Z. Hu et al. / Dyes and Pigments 86 (2010) 166e173
167
Previous work by the current authors showed that the intro-
duction of a diphenylamino group in the cyclometalated ligand
(400 MHz, CDCl3), ppm: 8.26 (d, 2H, J ¼ 8.4 Hz), 7.76 (d, 2H,
J ¼ 8.4 Hz), 7.41 (dd,1H, J ¼ 7.2, 7.6 Hz), 7.28 (dd, 2H, J ¼ 16.8, 7.6 Hz),
3.88 (dd, 2H, J ¼ 7.2, 7.6 Hz), 2.81 (dd, 2H, J ¼ 7.6, 7.2 Hz).
provided
a
high-efficiency, green-emitting [N,N-diphenyl-4-
(20-pyridyl) aniline-C3, N1] (diphenoxylmethane) platinum (II)
complex, [(PhNPPy)Pt(DBM)] [24]. This paper concerns red-emit-
ting, phosphorescent, cyclometalated platinum (II) complexes,
namely (Piq-G)Pt(acac), in which Piq-G is a 1-phenylisoquinoline
derivative that contains diarylamino groups at the 4-position of
the phenyl ring and acac is acetyl acetonate. As the Piq-G cyclo-
metalated ligand has a non-planar, triphenylamino configuration
and the triphenylamino group has excellent hole-transporting
characteristic, the diarylamino-functionalized (Piq-G)Pt(acac)
complexes are expected to display superior electroluminescence
than the corresponding non-functionalized (Piq)Pt(acac) complex.
Using (Piq-G)Pt(acac) rather than (Piq)Pt(acac) as emitter and
a blend of poly(9,9-dioctylfluorene) (PFO) and 2-(4-tert-butyl)-
phenyl-5-biphenyl-1,3,4-oxadiazole (PBD) as host matrix, fabri-
cated double-layer, polymer light-emitting diodes exhibited bright
red-emission at 641 ꢁ 4 nm and displayed an EQE of 8.6%.
2.2.3. 1-(4-Nitrophenyl)isoquinoline (3)
A mixture of 2 (13.9 g, 0.055 mol) and 1.18 g of 10% Pd/C in
250 mL of 1, 2, 3, 4-tetrahydronaphthalene was refluxed under
nitrogen for 15 h. The catalyst was removed from the hot mixture
by filtration and tetrahydronaphthalene was removed under
vacuum. The residue was dissolved in concentrated hydrochloric
acid and filtered, the filtrate being carefully neutralized with aq.
sodium hydroxide solution. The precipitate was extracted with
CH2Cl2. and the organic layer was dried over anhydrous magnesium
sulfate and evaporated to afford a yellow solid (9.8 g, 73.1%). m.p.
96 ꢂC. 1H NMR (400 MHz, CDCl3), ppm: 8.58 (d, 1H, J ¼ 5.6 Hz), 8.22
(d, 1H, J ¼ 8.4 Hz), 7.87 (d, 1H, J ¼ 8.0 Hz), 7.69 (dd, 1H, J ¼ 7.2,
8.0 Hz), 7.59 (m, 4H), 6.85 (d, 2H, J ¼ 8.0 Hz).
2.2.4. 4-(Isoquinolin-1-yl)benzenamine (4)
A mixture of 3 (9.8 g, 39.2 mmol) and 170 mL of ethanol was
heated to 50 ꢂC followed by the addition of 0.392 g of 5% Pd/C. A
further 0.392 g of 5% Pd/C and 9 mL of 80% hydrazine hydrate
(caution: incompatible with oxidizing agents, heavy metal oxides,
dehydrating agents, alkali metals, rust, silver salts; combustible;
contact with many materials may cause fire or explosive decom-
position; may react explosively with a variety of materials; vapour
may explode in fire) were added over 40 min. The ensuing mixture
was refluxed for 4 h after which time, the catalyst was removed
from the hot solution by filtration. The filtrate was evaporated to
remove the majority of ethanol and mixed with water; the yellow
solid was realized by filtration (8.1 g, 93.6%). m.p. 197e199 ꢂC. 1H
NMR (400 MHz, CDCl3), ppm: 8.58 (d, 1H, J ¼ 5.6 Hz), 8.22 (d, 1H,
J ¼ 8.4 Hz), 7.87 (d, 1H, J ¼ 8.0 Hz), 7.69 (dd, 1H, J ¼ 7.2, 8.0 Hz), 7.59
(m, 4H), 6.85 (d, 2H, J ¼ 8.0 Hz), 3.88 (s, 2H).
2. Experimental
2.1. Chemicals and instruments
All solvents were carefully dried and distilled prior to use.
Commercially available reagents were used without further purifi-
cation unless otherwise stated. All reactions were performed under
nitrogen atmosphere and were monitored by thin-layer chroma-
tography (TLC). Flash column chromatography and preparative TLC
were carried out using silica gel from Merck (200e300 mesh). All 1H
NMR spectra were acquired at a Bruker Dex-400NMR instrument
using CDCl3 as a solvent. Elemental analysis was performed on
a Harrios elemental analysis instrument.
2.2. Synthesis
2.2.5. 4-(Isoquinolin-1-yl)-N,N-diphenylbenzenamine (5a)
2.2.1. 4-Nitro-N-phenethylbenzamide (1)
To a solution of 4-nitrobenzoyl chloride (31.5 g, 169 mmol) in
350 mL of methylene chloride was added dropwise b-phenethyl-
A mixture of 4 (1.3 g, 5.9 mmol), iodobenzene (1.7 mL,
14.5 mmol), anhydrous K2CO3 (6.6 g, 47.8 mmol), 1.5 g bronze
powder, 0.4 g of dibenzo-18-crown-6 and 25 mL 1,2-dichloroben-
zene was refluxed under nitrogen for 24 h and cooled to room
temperature. The reaction mixture was filtered to remove the
precipitated base and evaporated under reduced pressure to
remove solvent. The resulting brown-yellow oily crude was purified
by silica gel column chromatography using dichloromethane/
hexane (1:20, v/v) as eluent provide a yellow solid (1.7 g, 77.6%). m.
p. 142e144 ꢂC. 1H NMR (400 MHz, CDCl3), ppm: 8.60 (d, 1H,
J ¼ 5.6 Hz), 8.26 (d, 1H, J ¼ 8.4 Hz), 7.9 (d, 1H, J ¼ 8.4 Hz), 7.73 (dd,
1H, J ¼ 7.2, 7.6 Hz), 7.64 (m, 4H), 7.32 (dd, 3H, J ¼ 8.4, 7.2 Hz), 7.23
(dd, 6H, J ¼ 8.8, 8.4 Hz), 7.08 (dd, 3H, J ¼ 7.2, 7.2 Hz).
amine (22.2 mL, 169 mmol) at 0 ꢂC followed by an addition of
triethylamine (26 mL, 169 mmol). The reaction mixture was then
warmed to room temperature and stirred for 26 h after which time,
the mixture was diluted with CH2Cl2 and neutralized with aq.
NaHCO3 solution. The organic phase was washed with aq. NaHCO3
solution and brine, dried over anhydrous Na2SO4 and residue was
purified by recrystallization from ethanol to form yellow coloured
crystals of 1 (35.5 g, 88%). m.p. 125 ꢂC. 1H NMR (400 MHz, CDCl3),
ppm: 8.27 (d, 2H, J ¼ 8.8 Hz), 7.85 (d, 2H, J ¼ 8.8 Hz), 7.37 (dd, 2H,
J ¼ 7.2, 7.6 Hz), 7.28 (dd, 3H, J ¼ 15.6, 7.2 Hz), 6.24 (s, 1H), 3.78 (ddd,
2H, J ¼ 6.4, 6.4, 6.4 Hz), 2.98 (dd, 2H, J ¼ 6.8, 6.8 Hz).
2.2.6. 4-(Isoquinolin-1-yl)-N,N-dip-tolylbenzenamine (5b)
The synthesis described for 5a was followed. A yellow solid 5b
was obtained in 72.3% yield. m.p. 153e155 ꢂC. 1H NMR (400 MHz,
CDCl3), ppm: 8.58 (d, 1H, J ¼ 6.0 Hz), 8.25 (d, 1H, J ¼ 8.4 Hz), 7.88 (d,
1H, J ¼ 8.4 Hz), 7.70 (dd, 1H, J ¼ 7.2, 7.2 Hz), 7.60 (m, 4H), 7.17 (d, 2H,
J ¼ 8.4 Hz), 7.12 (m, 8H), 2.33 (s, 6H).
2.2.2. 1-(4-Nitrophenyl)-3, 4-dihydroisoquinoline (2)
To a solution of 1 (35.5 g, 0.13 mol) in 54 mL of xylene was added
P2O5 (caution: incompatible with sodium, aluminum, potassium,
ammonia, peroxides and magnesium; reacts violently with water;
hazardous Decomposition Products; 37 g, 0.13 mol) and 103 mL of
POCl3 (caution: extremely reactive or incompatible with acids;
highly reactive with reducing agents, combustible materials,
organic materials, metals, alkalis, moisture; may undergo
hazardous decomposition, condensation or polymerization) with
stirring. The mixture was refluxed for 5 h and the concentrated
residue was carefully neutralized with 10% aq. sodium hydroxide
solution. The mixture was extracted with CH2Cl2., the organic layer
being dried over anhydrous magnesium sulfate and evaporated to
provide a brown-yellow solid (22.7 g, 69%). m.p. 88 ꢂC. 1H NMR
2.2.7. 4-Tert-butyl-N-(4-tert-butylphenyl)-N-(4-(isoquinolin-1-yl)
phenyl)benzenamine (5c)
The synthesis described for 5a was followed. A yellow solid 5c
was obtained in 62.9% yield. m.p. 186e188 ꢂC. 1H NMR (400 MHz,
CDCl3), ppm: 8.59 (d, 1H, J ¼ 6.0 Hz), 8.27 (d, 1H, J ¼ 8.4 Hz), 7.89
(d, 1H, J ¼ 8.0 Hz), 7.72 (dd, 1H, J ¼ 7.2, 7.2 Hz), 7.62 (m, 4H), 7.31
(d, 4H, J ¼ 8.8 Hz), 7.21 (d, 2H, 8.4 Hz), 7.13 (d, 4H, J ¼ 8.4 Hz), 1.33
(s, 18 H).