Preparation and luminescence properties of polymeric 2,5-bis[2′-(8″-alkoxyquinolin-2″-yl)ethenyl]hydroquinone derivatives

Article abstract of DOI:10.1071/CH02112

A PPV-type polymer (1) incorporating 5,5′-diquinolinyl moieties is prepared by a Yamamoto homo-coupling reaction from the dibromide (2). Since all the hydroxyl groups were alkylate this polymer showed high solubility in most organic solvents. It can be sp

Full text of DOI:10.1071/CH02112

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Aust. J. Chem. 2002, 55, 499–504
Preparation and Luminescence Properties of Polymeric
2,5-Bis[2´-(8´´-alkoxyquinolin-2´´-yl)ethenyl]hydroquinone Derivatives
Ming-Ann HsuA and Tahsin J. ChowA,B
A Institute of Chemistry, Academia Sinica, Taipei, Taiwan 115, Republic of China.
B Visiting Scholar, Institute for Fundamental Research of Organic Chemistry, Kyushu University, Fukuoka, Japan.
Author to whom correspondence should be addressed (e-mail: tjchow@chem.sinica.edu.tw).
A PPV-type polymer (1) incorporating 5,5´-diquinolinyl moieties is prepared by a Yamamoto homo-coupling
reaction from the dibromide (2). Since all the hydroxyl groups were alkylated, this polymer showed high solubility
in most organic solvents. It can be spin-coated readily to form a thin layer in the fabrication of light emitting diode
(LED) devices. The adjacent quinoline rings are twisted to form a dihedral angle due to steric hindrance, so that
π-conjugation is confined within each monomer unit. The emission spectra of (1) and (2) are nearly identical. The
reduction potential of (1) was estimated to be –1.10 V (onset), with a band gap of 2.53 eV (490 nm). A single
hetero-junction LED device fabricated by combining the films of poly(vinylkarbazol) (PVK) and (1) yielded
promising results. The device ITO/PVK/(1)/Ca/Al exhibited a turn-on voltage at 6 V and reached a maximal
brightness of 250 cd/m2 at 15 V. An alternate potential usage of (1) as an electron-injecting material was also
explored on a green-light device using coumarin-6 as an emitter.
Manuscript received: 29 May 2002.
Final version: 1 August 2002.
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Introduction
of (1) on the fabrication of organic light emitting diode
(OLED) devices is examined, both as an emitting material
and as an electron-transporter.
Designing organic materials for the fabrication of light
emitting diodes (LED) has been a area of intensive research
interest.[1] Following the pioneer works of Tang,[2]
a
tremendous amount of effort has gone into the development
of new materials and devices.[3] The fabrication of multilayer
structures and the usage of dopants has been quite successful
for producing LED devices of high quantum efficiency and
good stability.[4] The discovery by Friend using single-layer
poly(p-phenylenevinylene) (PPV) as an emitting material
represented another major breakthrough,[5] for it became
possible to produce large and flexible display devices at low
cost by a spin-coating technique. Further improvements on
device performance is still in demand through structural
modifications on organic polymers.[6] In particular,
polymers containing heterocycles such as pyrroles,
pyridines, and thiophenes have been found to exhibit
characteristic electrochemical effects. Due to their intrinsic
electron-withdrawing property and good thermal stability,
polymers containing a quinoline moiety have attracted
extensive interest.[7] In this report we describe the
preparation of a PPV-type polymer (1) (see Diagram 1)
containing 8-alkoxyquinoline moieties along the main chain.
Although tris(8-hydroxyquinolinato)aluminum (Alq3) has
been widely used as an effective electron-transporting
material, polymeric materials incorporating alkoxyquinoline
groups have not yet been fully investigated. The performance
n
O
OCH2Ph
N
N
OCH2Ph
O
(1)
Diagram 1
Results and Discussion
Synthesis
Polymer (1) can be envisioned as a modified derivative of
PPV in which some phenyl groups along the main chain are
replaced by 8-alkoxyquinoline moieties. It was synthesized
from the dibromide (2) through Yamamoto coupling,[8]
whereas (2) was prepared by a double Wittig reaction
condensing two units of hydroxquinolinylcarbaldehyde (7)
and one unit of p-hydroquinone-2,5-dicarbophosphonium
© CSIRO 2002
10.1071/CH02112
0004-9425/02/080499

500
M.-A. Hsu and T. J. Chow
yield. Connecting (7) and (11) was completed successfully
by a double Wittig reaction to give (2). The twofold
R
R
1
symmetry of the structure persisted as indicated by H and
N
13C NMR signals.
N
CHO
OCH2Ph
Polymerization of (2) was carried out by a Yamamoto
homo-coupling reaction of aromatic halides utilizing
Ni(COD)2 in the presence of 2,2´-bipyridyl and
cyclo-1,5-octadiene. The polymer was collected as an orange
product in 54% yield. It showed a number-averaged
molecular weight of 2.3 × 104 (Mn) and a weight-averaged
molecular weight of 3.8 × 104 (Mw), with a polydispersity
(Mw/Mn) of 1.67. It is readily soluble in most organic
solvents, such as tetrahydrofuran (THF), benzene, and
dichloromethane. This material shows a glass transition
temperature (Tg) of 210°C by differential scanning
calorimetry (DSC) analysis. The structure of (1) was
confirmed by IR and NMR spectra. It exhibits good thermal
stability, since no apparent decomposition can be observed
up to 350°C under an oxygen atmosphere.
OR'
(6) R = H
(7) R = Br
(3) R = R' = H
(4) R = H; R' = CH2Ph
(5) R = Br; R' = CH2Ph
OR'
R
(8) R = R' = H;
(9) R = H; R' = 2-ethylhexyl
(10) R = CH2Br; R' = 2-ethylhexyl
R
(11) R = CH2PPh3Br; R' = 2-ethylhexyl
OR'
(7)
Br
Physical Properties
O
The two adjacent quinoline rings, which are coupled by Ni,
cannot be kept co-planar due to steric hindrance. The
situation is similar to what happened for the structure of
binaphthyl. Electron delocalization across two adjacent
quinoline rings is limited, therefore the spectroscopic
property of (1) is expected to be analogous to that of (2).[9]
The ultraviolet (UV) absorption spectra of (1) and (2) are
nearly identical (Fig. 1), indicating a close resemblance
between these two chromophores. The emission spectra of
the two also showed high similarity. Both emit blue light at
OCH2Ph
N
N
OCH2Ph
O
Br
(2)
Scheme 1
bromide (11). The complete synthetic sequence is shown in
Scheme 1.
λ
em 490 nm with good quantum yields, i.e. 0.27 for (1) and
0.42 for (2) (Fig. 1).
The hydroxy group of 8-hydoxy-2-methylquinoline (3)
was first converted into a benzyl group in (4). The
subsequent transformation of (4) to (7) was accomplished
through either of two pathways. The first way is to brominate
first at C5 of (4), followed by oxidation of the methyl group
at C2. The second way is to go through a reverted sequence,
i.e. oxidation first followed by bromination. Both pathways
are applicable, yet the former sequence resulted in a slightly
higher overall yield. Bromination was achieved using
N-bromosuccinimide (NBS), while oxidation was achieved
using selenium dioxide in 1,2-dimethoxyethane (DME).
Compound (7) was collected as yellowish crystals, of which
the aldehyde group was confirmed by a stretching at 1710
UV-vis of (1)
UV-vis of (2)
PL of (1)
PL of (2)
PL of (1) film
1.2
1.0
0.8
0.6
0.4
0.2
0.0
cm–1 in the infrared (IR) and an signal at δ 193.5 in the 13
C
nuclear magnetic resonance (NMR) spectrum.
200
250
300
350
400
450
500
550
600
650
700
Another segment of compound (2) was prepared starting
from hydroquinone (8). Both the hydroxyl groups of (8) were
alkylated to give (9) by heating an ethanolic solution of
excess 2-ethylhexyl bromide in the presence of sodium
hydroxide. Subsequent bromomethylation was accomplished
by a reaction with paraformaldehyde in the presence of HBr
in acetic acid. The symmetrical structure of (10) was
evidenced by the number of 13C peaks, e.g. three lines
appeared in the aromatic region. Heating (10) with
triphenylphosphine produced (11) in nearly quantitative
Wavelength (nm)
Fig. 1. The absorption (left with λmax 427 nm) and emission
(middle with λem 490 nm) spectra of (1) and (2), where PL indicates
photoluminescence in THF. The broadband emission on the right (λem
573 nm) came from the solid film of (1).
The ethylhexyl and benzyl groups attached to the oxygen
atoms of (1) were intended to help increase the solubility of
the polymer. The solution of (1) therefore, can be easily
spin-coated to form thin layers. It was also expected that the

Preparation and Luminescence Properties of a PPV-Type Polymer
501
ethylhexyl side chains would be able to prevent local
crystallization and aggregation while forming films. It was
known that local crystallization may reduce the quantum
yield of emission, and aggregation may result in both
quenching as well as band broadening of luminescence.
Although with such a design, it was unfortunate to see that
the emission from the solid film of (1) did show a significant
band broadening (Fig. 1). A broad new emission band at λem
573 nm was observed, which seems to be induced from some
aggregated phase existing in the solid state.[10]
which reduced the quantum efficiency of the device. A
current versus voltage (I–V) plot of this device is shown in
Figure 2. The current density increased steadily with
increased applied voltage.
AsshownbyCV,thelowreductionpotentialof(1)rendered
it a good electron-transporting material. In order to enhance
light emission, it seemed necessary to add a layer of
hole-transporter. Chargerecombinationattheinterfaceoftwo
layers should result in more effective luminescence. Two
commonly used hole-transporting materials, poly(vinyl-
karbazol) [poly(carbazolylethylene), PVK] and 4,4´-bis[N-
(1-naphthyl)-N-phenylamino]biphenyl (NPB), are con-
sidered in this regard. Three additional devices were then
assembled, i.e. ITO/PVK/(1)/Ca/Al, ITO/PVK:(1)(3%)/
(1)/Ca/Al, and ITO/NPB:(1)(3%)/(1)/ Ca/Al, in order to find
out the optimal fabrication. Solutions of PVK (or NPB) in
1,2-dichloroethane were spin-coated onto ITO first. After
sufficient drying in vacuum, a layer of (1) in toluene was
spin-coated on top of the first layer. The amount of PVK (or
NPB) re-dissolved in toluene during the second spin-coating
process was limited due to its low solubility.
All three devices displayed electroluminescence upon
applied voltage, while the spectra appeared identical to the
photoluminescence of (1) in solution (Fig. 1). It was remark-
able to observe the absence of broadband emission at λem
578 nm, which was derived presumably from aggregation.
Upon the introduction of a hole-transporting layer, the
charge recombination happened more effectively at the
interface between two polymer layers. This phenomenon is
also evidenced by the absence of short-wavelength emission
of PVK (or NPB), which indicated that the charge
recombination did not happen within the bulk of the PVK
layer.
The redox behaviour of (1) was examined by cyclic
voltammetry (CV) using a Pt working electrode on which a
thin layer of the polymer was coated. Both reduction and
oxidation waves were observed within the range of 2.00 V.
A
reduction peak appeared at –1.42 V, which is
quasi-reversible and can be back-oxidized at –0.70 V. An
oxidation peak appeared at +1.00 V, which is irreversible.
The band gap thus measured is consistent with that measured
on UV absorption (2.53 eV) within experimental
uncertainty. The oxidative potential can be correlated to
HOMO and LUMO levels by the equation IP = Ered – Eg +
4.40 eV,[11] whereas –5.63 and –3.10 eV were depicted from
the reduction onset (–1.30 V) of (1), respectively. These
values are useful in designing LED device configuration.
Compared with the known values of poly(2-methoxy-5-(2´-
ethylhexoxy)-1,4-phenylenevinylene) (MEH-PPV) (–4.99
and –2.71 eV), our polymer has a wider band gap, yet is
easier to reduce.
600
500
400
300
200
100
0
Among the three devices, the one without blending
performed the best, i.e. ITO/PVK/(1)/Ca/Al. This device can
be turned on at 6 V, and reached a maximum intensity of
250 cd/m2 at 15 V (Fig. 3). Its optimal quantum efficiency
was estimated to be 0.020% at 9 V.
1200
250
0
2
4
6
8
10 12 14 16 18 20 22 24
Current density
Brightness
1000
800
600
400
200
0
Bias (V)
200
150
100
50
Fig. 2. The I–V plot for the device ITO/(1)/Al, which showed a
turn-on voltage of 9 V. The brightness of this device was low
(< 3 cd/m2).
LED Fabrication
A single-layer LED device was fabricated by spin-coating a
toluene solution of (1) (10 g/L) onto pre-treated indium tin
oxide (ITO) glass. The film was then dried under vacuum,
where it looked uniform and without pinholes. The film was
then covered by a layer of aluminum (to act as a cathode) by
vapour deposition. This simple device started emitting at 9 V,
but with low intensity. The emission spectrum was quite
close to that of the photoluminescence of the solid film
(Fig. 1). It was evident that aggregation appeared in the film,
0
0
2
4
6
8
10
12
14
16
18
20
Bias (V)
Fig. 3. The L(᭿)–I(᭺)–V plot for the device ITO/PVK/(1)/Ca/Al.
The turn-on voltage is 6 V, while brightness reached a maximum
intensity of 250 cd/m2 at 15 V along with current density of
830 mA/cm2. The optimal quantum efficiency was 0.020% at 9 V. A
small current appearing at ca. 4 V was a spurious signal caused by
initial charging of the device.

502
M.-A. Hsu and T. J. Chow
The ITO substrates were then treated with oxygen plasma for 1 min
before use. Polymer films were spin-coated at 3000 rpm onto the
substrate from a solution of the emitting material in toluene. The
devices were placed under vacuum (4 × 10–4 torr) for 12 h to remove
residual solvents. A 30 nm cathode layer was deposited by evaporation
of Ca at 2 × 10–5 torr. The device was completed by capping with an Al
layer with 120 nm thickness.
The electron-transporting property of (1) attracted our
attention for it to be used in a wider range of applications. We
went on testing the possibility by assembling it into a known
LED device, i.e. the green-light device of coumarin-6. Two
devices were fabricated for a comparison: (i) one without the
addition of (1) as standard, ITO/coumarin-6(0.5%): PVK/Al;
and (ii) one with an added layer of (1), ITO/
coumarin-6(0.5%):PVK/(1)/Al. Both devices successfully
displayed the green emission of coumarin-6 (Fig. 4). The
latter one with an added layer of (1) performed much better
than the standard. Its turn-on voltage at 8.5 V is lower than
the standard at 11.5 V. At 14–16 V it showed a maximum
brightness of 48 cd/m2, which was about 10 times that of the
standard, i.e. 5 cd/m2 at 16 V. This experiment showed that
polymer (1) can be used in the fabrication of OLED devices,
not only as an effective emitting material, but also as a good
electron-transporting material.
Instrumentation
1H and 13C NMR spectra were obtained on a Brucker APX-400
1
spectrometer. Chemical shifts of H were measured downfield from
tetramethylsilane (0) in δ units, while those of 13C were recorded with
the central peak of CDCl3 at δ 77.00 as an internal reference. Mass
spectra (MS) were carried out on a VG70-250S or a VG Trio-2000
spectrometer. Infrared spectra were recorded on a Perkin-Elmer 682
infrared spectrophotometer. Absorption and emission spectra were
recorded on a Hewlett–Packard 8453 absorption and a Hitachi F-4500
fluorescence spectrophotometer, emission quantum yields were
measured with reference to 9,10-diphenylanthracene. Elemental
analyses were obtained on a Perkin–Elmer 2400 CHN instrument.
Melting Points were measured by a Thomas–Hoover melting point
(m.p.) apparatus and were uncorrected. Light–current–voltage intensity
(L–I–V) of LEDs were measured using a Keithley 2400 source meter
and a Newport 1835C multifunction optical meter, equipped with a
silicon photodiode (Newport, model 818-ST). The measurements of
I–V–L were performed simultaneously through an IEEE interface to a
computer. All measurements were made at ambient temperature and
conditions.
50
ITO/C-6:PVK/Al
40
30
20
10
0
ITO/C-6:PVK/(1)/Al
1,4-Di(2´-ethylhexyloxy)-2,5-bis[2´-(8´-benzyloxy-5´-bromoquinolin-
2´-yl)ethenyl]benzene (2)
To a Schlenk flask (100 mL) were added compounds (7) (0.99 g,
2.9 mmol) and (11) (1.4 g, 1.3 mmol) under a nitrogen atmosphere. To
this was added freshly distilled DMF (5 mL) injected through a syringe,
followed by sodium ethoxide (0.20 g, 2.9 mmol) against a nitrogen flow.
The colour of the mixture turned from pale yellow to red. It was stirred
with a magnetic bar at ambient temperature for 24 h while its colour
changed gradually to orange-yellow. The mixture was poured into
distilled water, and was extracted three times with dichloromethane
(50 mL each). The combined organic portion was dried over anhydrous
Na2SO4, and was concentrated. The orange residue was acidified with
conc. HCl (36%, 0.5 mL). The brick-red precipitate was washed with
ether to remove triphenylphosphine oxide. The remaining salt was
dissolved in THF, and neutralized with saturated NaHCO3 to give a
yellow-green mixture. It was extracted several times with
dichloromethane. The combined organic layer was dried over
anhydrous Na2SO4, and was evaporated under vacuum. The residue was
subjected to a silica gel chromatographic column eluted with
hexane/ethyl acetate (2:1) to yield (2) as a yellow-orange solid. It was
recrystallized from cyclohexane (850 mg, 0.84 mmol, 65% yield); m.p.
178–179°C. IR (KBr) νmax 3452(br), 3063, 2957, 2927, 2869, 1592,
1500, 1453, 1390, 1221, 1202, 1000 cm–1. 1H NMR (CDCl3) δ 0.95, m,
6H; 1.04, m, 6H; 1.35–1.50, m, 8H; 1.35–1.75, m, 8H; 1.91, m, 2H;
4.01, d, J 6 Hz, 4H; 5.51, s, 4H; 6.90, d, J 8 Hz, 2H; 7.30–7.35, m, 2H;
7.30–7.45, m, 6H; 7.50–7.60, m, 6H; 7.65, d, J 17 Hz, 2H; 7.92, d, J
9 Hz, 2H; 8.06, d, J 17 Hz, 2H; 8.46, d, J 9 Hz, 2H. 13C NMR (CDCl3)
δ 11.57, 14.38, 23.39, 24.59, 27.16, 29.48, 31.20, 40.00, 71.45, 72.16,
110.51, 111.93, 112.73, 119.91, 127.17, 127.29, 127.53, 128.10,
128.88, 129.62 (2C), 136.05, 137.03, 141.45, 151.85, 154.19, 156.66.
MS (FAB) m/z 1010 (M+, 15%).
0
2
4
6
8
10
12
14
16
18
Bias (V)
Fig. 4. TheL–VplotforthedevicesITO/coumarin-6(0.5%):PVK/Al
(ᮀ) and ITO/coumarin-6(0.5%):PVK/(1)/Al (᭿).
Conclusion
The alkoxy side chains of polymer (1) increased its solubility
in organic solvents, allowing films to be prepared readily by
spin coating. The 5,5´-attachment of two adjacent quinoline
moieties resulted in their rings being twisted out of plane,
and therefore confined the conjugation within each
monomer unit. The absorption and emission spectra of (1)
are similar to those of (2). A LED device fabricated by two
layers of polymers, i.e. ITO/PVK/(1)/Ca/Al, exhibited
promising results; it showed a turn-on voltage at 6 V and
maximum brightness 250 cd/m2 at 15 V. Polymer (1) showed
a low reductive potential on CV, which rendered it a good
electron-transporting material. It can be fabricated into LED
devices using coumarin-6 as the emitting material, in which
it functions as an effective electron-injection layer.
Experimental
Polymerization of (2)
Device Fabrication
To a Schlenk flask was added compound (2) (300 gm, 0.30 mmol),
Ni(COD)2 (130 mg, 0.47 mmol), 2,2´-bipyridyl (81 mg, 0.52 mmol)
and cycloocta-1,5-diene (COD, 0.10 mL) under a nitrogen atmosphere.
To this was added freshly distilled DMF (10 mL) injected through a
syringe, and the resulting mixture was stirred at 80°C for 24 h. It was
poured into methanol (200 mL), and an orange precipitate formed. The
Prepatterned ITO substrates with an effective individual device area of
3.14 mm2, and sheet resistance of < 50 ohms/mm2, were cleaned by
sonication in a detergent solution for 3 min and then washed with a
large amount of doubly distilled water. Further sonication in ethanol for
3 min was performed before being blown dry with a stream of nitrogen.

Preparation and Luminescence Properties of a PPV-Type Polymer
503
precipitate was dissolved in dichloromethane, and re-solidified by
pouring into methanol. This processes was repeated twice. The
resulting polymer was extracted with acetone (100 mL) for 24 h using
a Soxhlet extractor to remove contaminated monomer and oligomers of
low molecular weight. Polymer (1) (0.136 gm) was collected in 54%
yield; Tg 210°C and Td 326°C. IR (KBr) νmax 3400(br), 3032, 2923,
2927, 2865, 1596, 1557, 1498, 1449, 1376, 1312 cm–1. 1H NMR
(CDCl3) δ 0.86, br s, 6H; 0.95, br s, 6H; 1.33, br s, 8H; 1.50, br s, 8H;
1.82, br s, 2H; 3.99, br s, 4H; 5.44, br s, 4H; 7.24, br s, 2H; 7.30–7.80,
br m, 20H; 8.20, br s, 2H. 13C NMR (CDCl3) δ 11.58, 14.42, 23.65,
24.83, 29.72, 31.41, 40.33, 71.68, 72.41, 110.43, 110.76, 119.24,
127.47, 128.48, 128.71, 129.27, 130.06, 130.32, 135.20, 137.69,
140.94, 152.11, 154.97, 156.13.
1,4-Di(2´-ethylhexyloxy)benzene (9)
A solution of hydroquinone (8) (17.6 g, 0.16 mol) and KOH (25.6 g,
0.457 mol) in ethanol (150 mL) was heated to reflux, and 2-ethylhexyl
bromide (92.5 g, 0.48 mol) was added. The mixture was heated
overnight under a nitrogen atmosphere. The precipitates were filtered
after being cooled. The filtrate was concentrated, and was passed
through a silica gel chromatographic column eluted with hexane/ethyl
acetate (v/v, 10:1) to remove unreacted hydroquinone. All non-polar
portions were combined and the resulting solution was distilled under
reduced pressure. Compound (9) was collected at 128°C at 0.1 torr
(41.7 g, 0.125 mol) in 78% yield. IR (KBr) νmax 2960, 2931, 2862,
1509, 1469, 1381, 1229 cm–1. 1H NMR (CDCl3) δ 0.92, m, 12H;
1.33–1.69, m, 16H; 1.71, m, 2H; 3.81, d, J 9 Hz, 4H; 6.84, s, 4H. 13C
NMR (CDCl3) δ 11.32, 14.29, 23.29, 24.10, 29.33, 30.78, 39.72, 71.45,
115.61, 153.70. MS (EI) m/z 334 (M+, 50%), 222 (12).
8-Benzyloxy-5-bromo-2-methylquinoline (5)
2,5-Di(bromomethyl)-1,4-di(2´-ethylhexyloxy)benzene (10)
To
a
round-bottom flask were added
a
solution of
To a round-bottomed flask containing (9) (20 g, 60 mmol) and
paraformaldehyde (4.0 g, 130 mmol) in acetic acid (50 mL) was added
a solution of HBr (33% in acetic acid, 26 mL, 150 mL). The mixture
was stirred with a magnetic bar at 100°C for 8 h, while a white
precipitate formed. The mixture was poured into distilled water, and the
precipitate was collected by filtration. The precipitate was dissolved in
dichloromethane, and the solution was washed with saturated NaHCO3.
The organic layer was separated, dried over anhydrous Na2SO4, and
concentrated under vacuum. The residue was recrystallized from
dichloromethane/methanol to give (10) (30 g, 58 mmol, 96% yield) as
a white solid, m.p. 59–61°C. IR (KBr) νmax 2960, 2921, 2872, 1509,
1469, 1411, 1317, 1229 cm–1. 1H NMR (CDCl3) δ 0.93, m, 12H; 1.34,
br s, 8H; 1.34–1.55, m, 8H; 1.78, m, 2H; 3.87, m, 4H; 4.53, s, 4H. 13C
NMR (CDCl3) δ 11.47, 14.31, 23.28, 24.27, 28.96, 29.35, 30.87, 39.85,
71.20, 114.49, 127.63, 153.96. MS (EI) m/z 520 (M+, 5%), 441 (6), 329
(10), 296 (12), 217 (15).
8-benzyloxy-2-methylquinoline (4) (1.00 g, 4.0 mmol) and NBS (1.4 g,
8.0 mmol) in chloroform (10 mL). The solution was stirred with a
magnetic bar at ambient temperature for 5 h, while the reaction was
monitored by thin-layer chromatography (TLC) till completion. It was
poured into distilled water (30 mL), and the resulting mixture was
extracted several times with dichloromethane. The combined organic
layer was dried over anhydrous Na2SO4, and concentrated under
vacuum. Compound (5) was isolated using a silica gel chromatographic
column eluted with hexane/ethyl acetate (v/v, 6:1), and was crystallized
from hexane to give a colourless wool-like solid (1.2 g, 3.6 mmol) in
91% yield, m.p. 108–109°C (Found: C, 62.2; H, 4.3; N, 4.3%.
C17H14BrNO requires C, 62.8; H, 4.1; N, 4.1%). IR (KBr) νmax 3063,
3034, 2930, 2871, 1593, 1499, 1462, 1379, 1315, 1238, 1093 cm–1. 1H
NMR (CDCl3) δ 2.89, s, 3H; 5.46, s, 2H; 6.90, d, J 8 Hz, 1H; 7.31, d, J
7 Hz, 1H; 7.38, t, J 7 Hz, 2H; 7.44, d, J 8 Hz, 1H; 7.51, d, J 7 Hz, 2H;
7.57, d, J 8 Hz, 1H; 8.41, d, J 8 Hz, 1H. 13C NMR (CDCl3) δ 25.29,
53.62, 111.71, 112.41, 124.04, 126.96, 127.29, 128.14, 128.85, 129.53,
136.68, 159.19. MS (EI) m/z 329 (M+, 5%), 252 (3), 239 (3), 223 (5),
210 (5).
1,4-Di(2´-ethylhexyloxy)-2,5-bis[(triphenylphosphonio)methyl]-
benzene Dibromide (11)
To a Schlenk flask (100 mL) fitted with a condenser was added (10)
(5.2 g, 10.0 mmol) and triphenyl phosphine (5.8 g, 22 mmol) under a
nitrogen atmosphere. To this was added freshly distilled DMF (40 mL)
injected through a syringe, and the resulting solution was heated to
reflux for 2 h. The solution was cooled and poured dropwise into ether,
which was vigorously stirred. A white precipitate formed and was
collected by filtration. It was dried under vacuum to give (11) (10.2 g,
9.8 mmol) in 98% yield, m.p. 263–266°C (dec.). IR (KBr) νmax
3400(br), 3058, 2960, 2931, 2862, 2774, 1587, 1514, 1435, 1313, 1219,
1111 cm–1. 1H NMR (CDCl3) δ 0.67, t, J 7 Hz, 6H; 0.88, t, J 7 Hz, 6H;
0.95–1.05, m, 16H; 1.22, m, 2H; 2.87, br s, 4H; 5.31, m, 4H; 7.60, m,
12H; 7.65, m, 12H; 7.76, t, J 7 Hz, 6H. 13C NMR (CDCl3) δ 14.20,
22.98, 23.40, 29.09, 30.26, 39.02, 70.82, 115.88, 116.37, 117.56,
118.42, 130.25, 134.25, 135.01, 150.86. MS (EI) m/z 1015 (0.2%), 965
([M–Br]+, 0.5%), 899 (0.5), 882 ([M–2Br]+, 2.5), 823 (1.2).
8-Benzyloxy-5-bromoquinoline-2-carbaldehyde (7)
Method A. To a round-bottom flask were added a solution of
8-benzyloxyquinoline-2-carbaldehyde (6)[12] (0.50 g, 1.9 mmol) and
NBS (0.68 g, 3.8 mmol) in chloroform (10 mL). The solution was
stirred with a magnetic bar at ambient temperature for 48 h, while the
reaction was monitored by TLC till completion. It was poured into
distilled water (30 mL), and the resulting mixture was extracted several
times with dichloromethane. The combined organic layer was dried
over anhydrous Na2SO4, and concentrated under vacuum. Compound
(7) was isolated using a silica gel chromatographic column eluted with
hexane/ethyl acetate (v/v, 6:1), and was crystallized from
hexane/dichloromethane to give yellowish crystals (0.46 g, 1.35 mmol)
in 71% yield.
Method B. To a Schlenk flask a DME (50 mL) solution of
compound (5) (3.3 g, 1.00 mmol) and SeO2 (1.4 g, 33 mmol) was
injected through a syringe under nitrogen atmosphere. The mixture was
heated to 80°C for 2 h while a red precipitate formed. The solution was
filtered through Celite and the filtrate was concentrated under vacuum.
Product (7) was collected using a silica gel chromatographic column
eluted with hexane/ethyl acetate (v/v, 6:1) in 82% yield (2.8 g,
0.82 mmol).
Physical data of (7). M.p. 114–115°C (Found: C, 68.5; H, 5.9; N,
2.5%. C17H12BrNO2 requires C, 68.9; H, 6.2; N, 2.8%). IR (KBr) νmax
3058, 2950, 2891, 2841, 1710, 1602, 1558, 1499, 1460 cm–1. 1H NMR
(CDCl3) δ 7.03, d, J 8 Hz, 1H; 7.35, d, J 7 Hz, 1H; 7.41, t, J 7 Hz, 2H;
7.54, d, J 7 Hz, 2H; 7.78, d, J 8 Hz, 1H; 8.14, d, J 8 Hz, 1H; 8.64, d, J 8
Hz, 1H; 10.71, s, 1H. 13C NMR (CDCl3) δ 71.50, 111.77, 112.47,
119.03, 127.30, 128.40, 128.96, 130.35, 132.98, 136.25, 137.30,
141.19, 151.97, 155.15, 193.47. MS (EI) m/z 343 (M+, 10%), 214 (2),
253 (2), 237 (2), 196 (10).
Acknowledgments
Financial support from Academia Sinica and the National
Science Council of the Republic of China is gratefully
acknowledged.
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