Synthesis of high-soluble and non-fluorescent perylene derivatives and their effect on the contrast ratio of LCD color filters

Article abstract of DOI:10.1016/j.dyepig.2016.08.061

We designed and synthesized perylene-based dyes for dye-based LCD color filters that highly soluble in organic industrial solvents, exhibit very weak fluorescence, and can be easily synthesized due to their simple molecular structures. The synthesized dyes were designed containing methoxy groups in the terminal-, bay-, or both positions for developing fluorescence quenched dyes. And, dyes with strong fluorescence and similar molecular structures to the fluorescence quenched dyes were also synthesized to clearly compare and analyze the effect of fluorescence on the optical properties. Finally, we fabricated dye-based color filters using the synthesized dyes and analyzed the optical performances of the color filters. The methoxy group in the bay-substituents has an enormous effect on the fluorescence quenching without the conspicuous influences on molecular behavior or dye aggregation. And, the fluorescence quenched dyes have remarkable effects in minimizing the increment of minimum brightness and prohibiting the contrast ratio decrease.

Full text of DOI:10.1016/j.dyepig.2016.08.061

Dyes and Pigments 136 (2017) 836e845
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Synthesis of high-soluble and non-fluorescent perylene derivatives
and their effect on the contrast ratio of LCD color filters
Jeong Yun Kim a, Tae Gyu Hwang a, Se Hun Kim a, Jin Woong Namgoong a, Ji Eon Kim b,
,
*
Chun Sakong a, Jun Choi c, Woosung Lee d, Jae Pil Kim a
a Lab. of Organic Photo-functional Materials, Department of Materials Science and Engineering, Seoul National University, Seoul 08826, Republic of Korea
b Department of Pharmacy, College of Pharmacy, Research Institute of Pharmaceutical Sciences, Seoul National University, Seoul 08826, Republic of Korea
c Human and Culture Convergence Technology R&BD Group, Korea Institute of Industrial Technology (KITECH), 143 Hanggaulro, Sangrokgu, Ansan-si,
Gyeonggi-do 15588, Republic of Korea
d ICT Textile & Apparel R&D Group, Korea Institute of Industrial Technology (KITECH), 143 Hanggaulro, Sangrokgu, Ansan-si, Gyeonggi-do 15588, Republic
of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
We designed and synthesized perylene-based dyes for dye-based LCD color filters that highly soluble in
organic industrial solvents, exhibit very weak fluorescence, and can be easily synthesized due to their
simple molecular structures. The synthesized dyes were designed containing methoxy groups in the
terminal-, bay-, or both positions for developing fluorescence quenched dyes. And, dyes with strong
fluorescence and similar molecular structures to the fluorescence quenched dyes were also synthesized
to clearly compare and analyze the effect of fluorescence on the optical properties. Finally, we fabricated
dye-based color filters using the synthesized dyes and analyzed the optical performances of the color
filters. The methoxy group in the bay-substituents has an enormous effect on the fluorescence quenching
without the conspicuous influences on molecular behavior or dye aggregation. And, the fluorescence
quenched dyes have remarkable effects in minimizing the increment of minimum brightness and pro-
hibiting the contrast ratio decrease.
Received 25 June 2016
Received in revised form
23 August 2016
Accepted 30 August 2016
Available online 31 August 2016
Keywords:
Liquid crystal displays
Perylene
Fluorescence quenching
Dye-based color filters
Contrast ratio
© 2016 Elsevier Ltd. All rights reserved.
1. Introduction
dye-based color filters due to their strong color strengths and
thermal stabilities [10e13]. However, perylene-based dyes show
Liquid crystal displays (LCDs) have captured a larger portion of
the display market share than other types of displays [1e4].
Research into high-performance LCD devices is very important in
order to exploit next-generation display industries such as large
format and low power consumption screens [5,6]. LCDs with
traditional pigment-based color filters have some advantages in
mass production and price competitiveness. However, pigment-
based color filters have draw backs with respect to contrast ratio
and brightness owing to their large particle size after heat treat-
ment in the manufacturing process [7e9]. Therefore, research and
development toward dye-based and pigment-dye hybrid color fil-
ters has been in demand in order to develop displays that exhibit
superior optical properties.
powerful fluorescence likewise the other dyes that are commonly
used for LCD color filters [14,15]. Generally, in almost every
report, bulky substituents were introduced to increase the solu-
bilities of the dyes [5,6,16e18]. These bulky substituents usually
make the fluorescence of the dyes stronger by broadening the
intermolecular distance [19e23]. Therefore, the fluorescence of
produced perylene derivatives that have bulky substituents
would be naturally increased [24e28]. As mentioned in our pre-
vious study [3,9], the fluorescence of the dyes can enhance the
brightness of the color filters, meanwhile, that is a key factor of
contrast ratio decrease by the unexpected increment of minimum
brightness.
In this study, we designed and synthesized perylene-based
dyes exhibiting sufficient solubilities in organic industrial sol-
vents as well as significantly inhibited fluorescence. Dye-based
color filters using the synthesized dyes were fabricated, and the
influence of dye fluorescence on optical performance of the pre-
pared color filters was investigated. Dyes have to be soluble at least
Perylene-based dyes have many merits for use as colorants in
* 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.2016.08.061
0143-7208/© 2016 Elsevier Ltd. All rights reserved.

J.Y. Kim et al. / Dyes and Pigments 136 (2017) 836e845
837
4e5 wt% in organic industrial solvents to be used for LCD color
filters [5,6,8,9]. Therefore, we introduced bulky substituents at the
terminal- and bay-positions of the perylene moiety. These sub-
stituents could enhance their solubilities by molecular distortion
and intermolecular steric hindrance [29,30]. However, the fluo-
rescence of the synthesized dyes could be increased due to the
bulky substituents which prevent dye aggregations and intermo-
lecular interactions [21,24e26]. Therefore, we designed the dyes to
have substituents containing methoxy groups to reduce the fluo-
rescence of the dyes [31]. Moreover, dyes with strong fluorescence
and similar molecular structures to the fluorescence quenched
dyes were also synthesized to clearly compare and analyze the
effect of fluorescence on the optical properties. The dye-based
color filters were fabricated in 1e3 wt% color content concentra-
tion to accurately investigate the relationship between the fluo-
rescence of the dyes and the optical properties of the prepared
color filters.
followed by washing several times with distilled water. The crude
product was dried at 80 ꢀC under reduced pressure and used in the
next step without further purification. The crude product con-
taining both mono- and di-bromoperylene derivatives was sepa-
rated by column chromatography in next step, after introducing
bulky substituents in the terminal-position to increase their
solubilities.
2.2.2. N,N0-bis(R1)-1,7-dibromoperylene-3,4,9,10-
tetracarboxydiimide: terminal-position substitution
Crude
1,7-dibromoperylene-3,4,9,10-tetracarboxydiimide
(8.00 g, 14.55 mmol), R1-NH2 (45.00 mmol), acetic acid (4.60 ml)
and N-methyl-2-pyrrolidone (NMP; 100 ml) were mixed and
heated to 120 ꢀC under nitrogen atmosphere for 96 h. Water was
added to the mixture and the resulting precipitate was collected by
suction filtration. The crude product was washed with water and
dried under reduced pressure. The crude product was purified by
column chromatography in silica gel using CH2Cl2 as an eluent.
Three bands were collected. The first band contained a small
amount of tribrominated diimide, the second band contained the
dibrominated diimide, and the third contained the mono-
brominated diimide. Detailed structural analysis was conducted
after the next step. To obtain the PI-series, 2,6-diisopropylaniline
was used as R1-NH2 and to obtain PM-series, 2-methoxy-6-
methylaniline was used.
2. Experimental
2.1. Materials and instrumentation
Perylene-3,4,9,10-tetracarboxylic dianhydride, iodine, sulfuric
acid, bromine, and acetic acid were purchased from Sigma-Aldrich;
2,6-diisopropylaniline,
2-methoxy-6-methylaniline,
4-
methoxyphenol, and 4-ethylphenol were purchased from TCI; po-
tassium carbonate anhydrous, methylene chloride, and other
chemical solvents were purchased from Samchun Pure Chemical.
All chemicals were used without any additional purification.
Elemental Analysis (EA) was completed on a CE Instruments
EA1112 analyzer. 1H and 13C Nuclear Magnetic Resonance (NMR)
spectra were recorded on a Bruker Avance 500 spectrometer
running at 500 MHz using chloroform-d as a solvent with TMS as an
internal standard. Matrix Assisted Laser Desorption/Ionization
Time of Flight (MALDI-TOF) mass spectra were recorded on an
Applied Biosystems Voyager-DE STR Biospectrometry Workstation
2.2.3. N,N0-bis(R1)-1,7-bis(R2)-perylene-3,4,9,10-
tetracarboxydiimide: bay-position substitution
N,N0-bis(R1)-1,7-dibromoperylene-3,4,9,10-tetracarboxydiimide
(0.58 mmol) was mixed with anhydrous potassium carbonate
(0.35 g, 2.54 mmol), R2-OH (1.60 mmol) and NMP (60 ml). The
mixture was heated at 40 ꢀC under nitrogen and was stirred for
1.5 h. The mixture was cooled to room temperature, and then
poured into HCl (400 ml, 5% aqueous). The precipitate was collected
by suction filtration, washed with water and dried under vacuum at
80 ꢀC. The crude product was purified by column chromatography
in silica gel using CH2Cl2 as an eluent to obtain the products as red
solids.
using a-cyano-4-hydroxycinnamic acid (CHCA) as a matrix.
Absorption spectra were measured using a Perkin Elmer Lambda
25 UV/Vis spectrophotometer. Fluorescence spectra and quantum
yield were measured on a Perkin Elmer LS 55 and a PTI Quanta
Master 40 fluorescence spectrometer, respectively. A Becker & Hickl
SPC-150 equipped with a Time-Correlated Single Photon Counting
(TCSPC) board was used to measure the time-resolved fluorescence
decay with a time channel of 17.1 ps? Contrast ratio and brightness
of color filters were measured by CT-1 of Tsubosaka and MC-
3700:28C of Otsuka Electronics.
2.3. Geometry optimization of the dyes
Density functional theory (DFT) calculations were carried out
with the GAUSSIAN09 package. We used the 6e311þþG(d,p) Pople
basis set for all elements and the conventional B3LYP exchange-
correlation function. The intermolecular interactions were
analyzed by examining the core twist angles and the size of sub-
stituents. Dihedral angles of perylene main body were calculated by
measuring the distortion angle of benzene ring in the center of
perylene main body. Calculated lengths of bay-substituents were
indicated by measuring the lineal distance from oxygen atom of
ether linkage to farthest atom in the substituents. And, calculated
lengths of terminal-substituents were indicated by measuring the
longest lineal distance in the substituents.
2.2. Syntheses of the dyes
All synthetic procedures were carried out by following our
previous reports [8,9]. We had reported previously that bay-
position substitution is possible at much lower temperature and
in a shorter reaction time than the widely known method.
2.2.1. 1,7-Dibromoperylene-3,4,9,10-tetracarboxydiimide:
bromination
2.4. Preparation of dye-based inks and color filters
Perylene-3,4,9,10-tetracarboxylic
dianhydride
(32.00
g,
The red inks for the dye-based color filters were composed of
propylene glycol methyl ether acetate (PGMEA; 0.1 g), acrylic
binder (0.8 g) and synthesized dye (1, 2 or 3 wt% of the acrylic
binder). The prepared dye-based inks were coated on a transparent
glass substrate using a MIDAS Systems SPIN-1200D spin coater. The
rotation speed was initially set at 100 rpm for 10 s, and then
increased to 500 rpm for 20 s. The dye-coated color filters were
dried at 80 ꢀC for 20 min, pre-baked at 150 ꢀC for 10 min and post-
baked at 200 ꢀC for 1 h.
81.40 mmol), iodine (0.78 g, 3.04 mmol) and sulfuric acid (98%,
450 ml) were mixed and stirred for 2 h at room temperature. The
temperature of the mixture was raised to 80 ꢀC and bromine
(8.33 ml, 162.80 mmol) was added dropwise over 1 h. The resulting
mixture allowed to react for 16 h, upon which time, it was cooled to
room temperature and the remaining bromine gas was displaced
by nitrogen gas. The mixture was slowly poured into 3 L of ice water
and the crude precipitate formed was collected by suction filtration

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J.Y. Kim et al. / Dyes and Pigments 136 (2017) 836e845
3. Results and discussion
Introduction of bulky substituents is the most popular method
to enhance the fluorescence of dyes by inhibiting both aggregation
€
3.1. Design concept of the synthesized dyes
quenching and energy transfer such as Forster resonance energy
transfer (FRET) [21,26,43]. Therefore, in addition to enhancing the
solubilities with structure distortion and steric hindrance, the
fluorescence of the dyes would be naturally increased when bulky
substituents were introduced to the perylene main body [14].
However, as mentioned in our previous study [9], dyes for LCD color
filters have to be highly soluble in organic solvents and show
minimized fluorescence. Accordingly, we designed dyes containing
methoxy groups in the terminal-, bay-, or both positions for
developing fluorescence quenched dyes. Generally, methoxy
groups are used to cause bathochromic shifts by electron donating
effects or to sterically broaden the intermolecular distance [44e47].
And, in some preceding reports [45,46], it has been reported that
the introduction of a methoxy group leads to decreased fluores-
cence in certain dyes. A methoxy group in the para-position of the
bay-substituents is highly efficient at decreasing dye fluorescence
[48]. Therefore, we designed dyes having a methoxy group at this
position. As a result, we successfully designed dyes that highly
soluble in organic solvents, exhibit very weak fluorescence, and can
be easily synthesized due to their simple molecular structures. Dyes
showing strong fluorescence were designed to contain alkyl groups
that have a similar geometrical size as methoxy groups in order to
minimize the differences in molecular behavior among them.
Synthetic routes and molecular structures of the synthesized dyes
are shown in Scheme 1 and Fig. 1. Generally, perylene-based dyes
have strong color strengths and thermal stabilities due to their high
degree of planarity [10,11,15,32]. However, they usually show inferior
solubility in organic industrial solvents such as propylene glycol
methyl ether acetate (PGMEA), a commonly used organic solvent in
the LCD manufacturing process [5,8,30]. Bulky substituents con-
taining a benzene ring were introduced in the terminal- and bay-
positions of the perylene main body in order to reduce planarity
and intermolecular interactions, as well as to increase the steric
hindrance of the synthesized dyes [33e35]. The solubilities of the
synthesized dyes in some organic solvents are listed inTable 1. All the
dyes show sufficient solubilities as colorants for LCD color filters due
to the contribution of the introduced bulky substituents.
All of the dyes were designed to have similar conjugation length.
Therefore, it can be regarded that they would exhibit similar spec-
tral properties [9,36e40]. Hence, the effect of the spectral properties
of the dyes on the optical performance of fabricated color filters
would be minimized. The size and structure of the introduced
substituents are also similar, thus, the geometrical structures of the
synthesized dyes would be naturally analogous to each other.
Geometry-optimized structures of the synthesized dyes are shown
in Fig. 2 and dihedral angle of the perylene main body and calcu-
lated lengths of the substituents are listed in Table 2 (Details related
to the measurements of Table 2 are presented in supplementary
data). As shown in Table 2, the differences in the geometrical
structures of the synthesized dyes were very small to relate the
influences on the intermolecular interactions. Especially, all syn-
thesized dyes show almost identical the dihedral angles that mostly
affect the planarities of them [8,41,42]. Therefore, the differences in
optical properties of the color filters resulting from dye aggregation
and intermolecular interactions would also be minimized.
3.2. Spectral and fluorescence properties of synthesized dyes
The absorption spectra of the synthesized dyes in chloroform
are shown in Fig. 3. As mentioned before, the conjugation systems
of all synthesized dyes are similar to each other. Therefore, the
synthesized dyes exhibit similar spectral properties as shown in
Fig. 3 and Table 3 [37,39,49]. Namely, the effect of the spectral
properties of synthesized dyes on the optical properties of the
fabricated color filters would be minimized. Although, the dyes
with methoxy groups in bay-positions show a small bathochromic
Scheme 1. Syntheses of the designed dyes.

J.Y. Kim et al. / Dyes and Pigments 136 (2017) 836e845
839
Fig. 1. Structure of the synthesized dyes.
Table 1
is not H-aggregation or energy transfer. This result also could be
verified from the presented data. For example, the solubilities in
Table 1 and the fluorescence intensities of the synthesized dyes in
Table 3 do not show a correlation. If the fluorescence of the syn-
thesized dyes resulted mainly from intermolecular behavior, the
solubility and the fluorescence intensity would show a certain
trend. Eventually, it could be concluded that the dyes synthesized
in this study exhibit different fluorescence properties which are
mainly attributed to the introduced methoxy groups.
Solubility of the synthesized dyes at room temperature in CH2Cl2, CHCl3 and PGMEA
(wt%).
Dye
PI-4EP
PI-4ME
PM-4EP
PM-4ME
CH2Cl2
CHCl3
PGMEA
5.8
6.0
5.0
5.9
6.0
5.1
5.2
5.7
4.7
5.1
5.8
4.8
shift of about 4 nm due to the electron donating effect of the
methoxy groups [45,46,50]. But, this shift would not seriously in-
fluence the optical properties of the manufactured color filters
because the color filters were fabricated with low color content
concentration.
The fluorescence properties of the synthesized dyes are listed in
Fig. 4 and Table 3. All of the measured fluorescence properties
except quantum yield were measured at an excitation wavelength
corresponding to the wavelength of maximum absorption. The
quantum yield was measured with an excitation wavelength of
480 nm [51,52]. Chloroform was used as a solvent for all mea-
surements in Table 3.
In our previous study [9], dyes with various geometrical struc-
tures would severely affect their molecular behavior and aggrega-
tion resulting in a variation of fluorescence properties. It is well-
known that the two main factors affecting fluorescence quench-
ing of organic dyes are static quenching derived from H-aggrega-
tion and energy transfer which occurs via intermolecular
interactions [20,22,53e55]. However, as shown in Table 2, the
synthesized dyes in this study have similar geometrical molecular
structures. Therefore, the intermolecular interactions of the dyes
would not be different from each other. In other words, the main
factor affecting the fluorescence properties of the synthesized dyes
The methoxy groups introduced in the terminal-positions have
no effect on the fluorescence quenching. On the contrary, methoxy
groups in the bay-positions severely diminish the fluorescence. It is
widely known that substituents at the bay-positions have a strong
conjugation link with the perylene main body [29,33,34].
Contrastively, the terminal-substituents have no or very slight
conjugation linkage [5,8]. Therefore, bay-substituents have a strong
influence on the
p-conjugation system and the electrochemical
properties of the dyes. This phenomenon could be verified from the
bathochromic shift of the spectral properties of the synthesized
dyes with methoxy groups in the bay-positions.
Dyes with bay-substituents containing ethyl groups exhibited
more powerful fluorescence in the visible region than dyes with
bay-substituents containing methoxy groups. The difference in the
total emission intensity is 22e34-fold and the difference in the
quantum yield is 12e18-fold between dyes with bay-substituents
containing methoxy groups and dyes with ethyl groups. Namely,
introduction of methoxy groups in the para-position of the bay-
substituents is a powerful method to quench dye fluorescence
that would rarely affect molecular behavior and aggregation. To
sum up, with just a simple modification, we successfully designed
and synthesized fluorescence reduced dyes exhibiting sufficient
solubilities in organic solvents. These novel perylene-based dyes

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J.Y. Kim et al. / Dyes and Pigments 136 (2017) 836e845
Fig. 2. Geometry-optimized structures of the synthesized dyes. (a) PI-4EP, (b) PI-4ME, (c) PM-4EP, and (d) PM-4ME.
Table 2
Dihedral angels of the perylene main body and calculated lengths of the substituents.a
Dye
PI-4EP
PI-4ME
PM-4EP
PM-4ME
Dihedral angle of the perylene main body (ꢀ)
Calculated lengths of substituents (Å)
13.13923
7.50721
8.91795
13.55246
7.39420
8.85661
13.18118
7.50609
7.76817
13.51070
7.39358
7.76834
Bay-substituent
Terminal-substituent
a
Dihedral angle and calculated lengths are not symmetric, average values are listed.
Table 3
Spectral and fluorescence properties of the synthesized dyes.
Dye
PI-4EP
PI-4ME
PM-4EP
PM-4ME
a
labs
εabs
546
62,049
581
550
56,653
586
548
56,508
580
552
59,998
582
b
c
lem
Max. Emission Intensity
241.82
29,305.99
35
7.07
856.53
36
226.75
27,623.99
32
10.20
1,257.39
30
S(emission)d
D
sse
f
Qy
0.966
0.054
0.948
0.079
a
labs: maximum absorption wavelength (nm).
εabs: molar extinction coefficient (L/mol cm).
lem: maximum emission wavelength (nm).
b
c
d
S(emission): integral of ‘Fluorescence Intensity’ in visible-ray region, total
emission intensity.
e
D
ss: stokes shift.
f
Qy: quantum yield (10ꢁ5 mol/L in chloroform, excited at 480 nm).
Fig. 3. Absorption spectra of the synthesized dyes in chloroform (10ꢁ5 mol/L).
3.3. Time-resolved fluorescence properties of synthesized dyes
The results of the time-resolved fluorescence decay of the syn-
have more desirable properties than those previously used as col-
thesized dyes measured by a time-correlated single photon
orants in LCD color filters.

J.Y. Kim et al. / Dyes and Pigments 136 (2017) 836e845
841
Table 4
Fluorescence decay time (t) of the synthesized dyes (ns).
Dye
PI-4EP
3.95
PI-4ME
0.23
PM-4EP
4.25
PM-4ME
0.35
Decay time
Table 5
Calculated radiative decay rate constant (Kr) and non-radiative decay rate constant
(Knr) (nsꢁ1).
Dye
PI-4EP
PI-4ME
PM-4EP
PM-4ME
Kr
Knr
0.244557
0.008608
0.234783
4.113043
0.223059
0.012235
0.225714
2.631429
however, their non-radiative decay constant (Knr) are tremen-
dously different depending on the substituents at the bay-position.
The dyes with methoxy groups in the bay-positions show
extremely higher value of non-radiative decay constant than that of
the dyes with ethyl groups. It could be regarded that the dyes with
bay-substituents containing methoxy groups exhibit intensely
stronger non-radiative energy release than the radiative form
[60,61,67], contrary to the dyes containing ethyl groups in the bay-
positions. Due to this reason, dyes with methoxy groups in bay-
positions seem to exhibit quenched fluorescence. The trend is
reversed in the case of the dyes with ethyl groups in bay-positions,
although all of the synthesized dyes have similar geometrical mo-
lecular structures and conjugation systems.
Fig. 4. Fluorescence of the synthesized dyes in chloroform (10ꢁ8 mol/L).
counting (TCSPC) system are illustrated in Fig. 5 and Table 4 [56,57].
The represented fluorescence decay data were measured with an
excitation wavelength of 520 nm and fitted using a bi-exponential
function [58,59].
The dyes with methoxy groups in the bay-positions exhibited
shorter fluorescence lifetimes than those with ethyl groups. In
other words, the methoxy group in the bay-position affects both
fluorescence intensity and lifetime. Therefore, the total emission
quantity from the dyes with methoxy groups in the bay-
substituents would be much smaller than that of the dyes with
ethyl groups. This is the same result as the tendencies of the total
emission intensity in the visible region and the quantum yield data
that were presented ahead.
3.4. Optical properties of fabricated dye-based color filters
Color filters are located between two polarizing films in the LCD
devices. Light radiated from a back light unit is polarized by the first
polarizer when entering into the color filters. Most light that passes
through the color filters maintains its polarized state, however,
non-polarized light can be generated by scattering or emission. This
non-polarized light can passes through the second polarizer even in
full-black state, and increases the minimum brightness. As scat-
tering from the traditional pigment-based color filters gives rise to
the unexpected increment of minimum brightness, fluorescence
emitted from the dye-based color filters also causes the same effect
in spite of the smaller particle size compared to pigment-based
ones. We reported this phenomenon in our previous study
through experimental investigations [9].
Dye-based color filters were fabricated using the synthesized
dyes that were added in the proportion of 1, 2 or 3 wt% to the
acrylate binder. The measured fluorescence spectrometer results
are shown in Fig. 6a. The measurements were obtained with an
excitation wavelength corresponding to the wavelength of
maximum absorption. Both the incident light that passed through
the color filters and the emission from the color filters can be
observed in all of the fluorescence spectra. The fluorescence spec-
trum of the color filter fabricated with PI-4EP with 3 wt% dye
content is separately illustrated in Fig. 6b. In the results of the color
filters fabricated with PM-4EP, the intensity of the incident light
exceeded the detectable range of our instrument. Therefore, the
intensity of the incident light is saturated in the maximum
detectable value of the instrument in every dye content concen-
tration. The absolute values of the spectra are not precise because
the measurements of the fluorescence spectrometer of the fabri-
cated dye-based color filters were operated without consideration
of the emission toward every spherical direction. However, it can be
argued that the observed trend of incident light and emission
varying according to dye content concentration is definitely a
meaningful result.
Energy injected from the excitation light is released in radiative
or non-radiative form [60e62]. The radiative decay rate constant
and the non-radiative decay rate constant can be simply calculated
from the fitted lifetime (t) and the quantum yield (Qy) with the
following equations [59,63e66]. The results are listed in Table 5.
Qy
t
1
tr
Kr ¼
¼
(1)
(2)
À
Á
1
tnr
1
t
1
tr
1
t
Knr
¼
¼
ꢁ
¼
1 ꢁ Qy
All synthesized dyes show similar radiative decay constants (Kr),
Fig. 5. Time-correlated single-photon-counting (TCSPC) results of the synthesized
dyes and instrumental response function of the TCSPC setup (10ꢁ5 mol/L in
chloroform).

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J.Y. Kim et al. / Dyes and Pigments 136 (2017) 836e845
Fig. 6. (a) Fluorescence spectrometer results of the fabricated dye-based color filters (each dye contents were 1, 2 and 3 wt% increasing toward right-side). (b) Detailed fluorescence
spectrometer results of the color filter fabricated with PI-4EP in 3 wt% dye content. (c) Plot of maximum emission intensity of the fabricated color filters. (For interpretation of the
references to colour in this figure legend, the reader is referred to the web version of this article.)
As shown in the spectra, the intensity of the incident light is
decreasing with increasing dye concentration. Contrastively, the
intensity of the emission from the color filters is increasing ac-
cording to the dye concentration. The maximum emission in-
tensities from the prepared color filters are plotted in Fig. 6c. As
shown in the figures, the emission intensity increase of the color
filters depends on the added dye concentration with a certain linear
trend. These phenomena result from the fact that the color filters
were fabricated with a low color content concentration [9]. In
accordance with the dye concentration increase, the increase of the
aggregation fluorescence quenching would be smaller than the
increase of the emission from the added dyes in the concentration
range of our investigation [68,69].
bay-positions exhibited strong fluorescence within the visible re-
gion in the film state. As mentioned in our previous study [9], the
fluorescence properties of the prepared color filters show a similar
tendency to the properties of the dyes in the solution state.
Therefore, the fluorescence of the added dyes would significantly
affect the optical properties of the color filters.
The optical properties of the fabricated color filters are listed in
Table 6. All represented data were measured 3 times and the
average value is provided. The brightness of the color filters
decreased with the increase in dye content concentration. This
results from the fact that the transmittance of the color filters
would decrease with the amount of additionally added dyes.
Namely, the effect of the fluorescence from the added dyes on the
brightness increase is much weaker than the effect of the
The color filters fabricated with dyes containing ethyl groups in

J.Y. Kim et al. / Dyes and Pigments 136 (2017) 836e845
843
Table 6
Optical properties of the fabricated dye-based color filters.
Dye
Dye content
Brightness
Rx
Contrast ratio - blank 30,000
Ry
Value
Max. brightness
Min. brightness
Value
PI-4EP
PI-4ME
PM-4EP
PM-4ME
1
2
3
1
2
3
1
2
3
1
2
3
0.3237
0.3244
0.3251
0.3228
0.3334
0.3310
0.3157
0.3168
0.3185
0.3310
0.3382
0.3483
0.2977
0.2953
0.2886
0.3023
0.2804
0.2765
0.3213
0.3187
0.3157
0.2918
0.2805
0.2674
62.1513
59.9033
52.3643
70.8803
56.4173
51.4653
82.4580
80.0553
73.0377
63.1287
55.9787
46.2667
1765.1667
1729.9333
1617.0000
1839.9000
1509.5667
1428.0000
2184.0667
2136.9667
2032.0000
1642.8000
1456.0000
1228.4333
20.8607
22.2023
27.6647
3.5033
4.2287
6.6037
7.3437
10.1030
17.5680
3.5767
3.3073
6.4457
84.62
77.92
58.45
525.19
356.98
216.24
297.41
211.52
115.66
459.31
440.23
190.58
transmittance reducing that derives the brightness decrease.
Therefore, it would be hard to expect a remarkable brightness in-
crease from the fluorescence of the dyes added in dye-based color
filters.
fluorescence quenching effect by the methoxy group in the
terminal-substituents. This difference seems to be caused by the
p
-
conjugation system of the substituents. The color filters fabricated
with the synthesized dyes containing methoxy groups in the bay-
positions exhibited lower minimum brightness than those with
ethyl groups. Therefore, they show superior performance in pre-
venting contrast ratio decrease caused by fluorescence of added
dyes.
Contrast ratio is the proportion of maximum brightness to
minimum brightness [5,8,70e72]. The maximum and minimum
brightness values are represented after normalization to a blank
brightness of 30,000. The minimum brightness of the color filters
was increased according to the fluorescence of the added dyes. Both
the maximum and minimum brightness of the color filters with
highly fluorescent dyes generally show higher values than those
with less fluorescent dyes. However, the influence of the fluores-
cence seems more effective on the minimum brightness. Therefore,
the color filters with highly fluorescent dyes exhibited a lower
contrast ratio than those with fluorescence quenched dyes.
It can be concluded that the fluorescence properties of the
fabricated color filters show the same tendency to those of the dyes
in the solution state. Additionally, the fluorescence of the added
dyes has a limitative effect on the maximum brightness increase of
the fabricated color filters. However, the fluorescence mainly in-
fluences the minimum brightness increase and causes the contrast
ratio decrease. In conclusion, color filters prepared with synthe-
sized dyes containing methoxy groups in the bay-substituents have
remarkable effects in minimizing the increment of minimum
brightness and prohibiting the contrast ratio decrease.
Acknowledgment
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 (SMBA).
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.dyepig.2016.08.061.
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