Synthesis and characterization of some perylene dyes for dye-based LCD color filters

Article abstract of DOI:10.1016/j.dyepig.2010.11.006

Eight red perylene dyes were synthesized to improve the optical performance of LCD color filters. Among them, dyes with bulky functional substituents at the bay and terminal positions were highly soluble in cyclohexanone, the industrial solvent currently used in the pigment dispersion method. The spectral properties and thermal stability of the dye-based color filters with these dyes were examined by comparing them with pigment-based ones. The prepared color filters exhibited superior spectral properties due to the smaller particle size of the dyes, which led to less light scattering. However, their thermal stability varied with the dye structures, and only the dyes mono-substituted at the bay position had sufficient thermal stability.

Full text of DOI:10.1016/j.dyepig.2010.11.006

Dyes and Pigments 90 (2011) 82e88
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Synthesis and characterization of some perylene dyes for dye-based
LCD color filters
,
Jun Choi a, Chun Sakong 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:
Eight red perylene dyes were synthesized to improve the optical performance of LCD color filters. Among
them, dyes with bulky functional substituents at the bay and terminal positions were highly soluble in
cyclohexanone, the industrial solvent currently used in the pigment dispersion method. The spectral
properties and thermal stability of the dye-based color filters with these dyes were examined by
comparing them with pigment-based ones. The prepared color filters exhibited superior spectral
properties due to the smaller particle size of the dyes, which led to less light scattering. However, their
thermal stability varied with the dye structures, and only the dyes mono-substituted at the bay position
had sufficient thermal stability.
Received 8 September 2010
Received in revised form
3 November 2010
Accepted 11 November 2010
Available online 19 November 2010
Keywords:
Color filters
Perylene
Ó 2010 Elsevier Ltd. All rights reserved.
Transmittance
Chromaticity
Solubility
Thermal stability
1. Introduction
In a previous report [6], water soluble dyes were applied to ink-
jetted color filters, but there are few reports on the application of
Liquid crystal display (LCD) modules are used widely in a variety
of electronic displays, such as computers and TVs. Among the
elements of LCD modules, the color filter, which converts the white
backlight into red (R), green (G) and blue (B) colored lights, is a vital
component [1,2].
dyes on the currently used photo lithography process.
In this study, a range of highly soluble red perylene dyes were
designed and synthesized for dye-based LCD color filters. Perylene-
3,4,9,10-tetracarboxylic diimide derivatives show excellent thermal
stability originating from their very high resonance stabilization
Currently, the pigment dispersion method to form RGB
patterned pixels using photo lithography has been adopted widely
to produce color filters because color filters with superior stability
can be achieved [3]. It is also advantageous to scale up the panel
size while maintaining its pixel uniformity. Although color filters
produced by this method have good thermal and photo-chemical
stability, they have low chromatic properties due to the aggregation
behavior of pigment particles used as colorants [4]. Dyes can be an
attractive alternative to overcome this limitation due to the
reduced light scattering because they are dissolved in the media
and exist in molecular form. However, in order for the dyes to be
applied successfully to a LCD manufacturing process, their low
thermal stability needs to be improved [5].
energy [7] and pep interactions due to the planar molecular
structure [8,9]. In addition, they have very strong and sharp
absorption at approximately 530 nm [10]. However, they have low
solubility in common industrial solvents, such as cyclohexanone,
which limits their applications [11]. In this study, the solubility of
the dyes was increased by substituting various bulky functional
groups at the bay and terminal positions. The absorbance, solubility
and thermal stability of the dyes substituted at one or both of the
bay positions were examined and compared. Dye-based color
filters were fabricated using both type of dyes, and their chromatic
properties and thermal stability were analyzed.
2. Experimental
2.1. Materials and instrumentation
Perylene-3,4,9,10-tetracarboxylic dianhydride, 2,6diisopropyla-
niline, m-cresol, iodine, sulfuric acid, bromine, acetic acid,
* 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.2010.11.006

J. Choi et al. / Dyes and Pigments 90 (2011) 82e88
83
potassium carbonate anhydrous, phenol, 4-tert-butylphenol, and
4-tert-octylphenol purchased from SigmaeAldrich, and isoquino-
line purchased from TCI were used as received. All the other
reagents and solvents were of reagent-grade quality and obtained
from commercial suppliers. Transparent glass substrates were
provided by Paul Marienfeld GmbH & Co. KG. Commercial pigment-
based color filter and acrylic binder LC20160 were supplied by
SAMSUNG Cheil industries Inc.
product was washed with water, dried, and purified by column
chromatography on silica gel using CH2Cl2 as the eluent. The band
containing tribrominated diimide could be separated firstly. Then,
the second band containing a mixture of dibrominated isomeric
diimides was collected. The mixture was washed with EtOH and
toluene and heated at 80 ꢀC for 12 h in toluene (50 ml). The pure
diimide, red compound 2b, was recrystallized from the hot toluene
solution [12].
1H NMR spectra were recorded on a Bruker Avance 500 spec-
trometer at 500 MHz using chloroform-d and TMS, as the solvent
and internal standard, respectively. Matrix Assisted Laser Desorp-
tion/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 the matrix. Absorption
and transmittance spectra were measured using a HP 8452A
spectrophotometer. Chromatic characteristics of the color filters
were analyzed on a Scinco color spectrophotometer. Thermogra-
vimetric analysis (TGA) was conducted under nitrogen at a heating
rate of 10 ꢀC minꢁ1 using a TA Instruments Thermogravimetric
Analyzer 2050. The thickness of the color filters was measured
using a Nano System Nanoview E-1000.
Yield 42.8%; 1H NMR (CDCl3, ppm): 9.56 (d, 2H), 9.01 (d, 2H),
8.80 (d, 2H), 7.52 (t, 2H), 7.36 (d, 4H), 2.74 (septet, 4H), 1.18 (d, 24H);
MALDI-TOF MS: m/z 869.83 (100%, [M þ 2K]þ).
2.2.3. N,N0-Bis(2,6-diisopropylphenyl)-1-bromoperylene-
3,4,9,10-tetracarboxydiimide (2a)
2a could be separated by column chromatography from the
same crude product of 2b. After obtaining a mixture of dibromi-
nated isomeric diimides, 2a was obtained as the third eluted
compound. The product 2a was used for the next step without
further purification because there was no isomer.
Yield 36.7%; 1H NMR (CDCl3, ppm): 9.85 (d,1H), 9.03 (s,1H), 8.80
(m, 3H), 8.72 (d, 1H), 8.71 (d, 1H), 7.51 (t, 2H), 7.36 (d, 4H), 2.76
(septet, 4H), 1.18 (d, 24H); MALDI-TOF MS: m/z 790.96 (100%,
[M þ 2K]þ).
2.2. Synthesis
The dyes 1, 2a, 2b, 4a, 4b are already known structures, and we
have modified and detailed the synthesis of them in this paper. The
dyes 3a, 3b, 3c are new structures.
2.2.4. N,N0-Bis(2,6-diisopropylphenyl)-1-phenoxy-perylene-
3,4,9,10-tetracarboxydiimide (3a)
2a (1 g, 1.27 mmol) was mixed with potassium carbonate
anhydrous (0.7 g), phenol (0.14 g, 1.50 mmol), and NMP (70 ml).
The mixture was heated to 120 ꢀC under argon and was stirred at
this temperature for 24 h. The reaction mixture was cooled to
room temperature and poured into 5% HCl (250 ml). The precip-
itate was filtered, repeatedly washed with water, and dried in
a vacuum at 70 ꢀC. The crude product was purified by column
chromatography on silica gel using CH2Cl2 as the eluent to obtain
3a as red solid.
2.2.1. N,N0-Bis(2,6-diisopropylphenyl)-perylene-
3,4,9,10-tetracarboxydiimide (1)
A
mixture of perylene-3,4,9,10-tetracarboxylic dianhydride
(3.92 g, 0.01 mol), 2,6diisopropylaniline (5.65 ml, 0.03 mol), m-cresol
(60 ml) and isoquinoline (6 ml) was stirred at 50 ꢀC for 2 h. The
temperature of the mixture was raised to 200 ꢀC and kept for 12 h.
The warm solution was poured into 60 ml of acetone, and the
precipitate was filtered out. The collected solution was poured into
1200 ml of n-Hexane and temperature of the mixture solution was
dropped to 0 w 5 ꢀC and kept for 24 h. The precipitate was filtered out
and dried at 80 ꢀC under vacuum. The crude product was purified by
column chromatography on silica gel using CH2Cl2/MeOH (40:1) as
the eluent to obtain 1 as red solid.
Yield 85.8%; 1H NMR (CDCl3, ppm): 9.65 (d, 1H), 8.81 (m, 2H),
8.75 (m, 3H), 8.40 (s, 1H), 7.47 (m, 4H), 7.33 (m, 4H), 7.26 (t, 1H), 7.19
(d, 2H), 2.73 (septet, 4H), 1.16 (d, 24H); MALDI-TOF MS: m/z 804.37
(100%, [M þ 2K]þ).
2.2.5. N,N0-Bis(2,6-diisopropylphenyl)-1-p-tert-butylphenoxy-
perylene-3,4,9,10-tetracarboxydiimide (3b)
Yield 56.4%; 1H NMR (CDCl3, ppm): 8.80 (d, 4H), 8.75 (d, 4H),
7.50 (t, 2H), 7.36 (d, 4H), 2.75 (septet, 4H), 1.19 (d, 24H); MALDI-TOF
MS: m/z 712.10 (100%, [M þ 2K]þ).
3b was synthesized in the same manner with 3a using 2a (1 g,
1.27 mmol), potassium carbonate anhydrous (0.7 g), and 4-
tert-butylphenol (0.23 g, 1.50 mmol).
2.2.2. N,N0-Bis(2,6-diisopropylphenyl)-1,7-dibromoperylene-
3,4,9,10-tetracarboxydiimide (2b)
Yield 86.1%; 1H NMR (CDCl3, ppm): 9.68 (d, 1H), 8.82 (m, 2H),
8.75 (m, 3H), 8.42 (s, 1H), 7.48 (m, 4H), 7.33 (m, 4H), 7.13 (d, 2H),
2.74 (septet, 4H), 1.36 (s, 9H), 1.16 (d, 24H); MALDI-TOF MS: m/z
860.28 (100%, [M þ 2K]þ).
Perylene-3,4,9,10-tetracarboxylic dianhydride (16.0 g, 40.7 mmol),
iodine (0.39 g, 1.52 mmol), and sulfuric acid (98%, 225 ml) were mixed
and stirred for 2 h at room temperature. The reaction temperature was
set at 80 ꢀC, and bromine (3.58 ml, 70 mmol) was added dropwise over
2 h. The mixture was reacted further at 80 ꢀC for 16 h, cooled to room
temperature, and the excess bromine gas was displaced by nitrogen
gas. The precipitate obtained after adding ice-water to the mixture was
collected by suction filtration. The precipitate was washed with water
several times until the aqueous layer became neutral to yield dibromo
dianhydride as crude product. The crude product was then dried at
100 ꢀC under reduced pressure and used for the next step without
further purification.
The crude 1,7-dibromoperylene-3,4,9,10-tetracarboxylic dia-
nhydride (8.0 g, 14.5 mmol), 2,6diisopropylaniline (8.8 ml,
46.7 mmol), and acetic acid (4.6 ml) were mixed and heated at
120 ꢀC in N-Methyl-2-pyrrolidone(NMP) (100 ml) under the
nitrogen atmosphere for 96 h. The precipitate obtained after adding
water to the mixture was collected by suction filtration. The crude
2.2.6. N,N0-Bis(2,6-diisopropylphenyl)-1-p-tert-octylphenoxy-
perylene-3,4,9,10-tetracarboxydiimide (3c)
3c was synthesized in the same manner with 3a using 2a (1 g,
1.27 mmol), potassium carbonate anhydrous (0.7 g), and 4-
tert-octylphenol (0.31 g, 1.50 mmol).
Yield 87.8%; 1H NMR (CDCl3, ppm): 9.68 (d, 1H), 8.81 (m, 2H),
8.75 (m, 3H), 8.39 (s, 1H), 7.46 (m, 4H), 7.34 (m, 4H), 7.11 (d, 2H),
2.73 (septet, 4H), 1.75 (s, 2H), 1.40 (s, 6H), 1.16 (d, 24H), 0.75 (s, 9H);
MALDI-TOF MS: m/z 916.31 (100%, [M þ 2K]þ).
2.2.7. N,N0-Bis(2,6-diisopropylphenyl)-1,7-dilphenoxy-perylene-
3,4,9,10-tetracarboxydiimide (4a)
4a was synthesized in the same manner with 3a using 2b (1 g,
1.15 mmol), potassium carbonate anhydrous (0.7 g), and phenol
(0.24 g, 2.50 mmol) (Fig. 1).

84
J. Choi et al. / Dyes and Pigments 90 (2011) 82e88
dye-coated color filters were then dried at 80 ꢀC for 20 min, pre-
baked at 150 ꢀC for 10 min, and postbaked at 230 ꢀC for 1 h. After
each step, the coordinate values of the color filters were measured.
All spin-coated dye-based color filters were 1.6 mm thick.
O
O
N
N
O
O
O
O
N
O
O
O
O
N
O
O
Br
2.4. Investigation of solubility
Br
Br
The solubility of the synthesized dyes in CH2Cl2 and cyclohexa-
none were examined to determine the effects of substituents at the
bay and terminal positions. The prepared dyes were added to the
solvents at various concentrations, and the solutions were sonicated
for 5 min using an ultrasonic cleaner ME6500E. The solutions were
left to stand for 48 h at room temperature, and checked for
precipitation to determine the solubility of the dyes (Scheme 1).
N
N
1
2a
2b
O
O
N
O
O
2.5. Measurement of spectral and chromatic properties
O
O
N
O
O
O
O
N
O
Absorption spectra of the synthesized dyes and the trans-
mittance spectra of pigment-based and dye-based color filters were
measured using a UVevis spectrophotometer. The chromatic values
were recorded on a color spectrophotometer (Scinco colormate).
O
O
O
N
N
N
O
2.6. Measurement of thermal stability
3a
3b
3c
The thermal stability of the synthesized dyes was evaluated by
thermogravimetry (TGA). The prepared dyes were heated to 110 ꢀC
and held at that temperature for 10 min to remove the residual
water and solvents. The dye was then, heated to 220 ꢀC and held at
that temperature for 30 min to simulate the processing thermal
conditions of color filter manufacturing. The dyes were finally
heated to 400 ꢀC to determine their degradationꢁt1emperature. The
heating was carried out at the rate of 10 ꢀC min under nitrogen
atmosphere [6,13].
O
O
N
N
O
O
N
O
O
O
O
O
To check the thermal stability of the dyes in color filters, the
fabricated color filters were heated to 230 ꢀC for 1 h in a forced
convection oven (OF-02GW Jeiotech Co., Ltd.). The color difference
O
O
N
O
values (DEab) before and after heating were measured on a color
spectrophotometer (Scinco colormate) in CIE L0a0b0 mode.
4a
4b
Fig. 1. Synthesized dyes.
2.7. Geometry optimization of the synthesized dyes
The difference of thermal stability due to the structural differ-
ences in the dyes were analyzed by optimizing the dye structures
using the Gaussian 03 program, and examining the core twist angles
that affect the intermolecular interaction. The optimized geometries
of the dye structures were calculated at the B3LYP/6-31G* level.
Yield 83.1%; 1H NMR (CDCl3, ppm): 9.64 (d, 2H), 8.70 (d, 2H),
8.43 (s, 2H), 7.46 (m, 6H), 7.31 (d, 4H), 7.24 (t, 2H), 7.18 (d, 4H), 2.70
(septet, 4H), 1.14 (d, 24H); MALDI-TOF MS: m/z 896.31 (100%,
[M þ 2K]þ).
2.2.8. N,N0-Bis(2,6-diisopropylphenyl)-1,7-bis
3. Results and discussion
(p-tert-butylphenoxy)-perylene-3,4,9,10-tetracarboxydiimide (4b)
4b was synthesized in the same manner with 4a using 2b (1 g,
1.15 mmol), potassium carbonate anhydrous (0.7 g), and 4-tert-
butylphenol (0.38 g, 2.50 mmol).
3.1. Design concept of dyes
The steric restriction caused by the imidization of bulky aryl
groups at the terminal positions of Perylene-3,4,9,10-tetracarbox-
ylic dianhydride decreases the crystal packing density of the dyes,
which in turn increases their solubility [14]. In particular, ortho-
alkyl-substituted aromatics maximize this effect. However, substi-
tution at the terminal position does not affect the UVeVis
absorption spectra significantly because the conjugation nodes
along the long axis of the molecule limit the electronic interactions
between the main body of the molecule and corresponding
substituents [15,16].
Yield 81.9%; 1H NMR (CDCl3, ppm): 9.66 (d, 2H), 8.71 (d, 2H), 8.45
(s, 2H), 7.46 (m, 6H), 7.31 (d, 4H), 7.12 (d, 4H), 2.71 (septet, 4H),1.35 (s,
18H), 1.15 (d, 24H); MALDI-TOF MS: m/z 1008.49 (100%, [M þ 2K]þ).
2.3. Preparation of dye-based inks and color filters
The red ink for a color filter was composed of the dye (0.1 g),
cyclohexanone (3.2 g), and LC20160 (1.4 g) as a binder based on
acrylate.
The prepared dye-based inks were coated on a transparent glass
substrate using a MIDAS System SPIN-1200D spin coater. The
coating speed was initially 100 rpm for 5 s, which was then
increased to 300 rpm and kept constant for 20 s. The wet
Although the solubility of dye 1 in common organic solvents,
such as CH2Cl2, was increased significantly, it was not soluble
enough in industrial solvents, such as cyclohexanone, to be suitable
as a color filter (Table 1). Additional bulky substituents were

J. Choi et al. / Dyes and Pigments 90 (2011) 82e88
85
O
O
O
O
O
O
O
N
O
O
N
O
NH2
°C
Isoquinoline
(1)
Br
Br
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
Br2, I2
°C
H2SO4
Br
Br
Br
O
N
O
O
N
O
O
N
O
O
N
O
NH2
°C
HOAc
Br
(2b)
(2a)
Ar
Ar
O
O
O
N
O
O
N
O
O
N
O
O
N
O
°C
Ar
HO
K2CO3
O
(3)
Ar
(4)
3a : Ar = phenyl
4a : Ar = phenyl
4b : Ar = 4-tert-butyl phenyl
3b : Ar = 4-tert-butyl phenyl
3c : Ar = 4-tert-octyl phenyl
Scheme 1. Synthesis of the prepared dyes.
introduced at their bay positions to further improve their solubility.
The solubility was increased remarkably when the bulky aryl
groups were substituted at the bay positions because they deviated
from the plane of the molecule and the planarity of the main body
was broken [14].
The introduction of substituents at the bay positions was
demonstrated to alter the UVeVis absorption spectra of dyes
significantly [17]. Substituents with an ether linkage group were
chosen to minimize the bathochromic shift in the absorption
spectra and have high affinity with industrial solvents. In particular,
phenoxy substituents were considered to be superior to alkoxy
ones due to the lower bathochromic shift [18] and greater steric
hindrance for high solubility.
structure, perylene derivatives have low solubility due to the planar
structure, which facilitates the formation of crystals with high
lattice energy [14].
The solubility of dye 1 in CH2Cl2 was significantly higher than
Perylene-3,4,9,10-tetracarboxylic dianhydride due to the terminal
bulky aryl groups that rotate 90ꢀ out of the plane of the molecule.
However, the solubility of dye 1 in cyclohexanone was still very low.
The molecular structure of dye 2b is no longer planar due to the
presence of Br atoms at the bay positions, which in turn decrease
the crystal packing density [19]. Therefore, the solubility of dye 2b
in CH2Cl2 and cyclohexanone was higher than that of dye 1 but was
still insufficient for use in LCD color filters.
There were significant improvements in the solubility of dye 3b
and 4b when the Br atoms were replaced with bulky phenoxy
substituents that induce further twisting of the two naphthalene
subunits in the perylene core [20]. The core twisting effect of the
mono-substituted dye was less than 1,7-di(substituted) dye (Fig. 7).
Consequently, dye 3b would have higher crystallinity than dye 4b,
but the asymmetric molecular structure of dye 3b could offset this
effect. Therefore, the solubility of both dyes was similar in both
solvents and sufficient for use in LCD color filters. In particular, their
high solubility in cyclohexanone was attributed to the affinity
between the ether linkage of the dyes and solvent molecules.
3.2. Solubility of dyes
The dyes need to be dissolved in industrial solvents to
a concentration of at least 4 w 5wt% to be suitable for LCD color
filters. Table 1 lists the solubility data of the four representative
dyes. Without the appropriate modification of the molecular
Table 1
Solubility of the dyes at 20 ꢀC.
1
2b
3b
4b
3.3. Spectral and chromatic properties of dyes and dye-based
color filters
CH2Cl2
Cyclohexanone
þ
þþ
þ
þþþ
þþþ
þþþ
þþþ
e
þþþ: 5.0 ꢂ 104 w 1.0 ꢂ 105 mg Lꢁ1; þþ: 5.0 ꢂ 103 w 5.0 ꢂ 104 mg Lꢁ1; þ:
Fig. 2 and Table 2 show the absorption spectra of dyes 3a w 4b
in CH2Cl2. To apply a dye to LCD red color filters, the dye needs to
5.0 ꢂ 102 w 5.0 ꢂ 103 mg Lꢁ1; ꢁ: <5.0 ꢂ 102 mg Lꢁ1
.

86
J. Choi et al. / Dyes and Pigments 90 (2011) 82e88
0.7
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
3a
3b
0.6
3a
3b
3c
4a
4b
3c
4a
0.5
4b
0.4
0.3
0.2
0.1
0.0
400
500
600
700
800
400
500
600
700
800
Wavelength(nm)
Wavelength(nm)
Fig. 2. Absorption spectra in CH2Cl2 (10ꢁ5 mol Lꢁ1).
Fig. 3. Absorption spectra in Cyclohexanone (10ꢁ5 mol Lꢁ1).
have a strong and sharp absorption maximum in the 525 w 550 nm
range. The absorption maxima of the above dyes with various
phenoxy substituents at the bay positions were slightly bath-
ochromic compared to Perylene-3,4,9,10-tetracarboxylic dianhy-
dride (lmax ¼ 526 nm) due to the electron donating effect of the
substituents [21]. The bathochromic shifts in the mono-substituted
dyes (3a w c) were less than those of 1,7-di(substituted) dyes
(4a w b) because such an effect of substituents diminishes. As can
be seen in comparison with 3a w c and 4a w b, the bulkier alkyl
group at the para position produces a larger red-shift in lmax due to
the increase in donating power.
The above dyes show spectral-broadening compared to Perylene-
3,4,9,10-tetracarboxylic dianhydride but still have satisfactory spec-
tral sharpness for use in LCD color filters. This spectral-broadening
was attributed to the increase in conjugation between the substitu-
ents and perylene core, as well as to twisting of the perylene core by
the substituents [12].
The molar extinction coefficients of the synthesized dyes were
quite high and varied with the dye structure. Therefore, the dye-
based color filters could have higher tinctorial strength compared
to the pigment-based one with considerably lower dye content. The
molar extinction coefficients of the mono-substituted dyes were
higher than the 1,7-di(substituted) dyes because their structural
planarity was less distorted. However, the molar extinction coeffi-
cient of dye 3c was lower than that of dyes 4a and 4b, probably due
to the steric effect of the tert-octyl group.
cyclohexanone, the absorption maxima were hypsochromic by
approximately 4 w 6 nm and the molar extinction coefficients
decreased by approximately 10000 w 20000 compared to those in
CH2Cl2. This would be attributed to the difference in affinity
between the dyes and solvents.
Fig. 4 shows the transmittance spectra of the pigment-based
color filter and the fabricated dye-based color filters with dyes
3a w 4b. All the dye-based color filters had similar or superior
transmittance spectra compared to the pigment-based one because
dyes dissolved in the media have a smaller particle size, which
leads to less light scattering [6,22]. In particular, the synthesized
perylene dyes can maintain a well-dissolved state due to their high
molar extinction coefficients so that only small amounts of dyes are
needed for LCD color filters. The color filter with dye 4b showed the
highest transmittance over 625 nm because of its two bulky tert-
butylphenoxy substituents, which lead to less aggregation of dye
molecules. Table 3 shows the transmittance of the pigment-based
and dye-based color filters at 650 nm; the dye-based color filters
had higher transmittance. However, all the dye-based color filters
had undesirable transmittance at 400e500 nm, as shown in Fig. 4,
and yellow color compensating dyes are needed to cut off these
undesirable transmittance.
Fig. 3 and Table 2 show the absorption spectra of dyes 3a w 4b
in cyclohexanone, the industrial solvent of LCD color filters. There
were some differences between the absorption spectra in cyclo-
hexanone and CH2Cl2. When the dyes were dissolved in
100
80
Pigment
60
3a
3b
Table 2
Absorption spectra of the prepared dyes in CH2Cl2 and Cyclohexanone.
40
3c
Solvent
CH2Cl2
Dye
lmax (nm)
3max (L molꢁ1 cmꢁ1
)
4a
4b
3a
3b
3c
4a
4b
3a
3b
3c
4a
4b
530
532
538
540
544
526
528
532
532
538
71919
77434
47014
55197
59145
60980
61991
41830
40529
41431
20
0
Cyclohexanone
400
500
600
700
Wavelength(nm)
Fig. 4. Transmittance spectra of the spin-coated color filters.

J. Choi et al. / Dyes and Pigments 90 (2011) 82e88
87
Table 3
Transmittance of the spin-coated color filters at 650 nm.
Color filter
Transmittance (%) at 650 nm
Pigment
3a
3b
3c
4a
94.5997
94.8496
97.7593
97.5466
96.7853
4b
100
Table 4 lists the coordinate values of the pigment-based color
filter and fabricated dye-based color filters with dyes 3a w 4b.
Although dye-based color filters had a lower colorant content, they
could have a similar color gamut with a pigment-based one due to
the high molar extinction coefficients. In particular, the color filters
with dyes 3a and 3b, which have higher molar extinction coeffi-
cients, had larger x values. However, the x, y values of the color
filters with dyes 4a and 4b decreased after postbaking due to their
low thermal stability, as shown in Fig. 5 and Table 4. Compared to
the pigment-based color filter, the dye-based ones had smaller y
values, which are advantageous for a wide color gamut. In partic-
ular, the color filters with more bathochromic dyes had smaller y
values. The dye-based color filters also had higher brightness (Y)
values than the pigment-based one due to their higher trans-
mittance [6].
Fig. 5. CIE 1931 chromaticity diagram of the pigment-based and dye-based color
filters.
that led to superior thermal stability [28]. Therefore, the thermal
stability of 1,7-di(substituted) dyes is insufficient for use in LCD color
filters, even though they exhibited excellent spectral properties. The
mono-substituted dye 3c showed less weight loss than dyes 4a and
4b but more weight loss than dyes 3a and 3b due to the low thermal
stability caused by the tert-octyl alkyl chain.
The
heating for one hour at 230 ꢀC for commercial applications. The
color filters with the mono-substituted dyes had satisfactory Eab
values that varied according to their structures, as shown in Table 4.
In contrast, the color filters with the 1,7-di(substituted) dyes had
DEab values of the color filters should be less than 3 after
3.4. Thermal stability of dyes and dye-based color filters
D
Dye molecules should have a strong intermolecular interaction
and form compact aggregates to have the high thermal stability
[23e25]. The synthesized perylene dyes contain many aromatic
rings and have a relatively flat molecular structure that contributes
DEab values bigger than 3, which means that their thermal stability
is insufficient.
to the strong pep stacked interactions [8,9]. In addition, their high
As shown in Table 4, the x, y coordinate values of the color filters
with the 1,7-di(substituted) dyes decreased and their brightness (Y)
values increased after postbaking. This suggests that their original red
color faded due to degradation of their molecular structure. However,
the thermal stability of dye-based color filters can be improved if the
commercial binder used for the pigments can be adjusted.
The difference in thermal stability between the two types of dyes
was analyzed partially by geometry calculations. Fig. 7 shows the
optimized geometries of dyes 3b and 4b, which showed molecular
core twisting due to the bulky phenoxy substituents at the bay posi-
tions [29]. The approximate dihedral angle between the two
molecular weight and polar substituents at the bay positions are
advantageous for intermolecular interactions, such as Van der
Waals Force and dipoleedipole interaction [6].
For dyes to be used as color filters, they should endure tempera-
ture of 220 ꢀC, which is the highest temperature in the LCD
manufacturing process, without significant weight loss [26,27].
Mono-substituted dyes 3a and 3b showed less than 1% weight loss
after 30 min at 220 ꢀC and were stable up to 250 ꢀC, whereas the 1,7-
di(substituted) dyes 4a and 4b showed approximately 5% weight loss,
as shown in Fig. 6. This was attributed to the lower core twisting and
less anti-aggregation effect of the substituents of the mono-
substituted dyes, which leads to close packing of the dye molecules
for high thermal stability. In a previous report, field emission scan-
ning electron microscopy (FE-SEM) studies of various dyes showed
that the dye with less steric hindrance had the bigger aggregate size
100
Table 4
95
The coordinate values corresponding to the CIE 1931 chromaticity diagram and the
color difference values of the pigment-based and dye-based color filters.
Color filter
x
y
Y
DEab
3a
90
Pigment
Prebake
Postbake
Prebake
Postbake
Prebake
Postbake
Prebake
Postbake
Prebake
Postbake
Prebake
Postbake
0.644
0.641
0.639
0.635
0.642
0.640
0.623
0.615
0.634
0.528
0.626
0.527
0.345
0.343
0.337
0.335
0.335
0.334
0.311
0.309
0.304
0.262
0.303
0.269
22.10
22.16
23.01
23.28
24.69
25.01
25.25
26.20
24.72
30.06
24.49
29.67
0.248
0.613
0.752
1.823
9.873
9.668
3b
3c
3a
3b
3c
4a
4b
4a
4b
85
80
50
100
150
200
250
300
350
400
o
Temperature ( C)
Fig. 6. Thermogravimetric analysis (TGA) of the prepared dyes.

88
J. Choi et al. / Dyes and Pigments 90 (2011) 82e88
References
[1] Tsuda K. Color filters for LCDs. Displays 1993;14:115e24.
[2] Sabnis RW. Color filter technology for liquid crystal displays. Displays
1999;20:119e29.
[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.
[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] Sugiura T. Dyed color filters for liquid-crystal displays.
1993;1:177e80.
J Soc Inf Disp
[6] Kim YD, Kim JP, Kwon OS, Cho IH. The synthesis and application of ther-
mally stable dyes for ink-jet printed LCD color filters. Dyes Pigm
2009;81:45e52.
[7] Langhals H. Cyclic carboxylic imide structures as structure elements of high
stability. Novel developments in perylene dye chemistry. Heterocycles
1995;40:477e500.
[8] Kim JH, Masaru M, Fukunishi K. Three dimensional molecular stacking and
functionalities of aminonaphthoquinine by intermolecular hydrogen bondings
and interlayer
p-p interactions. Dyes Pigm 1998;40:53e7.
[9] 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.
[10] Herbst W, Hunger K. Industrial organic pigments: production, properties,
applications. 3rd ed. Willey-VCH. 2004. p. 476.
[11] Langhals H. Control of the interactions in multichromophores: novel concepts.
Perylene bis-imides as components for larger functional units. Helv Chim Acta
2005;88:1309e43.
[12] Chao CC, Leung M. Photophysical and electrochemical properties of 1,7-diaryl-
substituted perylene diimides. J Org Chem 2005;70:4323e31.
[13] 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.
[14] Seybold G, Wagenblast G. New perylene and violanthrone dyestuffs for
fluorescent collectors. Dyes Pigm 1989;11:303e17.
Fig. 7. Geometry-optimized structures of dyes 3b and 4b.
[15] Chen Z, Debije MG, Debaerdemaeker T, Osswald P, Würthner F. Tetrachloro-
substituted perylene bisimide dyes as promising n-type organic semi-
conductors: studies on structural, electrochemical and charge transport
properties. Chem Phys Chem 2004;5:137e40.
[16] Lee SK, Zu Y, Herrmann A, Geerts Y, Müllen K, Bard AJ. Electrochemistry,
spectroscopy and electrogenerated chemiluminescence of perylene, terrylene,
naphthalene subunits attached to the central benzene ring was 8.6ꢀ
and 26.2ꢀ for dyes 3b and 4b, respectively. Therefore, the core twisting
that decreases pep stacked interaction was more severe in the 1,7-di
(substituted) dye, which in turn led to lower thermal stability.
and quaterrylene diimides in aprotic solution.
J Am Chem Soc 1999;
121:3513e20.
4. Conclusions
[17] Langhals H, Blanke P. An approach to novel NIR dyes utilising
a-effect donor
groups. Dyes Pigm 2003;59:109e16.
Eight red perylene dyes were synthesized, and among them five
solubility enhanced dyes were used in color filters. The difference in
solubility of the prepared dyes was attributed to the bulky func-
tional substituents at the bay and terminal positions and the core
twisting of the molecular structures.
All five dyes showed sharp absorption near 530 nm, and the
dye-based color filters could have a similar color gamut to the
pigment-based one despite the much lower colorant content used
due to their high molar extinction coefficients. In addition, the dye-
based color filters with those dyes could have higher transmittance
than the pigment-based one because they dissolved in the media,
would exist in the molecular phase and could have a smaller
particle size that leads to less light scattering.
[18] Zhao C, Zhang Y, Li R, Li X, Jiang J. Di(alkoxy)-and di(alkylthio)-substituted
perylene-3,4,9,10-tetracarboxy diimides with tunable electrochemical and
photophysical properties. J Org Chem 2007;72:2402e10.
[19] Ma YS, Wang CH, Zhao YJ, Yu Y, Han CX, Qiu XJ, et al. Perylene diimide dyes
aggregates: optical properties and packing behavior in solution and solid
state. Supramol Chem 2007;19:141e9.
[20] Würthner F, Sautter A, Thalacker C. Substituted diazadibenzoperylenes: new
functional building blocks for supramolecular chemistry. Angew. Chem.
2000;112;1298-1301. Angew Chem Int Ed 2000;39:1243e5.
[21] Sun B, Zhao Y, Qiu X, Han C, Yu Y, Shi Z. Substitution effect of 1,7-asymmet-
rically substituted 3,4:9,10-perylenebis(dicarboximide) dyes. Supramol Chem
2008;20:537e44.
[22] Tilley RJD. Colour and optical properties of materials. Chichester: John Wiley &
Sons Inc.; 2000. pp. 108e10.
[23] Giles CH, Duff DG, Sinclair RS. The relationship between dye structure and
fastness properties. Rev Prog Coloration 1982;12:58e65.
[24] Das S, Basu R, Minch M, Nandy P. Heat-induced structural changes in
The mono-substituted dyes had satisfactory thermal stability
due to the properly controlled aggregation, whereas the 1,7-di
(substituted) dyes did not meet the commercial criterion because
their two bulky substituents at the bay positions made them
thermally less stable.
merocyanine
1995;29:191e201.
dyes:
X-ray
and
thermal
studies.
Dyes
Pigm
[25] Chunlong Z, Nianchun M, Liyun L. An investigation of the thermal stability of
some yellow and red azo pigments. Dyes Pigm 1993;23:13e23.
[26] Ohmi T. Manufacturing process of flat display. JSME Int J Ser B (Jpn Soc Mech
Eng) 2004;47:422e8.
[27] Takamatsu T, Ogawa S, Ishii M. Color filter fabrication technology for LCDs.
Sharp Tech J 1991;50:69e72.
[28] Sakong C, Kim YD, Choi JH, Yoon C, Kim JP. The synthesis of thermally-stable
red dyes for LCD color filters and analysis of their aggregation and spectral
properties. Dyes and Pigments 2011;88:166e73.
[29] 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.
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.