Synthesis and characterization of novel triarylmethane-based dyes for thermally stable blue color filters

Article abstract of DOI:10.1166/jnn.2019.16682

Two new triarylmethane-based dye molecules with a dimeric structure, TAM-1 and TAM-2, were designed and synthesized as potential blue color filter materials for liquid-crystal displays. The dimeric structure of TAM-1 was designed to improve the thermal stability of a well-known blue dye, Victoria Blue BO. TAM-2 was designed to further improve the solubility of TAM-1 by introducing long alkyl ester groups. The synthesized dyes TAM-1 and TAM-2 were transmissive in the wavelength range of 410-460 nm and showed good thermal stability with 5% weight degradation temperatures (T_5d) of 259 °C and 289 °C, respectively, and less than 1% of weight loss at 230 °C. Moreover, TAM-2 showed excellent solubility (20.1 wt%) as opposed to Victoria Blue BO (0.03 wt%) and TAM-1 (3.5 wt%) in PGMEA.

Full text of DOI:10.1166/jnn.2019.16682

Article
Journal of
Nanoscience and Nanotechnology
Vol. 19, 4782–4786, 2019
Copyright © 2019 American Scientific Publishers
All rights reserved
Printed in the United States of America
www.aspbs.com/jnn
Synthesis and Characterization of Novel
Triarylmethane-Based Dyes for Thermally
Stable Blue Color Filters
1
ꢀ2
1
2
2
2
Chan Gyu Lee , Jeong Yong Park , Young Il Park , Seo-Hyun Jung , Gyu Sung Lee ,
2
1ꢀ∗
2ꢀ∗
Jong Mok Park , Do-Hoon Hwang , and Hoyoul Kong
1Department of Chemistry and Chemistry Institute for Functional Materials, Pusan National University, Busan 609-735, Korea
Research Center for Green Fine Chemicals, Korea Research Institute of Chemical Technology (KRICT), Ulsan 44412, Republic of Korea
2
Two new triarylmethane-based dye molecules with a dimeric structure, TAM-1 and TAM-2, were
designed and synthesized as potential blue color filter materials for liquid-crystal displays. The
dimeric structure of TAM-1 was designed to improve the thermal stability of a well-known blue dye,
Victoria Blue BO. TAM-2 was designed to further improve the solubility of TAM-1 by introducing long
alkyl ester groups. The synthesized dyes TAM-1 and TAM-2 were transmissive in the wavelength
range of 410–460 nm and showed good thermal stability with 5% weight degradation temperatures
ꢀ
ꢀ
ꢀ
(
T5dꢀ of 259 C and 289 C, respectively, and less than 1% of weight loss at 230 C. Moreover,
TAM-2 showed excellent solubility (20.1 wt%) as opposed to Victoria Blue BO (0.03 wt%) and
IP: 95.85.70.171 On: Thu, 04 Jul 2019 20:24:02
TAM-1 (3.5 wt%) in PGMEA.
Copyright: American Scientific Publishers
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Keywords: Triarylmethane, Victoria Blue BO, Blue Dyes, Image Sensors, Color Filters.
1
. INTRODUCTION
filter manufacture or use. Therefore, it is necessary to
develop new dyes with excellent thermal and light sta-
bility. Cyanine, azo, anthraquinone, dioxine, and triaryl-
methane are well-known blue or purple chromophores.
These chromophores have high transmittance, heat resis-
tance, and light fastness, and are more easily synthesized
than other dyes. In particular, triarylmethane dyes are blue
dyes that have attracted significant attention owing to their
Color filters are used in various electronic devices, includ-
ing liquid crystal displays (LCDs) and image sensors
such as smart phones, tablet PCs, and digital cameras.
Display devices based on a color filter are required to
have small color pixels and high contrast in order to
realize excellent image quality along with a miniaturiza-
1
–3
4
tion trend. The color filter used in current LCDs con-
sists of red, green, and blue color pixels, and the image
is implemented by controlling the amount of light pass-
ing through each color pixel. Pigment dispersion is the
most widely used method for producing patterned pix-
els in color filters; however, in this method, the parti-
cle size must be kept small, and light scattering occurs
high transmittance and excellent color strength in the blue
11ꢀ12
region (460–500 nm).
Chemical structures of the three
representative triarylmethane dyes are shown in Figure 1.
Among these dyes, Victoria Blue BO is known as a typ-
ical triarylmethane blue dye that transmits light at 420–
4
50 nm; however, it has low solubility and low thermal
1
ꢀ4–6
because of the agglomeration of the pigment particles.
6
ꢀ10–12
stability.
Research on dye-based color filters with good solubility
has been of interest to address the problem of pigment
particle size. Dyes used in color filters must be able to
withstand the high temperatures (>200 C) of color fil-
ter manufacturing processes and exhibit light stability to
In this study, we designed and synthesized highly sol-
uble and thermally stable triarylmethane-based blue dyes,
TAM-1 and TAM-2, for color filters. Long alkyl ester
groups were introduced to improve solubility, and the dyes
were designed to have a dimeric structure in order to
improve their thermal stability. The synthetic schemes and
structures of the triarylmethane-based dimeric dyes are
shown in Scheme 1.
ꢀ
7
–10
avoid backlighting.
mal and light stability and can be discolored during color
However, most dyes have low ther-
∗
Authors to whom correspondence should be addressed.
4782
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1533-4880/2019/19/4782/005
doi:10.1166/jnn.2019.16682

Lee et al.
Synthesis and Characterization of Novel Triarylmethane-Based Dyes for Thermally Stable Blue Color Filters
purchased from Sigma-Aldrich and used without further
N
N
N
N
N
N
purification. The synthesized compounds were identified
1
13
by H- and C-NMR (Ultrashield 300 MHz, Bruker,
Germany), with tetramethylsilane as an internal reference.
Thermal properties of the compounds were elucidated
by using a thermogravimetric analyzer (TA Instruments
Thermogravimetric Analyzer Q500) with a heating rate
SO OH
3
HO
O
S
O
HN
N
H
Methyl Violet
Patent Blue VF
Victoria Blue BO
Figure 1. Dyes of the triarylmethane series.
ꢀ
of 10 C/min. The molar masses of the compounds were
determined by using a MALDI–TOF (Bruker Autoflex
Speed TOF/TOF) spectrometer.
2
. EXPERIMENTAL DETAILS
2
.1. Reagents and Instruments
Ethylene glycol, p-toluenesulfonyl chloride, diethanol-
amine, difluorobenzophenone, 2-ethylhexanoyl chlo-
ride, 1-naphthylamine, phosphorus(V) oxychloride,
and bis(trifluoromethane)sulfonimide lithium salt were
2.2. Synthesis
2.2.1. Synthesis of Ethylene di(p-toluenesulfonate) (1)
Ethylene glycol (5.0 g, 80.5 mmol) and p-toluenesulfonyl
chloride (33.78 g, 177.2 mmol) were dissolved in 150 mL
IP: 95.85.70.171 On: Thu, 04 Jul 2019 20:24:02
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Scheme 1. Synthetic routes for TAM-1 and TAM-2.
J. Nanosci. Nanotechnol. 19, 4782–4786, 2019
4783

Synthesis and Characterization of Novel Triarylmethane-Based Dyes for Thermally Stable Blue Color Filters
Lee et al.
ꢀ
of anhydrous THF under nitrogen atmosphere at 0 C, and
aqueous sodium hydroxide solution (11.28 g, 281.9 mmol
in 5 mL of water) was added slowly into the reaction flask.
The mixture was stirred overnight at room temperature and
subsequently extracted with methylene chloride and dis-
tilled water. The organic layer was separated and dried
over magnesium sulfate. A white powder was obtained
was placed in a 250 mL two-neck round-bottom flask
and refluxed under a nitrogen atmosphere. 2-ethylhexanoyl
chloride (2.5 g, 15.4 mmol) was then slowly added to the
ꢀ
flask and reacted at 60 C for 24 h. After the reaction was
complete, the reaction mixture was extracted with methy-
lene chloride and brine. The combined organic extracts
were dried over anhydrous magnesium sulfate, filtered, and
evaporated to obtain a residue. This residue was purified
using column chromatography with acetone/methylene
in 70% yield (20.7 g) after solvent evaporation using a
rotary evaporator. H-NMR (300 MHz, CDCl , ppm): 7.72
d, 4H), 7.35 (d, 4H), 4.18 (s, 4H), 2.45 (s, 6H). C-NMR
75 MHz, CDCl , ppm): 145.41, 132.49, 130.10, 128.10,
1
3
1
3
(
(
chloride as the developing solvent to obtain a dark green
1
liquid (1.2 g, 55%). H-NMR (300 MHz, CDCl , ppm):
3
3
6
6.82, 21.80.
7.74 (d, 4H), 6.82 (d, 4H), 4.30 (t, 8H), 3.72 (t, 8H), 2.28
1
3
(
m, 4H), 1.24–1.55 (m, 32H), 0.87 (t, 24H). C-NMR
1
2
2
.2.2. Synthesis of N , N -di(naphthalen-1-yl)
Ethylenediamine (2)
(75 MHz, CDCl , ppm): 193.68, 176.43, 150.27, 132.56,
3
127.19, 110.87, 60.93, 49.62, 47.52, 31.80, 29.74, 25.49,
22.73, 14.06, 11.95.
Ethylene di(p-toluenesulfonate) (5.0 g, 13.5 mmol) and
-naphthylamine (6.7 g, 47.2 mmol) were mixed in a
1
flask, and aqueous sodium carbonate (3.6 g, 33.7 mmol
in 2 mL of water) was slowly added to the reaction mix-
ture under nitrogen atmosphere. The reaction mixture was
2.2.5. Synthesis of TAM-1
4,4 -bis(diethylamino)benzophenone (3.7 g, 11.4 mmol)
ꢁ
was placed in a 250 mL two-neck round-bottom flask
with 100 mL of anhydrous toluene. Phosphorus(V) oxy-
chloride (8.3 g, 54.3 mmol) was slowly injected into the
flask at room temperature for 12 h. Subsequently, N ,N -
di(naphthalen-1-yl)ethylenediamine (1.7 g, 5.4 mmol) was
dissolved in anhydrous toluene and slowly injected into
ꢀ
stirred for 5 days at 100 C. Subsequently, it was cooled
to room temperature and extracted with methylene chlo-
ride and distilled water. The organic layer was separated
and dried over magnesium sulfate. A pure solid product
was obtained after silica-gel column chromatography with
1
2
ꢀ
methylene chloride as the eluent. The product yield was
the flask. The reaction mixture was then stirred at 80 C
1
4
0% (1.69 g). H-NMR (300 MHz, CDCl , ppm): 7.79
for 10 h. After completion of the reaction, an organic
3
IP: 95.85.70.171 On: Thu, 04 Jul 2019 20:24:02
(
d, 4H), 7.32–7.44 (m, 8H), 6.77 (d, 2H), 4.67 (s, 2H),
layer was obtained with methylene chloride and water
Copyright: American Scientific Publishers
1
3
3
1
1
.74 (s, 4H). C-NMR (75 MHz, CDCl , ppm): 143.35,
having a pH of 3 or lower, and then the solvent was
removed. The solid product (1.2 g, 25%) was obtained by
column chromatography using ethanol/acetone/methylene
chloride as eluent. The obtained solid product (1.0 g,
1.0 mmol) was then added to a 100 mL one-neck round-
bottom flask with 50 mL of methanol, followed by the
addition of bis(trifluoromethane)sulfonimide lithium salt
(0.6 g, 2.2 mmol). Extraction of the organic layer and
3
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34.47, 128.84, 126.66, 126.01, 125.10, 123.86, 120.06,
18.28, 105.01, 43.64.
2
.2.3. Synthesis of Bis(4-(bis(2-hydroxyethyl)amino)
phenyl)Methanone (3)
,4 -difluorobenzophenone (1.0 g, 4.6 mmol) and
ꢁ
4
diethanolamine (6.7 g, 64.2 mmol) were added to a
1
00 mL round bottom flask fitted with a reflux con-
subsequent removal of the solvent yielded a solid prod-
ꢀ
1
denser and allowed to react at 180 C under nitrogen
for 3 days. After completion of the reaction, the mix-
ture was cooled and the aqueous layer was extracted
with diethyl ether and water, and then the water was
removed. Purification by column chromatography using
ethyl acetate/ethanol as a developing solvent, and removal
uct (1.2 g, 80%). H-NMR (300 MHz, CDCl , ppm): 9.76
3
(s, 2H), 9.04 (d, 2H, J = 7.5 Hz), 7.45 (t, 2H, J = 5.4
Hz), 7.13–7.33 (m, 16H), 6.71 (s, 8H), 4.23 (s, 4H), 3.53
1
3
(d, 16H, J = 6.6 Hz), 1.28 (t, 24H, J = 6.6 Hz). C-NMR
(75 MHz, CD OD, ppm): 176.59, 155.23, 153.43, 142.88,
3
140.64, 137.31, 128.94, 128.78, 128.34, 126.61, 126.40,
124.29, 123.50, 113.62, 105.42, 46.34, 43.92, 12.94, MS
of residual diethanolamine by distillation yielded a green
solid (1.12 g, 63%). H-NMR (300 MHz, CD OD, ppm):
1
+
(MALDI–TOF) 925.3 [M ].
3
7
.63 (d, 4H), 6.81 (d, 4H), 3.76 (t, 8H), 3.64 (t, 8H).
1
3
C-NMR (75 MHz, CD OD, ppm): 196.53, 152.83,
2.2.6. Synthesis of TAM-2
Compound 4 (5.0 g, 5.6 mmol) was placed in a
3
1
33.54, 126.72, 111.82, 60.18, 54.76.
2
50 mL two-neck round-bottom flask with 100 mL of
2
.2.4. Synthesis of ((carbonylbis(1,4-phenylene))
bis(azanetriyl))tetrakis(ethane-1,2-diyl)
tetrakis(2-ethylhexanoate) (4)
anhydrous toluene. Phosphorus(V) oxychloride (4.1 g,
26.6 mmol) was injected slowly into the flask at room
temperature for 12 h. Subsequently, N ,N -di(naphthalen-
1-yl)ethylenediamine (0.8 g, 2.6 mmol) was dissolved in
anhydrous toluene and slowly injected to the flask. The
1
2
A mixture of bis(4-(bis(2-hydroxyethyl)amino)phenyl)
methanone (1.0 g, 2.6 mmol), triethylamine (0.6 g,
5
ꢀ
.8 mmol), and anhydrous methylene chloride (100 mL)
reaction mixture was then stirred at 80 C for 10 h.
4784
J. Nanosci. Nanotechnol. 19, 4782–4786, 2019

Lee et al.
Synthesis and Characterization of Novel Triarylmethane-Based Dyes for Thermally Stable Blue Color Filters
Table I. Solubility, optical, and thermal properties of victoria blue BO, TAM-1, and TAM-2.
Solubility (wt%)
in PGMEA
Solubility (wt%)
in IPA
UVmax (nm)
in MeOH
ꢁmax
(L/mol·cm)
Transmittance (%)
at 450 nm
a
d
ꢀ
Blue dyes
T5 ( C)
5
Victoria blue BO
TAM-1
TAM-2
0ꢂ03
3ꢂ5
20ꢂ1
5ꢂ8
11ꢂ0
12ꢂ3
592
593
571
1.0×10
86.2
87.7
88.8
169
259
289
5
1.24×10
5
1.0×10
Note: aTemperature resulting in 5% weight loss based on initial weight.
After the completion of the reaction, an organic layer
was obtained with methylene chloride and water having
a pH of 3 or lower, and then the solvent was removed.
The product was obtained as a solid (1.06 g, 19%) after
column chromatography using ethanol/acetone/methylene
chloride as the eluent mixture. The obtained prod-
uct (1.0 g, 0.5 mmol) was then added to a 100 mL
one-neck round-bottom flask with 50 mL of methanol
and bis(trifluoromethane)sulfonimide lithium salt (0.3 g,
BO was synthesized and showed good thermal stability.
Furthermore, to improve the solubility, the short diethyl
side chains of TAM-1 were substituted with long alkyl
ester groups (TAM-2). Their chemical structures were ver-
1
13
ified by H- and C-NMR.
To measure the solubility of the synthesized dyes, they
were dissolved in propylene glycol methyl ether acetate
ꢀ
(PGMEA) at 25 C. The measured solubilities of Vic-
toria Blue BO, TAM-1, and TAM-2 were found to be
0.03, 3.5, and 20.1 wt%, respectively. The solubilities of
the newly synthesized triarylmethane dyes were highly
improved as compared with that of the commercial blue
dye, Victoria Blue BO. In particular, TAM-2 with long
alkyl ester groups showed significantly increased solubility
(∼670 times) compared to Victoria Blue BO.
1
.0 mmol). Extraction of the organic layer followed by
removal of the solvent gave a solid product (1.3 g, 98%).
1
H-NMR (300 MHz, CDCl , ppm): 10.82 (s, 2H), 8.99
3
(
2
d, 2H), 6.86–7.69 (m, 26H), 4.34 (t, 20H), 3.78 (t, 16H),
.29 (m, 8H), 1.25–1.60 (m, 64H), 0.87 (t, 48H), C-
1
3
NMR (75 MHz, CD OD, ppm): 177.39, 176.92, 155.78,
3
1
1
5
55.54, 145.51, 140.16, 137.62, 130.29, 129.60, 128.71,
27.33, 127.04, 124.51, 124.07, 114.23, 106.93, 62.10,
0.73, 48.43, 32.78, 30.74, 26.43, 23.66, 14.45, 12.30, MS
The UV-Vis absorptions of the synthesized triaryl-
methane blue dyes and Victoria Blue BO in solution were
measured and are shown in Figure 2. The UV-Vis absorp-
+
MALDI–TOF) 2050 [M ].
IP: 95.85.70.171 On: Thu, 04 Jul 2019 20:24:02
tion spectra of Victoria Blue BO and TAM-1 recorded
(
Copyright: American Scientific Publishers
at 592 and 593 nm, respectively, were very similar. The
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absorption maxima of TAM-2 (571 nm) with long alkyl
ester groups was blue-shifted as compared to the absorp-
tion maxima of TAM-1, and it showed a shoulder peak
at ∼660 nm. The coefficient (ꢁꢃ at maximum absorption
3
. RESULTS AND DISCUSSION
Two new blue dyes based on triarylmethane derivatives
were designed and synthesized as potential blue color filter
materials as shown in Scheme 1. The solubility, opti-
cal, and thermal properties of them are summarized in
Table I. To improve thermal stability, the dimeric struc-
ture (TAM-1) of the well-known blue dye Victory Blue
5
of TAM-1 (1.24 ×10 at 593 nm) with the dimeric struc-
5
ture was higher than that of Victoria Blue BO (1.0 × 10
5
at 592 nm). On the other hand, TAM-2 (ꢁ = 1.0 × 10
at 571 nm) with long alkyl ester groups showed a lower
absorption coefficient than TAM-1.
Figure 2. Absorption spectra of victoria blue BO, TAM-1, and TAM-2
−
5
(
1.0×10 M).
Figure 3. Transmission spectra of Victoria Blue, TAM-1, and TAM-2.
J. Nanosci. Nanotechnol. 19, 4782–4786, 2019
4785

Synthesis and Characterization of Novel Triarylmethane-Based Dyes for Thermally Stable Blue Color Filters
Lee et al.
concluded that the dimeric structure of the synthesized
dyes contributed greatly to their enhanced thermal
stability.
4
. CONCLUSION
In this study, we designed and synthesized TAM-1 as
a blue color filter material with a dimeric structure of
the well-known Victoria Blue BO. TAM-1 showed bet-
ter thermal stability and solubility than Victoria Blue BO.
To further improve the solubility of TAM-1, we intro-
duced long alkyl ester groups in the dimeric structure
and synthesized TAM-2. TAM-2 also showed good ther-
mal stability and much better solubility than Victoria
Blue BO and TAM-1. The synthesized triarylmethane-
based dimeric organic dyes are good candidates for highly
soluble and thermally stable blue color filter materials
for LCDs.
Figure 4. TGA analysis of Victoria Blue, TAM-1, and TAM-2.
The transmittances of the films of the two synthesized
dyes were measured and compared with that of the ref-
erence material, Victoria Blue BO, as shown in Figure 3.
The transmittance results are consistent with the results of
the absorption spectra. The transmittance of the color fil-
ters containing the new blue dyes, TAM-1 (87.7%) and
TAM-2 (88.8%), showed more than 80% transmittance at
Acknowledgment: This work was supported by grants
from the Korea Research Institute of Chemical Technology
project (KK1804-B00, KK1806-G16) and the National
Research Foundation (NRF) funded by the Korean Gov-
ernment (NRF-2017R1A2A2A05001345).
4
50 nm. The transmittance spectrum of TAM-1 was sim-
ilar to that of Victoria Blue BO but more transmissive
References and Notes
in the longer wavelength region, and TAM-2 was more
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Delivered by Ingenta
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4
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Kim, Dyes and Pigments 89, 1 (2011).
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ꢀ
heating to 230 C, the dyes should have a weight loss of
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C. Sakong, J. Choi, W. Lee, and J. P. Kim, Dyes and Pigments
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gen atmosphere at a heating rate of 10 C/min for 10 min.
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exhibit significantly improved thermal stabilities, losing
ꢀ
less than 5% of their weight upon heating to 259 C and
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ꢀ
2
89 C, respectively, as compared with Victoria Blue BO
14, 6435 (2014).
ꢀ
(
169 C).
1
1
1
0. H. Zollinger, Color Chemistry: Syntheses, Properties, and Applica-
tions of Organic Dyes and Pigments, VCH Publishers, New York
(1911), Chap. 4.
1. N. S. Kong, H. Jung, B. Kim, C. K. Lee, H. Kong, K. Jun, J. C.
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The residual weight of Victoria Blue BO, TAM-1, and
ꢀ
TAM-2 at 230 C were 82.92%, 99.20%, and 99.56%,
respectively. Both TAM-1 and TAM-2 showed a weight
ꢀ
loss of less than 1% at 230 C. This result confirmed
that the former dyes were more thermally stable than
Victoria Blue BO, which showed a weight reduction of
more than 17% at the same temperature. Therefore, it was
Received: 24 May 2018. Accepted: 31 August 2018.
4786
J. Nanosci. Nanotechnol. 19, 4782–4786, 2019