AXIMA-CFRꢀ plus instrument. UV-vis absorption spectra
were recorded on a UV-3100 spectrophotometer. Fluorescence
measurements were carried out with a RF-5301PC. The differ-
ential scanning calorimetry (DSC) analysis was determined using
a NETZSCH (DSC-204) instrument at 10 ꢁC minꢀ1 under
nitrogen flushing. Cyclic voltammetry (CV) was performed with
a BAS 100W Bioanalytical Systems, using a glass carbon disk
(F ¼ 3 mm) as the working electrode, a platinum wire as the
auxiliary electrode with a porous ceramic wick, Ag/Ag+ as the
reference electrode, standardized for the redox couple ferrici-
nium/ferrocene. All solutions were purged with a nitrogen stream
for 10 min before measurement. The procedure was performed at
room temperature and a nitrogen atmosphere was maintained
over the solution during measurements.
(PPh3)4 (50 mg, 0.06 mmol), sodium carbonate (2.06 g, 20 mmol),
THF (50 mL) and distilled water (10 mL) was refluxed for 48 h
under nitrogen. The crude product was concentrated by rotary
ꢁ
evaporation. After drying at 40 C under vacuum, the powder
was purified by column chromatography on silica gel using
CH2Cl2/CH3COOC2H5 (50 : 1, v/v) as an eluent to afford a light
yellow solid. (210.6 mg, yield: 75.0%)
Synthesis of PI-based compounds (shown in Scheme 1): A
mixture of aniline (50.0 mmol), phenanthrenequinone (10.0
mmol), corresponding aromatic aldehyde (10.0 mmol), ammo-
nium acetate (40.0 mmol), and acetic acid (80 mL) was refluxed
under nitrogen in an oil bath.11 After 2 h, the mixture was cooled
and filtered. The solid product was washed with an acetic acid/
water mixture (1 : 1, 150 mL) and water. It was then purified by
chromatography using CH2Cl2 as an eluent.
Device fabrication
1,2-diphenyl-1H-phenanthro[9,10-d]imidazole (PPI). White
1
powder (yield: 90.5%) H NMR (500 MHz, DMSO, ppm): 8.93
The EL devices were fabricated by vacuum deposition of the
materials at 10ꢀ6 Torr onto ITO glass with a sheet resistance of
25 U squareꢀ1. All of the organic layers were deposited at a rate of
(d, J ¼ 8.2 Hz, 1H), 8.75 (d, J ¼ 8.5 Hz, 1H), 8.69 (d, J ¼ 7.6 Hz,
1H), 7.78 (t, J ¼ 7.6 Hz, 7.0 Hz, 1H), 7.73–7.65 (m, 6H), 7.58 (dd,
J ¼ 7.9 Hz, 2.1 Hz, 2H), 7.55 (t, J ¼ 7.0 Hz, 7.3 Hz, 1H), 7.39–
7.30 (m, 4H), 7.08 (d, J ¼ 8.2 Hz, 1H). MALDI-TOF (m/z): [M+]
calcd for C27H18N2: 370.45; found: 370.20. Anal. calcd for
C27H18N2: C, 87.54; H, 4.90; N, 7.56; Found: C, 87.50; H, 4.92;
N, 7.55.
1.0 A sꢀ1. The cathode was deposited with LiF (1 nm) at
ꢀ
ꢀ1
ꢀ
a deposition rate of 0.1 A s and then capping with Al metal
(100 nm) through thermal evaporation at a rate of 4.0 A sꢀ1. The
ꢀ
electroluminescence (EL) spectra and Commission Inter-
nationale De L’Eclairage (CIE) coordination of these devices
were measured by a PR650 spectro scan spectrometer. The
luminance–current and density–voltage characteristics were
recorded simultaneously with the measurement of the EL spectra
by combining the spectrometer with a Keithley model 2400
programmable voltage–current source. All measurements were
carried out at room temperature under ambient conditions.
4,40-bis(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)biphenyl
(BPPI). Light yellow powder (yield: 80.5%) 1H NMR (500 MHz,
DMSO, ppm): 8.94 (d, J ¼ 8.5 Hz, 2H), 8.89 (d, J ¼ 8.2 Hz, 2H),
8.72 (d, J ¼ 8.2 Hz, 2H), 7.80–7.65 (m, 22H), 7.57 (t, J ¼ 7.9 Hz,
7.6 Hz, 2H), 7.35 (t, J ¼ 7.3 Hz, 7.3 Hz, 2H), 7.09 (d, J ¼ 8.2 Hz,
2H);MALDI-TOF (m/z): [M+] calcd for C54H34N4: 738.28;
found: 739.00. Anal. calcd for C54H34N4: C, 87.78; H, 4.64; N,
7.58; found: C, 87.80; H, 4.62; N, 7.57.
Synthesis
4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzaldehyde
(M2). Bis(pinacolato)diboron (2.8 g, 11 mmol), Pd(dppf)2Cl2
(0.3 g, 0.3 mmol) and potassium acetate (3 g, 30 mmol) were put
into a two-neck round-bottom flask equipped with a stirrer and
reflux condenser. DMSO (30 mL) was added and the mixture was
stirred under nitrogen for 10 min. After that M1 (1.85 g, 1.0
mmol) was added and the mixture was kept at 80 ꢁC for 24 h. The
mixture was cooled down and extracted with CH2Cl2. The
product was purified preliminarily and used directly for the next
step.
4,40,400-tris(1-phenyl-phenanthro[9,10-d]imidazol-2-yl)-1,3,5-tri-
1
phenylbenzene (TPPI). Yellow powder (yield: 76.5%) H NMR
(500 MHz, DMSO, ppm): 8.93 (d, J ¼ 8.8 Hz, 3H), 8.88 (d, J ¼
7.3 Hz, 3H), 8.72 (d, J ¼ 7.6 Hz, 3H), 7.98 (s, 3H), 7.93 (d, J ¼ 8.2
Hz, 6H), 7.80–7.66 (m, 27H), 7.57 (t, J ¼ 7.9 Hz, 7.6 Hz, 3H),
7.35 (t, J ¼ 8.2 Hz, 7.3 Hz, 3H), 7.09 (d, J ¼ 7.9 Hz, 3H).
MALDI-TOF (m/z): [M+] calcd for C87H54N6: 1182.44; Found:
1183.50. Anal. calcd for C87H54N6: C, 88.30; H, 4.60; N, 7.10;
Found: C, 88.26; H, 4.60; N, 7.08.
4,40-Biphenyldicarboxaldehyde (M3). A mixture of 4-bromo-
benzaldehyde (2.1 g, 11.2 mmol), 4,4,40,40,5,5,50,50-octamethyl-
2,20-bi(1,3,2-dioxaborolane) (1.5 g, 5.6 mmol), Pd(PPh3)4
(250 mg, 0.3 mmol), sodium carbonate (5.3 g, 50 mmol), THF
(150 mL) and distilled water (25 mL) was refluxed for 48 h under
nitrogen. The crude product was concentrated by rotary evapo-
ration. After drying at 40 ꢁC under vacuum, the powder was
purified by column chromatography on silica gel using CH2Cl2/
CH3COOC2H5 (20 : 1, v/v) as an eluent to afford a light yellow
solid. (1.89 g, yield: 80.5%) 1H NMR (500 MHz, DMSO, ppm):
10.90 (s, 2H), 8.01 (d, J ¼ 8.0 Hz, 4H), 7.82 (d, J ¼ 8.0 Hz, 4H).
Results and discussion
Synthesis and characterization
As shown in Scheme 1, all three new compounds PPI, BPPI and
TPPI were synthesized in a one-pot reaction. The mixtures of
aniline, phenanthrenequinone, ammonium acetate and corre-
sponding aromatic aldehyde were refluxed for 2 h, then cooled to
room temperature and filtered. The crude products of light
yellow powders were purified by chromatography and the yields
of all target products were above 75%.12 Such a synthetic method
provides a common and facile way to construct PI derivatives
with different structures and functions by simply tuning the
aromatic aldehyde precursor involved.13 In comparison with the
1,3,5-tri(4-benzaldehyde)benzene (M4). A mixture of M2 (0.58
g, 2.50 mmol), 1,3,5-tribromobenzene (227.6 mg, 0.72 mmol), Pd
5452 | J. Mater. Chem., 2011, 21, 5451–5456
This journal is ª The Royal Society of Chemistry 2011