Red-emitting materials derived from 2,3-dicyanopyrazine for organic light emitting devices

Article abstract of DOI:10.3184/174751912X13554011072941

Styryl-substituted derivatives of 2,3-dicyanopyrazine were designed and synthesised by the Knoevenagel condensation of 2,3-dicyano-5-methylpyrazines with 4-(diphenylamino)benzaldehyde for use as red-emitting fluorescent dyes in organic light-emitting devi

Full text of DOI:10.3184/174751912X13554011072941

JOURNAL OF CHEMICAL RESEARCH 2013
RESEARCH PAPER 57
JANUARY, 57–61
Red-emitting materials derived from 2,3-dicyanopyrazine for organic light
emitting devices
Chun Keun Jang, Cheol Jun Song, Ji Hyun Park, Wang Yao and Jae Yun Jaung*
Department of Organic and Nano Engineering, Hanyang University, Aengdang-dong, Seongdong-gu, Seoul, 133791, Korea
Styryl-substituted derivatives of 2,3-dicyanopyrazine were designed and synthesised by the Knoevenagel condensa-
tion of 2,3-dicyano-5-methylpyrazines with 4-(diphenylamino)benzaldehyde for use as red-emitting fluorescent dyes
in organic light-emitting devices. Structural analysis of the red-emitting styryl fluorescent dyes was carried out using
1H NMR, FT-IR, and elemental analysis. The electroluminescent performance of multi-layered organic light-emitting
devices fabricated with the triphenylamine-substituted dicyanopyrazine compound as the emitting layer achieved a
current efficiency of 1.57 cd A−1 in the green region with CIE coordinates of (0.37, 0.51). However, the green emission
(525 nm) observed from the tris-(8-hydroxyquinolinato)aluminum(III) (Alq3) electron-transport layer indicated the
action of a recombination phenomenon between the emitting layer and the Alq3 electron-transport layer. The device
fabricated with the tert-butylphenyl-substituted compound achieved a current efficiency of 0.238 cd A−1 in the red
region with CIE coordinates of (0.54, 0.42) and showed no recombination phenomenon.
Keywords: 2,3-dicyanopyrazine, triphenylamine, organic light-emitting devices, Knoevenagel reaction, computational chemistry,
quantum yield, red emitting material
Organic light-emitting devices (OLEDs) have potential appli-
cations in many fields including the manufacture of flat-panel
displays.1–5 Since the initial development of high efficiency
OLEDs,6–7 much research has been focused on the develop-
ment of full-colour displays with high efficiency and stability.
Efficient red–green–blue emitters with good colour purity are
essential for full-colour applications. Extensive study over the
past decade has promoted the commercialisation of OLED
devices having these required characteristics; nevertheless,
further advancements are necessary for improved device
performance.
dicyanopyrazine has a rather small molecular size but pos-
sesses a strong donor–acceptor chromophoric system. These
materials exhibit strong fluorescence in both the solution and
solid state, and the HOMO and LUMO electronic levels of the
chromophore have been determined to be appropriate for the
application of this emission layer in commonly used OLED
devices.23–25 We now report the synthesis of dicyanopyrazine
oriented styryl fluorescent dyes and evaluate their optical
properties with respect to the substitution effect. The photo-
physical behaviour and the EL of these new derivatives are
presented here.
In addition to efforts to modify the device structure, another
effective approach to advancing OLED technology is to iden-
tify new and suitable materials for use either as host emitters or
dopants. This has led to a search for materials with the desired
properties such as high emission quantum yield, high thermal
and photochemical stability, and good colour purity. A number
of strongly emissive dyes have emerged as dopants or host
emitters. Light-emitting materials for host emitters must meet
the requirement for high emission quantum yield in the solid
film state and must have the ability to form a thin, uniform
film. They should also have suitable lowest unoccupied molec-
ular orbital (LUMO) and highest occupied molecular orbital
(HOMO) electronic levels for electron-hole recombination
confinement within the desired region to produce excitons.
Besides the well-known host-emitter tris-(8-hydroxyquinolina
to)aluminum(III) (Alq3), other emitting materials have also
been used as the non-doping emitting layer of OLEDs to
achieve emission in additional wavelength regions and give
blue, yellow, and orange colours, thus meeting the require-
ments of various applications. These materials include triaryl-
amine derivatives,8 condensed aromatic compounds,9–11 and
compounds with donor–acceptor molecular structures.12–14
Furthermore, compounds with intramolecular charge transfer
properties are also attractive because the incorporation of the
donor and acceptor in the same molecule can lead to confine-
ment in the recombination zone15,16 and hence lead to good
emission.17–20
Results and discussion
1-(4-(Diphenylamino)phenyl)propan-1-one 1a and 1-(4-tert-
butylphenyl)propan-1-one 1b were synthesised using the
method described previously.26 The propanophenone deriva-
tive 1 was treated with bromine in CCl4 at room temperature to
produce the α-bromopropanophenone derivative 2 in 70–94%
yield. The reaction of α-bromo ketones with an excess of
anhydrous potassium acetate (3.5 equiv.) in acetone afforded
α-acetoxy ketones,27–28 and these compounds were reacted with
10% methanolic NaOH under reflux to produce the corre-
sponding 1-aryl-2-hydroxypropan-1-one 3. The α-diketones 4
were obtained through the oxidation of α-hydroxyketones 3
with copper(II) sulfate in aqueous pyridine solution. 2,3-Dicy-
anopyrazines 5 were synthesised from the condensation of α-
diketones 4 and diaminomaleonitrile (DAMN) in the presence
of a catalytic amount of p-toluenesulfonic acid in methanol.
The methyl protons in compounds 5a and 5b were strongly
deshielded and observed at 2.86 and 2.85 ppm respectively.
The strong electron withdrawing effect of the cyano groups on
the pyrazine ring activated the methyl group of compounds 5a
and 5b, facilitating the condensation reaction with aryl alde-
hydes. The styryl-substituted 2,3-dicyanopyrazines 6a and 6b
were synthesised by Knoevenagel condensation of the 5-
methyl group in 5a and 5b with 4-(diphenylamino)benzaldehy
de in the presence of piperidine as a catalyst which followed
the synthetic procedure for similar styryl dicyanopyrazines as
described in the literature.29 The synthetic strategy employed
herein is summarised in Scheme 1.
2,3-Dicyanopyrazine derivatives have become a subject of
investigation because of their potentially wide applicability in
colouring matters and nonlinear optical and electrolumines-
cent (EL) materials.21–22 Our prior research on dyes derived
from 2,3-dicyanopyrazine indicated that styryl-substituted
The new compounds were characterised by FT-IR, 1H NMR
spectroscopy, and elemental analysis. Absorption bands were
observed at 2227–2237 and 1604–1621 cm−1 in the FT-IR
spectra of compounds 6a and 6b, and were attributed to stretch-
ing vibrations of the CN and C=C groups, respectively. The
1H NMR spectra of 6a and 6b showed doublet signals at
* Correspondent. E-mail: jjy1004@hanyang.ac.kr

58 JOURNAL OF CHEMICAL RESEARCH 2013
Scheme 1 Synthetic route for preparation of 2,3-dicyanopyrazine derivatives.
ca 8.1–8.2 ppm indicating the presence of a typical trans (J =
15.6 Hz) configuration for the alkene proton at the β position
from the pyrazine ring.
The optical and electrochemical data of compounds 6a and
6b are presented in Table 1. Compounds 6a and 6b showed
maximum absorption wavelengths (λmax) of 512 nm and 510 nm,
and emission wavelengths (Fmax) of 603 nm and 599 nm,
respectively (Fig. 1). λmax and Fmax of compound 6a were
expected to be bathochromically shifted relative to those of 6b
because the triphenylamine substituent of 6a possesses a
greater electron-donating ability than the t-butyl phenyl group
of 6b; this is expected induce an increase in the electronic
density of the former HOMO level. However, λmax and Fmax
of 6a were only slightly red-shifted, which indicates that the
substituent exerts minimum effect on the electronic level of the
chromophore.
Geometric optimisation of the designed structure using
computational calculations was applied to explain the minimal
effect of the substituent. Accelrys Materials Studio 4.3 was
used for molecular design and the calculation employed the
Forcite tool (molecular mechanics) and VAMP (semi-empiri-
cal method) with PM3 Hamiltonian methods. As shown in
Fig. 2, the optimized structure of 6a shows a high degree of
distortion between the pyrazine ring and the bulky triphenyl-
amine substituent. The 5-styryl substituent is distorted by
16.576°, whereas the 6-triphenylamine substituent is distorted
by 53.326° relative to the 2,3-dicyanopyrazine ring. Hence, the
π-conjugation between the pyrazine ring and 6-triphenylamine
substituent may be more disturbed by torsional strain. In addi-
tion, the styryl substituent in the 5-position of the pyrazine ring
can undergo free rotation around the C5(pyrazine)–Cα(double-bond)
bond; therefore, the electron-donating effect of the 5-substitu-
ent is not adversely affected by steric hindrance, thus inducing
an increase in the electronic density in the HOMO level.30 The
Fig. 2 Geometrically optimised structure of 6a (calculated
with Materials Studio-Forcite MM and VAMP PM3 methods,
Top view (left) and torsional angle of substituents with 2,3-
dicyanopyrazine plane (right)).
Fig. 1 Absorption and fluorescence spectra of 6a and 6b in
chloroform.

JOURNAL OF CHEMICAL RESEARCH 2013 59
increased electronic density results in compounds 6a and 6b
exhibiting a bathochromic shift compared to compounds 5a
and 5b.
Cyclic voltammograms (CV) were acquired in order to
identify the energies of the HOMO levels of the synthesised
materials. The HOMO level was calculated by assessing the
oxidation potential at the first scan versus the ferrocene refer-
ence electrode. The CV results appeared stable even after 50
scanning cycles. The LUMO level was estimated from the
band-gap, which was confirmed by comparison with the onset
point of the UV-absorption band and from the HOMO values
measured using CV (Table 1). The HOMO levels of both
compounds were higher than that of N,N-bis-(1-naphthyl)-
N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) (–5.5 eV), a
known hole-transporting material. In addition, the LUMO
levels were higher than that of the known electron-transporting
material Alq3 (–3.1 eV), which demonstrated that the elec-
tronic levels were adequate for use as an emitting layer. The
HOMO level of 6a was a little higher than that of 6b, whereas
the LUMO levels of both 6a and 6b were similar.
Fig. 4 EL spectrum of ITO/m-MTDATA (80 nm)/NPB (15 nm)/
6a(○) or 6b (∆) (30 nm)/Alq3 (25 nm)/LiF (1.0 nm)/Al (200 nm)
devices at 1.0 mA cm−2.
A multi-layered OLED device was fabricated to identify the
electroluminescence (EL) properties of the synthesised materi-
als. EL devices were fabricated using 4,4′,4″-tris(N-3-methyl-
phenyl-N-phenylamino)triphenylamine (m-MTDATA) as the
hole-injection layer, NPB as the hole-transporting layer, Alq3
as the electron-transporting layer, and the synthesised materi-
als as the emitting layer. ITO and LiF/Al were used as the
anode and cathode, respectively, with the following arrange-
ment: ITO/m-MTDATA (80 nm)/NPB (15 nm)/6a or 6b
(30 nm)/Alq3 (25 nm)/LiF (1.0 nm)/Al (200 nm). Fig. 3 shows
the I-V curves of the devices. The device fabricated using
6a exhibited an I–V characteristic with a slightly increased
turn-on voltage.
649 nm, whereas the device containing 6a showed two maxima
at 525 and 668 nm. The ELmax value at 525 nm corresponds to
Alq3 emission. The two peaks observed in the EL spectrum of
the 6a device may have resulted from the recombination zone
shift to the EML/Alq3 interface.
The HOMO levels of 6a and 6b were similar, as shown in
Table 1, and were indicative of a low barrier similar to the
HOMO level of Alq3 (–5.7eV), which is well-known as a green
fluorescent material for OLEDs.31 Hence, 6a and 6b should
also be suitable to act as the hole-transporting layer in such
fabricated devices. However, emission from the Alq3 layer
was only observed in 6a, which indicates that 6a, containing
triphenylamine substituent with greater electron-donating
capacity, was simultaneously acting as a hole-transporting
layer and an emitting layer. Table 2 lists the efficiency of the
fabricated devices at a current density of 1.0 mA cm−2. The
device containing compound 6a had a green CIE coordinates
of (0.37, 0.51) in the green region and a current efficiency of
1.57 cd A−1, whereas that containing 6b had CIE coordinates
of (0.54, 0.42) in the red region and a current efficiency of
0.238 cd A−1.
Figure 4 shows the electroluminescence (EL) spectra of the
fabricated devices. The device containing 6b as the emitting
layer emitted in the red region with a single maximum at
Table 1 Optical and electrochemical properties of compounds
6a and 6b
λmax/nma
Fmax/nm
ΦF(MEK) LUMO HOMO Eg/eV
b
/eV
/eV
CHCl3
Film
Conclusions
6a
6b
512
510
603
599
690
685
0.53
0.13
–2.98 –5.16
–3.02 –5.18
2.18
2.16
2,3-Dicyanopyrazine derivatives synthesised in this study
exhibited emission properties suitable for application in
OLED devices. The electronic levels of the compounds were
appropriate for such applications, falling between those of
conventionally used hole- and electron-transporting layers.
Compound 6a, containing the triphenylamine substituent with
greater electron-donating capacity, acted as a hole-transporting
material in fabricated OLED devices, even though the HOMO
level of this compound was largely similar to that of the tert-
butylphenyl-substituted counterpart 6b, which did not exhibit
this capacity. Transfer of excitons from Alq3 to the electron-
transport layer of other materials that have a much lower
HOMO level increases the block barrier with the HOMO level
of the synthesised products. This represents a method for
enhancing device efficiency and verifies the suitability of
2,3-dicyanopyrazines for OLED applications.
a In chloroform.
b Measured by comparative method in methyl ethyl ketone
versus rhodamine B (ΦF = 0.67) in ethanol.
Table 2 EL performance of multi-layered devices with ITO/m-
MTDATA (80 nm)/NPB (15 nm)/6a or 6b (30 nm)/Alq3 (25 nm)/
LiF (1.0 nm)/Al (200 nm) arrangement at 1.0 mA cm−2
ELmax/nm
Voltage/V Efficiency/cd A−1
CIE (x,y)
Fig. 3 Current density-voltage characteristics of ITO/m-
MTDATA (80 nm)/NPB (15 nm)/6a(○) or 6b(∆) (30 nm)/Alq3
(25 nm)/LiF (1.0 nm)/Al (200 nm) devices.
6a
6b
525, 668
649
5
5
1.57
0.238
(0.37, 0.51)
(0.54, 0.42)

60 JOURNAL OF CHEMICAL RESEARCH 2013
1-(4-Tert-butylphenyl)-2-hydroxypropan-1-one (3b): Yellow liquid
(86%); 1H NMR (300 MHz, CDCl3) δ 7.86 (d, J = 9.0 Hz, ArH, 2H),
7.51 (d, J = 8.7 Hz, ArH, 2H), 5.16 (q, J = 6.6 Hz, 1H), 3.81 (s, –OH,
1H), 1.41 (d, J = 6.8Hz, –CH3, 3H), 1.35 (s, -t-Bu, 9H); Anal. Calcd
for C13H18O2: C, 75.69; H, 8.80. Found: C, 75.36; H, 9.01%; GC-MS
(m/z) 206.19. Calcd 206.28.
Experimental
General information
Flash chromatography was performed using Merck-EM type 60 (230–
400 mesh) silica gel (flash). Melting points are obtained using a capil-
lary melting point apparatus and are uncorrected. Elemental analysis
1
was performed using a Flash EA-1112 analyser. H NMR spectra
Synthesis of 1-aryl-propan-1,2-diones (4); general procedure
Compound 3 (0.018 mol) was added to a mixture of CuSO4·5H2O
(10.16 g, 0.038 mol) in pyridine (7 mL) and water (3 mL). The mix-
ture was heated under reflux and monitored using thin-layer chroma-
tography [TLC, ethyl acetate:n-hexane (1:3)] and then extracted with
ethyl acetate (100 mL) and water (150 mL). The organic layer was
dried with sodium sulfate and evaporated in vacuo. The crude product
was purified by column chromatography over silica gel with ethyl
acetate:n-hexane (1:3) as the eluent, to yield compounds 4a and 4b.
1-[4-(Diphenylamino)phenyl]propan-1,2-dione (4a): Orange solid,
(88%), m.p. 126 °C; 1H NMR (300 MHz, CDCl3) δ 7.88 (m, ArH, 3H),
7.42 (m, ArH, 4H), 7.25 (d, J = 8.7 Hz, ArH, 2H), 7.15 (d, J = 8.7 Hz,
ArH, 2H), 6.99 (m, ArH, 3H), 2.15 (s, –CH3, 3H); Anal. Calcd for
C21H17NO2; C, 79.98; H, 5.43; N, 4.44. Found: C, 79.64; H, 5.49;
N:4.28%; GC-MS (m/z) 315.04. Calcd 315.37.
were recorded on a VARIAN UnityInova 300 MHz FT NMR spec-
trometer. UV-Vis and fluorescence spectra were measured using
SCINCO S-4100 and Shimadzu RF-5301PC spectrophotometers.
The fluorescence quantum yield (Φ) was determined by a compara-
tive method using Rhodamine B (Φf = 0.69 in ethanol) as a reference
and using the following net equation.32
2


 
A  
 

PL
UV
nA
A  
ref  

ΦA = Φ
ref
2

UV
PL
n
ref
 

ref
where PL is the integrated area under the corrected emission spectrum
and UV is the absorbance of the solution at the given excitation wave-
length. Subscripts “A” and “ref” refer to the unknown and reference
solutions respectively, and “n” is the refractive index of the corre-
sponding solutions. Cyclic voltammetry (CV) experiments were
performed using a BAS-100 electrochemical analyser with a three-
electrode configuration consisting of a Pt disk working electrode, an
Ag/AgCl reference electrode, and Pt wire counter electrode. All mea-
surements were taken in acetonitrile with 0.1 M tetra-n-butylammo-
nium tetrafluoroborate (TBABF4) as the supporting electrolyte.
HOMO energy levels were calculated from the oxidation potential
using the following equation.33,34
1-(4-tert-Butylphenyl)propan-1,2-dione (4b):Yellow liquid, (75%);
1H NMR (300 MHz, CDCl3) δ 7.92 (d, J = 9.0 Hz, ArH, 2H), 7.51 (d,
J = 8.7 Hz, ArH, 2H), 2.13 (s, –CH3, 3H), 1.34 (s, t-Bu, 9H); Anal.
Calcd for C13H16O2: C, 76.44; H, 7.90. Found: C, 76.64; H, 8.09%;
GC-MS (m/z) 204.04. Calcd 204.26.
5-[4-(Diphenylamino)phenyl]-6-methylpyrazine-2,3-dicarbonitrile
(5a): A solution of 1-[4-(diphenylamino)phenyl]propane-1,2-dione
(5.0 g, 0.016 mol), diaminomaleonitrile (DAMN) (1.73 g, 0.016 mol)
in methanol (200 mL) and a small amount of p-toluenesulfonic acid as
the catalyst was heated under reflux for 2 h. Methanol was poured into
the mixture and stirred for 1 h at room temperature. The precipitate
was filtered off and washed with methanol. The crude product was
purified by column chromatography over silica gel with ethyl acetate:
n-hexane (1:5) as the eluent to yield compound 5a as a yellow solid,
(45%), m.p. 103 °C; 1H NMR (300 MHz, CDCl3) δ 7.60 (d, J = 8.7 Hz,
ArH, 2H), 7.46 (d, J = 8.7 Hz, ArH, 2H), 7.15–7.26 (m, ArH, 10H),
2.86 (s, –CH3, 3H); Anal. Calcd for C25H17N5; C, 77.50; H, 4.42; N,
18.08. Found: C: 77.41; H: 4.38; N: 18.16%; GC-MS (m/z) 386.96
Calcd 387.44.
5-(4-tert-Butylphenyl)-6-methylpyrazine-2,3-dicarbonitrile (5b): A
solution of 1-(4-tert-butylphenyl)propane-1,2-dione (40 g, 0.14 mol),
DAMN (15.2 g, 0.14 mol) in methanol (200 mL) and a small amount
of p-toluenesulfonic acid as the catalyst was heated under reflux for
2 h. Methanol was poured into the mixture and stirred for 1 h at room
temperature. The precipitate was filtered off and washed with metha-
nol. The crude product was purified by column chromatography over
silica gel with ethyl acetate:n-hexane (1:3) as the eluent, to yield com-
pound 5b as a white solid, (50%), m.p. 111 °C; 1H NMR (300 MHz,
CDCl3) δ 7.62 (d, J = 8.7 Hz, ArH, 2H), 7.54 (d, J = 8.7 Hz, ArH, 2H)
2.85 (s, –CH3, 3H), 1.39 (s, t-Bu, 9H); Anal. Calcd for C17H16N4:
C, 73.89; H, 5.84; N, 20.27. Found: C, 73.74; H, 5.99; N, 19.91%;
GC-MS (m/z) 276.15. Calcd 276.34.
(E)-5-[4-(Diphenylamino)phenyl]-6-[4-(diphenylamino)styryl]pyr
azine-2,3-dicarbonitrile (6a): A solution of 5a (3.0 g, 7.74 mmol),
4-(diphenylamino)benzaldehyde (2.12 g, 7.74 mmol) in benzene
(20 mL) and a small amount of piperidine as the catalyst was heated
under reflux for 21 h under an N2 atmosphere. After the reaction was
complete, the mixture was cooled to room temperature. Methanol was
poured into the mixture and stirred for 1 h at room temperature. The
precipitate was filtered off and washed with methanol. The crude
product was purified by column chromatography over silica gel with
ethyl acetate:n-hexane (1:3) as the eluent, to yield compound 6a as a
red solid, (45%); m.p. 150 °C, FT-IR (KBr pellet), νmax/cm−1 2232
(C≡N), 1602 (C=C), 1489, 1296; 1H NMR (300 MHz, CDCl3) δ 7.82
(m, ArH, 4H), 7.78 (d, J = 15.6 Hz, 1H), 7.42 (m, ArH, 8H), 7.32 (m,
ArH, 8H), 7.18 (d, J = 15.6 Hz, 1H), 7.15 (d, J = 8.7 Hz, ArH, 4H),
6.97 (m, ArH, 4H); Anal. Calcd for C36H29N5: C, 82.22; H, 4.70, N,
13.08. Found: C, 81.25; H, 5.61; N. 13.37%; FAB-MS (m/z) 642.12.
Calcd 642.75.
(E)-5-(4-tert-Butylphenyl)-6-[4-(diphenylamino)styryl]pyrazine-
2,3-dicarbonitrile (6b): A solution of compound 5b (5.0 g, 0.018 mol),
4-(diphenylamino)benzaldehyde (4.95 g, 0.018 mol) in benzene
(20 mL) and a small amount of piperidine as the catalyst was heated
under reflux for 21 h under an N2 atmosphere. After the reaction was
complete, the mixture was cooled to room temperature. Methanol was
poured into the mixture and stirred for 1 h at room temperature. The
HOMO (eV) = –4.8 – [Eonset – E1/2(ferrocene)]
where Eonset is the onset oxidation potential (V) and E1/2(ferrocene) is
the half-wave potential (V) of ferrocene in the solution. The electronic
level of the analytes was calculated from the difference between the
onset redox potential and the half-wave potential of ferrocene.
Synthesis of 1-aryl-2-bromopropan-1-ones (2); general procedure
One equivalent of Br2 was added dropwise to a solution of the appro-
priate 4-substituted propanophenone 1 (0.04 mol) in CCl4 (30 mL)
with stirring at 10°C. After subsequent stirring for 2 h at room tem-
perature, the mixture was diluted with ice water and extracted with
CHCl3 (100 mL). The organic layer was washed with water and dried
with anhydrous sodium sulfate. The mixture was concentrated under
reduced pressure to form the compounds 2a and 2b.
2-Bromo-1-[4-(diphenylamino)phenyl]propan-1-one (2a): Yellow
solid (70%), m.p. 64 °C; 1H NMR (300 MHz, CDCl3) δ 7.89 (m, ArH,
4H), 7.44–7.41 (m, ArH, 5H), 7.01 (m, ArH, 5H), 5.23 (q, J = 6.6 Hz,
Br–C–H, 1H), 1.88 (d, J = 6.3 Hz, –CH3, 3H). Anal. Calcd for
C21H18BrNO: C, 66.33; H, 4.77; N, 3.68. Found: C, 66.12; H, 4.82; N,
3.70%; GC-MS (m/z) 379.75. Calcd 380.28.
2-Bromo-1-(4-tert-butylphenyl)propan-1-one (2b): Yellow liquid
(94%); 1H NMR (300 MHz, CDCl3) δ 7.92 (d, J = 8.7 Hz, ArH, 2H),
7.48 (d, J = 8.7 Hz, ArH, 2H), 5.20 (q, J = 6.3 Hz, Br–C–H, 1H), 2.11
(d, J = 6.8 Hz, –CH3, 3H), 1.40 (s, t-Bu, 9H). Anal. Calcd for
C13H17BrO: C, 58.01; H, 6.37. Found: C, 58.19; H, 6.41%; GC-MS
(m/z) 269.04. Calcd 269.18.
Synthesis of 1-aryl-2-hydroxypropan-1-ones (3); general procedure
Brominated precursor 2 (0.047 mol) and potassium acetate (0.166
mol) were heated under reflux in acetone (100 mL). The solution was
filtered and the solvent was removed in vacuo. The intermediate α-
acetoxy ketone was hydrolysed using 10% methanolic NaOH solution
(100 mL) under reflux for 1 h. The mixture was diluted with water
(200 mL) and then extracted with ethyl acetate (100 mL). The organic
layer was washed with water, dried with sodium sulfate and evapo-
rated in vacuo. The crude product was purified by column chromato-
graphy over silica gel with ethyl acetate:n-hexane (1:3) as the eluent,
to yield the compounds 3a and 3b.
1-[4-(Diphenylamino)phenyl]-2-hydroxypropan-1-one (3a):Yellow
1
solid (45.9%), m.p. 79 °C; H NMR (300 MHz, CDCl3) δ 7.88 (m,
ArH, 3H), 7.46 (m, ArH, 4H), 7.42 (d, ArH, 2H, J = 8.7 Hz), 7.16 (d,
ArH, 2H, J = 8.7 Hz), 7.03 (m, ArH, 3H), 5.05 (q, J = 6.6Hz, 1H), 4.14
(s, –OH, 1H), 1.46 (d, J = 6.3 Hz, –CH3, 3H); Anal. Calcd for
C21H19NO2: C, 79.47; H, 6.03; N, 4.41. Found: C, 79.10; H, 6.26; N,
4.53%; GC-MS (m/z) 317.11. Calcd 317.38.

JOURNAL OF CHEMICAL RESEARCH 2013 61
3
4
5
6
7
Y. Shirota, J. Mater. Chem., 2000, 10, 1.
J.L. Segura, Acta Polym., 1998, 49, 319.
precipitate was filtered off and washed with methanol. The crude
product was purified by column chromatography over silica gel with
ethyl acetate:n-hexane (1:3) as the eluent, to yield compound 6b as
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8
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Fabrication and testing of OLED devices
OLED devices were fabricated using 4,4′,4″-tris(N-3-methylphenyl-
N-phenylamino)-triphenylamine (m-MTDATA), with a similar HOMO
level to indium tin oxide (ITO), as the hole-injection layer. N,N-Bis-
(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) was
used as the hole-transport layer. Synthesised materials 6a and 6b were
used as the emitting layer and Alq3 was used as the electron-transport
layer. LiF/Al was used as the cathode.
OLEDs were fabricated by deposition of the organic layer onto a
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under vacuum without breaking the vacuum. Prior to organic layer
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10 min following degreasing with acetone and isopropyl alcohol. All
organic layers were grown by thermal evaporation at a base pressure
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We thank Professor Jong-Wook Park of the Catholic Univer-
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research program between industrial, academic and research
institutes through the Korea Industrial Technology Association
(KOITA) funded by the Ministry of Education, Science and
Technology (KOITA-2010)
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Received 18 April 2012; accepted 3 December 2012
Paper 1201272 doi: 10.3184/174751912X13554011072941
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