The synthesis of thermally-stable red dyes for LCD color filters and analysis of their aggregation and spectral properties

Article abstract of DOI:10.1016/j.dyepig.2010.06.003

Three thermally-stable red dyes of azo, quinacridone and perylene derivatives were synthesized and dye-based color filters were manufactured for use in liquid crystal displays. The aggregation behavior of the dyes and their spectral properties in film sta

Full text of DOI:10.1016/j.dyepig.2010.06.003

Dyes and Pigments 88 (2011) 166e173
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
The synthesis of thermally-stable red dyes for LCD color filters
and analysis of their aggregation and spectral properties
,
Chun Sakong a, Young Do Kim a, Jae-Hong Choi b, Chun Yoon c, Jae Pil Kim a
*
a Department of Materials Science and Engineering, Seoul National University, Seoul 151-744, Republic of Korea
b Department of Textile System Engineering, Kyungpook National University, 1370 Sankyuk-dong, Buk-gu, Daegu 702-701, Republic of Korea
c Department of Chemistry, Sejong University,98 Gunja-dong, Gwangjin-gu, Seoul 143-747, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Three thermally-stable red dyes of azo, quinacridone and perylene derivatives were synthesized and dye-
based color filters were manufactured for use in liquid crystal displays. The aggregation behavior of the
dyes and their spectral properties in film state were investigated using field emission scanning electron
microscopy and concentration-dependent spectroscopy. Aggregate size was related to the geometry of
the three dye types rather than their size, with average aggregate sizes ranging from 35 nm (azo), 80 nm
(quinacridone) to 25 nm (perylene). Aggregation behavior affected the spectral property of the red color
filter, resulting in weaker and broader transmittance spectrum with higher aggregation.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 2 March 2010
Received in revised form
29 May 2010
Accepted 7 June 2010
Available online 16 June 2010
Keywords:
Color filters
Dye-based color filters
Thermal stability
Transmittance
Intermolecular interaction
Aggregation
1. Introduction
In our previous report [10], ink-jetted color filters with
thermally-stable dyes were prepared and their characteristics
Color filter is a key component of the thin-film transistor liquid
crystal displays (TFT-LCDs) [1,2]. Conventional fabrication process
of color filters is the pigment dispersion method where pigments
are used as colorants [3]. Although this process is widely used in the
flat panel displays industry, it has some disadvantages such as the
complicated process, waste of photoresist and low chromaticity of
the manufactured color filters [4].
Recently, pigment-based ink-jet printing method has been
studied to simplify the complicated process and to reduce
manufacturing cost of LCD color filters [5e8]. But, this method has
the limitation of easy blocking of ink-jet nozzle by pigment parti-
cles used and color filters manufactured by this method also have
low chromatic properties. In order to overcome these problems,
ink-jet printing method where dyes are used for higher solubility
and superior color saturation property has been proposed as an
alternative. However, for dyes to be used for color filters, their
lower thermal properties have to be overcome [9].
were examined. The dyes had sufficient thermal stabilities for
LCD color filters and the dye-based color filters had superior
chromatic properties compared to those of pigment-based
ones.
However, dyes generally have different aggregation behaviors
according to their chemical species and these aggregation effects
may change the spectral properties, such as transmittance and
sharpness of color filters. The aggregation behavior of dye is greatly
influenced by molecular geometry and intermolecular interaction.
Therefore, to enhance the chromatic properties of dye-based color
filters, especially transmittance, more understanding on the rela-
tionship between dye structures and their aggregation behaviors
should be necessary.
In this study, we synthesized three thermally-stable red dyes of
azo, quinacridone and perylene derivatives and the influence of dye
structure both on their aggregation behaviors and spectral prop-
erties in the prepared color filters was studied. The change of dye
aggregate size was investigated through the field emission scan-
ning electron microscopy (FE-SEM). The transmittance of dye-
based color filters was also measured to analyze the influence of
aggregation behavior on the spectral characteristics.
* Corresponding author. Tel.: þ82 2 880 7187; fax: þ82 2 880 7238.
E-mail address: jaepil@snu.ac.kr (J.P. Kim).
0143-7208/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2010.06.003

C. Sakong et al. / Dyes and Pigments 88 (2011) 166e173
167
2. Experimental
The crude product was dissolved in 3,000 ml of DMF, then the
yelloweorange solution was filtered and the solvent was removed
by rotary evaporation. The resulting dye was dried in a vacuum
oven at 50 ꢀC and its purity was confirmed by thin layer chroma-
tography using isopropanol/acetone/ammonium water (2:2:1) as
the mobile phase. The yields, 1H NMR, FT-IR and Mass data of the
dye are given below. Yield 73.6%;
2.1. Materials and instrumentations
5-amino-1-naphthalene sulfonic acid and 5,12-dihydro-quino
[2,3-b]acridone-7,14-dione purchased from TCI, 1-naphthol-
3,6-disulfonic acid sodium salt, perylene-3,4,9,10-tetracarboxylic
dianhydride, 4-chloroaniline, m-cresol, isoquinoline, fuming
sulfuric acid (20%) and sulfuric acid (98%) from SigmaeAldrich were
used without purification further. All chemicals used in this study
were of Synthesis-grade agent. Transparent glass substrate was
provided from Paul Marienfeld GmbH & Co. KG. and hydrophilic
acrylic binder of LGM 3050 was supplied by LG Micron Co., Ltd.
1H NMR spectra were recorded by Bruker Avance 500 at
500 MHz using DMSO-d6 as the solvent and TMS as the internal
standard. Fourier transform infrared (FT-IR) spectra were recorded
in the form of KBr pellets on a Perkin Elmer Spectrum 2000 FT-IR
spectrometer. Matrix Assisted Laser Desorption/Ionization Time of
Flight (MALDI-TOF) mass spectra were collected on a Voyager-DE
STR Biospectrometry Workstation with a-cyano-4-hydroxy-
cynamic acid (CHCA) as matrix. Absorption and transmittance
spectra were measured with an HP 8452A spectrophotometer.
Thermogravimetric analysis (TGA) was conducted under nitrogen
at a heating rate of 10 ꢀC minꢁ1 with a TA Instruments Thermog-
ravimetric Analyzer 2050.
1H NMR (DMSO-d6, ppm): 11.93 (s, 2H), 8.49 (s, 2H), 8.47 (s, 2H),
7.94 (d, 2H), 7.48 (d, 2H);
FT-IR (KBr, cmꢁ1): 3420 (NeH), 1619 (C]O), 1233, 1069 (S]O),
625 (SeO);
MALDI-TOF MS: m/z 548.63 (100%, [M þ 2K]þ).
2.2.3. Synthesis of a perylene dye (Dye 3) [10,13]
A
mixture of perylene-3,4,9,10-tetracarboxylic dianhydride
0.98 g (2.5 mmol), 4-chloroaniline 1.28 g (10 mmol), 40 ml of m-
cresol and 4 ml of isoquinoline was heated at 50 ꢀC for 2 h under
a nitrogen atmosphere. The reaction mixture was additionally
heated under nitrogen for 5 h at 130 ꢀC, 4 h at 150 ꢀC and 2 more
hours at 200 ꢀC. After cooling, the reaction mixture was added
dropwise to acetone to give
a
red precipitate (N,N0-Bis
(4-chlorophenyl)perylene-3,4,9,10-tetracarboxylic diimide) which
was filtered, washed several times with methanol and 5% aq
sodium hydroxide solution to remove isoquinoline and unreacted
anhydride, then dried at 50 ꢀC.
The prepared N,N0-Bis(4-chlorophenyl)perylene-3,4,9,10-tetra-
carboxylic diimide 6.11 g (10 mmol) was dissolved in 20 ml of
oleum (20% SO3) and the ensuing violet solution was heated at
145 ꢀC for 6 h. The reaction mixture was cooled and poured into
300 ml DMF and was then added dropwise to 2,000 ml acetone, the
ensuing red precipitate being filtered, washed with acetone, dried
in a vacuum oven at 50 ꢀC. Purity of the dye was confirmed by thin
layer chromatography using isopropanol/acetone/ammonium
water (2:2:1) as the mobile phase. The yields, 1H NMR, FT-IR and
Mass data of the dye are given below. Yield 65.4%;
2.2. Synthesis and characterizations
2.2.1. Synthesis of an azo dye (Dye 1) [11]
5-amino-1-naphthalene sulfonic acid 2.45 g (10 mmol) in 80 ml
of water was dissolved by adding 10 ml of 7% potassium hydroxide
aqueous solution. After cooling to 0e5 ꢀC, 0.76 g (11 mmol) of
sodium nitrite in 5 ml of water was added to the solution followed
by the dropwise addition of 3 ml of 37% hydrochloric acid, main-
taining the reaction temperature at 0e5 ꢀC. After diazotization was
complete (w2 h), the prepared diazonium salt liquor was added to
1-Naphthol-3,6-disulfonic acid sodium salt 5.8 g (10 mmol), dis-
solved in 70 ml of water at pH 5, maintaining the coupling solution
at 0e5 ꢀC and pH 4 and 5. The solution was stirred for 2 h and aq
potassium chloride solution (3 mass %) was added to salt out the
dye. The precipitate formed was filtered, washed with water and
dried in a vacuum oven at 50 ꢀC. The crude product was refluxed in
ethanol for 2 h, hot filtered, washed with hot ethanol and subse-
quently dried in a vacuum oven at 50 ꢀC. Purity of the dye was
confirmed by thin layer chromatography using isopropanol/
acetone/ammonium water (2:2:1) as the mobile phase. The yields,
1H NMR, FT-IR and Mass data of the dye are given below.
Yield 85.5%;
1H NMR (DMSO-d6, ppm): 8.80 (d, 4H), 8.50 (d, 4H), 7.91 (s, 2H),
7.58 (d, 2H), 7.43 (d, 2H);
FT-IR (KBr, cmꢁ1): 1701 (C]O), 1360 (CeN), 1233, 1069 (S]O),
625 (SeO);
MALDI-TOF MS: m/z 772.05 (100%, [M þ 2H]þ).
2.3. Thermal stabilities of the prepared dyes
The thermal stabilities of Dye 1eDye 3 were evaluated by
thermogravimetry (TGA). The prepared dyes were heated to 110 ꢀC
for 10 min to remove any residual water and solvent. Then, it was
heated to 220 ꢀC and held it for 30 min to simulate the processing
thermal conditions of color filters manufacturing. The dyes were
finally heated to 500 ꢀC to determine their degradation tꢁe1mpera-
ture. The heating was carried out at the rate of 10 ꢀC min under
nitrogen atmosphere [10,14].
1H NMR (DMSO-d6, ppm): 17.42 (s, 1H), 8.87 (d, 1H), 8.25 (d, 2H),
8.11 (d, 1H), 7.93 (s, 1H), 7.78 (d, 1H), 7.75 (t, 1H), 7.69 (s, 1H);
FT-IR (KBr, cmꢁ1): 1619 (C]O), 1233, 1069 (S]O), 625 (SeO);
MALDI-TOF MS: m/z 652.80 (100%, [M þ 2K]þ).
2.4. Preparation of color inks and dye-based color filters
2.2.2. Synthesis of a quinacridone dye (Dye 2) [12]
5,12-dihydro-quino[2,3-b]acridine-7,14-dione 1.56 g (5 mmol)
was dissolved in 50 ml of sulfuric acid (98%) and the ensuing purple
solution was heated at 110 ꢀC for 14 h under a nitrogen atmosphere.
The solution was cooled and poured into 300 ml of DMF, and slowly
added to 2,000 ml of acetone to give a red precipitate which was
filtered, washed with acetone and dried. The precipitate was dis-
solved in 300 ml of water and the solution was carefully neutralized
using 7% aq potassium bicarbonate solution over 1 hr. After the
addition of potassium chloride (100 g) to the solution, the precip-
itate formed was filtered, washed with ethanol and dried at 50 ꢀC.
Three aqueous inks were prepared with different concentration
(0.2 mmol, 0.22 mmol, 0.25 mmol) of synthesized dyes, distilled
water (2 g) and LGM 3050 (0.68 g) as a binder based on acrylate.
The binder used in this study had excellent compatibility with three
dyes. Prepared dye-based inks were coated on transparent glass
substrates using MIDAS System SPIN-1200D spin coater. The
coating speed was kept at the rate of 300 rpm for 5 s, and then
raised to 1000 rpm and kept constant for 10 s. The dye-coated color
filters were prebaked at 180 ꢀC for 30 min and subsequently baked
for 1 h at 230 ꢀC.

168
C. Sakong et al. / Dyes and Pigments 88 (2011) 166e173
2.5. Geometry optimization of synthesized dyes
perturb the induced mesomerism and slow down the rate of dye
decomposition [15]. The proton peaks involved in hydrogen bonds
between NeH/OaC appear at much lower field than the normal
proton peak [16] and this was confirmed by 1H NMR (17.42 ppm).
To analyze the difference of aggregation behaviors due to the
structural difference of the dyes, dye structures were optimized
through the CAChe 6.1.8 program and the intermolecular interac-
tions that affect the aggregation were analyzed. CAChe 6.1.8 soft-
ware package optimized the geometry of dye structures by using
molecular mechanics MM3, conducting the iteractive energy
minimizing routines with the conjugate gradient minimizer algo-
rithm. CONFLEX conformational search procedure was used to find
low-energy conformations of dye molecules. The semi-empirical
method, PM5, was also examined with respect to geometry opti-
mization, but was found to be no more satisfactory than the
molecular mechanical method.
Dye
2 has two NeH/O intermolecular hydrogen bonds
between the NH group and the O atom. The proton peaks involved
in intermolecular hydrogen bonds appear at slightly lower field
than the normal proton peak of NeH [17] and were confirmed by 1H
NMR (11.93 ppm). Dye 1eDye 3 contain two or three sulfonic acid
groups in their structures, S]O (1233, 1069) and SeO (625) peaks
were confirmed by FT-IR.
3.2. Characterization of spectral properties
and thermal stabilities of dyes
2.6. Field emission scanning electron microscopy (FE-SEM)
UVeVisible absorption spectra of the prepared dyes in water are
shown in Fig. 1 and their optical properties are collected in Table 1.
Dye 2 and Dye 3 exhibited double absorption maxima (lmax) at 506,
542 nm and 506, 544 nm, while Dye 1 exhibited single absorption
maxima at 518 nm. All three dyes have appropriate absorption
spectra for red colorants of color filters.
The thermal stabilities of Dye 1eDye 3 through the thermog-
ravimetric analysis (TGA) are shown in Fig. 1. The weight loss
starting temperatures of the prepared dyes were 310 ꢀC for Dye 1,
370 ꢀC for Dye 2 and 330 ꢀC for Dye 3. Dye 2 showed much higher
thermal stability than Dye 1 and Dye 3 that could be attributed to
The aggregation size and morphology of the dyes in color filters
were investigated through field emission scanning electron
microscope (JEOL JAMP 9500-F). The dye aggregates were observed
at an acceleration voltage of 15 kV and working distance (WD) of
8 mm, FE-SEM images of dye-based color filters were taken at the
100,000 and 150,000 magnifications.
2.7. Concentration-dependent transmittance
of dye-based color filters
its
pep stacked interaction, planar structure and intermolecular
hydrogen bonding as explained later.
Transmittance spectra of the prepared dye-based color filters
were measured with an HP 8452A spectrophotometer and the
spectral-dependent changes were observed.
Thermal stabilities of the dyes were also investigated through
measuring of their color change at 250 ꢀC e the highest tempera-
ture in LCD manufacturing process [18,19]. As shown in Fig. 2, after
heating for an hour at 250 ꢀC absorption spectra of the three dyes
were identical to those of the original dyes. Consequently, we
concluded that the prepared dyes were stable at the processing
thermal conditions of color filters manufacturing.
3. Results and discussion
3.1. Synthesis of dyes
Dye 1eDye 3 were prepared through the synthetic routes
illustrated in Scheme 1 and overall characterization of dye struc-
tures were carried out by 1H NMR, FT-IR and Mass spectroscopy.
Dye 1 is believed to exist predominantly in the hydrazone form via
intramolecular hydrogen bonds. Involving the azo linkage in
intramolecular hydrogen bonding, as in the case of Dye 1, would
stabilize the thermally more stable hydrazone form, which could
3.3. Influence of dye structure on the aggregation
behaviors of dyes in color filters
3.3.1. Geometry optimization by CAChe
Fig. 3 shows the molecular geometry of Dye 1eDye 3 optimized
through CAChe program. Factors related to the intermolecular
Scheme 1. Synthetic routes for the synthesis of thermally-stable red dyes.

C. Sakong et al. / Dyes and Pigments 88 (2011) 166e173
169
0.6
2.5
2.0
1.5
1.0
0.5
0.0
a
Dye 1-before
Dye 1-after
Dye 1
Dye 2
0.5
Dye 3
0.4
0.3
0.2
0.1
0.0
300
300
300
400
400
400
500
600
700
800
300
400
500
600
700
800
Wavelength (nm)
Wavelength (nm)
2.5
2.0
1.5
1.0
0.5
0.0
Dye 2-before
Dye 2-after
b
Dye 1
Dye 2
Dye 3
100
90
80
70
60
50
500
600
700
800
100
200
300
400
500
Wavelength (nm)
Temperature (oC)
0.8
0.6
0.4
0.2
0.0
Fig. 1. Absorption spectra (a) and TGA profile (b) of the prepared dyes.
Dye 3-before
Dye 3-after
interactions that affect aggregation of dyes can be divided into
three including (1) stacked interaction by the aromatic ring (2)
flatness of the molecular structure and (3) intermolecular hydrogen
bond. There is close correlation between the factor (1) and (2) and
the flatter the molecule the stronger the
pep
pep stacked interaction
[20,21].
The intermolecular
pep stacked interaction is related to the
number and type of the aromatic rings included in dye molecule.
The three dyes used have different numbers of aromatic rings, four
for Dye 1, five for Dye 2 and nine for Dye 3. Therefore, if only the
intermolecular pep stacked interaction is considered, the degree of
intermolecular interaction will be in the order of Dye 3 >> Dye
2 > Dye 1. However, from the geometrical point of view, Dye 3 has
twisted perylene core, while Dye 1 and Dye 2 have excellent flat-
ness as shown in Fig. 3.
500
600
700
800
Wavelength (nm)
Fig. 2. Spectral changes of the prepared dyes after heating for an hour at 250 ꢀC.
(before: solid line, after: dotted line).
Table 1
Optical and thermal properties of Dye 1eDye 3.
3max (1 molꢁ1 cmꢁ1
)
Melting point (ꢀC)
a
a
Such twisted geometry of Dye 3 is caused by the introduction of
bulky N-aryl groups at nitrogen atom and sulfonic acid groups at
the bay position [22,23]. Therefore, the twisted structure of Dye 3
will introduce strong steric hindrance between the molecules,
Dye
lmax (nm)
1
2
3
518
506, 542
506, 544
21,300
17,500/33,700
32,120/38,750
>300 (Decomp.)
>300 (Decomp.)
>300 (Decomp.)
which results in the low degree of the intermolecular
interaction.
pep stacked
lmax: absorption maximum wavelength; 3max: molar extinction coefficient at lmax
.
a
Absorption spectra were measured in water.

170
C. Sakong et al. / Dyes and Pigments 88 (2011) 166e173
Fig. 3. Optimized molecular geometry of the prepared dyes.
On the contrary, Dye 1 and Dye 2 with less aromatic rings are too
flat to decrease their intermolecular stacked interaction.
Dye 1 and Dye 2 that have four and five aromatic rings, respectively.
p
ep
This result corresponded with the intermolecular interaction
analyzed in the optimization of the molecular structure (3.2.1).
Although Dye 3 had more aromatic rings compared to the other
dyes, steric hindrance causing twisted molecular structure
Especially, Dye 2 can have bifurcated NeH/O intermolecular
hydrogen bonds between the NH group of one molecule and the O
atom of the neighbouring one [17,24]. These interactions form
a two-dimensional hydrogen-bonded network and act as an addi-
tional factor to increase the intermolecular interaction.
Table 2
3.3.2. Field emission scanning electron microscopy study (FE-SEM)
The aggregate sizes of Dye 1eDye 3 in color filters are listed in
Table 2 and their FE-SEM images are shown in Fig. 4. The aggregate
size decreased in the order of Dye 2 (46e100 nm) > Dye 1
(20e45 nm) > Dye 3 (15e35 nm). In order words, the aggregate
size of Dye 3 that has nine aromatic rings was smaller than those of
The aggregate size and distribution of Dye 1eDye 3 in dye-based color filters.
Dye
Range of size distribution
Average size
1
2
3
20e45 nm
46e100 nm
15e35 nm
35 nm
80 nm
25 nm

C. Sakong et al. / Dyes and Pigments 88 (2011) 166e173
171
decreased the intermolecular
p-
p
stacked interaction between the
molecules, and resulted in the relatively smaller aggregations. Even
though Dye 1 and Dye 2 had less aromatic rings, they formed larger
dye aggregates owing to their planar structure. Especially, Dye 2
could form four intermolecular hydrogen bonds with its neigh-
bouring molecules and its aggregate size reached almost 100 nm as
shown in the FE-SEM results (Fig. 4).
Fig. 5 shows the images of dye aggregates in color filters at
higher dye concentration of 0.25 mmol. The sizes of dye aggregates
for Dye 1 and Dye 3 increased considerably as the concentration of
dye in color filters increased. Whereas dye concentration in color
filters only increased by 1.25 times, the size of dye aggregates
rapidly increased by 1.7 times and 1.6 times for Dye 1 and Dye 3. In
case of Dye 2, the size of dye aggregate was so large that we could
not report the image of aggregates in this paper.
3.3.3. The influence of dye aggregation on the spectral
properties of the color filters
Fig. 6 shows the transmittance spectra of the dye-based color
filters. Dye 1 and Dye 3 showed very small change of the trans-
mittance spectrum for each concentration within the long wave-
length region (600 nme700 nm). However, the spectra became
Fig. 4. FE-SEM images of dye aggregates in 0.2 mmol dye-based color filters.
Fig. 5. FE-SEM images of dye aggregates in 0.25 mmol dye-based color filters.

172
C. Sakong et al. / Dyes and Pigments 88 (2011) 166e173
Table 3
100
90
80
70
60
50
40
30
20
10
0
a
The color coordinate values corresponding to CIE 1931 chromaticity diagram of
dye-based color filters.
Dye 1 (0.25 mmol)
Dye 1 (0.22 mmol)
Dye 1 (0.20 mmol)
Color filters
Concentration
x
y
Y
Dye 1
0.20 mmol
0.22 mmol
0.25 mmol
0.20 mmol
0.22 mmol
0.25 mmol
0.20 mmol
0.22 mmol
0.25 mmol
0.435
0.467
0.503
0.421
0.453
0.486
0.397
0.407
0.433
0.303
0.304
0.305
0.297
0.298
0.299
0.286
0.284
0.279
36.52
30.98
26.05
28.23
25.48
20.39
48.64
44.76
38.29
Dye 2
Dye 3
influences the ground state of dyes and creates additional absorp-
tion band [25e27]. As a result, new absorption band can appear
within the longer wavelength range which could decrease the
transmittance of red color filters. In case of Dye 1 and Dye 3, new
absorption band within the longer wavelength was very small
compared to that of Dye 2 and this was believed to be due to less
aggregation of them.
Table 3 illustrates the measured color coordinate values of (x, y)
and the brightness of Y in the CIE 1931 chromatic diagram for
different concentration of dye-based color filters. Color coordinate
values of x tend to be wider with an increase in concentration of red
dyes.
200
300
400
500
Wavelength (nm)
600
700
800
100
90
80
70
60
50
40
30
20
10
0
b
Dye 2 (0.25 mmol)
Dye 2 (0.22 mmol)
Dye 2 (0.20 mmol)
4. Conclusion
Three thermally-stable red dyes were synthesized and dye-
based color filters were manufactured with them. The relationship
between dye aggregation and spectral characteristics of the
prepared color filters was analyzed. The aggregate sizes of prepared
dyes were proportional to their strength of intermolecular inter-
200
300
400
500
Wavelength (nm)
600
700
800
action involving
pep stacked interaction, hydrogen bonding and
molecular geometry. As the aggregate sizes of dyes increased, the
transmittance of color filters decreased.
100
90
80
70
60
50
40
30
20
10
0
c
To improve the thermal stability of dyes for LCDs color filters,
molecular structures of the dyes should be designed to increase
their intermolecular interactions. However, stronger intermolec-
ular interaction could lead to higher dye aggregation, resulting in
significantly decreased transmittance of color filters. Therefore, the
aggregation of dye molecule should be carefully controlled so that
the color filters could have good transmittance while its thermal
resistance is not impaired.
Dye 3 (0.25 mmol)
Dye 3 (0.22 mmol)
Dye 3 (0.20 mmol)
Acknowledgements
This work was supported by a grant from the Fundamental R&D
Program for Core Technology of Materials funded by the Ministry of
Knowledge Economy, Republic of Korea.
200
300
400
500
Wavelength (nm)
600
700
800
References
[1] Sabnis RW. Color filter technology for liquid crystal displays. Displays
1999;20:119e29.
[2] Tsuda K. Color filters for LCDs. Displays 1993;14:115e24.
[3] Takanori K, Yuki N, Yuko N, Hidemasa Y, Kang WB, Pawlowski PG. Polymer
optimization of pigmented photoresists for color filter production. Jpn J Appl
Phys 1998;37:1010e6.
Fig. 6. Concentration-dependent transmittance spectra of dye-based color filters. (a)
Dye 1 with concentrations of 0.25, 0.22, 0.20 mmol (b) Dye 2 with concentrations of
0.25, 0.22, 0.20 mmol (c) Dye 3 with concentrations of 0.25, 0.22, 0.20 mmol.
[4] Na DY, Jung IB, Nam SY, Yoo CW, Choi YJ. The rheological behavior and
dispersion properties of millbase for LCD colorfilters. J Korean Inst Electr
Electron Mater Eng 2007;20:450e5.
[5] Calvert P. Inkjet printing for materials and devices. Chem Mater
2001;13:3299e305.
[6] Chang CJ, Chang SJ, Shin KC, Pan FL. Improving mechanical properties and
chemical resistance of ink-jet printer color filter by using diblock polymeric
dispersants. J Polym Sci B Polym Phys 2005;43:3337e53.
broader across the whole wavelength as the concentration
increased. In case of Dye 2, in particular, formation of a new
absorption band was observed within the longer wavelength
region near 700 nm as the concentration of dye increased. This is
considered due to the higher aggregation of Dye 2 as shown in the
FE-SEM results (Fig. 4). It has been known that dye aggregation

C. Sakong et al. / Dyes and Pigments 88 (2011) 166e173
173
[7] Koo HS, Chen M, Pan PC, Chou LT, Wu FM, Chang SJ, et al. Fabrication and
chromatic characteristics of the greenish LCD colour-filter layer with nano-
particle ink using inkjet printing technique. Displays 2006;27:124e9.
[8] Koo HS, Chen M, Pan PC. LCD-based color filter films fabricated by pigment-
based colorant photo resist inks and printing technology. Thin Solid Films
2006;515:896e901.
[17] Mizuguchi J, Senju T. Solution and solid spectra of quinacridone derivatives as
viewed from the intermolecular hydrogen bond.
J
Phys Chem
B
2006;110:19154e61.
[18] Das S, Basu R, Minch M, Nandy P. Heat-induced structural changes in
merocyanine dyes: X-ray and thermal studies. Dyes Pigm 1995;29:
191e201.
[9] Sugiura T. Dyed color filters for liquid-crystal displays.
1993;1:177e80.
J
Soc Inf Disp
[19] Chunlong Z, Nianchun M, Liyun L. An investigation of the thermal stability of
some yellow and red azo pigments. Dyes Pigm 1993;23:13e23.
[20] Kim JH, Masaru M, Fukunishi K. Three dimensional molecular stacking and
functionalities of aminonaphthoquinine by intermolecular hydrogen bond-
[10] Kim YD, Kim JP, Kwon OS, Cho IH. The synthesis and application of thermally
stable dyes for ink-jet printed LCD color filters. Dyes Pigm 2009;81:45e52.
[11] Song DH, Yoo HY, Kim JP. Synthesis of stilbene-based azo dyes and application
for dichroic materials in poly(vinyl alcohol) polarizing films. Dyes Pigm
2007;75:727e31.
ings and interlayer
p-p interactions. Dyes Pigm 1998;40:53e7.
[21] Thetford D, Cherryman J, Chorlton AP, Docherty R. Theoretical molecular
modeling calculations on the solid state structure of some organic pigments.
Dyes Pigm 2004;63:259e76.
[22] Würthner F, Thalacker C, Diele S, Tschierske C. Fluorescent J-type aggregates
and thermotropic columnar mesophases of perylene bisimide dyes. Chem Eur
J 2001;7:2245e52.
[23] Chao CC, Leung M. Photophysical and electrochemical properties of 1,7-diaryl-
substituted perylene diimides. J Org Chem 2005;70:4323e31.
[24] Keller U, Müllen K, De Feyter S, De Schryver FC. Hydrogen-bonding and
[12] Smith JA, West RM, Allen M. Acridones and quinacridones:Novel fluorophores
for fluorescence lifetime studies. J Fluoresc 2004;14:151e71.
[13] Bodapati JB, Icil H. Highly soluble perylene diimide and oligomeric diimide dyes
combining perylene and hexa(ethylene glycol) units: synthesis, characteriza-
tion, optical and electrochemical properties. Dyes Pigm 2008;79:224e35.
[14] Guerrero DJ, DiMenna B, Flaim T, Mercado R, Sun S. Dyed red, green, and blue
photoresist for manufacture of high-resolution color filter arrays for image
sensors. Proc Soc Photo Opt Instrum Eng 2003;5017:298e306.
phase-forming behavior of
a soluble quinacridone. Adv Mater 1996;8:
[15] Moien B, Ezzeldine HM, Ibrahim M, Ismail M. Thermal decomposion stages of
the azo linkages in novel azo phosphorus compounds; A correlative DTA
study. Thermochimica Acta 1992;198:21e31.
[16] Skrabal P, Zollinger H. Mechanism of azo coupling reactions: part XXXV. pH-
dependence and ortho/para ratio in coupling reactions of amino-
hydroxynaphthalenesulfonic acids. Dyes Pigm 1988;9:201e7.
490e3.
[25] Kobayashi T. J-Aggregates. Singapore: World Scientific; 1996.
[26] Mishra A, Behera RK, Behera PK, Mishra BK, Behera GB. Cyanines during the
1990s: a review. Chem Rev 2000;100:1973e2011.
[27] Eisfeld A, Briggs JS. The J- and H-bands of organic dye aggregates. Chem Phys
2006;324:376e84.