΦF = 0.47). The introduc-
tion of organoboron benzo[h]quinolate into the π-con-
jugated polymer main chain, however, enhances the quan-
tum yield (ΦF = 0.16 or 0.18). This would mean that
the bulky π-conjugated linkers prevent benzo[h]quinolate
quenching.
Figure 3. Molecular orbital diagrams for the HOMO and LUMO of
(A) 1 and (B) 5 (B3LYP/6-31G(d)//B3LYP/6-31G(d)).
ring with boron similar to the X-ray crystal structure. The
HOMO of 1 is located predominantly on the phenolate ring,
and the LUMO is mainly on the pyridinyl ring. This orbital
localization probably causes ILCT as shown in organobo-
ron quinolates. TD-DFT calculation reveals that HOMO-
LUMO transition occurs at 431 nm with small oscillator
strength ( f = 0.0618), and this peak position gives good
agreement with that of UV-vis spectra (420 nm). In com-
pound 5, which has π-conjugated linkers, the HOMO is not
on the benzo[h]quinolate ligand but localized on the one side
of the π-conjugated linker and the LUMO is localized on the
ligand (Figure 3B). This result supports that π-conjugation is
unable to extend through tetracoordinated boron and that
the π-conjugated linkers are irresponsible to the electronic
structure of the ligand. From the TD-DFT calculation,
major oscillator strength of 5 is above 1 at 390 nm ( f =
1.9901), and this absorption process predominantly consists
of the electronic transitions from orbitals on the linker to
other orbitals on the linker. This means that the absorption
peak of the polymer 4O at 373 nm is assignable to the
π-conjugated linker, and the electronic transition in the
linker can more easily take place in comparison with that
concerned with the benzo[h]quinolate ligand.
Molecular Orbital Calculations. To provide more effective
understanding for the photophysical behavior of the poly-
mers and the model compounds, we employed the theoretical
calculation for compounds 1 and 5 using density-functional
theory (DFT) and time-dependent DFT (TD-DFT) method
at the B3LYP/6-31G(d)//B3LYP/6-31G(d) level.23 Figure
3A exhibits HOMO and LUMO of the compound 1. The
geometry optimization of 1 provided the puckered chelate
Conclusion
We have successfully prepared the novel low-molecular-mass
organoboron benzo[h]quinolate complexes (model compound)

Note
Macromolecules, Vol. 43, No. 14, 2010 6233
and the main-chain-type organoboron benzo[h]quinolate poly-
mers. These polymers were obtained by Sonogashira-Hagihara
coupling in moderate yields. The emission of the organoboron
benzo[h]quinolate was responsible for ILCT and shifted to longer
wavelength as compared with BPh2q. Emission behavior of the
polymers was originated from efficient energy transfer from
π-conjugated main chain to benzo[h]quinolate ligand, and they
showed no difference in the emission between donating π-con-
jugated linker and accepting one. Low-molecular-mass organo-
boron benzo[h]quinolate displayed moderate fluorescence quan-
tum yield (ΦF = 0.10), and the polymers containing that showed
higher quantum yield (ΦF = 0.16 or 0.18).
(10) Nagata, Y.; Otaka, H.; Chujo, Y. Macromolecules 2008, 41,
737–740.
(11) Tokoro, Y.; Nagai, A.; Kokado, K.; Chujo, Y. Macromolecules
2009, 42, 2988.
(12) Chen, K.-Y.; Hsieh, C.-C.; Cheng, Y.-M.; Lai, C.-H.; Chou, P.-T.
Chem. Commun. 2006, 4395.
(13) Higashi, T. ABSCOR. Program for Absorption Correction,
Rigaku Corp., Japan, 1995.
(14) Sheldrick, G. M. SHELX-97. Programs for Crystal Structure
€
Analysis, University of Gottingen, Germany, 1997.
(15) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori,
G.; Spagna, R. J. Appl. Crystallogr. 1999, 32, 115.
(16) Wakita, K. Yadokari-XG. Program for Crystal Structure Analysis,
2000.
(17) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
(18) Dick, A. R.; Hull, K. L.; Sanford, M. S. J. Am. Chem. Soc. 2004,
126, 2300.
(19) Swager, T. M.; Gil, C. J.; Wrighton, M. S. J. Phys. Chem. 1995, 99,
4886.
Supporting Information Available: Emission and excitation
spectra, Lippert plot, and crystallographic data in CIF format.
This material is available free of charge via the Internet at
http://pubs.acs.org.
(20) Kokado, K.; Chujo, Y. Macromolecules 2009, 42, 1418.
(21) Egbe, D. A. M.;Roll, C. P.;Brickner, E.;Grummt, U.-W.;Stockmann,
R.; Klemm, E. Macromolecules 2002, 35, 3825.
References and Notes
(1) Haugland, R. P. In The Handbook;A Guide to Fluorescent Probes
and Labeling Technologies, 10th ed.; Spence, M. T. Z., Ed.; Molecular
Probes: Eugene, OR, 2005; Chapter 1, Section 1.4.
(2) Gorman, A.; Killoran, J.; O’Shea, C.; Kenna, T.; Gallagher,
W. M.; O’Shea, D. F. J. Am. Chem. Soc. 2004, 126, 10619.
(3) (a) Garcıa-Moreno, I.; Costela, A.; Campo, L.; Sastre, R.; Amat-
(22) (a) Lippert, E. Z. Electrochemistry 1957, 61, 962. (b) Mataga, N.;
Kaifu, Y.; Koizumi, M. Bull. Chem. Soc. Jpn. 1956, 29, 465.
(23) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi,
J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.;
Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.;
Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.;
Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian,
H. P.; Cross, J. B.; Adamo, C.; Jaramillo, J.; Gomperts, R.;
Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli,
C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.;
Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.;
Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck,
A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.;
Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox,
D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong,
M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, revision D.01;
Gaussian, Inc.: Wallingford, CT, 2004.
ꢀ
Guerri, F.; Liras, M.; Lopez Arbeloa, I. J. Phys. Chem. A 2004, 108,
3315. (b) Pavlopoulos, T. G.; Boyer, J. H.; Sathyamoorthi, G. Appl.
Opt. 1998, 37, 7797.
(4) Wu, Q.; Esteghamatian, M.; Hu, N.-X.; Popovic, Z.; Enright, G.;
Tao., Y.; D’Iorio, M.; Wang, S. Chem. Mater. 2000, 12, 79.
(5) Tang, C. W.; Vanslyke, S. A. Appl. Phys. Lett. 1987, 51, 913.
(6) (a) Cheng, Y. M.; Yeh, Y. S.; Ho, M. L.; Chou, P. T.; Chen, P. S.;
Chi, Y. Inorg. Chem. 2005, 44, 4594. (b) Shi, Y.-W.; Shi, M.-M.;
Huang, J.-C.; Chen, H.-Z.; Wang, M.; Liu, X.-D.; Ma, Y.-G.; Xu, H.;
Yang, B. Chem. Commun. 2006, 1941.
€
(7) (a) Qin, Y.; Pagba, C.; Piotrowiak, P.; Jakle, F. J. Am. Chem. Soc.
€
2004, 126, 7015. (b) Qin, Y.; Kiburu, I.; Shah, S.; Jakle, F. Macro-
molecules 2006, 39, 9041.
(8) Wang, X.-Y.; Weck, M. Macromolecules 2005, 38, 7219.
(9) Nagata, Y.; Chujo, Y. Macromolecules 2007, 40, 6.