Synthesis of new metal complex derivatives based on azo, naphthol and pyrazole moieties for color filter pigments

Article abstract of DOI:10.1080/15421406.2010.495682

Four Cr and Co based metal complex derivatives for new violet and red color filters were first synthesized by using naphthol and pyrazole groups as well as azo moiety. The UV-visible maximum values of Co(HPANT)2 and Cr(HPANT)2, the naphthol derivatives, w

Full text of DOI:10.1080/15421406.2010.495682

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Synthesis of New Metal Complex
Derivatives Based on Azo, Naphthol
and Pyrazole Moieties for Color Filter
Pigments
Chang-Hun Seok a , Jae-Yun Jaung b & Jongwook Park a
a Department of Chemistry/Display Research Center , The Catholic
University of Korea , Wonmi, Bucheon, Korea
b Department of Fiber and Polymer Engineering , Hanyang
University , Seongdong-gu, Seoul, Korea
Published online: 11 Nov 2010.
To cite this article: Chang-Hun Seok , Jae-Yun Jaung & Jongwook Park (2010) Synthesis of New
Metal Complex Derivatives Based on Azo, Naphthol and Pyrazole Moieties for Color Filter Pigments,
Molecular Crystals and Liquid Crystals, 529:1, 80-87
To link to this article: http://dx.doi.org/10.1080/15421406.2010.495682
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Mol. Cryst. Liq. Cryst., Vol. 529: pp. 80–87, 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421406.2010.495682
Synthesis of New Metal Complex Derivatives
Based on Azo, Naphthol and Pyrazole Moieties
for Color Filter Pigments
CHANG-HUN SEOK,1 JAE-YUN JAUNG,2 AND
JONGWOOK PARK1
1Department of Chemistry=Display Research Center, The Catholic
University of Korea, Wonmi, Bucheon, Korea
2Department of Fiber and Polymer Engineering, Hanyang University,
Seongdong-gu, Seoul, Korea
Four Cr and Co based metal complex derivatives for new violet and red color filters
were first synthesized by using naphthol and pyrazole groups as well as azo moiety.
The UV-visible maximum values of Co(HPANT)2 and Cr(HPANT)2, the naphthol
derivatives, were 560 and 561 nm respectively in solution state where both were violet
colored solids. Co(HPAPMP)2 and Cr(HPAPMP)2, the pyrazole derivatives also
showed UV-visible maximum values of 465 and 510 nm respectively in solution state,
indicating brown and red colored solids. And all these compounds exhibited better
clear colors based on higher molar extinction coefficient value compared to the
commercial pigments.
Keywords Azo group; color filter; metal-azo complex; pigment
Introduction
In the past, dyes and pigments were used in general fields like paint, ink, plastic and
fabric [1–3]. However, as the display industry has rapidly developed, dyes and pig-
ments have been widely used as core materials of color filter (CF), which is used
to make full color in liquid crystal display (LCD). In CF of LCD, the role of dyes
and pigments is to express full color by reflecting or absorbing light at specific wave-
lengths when white-backlight is passing through [4–6]. Therefore, optical character-
istics of pigments used in CF must allow light with specific wavelength to pass
through and filter remaining wavelengths to the best possible extent. Such pigments
are thus required to have specific absorption spectrum and high molar extinction
coefficient [7]. Moreover, similar color filter materials are required for image sensors
widely being used in charge-coupled device (CCD) cameras and web-cameras [7].
Accordingly, there is a demand for development of new pigment materials to be
Address correspondence to Prof. Jongwook Park, Department of Chemistry=Display
Research Center, The Catholic University of Korea, 43-1, Yeokgok, Wonmi, Bucheon
420-743, Korea (ROK). Tel.: (þ82)2-2164-4821; Fax: (þ82)2-2164-4764; E-mail: hahapark@
catholic.ac.kr
80

Metal Complex Derivatives for Color Filter Pigments
81
used. This study focuses on the combination of azo group and pyrazole or naphthol
group in cobalt and chrome metals for development of new materials.
=
Azo (ꢀN Nꢀ) has high molar extinction coefficient and can obtain broad
range of colors through introduction of diverse aromatic groups using a simple coup-
ling synthesis, resulting in an advantage of realizing diverse colors [8–11]. As an
advantage of material system, creation of metal-azo complexes using metallization
can adjust absorption wavelength by metal to ligand charge transfer (MLCT) or
ligand to metal charge transfer (LMCT) [12–15].
In the previous paper, H. Kocaokutgen et al. reported the 1-(2-hydroxy-
4-methylphenylazo)-2-naphthol [16]. In this study, in order to increase molecular
interaction we remove methyl group at para-position of naphthol group as similar
chemical structure. The chemical structure removed methyl group is considered as
the increased planarity of chemical structure and molecular interaction.
In this report, four pigments for color filter were newly synthesized by synthesiz-
ing new azo derivatives which include aromatic groups of naphthol and pyrazole and
performing metallization on cobalt ion and chrome ion. UV-visible absorption spec-
tra of synthesized materials were measured with changes in aromatic groups and
metal ions to verify changes in absorption property according to pigment structure.
Experimental
Synthesis
1) Synthesis of 1-(2-Hydroxy phenylazo)-2-naphthol (HPANT). 2-Aminophenol
(50 mmol, 5.51 g) was mixed with hydrochloric acid (150 mmol, 13 ml) in distilled
water (100 ml) and diazotized below 5ꢁC with sodium nitrite (55 mmol, 3.94 g).
After stirring for 1 h, 2-naphthol (50 mmol, 7.21 g) was dissolved in 0.1 M sodium
hydroxide solution (10 ml) and cooled to 0 to 5ꢁC in an ice bath. Then the above
diazo salt solution was stirred into the coupling component solution. The mixture
was stirred for 2 h and then filtered. The solid was washed with to of water and
recrystallized with ethanol. (7.73 g Yield: 58%).
1H-NMR (300 MHz, Acetone-d6) d (ppm): 8.52 (d, 1H), 8.00 (d, 1H) 7.97 (d,
1H) 7.76 (d, 1H) 7.64 (d, 1H) 7.59 (t, 1H), 7.43 (t, 1H) 7.16 (t, 1H) 7.01 (q, 2H)
6.85 (d, 1H) FT-IR (KBr cmꢀ1): 3060, 1614, 1567, 1465, 1411, 1299, 1272, 1240,
1213, 1151, 819, 752.
2) Synthesis of 4-(2-Hydroxy phenylazo)-1-phenyl-3-methyl-5-pyrazolone (HPAPMP).
2-Aminophenol (46.3 mmol, 5.0 g) was mixed with hydrochloric acid (138.9 mmol,
8.90 ml) in distilled water (100 ml) and diazotized below 5ꢁC with sodium nitrite
(50.963 mmol, 3.623 g). After stirring for 1 h, 3-methyl-1-pyrazolone (46.3 mmol,
7.663 g) was dissolved in 0.1 M sodium hydroxide solution (10 ml) and cooled to 0
to 5ꢁC in an ice bath. Then the above diazo salt solution was stirred into the
coupling component solution. The mixture was stirred for 2 h and then filtered.
The solid was washed with to of water and recrystallized with ethanol (5.16 g
Yield: 38%).
1H-NMR (300 MHz, DMSO-d6) d (ppm): 13.61 (s, 1H), 10.65 (s, 1H), 7.66
(d, 2H), 7.48 (d, 1H), 7.24 (t, 2H), 7.11 (t, 1H), 7.06 (t, 1H), 6.95 (m, 2H), 2.32
(s, 3H) FT-IR (KBr cmꢀ1): 3353, 1654, 1587, 1546, 1469, 1427, 1349, 1313, 1278,
1145, 1076, 1006, 952, 869, 754.

82
C.-H. Seok et al.
3) Synthesis of Cobalt-Azo Complex. A solution of cobalt sulfate (1.89 mmol, 0.49 g)
and sodium acetate (0.1 g) in 5 ml of DMF was added to a magnetically stirred
suspension of the azo compounds (7.56 mmol, 2.0 g) in DMF (10 ml). After the
mixture was refluxed for 4 h. After the reaction had finished, the reaction mixture
was extracted with ethyl acetate and water. The organic layer was dried with
anhydrous MgSO4 and filtered. The solution was evaporated. The mixture powder
was separated by using column chromatography with ethyl acetate.
Bis(1-(2-hydroxy phenylazo)-2-naphthol) cobalt (Co(HPANT)2). (2.59 g,
1
Yield: 58%) H-NMR (300 MHz, Acetone-d6) d (ppm): 9.06 (d, 1H), 8.65 (d, 1H)
7.9758 (m, 2H) 7.40 (d, 1H) 7.22 (t, 1H) 6.99 (t, 1H), 6.79 (t, 1H) 6.68 (t, 1H) 6.58
(d, 1H). FT-IR (KBr cmꢀ1): 3401, 1614, 1589, 1544, 1496, 1467, 1384, 1349, 1315,
1276, 1211, 1178, 1145, 1093, 995, 823, 748. FAB-Mass: 583 m=z.
Bis(1-(2-hydroxyphenylazo)-1-phenyl-3-methyl-5-pyrazololne)
cobalt
(Co
(HPAPMP)2). (2.55 g, Yield: 40%) 1H-NMR (300 MHz, Acetone-d6) d(ppm):
8.33 (d, 1H), 7.68 (d, 2H), 7.12 (t, 2H), 6.95 (t, 1H), 6.87 (t, 1H), 6.58 (t, 2H),
2.58 (s, 3H). FT-IR (KBr cmꢀ1): 3357, 1587, 1471, 1347, 1311, 1276, 1213, 1145,
1676, 1006, 954, 848, 800, 754. FAB-Mass 645 m=z.
4) Synthesis of Chrom-Azo Complex. A solution of chrome sulfate (1.89 mmol,
2.96 g) and sodium acetate (0.1 g) in 5 ml of DMF was added to a magnetically
stirred suspension of the azo compounds (7.56 mmol, 2.0 g) in DMF (10 ml). After
the mixture was refluxed for 4 h. After the reaction had finished, the reaction
mixture was extracted with ethyl acetate and water. The organic layer was dried
with anhydrous MgSO4 and filtered. The solution was evaporated. The mixture
powder was separated by using column chromatography with ethyl acetate.
Bis(1-(2-hydroxy phenylazo)-2-naphthol) chrome (Cr(HPANT)2). (2.54 g,
Yield: 48%). FT-IR (KBr cmꢀ1): 3407, 1662, 1590, 1544, 1498, 1465, 1346, 1309,
1272, 1205, 1178, 1145, 1097, 995, 916, 829, 752. FAB-Mass: 577 m=z.
Bis(1-(2-hydroxyphenylazo)-1-phenyl-3-methyl-5-pyrazololne)
chrome
(Cr
(HPAPMP)2). (2.52 g, Yield: 42%) FT-IR (KBr cmꢀ1): 3390, 1656, 1550, 1467,
1340, 1272, 1207, 1170, 1147, 1056, 1004, 842, 752 FAB-Mass: 637 m=z.
Measurements
1H-NMR spectra were recorded on Bruker, Advance-300 and Fast atom bombard-
ment (FAB) mass spectra were recorded by JEOL, JMS-AX505WA, HP5890 series
II. The optical absorption spectra were obtained by HP 8453 UV-VIS-NIR
spectrometer.
Results and Discussion
Schemes 1–3 are structural formula and synthetic scheme of naphthol and pyrazole
derivatives, Co(HPANT)2, Cr(HPANT)2, Co(HPAPMP)2, and Cr(HPAPMP)2 as
well as commercial pigments. After synthesizing ligand through azo coupling reac-
tion, Co or Cr complex including azo group can be synthesized by adding cobalt
(Co) sulfate or chrome (Cr) sulfate under basic condition. In addition, pyrazole
derivatives, Co(HPAPMP)2 and Cr(HPAPMP)2 were synthesized by azo coupling
reaction and similar metal-ligand reaction [17].

Metal Complex Derivatives for Color Filter Pigments
83
Scheme 1. Synthetic route of naphthol derivatives.
Scheme 2. Synthetic route of pyrazole derivatives.
Scheme 3. Structure of commercial pigments.

84
C.-H. Seok et al.
&
Figure 1. UV-Visible absorption spectra of HPANT (- -), Co(HPANT) (- -), Cr(HPANT)
ꢁ
2
2
4
(-4-), and Pigment Violet 23 (- -) (three samples: acetone solution of 4 ꢂ 10ꢀ5 M; Pigment
Violet 23: THF solution of 2.5 ꢂ 10ꢀ4 M).
UV-visible absorption spectra and molar extinction coefficient value of four
newly synthesized metal-azo complexes and two ligands in acetone solution were
measured under 4 ꢂ 10ꢀ5 M concentration. The results are shown in Figures 1, 2
and Table 1. As shown in Figure 1, UV-visible maximum of naphthol derivatives
Co(HPANT)2 and Cr(HPANT)2 was respectively 560 and 561 nm, which was 74
and 75 nm red shifted compared to 486 nm of ligand HPANT. Therefore, while
HPANT was a red colored solid, Co(HPANT)2 and Cr(HPANT)2 were violet
&
Figure 2. UV-Visible absorption spectra of HPAPMP (- -), Co(HPAPMP)2 (-.-),
~
Cr(HPAPMP)2 (- -), and Pigment Red 177 (-!-). (three samples: acetone solution of
4 ꢂ 10ꢀ5 M; Pigment Red 177: THF solution of 2.5 ꢂ 10ꢀ4 M).

Metal Complex Derivatives for Color Filter Pigments
Table 1. Optical properties of synthesized compounds
85
UVmax Edge
(nm) (nm) (L=mol ꢃ cm)
e
Log Solid
color
Compound
HPANTa
e
Naphthol
derivatives
486
560
561
568
557
612
671
690
21600
30200
22300
6196
4.33 red
a
Co(HPANT)2
Cr(HPANT)2
4.48 violet
4.34 violet
3.79 violet
a
Commercial violet Pigment violet 23b
pigment
Pyrazole
derivatives
HPAPMPa
Co(HPAPMP)2
Cr(HPAPMP)2
Pigment Red 177b
413
465
510
570
517
566
599
605
18700
27500
29500
6792
4.27 orange
4.43 brown
4.46 red
a
a
Commercial red
pigment
3.83 red
aIn acetone solution (4 10ꢀ5 M).
*
bIn THF solution (2.5 10ꢀ4 M).
*
colored solids [1]. Solid color of these two metal-azo complexes is similar to absorp-
tion maximum wavelength of 568 nm shown by a commercial violet pigment called
Pigment Violet 23. Red shift in absorption wavelength according to metal substi-
tution of ligand is probably caused by combination of HPANT with metal ion
[15,18]. In addition, metal complex Cr(HPANT)2 was more red shifted than
Co(HPANT)2 with the edge of UV-visible spectrum at 671 and 612 nm respectively.
This shows a trend of more red shift in chrome ion because chrome ion has larger
positive electron ability than cobalt ion and electron push effect in azo group is
relatively stronger [18].
Also as shown by Figure 2, pyrazole derivatives, Co(HPAPMP)2 and
Cr(HPAPMP)2 had UV-visible spectrum at maximum value of 465 and 510 nm,
which were 52 and 97 nm red shifted compared to 413 nm of ligand HPAPMP. This
is a similar trend shown by azo-complexes with naphthol derivatives and more red
shift was also shown by Cr(HPAPMP)2 than Co(HPAPMP)2. While ligand
HPAPMP was an orange colored solid, Co(HPAPMP)2 and Cr(HPAPMP)2 were
brown and red colored solids [1]. In particular, Cr(HPAPMP)2 showed similar
absorption wavelength as a commercial red pigment called Pigment Red 177 and
is expected to show commercial application.
UV-visible maximum absorption wavelength and molar extinction coefficient
value of synthesized materials are summarized in Table 1. Naphthol derivatives,
Co(HPANT)2 and Cr(HPANT)2 were more strongly red shifted compared to pyra-
zole derivatives, Co(HPAPMP)2 and Cr(HPAPMP)2. This could be interpreted as a
longer conjugation length of naphthol group. Longer conjugation length effect was
shown identically in metal complexes with Co and Cr. These results suggest that
pigments with diverse colors can be made by absorbing specific wavelengths and
controlling UV-visible absorption spectrum according to the changes in aromatic
groups and metal ions.
Molar extinction coefficient value of naphthol derivatives HPANT,
Co(HPANT)2 and Cr(HPANT)2 was respectively 21600, 30200 and 22300 L=
mol ꢃ cm. Converted to log, high molar extinction coefficient of about 4 is obtained.

86
C.-H. Seok et al.
This is higher than the molar extinction coefficient of 6200 L=mol ꢃ cm shown by
commercial Pigment Violet 23. Accordingly, since high molar extinction coefficient
is expected to show more vivid colors, synthesized materials can possibly be used as
pigments for LCD color filter as well as image sensors [7]. In addition, pyrazole deri-
vatives HPAPMP, Co(HPAPMP)2 and Cr(HPAPMP)2 showed molar extinction
coefficient of 18700, 27500 and 29500 L=mol ꢃ cm, which is higher than about
6800 L=mol ꢃ cm of commercial Pigment Red 177. New chemical structural changes
in ligand and substitution of metal ion can adjust the maximum value and range
of UV-visible absorption spectrum and absorb only the specific wavelengths, thereby
realizing pigments with diverse colors. Higher molar extinction coefficients than
commercial violet and red pigments will show more clear colors. Synthesized materi-
als can thus be used as pigments for LCD color filter. Mill-base experiment and
study on dispersion stability are currently being conducted.
Conclusions
This study synthesized 4 types of new metal-azo complexes by synthesizing 2 types of
new azo ligands that include pyrazole and naphthol, an aromatic group based on azo
group and metalizing cobalt ion and chrome ion. As a result of measuring UV-visible
absorption spectra of synthesized materials, metal-azo complexes were found to be
red shifted farther compared to maximum absorption wavelength of ligands.
The UV-visible maximum values of Co(HPANT)2 and Cr(HPANT)2, the naph-
thol derivatives, were 560 and 561 nm respectively in solution state where both were
violet colored solids, and these absorption wavelengths are similar to that of Pigment
Violet 23, a commercial violet pigment, 568 nm. Co(HPAPMP)2 and Cr(HPAPMP)2,
the pyrazole derivatives also showed UV-visible maximum values of 465 and 510 nm
respectively in solution state, indicating brown and red colored solids, and in parti-
cular, Cr(HPAPMP)2 showed absorption wavelength similar to that of Pigment Red
177, a commercial red pigment. In addition, the basic colors of Cr and Co were
similar, but Cr complex showed more red shift compared to Co complex. These
results suggest that mutual minute color tuning can be done based on similar
metal-azo complexes structural formula. The molar extinction coefficient values of
Co(HPANT)2 and Cr(HPANT)2, naphthol derivatives, were respectively 30200
and 22300 L=mol ꢃ cm, both of which were higher than that of Pigment Violet 23,
6200 L=mol ꢃ cm, and the values of Co(HPAPMP)2 and Cr(HPAPMP)2, pyrazole
derivatives, were 27500 and 29500 L=mol ꢃ cm. Particularly, Cr(HPAPMP)2 showed
much higher molar extinction coefficient value compared to that of commercial
Pigment Red 177, 6800 L=mol ꢃ cm. Such high molar extinction coefficient values
are expected to show clearer and more vivid colors, suggesting the possibility of
use as pigments for LCD color filtering pigment and image sensors.
Acknowledgments
This research was supported by a grant (Catholic Univ.) from the Fundamental
R&D Program for Core Technology of Materials funded by the Ministry of Knowl-
edge Economy (MKE), Republic of Korea. This work was supported by the
National Research Foundation of Korea (NRF) grant funded by the Korea govern-
ment (No. M2009A010800007). This study was supported by a grant (Hanyang
Univ.) from the Fundamental R&D Program for Core Technology of Materials

Metal Complex Derivatives for Color Filter Pigments
87
funded by the Ministry of Knowledge Economy (MKE), Republic of Korea. This
work was supported by the Technology Innovation Program funded by the Ministry
of Knowledge Economy (MKE, Korea). This study was supported by a grant
from the Strategy Project funded by the Ministry of Knowledge Economy (MKE),
Republic of Korea.
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