Comparative syntheses of arylamine monomer with styrylpyridyl photo-crosslinker of polyarylamine for OLED hole-injection material

Article abstract of DOI:10.1080/15421406.2010.499316

A new arylamine monomer with photo-crosslinkable styrylpyridinyl moiety of conjugated polyarylamine for OLED hole injection material was synthesized through two synthetic routes, BOC-amine protection/deprotection and nitro group reduction methods. Both sy

Full text of DOI:10.1080/15421406.2010.499316

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Comparative Syntheses of Arylamine
Monomer with Styrylpyridyl Photo-
Crosslinker of Polyarylamine for OLED
Hole-Injection Material
Heung-Jin Choi a , Moo-Gon Song a , Youn-Hee Sim b , Heung-Kwon
Bae b , Jin-Woo Kim b & Lee Soon Park b c
a Department of Applied Chemistry , Kyungpook National University ,
Daegu, Korea
b Department of Polymer Science , Kyungpook National University ,
Daegu, Korea
c Advanced Display Manufacturing Research Center, Kyungpook
National University , Daegu, Korea
Published online: 14 Nov 2010.
To cite this article: Heung-Jin Choi , Moo-Gon Song , Youn-Hee Sim , Heung-Kwon Bae , Jin-Woo
Kim & Lee Soon Park (2010) Comparative Syntheses of Arylamine Monomer with Styrylpyridyl Photo-
Crosslinker of Polyarylamine for OLED Hole-Injection Material, Molecular Crystals and Liquid Crystals,
531:1, 47/[347]-54/[354], DOI: 10.1080/15421406.2010.499316
To link to this article: http://dx.doi.org/10.1080/15421406.2010.499316
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Mol. Cryst. Liq. Cryst., Vol. 531: pp. 47=[347]–54=[354], 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421406.2010.499316
Comparative Syntheses of Arylamine Monomer
with Styrylpyridyl Photo-Crosslinker of
Polyarylamine for OLED Hole-Injection Material
HEUNG-JIN CHOI,1 MOO-GON SONG,1
YOUN-HEE SIM,2 HEUNG-KWON BAE,2
JIN-WOO KIM,2 AND LEE SOON PARK2,3
1Department of Applied Chemistry, Kyungpook National University,
Daegu, Korea
2Department of Polymer Science, Kyungpook National University,
Daegu, Korea
3Advanced Display Manufacturing Research Center, Kyungpook
National University, Daegu, Korea
A new arylamine monomer with photo-crosslinkable styrylpyridinyl moiety of
conjugated polyarylamine for OLED hole injection material was synthesized
through two synthetic routes, BOC-amine protection=deprotection and nitro group
reduction methods. Both synthetic routes yielded practically pure amine product
by standard aqueous workup and crystallization in 61% overall yield from pyridinyl-
vinylphenol 2. Their reaction efficiencies were comparatively studied in views of
practicality and reaction scale. Also, the synthetic conditions of key compound of
photo-crosslinker, pyridinylvinylphenol 2 was reinvestigated and established for
the reproducible and reliable preparation.
Keywords Conjugated polyarylamine; hole-injection material; organic light-
emitting devise; photo-cross linker; styrylpyridine
Introduction
In the emerging field of organic electronics, such as OLED, PLED and organic
photovoltaics, there is a significant need for improved organic conducting materials.
Especially arylamines are widely used as itself for hole-injection molecules or as
monomers for conjugated aromatic amine polymers [1–7]. Recently our group dis-
closed a conjugated arylamine polymer, poly(diotylfluorene-alt-biphenylamine) [8]
prepared from the corresponding fluorene dibromide and biphenylamine by poly-
merization with Buchwald-Hartwig palladium-catalyzed aromatic amination [9].
The new arylamine polymer showed higher efficiency of hole-injection than the com-
monly used PEDOT:PSS did [10]. Most of recent OLED devises are fabricated by
Address correspondence to Prof. Heung-Jin Choi, Department of Applied Chemistry,
Kyungpook National University, Sankyuk-dong, Buk-gu, Daegu 702-701, Korea (ROK).
Tel.: (þ82)53-950-5582; Fax: (þ82)53-950-6594; E-mail: choihj@knu.ac.kr
47=[347]

48=[348]
H.-J. Choi et al.
multi-layering polymeric materials with solution processing such as spin-coating or
ink-jet printing techniques by which each layering component efficiently perform
desired properties, such as EIL, ETL, EML, HTL and HIL. However, the new
hole-injection polyarylamine was liphophilic unlike hydrophilic PEDOT:PSS which
commonly used for hole-injection layer. Thus, practical solution processing of the
new polyarylamine to prepare the multi-layered OLED devices was hampered
because of the erosion of the subsequent layers of liphophilic organic solution. Thus,
we devised crosslinkable polyarylamine polymers which could provide excellent
solvent resistance after curing. An arylamine monomer with photo-crosslinkable
styrylpyridyl group could be introduced into the conjugated polyarylamine polymers
during copolymerization with arylamine monomers and countpart dihalide mono-
mers by Buchwald-Hartwig palladium-catalyzed aromatic amination. The styryl-
pyridyl moiety is well known and used as photo-cross linkers on a number of
polymers by [2 þ 2] cycloaddition reaction [11–13].
In this work we report comparable synthetic methods and optimal reaction
conditions of a new arylamine monomer with photo-crosslinkable styrylpyridyl
moiety, which can be used as an amine monomer to synthesize conjugated poly aro-
matic amines, and also reinvestigated the optimized and reproducible preparation of
styrylpyridine, the key component of [2 þ 2] photo-cycloaddition.
Experimental
General remarks. All commercially obtained solvents and reagents were used as
purchased. THF was freshly distilled from sodium–benzophenone under a nitrogen
gas atmosphere. N,N-Dimethylformamide (DMF) was obtained as anhydrous,
99.8% grade. Methanol was obtained as reagent plus grade, 99.9þ% and fresh
methanol must be used for hydrogenation reaction. Lindlar catalyst was purchased
from Aldrich. TLC analysis was performed using silica gel 60 F254 coated glass slides
from Merck. Chromatographic purifications were performed by flash chromato-
graphy using silica gel (70–230 mesh). NMR data were obtained at 400 MHz for
proton and at 100 MHz for carbon in the indicated solvent. Chemical shifts (d) were
recorded in ppm using either relative to TMS or residual undeuterated solvent and
coupling constants in hertz (Hz). Melting points were measured on an opti melt auto-
mated melting point system and were uncorrected. Infrared spectra were recorded on
a Shimadzu IR Prestige-21 spectrometer. MS spectra were obtained in EI mode by a
HP6890 Agilent 5973N gas chromatograph mass spectrometer. Elemental analyses
were performed from Kyungpook center for scientific instruments.
Synthesis
4-[2-(2-Pyridinyl)ethenyl]phenyl acetate [14]. A mixture of 4-hydroxybenzaldehyde
(12.2 g, 0.1 mol), 2-picoline (11.2 g, 0.12 mol), acetic anhydride (20.4 g, 0.2 mol) and
acetic acid (1.2 g, 0.02 mol) in a round bottomed flask equipped with a condenser
and an anhydrous CaCl2 drying tube was vigorously heated under reflux with a
heating mantle for 24 hrs. Volatile solvent was distilled out and the reaction
residue was cooled. The residue was dissolved in CH2Cl2 (80 mL), washed with
20% NaHCO3 aqueous solution (80 mL) and then with distilled water (50 mL ꢀ 2).
The separated organic layer was dried over anhydrous MgSO4, filtered, and

Arylamine with Styrylpyridyl Photo-Crosslinker
49=[349]
concentrated by a rotary evaporator. The solid was dissolved in hot EtOH (50 mL)
and crystallized to give white crystalline product (14.7 g, 62%).
1
mp 109.6 ꢁ 110.8ꢂC (109.2 ꢁ 110.3ꢂC) [14]; H NMR (400 MHz, CDCl3) d 8.60
(br dd, J ¼ 0.8 and 4.8 Hz, 1 H), 7.66 (dt, J ¼ 1.6 and 7.6 Hz, 1 H), 7.62 (d, J ¼ 16 Hz,
1 H), 7.58 (d, J ¼ 8.4 Hz, 2 H), 7.37 (br d, J ¼ 7.6 Hz, 1 H), 7.15 (dd, J ¼ 0.8 and
4.8 Hz, 1 H), 7.11 (d, J ¼ 16 Hz, 1 H), 7.10 (d, J ¼ 8.4 Hz, 2 H), 2.31 (s, 3H); 13C
NMR (100 MHz, CDCl3) d 169.5, 155.6, 150.7, 149.8, 136.7, 134.6, 131.8, 128.3,
128.2, 122.3, 122.2, 122.0, 21.3.
4-[2-(2-Pyridinyl)ethenyl]phenol (2) [14]. To a solution of 4-[2-(2-pyridinyl)
ethenyl]phenyl acetate (9.57 g, 0.04 mol) in ethanol (70 mL) was added a 2 M KOH
aqueous solution (10 mL). The mixture was heated at reflux for 12 hrs. To the
warm yellow solution was added 1 M HCl solution (ca. 5 mL) to acidify to pH
5–6. The solid product was precipitated upon cooling to room temperature. The
precipitate was collected by filtration, washed with distilled water and then dried
under vacuum. The crude product was further crystallized from ethanol to give a
white crystalline product (7.31 g, 93%).
1
mp 217.1 ꢁ 217.6ꢂC (216.4 ꢁ 217.6ꢂC) [14]; H NMR (400 MHz, DMSO-d6) d
9.69 (br s, 1 H), 8.52 (br dd, J ¼ 1.0 and 4.8 Hz, 1H), 7.74 (dt, J ¼ 2.0 and 7.6 Hz,
1H), 7.57 (d, J ¼ 16.1 Hz, 1H), 7.48 (d, J ¼ 8.4 Hz, 2H), 7.45–7.49 (m, 1H), 7.19
(dd, J ¼ 7.6 and 1.2 Hz, 1H), 7.07 (d, J ¼ 16.1 Hz, 1H), 6.79 (d, J ¼ 8.4 Hz, 2H);
13C NMR (100 MHz, DMSO-d6) d 158.3, 155.9, 149.7, 137.1, 132.5, 129.0, 127.8,
125.1, 122.2, 122.1, 116.0.
2-(4-(6-Bromohexyloxy)styryl)pyridine (3). A mixture of 4-[2-(2-pyridinyl)ethenyl]
phenol (1.98 g, 10 mmol) and K2CO3 (1.38 g, 10 mmol) in DMF (15 mL) was stirred
at room temperature for 30 min and then added 1,6-dibromohexane (7.32 g,
30 mmol). The mixture was further stirred at room temperature overnight. The
volatile solvent and excess dibromide was distilled out by vacuum distillation. The
residue was suspended in CH2Cl2 and filtered through a short pad of silica gel.
The filtrate was concentrated by a rotary evaporator. The solid residue was
dissolved in hot hexane (20 mL ꢀ 3) and cooled in a refrigerator, and then the
supernatant was taken out from precipitates by decantation. White crystals
(2.90 g, 80%) were collected by filtration.
mp 82.5 ꢁ 82.9ꢂC; 1H NMR (400 MHz, CDCl3) d 8.58 (br dd, J ¼ 0.8 and 4.4 Hz,
1H), 7.64 (dt, J ¼ 1.6 and 7.6 Hz, 1H), 7.58 (d, J ¼ 16.0 Hz, 1H), 7.51 (d, J ¼ 8.7 Hz,
2H), 7.35 (d, J ¼ 7.9 Hz, 1H), 7.11 (ddd, J ¼ 0.8, 4.8 and 7.2 Hz, 1H), 7.04 (d,
J ¼ 16.0 Hz, 1H), 6.89 (d, J ¼ 8.7 Hz, 2H), 3.99 (t, J ¼ 6.4 Hz, 2H), 3.43 (t, J ¼ 6.8 Hz,
Hz, 2H), 1.90 (m, 2H), 1.81 (m, 2H), 1.51 (m, 4H); 13C NMR (100 MHz, CDCl3) d
159.5, 156.1, 149.7, 136.6, 132.5, 129.4, 128.6, 125.8, 121.9, 121.8, 114.8, 67.9, 34.0,
32.8, 29.2, 28.0, 25.4.
t-Butyl 4-hydroxyphenylcarbamate. A mixture of 4-aminophenol (1.456 g, 10 mmol),
di-tert-butyl carbonate (2.400 g, 11 mmol), triethylamine (1.4 mL) and MeOH
(15 mL) was stirred at room temperature overnight. The mixture was concentrated
by a rotary evaporator. The residue was dissolved in CH2Cl2 (30 mL) and washed
with acidic water (30 mL) containing acetic acid (15 drops) and then with water
(30 mL). The organic layer was separated, dried and concentrated by a rotary
evaporator. The solid residue was recrystallized from toluene=hexane to afford
1
white crystalline product (1.758 g, 84%). mp 142.8 ꢁ 143.3ꢂC; H NMR (400 MHz,

50=[350]
H.-J. Choi et al.
CDCl3) d 7.16 (d, J ¼ 8.4 Hz, 2H), 6.73 (d, J ¼ 8.4 Hz, 2H), 6.35 (br s, 1H), 5.33 (br s,
1H), 1.51 (s, 9H); 13C NMR (100 MHz, CDCl3) d 154.0, 152.4, 131.2, 121.8, 116.1,
80.9, 28.8.
t-Butyl 4-(6-(4-(2-(2-pyridinyl)vinyl)phenoxy)hexyloxy)phenylcarbamate (4). To a
mixture of t-butyl 4-hydroxyphenylcarbamate (0.87 g, 4.2 mmol) and K2CO3 (0.58 g,
4.2 mmol) in DMF (10 mL) at room temperature was added 2-(4-(6-bromohexyloxy)
styryl)pyridine (1.45 g, 4 mmol). The mixture was further stirred at room temperature
overnight. The solvent was removed in vacuo. The residue was suspended in a
mixture of CH2Cl2=water (2:1, 45 mL), filtered and washed with CH2Cl2 and then
water. After drying under vacuum the white power (1.58 g, 80%) was obtained.
1
mp 185.4 ꢁ 186.2ꢂC; H NMR (400 MHz, CDCl3) d 8.59 (br dd, J ¼ 0.8 and
4.4 Hz, 1H), 7.64 (dt, J ¼ 1.6 and 7.6 Hz, 1H), 7.58 (d, J ¼ 16.0 Hz, 1H), 7.51 (d,
J ¼ 8.8 Hz, 2H), 7.36 (d, J ¼ 8.0 Hz, 1H), 7.12 (ddd, J ¼ 0.8, 4.8 and 7.6 Hz, 1H),
7.04 (d, J ¼ 16.0 Hz, 1H), 6.90 (d, J ¼ 8.8 Hz, 2H), 6.83 (d, J ¼ 8.8 Hz, 2H), 6.37
(br s, 1H), 4.00 (t, J ¼ 6.6 Hz, 2H), 3.94 (t, J ¼ 6.4 Hz, 2H), 1.81 (m, 4H), 1.54 (m,
4H), 1.51 (s, 9H); 13C NMR (100 MHz, CDCl3) d 159.8, 156.6, 155.7, 153.4,
149.9, 136.4, 132.8, 131.8, 129.9, 128.6, 126.3, 121.7, 121.7, 121.1, 115.4, 115.2,
80.4, 68.7, 68.4, 29.5, 29.5, 28.6, 26.1 (double intensity).
1-(6-Bromohexyl)oxy-4-nitrobenzene (5). A mixture of 4-nitrophenol (1.39 g,
10 mmol) and K2CO3 (1.4 g, 10 mmol) in DMF (10 mL) was stirred at room
temperature for 30 min and then added 1,6-dibromohexane (7.32 g, 30 mmol). The
mixture was further stirred at room temperature for 20 hrs. The volatile solvent
and excess dibromide was distilled out by vacuum distillation. The residue was
suspended in CH2Cl2 and filtered through a short pad of silica gel. The filtrate
was concentrated by a rotary evaporator. The oily residue was dissolved in hot
hexane (10 mL) and cooled in a refrigerator, and then the supernatant above
precipitates was taken by decantation. This process was performed three times
and the combined supernatant was concentrated and filtered again through a
short pad of silica gel with hexane. The filtrate was concentrated to give yellowish
oily product (2.72 g, 90%).
1H NMR (400 MHz, CDCl3) d 8.19 (d, J ¼ 9.2 Hz, 2H), 6.93 (d, J ¼ 9.2 Hz, 2H),
4.05 (t, J ¼ 6.4 Hz, 2H), 3.43 (t, J ¼ 6.8 MHz, 2H), 1.90 (quin, J ¼ 6.8 Hz, 2H), 1.84
(quin, J ¼ 6.8 Hz, 2H), 1.52 (m, 4H); 13C NMR (100 MHz, CDCl3) d 164.2, 141.5,
126.0, 114.5, 68.7, 33.9, 32.7, 28.9, 27.9, 25.3.
2-(4-(6-(4-Nitrophenoxy)hexyloxy)styryl)pyridine (6). A mixture of 4-[2-(2-
pyridinyl)ethenyl]phenol (1.03 g, 5.2 mmol) and K2CO3 (0.73 g, 5.3 mmol) in DMF
(15 mL) was stirred at room temperature for 30 min and then added 1-(6-bromohexyl)
oxy-4-nitrobenzene (1.57 g, 5.2 mmol). The mixture was further stirred at room
temperature for 20 hrs. The solvent was removed in vacuo and the solid residue
was taken in CH2Cl2 (20 mL), and filtered through a short pad of silica gel. The
filtrate was concentrated by a rotary evaporator. The solid residue was crystallized
from ethanol to give white solid product (1.85 g, 85%).
mp 146.6 ꢁ 147.2ꢂC; 1H NMR (400 MHz, CDCl3) d 8.58 (br d, J ¼ 4.8 Hz, 1 H),
8.20 (d, J ¼ 9.2 Hz, 2H), 7.65 (dt, J ¼ 2.0 and 7.6 Hz, 1H), 7.58 (d, J ¼ 16.1 Hz, 1H),
7.51 (d, J ¼ 8.7 Hz, 2H), 7.36 (d, J ¼ 7.6 Hz, 1H), 7.12 (dd, J ¼ 4.8 and 7.2 Hz, 1H),
7.04 (d, J ¼ 16.1 Hz, 1H), 6.94 (d, J ¼ 9.2 MHz, 2H), 6.89 (d, J ¼ 8.7 Hz, 2H), 4.06 (t,
J ¼ 6.4 Hz, 2H), 4.01 (t, J ¼ 6.4 Hz, 2H), 1.85 (m, 4H), 1.57 (m, 4H); 13C NMR

Arylamine with Styrylpyridyl Photo-Crosslinker
51=[351]
(100 MHz, CDCl3) d 164.6, 159.8, 156.3, 150.0, 141.7, 136.9, 132.7, 129.7, 128.8,
126.3, 126.1, 122.2, 122.1, 115.1, 114.8, 69.1, 68.2, 29.5, 29.3, 26.2, 26.1.
4-(6-(4-(2-(2-Pyridinyl)vinyl)phenoxy)hexyloxy)aniline (1)
BOC-Protection=deprotection method. To a suspension of t-butyl 4-(6-(4-(2-(2-
-pyridinyl)vinyl)phenoxy)hexyloxy)phenylcarbamate (978 mg, 2 mmol) in CH2Cl2
(40 mL) was added trifluoroacetic acid (1.0 mL). The mixture was stirred at room
temperature overnight. To the mixture was added NaOH aqueous solution (1 M,
20 mL) to basicify to be basic. The organic layer was separated, washed with water,
dried over anhydrous MgSO4, filtered and concentrated in vacuo to give brownish
solid product (677 mg, 87%).
Reduction method. A suspension of 2-(4-(6-(4-nitrophenoxy)hexyloxy)styryl)
pyridine (293 mg, 0.7 mmol) in methanol (300 mL) was heated at reflux for 30 min.
The resulting hot solution was cooled to room temperature under hydrogen gas.
To the cooled suspension in methanol was added Lindlar catalyst (120 mg). The mix-
ture was stirred at room temperature under atmospheric pressure of hydrogen gas in
a rubber balloon. The hydrogenation reaction was monitored by TLC analysis (ca.
15 hrs). The suspension was filtered through a pad of celite to remove the catalyst.
The filtrate was concentrated in vacuo and the oily residue was purified by a fresh
column chromatography (silica gel, CH2Cl2=EtOAc, 9:1) to afford a yellowish solid
product (220 mg, 80%).
mp 92.4 ꢁ 93.1ꢂC; 1H NMR (400 MHz, CDCl3) d 8.58 (br dd, J ¼ 0.8 and 4.8 Hz,
1H), 7.64 (dt, J ¼ 1.6 and 7.6 Hz, 1H), 7.58 (d, J ¼ 16.0 Hz, 1H), 7.51 (d, J ¼ 8.7 Hz,
2H), 7.36 (d, J ¼ 8.0 Hz, 1H), 7.11 (ddd, J ¼ 0.8, 4.8 and 7.4 Hz, 1H), 7.04 (d,
J ¼ 16.0 Hz, 1H), 6.90 (d, J ¼ 8.7 Hz, 2H), 6.74 (d, J ¼ 8.8 Hz, 2H), 6.64 (d,
J ¼ 8.8 Hz, 2H), 3.99 (t, J ¼ 6.5 Hz, 2H), 3.90 (d, J ¼ 6.5 Hz, 2H), 1.80 (m, 4H),
1.53 (m, 4H); 13C NMR (400 MHz, CDCl3) d 159.5, 156.1, 152.4, 149.7, 140.0,
136.6, 132.5, 129.3, 128.5, 125.7, 121.9, 121.8, 116.5, 115.8, 114.8, 68.6, 68.0, 29.5,
29.3, 26.0 (double intensity); IR (KBr) 3425, 3390, 3040, 2940, 2860, 1605, 1582,
1512, 1474, 1250, 1170 cmꢁ1; MS (EI, relative intensity) m=z 390 (M þ 2, 15), 389
(M þ 1, 55), 388 (Mþ, 100), 387 (84), 280 (80), 196 (83), 167 (26), 109 (97); Anal.
Calcd for C25H28N2O2: C, 77.29; H, 7.26; N, 7.21. Found: C, 76.93; H, 7.12; N, 7.52.
Results and Discussion
The devised new arylamine monomer 1 with photo-crosslinkable group has aniline
and styrylpyridine moieties which are linked together through 1,6-hexylene bridge.
A flexible hexylene bridging linker is chosen for two rigid styrylpyridine moieties
which are freely aligned in head-to-tail fashion during [2 þ 2] photo-cycloaddion
reaction. Reasonable synthetic approach might be through ether functional connec-
tions two phenolic nucleophiles, 4-aminophenol and 4-[2-(2-pyridinyl)ethenyl]phenol
2, with 1,6-dihalohexane (Scheme 1). Amino group of p-aminophenol was protected
with di-t-butyl carbonate in a polar methanol solvent because of insolubility of Zwit-
terionic p-aminophenol in conventional ethereal solvents. Pyridinylvinylphenol 2 as
styrylpyridine moiety was alkylated with excess 1,6-dibromohexane to yield
mono-alkylated product styrylpyridinyl bromohexyl ether 3 in reasonably good
yield. The styrylpyridinyl bromohexyl ether 3 was further reacted with the other phe-
nolic countpart, t-butyl 4-hydroxyphenylcarbamate to afford diether 4 in a good

52=[352]
H.-J. Choi et al.
Scheme 1. Crosslinkable arylamine monomer 1 by BOC-protection=deprotection method;
Reagents and conditions: (a) 1,6-dibromohexane, K2CO3, DMF, rt, 82%; (b) t-butyl 4-hydro-
xyphenylcarbamate, K2CO3, DMF, rt, 85%; (c) CF3COOH, CH2Cl2, rt, 88%.
yield. BOC group on aniline moiety of diether 4 was deprotected with trifluoroacetic
acid to the aniline-styrylpyridine diether 1 after basicifying the protonated product.
In this synthetic route all adapted reaction conditions are simple alkylation reac-
tions and protection=deprotection in DMF solvent, and all synthetic intermediates
were solid which could be isolated by crystallization. It is practically useful for large
scale synthesis. Without difficulties, the reactions could be scaled up to gram scale.
Three reaction steps and a protection of aminophenol resulted to give in 61% overall
yield. However, relatively expensive di-tert-butyl carbonate did not allow large
reaction scales.
It is worth to reinvestigate the preparation of the known key compound 2
because this simple reaction was not reproducible or produced only low yield of pro-
duct, 4-[2-(2-pyridinyl)ethenyl]phenyl acetate when a mixture of hydroxybenzalde-
hyde and 2-picoline in acetic anhydride was heated at reflux. Rationalized
reaction mechanism suggests that the limiting species of rate determining reaction
is probably 2-methylene-1,2-dihydropyridine, a tautomer formed from 2-picoline
which react with aldehyde countpart as aldol condensation fashion. Formation of
the non-aromatic tautomer is apparently high energy process because overcoming
resonance energy of aromatic pyridine moiety is required. When the reaction mixture
was vigorously heated on a heating mantle rather than oil bath, reasonable yield of
the desired product was formed reproducibly. Using excess 2-picoline balanced with
the corresponding amount of acetic acid the reaction was optimized and reproduc-
ible. The detailed reaction condition is described in the experimental section.
Nitro group was often used as amine precursor and equivalent to amino protec-
tion functional group. Introducing p-nitorophenol instead of aminophenol could
reduce the number of reaction steps (Scheme 2).

Arylamine with Styrylpyridyl Photo-Crosslinker
53=[353]
Scheme 2. Crosslinkable arylamine monomer 1 by nitro-to-amine reduction method;
Reagents and conditions: (a) K2CO3, DMF, rt, 90%; (b) pyridinylvinylphenol 2, K2CO3,
DMF, rt, 85%; (c) H2 (1 atm), Lindlar catalyst, rt, 80%.
Two starting alkylation reactions were easily performed and gave high yields of
products by aqueous workup and crystallization methods. The selective reductions
of nitro group of 6 to aniline product 1 were performed with common reduction con-
ditions such as with metal hydrides, with metals. These reduction conditions were
not practical to isolate the desired pure product without contamination or decompo-
sition. However, catalytic hydrogenations in the presence of Pd and Pt catalysts were
apparently practical to isolate the pure product. Both Pt and Pd catalysts fully
reduced nitro and vinyl groups non-selectively even under atmospheric pressure of
hydrogen. Lindlar catalyst showed some selectivity for the desired product 1 over
the over hydrogenated product in methanol at room temperature. The starting
material, nitrophenyl pyridinylvinylphenlyl diether 6 were nearly soluble in methanol
(10 mg=30 mL) but the reduced amine product 1 was freely soluble. At the elevated
temperature to solubilize the starting material 6 the reduction was retarded and
finally ceased probably due to low solubility of hydrogen gas under atmospheric
pressure and deactivation of catalyst in prolonged reaction time. In other non-protic
solvents such as toluene, THF and dioxane under the same reaction condition only
over hydrogenated product was obtained without any selectivity. It was found that
moisture in the methanol caused deactivation of catalyst but also lose selectivity. The
balanced amount of the starting material over Lindlar catalyst in the dried methanol
was important factor to get selective reduction to the product 1 with complete
reduction of the starting material without over-hydrogenation. To avoid over-
hydrogenation the reaction in a flask was monitored at room temperature and under
atmospheric pressure of hydrogen. Complete and selective reduction to the product 1
could be achieved, but it was hardly reproducible and unavoidable to isolate and
purify the product using chromatographic method.
With BOC protection=deprotection of amino group, the product was straightfor-
wardly obtained by aqueous workup and crystallization without laborious chromato-
graphic isolation of product, and reactions could be scaled up. However, the extra
protection step and expensive di-tert-butyl carbonate hampered large scale reactions.
With catalytic hydrogenation of nitro group, the protection step with expensive

54=[354]
H.-J. Choi et al.
protection reagent was unnecessary and easy workup of filtration to get rid of catalyst
and concentration allowed to access the catalytic hydrogenation. However, it also has
drawback on reproducibility, but it has advantage to scale up without any limiting
factors if reactions were carefully monitored to avoid over-hydrogenation.
Summary
An arylamine monomer 1 with styrylpydine moiety devised for hole-injection conju-
gated polyarylamine in OLED was efficiently synthesized. Two reaction approaches,
protection=deprotection of amine group and catalytic hydrogenation of nitro precur-
sor were comparatively performed. Both synthetic routes afforded reasonable yields
of the arylamine product 1 in three consecutive reaction steps, ether formations of
phenolic nucleophile with hexylene dibromide and deprotection of BOC-protected
precursor or reduction of nitro precursor. BOC-Protection synthetic route is useful
to obtain pure product in small reaction scale, but catalytic hydrogenation approach
are economically viable from the precisely controlling complete hydrogention of
selective reduction with Lindlar catalyst. An optimized and reproducible preparation
of a valuable photo-cross linking moiety of styrylpyridine was also reestablished
based on the rationalized reaction mechanism.
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