The effect of fluorescence of perylene red dyes on the contrast ratio of LCD color filters

Article abstract of DOI:10.1016/j.dyepig.2016.03.041

Dye-based and pigment-dye hybrid color filters are recommended to overcome the drawbacks such as light scattering of traditional pigment-based color filters. However, dyes used as colorants for LCD color filters may exhibit strong fluorescence. Fluorescence lowers the contrast ratio of color filters by increasing brightness in the full-black state and affects optical performance of displays. In this study, the correlation between dye fluorescence and the optical properties of color filters was investigated. Six perylene-based dyes were synthesized, and dye-based and pigment-dye hybrid color filters were prepared with each dye. The fluorescence properties of the synthesized dyes in solution and the prepared color filters were evaluated. The maximum brightness and the contrast ratio of the color filters were measured, from which the minimum brightness of the color filters was calculated. All dye-based and pigment-dye hybrid color filters showed greater minimum brightness than pigment-based one due to emission in the visible region.

Full text of DOI:10.1016/j.dyepig.2016.03.041

Dyes and Pigments 131 (2016) 293e300
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
The effect of fluorescence of perylene red dyes on the contrast ratio of
LCD color filters
a
a
a
a
a
Jeong Yun Kim , Chun Sakong , Sang-a Choi , Hyeyoun Jang , Se Hun Kim ,
b
b
b
a, *
Kil Seong Chang , Myoung Sic Han , Jeong Su Lee , Jae Pil Kim
Lab. of Organic Photo-functional Materials, Department of Materials Science and Engineering, Seoul National University, Seoul, 151-744, Republic of Korea
Department of Electronic Material, Alphachem Corporation, 280-3, Donghwa-ri, Bongdam-eup, Hwaseong-si, Gyeonggi-do, Republic of Korea
a
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 21 January 2016
Received in revised form
Dye-based and pigment-dye hybrid color filters are recommended to overcome the drawbacks such as
light scattering of traditional pigment-based color filters. However, dyes used as colorants for LCD color
filters may exhibit strong fluorescence. Fluorescence lowers the contrast ratio of color filters by
increasing brightness in the full-black state and affects optical performance of displays. In this study, the
correlation between dye fluorescence and the optical properties of color filters was investigated. Six
perylene-based dyes were synthesized, and dye-based and pigment-dye hybrid color filters were pre-
pared with each dye. The fluorescence properties of the synthesized dyes in solution and the prepared
color filters were evaluated. The maximum brightness and the contrast ratio of the color filters were
measured, from which the minimum brightness of the color filters was calculated. All dye-based and
pigment-dye hybrid color filters showed greater minimum brightness than pigment-based one due to
emission in the visible region.
18 March 2016
Accepted 22 March 2016
Available online 23 March 2016
Keywords:
Color filter
Dye-based color filter
Pigment-dye hybrid color filter
Perylene
Fluorescence
© 2016 Elsevier Ltd. All rights reserved.
1. Introduction
Perylene-based dyes are suitable colorants for LCD color filters
due to their strong color strengths and high thermal stabilities
Color filters are essential components of liquid crystal displays
LCDs) [1e8]. The desirable properties of color filters are color
purity, contrast ratio, and brightness [9e12]. High-contrast color
filters are the most important components in the manufacture of
displays with superior optical properties [9,10].
[2e4,10,12]. However, perylene derivatives with bulky substituents
commonly exhibit strong fluorescence, because these groups can
prevent intermolecular interactions and irradiative energy trans-
fers that are the most important mechanisms of fluorescence
quenching [13e15].
(
Contrast ratio is the proportion of maximum brightness to
minimum brightness [6,9,10]. To obtain a high contrast ratio, light
should not be transmitted when the polarizers are closed to pro-
duce a dark image (full-black state) [9]. In traditional pigment-
based color filters, a small amount of light is transmitted in the
full-black state due to light scattering [5,6,10]. The problem, which
is caused by the large size of the pigments, can be resolved by
replacing pigments with dyes of smaller particle size [2,4,10].
However, many dyes that are used as colorants in LCD color filters
exhibit fluorescence, which significantly brightens the full-black
state of the device due to their emission. Consequently, dye-
based color filters may exhibit a lower contrast ratio than expected.
This paper will discuss the effect of fluorescence on the contrast
ratio of dye-based and pigment-dye hybrid color filters. Perylene-
based red dyes were synthesized with bulky substituents at ter-
minal- and bay-positions to improve their solubilities in industrial
solvents [2,10]. Color filters were prepared with low color content
to minimize the effect of aggregation on optical properties for the
obvious investigation about the influence of the fluorescence on the
contrast ratio. The fluorescence of the synthesized dyes in solution
and the fabricated dye-based and pigment-dye hybrid color filters
were measured and compared. The maximum brightness and the
contrast ratio of the color filters were measured, and the minimum
brightness was calculated from the results. Finally, the correlation
between fluorescence and optical properties of the color filters was
analyzed.
*
Corresponding author. Tel.: þ82 2 880 7187.
E-mail address: jaepil@snu.ac.kr (J.P. Kim).
http://dx.doi.org/10.1016/j.dyepig.2016.03.041
143-7208/© 2016 Elsevier Ltd. All rights reserved.
0

294
J.Y. Kim et al. / Dyes and Pigments 131 (2016) 293e300
0
2
. Experimental
2.2.3. N,N -Bis(2,6-diisopropylphenyl)-1,7-bis(o-allylphenoxy)-
perylene-3,4,9,10-tetracarboxydiimide (PI2-AP); bay-position
substitution
2.1. Materials and instrumentations
0
N,N -Bis(2,6-diisopropylphenyl)-1,7-dibromoperylene-3,4,9,10-
Perylene-3,4,9,10-tetracarboxylic dianhydride, 4-tert-octylphe-
tetracarboxydiimide (0.50 g, 0.575 mmol) was mixed with potas-
nol, iodine, sulfuric acid, bromine and acetic acid purchased from
SigmaeAldrich, 2,6-diisopropylaniline, 2,4,6-trimethylphenol and
sium carbonate anhydrous (0.35 g), 2-allylphenol (0.20 g,
ꢀ
1.50 mmol) and NMP (50 ml). The mixture was heated at 40
C
2
-allylphenol purchased from TCI, K
2
CO
3
anhydrous, methylene
under nitrogen atmosphere and was stirred at for 1.5 h. The mixture
was cooled to room temperature, and then poured into 400 ml of
5% HCl aqueous solution. The precipitate was filtered, washed with
water, and dried in vacuum at 80 C. The crude product was purified
2 2
by column chromatography in silica gel using CH Cl as the eluent
chloride and other chemical solvents purchased from SAMCHUN
pure chemical were used without any additional purification.
Transparent glass substrates were purchased from Paul Marienfeld
GmbH & CO. KG.
ꢀ
1H NMR and 13C NMR spectra were recorded by a Bruker Avance
to obtain PI2-AP as red solid.
1
5
00 spectrometer at 500 MHz using chloroform-d and TMS as the
Yield 71.5%; H NMR (CDCl
3
, ppm): 9.72 (d, 2H), 8.67 (d, 2H),
solvent and internal standard. Matrix Assisted Laser Desorption/
Ionization Time Of Flight (MALDI-TOF) mass spectra were recorded
7.46 (t, 2H), 7.35 (d, 2H), 7.30 (m,10H), 6.97 (t, 2H), 6.06 (septet, 2H),
5.14 (d, 2H), 5.07 (d, 2H), 3.59 (d, 4H), 2.71 (septet, 4H), 1.14 (d,
13
by a Voyager-DE STR Biospectrometry Workstation with
hydroxycinnamic acid (CHCA) as the matrix. Elemental analysis
EA) was completed on a CE Instrument EA1112. Absorption spectra
a-cyano-4-
24H); C NMR (126 MHz, CDCl
3
):
d
¼ 24.18, 24.22, 29.40, 34.61,
116.82,119.54,122.53,123.94,124.24,125.80,125.96,128.70,129.33,
129.83, 129.93, 130.68, 130.86, 131.75, 131.98, 133.98, 136.42, 145.83,
152.98, 155.74, 163.12, 163.69; MALDI-TOF MS: m/z 976.3 (100%,
(
were measured using a Perkin Elmer Lambda 25 UV/Vis spectro-
photometer. Fluorescence spectra were measured using a Perkin
Elmer LS 55 Fluorescence spectrometer. Contrast ratio and bright-
ness of color filters were measured using a CT-1 of TSUBOSAKA and
MC-3700:28C of OTSUKA ELECTRONICS. The thickness of the spin-
coated film was measured using a Nano System Nanoview E-1000.
þ
[M þ2K] ); EA Found(%): C, 81.51; H, 6.14; N, 2.80; O, 9.56. Calc.(%)
58 2 6
for C66H N O : C, 81.29; H, 5.99; N, 2.87; O, 9.84.
0
2.2.4. N,N -Bis(2,6-diisopropylphenyl)-1,7-bis(2,4,6-
trimethylphenoxy)-perylene-3,4,9,10-tetracarboxydiimide (PI2-
TMP)
PI2-TMP was synthesized in the same manner with PI2-AP
2.2. Synthesis
0
using
N,N -Bis(2,6-diisopropylphenyl)-1,7-dibromoperylene-
3
,4,9,10-tetracarboxydiimide (0.50 g, 0.575 mmol), potassium car-
The dyes PI2-AP, PI2-TMP, PI2-S2, and PI1-S2 were already
reported in our previous study [2,10]. The syntheses of these dyes
are detailed in this paper.
bonate anhydrous (0.35 g) and 2,4,6-trimethylphenol (0.21 g,
ꢀ
1.50 mmol). The reaction temperature was set at 60 C for 2 h.
1
Yield 78.0%; H NMR (CDCl
3
, ppm): 9.69 (m, 2H), 8.72 (d, 2H),
7
.48 (t, 2H), 7.32 (m, 6H), 7.03 (s, 4H), 2.74 (septet, 4H), 2.34 (s, 6H),
2
.2.1. 1,(7)-(di)bromoperylene-3,4,9,10-tetracarboxydiimide (1,2);
bromination
Perylene-3,4,9,10-tetracarboxylic
1.4 mmol), iodine (0.78 g, 3.04 mmol), and sulfuric acid (98%,
13
2
2
1
1
.18 (m, 12H), 1.19 (m, 24H); C NMR (126 MHz, CDCl
4.15, 24.21, 24.26, 29.38, 29.48, 120.17, 122.13, 122.76, 124.16,
24.21, 124.92, 125.27, 128.17, 129.17, 129.30, 129.50, 129.98, 130.15,
30.24, 130.41, 130.50, 130.54, 130.72, 130.77, 133.62, 133.93, 136.46,
3
):
d
¼ 16.62,
dianhydride
(32.0
g,
8
4
50 ml) were mixed and stirred for 2 h at room temperature. The
138.65, 145.83, 147.79, 162.97, 163.12; MALDI-TOF MS: m/z 980.3
ꢀ
temperature of the mixture was raised to 80 C, bromine (7.5 ml,
þ
(
100%, [M þ2K] ); EA Found(%): C, 80.96; H, 6.14; N, 2.98; O, 9.91.
146.65 mmol) was added dropwisely for 1 h. The mixture was
62 2 6
Calc.(%) for C66H N O : C, 80.95; H, 6.38; N, 2.86; O, 9.80.
reacted for 16 h. Then, it was cooled to room temperature and
bromine gas was displaced by nitrogen gas. The mixture was slowly
poured into 3L of ice-water, producing precipitate collected by
suction filtration in crude product form. The crude product was
washed with distilled water several times. Then, the crude product
was dried at 100 C under reduced pressure and used in the next
step without further purification. The crude containing both 1 and
2
0
.2.5. N,N -Bis(2,6-diisopropylphenyl)-1,7-bis(p-tert-
2
octylphenoxy)-perylene-3,4,9,10-tetracarboxydiimide (PI2-S2)
PI2-S2 was synthesized in the same manner with PI2-AP using
0
N,N -Bis(2,6-diisopropylphenyl)-1,7-dibromoperylene-3,4,9,10-
tetracarboxydiimide (0.50 g, 0.575 mmol), potassium carbonate
anhydrous (0.35 g) and 4-tert-octylphenol (0.31 g, 1.50 mmol).
ꢀ
was separated by column chromatography in next step, after
1
Yield 76.9%; H NMR (CDCl
3
, ppm): 9.66 (d, 2H), 8.69 (d, 2H),
importing derivatives in terminal-position to increase solubility.
8
.38 (d, 4H), 7.45 (m, 2H), 7.32 (m, 4H), 7.25 (s, 2H), 7.10 (d, 4H), 2.72
13
(septet, 4H),1.39 (s, 4H),1.16 (d, 24H), 0.75 (s,18H), 0.73 (s,12H);
C
0
2
3
.2.2. N,N -Bis(2,6-diisopropylphenyl)-1,(7)-(di)bromoperylene-
,4,9,10-tetracarboxydiimide (3,4); terminal-position substitution
NMR (126 MHz, CDCl
3
):
d
¼ 24.18, 24.22, 29.39, 31.72, 32.00, 32.63,
38.66, 57.38, 118.89, 119.02, 122.49, 123.34, 124.12, 124.20, 124.26,
124.58, 124.75, 126.00, 128.18, 128.45, 129.25, 129.83, 129.92,
130.73, 130.90, 131.98, 133.97, 145.88, 147.47, 147.59, 152.78, 155.71,
162.94, 163.10, 163.71; MALDI-TOF MS: m/z 1120.5 (100%,
The
crude
1,(7)-(di)bromoperylene-3,4,9,10-
tetracarboxydiimide (8.0 g, 14.5 mmol), 2,6-diisopropylaniline
(
8.28 g, 46.7 mmol), acetic acid (4.6 ml), and N-Methyl-2-
ꢀ
þ
pyrrolidone(NMP) (100 ml) were mixed and heated at 120 C un-
der the nitrogen atmosphere for 96 h. The precipitate was obtained
by adding water to the mixture and be collected by suction filtra-
tion. The crude product was washed with water and dried. The
crude product was purified by column chromatography in silica gel
[M þ2K] ); EA Found(%): C, 81.76; H, 7.41; N, 2.47; O, 8.35. Calc.(%)
82 2 6
for C76H N O : C, 81.54; H, 7.38; N, 2.50; O, 8.58.
0
2.2.6. N,N -Bis(2,6-diisopropylphenyl)-1-o-allylphenoxy-perylene-
3,4,9,10-tetracarboxydiimide (PI1-AP)
using CH
2
Cl
2
as the eluent. The first reddish band containing tri-
PI1-AP was synthesized in the same manner with PI2-AP using
N,N -Bis(2,6-diisopropylphenyl)-1-bromoperylene-3,4,9,10-
tetracarboxydiimide (0.50 g, 0.575 mmol), potassium carbonate
0
brominated diimide could be separated. Second reddish band
containing dibrominated diimide and third one containing mono-
brominated diimide could be collected. Detailed structure analysis
was done after next step.
anhydrous (0.21 g) and 2-allylphenol (0.15 g, 1.13 mmol).
1
Yield 73.4%; H NMR (CDCl
3
, ppm): 9.71 (d, 2H), 8.83 (d, 2H),

J.Y. Kim et al. / Dyes and Pigments 131 (2016) 293e300
295
8
5
.75 (t, 2H), 8.26 (s, 1H), 7.48 (t, 2H), 7.34 (m, 8H), 6.06 (septet, 2H),
content were adjusted to show appropriate color coordination as
red color filters. The prepared inks were coated on a transparent
glass substrate using a spin coater. The spin-coated color filters
were pre-baked at 80 C for 10min and post-baked at 230 C for
30min. The contrast ratio of the color filters were measured by CT-1
instrument of TSUBOSAKA and the brightness of them were
measured by MC-3700: 28C of OTSUKA ELECTRONICS.
13
.12 (d, 1H), 3.56 (d, 2H), 2.77 (septet, 4H), 1.19 (d, 24H); C NMR
):
¼ 24.18, 24.22, 28.71, 29.44, 34.55, 116.87,
19.84, 122.79, 122.85, 123.19, 123.40, 124.15, 124.27, 124.30, 124.38,
24.62, 124.75, 126.08, 126.46, 127.65, 128.77, 129.06, 129.26,
29.38, 129.87, 130.09, 130.51, 130.84, 131.73, 131.86, 132.06, 132.85,
34.50, 135.06, 135.27, 136.34, 145.81, 145.89, 146.41, 152.60, 156.72,
62.90, 163.70, 163.94; MALDI-TOF MS: m/z 844.2 (100%,
(
126 MHz, CDCl
3
d
ꢀ
ꢀ
1
1
1
1
1
þ
[
M þ2K] ); EA Found(%): C, 81.21; H, 5.95; N, 3.57; O, 9.27. Calc.(%)
3. Results and discussion
for C57 : C, 81.21; H, 5.98; N, 3.32; O, 9.49.
50 2 5
H N O
3.1. Design concept and synthesis of the dyes
0
.2.7. N,N -Bis(2,6-diisopropylphenyl)-1-2,4,6-trimethylphenoxy-
2
perylene-3,4,9,10-tetracarboxydiimide (PI1-TMP)
Perylene-based dyes have many advantages as colorants in op-
PI1-TMP was synthesized in the same manner with PI2-AP
using N,N -Bis(2,6-diisopropylphenyl)-1-bromoperylene-3,4,9,10-
tical devices including high color strength and thermal stability
[2,4,10,12]. However, their applications are limited by low solubility
in industrial solvents due to their planar molecular structures
[10,12].
0
tetracarboxydiimide (0.50 g, 0.575 mmol), potassium carbonate
anhydrous (0.21 g) and 2,4,6-trimethylphenol (0.16 g, 1.13 mmol).
ꢀ
The reaction temperature was set at 60 C for 2 h.
The synthetic routes and molecular structures of the synthe-
sized dyes are shown in Scheme 1 and Fig. 1. All dyes are designed
to have increased solubility in organic solvents. Un-substituted
perylene dyes are not soluble in industrial solvents such as
PGMEA and cyclohexanone [2,10,12]. Introduction of substituents
at their terminal- and bay-positions increases the solubility of the
dyes in organic solvents. The substituents introduced on perylene-
based dyes effectively decrease the intermolecular interactions and
planarities of the dyes [2,10]. Solubilities of the synthesized dyes
are listed in Table 1. Dyes should have solubilities greater than 5 wt
% in industrial solvents to be used as colorants in color filters
1
Yield 77.3%; H NMR (CDCl
3
, ppm): 9.89 (d, 2H), 8.83 (t, 2H), 8.05
(
(
(
2
1
1
1
8
9
s, 1H), 7.50 (m, 2H), 7.34 (d, 4H), 7.04 (s, 4H), 3.03 (s, 1H), 2.78
13
septet, 4H), 2.35 (s, 2H), 2.18 (s, 6H), 1.19 (m, 24H); C NMR
126 MHz, CDCl ):
¼ 16.49, 21.05, 23.09, 23.46, 24.13, 28.38, 28.71,
9.36, 29.44, 120.02, 121.01, 122.40, 122.63, 123.18, 123.25, 123.37,
24.29, 124.39, 124.73, 125.81, 127.66, 127.77, 129.49, 129.95, 130.16,
30.66, 130.75, 130.90, 131.66, 131.86, 132.93, 134.91, 135.07, 135.45,
3
d
45.81, 147.81, 157.28, 163.03, 163.76, 164.01; MALDI-TOF MS: m/z
þ
46.3 (100%, [M þ2K] ); EA Found(%): C, 81.22; H, 6.07; N, 3.42; O,
52 2 5
.29. Calc.(%) for C57H N O : C, 81.02; H, 6.20; N, 3.32; O, 9.47.
[
2,10,12]. As indicated in Table 1, most of the synthesized dyes
0
2
.2.8. N,N -Bis(2,6-diisopropylphenyl)-1-p-tert-octylphenoxy-
showed suitable solubility in industrial organic solvents.
perylene-3,4,9,10-tetracarboxydiimide (PI1-S2)
Bromination and substitution reactions at terminal-positions
were carried out by well-known procedures [1,2,4,16e18]. Bay-
position substitution reactions were performed at a lower tem-
perature and for a shorter time than the standard method by the
procedure reported in our previous study [10]. The reaction yields
of all bay-position substitution reactions exceeded 70%.
PI1-S2 was synthesized in the same manner with PI2-AP using
0
N,N -Bis(2,6-diisopropylphenyl)-1-bromoperylene-3,4,9,10-
tetracarboxydiimide (0.50 g, 0.575 mmol), potassium carbonate
anhydrous (0.21 g) and 4-tert-octylphenol (0.23 g, 1.12 mmol).
1
Yield 79.2%; H NMR (CDCl
3
, ppm): 9.68 (d, 2H), 8.82 (d, 2H),
8
4
CDCl
1
1
.76 (d, 4H), 8.39 (s, 1H), 7.49 (m, 4H), 7.34 (m, 4H), 2.78 (septet,
13
H), 1.40 (s, 2H), 1.18 (d, 24H), 0.74 (s, 15H); C NMR (126 MHz,
):
¼ 24.22, 29.42, 29.45, 31.72, 32.00, 32.64, 57.40, 119.12,
22.75, 122.81, 123.38, 124.08, 124.31, 124.61, 125.37, 126.56, 127.66,
28.54, 129.08, 129.24, 129.85, 130.06, 130.51, 130.86, 131.70, 132.91,
3.2. Spectral properties of the synthesized dyes
3
d
All dyes were designed to have a similar length of conjugation.
Therefore, they exhibited similar absorption spectra as shown in
Fig. 2 [19,20]. Consequently, the spectral properties of the synthe-
sized dyes rarely affected the optical properties of the color filters.
However, the varied size and shape of the substituents affected the
planarity and crystal packing structure of the dyes. Therefore, the
synthesized dyes exhibited different fluorescence properties
depending on their molecular structures [21].
134.51, 135.07, 135.28, 147.82, 152.43, 156.80, 162.89, 163.70, 163.95;
þ
MALDI-TOF MS: m/z 916.3 (100%, [M þ2K] ); EA Found(%): C, 81.40;
H, 6.85; N, 3.00; O, 8.74. Calc.(%) for C62
N, 3.06; O, 8.74.
62 2 5
H N O : C, 81.37; H, 6.83;
2.3. Fabrication of dye-based color filters
As shown in Fig. 3, the synthesized perylene dyes exhibited
strong fluorescence over 500e700 nm [16,22e24]. Fluorescence
was measured at an excitation wavelength corresponding to the
wavelength of maximum absorption, respectively. The emission
spectra of synthesized dyes exhibited different maximum wave-
lengths and intensities depending on their molecular structures.
The bay-substituted dyes with three methyl groups at ortho- and
para-positions exhibited the highest fluorescence intensity than
other dyes. Furthermore, di-bay-substituted dyes showed stron-
ger fluorescence than mono-bay-substituted dyes. This behavior
evidently results from the difference in conjugation length and
crystal packing of the dyes [13,15,25,26]. All emission maxima are
shifted bathochromically from the wavelength of maximum ab-
sorption by 18e30 nm. The intensity at the wavelength of
maximum emission and the total emission intensity within
the visible region (400e700 nm) are listed in Table 2. The
total emission intensity of the most strongly fluorescent dye (PI2-
TMP) was about twice as large as that of the most weakly
The red inks for dye-based color filters composed of the syn-
thesized dye (0.01 g), propylene glycol methyl ether acetate
PGMEA) (0.1 g), and acrylic binder (0.8 g). The prepared dye-based
(
inks were coated on a transparent glass substrate using a MIDAS
System SPIN-1200D spin coater. The rotating speed was initially set
at 100 rpm for 10s, and then increased to 500 rpm for 20s. The dye-
ꢀ
coated color filters were dried at 80 C for 20min, pre-baked at
ꢀ
ꢀ
1
50 C for 10min and post-baked at 200 C for 1 h. All spin-coated
dye-based color filters were 1.6 m thick.
m
2.4. Fabrication of pigment-dye hybrid color filters
The red inks for pigment-dye hybrid color filters were composed
of the pigment red 177 (13e15%), acrylic polymer dispersant
3e5%), acrylic polymer (3e5%), propylene glycol methyl ether
acetate (PGMEA) (75e80%), and synthesized dyes (0.5wt% or 1.0wt
compared with pigment red 177). The concentrations of color
(
%

296
J.Y. Kim et al. / Dyes and Pigments 131 (2016) 293e300
Scheme 1. Synthetic routes of the designed dyes.
Fig. 1. Structure of the synthesized dyes.
fluorescent dye (PI1-S2).
concentrations to minimize the effect of dye aggregation on optical
properties of the color filters. As shown in Fig. 4, the fabricated
color filters exhibited strong fluorescence in the visible region
despite their low color content. The total emission of the color fil-
ters in the visible region correlates with the emission of the dyes in
3
.3. Optical properties of the fabricated dye-based color filters
Dye-based color filters were prepared with low color content

J.Y. Kim et al. / Dyes and Pigments 131 (2016) 293e300
297
Table 1
Solubility of the synthesized dyes at 20 C in CH
100
ꢀ
2
2
Cl and PGMEA (wt%).
PI2-AP
PI2-TMP
PI2-S2
PI1-AP
PI1-TMP
PI1-S2
90
80
70
60
50
Dye
CH
PI2-AP
PI2-TMP
PI2-S2
PI1-AP
PI1-TMP
PI1-S2
2
Cl
PGMEA
2
5.1
4.4
8.5
7.8
6.2
5.7
6.0
5.0
8.9
7.9
6.7
6.1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
PI2-AP
PI2-TMP
PI2-S2
PI1-AP
PI1-TMP
PI1-S2
40
30
20
10
0
575
600
625
650
675
700
Wavelength (nm)
Fig. 4. Fluorescence of fabricated dye-based color filters.
dyes in solution would be maintained in the film state with similar
tendency.
4
00
450
500
550
600
650
700
The optical properties of the fabricated dye-based color filters
are shown in Table 3. The contrast ratios are very small, because the
inks for the color filters have low color content concentrations. The
value of RY (Max. Y) is the maximum brightness of the color filter
with the polarizer entirely open. Min. Y is the brightness in the full-
black state, which is calculated from the maximum brightness and
contrast ratio. The minimum brightness shows the same behavior
in pre- and post-baked color filters. This phenomenon suggests that
the influence of heat treatment on optical properties was mini-
mized by the low color contents [6,10]. Moreover, the sequence of
increasing minimum brightness of the fabricated color filters is
identical to that of the total emission intensity of the dyes within
the visible region. Therefore, it could be argued that the total
emission intensity within visible region of the dyes significantly
influences the minimum brightness of the fabricated color filters.
Wavelength (nm)
Fig. 2. Absorption spectra of synthesized dyes in chloroform (10ꢁ5 mol/L).
5
4
4
3
3
2
2
1
1
00
50
00
50
00
50
00
50
00
PI2-AP
PI2-TMP
PI2-S2
PI1-AP
PI1-TMP
PI1-S2
3.4. Optical properties of the fabricated pigment-dye hybrid color
filters
50
Pigment-dye hybrid color filters were prepared by adding 0.5 or
1
.0 wt% of the synthesized dyes in proportion to Pigment Red 177.
0
4
The perylene-based dyes are well-known that they would easily
exhibit H-aggregation and quench the fluorescence. Therefore, dye
concentrations were carefully restricted lower than what is used in
industry. FE-SEM images and average particle size were shown in
00
450
500
550
600
650
700
Wavelength (nm)
Fig. 3. Fluorescence of synthesized dyes in chloroform (10 8 mol/L).
ꢁ
Table 2
Spectral and fluorescence properties of the synthesized dyes.
Dye
PI2-AP
PI2-TMP
PI2-S2
PI1-AP
PI1-TMP
PI1-S2
a
l
em
571
574.5
403.16
47443.33
556
567.5
231.50
29065.89
546
565
566
568
Max. Emission Intensity
363.74
45751.41
546
298.16
32892.27
542
327.48
39489.99
548
200.29
22455.93
538
b
S(emission)
c
l
D
abs
ssd
25
18.5
21.5
23
18
30
a
b
c
l
em: maximum emission wavelength (nm).
S(emission): integral of fluorescence intensity in visible-ray region, total emission intensity.
abs: maximum absorption wavelength (nm).
ss: stokes shift.
l
D
d
solution as listed in Table 2. Thus, the fluorescence properties of the
Fig. 5 and Table 4. The fabricated pigment-based and pigment-dye

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J.Y. Kim et al. / Dyes and Pigments 131 (2016) 293e300
Table 3
a
Optical properties of the fabricated dye-based color filter.
Dye
PI2-AP
PI2-TMP
PI2-S2
PI1-AP
PI1-TMP
PI1-S2
Pre-baked
Rx
Ry
0.37828
0.23125
37.294
38
0.9814
0.37487
0.23423
39.093
45
0.35346
0.21607
37.022
33
1.1219
0.35348
0.21973
36.704
35
0.40584
0.25125
38.776
57
0.6803
0.40381
0.25306
39.606
58
0.39646
0.26480
40.451
54.5
0.7422
0.39449
0.24776
40.480
57.5
0.39021
0.23116
37.263
47.5
0.7845
0.39130
0.23216
37.427
47
0.36881
0.23712
38.776
87.5
0.4432
0.37452
0.23564
39.151
85.5
b
RY (Max. Y)
C/Rc
d
Min. Y
Rx
Ry
RY (Max. Y)
C/R
Post-baked
Min. Y
0.8687
1.0487
0.6829
0.7040
0.7963
0.4579
a
The inks for dye-based color filters composed of the synthesized dye (0.01 g), propylene glycol methyl ether acetate (PGMEA) (0.1 g), and acrylic binder (0.8 g).
RY (Max. Y): measured maximum brightness.
C/R: contrast ratio.
b
c
d
Min. Y: calculated brightness of full-black state.
hybrid color filters have similar particle size within the difference of
e7 nm. Transmittance spectra of the prepared color filters were
Table 4
Average particle size in FE-SEM images.
6
illustrated in Fig. 6 and Table 5. The transmittance spectra of the
hybrid color filters were match up with the spectra of the pigment-
based color filter within the whole visible region. By these results, it
could be regarded that the added dyes would have very limited
effect on the aggregation behavior or optical performance of the
color filters.
Color filter
Pigment-based 0.5 wt% dye added 1.0 wt% dye added
Average size (nm) 39.667
33.522
34.524
The fluorescence spectra of the fabricated pigment-dye hybrid
color filters are illustrated in Fig. 7. The fluorescence of all hybrid
color filters was measured with an excitation wavelength of 530 nm
[27]. Therefore, the fabricated hybrid color filters have similar
maximum emission peaks. All fabricated pigment-dye hybrid color
filters exhibited an absorption maximum at 530 nm, because they
consisted primarily of Pigment Red 177. However, the fluorescence
properties of the color filters differed as shown in Fig. 7. These
properties exhibited tendencies similar to those of dyes in solution
and dye-based color filters. Color filters with 1.0 wt% dye showed
stronger fluorescence than those with 0.5 wt%. These observations
demonstrate that the fluorescence features of the dyes are retained
in dye-based color filters and pigment-dye hybrid color filters.
The optical properties of the fabricated pigment-dye hybrid
color filters are listed in Table 6. All hybrid color filters showed
greater Min. Y values than pigment-based color filter (STD; Pigment
Red 177, 100%). This result indicates that the minimum brightness
of pigment-dye hybrid color filters was increased by the emission of
the added dyes. In addition, the sequence of minimum brightness
of the hybrid color filters was the same as that of dye-based ones.
As mentioned before, added dyes have limited effect on the ag-
gregation and optical properties of the fabricated color filters.
Therefore, the minimum brightness and contrast ratio of pigment-
dye hybrid color filters also were affected by the total emission
Fig. 6. Transmittance spectra of pigment-based and pigment-dye hybrid color filters.
within the visible region. Thus, color filters with strongly emitting
dyes would exhibit a high minimum brightness and low contrast
ratio.
The fluorescence of a dye could increase maximum brightness.
Fig. 5. FE-SEM images of pigment-based and pigment-dye hybrid color filters fabricated with PI2-TMP ((a) pigment-based, (b) 0.5 wt% dye added, (c) 1.0 wt% dye added color filter).

J.Y. Kim et al. / Dyes and Pigments 131 (2016) 293e300
299
Table 5
to one another. The total visible-range emission intensity of the
synthesized dyes in solution and the prepared color filters showed
the same trend regardless of their states. The minimum brightness
of the color filters calculated from the maximum brightness and
contrast ratio showed a similar trend to the total emission intensity.
Therefore, it is concluded that the total emission in the visible re-
gion is a key factor in determining the minimum brightness and
contrast ratio of color filters. Consequently, color filters fabricated
with strongly fluorescent dyes will exhibit high minimum bright-
ness and low contrast ratio.
Transmittance of fabricated pigment-based and pigment-dye hybrid color filters at
645 and 650 nm.
Dye
At 645 nm (%)
At 650 nm (%)
PI2-AP
PI2-TMP
PI2-S2
PI1-AP
PI1-TMP
PI1-S2
96.41
97.62
97.33
96.70
96.81
97.90
97.46
95.72
97.02
96.48
95.99
96.34
97.03
97.56
Pigment-based
Fig. 7. Fluorescence of fabricated pigment-based and pigment-dye hybrid color filters (dye contents (a) 0.5 wt%, (b) 1.0 wt%).
Table 6
Optical properties of the fabricated pigment-dye hybrid color filters.
Dye
PI2-AP
PI2-TMP
PI2-S2
PI1-AP
PI1-TMP
PI1-S2
0.5 wt%
Rx
0.656
0.656
0.656
0.656
0.656
0.656
Ry
0.30311
13.187
11294
0.0011676
0.656
0.30314
13.132
11130
0.0011799
0.656
0.30362
13.234
11824
0.0011192
0.656
0.30310
13.110
11568
0.0011333
0.656
0.30312
13.133
11428
0.0011492
0.656
0.30283
13.316
11849
0.0011238
0.656
a
RY (Max. Y)
C/R
Min. Y
Rx
b
c
1.0 wt%
Ry
0.30392
13.337
10238
0.30375
13.416
9234
0.30381
13.351
11325
0.30394
13.403
11124
0.30940
13.420
11070
0.30384
13.445
11727
RY (Max. Y)
C/R
Min. Y
0.0013027
0.0014529
0.0011789
0.0012049
0.0012123
0.0011465
STD (pigment 100%)d
Rx: 0.656, Ry: 0.30391, RY: 13.492, C/R: 12304, Min. Y: 0.0010966
a
RY (Max. Y): measured maximum brightness.
C/R: contrast ratio.
Min. Y: calculated brightness of full-black state.
STD: pigment-based color filter (Pigment Red 177, 100%).
b
c
d
However, as listed in Table 6, maximum brightness of the fabricated
pigment-dye hybrid color filters were maintained in every case.
There is no increase of maximum brightness from the added dyes.
On the contrary to this result, the minimum brightness of the
fabricated hybrid color filters were increased in all cases. Even
though the increases in figures were small, they raised the mini-
mum brightness considerably in proportion, which lowered
contrast ratio values accordingly.
Acknowledgments
This work was supported by the Advanced Technology Center
Program (No.10039098, Development of pigment-dye hybrid type
of color mill base with ultra-brightness for LED TV) funded by the
Small and Medium Business Administration.
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