Development of dimeric triarylmethine derivatives with improved thermal and photo stability for color filters

Article abstract of DOI:10.1016/j.dyepig.2017.05.035

Five novel triarymethine derivatives containing a two chromophore moiety within the molecule have been designed, synthesized and investigated as potential color filter dyes. These new “dimer-type” triarylmethines showed increased photostability and thermal stability compared to the Victoria Blue BO unit and notably manipulation of the dye counter ion also led to increased thermal stability. To evaluate the dyes in color filters, filters were fabricated and the photo- and thermo-stability was determined after heat treatment (230 °C for 30 min). The fabricated color filters showed approximately 80% transmittance at 450 nm and the ΔE_ab values were in the range 3.03–9.26. These results indicate that the synthesized dimer-type triarylmethine derivatives have the potential for application as color filters for blue dyes.

Full text of DOI:10.1016/j.dyepig.2017.05.035

Accepted Manuscript
Development of dimeric triarylmethine derivatives with improved thermal and photo
stability for color filters
Nam Sik Kong, Hyocheol Jung, Beomjin Kim, Chan Kyu Lee, Hoyoul Kong, Kun Jun,
Jin Chul Kim, Seung Man Noh, In Woo Cheong, Jongwook Park, Young I.L. Park
PII:
S0143-7208(17)30692-7
10.1016/j.dyepig.2017.05.035
DYPI 5997
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 4 April 2017
Revised Date: 16 May 2017
Accepted Date: 16 May 2017
Please cite this article as: Kong NS, Jung H, Kim B, Lee CK, Kong H, Jun K, Kim JC, Noh SM, Cheong
IW, Park J, Park YIL, Development of dimeric triarylmethine derivatives with improved thermal and photo
stability for color filters, Dyes and Pigments (2017), doi: 10.1016/j.dyepig.2017.05.035.
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ACCEPTED MANUSCRIPT
Submitted to Dye and Pigment
Development of Dimeric Triarylmethine Derivatives with
Improved Thermal and Photo Stability for Color Filters
Nam Sik Kong1,3, Hyocheol Jung2 Beomjin Kim1, Chan Kyu Lee1, Hoyoul Kong1, Kun Jun1,
,
Jin Chul Kim1, Seung Man Noh1, In Woo Cheong3*, Jongwook Park2*, Young IL Park1*
1Research Center for Green Fine Chemicals, Korea Research Institute Technology, Jongga-ro, Jung-
gu, Ulsan 44412, Republic of Korea
2Department of Chemical Engineering, Kyung Hee University, Gyeonggi-do 17104, Republic of
Korea
3Department of Applied Chemistry and Department of Nano-Science and Technology, Graduate
School, Kyungpook National University, 80 Daehakro, Bukgu, Daegu 41566, Republic of Korea
*Nam Sik Kong and Hyocheol Jung contributed equally to this work as the first coauthor.
Abstract
Five novel triarymethine derivatives containing a two chromophore moiety within the
molecule have been designed, synthesised and investigated as potential color filter dyes.
These new “dimer-type” triarylmethines showed increased photostability and thermal
stability compared to the Victoria Blue BO unit and notably manipulation of the dye counter
ion also led to increased thermal stability. To evaluate the dyes in color filters, filters were
o
fabricated and the photo- and thermo- stability was determined after heat treatment (230 C
for 30 min). The fabricated color filters showed approximately 80 % transmittance at 450 nm
and the ΔEab values were in the range 3.03 - 9.26. These results indicate that the synthesized
dimer-type triarylmethine derivatives have the potential for application as color filters for
blue dyes.
Keywords: Triarylmethine, Blue Dye, Color Filter, Thermal Stability, Photo Stability, Victoria
Blue BO

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1. Introduction
In the display market, color filters are essential for use in various devices based on liquid
crystal displays (LCDs) and charge-coupled devices (CCDs). They are applied for portable
electronic devices, such as smart phones, tablet PCs, and digital cameras. Recently, technical
issues in electronic devices based on color filters require a smaller color pixel size and high-
contrast, which are important factors for creating compact devices and superior image
quality.[1]
Currently, the color filter consists of red (R), green (G), and blue (B) color pixels and an
LCD. The image is realized by controlling the amount of light passing through each color
pixel by a liquid crystal shutter.[2] The pigment dispersion method for making R, G, and B
patterned pixels has been most widely used in color filters due to its reproducibility and the
photo-thermal stability of the pigment itself. However, this method has limitations in terms of
making smaller particle sizes, and it also creates light scattering due to the aggregation
behavior of the pigment particles.[1-3] The particle size problem of pigments due to low
solubility has caused limitations for smaller color pixels and improving high-contrast imaging.
In order to resolve the particle size problem of the pigment, dye-based color filters have been
investigated due to their good solubility. To apply to a dye-based color filter, a dye must
withstand the high processing temperatures of color filters above 200 °C and possess light
stability due to backlighting. However, most dyes have low thermal/light stability and will be
decolorized at high temperature under the color filter processing and a light source. Therefore,
new dyes with appropriate thermal and light stabilities must be designed and developed.
There are several kinds of blue/violet chromophores for blue color filters, such as xanthene,
cyanine, azo, anthraquinone, dioxazine, and triarylmethine.[4-6] These chromophores have
relatively important advantages, which are high transmittance, heat/light resistance, and an
ease of synthesis over other dyes for applying to a color filter. In particular, triarylmethine
dyes are a potential blue colorant for color filters due to their high transmittance in the blue
region of 460−500 nm and intense color strengths.[7] However, in order to apply to the color
filter, there are still weaknesses concerning stability, such as heat and light resistance.[2,8]
In this study, we report the designed and synthesis of novel blue dyes for color filters based
on dimeric triarylmethine derivatives, which have a two chromophore moiety in a single
molecule as shown in Figure 1. The dimeric triarylmethine derivatives were studied for three

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types of effects as follows. 1) Dimeric chromophore effect: dimeric triarylmethine can induce
high absorption properties and solubility due to the two chromophores and the highly twisted
chemical structure between the chromophores. 2) Counter ion effect: a chloride (Cl) counter
ion
was
substituted
with
trifluoromethanesulfonate
(TFMS)
and
bis((trifluoromethyl)sulfonyl)amide (DHFMS). 3) Substitution effect: a 1,4-phenylene group
(H-BTM) in the triarylmethine derivatives was substituted with methyl substituted 1,4-
phenylene (Me-BTM) and a 1,4-naphthylene (Na-BTM) groups, as shown in Figure 1. The
synthesized triarylmethine derivatives were studied to determine their optical and thermal
properties depending on the chemical structures, and their potential to be used as color filter
materials were evaluated.
2. Experimental
2.1. Materials and Instrumentation
All reagents and solvents were purchased from Aldrich or TCI and used without further
purification. The chemical structures of the synthesized triarylmethine derivatives were
measured using 1H and 13C NMR spectrometer (Ultrashield 300 MHz, Bruker, Germany), an
FT-IR spectrometer (Nicolet 6700/ Nicolet Continuum, Thermo Fisher Scientific Inc.,
Walthum, MA, USA), Elemental Analyzer (EA) (FLASH EA-2000, Thermo Scientific) and
MALDI-TOF (Autoflex Speed TOF/TOF). The degradation temperatures (Td) of the
compounds were measured via thermogravimetric analysis (TGA) (Thermogravimetric
Analyzer Q500, TA Instruments). The absorption spectra and transmittance spectra were
obtained by using a UV-Vis-NIR spectrophotometer (UV-3600, Shimadzu).
2.2. Synthesis and characterization of the synthesized dimeric triarylmethine derivatives
2.2.1. General synthesis of dimeric triarylmethine, H-BTM-Cl[9]
4,4'-Bis(diethylamino)benzophenone (3.0 g, 9.3 mmol) was dissolved in toluene (30 mL)
and POCl3 (4.3 mL, 46.3mmol) was dropped into the mixture and allowed to stir for 1h at
room temperature. 1,1'-Dinaphthylamine (1.0 g, 3.7 mmol) was added into the mixture in a
single portion. The reaction was refluxed for 1day. The reaction was extracted with
methylene chloride and brine. The extracted organic solution was dried over MgSO4, filtered

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and the solvent was removed in vacuum. The product was precipitated in acetone/ethyl
acetate as a blue solid (2.7 g, 84 %). 1H NMR (DMSO-d6, 300 MHz): δ = 9.80 (s, 1H), 8.48 (d,
J = 8.1 Hz, 2H), 7.49 (m, 18H), 7.04 (d, J = 9.3 Hz, 8H), 3.64 (d, J = 6.9 Hz, 16H), 1.20 (t, J
13
= 6.9 Hz, 24H); C NMR(DMSO-d6, 300 MHz,): δ = 12.69, 21.10, 45.24, 113.70, 115.32,
123.82, 126.34, , 126.64, 127.35, 128.05, 131.35, 134.93, 135.14, 139.70, 144.90, 154.57,
172.02, 172.82; FT-IR (KBr, cm-1): 3385, 2969, 1615, 1577, 1520, 1449, 1412, 1380, 1272,
1183, 1069, 1002, 913, 794, 678; MALDI-TOF MS: Found [M+H]+ = 882.5 m/z C62H69N5
requires 883.5 m/z; EA Found (%): C, 76.3; H, 7.0; N, 7.1, Calc. (%) for C62H69Cl2N5: C,
76.5; H, 7.2; N, 7.2.
2.2.2. Synthesis of H-BTM-TFMS[10]
H-BTM-Cl (0.5 g, 0.5 mmol) was dissolved in methanol (50 mL) and
trifluoromethanesulfonic acid (0.2 g, 1.1 mmol) was dropped into the mixture and allowed to
stir for 3h at room temperature. The reaction was extracted methylene chloride and water.
The extracted organic solution was dried over MgSO4, filtered and the solvent was removed
in vacuum. The product was obtained as a blue solid (0.3 g, 49 %). 1H NMR (DMSO-d6, 300
MHz): δ = 9.72 (s, 1H), 8.48 (d, J = 8.7 Hz, 2H), 7.50 (m, 18H), 7.04 (d, J = 9.3 Hz, 8H),
13
3.65 (d, J = 6.9 Hz, 16H), 1.21 (t, J = 7.2 Hz, 24H); C NMR (DMSO-d6, 300 MHz,): δ =
12.86, 13.03, 13.10, 14.40, 44.25, 45.67, 110.43, 113.51, 114.17, 115.67, 119.00, 123.27,
124.03, 125.05, 126.84, 126.90, 127.03, 127.54, 127.78, 128.22, 128.52, 131.82, 132.32,
135.35, 135.55, 140.14, 145.16, 150.44, 155.01, 173.23; FT-IR (KBr, cm-1): 2971, 1578, 1520,
1413, 1382, 1273, 1219, 1185, 1152, 1071, 1028, 941, 826, 764, 636; MALDI-TOF MS:
Found [M+H]+ = 882.6 m/z C62H69N5 requires 883.5 m/z; EA Found (%): C, 65.2; H, 6.2; N,
5.9, Calc. (%) for C66H69F12N7O8S4: C, 65.0; H, 6.2; N, 5.9.
2.2.3. Synthesis of H-BTM-DHFMS[9-10]
H-BTM-Cl (0.5 g, 0.5 mmol) was dissolved in methanol (50 mL) and lithium
bis(trifluoromethanesulfonyl)amide (0.3 g, 1.1 mmol) was dropped into the mixture and
allowed to stir for 3h at room temperature. The reaction was extracted methylene chloride and
water. The extracted organic solution was dried over MgSO4, filtered and the solvent was
1
removed in vacuum. The product was obtained as a blue solid (0.4 g, 53 %). H NMR
(DMSO-d6, 300 MHz): δ = 9.71 (s, 1H), 8.48 (d, J = 8.4 Hz,2H), 7.36 (m, 20H), 7.03 (d, J =
13
9.0 Hz, 8H), 3.64 (d, J = 6.0 Hz, 16H), 1.21 (t, J = 6.3 Hz, 24H); C NMR(DMSO-d6, 300

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MHz,): δ = 12.80, 13.00, 13.07, 44.38, 45.41, 45.67, 110.61, 113.55, 114.09, 115.65, 117.82,
122.08, 124.03, 126.34, 126.81, 126.91, 127.04, 127.79, 128.50, 131.82, 132.31, 135.36,
135.56, 140.14, 140.17, 154.60, 155.01, 173.27; FT-IR (KBr, cm-1): 3366, 2975, 1616, 1579,
1520, 1414, 1384, 1275, 1184, 1072, 1055, 914, 828, 706, 651; MALDI-TOF MS: Found
[M+H]+ = 882.6 m/z C62H69N5 requires 883.5 m/z; EA Found (%): C, 54.3; H, 4.8; N, 6.5,
Calc. (%) for C66H69F12N7O8S4: C, 54.9; H, 4.8; N, 6.8.
2.2.4. Synthesis of Me-BTM-DHFMS
Me-BTM-DHFMS was synthesized using same method with H-BTM-DHFMS and the
1
product was obtained as a blue solid (0.4 g, 23 %). H NMR (DMSO-d6, 300 MHz): δ = 9.91
(s, 1H), 8.43 (d, J = 7.5 Hz, 2H), 7.28 (m, 24H), 3.67 (d, J = 21.3 Hz, 16H), 1.73 (s, 6H), 1.19
13
(m, 24H); C NMR (300 MHz, DMSO) δ: 13.12, 14.57, 22.15, 22.36, 24.76, 26.91, 30.05,
32.54, 37.65, 41.78, 45.00, 45.84, 56.29, 68.97, 110.79, 113.56, 114.28, 115.81, 116.19,
117.83, 122.09, 124.32, 126.36, 126.96, 128.81, 129.36, 129.58, 129.64, 129.75, 135.35,
135.40, 136.68, 140.58, 145.38, 155.46; FT-IR (KBr, cm-1): 3356, 2972, 2925, 1585, 1523,
1420, 1375, 1339, 1277, 1182, 1056, 911, 825, 787, 682; MALDI-TOF MS: Found [M+H]+ =
910.6 m/z C64H73N5 requires 911.5 m/z; EA Found (%): C, 56.6; H, 5.1; N, 6.3, Calc. (%) for
C68H73F12N7O8S4: C, 55.4; H, 5.0; N, 6.6.
2.2.5. Synthesis of Na-BTM-DHFMS
Na-BTM-DHFMS was synthesized using same method with H-BTM-DHFMS and the
product was obtained as a dark blue solid (0.2 g, 13 %). 1H NMR (DMSO-d6, 300 MHz): δ =
10.05 (s, 1H), 8.29 (d, J = 8.4 Hz, 2H), 8.15 (d, J = 8.4 Hz, 2H), 7.63 (d, J = 7.8 Hz, 2H), 7.34
(m, 20H), 7.20 (d, J = 9.3 Hz, 4H), 6.73 (d, J = 8.4 Hz, 2H), 3.55 (d, J = 38.1 Hz, 16H), 1.18
13
(m, 24H); C NMR(DMSO-d6, 300 MHz,): δ = 12.72, 13.08, 30.05, 45.49, 47.39, 113.56,
115.70, 115.99, 117.83, 122.09, 125.30, 125.64, 126.13, 126.36, 126.64, 126.82, 127.13,
128.10, 128.84, 129.10, 129.88, 131.66, 133.30, 135.05, 135.41, 138.01, 138.51, 153.16; FT-
IR (KBr, cm-1): 2969, 1601, 1561, 1502, 1421, 1349, 1270, 1183, 1151, 1056, 893, 762, 712,
657, 614; MALDI-TOF MS: Found [M+H]+ = 982.7 m/z C70H73N5 requires 983.5 m/z; EA
Found (%): C, 57.8; H, 5.0; N, 6.2, Calc. (%) for C74H73F12N7O8S4: C, 57.5; H, 4.8; N, 6.4.
2.3. Irradiation and comparison of the degradation rates of the synthesized materials
The degree of decolorization of the synthesized materials was measured by using UV
spectroscopy (DRIEL instruments, 66902 Model). The synthesized materials were prepared

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by dissolving 0.5 wt% in chloroform. To achieve a film, the prepared solutions were spin-
coated on top of glass at 1,000 rpm for 30 seconds. The UV light was irradiated for 180
minutes, and the UV spectrum was obtained at 10, 20, 40, 60, 90, 120, and 180 minutes. The
degradation rate (DR) was determined from the value of the slope of the change in the
absorbance at the maximum spectrum of each synthesized material. The calculation of DR is
as shown below:[8]
∆Maximum UV Absorption
Degradation Rate (DR,%/ min) =
×100
Irradiation Time (min)
2.4. Fabrication and measurement of the dye-based color filters
The solutions for color filters were composed of an acrylic binder and the synthesized
triarylmethine (1.5 wt% of the total amount), propylene glycol methyl ether acetate
(PGMEA), photo-initiator (PI OXE-57), cross-linker multifunctional monomer
(dipentaerythritol hexaacrylate), and additives (fluorinated acrylic polymer and 4-
methoxyphenol). The solution was coated on a 2.5 cm x 2.5 cm transparent glass substrate
using a MIDAS System SPIN-1200D spin-coater at 1,000 rpm for 10 seconds. The wet dye-
coated color filters were pre-baked at 100 °C for 100 seconds and under UV irradiation (365
nm, 60 mJ/cm2). All fabricated color filters were treated at 230 °C for 1 h, and the △Eab value
was measured by a Lambda1050 (Perkin Elmer) before and after treatment.
3. Results and Discussion
3.1. Design and synthesis of the new dimeric triarylmethine derivatives for color filters
The new blue dyes based on the triarylmethine derivatives were designed and synthesized as
shown in Figure 2. The new dyes have a two chromophore moiety in the molecule because
the dimeric-type chromophore can induce high absorption properties and solubility due to its
highly twisted structure. The counter ion of the dimeric triarylmethine derivatives was
substituted from the chloride ion to TFMS and DHFMS to increase the stability of the dye.
The phenyl groups (H-BTM) of triarylmethine derivatives were substituted with methyl-
phenyl (Me-BTM) and naphthalene (Na-BTM) groups to study the thermal/optical property
according to the chemical structure.

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The reaction scheme of the new dimeric triarylmethine derivatives is depicted in Figure 2.
The ketone compound (2) with a diethylamino group was synthesized using alkylation[11] and
a Friedel-Crafts reaction. The triarylmethine derivatives were reacted with ketone derivatives
and di(naphthalen-1-yl)amine in phosphorus (V) oxychloride solution in toluene and refluxed
overnight.[9-10] The reaction mixture was extracted with methylene chloride/brine and the
residue was purified with acetone/ethyl acetate to yield a deep blue colored solid. The counter
ion of the synthesized triarylmethine derivatives was substituted with other counter ions,
including trifluoromethanesulfonate (TFMS) and bis((trifluoromethyl)sulfonyl)amide
(DHFMS), in a methanol solution at room temperature. The reaction mixture was purified
with methylene chloride and deionized water.[9-10] The newly synthesized triarylmethine
derivatives were assigned by NMR spectra and arranged as shown in Figure 3. The proton
peaks of amine (–NH) and naphthalene of the triarylmethine center showed approximately
9.8 and 8.5 ppm, respectively. The proton peak of the amine (–NH) group also was shifted
from 9.9 to 9.7 ppm and the shift is probably due to changing counter ion from the chloride
ion to TFMS or DHFMS.
3.2. Solubility, optical property, and thermal/photo stability of the synthesized
triarylmethine derivatives
For a color filter application the dye, the dye should exhibit a solubility of at least 3 wt% in
PGMEA.[12-13] Therefore, the solubility of the synthesized dyes was evaluated and are
summarized in Table 1. The solubility of the newly synthesized triarylmethine derivatives
improved from the solubility of the commercial blue dye, Victoria Blue BO (0.03 wt%). In
particular, H-BTM-DHFMS showed a 213-fold increase in solubility compared to the
solubility of Victoria Blue BO. This is because the dimeric-type dye has a twisted structure
rather than the monomer-type dye and contributes to solubility enhancement. Also, the
solubility of DHFMS as a counter ion is excellent. This combines with a bulky counter ion to
prevent stacking between molecules, thereby contributing to the improvement of solubility.[14-
15]
The UV-Vis absorption in solution and transmittance in the films of the newly synthesized
dimeric triarylmethine derivatives and Victoria Blue BO was measured and is shown in
Figure 4 and Table 2. As seen in Figure 4, UV-Vis absorption at the maximum peak was at
625−626 nm for H-BTM, H-BTM-TFMS, and H-BTM-DHFMS and red shifted compared to
the peak at 593 nm for Victoria Blue BO. This indicates that the dimeric triarylmethine

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derivatives are more conjugated than the single-type triarylmethine materials such as Victoria
Blue BO, and that the counter ion has no effect in the absorption spectra. In the dimeric
triarylmethine derivatives, UV-Vis absorption of the methyl- and naphthalene-substituted
dimeric triarylmethine derivatives such as Me-BTM-DHFMS and Na-BTM-DHFMS was red
shifted by 8−24 nm and broadened compared to the peak maximum of H-BTM. This means
that methyl and naphthalene substituted in dimeric triarylmethine create a more conjugated
structure and various transition states compared to H-BTM and Victoria Blue BO.
The thermal stability of the synthesized dimeric triarylmethine derivatives was measured by
TGA and is shown in Figure 5 and Table 2. The degradation initiation temperatures at 5 wt%
losses of the synthesized dimeric triarylmethine derivatives were in the broad range 107.9 -
248.0 °C and they have higher thermal stabilities than Victoria Blue BO. When the counter
ion in triarylmethine was changed from chloride (H-BTM-Cl) to TFMS (H-BTM-TFMS) or
DHFMS (H-BTM-DHFMS), the degradation initiation temperature was increased from
107 °C to 239.6 °C or 241.7 °C, respectively. These results mean that the dimer-type
triarylmethine is more stable than the single-type such as Victoria Blue BO, and the
substituted TFMS and DHFMS ions also increased the thermal stability because these ions
have larger molecular weight than chloride and it maybe make better thermal stability.
The photo stability of the new dimeric triarylmethine derivatives and Victoria Blue BO was
monitored by changing the intensity of the maximum UV absorption under UV irradiation
using a spin-coated film on glass and is shown in Figure 6 and Table 3. The photo
degradation rate (DR) of the synthesized dimeric triarylmethine and Victoria Blue BO
showed increasing values of 7.48 (Na-BTM-DHFMS), 21.82 (H-BTM-DHFMS), 33.04 (Me-
BTM-DHFMS), 35.71 (H-BTM-Cl), 37.45 (H-BTM-TFMS), and 47.44 (Victoria Blue BO).
Above all, this means that the dimer-type triarylmethine has approximately 6.3−1.2 times
increased photo stability than commercial Victoria Blue BO, which has a single
chromophore.[8] The naphthalene-substituted triarylmethine (Na-BTM-DFMS) and DHFMS
ion showed the most increased photo stability among the synthesized dimeric triarylmethine
derivatives. These results mean that the newly designed and synthesized dimeric
triarylmethine show enhanced thermal/photo stability than a single chromophore, and the
counter ion is also effective to control these stabilities.

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3.3. Thermal stability of the dye-based color filter using the synthesized triarylmethine
derivatives
To validate applicability of the synthesized triarylmethine derivatives in a color filter, the
solution containing the acrylic binder, new dyes, and photo-initiator in PGMEA was prepared
and spin-coated on a glass substrate. The coated color filter samples were pre-baked at
100 °C and under UV irradiation. To evaluate the fabricated color filters, they were treated at
230 °C for 1 h, which is the color filter temperature, and the transmittance and △Eab values
before and after the treatment were measured and the results are shown in Figure 7 and Table
4.
As shown in Figure 7, the transmittance of the color filters containing the synthesized
triarylmethine derivatives showed more than 80% transmittance at 450 nm except the Na-
BTM-DHFMS compound, and the transmittance change of the color filters containing the
synthesized triarylmethine and Victoria Blue BO before and after the thermal treatment
showed a changed transmittance intensity at the 500−700 nm wavelength range and de-
colorization. In particular, H-BTM-Cl and Victoria Blue BO were the most changed before
and after heat treatment. In contrast, the transmittance of the other synthesized triarylmethine
derivatives, including H-BTM-TFMS, H-BTM-DHFMS, Me-BTM-DHFMS and Na-BTM-
DHFMS, were hardly changed.
The larger △Eab values of the color filter after heat treatment at 230 °C means that their
thermal stability is insufficient. The △Eab values of the synthesized dimeric triarylmethine
derivatives were 3.03−9.26. These △Eab values of the synthesized triarylmethine derivatives
were greatly decreased and improved compared with the Victoria Blue BO value of 18.51. In
particular, the △Eab values of H-BTM-Cl, H-BTM-TFMS, and H-BTM-DHFMS were 9.26,
6.70, and 3.03, respectively. This means that the TFMS and DHFMS counter ions in
triarylmethine can improve the thermal stability more than the Cl counter ion.
The △Eab values of the color filters should be less than 3 for commercial applications.[14-15]
Only H-BTM-DHFMS showed a satisfactory value. However, we found that the designed
dimeric triaylmethine, having a double chromophore, has the potential to be applied for dye-
based color filters, and the counter ions can improve the thermal and photo stabilities.

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4. Conclusion
The dimeric triarylmethine derivatives with various functional groups and counter ions have
been newly designed and successfully synthesized as blue dyes, having a two chromophore
moiety in a single molecule, for dye-based color filters. The optical and thermal/photo
stabilities of the synthesized blue dyes were measured by UV-Vis absorption and TGA. The
maximum UV-Vis absorption peak of these dyes was 625−650 nm and showed typical blue
dye absorption. The photo stability was monitored by changing the UV-Vis maximum
intensity under UV light irradiation on a spin-coated film, and the thermal stability was
measured by the thermal degradation temperature at 5 wt% loss. The results showed that the
dimer-type triarylmethine has more increased thermal/photo stability than the single type,
such as Victoria Blue BO, and the substituted TFMS and DHFMS ions also increased the
thermal stability more than chloride. To evaluate the applicability of the synthesized blue
dyes, a color filter was prepared and transmittance was measured with heat treatment at
230 °C for 30 min. The fabricated color filter containing the synthesized blue dyes showed
approximately 80% transmittance at 450 nm after the thermal treatment and the △Eab values
were 3.03−9.26. In particular, the △Eab value of H-BTM-DHFMS was 3.03, which means
that it has potential to be applied as a commercial color filter dye. This study found that the
designed dimeric triarylmethine, which has a double chromophore, has the potential to be
applied to a dye-based color filter, and the counter ion can improve the thermal and photo
stabilities.
5. Acknowledgment
This research was supported by a grant from the Core Technology Development Program for
the Commercialization of Functional Chemicals funded by the Ministry of Trade, Industry
and Energy, Republic of Korea (Project No. 10060523). This research was supported by the
Basic Science Research Program through the National Research Foundation of Korea (NRF)
funded by the Ministry of Education (No. 2016R1D1A1B03931477)

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5. Reference
[1] Jun Choi, Chun Sakong, Jae-Hong Choi, Chun Yoon and Jae Pil Kim, “Synthesis and
characterization of some perylene dyes for dye-based LCD color filters”, Dyes and
Pigments, 90, 82-88 (2011)
[2] Masato Inoue, Toru Ashida, “Development of Color Resists Containing Novel Dyes for
Liquid Crystal Displays”, This paper is translated from R&D Report, “SUMITOMO
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Schemes, Figures, Tables
Figure 1. Chemical structure of the new synthesized dimeric triarylmethine derivatives and
Victoria Blue BO

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Figure 2. Synthetic scheme of the dimeric triarylmethine derivatives

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Figure 3. H-NMR data of the synthesized dimeric triarylmethine derivatives: (a) BTM-Cl, (b)
BTM-TFMS, and (c) BTM-DHFMS.

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Table 1. Solubility of the synthesized dimeric triarylmethine derivatives and Victoria Blue
BO
Solubility in PGMEA
Compounds
(wt%)
H-BTM-Cl
3.11
0.83
6.41
4.87
4.50
0.03
H-BTM-TFMS
H-BTM-DHFMS
Me-BTM-DHFMS
Na-BTM-DHFMS
Victoria Blue BO

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Figure 4. (a) UV-Vis absorption spectrum and (b) normalized spectrum of the synthesized
dimeric triarylmethine derivatives and Victoria Blue BO in methanol (at 1.0×10-5 M)

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Figure 5. Thermogravimetric Analysis (TGA) of the synthesized dimeric triarylmethine
derivatives and Victoria Blue BO

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Table 2. Optical and thermal properties of the synthesized dimeric triarylmethine derivatives
and Victoria Blue BO
UVmax (nm)
in MeOH
Ɛmax
Tda
(oC)
Compounds
(L/mol∙cm)
H-BTM-Cl
626
625
626
634
650
593
1.46×105
1.65×105
1.45×105
5.50×104
4.60×104
1.00×105
107.9
239.6
241.7
248.0
244.2
85.4
H-BTM-TFMS
H-BTM-DHFMS
Me-BTM-DHFMS
Na-BTM-DHFMS
Victoria Blue BO
a: 5 wt% Loss, Nitrogen, 10 oC/min

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100
80
60
40
20
0
BTM-Cl
BTM-TFMS
BTM-DHFMS
Me-BTM-DHFMS
Na-BTM-DHFMS
Victoria Blue BO
0
30
60
90
120
150
180
Irradiation Time T (min)
Figure 6. Photo degradation data of the synthesized dimeric triarylmethine derivatives and
Victoria Blue BO.

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Table 3. Degradation Rate (DR) value of the synthesized dimeric triarylmethine derivatives
and Victoria Blue BO
Sample
DR (%/min)
35.71
H-BTM-Cl
H-BTM-TFMS
H-BTM-DHFMS
Me-BTM-DHFMS
Na-BTM-DHFMS
Victoria Blue BO
37.45
21.82
33.04
7.48
47.44

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Figure 7. Transmittance of the synthesized dimeric triarylmethine derivatives and Victoria
Blue BO (□) before and (○) after post baking. (a) H-BTM-Cl, (b) H-BTM-TFMS, (c) H-
BTM-DHFMS, (d) Me-BTM-DHFMS, (e) Na-BTM-DHFMS, and (f) Victoria Blue BO

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Table 4. The transmittance at 450 nm and the color difference values of the synthesized
dimeric triarylmethine derivatives and Victoria Blue BO after post baking
Transmittance (%)
Compounds
△Eab
at 450 nm
H-BTM-Cl
81.4
9.26
6.70
3.03
4.97
4.24
18.51
H-BTM-TFMS
83.8
83.7
81.3
77.4
90.3
H-BTM-DHFMS
Me-BTM-DHFMS
Na-BTM-DHFMS
Victoria Blue BO

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Graphical Abstract
Highlight
1. Five novel triarymethine derivatives have been designed, synthesised and investigated as
potential color filter dyes.
2. New designed “dimer-type” triarylmethines showed increased photo/thermal stability.
3. Substitution such as methyl phenylene and naphthylene (Na-BTM) groups can control
photo stability.
4. Counter ion substituted with TFMS and DHFMS ions increased the thermal stability more
than chloride.