Advances in Materials Physics and Chemistry, 2011, 1, 91-93
doi:10.4236/ampc.2011.13015 Published Online December 2011 (
Copyright © 2011 SciRes. AMPC
Column Chromatography: A Facile and
Inexpensive Procedure to Purify the Red Dopant DCJ
Applied for OLEDs
Khadijeh Ghanbari1, Hassan Aghajani1, Maryam Golbabaee1, Elham Naemi Khah1,
Seyed Hassan Nabavi2, Ata Koohian1
1Department of Physics, University of Tehran, Tehran, Iran
2Faculty of Physics, Modares University, Tehran, Iran
Received September 17, 2011; revised October 20, 2011; accepted November 3, 2011
DCJ, one of the DCM derivatives, has been used as a laser dye and a red emitter or a red dopant for OLED
devices in recent decade. 4-(dicyanomethylene)-2-methy l-6-(julolidyl-9-enyl)-4H-pyran (DCJ) containing
julolidine group has been synthesized for use as a red fluorescent dye molecule in organic light-emitting di-
odes (OLEDs). In this paper, we reported a facile, simple and inexpensive procedure of purification of DCJ
without necessity of HPLC analysis. The maximum absorption, emission, quantum efficiency are increasing
in DCJ with the electron-donating of julolidine group.
Keywords: Purification, Column Chromatography, Absorption, Emission, Quantum Efficiency
1. Introduction
In recent years, the study of synthesis, structure and
chemical properties of organic light emitting diodes
(OLED) electronic materials has become one of the
foremost topics in chemistry and physics [1-3]. Since the
introduction of first multi-layer high efficiency thin-film
OLEDs devices by Tang and Van Slyke [4], OLEDs
have attracted considerable interests for flat-panel
display applications. For the flat panel and full color
display, it is necessary to have a set of green, blue and
red emitters with sufficiently high luminous efficiency
and proper chromaticity. At present time, the OLED
materials with blue and green emission have been well
developed; however, the red OLED materials require
more investigation [5]. In 1989, C. W. Tang in Kodak
has improved the efficiency and synthesis of DCM
compounds as red dopants [6]. Then Shim et al. deter-
mined the julolidyl substituted aniline group in the DCM
molecule as DCJ for organic electro-luminescent de-
vices. It is wellknown that the pyran containing dyes such
as DCM and DCJ (4-(dicyanomethylene)-2-methyl-6-
(julolidyl-9-enyl)-4H-pyran) have been widely used as
red emitters OLEDs. Maximum emission and absorption
wavelength increases with the electron-donating or the
electron-withdrawing abilities of different substituents in
the aniline as electro-donating group or the pyran as
electron-withdrawing group of DCM derivatives [7]. The
enhanced electron donating ability of julolidine origi-
nated from the increased communications between the
lone electron pair on the nitrogen atom and phenyl π
system with the help of two six member locking rings [8].
The symmetrical electron acceptor procedure, 4-(dicya-
nomethylene)-2,6-dimethyl-4H-pyran, 1, (Scheme 1) was
used to prepare DCJ.
However, under the normal Knovenagel reaction con-
ditions, the bis-condensed byproduct is inevitably in the
precursor, which is quite difficult to be separated from
the DCJ product and tends to quench the fluorescence of
DCJ, 1 [9,10].
Therefore, in this paper to eliminate the bis-con-
densed by product, we purpose a simple way for com-
plete purification of DCJ dye.
Purification was carried out by Column chromatogra-
phy instead of HPLC analysis with variety ratio of sol-
vents. This method is very simple and needs no expen-
sive equipments in comparison with HPLC analysis.
Scheme 1. Synthesis of DCJ.
2. Experimental
2.1. Materials and Apparatus
The chemicals were obtained from Merck Chemical Com-
pany and Aldrich Chemical Company and were used
without further purification. Melting point was analyzed
with an electro thermal melting point apparatus. The 1H
NMR spectrum was obtained on FT-NMR (500.3 MHz)
Brucker spectrometer. The chemical shifts are expressed
in δ ppm using TMS as an internal standard. Mass
spectra were recorded on a FINNIGAN-MATT 8430
mass spectrometer operating at an ionization potential of
20 eV. Absorption and fluorescence spectra in solutions
were recorded using an Avantes Avaspec-2048 UV-Vis
spectrophotometer. The fluorescence quantum yield of the
compound was measured by thermal lens effect method.
Chromatography columns were prepared from Merck
silica gel 60 mesh.
2.2. Synthesis of 4-Dicyano
A mixture of malonitirile (1 mmol), 2,6-dimethyl-4H-
pyran-4-one (1 mmol) and acetic anhydride (0.5 cm3)
was refluxed for 1.5 h. The unreacted acetic acid was
removed and the residue was washed with 50 ml. of
boiling water and was collected to give soft brown mate-
rial. Recrystallization from boiling heptane produced a
brown powder [11].
2.3. Synthesis of DCJ
A solution of (0.8 mmol) 9-julolidine carboxaldehyde, 2
(1 mmol) 4-dicynomethylene-2,6-dimethyl-4H-pyran, 1
shown in Scheme 1 and 13 drops of piperidine and 15
drops of HOAc in 14 cm3 of toluene were refluxed under
argon gas for 18 hours. On cooling, the precipitated dye
was filtered (yield: 65%). The product was purified by
column chromatography using n-hexane-ethyl acetate
(6:1) as eluent. The yield of separated bis-condensed
from the DCJ, 3 is 99% and the result was contaminated
with 1% of bis-condensed byproduct.
The chemical structure of DCJ was characterized as
Dark green crystals (from 6:1 hexane-ethyl acetate),
MS, m/z (%): 356 (M+, 100), 1H NMR (500 MHZ,
DMSO): δ 1.88 (4H, m, 2CH2CH2N), 2.4 (3H, s, CH3),
3.2 (4H, t, J = 5.6 Hz, 2Ar-CH2), 2.7 (4H, t, J = 6.1 Hz,
2CH2N), 6.1 (2H, s, 2ArH), 6.5 (1H, s, 1pyran-H), 6.6
(1H, s, 1pyran-H), 6.9 (1H, d, J = 15.8 Hz, CH = CH),
7.3 (1H, d, J = 15.8 Hz CH = CH), 7.1 (2H, s, Ar).
3. Results and Discussion
DCJ is intermolecular charge-transfer compound, which
its emission wavelength has been affected by the relative
electron-donating abilities of the donor group. In this
study, DCJ containing julolidine as an electron donor has
been synthesized and its purification procedure was re-
ported Section 2. Maximum fluorescence and maximum
absorption wavelength and quantum efficiency of DCJ
dye (630.6 nm, 486.6 nm, 65%) increased in comparison
with DCM dye (619.4 nm, 459.1 nm, 46.5%) [10].
The concentration of dye solutions was 2.8 × 104 M/l
in ethyl acetate solvent. Normalized fluorescence and
absorption spectra are shown in Figure 1. Unwanted bis
-condensed byproducts was to substitute the methyl
group with julolidine group. The intermediate of one way
to circumvent the difficulties in synthesis and subsequent
purification of DCJ for removing the the new red dopants
Figure 1. UV-Vis normalized absorption (left curve) and
normalized fluorescence (right curve) spectrum of DCJ dye.
Copyright © 2011 SciRes. AMPC
Copyright © 2011 SciRes. AMPC
has a symmetrical structure, the byproducts are the re-
sults of the reaction of two symmetrical methyls, in two
sides of intermediate molecule with jolulidine carboxal-
dehyde. This byproduct tends to decrease the fluores-
cence efficiency of DCJ, counteracting the effect of re-
duction of concentration quenching, which only has a
very weak fluorescence in the near infra-red region of the
visible spectrum.
In this work, we reported a facile, simple and inexpensive
method for purification of DCJ. It was shown the product
can be purified by column chromatography using hex-
ane-ethyl acetate as an eluent. At first stage, recrystaliza-
tion method seems to be a useful way for byproducts
separation. By using this procedure the ratio of unwanted
byproducts was decreased but not separated completely.
At second stage column chromatography improved our
aim for complete purification. Initially, a more polar ra-
tio of solvents was used. Thin layer chromatography
showed that unwanted byproducts weren’t separated
completely. To improve the purification, we used a less
polar ratio of solvents, then TLC showed unwanted DCJ
dye byproducts were almost removed. Finally, we used a
non-polar ratio of solvents (6:1 n-hexane-ethyl acetate)
and TLC showed that unwanted byproducts were com-
pletely separated. The 1H NMR spectrum of DCJ exhibit
characteristic signals with appropriate chemical shifts
which showed that purification by column chromatogra-
phy was successful.
As expected, both the absorption and fluorescence
spectra of DCJ (Figure 1) exhibited an increase in the
electron donating julolidine group relative to that of
DCM [10]. In other words, DCJ indicated larger quan-
tum efficiency than DCM.
4. Conclusions
One of the DCM type red light emitter, DCJ, was syn-
thesized and successfully purified by a facile and inex-
pensive method. Purification was carried out by column
chromatography instead of HPLC analysis with different
ratio of solvents. We used n-hexane-ethy acetate (6:1) as
an eluent for separation of unwanted DCJ byproduct.
Maximum fluorescence, maximum absorption wave-
length and quantum efficiency of DCJ increased in com-
parison to DCM, because of the existence of the electron
donating julolidine group.
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