New copper complex derivatives including bis-dipyrrinato ligand for color filter pigments

Article abstract of DOI:10.1080/15421406.2012.688596

Four red compounds for color filter (CF) pigments in which phenyl, 4-chloro-phenyl, 4-fluoro-phenyl and pentafluorophenyl groups are substituted to 5-position of dipyrrinato group based on bis-dipyrrinato ligand were synthesized, and physical properties f

Full text of DOI:10.1080/15421406.2012.688596

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New Copper Complex Derivatives
Including Bis-Dipyrrinato Ligand for Color
Filter Pigments
Junghyo Park a , Hawnkyu Shin a , Youngil Park a , Yunseop Shin a ,
Seungho Kim a & Jongwook Park a
a Department of Chemistry, The Catholic University of Korea,
Bucheon, 420-743, Korea
Published online: 02 Aug 2012.
To cite this article: Junghyo Park , Hawnkyu Shin , Youngil Park , Yunseop Shin , Seungho
Kim & Jongwook Park (2012) New Copper Complex Derivatives Including Bis-Dipyrrinato
Ligand for Color Filter Pigments, Molecular Crystals and Liquid Crystals, 563:1, 43-49, DOI:
10.1080/15421406.2012.688596
To link to this article: http://dx.doi.org/10.1080/15421406.2012.688596
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Mol. Cryst. Liq. Cryst., Vol. 563: pp. 43–49, 2012
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2012.688596
New Copper Complex Derivatives Including
Bis-Dipyrrinato Ligand for Color Filter Pigments
JUNGHYO PARK, HAWNKYU SHIN, YOUNGIL PARK,
YUNSEOP SHIN, SEUNGHO KIM, AND JONGWOOK PARK∗
Department of Chemistry, The Catholic University of Korea,
Bucheon, 420-743, Korea
Four red compounds for color filter (CF) pigments in which phenyl, 4-chloro-phenyl, 4-
fluoro-phenyl and pentafluorophenyl groups are substituted to 5-position of dipyrrinato
group based on bis-dipyrrinato ligand were synthesized, and physical properties from
changing the substitution groups of the synthesized materials were systematically exam-
ined. The UV-visible spectra of the synthesized materials showed maximum absorption
wavelengths of about 460∼477 nm in solution state and 510∼530 nm in film state,
indicating red color. It was confirmed that the extinction coefficient values (log ε) of all
the synthesized materials are very excellent at 4.7 or above. All HOMO levels measured
through cyclic voltammograms showed similar values at 5.4 through 5.5 eV, regardless
of the substitution group. They were also shown to possess high potential to be applied
as pigment for LCD color filter, since Tm and Td values of three synthesized materials
exhibit thermal stability higher than 250◦C. In film surface property, the synthesized
compounds showed smooth surface overall.
Keywords Bis(dipyrrinato)copper complex; color filter; molar extinction coefficiency;
pigment
Introduction
In the past, dyes and pigments have been mainly used for paints, inks, plastics, fabrics
and etc. [1–3]. However, recently with rapid development of display industry in the con-
temporary society along with the development of information technology industry, these
materials are extending their potential of application as the core material of color filter
(CF) that implements full color spectrum of liquid crystal display (LCD). Furthermore in
these days, the same dye and pigment materials are widely applied in image sensors which
are used in charge-coupled device (CCD) camera and web-camera [4]. The way dyes and
pigments work in CF is that when white-backlight is injected to CF, red, green and blue
pigments, it implements full color spectrum by respectively reflecting or absorbing light of
particular wavelength [5–7]. Therefore, since light of desired wavelength should be pen-
etrated massively and light of the remaining wavelengths be filtered to maximum extent,
the optical property required of pigments used in CF should have high molar extinction
coefficient on the wavelength that requires absorption [4]. Also, another property is that
∗Address correspondence to Prof. J. W. Park, Department of Chemistry/Display Research center,
The Catholic University of Korea, 43-1, Yeokgok, Wonmi, Bucheon, 420-743, Korea (ROK). Tel.:
(+82) 2-2164-4331. Fax: (+82)2-2164-4764. E-mail: hahapark@catholic.ac.kr
43

44
J. Park et al.
the improvement of thermal stability is required since thermal stability of 250◦C or above
is necessary during CF manufacturing process. The molecular design for new colorant
materials is mainly considered through this concept.
Bis(dipyrrinato)metal complex was first reported by Fischer in 1924 [8]. Thereafter,
many research groups synthesized many derivatives of bis(dipyrrinato) metal complex and
studied the change of optical property. However, there had not been significant reports on
fundamental researches on the potential of bis(dipyrrinato) metal complex derivatives for
use as material of color filter through electro-optical property. Therefore, in this study, new
red pigments based on bis(dipyrrinato) copper complex were synthesized where various
substitution groups like phenyl, 4-chloro-phenyl, 4-fluoro-phenyl and pentafluorophenyl
groups were substituted to 5-postion of dipyrrinato group (see Scheme 1). Also through
systematic investigation on the change in physical properties such as optical and thermal
properties by the structures, their potentials for use as color filter materials in LCD were
evaluated.
Scheme 1.
Experimental
Synthesis
2.1. Synthesis of Bis[5-(phenyl)-dipyrrinato]copper Complex (Cu(PPN)2). 2,2ꢀ-
(phenylmethylene)bis(1H-pyrrole) (1 g, 4.5 mmol) and 2,3-dichloro-5,6-dicyano-1,4-
benzoquinone (DDQ) (1.123 g, 4.95 mmol) were stirred in acetonitrile (AN) (20 ml)
at room temperature for 4 hours. They were then quenched with triethylamine (TEA)
(0.06 ml, 0.45 mmol). Saturated methanol solution of copper acetate (0.413 g, 2.25 mmol)
was added to the reaction mixture and stirred for 5 hours. After completion of the re-
action, the solvent was evaporated under vacuum and the product was extracted with
dichloromethane (CH2Cl2). The CH2Cl2 solution was washed with water and dried with
magnesium sulfate anhydrous (MgSO4). The solvent was evaporated to give Cu(PPN)2 as
green solid, which was recrystallized from dichloromethane (CH2Cl2) and methanol. (Yield
22%), C30H22CuN4, found C,71.79; H,4.41; N,11.11 calculated C,71.77; H,4.42; N,11.16,
FAB-Mass: 501 m/z

New Copper Complex Derivatives
45
2.2. Bis[5-(4-fluorophenyl)-dipyrrinato]copper Complex (Cu(4-FPN)2). The synthetic
procedure is similar to that of Cu(PPN)2. (Yield 48%), C30H20CuF2N4, found C,66.89;
H,3.79; N,10.40, calculated C,66.97; H,3.75; N,10.41, FAB-Mass: 537 m/z
2.3. Bis[5-(pentafluorophenyl)-dipyrrinato]copper Complex (Cu(PFPPN)2). The syn-
thetic procedure is similar to that of Cu(PPN)2. (Yield 48%), C30H12CuF10N4, found
C,53.24; H,1.75; N,8.24, calculated C,52.84; H,1.77; N,8.22, FAB-Mass: 681 m/z
2.4. Bis[5-(4-chlorophenyl)-dipyrrinato]copper Complex (Cu(4-ClPN)2). The synthetic
procedure is similar to that of Cu(PPN)2. (Yield 18%), C30H20Cl2CuN4, found C,63.17;
H,3.57; N,9.75, calculated C, 63.11; H, 3.53; N, 9.81, FAB-Mass: 569 m/z
Measurements
1H-NMR spectra were recorded on Bruker, Advance 300 and 500, and fast atom bombard-
ment (FAB) mass spectra were recorded by JEOL, JMS-AX505WA, HP5890 series II. The
optical absorption spectra were obtained using HP 8453 UV-VIS-NIR spectrometer. The
melting temperatures (Tm) and degradation temperatures (Td) of the compounds were mea-
sured by carrying out differential scanning calorimetry (DSC) under nitrogen atmosphere
using a DSC2910 (TA Instruments) and thermogravimetric analysis (TGA) using a SDP-
TGA2960 (TA Instruments). The redox potentials of the compounds were determined with
cyclic voltammetry (CV) using AUTOLAB/PG-STAT128N model system with a scanning
rate of 100 mV/s. We used synthesized material coated ITO as working electrode, a saturated
Ag/AgNO3 as a reference electrode and Acetonitrile (AN) with 0.1M tetrabutylammonium
tetrafluoroborate (TBAT) as electrolyte. Ferrocene was used for potential calibration and
reversibility criteria.
Results and Discussion
The synthesized materials, substitution groups existing in 5-position of dipyrrinato moiety
in bis(dipyrrinato)copper complex core, are the new red pigments that connect phenyl,
4-chloro-phenyl, 4-fluoro-phenyl and pentafluorophenyl groups, and their molecular struc-
tures are depicted in Scheme 1.
Some metal complexes can be paramagnetic. This can lead the very large shifts and
unobservable data in the NMR resonances [9–11].
As for the specific synthesis method, as shown in Scheme 2, the substituted aromatic
aldehyde and pyrrole were reacted at room temperature under presence of trifluoroacetic
acid (TFA), synthesizing the two substituted dipyrromethane 1. After oxidizing the synthe-
sized 1 compound with DDQ and reacting it with copper acetate, final Cu complexes were
synthesized through combination with Cu metal and ligands.
Optical properties of the synthesized materials were evaluated by UV-visible absorption
(UV-Vis.) spectra and were summarized in Fig. 1 and Table 1. Cu(PPN)2, Cu(4ClPN)2, and
Cu(4FPN)2 to which phenyl, 4-chloro-phenyl and 4-fluoro-phenyl groups were substituted
showed maximum absorption wavelengths between 463 and 467 nm and shoulder peaks
of about 500 nm. On the other hand, Cu(PFPPN)2 to which pentafluorophenyl group was
substituted showed maximum absorption wavelength of 477 nm and shoulder peak of
513 nm, indicating that both maximum peak and shoulder peak were red-shifted by about
10 nm or more, respectively. This may be due to strong electron withdrawing effect of
five fluoride atoms attached to phenyl ring. In addition, the results of the UV-vis spectra

46
J. Park et al.
Scheme 2.
were measured from the films which were prepared by through chloroform (1 w/wt%)
solution and spin-coating method. The maximum absorption wavelengths of Cu(PPN)2,
Cu(4ClPN)2 and Cu(4FPN)2 were about 513
1 nm, and in the case of Cu(PFPPN)2,
maximum absorbing wavelength appeared at 530 nm, which is about 18 nm red-shifted
Figure 1. UV-Visible absorption spectra of Cu(PPN)2(ꢀ), Cu(4-ClPN)2(ꢁ), Cu(4-FPN)2 (◦) and
Cu(PFPPN)2 (ꢂ) in THF solution.

New Copper Complex Derivatives
47
Table 1. Optical properties of synthesized materials
Solutiona
Compounds UVmax (nm) UVmax (nm) (L/mol·cm)
Film
Log ε
HO MO LU MO Band Gap
(eV)
(eV)
(eV)
Cu(PPN)2
463
467
466
477
512
513
514
530
4.89
4.89
4.81
4.78
5.48
5.51
5.46
5.51
3.25
3.28
3.24
3.35
2.23
2.23
2.22
2.16
Cu(4ClPN)2
Cu(4FPN)2
Cu(PFPPN)2
a: THF solution (1 × 10−5 M).
compared with Cu(PPN)2 (see Fig. 2). However, all the synthesized pigments showed red
color in appearance [1].
As a result of measuring the extinction coefficient (ε) of the synthesized materials
in THF solution, all pigments showed very high values of log scale 4.78 or higher (see
Table 1), which are very excellent values beyond average (log ε: 4.24) of the derivatives
of diketopyrrolopyrrole (DPP), major red pigment widely known as a commercial material
[12]. It means that such high molar extinction coefficient can be applied as a pigment for
color filter of LCD.
Using the band gap calculated through cyclic voltammogram (CV) and UV-vis. spectra
of the synthesized materials, HOMO and LUMO levels were calculated (see Table 1). In the
case of HOMO levels of the synthesized materials, all compounds showed similar values of
5.4∼5.5 eV. However, LUMO levels of Cu(PPN)2, Cu(4ClPN)2 and Cu(4FPN)2 had similar
values of about 3.2eV, but Cu(PFPPN)2 substituted by pentafluorophenyl group with large
electron-accepting ability showed LUMO level of 3.35 eV, indicating a decrease of about
0.15 eV.
Figure 2. UV-Visible absorption spectra of Cu(PPN)2(ꢀ), Cu(4-ClPN)2(ꢁ), Cu(4-FPN)2(◦), and
Cu(PFPPN)2(ꢂ) in spin-coated (1 w/w% CHCl3 solution) films on glass substrate.

48
J. Park et al.
Table 2. Thermal properties of synthesized materials
Compounds
Tm/◦C
Td/◦C
Cu(PPN)2
276
262
—
270
262
234
277
Cu(4ClPN)2
Cu(4FPN)2
Cu(PFPPN)2
—
Tm: melting-point temperature, Td: decomposition temperature (5% weight loss).
As for thermal stability of the synthesized materials, Td values of Cu(PPN)2,
Cu(4ClPN)2, Cu(4FPN)2 and Cu(PFPPN)2 were respectively 270, 262, 234, and 277◦C.
For Tm, Cu(4FPN)2 and Cu(PFPPN)2 did not show clear values of Tm and Cu(PPN)2 and
Cu(4ClPN)2 respectively had 276 and 262◦C. In conclusion, Cu(PPN)2, Cu(4ClPN)2 and
Cu(PFPPN)2, excluding Cu(4FPN)2, possess relatively high thermal stability (see Table 2).
This is equivalent to the level of thermal stability higher than 250◦C, which is the highest
temperature applied during LCD manufacturing process. This material has high potential
for application as a pigment for LCD.
In order to evaluate thin film property of the synthesized compounds, scanning electron
microscopy (SEM) was examined after spin-coating the compounds onto a glass (see Fig. 3).
Commercial product called Red 254 exhibited a rough surface shown in Fig. 3(a), but the
synthesized compounds generally showed smooth surfaces.
Figure 3. SEM images (×8000) of bis(dipyrrinato)copper complex derivatives and Red 254: spin-
coating (0.1 wt%, THF solution) films on glass substrate, (a) Red 254, (b) Cu(PPN)2, (c) Cu(4ClPN)2,
(d) Cu(4FPN)2, (e) Cu(PFPPN)2.

New Copper Complex Derivatives
49
Conclusions
Four red compounds for CF pigment substituted with phenyl, 4-chloro-phenyl, 4-
fluoro-phenyl and pentafluorophenyl groups to 5-position of dipyrrinato group based on
bis(dipyrrinato)copper complex were synthesized. UV-visible absorption spectra of the
synthesized materials showed maximum absorbing wavelengths of about 460∼477 nm in
solution state and 510∼530 nm in film state, indicating red color. Extinction coefficient
values (log ε) of all the synthesized materials were confirmed to be very excellent at 4.7 or
above. In addition, all HOMO levels measured through CV showed similar values between
5.4 and 5.5 eV regardless of substitution group. In addition, since Tm and Td values of
three synthesized materials showed thermal stability higher than 250◦C, they possess high
potential for application as pigments for LCD color filter. In thin film surface property, the
synthesized compounds generally showed smooth surface.
Acknowledgment
This work was supported by the Catholic University of Korea, Research Fund, 2011 and by
the National Research Foundation of Korea (NRF) grant funded by the Korea government
(MEST) (No. 2012001846).
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