The synthesis, crystal structures and photophysical properties of a series of novel 4,6-diphenyl-1,9-anthrazolines

Article abstract of DOI:10.1016/j.dyepig.2011.02.011

The synthesis and properties of a series of nine new 4,6-diphenyl-1,9- anthrazolines molecules 1a-1i are reported. Compounds 1a-1i were synthesized by Friedl?nder condensation of 4,6-dibenzoyl-1,3-phenylenediamines and acetyl-functionalized compounds in the presence of polyphosphoric acid as catalyst, in yields ranging from 60% to 94%. The 4,6-diphenyl-1,9-anthrazolines are thermally robust with high decomposition temperatures (>371.0 °C) and high melt transitions (215.1-322.8 °C). Compounds 1a and 1f crystallized in the triclinic system with the space groups P-1. All of them show the lowest energy absorption bands (λ_max^Abs: 397-454 nm), revealing low optical band gaps (2.55-3.00 eV). The compounds emit blue fluorescence with λ_max^Em ranging from 432 to 493 nm in dilute toluene solution. 4,6-Diphenyl-1,9-anthrazolines 1a-1i have a formal reduction potential in the range -1.02 to -1.19 V (versus SCE) and estimated electron affinities (LUMO levels) of 3.21-3.38 eV. These results demonstrate that the new 4,6-diphenyl-1,9-anthrazolines are promising thermally stable n-type semiconductors for organic electronics.

Full text of DOI:10.1016/j.dyepig.2011.02.011

Dyes and Pigments 91 (2011) 89e97
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
The synthesis, crystal structures and photophysical properties of a series
of novel 4,6-diphenyl-1,9-anthrazolines
*
Qin Zhang, Peng Jiang, Kunyan Wang, Guangliang Song, Hongjun Zhu
Department of Applied Chemistry, College of Science, Nanjing University of Technology, Nanjing 210009, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis and properties of a series of nine new 4,6-diphenyl-1,9-anthrazolines molecules 1ae1i are
reported. Compounds 1ae1i were synthesized by Friedländer condensation of 4,6-dibenzoyl-1,3-phe-
nylenediamines and acetyl-functionalized compounds in the presence of polyphosphoric acid as catalyst,
in yields ranging from 60% to 94%. The 4,6-diphenyl-1,9-anthrazolines are thermally robust with high
decomposition temperatures (>371.0 ꢀC) and high melt transitions (215.1e322.8 ꢀC). Compounds 1a and
Received 10 November 2010
Received in revised form
30 December 2010
Accepted 21 February 2011
Available online 9 March 2011
1f crystallized in the triclinic system with the space groups P-1. All of them show the lowest energy
Abs
absorption bands
(
lmax
: 397e454 nm), revealing low optical band gaps (2.55e3.00 eV). The
Keywords:
Em
compounds emit blue fluorescence with lmax ranging from 432 to 493 nm in dilute toluene solution.
4,6-Diphenyl-1,9-anthrazolines 1ae1i have a formal reduction potential in the range ꢁ1.02 to ꢁ1.19 V
(versus SCE) and estimated electron affinities (LUMO levels) of 3.21e3.38 eV. These results demonstrate
that the new 4,6-diphenyl-1,9-anthrazolines are promising thermally stable n-type semiconductors for
organic electronics.
Organic light-emitting materials
4,6-Diphenyl-1,9-anthrazoline
Synthesis
Fluorescence
Optical properties
Electrochemical properties
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
molecules can be applicable as an electron-transporting electrolu-
minescent material [11,12]. 4,6-Diphenyl-1,9-anthrazolines are the
Research on organic light-emitting diodes (OLEDs) received
a boost by the development of conjugated -electron materials
isomers of 4,8-diphenyl-1,5-anthrazolines, they may have similarly
excellent photophysical properties. However, the reports concern-
ing the photophysical properties of small molecules based on the
4,6-diphenyl-1,9-anthrazoline core are limited. In this context, we
aim to develop new 4,6-diphenyl-1,9-anthrazoline molecules and
do the further study of the underlying structureeproperty
relationships.
In this paper, we report the synthesis, detailed structural char-
acterization and investigation of the thermal stabilities, electro-
chemical and photophysical properties of a series of new n-type
organic semiconductors based on 4,6-diphenyl-1,9-anthrazolines,
that contain various aromatic substituents (Scheme 1). Their pho-
tophysical properties and crystal structures were investigated with
the aim of understanding structureephysical property relation-
ships in the context of novel organic light-emitting materials.
p
using as light emitters and charge transporters [1e12]. However, for
developing more efficient organic light-emitting devices, they are
challenges to balance charge carrier injection from both cathode
and anode and balance charge transport to the emissive layer
[13e16]. Since hole mobility is typically orders of magnitude larger
than electron mobility in most current OLED systems, the intro-
duction of an electron-transport layer can dramatically reduce the
hole current and thereby result in more efficient OLEDs [17e19].
Heterocyclic molecules, oligomers, and polymers have been used as
electron-transport materials to varied degrees of success in
improving device performance [6,17,18,20e24]. Among these
materials, diphenylanthrazoline derivatives are of immense
interest because these small molecules have high electron affinity
and high thermal stability and are promising electron-transport
materials for OLED [6]. Recently, our group has reported a series of
thermally stable 4,8-diphenyl-1,5-anthrazolines, which also exhibit
high decomposition temperature, high melt transitions, low optical
band gaps and high electron affinity, suggesting that these
2. Experimental section
2.1. Materials
Pyromellitic dianhydride was purchased from Zhejiang Sheng-
xiao Chemical Company. Fluorene was purchased from Beijing
Rizhaoshilide Chemical Company. Acetophenone (a), 4-iodoaceto-
phenone and other reagents were purchased from Sinopharm
* Corresponding author. Tel.: þ86 25 83172358; fax: þ86 25 83587443.
E-mail address: zhuhjnjut@hotmail.com (H. Zhu).
0143-7208/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2011.02.011

90
Q. Zhang et al. / Dyes and Pigments 91 (2011) 89e97
polyphosphoric acid
O
5
6
4
7
8
3
2
2
R
+
O
O
H3C
R
N
N
1
R
H2N
NH2
9
a - i
1a - 1 i
1a: R =
1c: R =
o
1b: R =
N
1d: R =
1g: R =
1e: R =
1h: R =
O
1f: R =
1i: R =
CH2CH3
N
N
Scheme 1. Synthesis of 4,6-diphenyl-1,9-anthrazolines (1ae1i).
Chemcial Reagent Co. Ltd and used as received. 4,6-Dibenzoyl-1,3-
phenylenediamine (1) [25], other acetylfunctionalized compounds
def [26e28], g [29], h [30] and i [31], and 4,6-Diphenyl-1,9-
anthrazoline derivatives (1ae1i) [25] were synthesized according
to the methods reported in literatures with some modification. The
synthetic routines are shown in Figs. 1e5, respectively.
65e70 ꢀC for 4 h. During the period, hydrogen chloride gas was
evolved, and the suspension turned brown. The reaction mixture
was then poured into water (200 ml) containing concentrated
hydrochloric acid (17.0 ml). After removal of the benzene by steam
distillation, a mixture of 4,6-dibenzoylisophthalic acid (5) and 2,5-
dibenzoylterephthalic acid (4) was obtained as off-white, granular
material. The acids were collected by filtration, washed with water,
and dissolved in dilute potassium hydroxide solution. After filtra-
tion to remove a small amount of insoluble matter, the acids were
reprecipitated with hydrochloride acid, washed with water, and
dried at 80 ꢀC for 8 h. After 4 was obtained by recrystallization from
acetic acid, the residual products were recrystallized twice from
acetone to give 5 (4.8 g, 12.8 mmol) as block solids in 25.6% yield,
m.p. 277e279 ꢀC (lit. [25]: 277e278 ꢀC). 1H NMR (DMSO,
2.2. Measurements
1H NMR and 13C NMR spectra were recorded on a Bruker AV-500
spectrometer at 500 MHz or a Bruker AV-300 spectrometer at
300 MHz using CDCl3 and trifluoroacetic acid (TFA) as the solvent,
with tetramethylsilane as internal standard. Fourier transformation
infrared (FTIR) spectra were recorded in KBr pellets using an
AVATAR 370 FTIR spectrometer (Thermo Nicolet). The elemental
analyses were performed with a Vario El III elemental analyzer.
Thermogravimetric analysis (TGA) of the molecules and differential
scanning calorimetry (DSC) were conducted on a TA Instruments
NETZSCH TG 209 and a DSC Instruments NETZSCH DSC 204,
respectively. Optical absorption spectra were obtained by using
a HP-8453 UV/vis/near- IR Spectrophotometer (Agilent). Photo-
luminescence spectra were carried out on a LS-55 spectrofluo-
rometer (PerkineElmer). The electrochemical experiments were
carried out using a CHI 660C electrochemistry workstation (CHI
USA). A standard one-compartment three-electrode cell was used
with a Pt electrode as the working electrode, a Pt wire as the
counter electrode and a Ag/Agþ electrode (Ag in 0.1 M AgNO3
solution, from CHI, Inc.) as the reference electrode. TBAP (0.1 M)
was used as the supporting electrolyte. The films of 4,6-diphenyl-
1,9-anthrazolines were coated on the Pt working electrode and the
scan rate was 40 mV sꢁ1 [20].
500 MHz):
d ppm 7.49 (s, 1H), 7.50e7.57 (m, 4H), 7.64 (t, 2H), 7.70
(d, 4H), 8.56 (s, 1H), 13.66 (s, 2H).
O
O
COOH
O
O
HOOC
C6H6 / AlCl3
O
HOOC
O
COOH
O
O
+
O
O
5
4
Cl
Cl
O
NH3
SOCl2
O
O
O
O
O
H2NOC
CONH2
HOOC
COOH
O
O
2
3
5
2.3. Synthesis
NaOCl, H2O
O
H2N
O
NH2
2.3.1. 4,6-Dibenzoylisophthalic acid (5)
A mixture of finely ground pyromellitic dianhydride (10.9 g,
50.0 mmol), powdered anhydrous aluminum chloride (30.0 g,
225 mmol) and benzene (250 ml) was heated with stirring at
1
Fig. 1. Synthesis of 4, 6-Dibenzoyl- 1, 3-phenylenediamine (1).

Q. Zhang et al. / Dyes and Pigments 91 (2011) 89e97
91
d: R1=C12H10N ;
e: R1=C6H5 ;
O
O
CH3COCl
Lewis acid
R1
R1
(CH3CO)2O
CH3
f: R1=C6H5O ;
CS2, AlCl3
Fig. 2. Synthesis of acetyl-functionalized compounds (def).
Fig. 4. Synthesis of acetyl-functionalized compounds (h).
2.3.2. Pseudo-4,6-dibenzoylisophthaloyl chloride (3)
(2.0 M, 150 ml). The dichloromethane layer was separated and
washed with water to pH 7. The dichloromethane was removed
using a rotary evaporator and the residue purified by column
chromatography (petroleum ether/chloroform ¼ 3:1 as elution) to
afford d (4.37 g, 15.0 mmol) as yellow crystals in 83.3% yield, m.p.
146e147 ꢀC. (lit. [26]: 143e145 ꢀC). 1H NMR (CDCl3, 500 MHz):
A mixture of 2,4-dibenzoylisophthalic acid (14.0 g, 37.4 mmol),
thionyl chloride (90.0 ml) and dimethyl formamide (0.6 ml) was
heated at the reflux temperature (76e78 ꢀC) for 2 h with stirring.
Then the excess thionyl chloride was removed by distillation.
Benzene (2 ꢂ 50.0 ml) was added and distilled to remove the last
traces of thionyl chloride. Pseudo-4, 6-dibenzoylisophthaloyl chlo-
ride was obtained as white crystals in 99.0% yield, m.p. 183e185 ꢀC
(recrystallized from 1:1 dichloromethane /cyclohexane solvent
d
ppm 2.52 (s, 3H), 6.97e6.99 (m, 2H), 7.11e7.16 (m, 6H), 7.29e7.33
(m, 4H), 7.79 (d, 2H).
mixture). 1H NMR (CDCl3, 500 MHz):
d ppm 7.47e7.49 (m, 6H),
2.3.5.2. p-Phenylacetophenone (e). To a suspension of powdered
anhydrous aluminum chloride (29.3 g, 220 mmol) in carbon
disulfide (150 ml) was added dropwise acetyl chloride (15.6 ml,
220 mmol) during 30 min with vigorous stirring and cooling in an
ice-bath. A solution of biphenyl (30.8 g, 200 mmol) in carbon
disulfide (100 ml) was then added dropwise over a period of
30 min. After the addition was complete, the mixture was stirred at
the reflux temperature for additional 4 h. Carbon disulfide was
removed by distillation and the residue was hydrolyzed by pouring
into a mixture of ice and water (500 ml) containing concentrated
hydrochloric acid (20.0 ml) with stirring. A yellow solid material
was formed when the mixture was cooled to room temperature.
After filtration, the yellow solid material was recrystallized from
ethyl alcohol twice to give e (32.4 g, 165 mmol) as yellow plates in
82.5% yield, m.p. 121e122 ꢀC (lit. [27]: 121 ꢀC). 1H NMR (CDCl3,
7.66e7.68 (m, 4H), 7.79 (s, 1H), 8.46 (s, 1H).
2.3.3. 4,6-Dibenzoylisophthalamide (2)
To a stirred solution of concentrated ammonium hydroxide
(45.0 ml) and N-methyl-2-pyrrolidone (NMP) (60.0 ml) was added
a solution of Pseudo-4, 6-dibenzoylisophthaloylchloride in NMP
(50.0 ml) at 0e5 ꢀC over a 30 min period. The mixture was further
stirred for 5 h at 25 ꢀC and then diluted with water (300 ml). The
mixture was allowed to stand overnight. The white precipitate
which formed was collected and dried to give 2 (13.4 g, 36.0 mmol)
as a white powder in 96.2% yield, m.p. 289e293 ꢀC (lit. [25]:
290e295 ꢀC). 1H NMR (DMSO, 500 MHz):
d ppm 7.01 (s, 2H), 7.10 (d,
1H), 7.20e7.26 (m, 6H), 7.37e7.39 (m, 4H), 7.74 (d, 1H), 9.37 (s, 2H).
2.3.4. 4,6-Dibenzoyl- 1,3-phenylenediamine (1)
500 MHz): d ppm 2.63 (s, 3H), 7.40e7.41 (m, 1H), 7.45e7.48 (m, 2H),
To a solution of potassium hydroxide (42.9 g, 766 mmol) in
water (300 ml) cooled in an ice water bath, was added 4,6-diben-
zoylisophthalamide (26.7 g, 71.8 mmol). The amide dissolved
rapidly and completely. To the stirred solution was added 5.25%
sodium hydrochlorite solution (215 ml, 249.8 mmol) at 5e7 ꢀC
during a period of 30 min. The pale yellow, clear solution was then
warmed rapidly on a water bath to 80 ꢀC. The solution became
orange and a precipitate began to separate within 15 min. The
mixture was heated for an additional hour at 76e80 ꢀC. After
cooling the mixture to room temperature, the precipitate was
filtered, washed thoroughly with hot water, and dried to give the
crude 4,6-dibenzoyl- 1,3-phenylenediamine (18.5 g, 58.2 mmol) in
81.6% yield. Recrystallization from chloroform and subsequently
from methanol gave pale yellow powder, m.p. 253e254 ꢀC (lit. [25]:
7.61e7.63 (m, 2H), 7.68 (d, d, 2H), 8.03 (d, d, 2H).
2.3.5.3. p-Phenoxyacetophenone (f). Compound f was synthesized
according to the method described for compound e. Yield was 81.5%
as yellow plates; m.p. 47e49 ꢀC (lit. [28]: 49 ꢀC). 1H NMR (CDCl3,
500 MHz):
d ppm 2.56 (s, 3H), 7.00 (d, d, 2H), 7.06e7.08 (m, 2H),
7.19 (q, 1H), 7.37e7.41 (m, 2H), 7.94 (d, d, 2H).
2.3.5.4. 1-(4-(9H-carbazol-9-yl)phenyl)ethanone (g). A mixture of
carbazole (33.4 g, 200 mmol), Cu (17.0 g, 26.8 mmol), 18-crown-6
(17.3 g, 65.5 mmol), 4-iodoacetophenone (50.2 g, 210 mmol), K2CO3
(111.0 g, 803 mmol) and DMF (400 ml) was heated at the reflux
temperature (152e153 ꢀC) for 50 h with stirring. After
cooling to room temperature, it was poured into water. After filtered,
the solution was extracted with chloroform. Organic layer was
separated and dried over anhydrous Na2SO4. The precipitate
was purified by column chromatography (petroleum ether/
dichloromethane ¼ 1:1 as the elution) to give g (39.0 g,136.5 mmol)
as a yellow powder in 68.3% yield [29], m.p. 208e209 ꢀC. 1H NMR
255e257 ꢀC). 1H NMR (DMSO, 500 MHz):
d ppm 6.02 (s, 1H),
7.34e7.42 (m, 6H), 7.44e7.46 (m, 6H), 7.56 (s, 1H), 7.59 (s, 4H).
2.3.5. Synthesis of acetyl-functionalized compounds (def, gei)
2.3.5.1. (4-Acetylphenyl)diphenylamine (d). Triphenylamine (4.42 g,
18.0 mmol), zinc chloride (2.45 g, 18.0 mmol) and dichloromethane
(36.0 ml) were added slowly to a solution of acetyl chloride (1.42 g,
18.0 mmol) in dichloromethane (4.0 ml) with vigorous stirring at
room temperature over 5 min. The mixture was refluxed for 20 h.
After cooling to room temperature, it was poured into aqueous HCl
(CDCl3, 500 MHz):
d ppm 2.70 (s, 3H), 7.30e7.33(m, 2H), 7.41e7.44
(m, 2H), 7.48 (d, 2H), 7.71 (d, d, 2H), 8.14 (d, 2H), 8.21 (d, d, 2H).
2.3.5.5. 2-Acetylfluorene (h). Fluorene (20.0 g, 120 mmol) and
carbon disulfide (250 ml) were added in a three-necked flask
I
H
N
K2CO3 , Cu ,18-crown-6
DMF,N2, 1700C
O
N
+
O
Fig. 3. Synthesis of acetyl-functionalized compounds (g).

92
Q. Zhang et al. / Dyes and Pigments 91 (2011) 89e97
C2H5
N
C2H5
N
H
N
Ac2O / BF3. Et2O
C2H5Br
KOH
CH3
O
Fig. 5. Synthesis of acetyl-functionalized compounds (i).
equipped with a mechanical stirrer, stirring until fluorene was
dissolved, anhydrous aluminum chloride (32.0 g, 240 mmol) was
added in. Keeping the carbon disulfide refluxing slowly, acetic
anhydride (12.2 g, 120 mmol) was added drop-by-drop. Then the
reaction was kept 2 h in 46e47 ꢀC water bathe. After filtration, the
precipitate was transferred to a beaker and 40 ml of carbon disul-
fide was added, stirred for 30 min (to dissolve the fluorene which
did not react and other impurities) and filtration was done. 200 ml
of dilute hydrochloric acid solution (1000 g water: 40.0 g concen-
trated hydrochloric acid) was added in and fully stirred, then the
first hydrolysis was coupled with the second hydrolysis. Then
a light orange solid was obtained by water washing and drying after
filtration. The precipitate was recrystallized from ethyl alcohol
twice to give h (14.5 g, 69.6 mmol) in 58.0% yield, m.p. 126e129 ꢀC
500 MHz):
(m, 4H), 7.88e7.92 (m, 2H), 8.18e8.20 (m, 4H), 8.31 (s, 2H), 9.23 (s,
1H), 9.56 (s, 1H). 13C NMR (CDCl3 and TFA, 500 MHz):
ppm 160.03,
138.68, 136.29, 133.66, 132.59, 132.36, 130.85, 130.29, 129.92,
129.63, 129.40, 128.07, 127.71, 125.40, 122.01. FTIR (KBr, cmꢁ1):
3052, 1576, 1532, 1492, 1449, 883, 844, 762, 695. Anal. Calcd. (%) for
C36H24N2: C, 89.23; H, 4.99; N, 5.78. Found: C, 89.29; H, 5.01; N,
5.68.
d ppm 7.66e7.67 (m, 8H), 7.50e7.73 (m, 2H), 7.61e7.80
d
2.3.6.2. 2,8-Bis(4-tert-butylphenyl)-4,6-diphenyl-1,9-anthrazoline
(1b). Yield was 60.4% as orange plates; m.p. 280.9 ꢀC. 1H NMR
(CDCl3 and TFA, 500 MHz):
7.79 (d, 4H), 8.13 (d, 4H), 8.26 (s, 2H), 9.12 (s, 1H), 9.46 (s, 1H). 13C
NMR (CDCl3 and TFA, 300 MHz): ppm 159.71, 159.11, 138.57,
d ppm 1.43(s, 18H), 7.65e7.70 (m, 10H),
d
(lit. [30]: 124e126 ꢀC). 1H NMR (CDCl3, 500 MHz):
d
ppm 2.66 (s,
133.90, 132.06, 131.48, 130.59, 129.67, 129.55, 129.36, 127.82, 126.48,
125.02, 121.53, 120.09, 35.71, 30.73. FTIR (KBr, cmꢁ1): 3053, 2958,
2955, 2902, 2865, 1571, 1522, 1457, 890, 842, 765, 701. Anal. Calcd.
(%) for C44H40N2: C, 88.55; H, 6.76; N, 4.69. Found: C, 88.49; H, 6.68;
N, 4.73.
3H), 3.96 (s, 2H), 7.26e7.43 (m, 2H), 7.59 (d, 1H), 7.83e7.86 (m, 2H),
8.01 (d, d, d, 1H), 8.15 (d, 1H).
2.3.5.6. N-ethylcarbazole (j). A mixture of carbazole (26.4 g,
0.16 mol), potassium hydroxide (56.0 g, 1.0 mol) and DMF (320 ml)
was stirred at room temperature for 40 min. A solution of bromo-
ethane (18.0 ml, 0.24 mol) in DMF (60.0 ml) at room temperature was
added dropwise over a period of 30 min, with stirring. After the
addition was complete, the mixture was stirred at room temperature
for additional 10 h. The mixture was then poured into water (4000 ml),
and white precipitate was formed immediately. After filtration, the
precipitate was recrystallized from ethanol to give j (23.3 g, 0.12 mol)
as white needles in 75.0% yield, m.p. 67e68 ꢀC (lit. [31]: 72e74 ꢀC).
2.3.6.3. 2,8-Bis(4-methoxyphenyl)-4,6-diphenyl-1,9-anthrazoline
(1c). Yield was 64.3% as yellow needles; m.p. 266.5 ꢀC. 1H NMR
(CDCl3 and TFA, 500 MHz):
(m, 10H), 8.21 (s, 2H), 8.23 (d, d, 4H), 9.02 (s, 1H), 9.32 (s, 1H). 13C
NMR (CDCl3 and TFA, 300 MHz): ppm 160.18, 153.30, 147.52,
d ppm 4.03(s, 6H), 7.27(q, 4H), 7.61e7.70
d
139.67, 132.60, 131.36, 129.99, 129.67, 127.81, 126.86, 125.43, 122.10,
121.77, 120.90, 119.95, 58.82. FTIR (KBr, cmꢁ1): 3050, 2833, 1598,
1569,1513,1446, 884, 836, 758, 701. Anal. Calcd. (%) for C38H28N2O2:
C, 83.80; H, 5.18; N, 5.14; O, 5.88. Found: C, 83.87; H, 5.19; N, 5.16; O,
5.82.
2.3.5.7. 3-Acetyl-N-ethylcarbazole (i). A mixture of
j (31.2 g,
160 mmol) and acetic anhydride (16.3 g, 160 mmol) in boron tri-
fluoride diethyl etherate (BF3$Et2O) (400 ml) was stirred at room
temperature for 4 h. Then the mixture was hydrolyzed by pouring
into a mixture of ice and water (1600 ml) containing concentrated
hydrochloric acid (5.0 ml) with stirring. Then diethyl ether was
removed by distillation, and brown precipitate was got by filtration.
The precipitate was recrystallized from ethyl alcohol twice to give i
(30.5 g, 128.6 mmol) as a shallow pink powder in 80.4% yield, m.p.
2.3.6.4. 2,8-Bis(4-triphenylamino)-4,6-diphenyl-1,9-anthrazoline
(1d). Yield was 81.2% as orange crystals; m.p. 294.1 ꢀC. 1H NMR
(CDCl3 and TFA, 500 MHz):
d ppm 7.12 (d, 4H), 7.29 (d, 8H), 7.35 (t,
4H), 7.47 (t, 8H), 7.55 (d, 4H), 7.59e7.65 (m, 6H), 8.00 (s, 2H), 8.03 (d,
4H), 8.71 (s, 1H), 8.99 (s, 1H). 13C NMR (CDCl3 and TFA, 300 MHz):
d
ppm 160.47, 157.56, 155.36, 155.28, 144.29, 139.38, 134.26, 131.55,
131.14, 130.21, 129.80, 129.51, 129.12, 127.20, 126.90, 124.02, 120.26,
119.90, 119.09. FTIR (KBr, cmꢁ1): 3036, 1584, 1450, 1455, 883, 838,
755, 697. Anal. Calcd. (%) for C44H40N2: C, 87.99; H, 5.17; N, 6.84.
Found: C, 88.36; H, 5.03; N, 6.73.
113e115 ꢀC. (lit. [31]: 116e118 ꢀC). 1HNMR (CDCl3, 500 MHz):
d ppm
1.45 (s, 3H), 2.72 (s, 3H), 4.38 (q, 2H), 7.30 (t, 1H), 7.40 (d, 1H), 7.44
(d, 1H), 7.51 (t, 1H), 8.12 (d, d, 1H), 8.15 (d, 1H), 8.74 (d, 1H).
2.3.6. General procedure for synthesis of 1ae1i
2.3.6.5. 2,8-Bis(biphenyl)-4,6-diphenyl-1,9-anthrazoline (1e). Yield
A mixture of 4,6-dibenzoyl-1,3-phenylenediamine (2.0 mmol),
acetyl-functionalized compound (aei) (4.2 mmol), polyphosphoric
acid (PPA) (4.0 g), and m-cresol (10.0 ml) was heated at 130e140 ꢀC
for 48 h. The reaction mixture was then diluted with methanol and
poured into 1.0 M potassium hydroxide solution (500 ml) and
collected by vacuum filtration. The precipitate was washed with hot
water (3 ꢂ 500 ml), and dried at 80 ꢀC. The resulting product was
then recrystallized from tetrahydrofuran (THF)/methanol solutions
ranging from 30% to 50% methanol. Each was recrystallized twice.
was 94.5% as yellow plates; m.p. 267.2 ꢀC. 1H NMR (CDCl3 and TFA,
500 MHz):
2H), 8.31 (d, 2H), 8.36 (s, 2H), 9.20 (s, 1H), 9.52 (s, 1H). 13C NMR
(CDCl3 and TFA, 500 MHz): ppm 160.94, 159.21, 149.93, 138.94,
d ppm 7.50e7.57 (m, 6H), 7.68e7.75 (m, 14H), 8.03 (d,
d
138.27, 137.77, 132.59, 132.20, 130.04, 129.98, 129.86, 129.61, 129.48,
129.40, 127.66, 127.54, 125.38, 121.77, 117.86. FTIR (KBr, cmꢁ1): 3027,
1568, 1486, 1449, 890, 842, 763, 731, 696. Anal. Calcd. (%) for
C48H32N2: C, 90.54; H, 5.06; N, 4.40. Found: C, 90.50; H, 5.13; N,
4.25.
2.3.6.1. 2,4,6,8-Tetraphenyl-1.9-anthrazoline (1a). Yield was 80.5%
2.3.6.6. 2,8-Bis(4-phenoxylphenyl)-4,6-diphenyl-1,9-anthrazoline
as orange crystals; m.p. 265.4 ꢀC. 1H NMR (CDCl3 and TFA,
(1f). Yield was 75.6% as yellow needles; m.p. 215.1 ꢀC. 1H NMR

Q. Zhang et al. / Dyes and Pigments 91 (2011) 89e97
93
Table 1
Physical properties of 1ae1i.
Abs
Em
Compd. Tm
(ꢀC)
Td
(ꢀC)
3
l
l
Stokes Egopt
max
max
(104 Mꢁ1 cmꢁ1
)
(nm) (nm) shift
(nm)
(eV)
1a
1b
1c
1d
1e
1f
1g
1h
1i
265.4
280.9
266.5
294.1 >450
267.2
215.1
225.8 >450
307.6 >450
322.8 >450
371.0 1.89
403.6 2.27
406.2 2.54
3.82
435.5 2.87
425.0 2.51
397
401
411
454
408
406
414
419
435
432
435
463
493
458
448
450
469
458
35
34
52
39
50
42
36
50
23
3.00
2.96
2.89
2.55
2.90
2.92
2.79
2.84
2.71
2.72
3.31
4.20
(CDCl3 and TFA, 500 MHz):
d ppm 7.10 (d, 4H), 7.14e7.19 (m, 6H),
7.39 (q, 4H), 7.45e7.51 (m, 6H), 7.58 (q, 4H), 7.81 (s, 2H), 8.30 (d,
4H), 8.56 (s, 1H), 9.11 (s, 1H). 13C NMR (CDCl3 and TFA, 300 MHz):
d
ppm 159.25, 157.87, 156.81, 149.46, 147.97, 138.18, 134.44, 129.97,
129.61, 129.54, 128.94, 128.74, 128.61, 124.56, 124.35, 123.84, 119.45,
118.93, 118.75. FTIR (KBr, cmꢁ1): 2975, 1582, 1486, 873, 835, 782,
698. Anal. Calcd. (%) for C48H32N2O2: C, 86.20; H, 4.82; N, 4.19; O,
4.79. Found: C, 86.26; H, 4.95; N, 4.17; O, 4.76.
2.3.6.7. 2,8-Bis(4-(9H-carbazol-9-yl)phenyl)-4,6-diphenyl-1,9-anthr-
azoline (1g). Yield was 64.5% as a yellow powder; m.p. 225.8 ꢀC. 1H
NMR (CDCl3 and TFA, 500 MHz):
d ppm 7.32 (t, 4H), 7.44e7.47 (m,
4H), 7.48e7.55 (m, 10H), 7.64 d, 4H), 7.81 (d, 4H), 7.96 (s, 2H), 8.17
(d, 4H), 8.58 (d, 4H), 8.67 (s, 1H), 9.27 (s, 1H). 13C NMR (CDCl3 and
TFA, 300 MHz): d ppm 159.69, 157.85, 154.56, 149.82, 147.96, 140.70,
139.36, 138.35, 137.98, 129.58, 129.42, 128.84, 128.64, 127.30, 126.11,
124.87, 124.59, 123.65, 120.40, 120.23, 118.93. FTIR (KBr, cmꢁ1):
3048, 1595, 1516, 1449, 887, 847, 746. Anal. Calcd. (%) for C60H38N4:
C, 88.43; H, 4.70; N, 6.87. Found: C, 88.30; H, 4.72; N, 6.92.
2.3.6.8. 2,8-Bis(2-flourenyl)-4,6-diphenyl-1,9-anthrazoline (1h). Yield
was 61.4% as a yellow powder; m.p. 307.6 ꢀC.1H NMR (CDCl3 and TFA,
Fig. 6. Single crystal structure of 1a (a), view down the a axis (b).
500 MHz): d ppm 4.11 (s, 4H), 7.52 (t, 4H), 7.63e7.70 (m,12H), 7.97 (q,
2H), 8.11 (d, 2H), 8.26 (d, d, 2H), 8.29 (s, 2H), 8.43 (s, 2H), 9.03 (s, 1H),
9.56 (s, 1H). 13C NMR (CDCl3 and TFA, 500 MHz):
ppm 159.33,
d
Table 2
Crystallographic data for 4,6-diphenyl-1,9-anthrazoline 1a and 1f.
151.07, 146.14, 145.42, 139.25, 139.08, 133.89, 132.42, 131.75, 130.40,
129.92, 129.52, 129.23, 128.17, 127.94, 126.81, 125.78, 125.72, 125.48,
125.17, 122.11, 121.87, 121.38, 36.90. FTIR (KBr, cmꢁ1): 3050, 1573,
1472, 1493, 885, 830, 765, 736, 701. Anal. Calcd. (%) for C50H32N2: C,
90.88; H, 4.88; N, 4.24. Found: C, 90.77; H, 4.86; N, 4.29.
Compound
1a
1f
Chemical formula
Formula weight
Crystal system
Space group
a (Å)
C36H24N2
484.57
Triclinic
P-1
10.111(2)
10.750(2)
12.736(3)
107.12(3)
96.36(3)
96.68(3)
1298.6(5)
1.239
C48H32N2O2
668.77
Triclinic
P-1
9.668 (16)
14.808(2)
15.150(4)
115.43(3)
106.26(3)
97.39(2)
1801.3(6)
1.266
2.3.6.9. 2,8-Bis(3-(N-ethyl-carbazole))-4,6-diphenyl-1,9-anthrazoline
b (Å)
c (Å)
(1i). Yield was 70.3% as yellow plates; m.p. 322.8 ꢀC. 1H NMR
a
b
g
(ꢀ)
(ꢀ)
(ꢀ)
(CDCl3 and TFA, 500 MHz):
d ppm 1.57 (t, 6H), 4.52 (q, 4H),
7.44e7.47 (m, 2H), 7.58 (d, 2H), 7.65-7.74 (m, 14H), 8.23 (d, 2H), 8.33
(d, d, 2H), 8.37 (s, 2H), 8.92 (s,1H), 8.98 (d, 2H), 9.22 (s,1H). 13C NMR
V (Å3)
(CDCl3 and TFA, 500 MHz):
d ppm 158.81, 158.45, 145.01, 141.43,
Dcalc (gcmꢁ3
m
)
(mmꢁ1
)
0.072
508
0.079
720
139.53, 134.22, 132.03, 130.88, 129.82, 129.33, 128.56, 126.51, 125.77,
124.55, 123.22, 177.73, 122.22, 121.36, 121.21, 121.11, 118.80, 117.81,
38.57, 13.59. FTIR (KBr, cmꢁ1): 3048, 2972,1570,1486, 876, 814, 750,
701. Anal. Calcd. (%) for C52H38N4: C, 86.88; H, 5.33; N, 7.79. Found:
C, 86.76; H, 5.43; N, 7.68.
F (000)
range (ꢀ)
Index range
q
1.7e25.3
0 ꢃ h ꢃ 12
ꢁ12 ꢃ k ꢃ 12
ꢁ15 ꢃ l ꢃ 15
4999
1.6e27.1
ꢁ12 ꢃ h ꢃ 12
ꢁ18 ꢃ k ꢃ 18
ꢁ18 ꢃ l ꢃ 19
13,786
Reflns collected
Unique reflns (Rint
)
4711 (0.028)
7913 (0.039)
2.4. X-ray diffraction crystallography
Refinement method on F2 Full-matrix least-squares Full-matrix least-squares
GOF on F2
R1 [I > 2 (I)]
wR2 [I > 2 (I)]
1.000
0.0600
0.1660
0.1161
0.2014
0.235 and ꢁ0.191
1.001
0.1359
0.2003
0.0772
0.1687
0.723 and ꢁ0.766
Crystals of 1a and 1f suitable for single crystal X-ray diffraction
were obtained by slow evaporation of THF/methanol solutions. The
diffraction data were collected on a Nonius CAD4 single crystal
s
s
R1 (all data)
wR2 (all data)
diffractometer equipped with a graphite-monochromated MoK
a
Residual (e Åꢁ3
)
radiation ( /2 scan mode at 293 K. The
l
¼ 0.71073 Å) by using an
u q

94
Q. Zhang et al. / Dyes and Pigments 91 (2011) 89e97
Fig. 9. PL spectra of 1ae1i in toluene solution (10ꢁ8 M).
positions. The crystal and structure refinement data of 1a and 1f are
listed in Table 2.
3. Results and discussion
3.1. Synthesis and characterization
The synthetic route of 4,6-dibenzoyl-1,3-phenylenediamine is
shown in Fig. 1. According to the recrystallization method reported
in literature [25], the pure 4,6-dibenzoylisophthalic acid (5) could
not be obtained. When 5 were recrystallized from acetone, instead
of a mixture of acetic acid and water (1:3), we succeeded in getting
the pure product. Scheme 1 outlines the synthesis of the series of
4,6-diphenyl-1,9-anthrazolines. The acid-catalyzed Friedländer
condensation reactions [25] yielded the desired products in
60e94% yields. The polyphosphoric acid catalyst was readily
removed by precipitation into a 1.0 M potassium hydroxide solu-
tion. The precipitation was washed by hot water three times. They
were subsequently recrystallized in THF/methanol mixture ranging
from 30% to 50% methanol. Compounds 1a and 1d were obtained as
orange crystals; 1b was obtained as orange plates; 1c and 1f were
obtained as yellow needles; 1e and 1i were obtained as yellow
plates; 1g and 1h were obtained as a yellow powder. 1H NMR
spectra, 13C NMR spectra, FTIR spectra and element analysis on
1ae1i confirmed the proposed structures. All the 4,6-diphenyl-1,9-
anthrazolines were soluble in common organic solvents in varying
degrees such as tetrahydrofuran, chloroform, toluene and formic
acid.
Fig. 7. Single crystal structure of 1f (a), view down the a axis (b).
crystal structures were solved by the direct method and refined by
the full-matrix least-squares procedure on F2 using SHELXL-97
program [32]. All non-hydrogen atoms were refined anisotropi-
cally, and the hydrogen atoms were introduced at calculated
The thermal properties, including melting and decomposition
temperatures, of these molecules are shown in Table 1. Differential
scanning calorimetry (DSC) was used to investigate phase transi-
tions. No glass transitions events were observed by DSC scans of the
molecules. All compounds had melting transitions ranging from
215.1 to 322.8 ꢀC, with p-phenoxyl phenyl substituted 1f melting
at the lowest temperatures, 215.1 ꢀC, and N-ethylcarbazolyl
substituted 1i melting at the highest temperature, 322.8 ꢀC,
respectively. Compared to 4,8-diphenyl-1,5-anthrazolines [6,11], the
melting temperatures of 4,6-diphenyl-1,9-anthrazolines are lower
due to their lower lattice energy. Also, it is evident that the solubility
of 4,6-diphenyl-1,9-anthrazolines is better than 4,8-diphenyl-1,5-
anthrazolines.
The decomposition temperatures determined by thermogravi-
metric analysis (TGA) were above 371.0 ꢀC. Compared to 1a, with
electron-donating moiety substituted 1be1i are more thermally
Fig. 8. UVevis absorption spectra of 1ae1i in toluene solution (10ꢁ5 M).

Fig. 10. Cyclic voltammograms of thin films of 1ae1i coated on a Pt wire electrode. Scan rate ¼ 40 mV/s.

96
Q. Zhang et al. / Dyes and Pigments 91 (2011) 89e97
Em
stable. All of these results demonstrate that the series of 4,6-
diphenyl-1,9-anthrazolines 1ae1i are very robust molecules.
band gap (2.55 eV) and the largest lmax
(493 nm) with high
thermal stability (Tm ¼ 294.1 ꢀC, Td > 450 ꢀC) and is expected to be
applicable as an electron-transporting electroluminescent material.
3.2. X-ray crystal structures
Crystals were grown by slow evaporation of THF/methanol
solutions. Single crystals from two of the nine 4,6-diphenyl-1,9-
anthrazolines (1a and 1f) were suitable for the determination of X-
ray crystal structures. 1a was obtained as orange prisms, and 1f was
obtained as thin yellow needles. In the molecule of 1f, it contains
two molecules of H2O. 1a and 1f were found to have the same
triclinic crystal systems, with a space group P-1. The unit cell
parameters of a ¼ 10.111 (2) Å, b ¼ 10.750 (2) Å, c ¼ 12.736 (3) Å,
3.4. Electrochemical properties
Cyclic voltammetry was done on thin films of 1ae1i. The cyclic
voltammograms (CVs) of these nine molecules are shown in Fig. 10.
Irreversible reduction peaks were seen in CVs of 1ae1i. Molecules
1c, 1d had one irreversible oxidation peak. In the case of 1a, 1b, 1e,
1f, 1g, 1h, 1i, the irreversible oxidation peak was not seen when
scanned to 2.0 V.
a
¼ 107.12ꢀ (3),
b
¼ 96.36ꢀ (3), and
g
¼ 96.68ꢀ (3) for 1a are reported
Table 3 shows the solid-state electrochemical data for 1ae1i.
HOMO and LUMO levels were estimated from the onset potentials
by using an SCE energy level of 4.4 eV versus a vacuum [12,20].
Electron affinities (LUMO) were estimated from the onset of the
reduction wave (EA ¼ Eonsetred þ 4.4). 1ae1i have electron affinities
between 3.21 and 3.38 eV (below vacuum), revealing the promising
electron-transport properties (n-type) for OLEDs. The reduction
potentials of all the molecules are relatively unchanged by the
substituent (R groups), indicating that the LUMOs lie on the 1,9-
anthrazoline moiety. Even the electron-rich carbazole substituted
molecule (1i), which as expected has the lowest oxidation poten-
tial, has essentially the same LUMO level as the other molecules.
The formal reduction potential (Eredpeak) varies from ꢁ1.34 V (vs
SCE) for 1i to ꢁ1.64 V for 1e (Table 3). The electron-donating
strength of the 2,8-substituents on the 1,9-anthrazoline unit (R
group) shifts the formal reduction potential to less positive values.
As a result the estimated ionization potential (IP ¼ Eoxonset þ 4.4 eV)
is reduced from 6.05 eV in 1a to 5.60 eV in 1d. Also shown in Table 3
are the electrochemically derived band gap (Egel) of thin films of
for the molecules, while 1f forms the unit cell dimensions of
a ¼ 9.668 (16) Å, b ¼ 14.808 (2) Å, c ¼ 15.150 (4) Å,
a
¼ 115.43 (3),
b
¼ 106.26 (3), and
g
¼ 97.39 (2). The detailed crystallographic data
for 1a and 1f are collected in Table 2.
The single crystal structures and packing diagrams of 1a and 1f
are shown in Figs. 6 and 7. In 1a and 1f, the crystal structures reveal
that the 1,9-anthrazoline units are relatively planar. The pendant
4,6-diphenyl groups have a twist angle of 67ꢀ and 130ꢀ in 1a, 49ꢀ
and 128ꢀ in 1f, respectively, from the plane of the 1,9-anthrazoline
unit. The
and 29ꢀ in 1f from the plane of the 1,9-anthrazoline unit. In the
molecular packing of 1a, the edge-to-face -stacking interactions
between neighboring molecular units are observed; 4,6-diphenyl
groups and -linked phenyl groups are contacted via CeH.
stacking interactions, which are separated by a distance of 2.94 Å.
However, in the molecular packing of 1f, it exhibits face-to-face
a
-linked phenyl groups are twisted 14ꢀ and 21ꢀ in 1a, 9ꢀ
p
a
p
p-
stacking interactions between neighboring molecular units; the
intermolecular distance is 3.39 Å.
el
1ae1i. The Eg varies from 2.31 eV for 1d to 2.76 eV for 1f. The
3.3. Optical properties
electrochemical band gap is the smallest in 1d as expected from the
large delocalization length facilitated by the substituted groups of
triphenylamino. The measured electrochemical band gap of each
4,6-diphenyl-1,9-anthrazolines is higher than the corresponding
optical band gap (Egopt). Such a difference between Egopt and Egel has
been observed in the literature [11,20,33] and arises from the finite
The absorption spectra of the nine 4,6-diphenyl-1,9-anthrazo-
lines in toluene solution (10ꢁ5 M) are shown in Fig. 8. The lowest
energy absorption bands are from the
their large molar extinction coefficients (
solution absorption spectra of 1ae1i are structured. Unsubstituted
pep* transitions by virtue of
3
¼ 104 Mꢁ1 cmꢁ1). All the
binding energy of excitons in the material.
peak
1a and alkyl substituted 1b have nearly identical absorption
Comparison of the Ered
values of the 4,6-diphenyl-1,9-
Abs
maxima
(
lmax
)
at 397 nm and 401 nm, respectively. The
of methoxyl substituted 1c and phenoxyl
anthrazolines to other nitrogen heterocycles [6] confirms the
Abs
absorption lmax
expected progression of reduction potential and thus electron
peak
substituted 1f are red shifted by 14 nm and 9 nm compared to 1a as
a result of the electron-donating methoxyl and phenoxyl moiety,
respectively. Phenyl substituted 1e and N-carbazolyl substituted 1g
have absorption lmax
affinity. The average Ered
value of 1ae1i, ꢁ1.49 ꢄ 0.15 V, is
similar to 4,8-diphenyl-1,5-anthrazolines’ [6,11], and falls between
acridine and phenazine. This average reduction potential of 1ae1i
is also significantly more positive compared to those of oxadiazole
and benzothiadiazole, both which have been widely explored as
building blocks for electron-transport materials for OLEDs [34e38].
The formal reduction potentials for 1ae1i suggest that these small
molecules are expected to be applicable as an electron-transporting
electroluminescent material. These results show that a series of
Abs
that are red shifted 11 nm and 17 nm
compared to 1a as the phenyl and N-carbazolyl moiety extend the
conjugated backbone, respectively. The increase in conjugation
length and the increased electron density associated with triphe-
nylamino groups in 1d, fluoryl groups in 1h and N-ethylcarbazolyl
groups in 1i lead to a large bathochromic shift of absorption
maximum in 1d to 454 nm, in 1h to 419 nm and in 1i to 435 nm,
respectively.
Optical band gaps (Egopt) determined from the absorption edge
of the solution spectra are given in Table 1. The optical band gap
varies from 2.55 eV in 1d to 3.00 eV in 1a, which is lightly bigger
than 4,8-diphenyl-1,5-anthrazolines [6,11].
Table 3
Electrochemical properties of 1ae1i.
peak
red
peak
ox
onset
red
onset
(V) IP (eV) Egel (eV)
ox
Compd.
E
(V)
E
(V) EA (eV)
E
(V)
E
1a
1b
1c
1d
1e
1f
1g
1h
1i
ꢁ1.37
ꢁ1.39
ꢁ1.41
ꢁ1.41
ꢁ1.60
ꢁ1.64
ꢁ1.39
ꢁ1.36
ꢁ1.34
ꢁ1.11
ꢁ1.08
ꢁ1.12
ꢁ1.11
ꢁ1.19
ꢁ1.19
ꢁ1.10
ꢁ1.06
ꢁ1.02
3.29
3.32
3.28
3.29
3.21
3.21
3.30
3.34
3.38
*
*
1.65
1.61
1.38
1.20
1.44
1.55
1.58
1.61
1.58
6.05
6.01
5.78
5.60
5.84
5.95
5.98
6.01
5.98
2.76
2.69
2.50
2.31
2.63
2.74
2.68
2.67
2.60
The dilute solution (10ꢁ8 M) photoluminescence (PL) spectra of
1ae1i are shown in Fig. 9. All nine compounds emit blue light with
the emission maximum ranging from 432 nm for 1a to 493 nm for
1d. All the lmaxEm of 1be1i are slightly red shifted compared to 1a.
Triphenylamino substituted 1d has the maximum red shift (61 nm).
The Stoke shifts are small for all the compounds, ranging from 23 to
52 nm. Of the nine compounds synthesized, 1d showed the lowest
1.60
1.26
*
*
*
*
*

Q. Zhang et al. / Dyes and Pigments 91 (2011) 89e97
97
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4,6-diphenyl-1,9-anthrazolines have high electron affinity and are
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We have synthesized and investigated the thermal stabilities,
electrochemical and photophysical properties of a series of nine
new n-type organic semiconductors based on 4,6-diphenyl-1,9-
anthrazolines core. TGA and DSC measurements indicated that
1ae1i were thermally robust with high decomposition tempera-
ture (above 371.0 ꢀC) and high melt transitions (215.1e322.8 ꢀC).
Single crystal X-ray structures of 1a and 1f showed that they
crystallized in the triclinic system with the space groups P-1. The
2,7-linked phenyl groups were twisted 14ꢀ and 21ꢀ from the plane
of the anthrazoline unit, respectively, demonstrating the high
degree of planarity of the molecules. Compared to 1a, both
maximum peaks of the UVevis absorption (from 401 to 454 nm)
and PL emission peaks in toluene solution (from 435 to 493 nm) are
slightly red shifted due to the electron-donating effect in 1b, 1c, 1f
and the extension of the conjugated backbone of 1,9-anthrazoline
in 1d, 1e, 1g, 1h and 1i. The high electron affinities of the new
compounds (3.21e3.38 eV) together with their robust thermal
stability suggested that they have promising electron-transport
properties for OLEDs.
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