Facile synthesis and characterization of novel coronene chromophores and their application to LCD color filters

Article abstract of DOI:10.1016/j.dyepig.2011.11.009

New coronene derivatives, diphenylcoronene tetracarboxdiimide and monophenylbenzoperylene tetracarboxdiimide, were synthesized from N,N'-bis(2,6-diisopropylphenyl)-1,7-dibromoperylene-3,4,9,10-tetracarboxdiimide via a one-step reaction. The suggested synthetic route is the simplest and most economical among the methods to extend the aromatic systems along the short molecular axis of perylene. The synthesized molecules exhibited superior stability and color strength as yellow chromophores. They were characterized by significant hypsochromic shifts of the absorption compared to perylene tetracarboxdiimide and high fluorescence quantum yields.

Full text of DOI:10.1016/j.dyepig.2011.11.009

Dyes and Pigments 94 (2012) 34e39
Contents lists available at SciVerse ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Facile synthesis and characterization of novel coronene chromophores
and their application to LCD color filters
,
Jun Choi a, Woosung Lee a, Chun Sakong a, Sim Bum Yuk a, Jong S. Park b, Jae Pil Kim a
*
a Department of Materials Science and Engineering, Seoul National University, Seoul 151-744, Republic of Korea
b Department of Polymer & Textile Industry, Dong-A University, Busan 604-714, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
New coronene derivatives, diphenylcoronene tetracarboxdiimide and monophenylbenzoperylene tetra-
carboxdiimide, were synthesized from N,N0-bis(2,6-diisopropylphenyl)-1,7-dibromoperylene-3,4,9,10-
tetracarboxdiimide via a one-step reaction. The suggested synthetic route is the simplest and most
economical among the methods to extend the aromatic systems along the short molecular axis of
perylene. The synthesized molecules exhibited superior stability and color strength as yellow chromo-
phores. They were characterized by significant hypsochromic shifts of the absorption compared to
perylene tetracarboxdiimide and high fluorescence quantum yields.
Received 27 September 2011
Received in revised form
17 November 2011
Accepted 19 November 2011
Available online 27 November 2011
Keywords:
Coronene
Ó 2011 Elsevier Ltd. All rights reserved.
Benzoperylene
One-step reaction
Chromophores
Fluorescence
Color filters
1. Introduction
they are considerably stable and show high color strengths
compared to other yellow chromophores. In general, stability and
Rylene tetracarboxdiimide derivatives including Perylene-
3,4,9,10-tetracarboxdiimide are useful chromophores exhibiting
exceptional chemical, thermal, and photochemical stability with
high extinction coefficients [1]. They have a wide range of appli-
cations, such as reprographic processes [2], photovoltaic cells [3],
fluorescent solar collectors [4], energy relaying dyes for solar cells
[5], optoelectronic devices [6], light emitting diodes [7] as well as
usual colorant usage. Therefore, diverse methodologies to func-
tionalize the aromatic core of perylene tetracarboxdiimide have
been reported to extend the range of application of these chro-
mophores as functional dyes [8e13]. The extension of the
aromatic systems along the long molecular axis of perylene
usually induced bathochromic shifts of the absorption spectra
with increasing extinction coefficients [8]. However, their
absorption maxima shifted hypsochromically when the aromatic
systems of those molecules were enlarged along the short
molecular axis, such as coronenetetracarboxdiimides 1 (Fig. 1) [9].
These coronene derivatives can be extremely valuable because
color strength of dye molecules often increase with increasing size
of the aromatic system, which inevitably causes a bathochromic
shift in absorption [10].
Several synthetic routes from perylene to coronene have been
reported. The core extension of perylenediimides using a Dielse
Alder reaction with maleic anhydride [11] and synthesizing bisal-
kynyl substituted perylenediimides and their successive cyclization
to coronene were reported [9]. In addition, the further core
expanded structure, dibenzocoronene 2 (Fig. 1), was synthesized
by palladium-catalyzed dehydrobromination after Suzuki-coupling
of 2-bromophenylboronic acid at the bay position of bromo-
substituted perylene [12]. This is also possible by palladium-
assisted cycloaddition of benzyne [8] or by the photocyclization
of Suzuki-coupled phenylboronic acid [13]. However, all these
synthetic methods were limited to some degree by the moderate
yields, side reactions, and severe synthetic conditions.
In this study, new coronene derivatives were synthesized
through a novel simple one-step synthetic route and their charac-
teristics were discussed as well. In particular, their properties for
yellow compensating dyes for color filters, which converts the
white backlight into red (R), green (G) and blue (B) colored lights in
LCD display panel, were investigated.
* Corresponding author. Tel.: þ82 2 880 7187; fax: þ82 2 880 7238.
E-mail address: jaepil@snu.ac.kr (J.P. Kim).
0143-7208/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2011.11.009

J. Choi et al. / Dyes and Pigments 94 (2012) 34e39
35
R
N
R
N
O
O
O
O
O
R'
R'
O
O
N
R
O
O
O
O
N
R
1
2
N
O
N
HN
O
O
N
O
N
O
N
NH
N
O
O
N
O
O
N
O
DC-R
DC-G
Fig. 1. Coronene carboximide derivatives and prepared dyes for color filters.
2. Experimental
2.2. Synthesis
2.1. Materials and instrumentation
N,N0-Bis(2,6-diisopropylphenyl)-1,7-dibromoperylene-3,4,9,10-
tetracarboxdiimide 5, N,N0-Bis(2,6-diisopropylphenyl)-1-bromopery
lene-3,4,9,10-tetracarboxdiimide 50, and DC-R were synthesized
according to the previously reported procedures [14]. DC-G was
synthesized according to the procedures reported elsewhere [15].
1-phenylvinylboronic acid, Pd(PPh3)4, and Na2CO3 purchased
from SigmaeAldrich were used as received. All the other reagents
and solvents were of reagent-grade quality and obtained from
commercial suppliers. Transparent glass substrates were provided
by Paul Marienfeld GmbH & Co. KG. Commercial acrylic binder
LC20160 was supplied by SAMSUNG Cheil industries Inc.
2.2.1. N,N0-Bis(2,6-diisopropylphenyl)-5,11-diphenylcoronene-
2,3,8,9-tetracarboxdiimides 7
1H NMR and 13C NMR spectra were recorded on a Bruker
Avance 500 spectrometer at 500 MHz using chloroform-d
and TMS, as the solvent and internal standard, respectively.
Matrix Assisted Laser Desorption/Ionization Time Of Flight
(MALDI-TOF) mass spectra were collected on a Voyager-DE STR
A deaerated mixture of EtOH (5.79 mL), benzene (33.12 mL), H2O
(8.13 mL) was added to a solid mixture of 5 (1.0 g, 1.15 mmol),
1-phenylvinylboronic acid (0.68 g, 4.6 mmol), Pd(PPh3)4 (66.57 mg,
5.0 mol%), and Na2CO3 (1.2 g,11.5 mmol) under nitrogen. The mixture
was reacted at 80 ꢀC for 120 h. The reaction was quenched by the
addition of water. The mixture was extracted with dichloromethane
several times. The combined organic layer was dried over anhydrous
MgSO4 and concentrated under reduced pressure to provide a crude
solid. The crude solid was further purified by column chromatog-
raphy on silica gel using dichloromethane as the eluent. The band
containing a trace of compounds synthesized from tribrominated
diimide could be separated firstly. Then, the second band containing
yellow compound 7 was collected.
Biospectrometry Workstation with
a-cyano-4-hydroxy-cynamic
acid (CHCA) as the matrix. Elemetal analysis was done on CE
Instrument EA1112. Absorption and transmittance spectra were
measured using an HP 8452A spectrophotometer. Fluorescence
spectra were measured using a Shimadzu RF-5301PC spectroflu-
orometer. Chromatic characteristics of the color filters were
analyzed on a Scinco color spectrophotometer. Thermogravi-
metric analysis (TꢁG1A) was conducted under nitrogen at a heating
rate of 10ꢀC min
Analyzer 2050.
using a TA Instruments Thermogravimetric
Yield 52.1%; Mp > 300 ꢀC (decomp.). 1H NMR(500 MHz, CDCl3):
d
¼ 1.24 (d, J ¼ 6.5 Hz, 24H), 2.99 (septet, J ¼ 40.0 Hz, 4H), 7.42

36
J. Choi et al. / Dyes and Pigments 94 (2012) 34e39
(d, J ¼ 8.5 Hz, 4H), 7.54 (t, J ¼ 9.2 Hz, 2H), 7.70 (t, J ¼ 9.0 Hz, 2H), 7.76
(t, J ¼ 13.5 Hz, 4H), 7.97 (t, J ¼ 10.2 Hz, 4H), 9.27 (s, 2H), 10.17 (s, 2H),
129.35, 129.42, 129.93, 130.05, 130.37, 130.44, 131.15, 131.21, 131.46,
131.76, 139.38, 139.49, 142.93, 143.13, 145.96, 146.07, 164.99, 165.13;
MALDI-TOF MS: m/z 911.07 (100%, [M þ Hþ]); Found: C, 84.52;
H, 5.45; N, 3.10%. Calc. for C64H50N2O4: C, 84.37; H, 5.53; N, 3.07%.
10.22 (s, 2H); 13C NMR(126 MHz, CDCl3):
d
¼ 23.98, 24.34, 29.52,
29.92, 122.20, 122.38, 124.00, 124.26, 124.39, 124.49, 125.21, 129.03,
Scheme 1. Synthesis of coronene carboximide derivatives.

J. Choi et al. / Dyes and Pigments 94 (2012) 34e39
37
2.2.2. N,N0-Bis(2,6-diisopropylphenyl)-5-phenylbenzoperylene-
2,3,8,9-tetracarboxdiimides 8
removed because both isomers react with phenylvinylboronic acid to
form the same desired product 7, and 1,7-dibromoperylenediimide 5
and mono-bromoperylenediimide 50 could be obtained from the
same crude product after column chromatography [14]. The yield of
monophenylbenzoperylene 8 (66.8%) was higher than that of
diphenylcoronene 7 (52.1%) because there were more side products
such as mono-substituted compound when diphenylcoronene 7 was
synthesized. In column chromatography process of diphenylcor-
onene 7, the first band of the eluent was carrying the impurity reacted
from the trace of tribrominated diimide, and the second band was
for diphenylcoronene 7. Monophenylbenzoperylene 8 was also ob-
tained as a side product at the fourth band of the eluent, and the
sixth band was for N,N0-bis(2,6-diisopropylphenyl)-perylene-
3,4,9,10-tetracarboxdiimide 9, all bromines were removed. The
described synthetic route is the simplest and most economical
method with a considerable yield under mild conditions.
8 was synthesized in the same manner with 7 using 50 (1.0 g,
1.27 mmol), 1-phenylvinylboronic acid (0.38 g, 2.54 mmol),
Pd(PPh3)4 (66.57 mg, 5.0 mol%), and Na2CO3 (1.2 g, 11.5 mmol).
Yield 66.8%; Mp > 300 ꢀC (decomp.). 1H NMR(500 MHz, CDCl3):
d
¼ 1.21 (d, J ¼ 7.0 Hz, 24H), 2.84 (septet, J ¼ 38.5 Hz, 4H), 7.38 (dd,
J ¼ 26.2 Hz, 4H), 7.52 (m, J ¼ 18.4 Hz, 2H), 7.61 (t, J ¼ 9.9 Hz,1H), 7.67
(t, J ¼ 14.5 Hz, 2H), 7.77 (t, J ¼ 9.4 Hz, 2H), 8.81 (s, 1H), 9.22
(d, J ¼ 8.2 Hz, 2H), 9.49 (d, J ¼ 10.8 Hz, 2H), 9.56 (s, 1H), 9.63 (s, 1H);
13C NMR(126 MHz, CDCl3):
d
¼ 24.25, 24.32, 29.55, 29.92, 122.41,
122.60, 123.22, 123.62, 123.71, 124.30, 124.42, 124.49, 124.73,
124.88,126.08,128.02,128.10,128.93, 129.03, 129.31,129.72,129.86,
129.88, 130.00, 130.25, 130.75, 130.92, 130.96, 131.10, 133.50, 133.94,
134.29, 135.21, 138.91, 143.15, 145.91, 145.96, 164.17, 164.26, 164.35;
MALDI-TOF MS: m/z 811.09 (100%, [M þ Hþ]); Found: C, 83.12;
H, 5.58; N, 3.42%. Calc. for C56H46N2O4: C, 82.94; H, 5.72; N, 3.45%.
3.2. Photophysical properties of dyes
2.3. Preparation of dye-based inks and color filters
Both coronene derivatives 7 and 8 are highly soluble in most
organic solvents, such as dichloromethane, hexane, and toluene
since the aggregation between dyes is suppressed by steric
hindrance of the phenyl groups at the bay positions as well as the
diisopropylphenyl groups at the terminal positions, which are
distorted from the plane of the main body of the coronene deriv-
atives [14]. Monophenylbenzoperylene 8 shows the main absorp-
tion maximum at 472 nm (Fig. 2), which originated from the typical
vibronic structure of perylene, giving this chromophore a very
strong and vivid yellow color. The shape of this characteristic main
peak is analogous to that of dibenzocoronene 2, but hyp-
sochromically shifted by approximately 22 nm [12]. Mono-
phenylbenzoperylene 8 is an ideal yellow chromophore since its
main peak is very sharp and there is no absorption over 500 nm.
The dye-based ink for a color filter was composed of the
cyclohexanone (3.2 g), acrylic binder (1.4 g), and dye (0.1 g).
The prepared dye-based inks were coated on a transparent glass
substrate using a MIDAS System SPIN-1200D spin coater. The
coating speed was initially 100 rpm for 5 s, which was then
increased to 500 rpm and kept constant for 20 s. The wet dye-
coated color filters were then dried at 80 ꢀC for 20 min, prebaked
at 150 ꢀC for 10 min, and postbaked at 230 ꢀC for 1 h. After each
step, the coordinate values of the color filters were measured.
2.4. Measurement of thermal stability
Thermal stability of the synthesized dyes was evaluated by
thermogravimetry (TGA). The prepared dyes were heated to 110 ꢀC
and held at that temperature for 10 min to remove residual water
and solvents. The dyes were then, heated to 220 ꢀC and held at that
temperature for 30 min to simulate the processing thermal
conditions of color filter manufacturing. The dyes were finally
heated to 400 ꢀC to determine their degradationꢁt1emperature. The
temperature was raised at the rate of 10ꢀC min under nitrogen
atmosphere.
The extinction coefficient of monophenylbenzoperylene
8 at
472 nm (ε ¼ 65,688 Mꢁ1 cmꢁ1) is similar to that of dibenzocoronene
2 at 494 nm (ε ¼ 66,000 Mꢁ1 cmꢁ1) and higher than that of coro-
nene 1 at 428 nm (ε ¼ 62,000 Mꢁ1 cmꢁ1) [12]. Diphenylcoronene 7
shows its main absorption maximum at a much shorter wavelength
(426 nm, ε ¼ 59,988 Mꢁ1 cmꢁ1) with minor absorption at
approximately 512 nm (Fig. 2). The shape of these absorption peaks
is similar to that of coronene 1, which has an alkyl chain introduced
at the R0 position, but the distance between the two absorption
maxima is slightly different [9]. The minor absorption around
To check the thermal stability of the dyes in color filters, the
fabricated color filters were heated to 230 ꢀC for 1 h in a forced
convection oven (OF-02GW Jeiotech Co., Ltd.). The color difference
values (DEab) before and after heating were measured on a color
spectrophotometer (Scinco colormate) in CIE L’a’b’ mode.
3. Results and discussion
0.8
0.6
0.4
0.2
0.0
0.8
0.6
0.4
0.2
0.0
7(Absorbance)
8(Absorbance)
7(Fluorescence)
8(Fluorescence)
472 497
426
524
3.1. Synthesis
Different types of linear alkyl chains were introduced selectively
at the R0 position of coronenetetracarboxdiimides 1 through reac-
tions c and d of Scheme 1 as described in literature [9]. In this
reference, sterically demanding substituents, such as tert-butyl or
a phenyl group, could not be introduced because the bulky substit-
uents at the CeC triple bond restricted the cyclization reaction.
However, as shown in the experimental section of this paper, phe-
nylvinylboronic acid, inherent with an aryl group, was reacted
successfully with bromo-substituted perylenediimides 5, and 50
under similar conditions to Suzuki-coupling and spontaneously
cyclized to afford two novel compounds diphenylcoronene tetra-
carboxdiimide 7 and monophenylbenzoperylene tetracarboxdiimide
8. The conveniences of this synthesis are that the 1,6-isomer of 1,7-
350
400
450
500
550
600
650
Wavelength (nm)
Fig. 2. Absorption and fluorescence spectra of compounds
7
and
8
in CH2Cl2
dibromoperylene tetracarboxdiimide
5
does not have to be
(10ꢁ5 mol Lꢁ1).

38
J. Choi et al. / Dyes and Pigments 94 (2012) 34e39
Table 1
100
Transmittance of the spin-coated color filters.
DC-G
Prepared dyes
lmax(nm)
Transmittance(%)
80
DC-G + 8
DC-R
626
628
498
524
95.89
94.78
85.05
DC-R þ 8
DC-G
60
DC-G þ 8
85.39
40
512 nm gives diphenylcoronene 7 a somewhat dull color in solution
compared to the much brighter and greener color of mono-
phenylbenzoperylene 8. The absorption spectra of these molecules
make them very suitable as yellow compensating dyes for LCD color
filters. In particular, monophenylbenzoperylene 8 can be used to
cut off the undesirable transmittance in short wavelength range of
red color, and extremely useful for making the green color with
narrow half-band width [16].
20
0
400
450
500
550
600
650
700
Wavelength(nm)
Diphenylcoronene 7 and monophenylbenzoperylene 8 show
fluorescence maxima at 524 and 497 nm, respectively (Fig. 2). Their
quantum yields are 82 and 86%, respectively, which are much
higher than other yellow fluorophores, e.g. acridine yellow, which
has a fluorescence quantum yield of 47% [17]. In particular, diphe-
nylcoronene 7 can be an excellent donor dye for DSSCs using För-
ster resonance energy transfer (FRET) because the emission of
Fig. 4. Transmittance spectra of green spin coated color filters. (For interpretation of
the references to colour in this figure legend, the reader is referred to the web version
of this article.)
transmittance of given red dye effectively with maintenance of the
desired transmittance range. This kind of compensation effect is
more prominent in green color. The main dyes for green color,
such as DC-G, transmit wide range of wavelength to have dull
bluish green color. However, the dye composite including mono-
phenylbenzoperylene 8 exhibited sharp transmittance spectrum cut
off under 500 nm as shown in Fig. 4. Therefore, vivid and clear green
color could be realized by blending monophenylbenzoperylene 8.
With less amount of the green dye in the mixture with the yellow
dye, lmax of the color filter red shifted about 20 nm to be closer to the
green color for conventional LCD color filters [16].
Table 2 and Fig. 5 shows the coordinate values of spin coated
color filters. The coordinate values of DC-R were rarely affected by
blending of monophenylbenzoperylene 8, but the x value of DC-G
was increased to be close to the conventional green coordinate
(0.274, 0.572) of the LCD color filters.
diphenylcoronene
7 is strong and barely overlaps with the
absorption range [18].
3.3. Spectral and chromatic properties of spin coated color filters
Currently, dyes are extensively investigated to replace pigments
in LCD manufacturing process since there are growing needs for
enhancing the picture quality [14]. The dye-based color filters have
superior transmittance compared to the pigment-based one because
dyes dissolved in the media have a smaller particle size, which leads
to less light scattering [19]. Monophenylbenzoperylene 8 can make
ideal transmittance spectra of red and green color filters when used
as a yellow compensating dye, shown at Table 1, Fig. 3, and 4. The
common red dyes, such as DC-R, which have undesirable trans-
mittance under 500 nm as shown in Fig. 3 can not be solely used to
color filters without yellow compensating dye [14]. Mono-
3.4. Thermal stability of dyes and spin coated color filters
phenylbenzoperylene
8 absorbing under 500 nm intensively
without any residual absorption over 500 nm can cut off undesirable
Although the dyes have superior optical properties than the
pigments, they were hardly applied for LCD color filters owing to
their inferior thermal stability. For dyes to be used as color filters,
they should endure temperature of 220 ꢀC, which is the current
highest temperature in the LCD manufacturing process, without
significant weight loss [20,21]. The synthesized novel dyes 7 and 8
have more rigid structures than other yellow chromophores to be
suitable for the colorants of LCD color filters. However, their
thermal stabilities are somewhat different according to the degree
of substitution. In our earlier report, the 1,7-di(substituted) per-
ylenediimides exhibited lower thermal stability than the mono-
substituted one due to the higher core twisting of their main
body resulted from bulky aryl substituents at both side bay
100
DC-R
DC-R + 8
80
60
40
20
0
Table 2
The coordinate values corresponding to the CIE 1931 chromaticity diagram and the
color difference values of the spin coated color filters.
400
450
500
550
600
650
700
750
Prepared dyes
Y
x
y
6Eab
Wavelength(nm)
DC-R
25.01
24.33
54.28
58.54
0.640
0.631
0.205
0.286
0.334
0.339
0.572
0.563
0.752
1.04
1.69
1.77
DC-R þ 8
Fig. 3. Transmittance spectra of red spin coated color filters. (For interpretation of the
references to colour in this figure legend, the reader is referred to the web version of
this article.)
DC-G
DC-G þ 8

J. Choi et al. / Dyes and Pigments 94 (2012) 34e39
39
4. Conclusions
In summary, we have successfully synthesized two novel
compounds diphenylcoronene 7 and monophenylbenzoperylene 8
by a simple one-step reaction. These chromophores are stable,
have largely hipsochromic shifted absorption peaks compared to
perylene-3,4,9,10-tetracarboxdiimide and exhibit strong, bright
emission. They can be used as good yellow chromophores or fluo-
rophores for a wide range of applications according to their
characteristic range of absorption and emission peaks. While
diphenylcoronene 7 draws attention to be applied for energy
relaying dye of DSSC, monophenylbenzoperylene 8 was success-
fully applied as a yellow compensating dye for LCD color filters.
Acknowledgments
This work was supported by a grant from the Fundamental R&D
Program for Core Technology of Materials funded by the Ministry of
Knowledge Economy, Republic of Korea.
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D
8 were less than 3 desired for LCD manufacturing process, as
shown in Table 2.