Novel, soluble diphenyl-diketo-pyrrolopyrroles: Experimental and theoretical study

Article abstract of DOI:10.1016/j.dyepig.2009.07.014

Derivatives of diphenyl-diketo-pyrrolopyrrole, possessing electron-donating or withdrawing groups in the p-position of the phenyl, were synthesized and studied using optical characterization (absorption, fluorescence, time-resolved fluorescence) and quant

Full text of DOI:10.1016/j.dyepig.2009.07.014

Dyes and Pigments 84 (2010) 176–182
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Novel, soluble diphenyl-diketo-pyrrolopyrroles: Experimental
and theoretical study
,
b
c
a
d
M. Vala a , J. Vynuchal , P. Toman , M. Weiter , S. Lunak Jr.
*
ˇ
ˇ ´
a
ˇ
Faculty of Chemistry, Brno University of Technology, Purkynova 464/118, CZ-612 00 Brno, Czech Republic
b Research Institute of Organic Syntheses, Rybitv´ı 296, CZ-533 54 Rybitv´ı, Czech Republic
c
ꢀ
Institute of Macromolecular Chemistry v. v. i., Academy of Sciences of the Czech Republic, Heyrovsky Sq. 2, CZ-162 00 Prague, Czech Republic
Faculty of Chemical Technology, University of Pardubice, Studentska 95, CZ-530 09 Pardubice, Czech Republic
d
´
a r t i c l e i n f o
a b s t r a c t
Article history:
Derivatives of diphenyl-diketo-pyrrolopyrrole, possessing electron-donating or withdrawing groups in
the p-position of the phenyl, were synthesized and studied using optical characterization (absorption,
fluorescence, time-resolved fluorescence) and quantum chemical calculation. An increase in absorption
coefficient ꢀ105 dm3 molꢁ1 cmꢁ1 was observed using electron–donor groups; a bathochromic shift in
both absorption and luminescence peaks was observed as a result of increased conjugation. Soluble
derivatives were obtained by the introduction of alkyl groups (by N-alkylation) in the central pyrrolo-
pyrrole unit. Calculated phenyl torsion angles using HF and B3LYP methods showed that the loss of
Received 16 March 2009
Received in revised form
29 July 2009
Accepted 30 July 2009
Available online 14 August 2009
Keywords:
Diketo-pyrrolo-pyrrole
DPP
Photoluminescence
Fluorescence
Absorption
molecule planarity reduced the extent of overlap between the
p-orbitals of the central pyrrolopyrrole
unit and phenyls after N-alkylation. This treatment thus reduced both the bathochromic shift and
increased absorption coefficient. The presence of the donor or acceptor groups in itself does not influence
molecule planarity.
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
The key issue for the construction of any device either in the
form of thin film composed of DPP or incorporation of the DPP unit
Derivatives of 3,6-diphenyl-2,5-dihydro-pyrrolo[3,4-c]pyrrole-
1,4-dione, commonly referred to as DPPs, constitute an important
class of high-performance pigments [1–13] (parent molecule I in
Fig. 1). The compounds are endowed with brilliant shades (ranging
from yellow-orange to red-violet) and exhibit exceptional resis-
tance to chemical, heat, light, and weather. Furthermore, some of
their physical properties such as high melting points are excep-
tional in view of their very low Mr, in conventional pigment
molecule terms. It has been shown that DPP units introduced into
various materials, such as polymers [14–23] dendrimers [24],
polymer–surfactant complexes [25], and oligomers [26] results in
deeply coloured, highly photoluminescent [15–26] and electrolu-
minescent [19,20] materials. Owing to their interesting properties,
there is wide range of possible applications which have been
already investigated covering for example latent pigment [27],
charge generating materials for laser printers and information
storage systems [28–33], solid-state dye lasers [30] or gas detectors
[34,35].
into supporting matrix, is solubility. DPPs are insoluble in the
majority of common solvents. Whilst this is favourable for many
applications, the ability to solubilize the compounds would offer
the possibility of using solution-based techniques (spin-coating,
drop-casting, inject printing, etc.) to prepare devices from DPPs.
One reason for their insolubility is the existence of H-bonds
between the –NH group and oxygen. Since the basic DPP core is
perfectly planar, p–p electron overlap occurs in the solid state and
also contributes to their insolubility. These interactions can be so
strong as to impart colour change between the solid and dissolved
forms and influence other properties, such as fluorescence and
Stokes shift [36]. It is therefore clear, that modified solubility can be
achieved either through N-substitution and/or disruption of
molecular planarity [8].
A previous contribution by the present workers [37] discussed
the influence of N-alkylation on optical properties and employed
quantum chemical calculations to correlate the results with mole-
cule geometry. In this paper, electron-donating (IV–VIII) or
accepting (IX, X) groups were introduced at the p-position on the
phenyl so as to influence the electronic spectra of the compounds.
Further, some of these derivatives were N-alkylated in order to
modify their solubility (VII–X). These derivatives were compared
* Corresponding author. Tel.: þ420 541 149 411; fax: þ420 541 149 398.
E-mail address: vala@fch.vutbr.cz (M. Vala).
0143-7208/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2009.07.014

M. Vala et al. / Dyes and Pigments 84 (2010) 176–182
177
Fig. 1. The basic structure of 3,6-diphenyl-2,5-dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione (I), also known as DPP and the respective derivatives used in this study. The definition of
calculated torsion angles and
a
b.
with the parent (I) and N-alkylated (II, III) 3,6-diphenyl-2,5-dihy-
dro-pyrrolo[3,4-c]pyrrole-1,4-dione (Fig. 1). The observed optical
properties of both, the donor or acceptor substituted only and
substituted and N-alkylated derivatives are explained according to
the results obtained by quantum chemical calculations.
more pronounced. The loss of vibration structure can be attributed
to the increased dipole moment interacting with polar DMSO
solvent [39]. The dipole–dipole interaction of bi-substituted
derivatives with the completely non-planar structure is the most
pronounced. No dependency on the length of the alkyl used was
found in our previous work [37].
Introduction of electron-donating groups has significant effect
on the DPP absorption [40]. Increase of the absorption coefficient
2. Experimental
from
3
¼ 3.4 ꢂ 104 dm3 molꢁ1 cmꢁ1 of the parent compound I to
The UV–VIS absorption and photoluminescence spectra were
recorded in dimethylsufoxide (DMSO) purchased from Aldrich. The
molar absorption coefficients were calculated from the linear part
of the concentration dependence of absorption A ¼ f(c) measured in
5 cm quartz cuvette. The photoluminescence spectra and quantum
yields (PLQYs) were obtained according to the comparative method
[38], where for each test sample gradient of integrated fluorescence
intensity vs. absorbance PL ¼ f(A) is used to calculate the PLQY using
two known standards. The standards were previously cross-
calibrated to verify the method. This calibration revealed accuracy
better than w3%. The photoluminescence lifetime sPL was
measured using spectrograph and fast ICCD camera. The samples
were excited by second or third harmonic of Nd:YAG laser (532 or
355 nm) with light pulse time duration of w30 ps. The temporal
resolution of the system is approximately 25 ps.
3
¼ 1.3 ꢂ 105 dm3 molꢁ1 cmꢁ1 for compound V bi-substituted by
N,N-dimethylamin in p-position on phenyls, accompanied with
strong bathochromic shift (up to 55 nm), was observed (Fig. 2b).
This behaviour implies that charge separation occurs via electron
delocalization leading to creation of permanent dipole moment.
Therefore, the central part composed of H-chromophores behaves
as an electron-accepting group. Blurring of vibration structure in
case of the mono-substituted derivative (IV) was observed,
whereas for the bi-substituted (V) was not. We explain this finding
by the fact that due to symmetry of the bi-substituted derivative is
its resulting dipole moment smaller than for the mono-substituted
asymmetric derivative.
Similar increase of the absorption coefficient 3 value and change
of the peak position was achieved using piperidine group (VI)
(Fig. 2c). For this derivative, we studied also the impact of
N-alkylation. Introduction of one alkyl (VII) decreased the
3 only
3. Results and discussion
slightly. After addition of second alkyl (VIII) we observed almost
the same value as for the parent molecule (I). This was accompa-
nied by the hypsochromic shift and blurring of the vibration
structure. We propose the same mechanism as for the N-alkylated
only derivatives: the N-alkylation causes rotation of the phenyls
and consequently breaks the molecule symmetry and hence the
effective conjugation and increases the polarity.
To describe the influence of groups with the electron-with-
drawing character, derivatives with the halogen element (chloride)
were prepared. Since the aim was to prepare soluble derivatives we
will discuss the alkylated only derivatives. Fig. 2d compares the
3.1. Absorption
The spectral properties of the prepared derivatives are
compared in Figs. 2 and 3 and summarised in Table 1. The Influence
of N-substitution on the parent derivative I on absorption is
depicted in Fig. 2a. It can be seen, that insertion of an alkyl group
decreases molar absorption coefficient (hypochromic shift) and
simultaneously the longer wavelength maximum is shifted towards
higher energy region (hypsochromic shift). Furthermore, the
vibration structure is less pronounced. As was pointed out in our
previous paper [37], this is caused by torsion between pyrrolinone
central part and phenyl adjacent to the alkyl group and conse-
quently, is caused by loss of molecule planarity which is in turn
responsible for loss of effective conjugation. Since the addition of
second alkyl rotates also the second phenyl group, this effect is even
observed absorption coefficients
3. The introduction of the chloride
did not caused increase of . This is further evidence for the elec-
3
tron-accepting character of the central part. For the alkylated
derivatives we observed hypso- and hypochromic shift with the
loss of vibration structure again.

178
M. Vala et al. / Dyes and Pigments 84 (2010) 176–182
2x105
a
b
I
II
III
I
IV
V
4x104
1x105
2x104
5x104
0
0
300
400
500
600
300
400
500
600
wavelength (nm)
wavelength (nm)
2x105
1x105
c
d
I
I
IX
X
VI
VII
VIII
4x104
2x104
5x104
0
0
300
400
500
600
300
400
500
600
wavelength (nm)
wavelength (nm)
Fig. 2. The influence of N-alkyl substitution (a), and various donor (b, c) and acceptor (d) groups on the DPP central part on molar absorption coefficient.
a
1,0
0,8
0,6
0,4
0,2
0,0
1,0
0,8
0,6
0,4
0,2
0,0
b
I
II
III
I
IV
V
PL
PL
500
600
700
500
600
700
wavelength (nm)
wavelength (nm)
c
1,0
0,8
0,6
0,4
0,2
0,0
1,0
0,8
0,6
0,4
0,2
0,0
d
I
I
IX
X
V I
VII
VIII
PL
PL
500
600
700
500
600
700
wavelength (nm)
wavelength (nm)
Fig. 3. Comparison of photoluminescence spectra scaled using the PL quantum yields (PLQY$PL/PLmax) of N-alkylated (a), donor (b, c) and acceptor (d) substituted DPP derivatives.

M. Vala et al. / Dyes and Pigments 84 (2010) 176–182
179
Table 1
caused slight increase of the lifetime. As for the PLQY, the lifetime of
the donor-substituted derivatives decreased relative to the parent I.
Subsequent alkylation caused further reduction of the observed
lifetime. The longest lifetime was observed for chlorine substituted
derivative with broken symmetry (IX). The shortest lifetime was
observed for the compound IV mono-substituted by N,N-dime-
thylamin in p-position on phenyl. The lifetime of its bi-substituted
counterpart V was found to be higher.
Experimental values for molar absorption coefficient 3, position of absorption lAbs
and luminescence lPL peak maximums, Stokes shift DlStokes, and photoluminescence
quantum yield PLQY and lifetime sPL of the prepared DPPs in dimethylsulfoxide.
3
lAbs
lPL
DlStokes
(nm)
PLQY
(ꢁ)
sPL
(ns)
(dm3 molꢁ1 cmꢁ1
)
(nm)
(nm)
I
II
34 300
21 300
18 500
86 500
126 000
108 000
100 600
42 400
36 000
24 500
507
493
467
544
562
562
553
536
501
473
519
525
530
580
580
582
592
599
534
538
12
32
63
36
18
20
39
63
33
65
0.74
0.69
0.69
0.49
0.57
0.58
0.42
0.41
0.60
0.51
6.21
6.67
6.57
2.88
3.46
3.66
3.38
3.37
6.79
6.63
III
IV
V
VI
VII
VIII
IX
X
3.3. Quantum chemical study
3.3.1. Methods
The molecular conformations and absorption and luminescence
spectra of the synthesized derivatives were characterized by means
of the quantum chemical methods in order to better understand
the observed behaviour.
3.2. Photoluminescence
The molecular conformations were optimized by means of both
the Hartree-Fock (HF) and the hybrid HF/density functional theory
method B3LYP [41,42] at the 6–31G* level. The HF method usually
provides a fairly good description of the ground state molecular
conformations and is used for a major part of the present-day
calculations of the electronic properties. The latter method was
successfully used for the conformation study of many different
The photoluminescence (PL) spectra are compared in Fig. 3. The
PL intensity is recalculated using PL quantum yield (PLQY): the
measured spectra were normalised to its maximum and multiplied
by PL quantum yield (PL ¼ PLQY$PLl/PLMax). After this trans-
formation, the heights of the curves give direct evidence of the
efficiency of the light emission similarly to the
absorption.
3 in the case of light
p–conjugated systems [43–45]. Although the B3LYP method
requires more computational time than the HF method, its
computational requirements are much lower than demands of other
‘‘correlated’’ methods. The main difference of the HF and B3LYP
methods is that usually the former underestimates and the latter
slightly overestimates the electron delocalization and the degree of
conjugation in the conjugated molecules. The B3LYP conformations
are usually close to the conformations either calculated by the
Møller–Plesset method or obtained experimentally, see e.g. [46–48].
First excited states S1 of the studied derivatives were calculated
using time-dependent B3LYP (TD–B3LYP) method at the optimized
HF geometry. Time-dependent density functional methods recently
became an effective and rather accurate tool for single point calcu-
lations of electronic excitations in various, namely conjugated,
molecular systems [49–51]. However, this method is not suitable for
the excited state conformation optimization necessary for lumi-
nescence spectra calculations. For this reason, relaxed (exciton)
conformations of the S1 state were optimized by means of ab initio
configuration interaction method with single-excitation (CIS)
method. The exciton conformations were subsequently used for the
luminescence spectra calculations using TD–B3LYP method.
Keeping the same level of the calculations enabled determination of
For the N-alkylated derivatives, we found practically the same
PLQY in the accuracy range of the method. The Stokes shift was
increased from 12 nm for the parent derivative to 32 nm and 63 nm
for the monoalkylated and dialkylated derivatives, respectively. The
observed spectra (Fig. 3a) were characteristic by graduate loss of
mirror symmetry of absorption-fluorescence and vibronic struc-
ture. As was pointed out, the phenyl torsion due to the N-alkylation
is the main mechanism for this behaviour in polar DMSO.
Fig. 3b and c show the influence of electron-donating groups. The
mono-substituted derivative shows a smaller PLQY compared to
the di-substituted one. This is in accordance with the values of the
absorption coefficient
3: the polarity of the mono-substituted
molecule (IV) is higher compared to the symmetric V and VI. The
observed Stokes shifts confirm this hypothesis: for the mono-
substituted IV reaches the value 63 nm whereas for di-substituted V
and VI is only 18 nm and 20 nm, respectively. The N-alkylation
causes further decrease of PLQYaccompanied with increasing Stokes
shift similarly to the N-alkylated only derivatives. The electron-
withdrawing group (IX and X) causes analogous behaviour (Fig. 3d).
We also determined fluorescence lifetime sPL of the prepared
derivatives. Table 1 summarises the obtained results. All of the
observed fluorescence decays followed first order kinetics, i.e.
showed monoexponencial decay, see Fig. 4. The N-alkylation only
the Stokes shift
exciton state.
DEStokes and deformation energy Edef of the relaxed
3.3.2. Results
The calculated molecular parameters of the studied derivatives
are presented in Table 2. Comparison of the phenyl torsion angles
calculated by means of HF and B3LYP methods, respectively, shows
the same trends determined by both methods. The differences in
absolute values can be explained by the different electron delo-
calization predicted by these methods. The results show that the N-
alkylated derivatives possess significantly rotated phenyl groups of
the central DPP unit in the position adjacent to the alkyl, while the
basic I molecule is completely planar. Phenyl group rotation
10000
1000
1
0
significantly decreases the overlap between
p-orbitals of the
central DPP unit and the respective phenyl. As a result, the frontier
orbital (HOMO and LUMO) energetic levels are shifted and conse-
quently, absorption and luminescence spectra are modified. The
absorption peak energies ES0/S1 of the N-alkylated derivatives
show a hypsochromic shift strongly correlated with the phenyl
-1
0
5
10
Time (ns)
15
20
Fig. 4. Typical photoluminescence decay of DPP (here V) after 30 ps excitation at
532 nm (on top) with weighted residuals to monoexponential fit (on bottom).
torsion angles a and b (for the definition of the angles see Fig. 1).

180
M. Vala et al. / Dyes and Pigments 84 (2010) 176–182
Table 2
product was filtered and the filter cake washed with hot water to
neutral washings. The filter cake was dried and suspended in
100 ml of methanol. The suspension was heated to boiling and
refluxed for 1 h; the ensuing hot suspension was filtered, washed
with methanol and hot water. Yield: 2 g (30%) of IV compound.
Calculated: C (72.49), H (5.17), N (12.68). Found: C (71.96), H
(5.18), N (12.43). MW ¼ 331 Da; Negative-ion APCI-MS: m/z 330
[M ꢁ H]ꢁ (100%). 1H chemical shifts: chemical shifts were not
determined due to a very low solubility of the sample.
Phenyl torsion angles calculated by the HF and B3LYP methods. Lowest absorption
energy ES0/S1, oscillator strength fS0/S1 of this transition, 1st luminescence peak
Elum, Stokes shift
calculated by the ab initio CIS method.
DEStokes, and deformation energy Edef of the relaxed excited state
B3LYP
method
HF
ES0/S1 fS0/S1 Elum
DEStokes Edef
method
(eV)
(eV)
(eV)
(eV)
a
(ꢃ)
b
(ꢃ)
a
(ꢃ)
b
(ꢃ)
I
II
III
IV
V
0.0
0.0
6.7
36.5
0.0
0.0
3.1
6.3
29.7
6.7
0.0
0.0
2.837
2.935
3.012
2.691
2.640
2.624
2.714
2.786
2.875
2.949
0.49
0.40
0.37
0.79
1.03
1.13
0.95
0.78
0.49
0.43
2.427 0.410
2.424 0.511
2.441 0.571
2.365 0.327
2.325 0.315
2.293 0.331
2.296 0.417
2.262 0.482
2.366 0.508
2.382 0.567
0.339
0.437
0.482
0.309
0.294
0.326
0.394
0.459
0.439
0.483
36.0
36.5
0.0
0.0
3.1
46.9
46.1
0.0
16.9
46.1
0.0
3.4.2. Synthesis of 3,6-bis-(4-dimethylamino-phenyl)-2,5-dihydro-
pyrrolo[3,4-c]pyrrole-1,4-dione (V)
0.0
0.0
VI
10.5
42.6
41.6
45.7
44.9
10.5
12.5
41.6
16.2
44.9
182 ml of tert-amyl alcohol and 11.4 g (0.50 mol) of sodium
metal (in three portions) were charged into the 0.5 dm3 Keller flask
equipped with a stirrer, a reflux condenser, a thermometer and
a nitrogen inlet. The sodium metal was dissolved under the reflux
in the presence of catalytic amount of FeCl3 (approximately 2 h),
and 25 g (0.7 mol) of 4-dimethylamino-benzonitrile was added.
Diisopropyl succinate (16.9 g, 0.08 mol) dissolved in 16.9 g of tert-
amyl alcohol was introduced over 3 h and the mixture stirred at
reflux for 1 h. The reaction mixture was cooled to 60 ꢃC and then
500 ml of distilled water was added to protolyse the salt. The
protolysis was carried out at 80 ꢃC for 2 h. The resulting hot
suspension was filtered and the filter cake washed with hot water
to neutral washings. The filter cake was dried and suspended in
500 ml of acetone. The suspension was heated to boiling and
refluxed for 1 h; the hot suspension was filtered, washed with
acetone and hot water. Yield: 3.1 g (10%) of V compound.
VII 27.5
VIII 29.7
IX
X
34.1
34.4
34.4
Simultaneously, the oscillator strengths of the absorption peaks of
the molecules IV–VIII are notably higher than that of the basic I
molecule. On the other hand, the absorption peaks of the molecules
II, III, and X are reduced. These findings are in a good agreement
with the experimentally measured molar absorption coefficients
shown in Fig. 2. The calculated results further show, that Stokes
shifts DEStokes and deformation energies Edef of the excited state of
the N-alkylated derivatives are considerably increased. The calcu-
lated luminescence peak Elum depends only slightly on the phenyl
torsion angles
a and b.
The substitution of phenyls by donor or acceptor groups has
almost no influence on the phenyl torsion angles and the molecular
conformation of the central DPP unit. However, it leads to the
bathochromic shift of the absorption and luminescence peaks due
to the increased effective extent of the conjugation.
Calculated: C (70.57), H (5.92), N (14.96). Found: C (69.14), H
(5.95), N (14.40). MW ¼ 374 Da; Negative-ion APCI-MS: m/z 373
[M ꢁ H]ꢁ (100%). 1H chemical shifts: chemical shifts were not
determined due to a very low solubility of the sample.
3.4.3. Synthesis of 3,6-di-(4-piperidinophenyl)-2,5-dihydro-
pyrrolo[3,4-c]pyrrole-1,4-dione (VI)
3.4. Syntheses and analyses
Synthesis of 4-piperidine-1-yl-benzonitrile (starting nitrile):
Dry, pure N,N-dimethylacetamide (400 ml), 47.8 g (0.4 mol) p-flu-
orobenzonitrile (caution: incompatible with strong oxidizing
agents, strong acids, strong bases) and 84 g (0.99 mol) of piperidine
were charged into a 1 dm3 Erlenmeyer flask equipped with stirrer
and condenser. Reaction was carried out at 100O110 ꢃC for 8 h, the
gases from the reaction being exhausted via the fume-chamber.
Subsequently, the reaction mixture was poured onto 1 kg ice and
the crude product was collected by filtration and recrystallized
from 80% ethanol. Yield: 43.5 g (60%) of 4-piperidine-1-yl-benzo-
nitrile (m.p. 53O55 ꢃC).
The synthesis of the starting ethyl 4,5-dihydro-5-oxo-2-phenyl(1-
H)pyrrole-3-carboxylate (pyrrolinone ester) was described previously
[52], as was the syntheses of 3,6-diphenyl-2,5-dihydro-pyrrolo[3,4-
c]pyrrole-1,4-dione (I), 3,6-Diphenyl-2-butyl-2,5-dihydro-pyrrolo
[3,4-c]pyrrole-1,4-dione (II) and 3,6-Diphenyl-2,5-dibutyl-2,5-dihy-
dro-pyrrolo[3,4-c]pyrrole-1,4-dione (III) [37]. The 4-fluorobenzoni-
trile, diisopropyl succinate, natrium, tert-amyl alcohol and the
remaining common solvents were obtained from the Research Insti-
tute of Organic Syntheses.
3.4.1. Synthesis of 3-(phenyl)-6-(4-dimethylamino-phenyl)-2,
5-dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione (IV)
Synthesis of VI: 390 ml of tert-amyl alcohol and 24.4 g (1 mol) of
sodium metal (in three portions) were charged to a 1.5 dm3 Keller
flask equipped with stirrer, reflux condenser, thermometer and
a nitrogen inlet. The sodium metal was dissolved under reflux in
the presence of a catalytic amount of FeCl3 (which took approxi-
mately 2 h), and 67 g (0.36 mol) of 4-piperidine-1-yl-benzonitrile
was added. After that, diisopropyl succinate (36.3 g, 0.18 mol) dis-
solved in 36.3 g of tert-amyl alcohol was added over 3 h. Subse-
quently, the mixture was stirred at reflux for 1 h and the ensuing
mixture was cooled to 60 ꢃC, and then 700 ml distilled water was
added to protolyse the salt. Protolysis was carried out at 80 ꢃC for
2 h. The resulting hot suspension was filtered and the filter cake
was washed with hot water to neutral washings. The filter cake was
dried and suspended in 800 ml acetone. The suspension was heated
to boiling and refluxed for 1 h. The hot suspension was filtered,
washed with acetone and hot water. Yield: 12 g (15%) of VI
compound.
80 ml of tert-amyl alcohol and 2.8 g (0.12 mol) of sodium metal
(caution: extremely dangerous and corrosive; highly unstable;
reacts violently with water; can form flammable hydrogen in
contact with air.; incompatible with water, oxygen, carbon dioxide,
carbon tetrachloride, halogens, acetylene, metal halides, ammo-
nium salts, oxides, oxidizing agents, acids, alcohols, chlorinated
organic compounds, many other substances) (in three portions)
were charged into the 250 ml three-necked flask equipped with
a
magnetic stirrer, a reflux condenser, a thermometer and
a nitrogen inlet. The sodium metal was dissolved under reflux in
the presence of a catalytic amount of FeCl3 (approximately 2 h) and
5.8 g (0.04 mol) of 4-dimethylamino-benzonitrile was added. After
that, pyrrolinone ester [44] (9.2 g, 0.04 mol) was continuously
introduced in small portions within 0.5 h. Subsequently, this
mixture was stirred under reflux for 2 h and the ensuing hot salt
was filtered. The protolysis was made separately in 120 ml of 2-
propanol and 80 ml of distilled water under reflux for 2 h. The
Calculated: C (73.98), H (6.65), N (12.33). Found: C (73.23), H
(6.55), N (12.11). MW ¼ 454 Da; Negative-ion APCI-MS: m/z 453

M. Vala et al. / Dyes and Pigments 84 (2010) 176–182
181
[M ꢁ H]ꢁ (100%). 1H chemical shifts: 10.93 (2H, br s, NH), 8.36 (4H,
m, ArH); 7.07 (4H, m, ArH); 3.43 (8H, m, –CH2 CH2CH2N); 1.65 (12H,
m, –CH2CH2 CH2N and –CH2CH2CH2N)
The reaction mixture was added to 4500 ml of distilled water and
boiled; the final mixture was cooled to 10 ꢃC and the product was
filtered
The filter cake was reslurried in the mixture of methanol
(300 ml) and acetone (300 ml) and the ensuing suspension was
boiled and filtered. The filter cake (10.8 g) was identified as
a starting material. After cooling of the filtrates, a reddish substance
(a mixture of IX and X) was obtained which was recrystallized from
ethanol. The more soluble X was separated from the filtrate by
evaporation of ethanol and the less-soluble derivative IX was
obtained from the filter cake. Derivatives IX a X were three times
recrystallized from ethanol.
IX: Calculated: C (63.93), H (4.39), N (6.78), Cl (17.16). Found: C
(63.51), H (4.5), N (6.70), Cl (N/N). MW ¼ 412 Da; Negative-ion
APCI-MS: m/z 411 [M ꢁ H]ꢁ (100%). 1H chemical shifts: 11.30 (1H, br.
s, NH); 8.53 (2H, m, H-ortho); 7.91 (2H, m, H-ortho); 7.73 (4H, m, H-
meta); 3.83 (2H, t, NCH2); 1.45 (2H, m, CH2); 1.20 (2H, m, CH2); 0.80
(3H, t, CH3).
3.4.4. Synthesis of 3,6-di-(4-piperidinophenyl)-2-butyl-2,
5–dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione (VII) and 3,6-di-
(4-piperidinophenyl)-2,5-butyl-2,5–dihydro-pyrrolo[3,4-c]pyrrole-
1,4-dione (VIII)
13.7 g (0.03 mol) of the intermediate VI and 90 g of dry DMF were
charged into an evaporating flask and stirred. 12.2 g of 30% meth-
anolic solution of sodium methylate was added. The fine slurry of
sodium salt of VI was stirred for 20 min, methanol was distilled
under vacuum (t < 40 ꢃC, p ¼ 40 mbar) and then 12.6 g (0.093 mol) of
n-butyl bromide was added. The mixture was heated to 80 ꢃC and
stirred for 20 h after which time, the temperature was increased to
80–100 ꢃC and this was maintained with stirring for a further 2 h.
The reaction mixture was added to1000 ml of distilled waterand the
ensuing solution boiled. The final mixture was cooled to 10 ꢃC and
the product filtered. The filter cake was reslurried in 200 ml of
methanol, the suspension boiled and then filtered. In this step all by-
products from alkylation were removed by TLC (mobile phase:
acetone:n-hexane (2:3), thin layer: Alugram Sil G/UV). The filter cake
from the previous step (a mixture of mono-, di-substituted product
and starting material) was reslurried in 300 ml of acetone. The
suspension was boiled and filtered. After cooling, the di-substituted
product was obtained. This extractionprocedurewas repeated twice
after which, the raw, di-substituted product was recrystallized from
acetone. In this way 1.7 g of dark blue VIII was obtained. The filter
cake from the previous step (a mixture of mono-alkylate product
and starting material) was reslurried in 300 ml of acetone together
with 10 g silica gel for column chromatography (0.06–0.2 mm, pore
diameter 6 nm). The suspension was boiled and filtered; acetone
from the filtrate was evaporated and 0.22 g of dark blue VII was
obtained after the filtration.
X: Calculated: C (66.53), H (5.58), N (5.97), Cl (15.11). Found: C
(66.42), H (5.73), N (5.92), Cl (15.81). MW ¼ 468 Da; Positive-ion
APCI-MS: m/z 469 [M ꢁ H]ꢁ (100%). 1H chemical shifts: 7.83 (4H,
m); 7.65 (4H, m); 3.67 (4H, t, NCH2); 1.35 (4H, m, CH2); 1.11 (4H, m,
CH2); 0.73 (6H, t, CH3).
3.5. Experimental equipment
3.5.1. Mass spectrometry
The ion trap mass spectrometer MSD TRAP XCT Plus system
(Agilent Technologies, USA) equipped with APCI probe was used.
Positive-ion and negative-ion APCI mass spectra were measured in
the mass range of 50–1000 Da in all the experiments. The ion trap
analyzer was tuned to obtain the optimum response in the range of
the expected m/z values (the target mass was set from m/z 289 to
m/z 454). The other APCI ion source parameters: drying gas flow
VII: Calculated: C (75.26), H (7.50), N (10.97). Found: C (74.21), H
(7.23), N (10.83). MW ¼ 510 Da; Negative-ion APCI-MS: m/z 511
[M ꢁ H]ꢁ (100%). 1H chemical shifts: 10.90 (1H, br. s, NH); 8.38 (2H,
m, H-ortho); 7.81 (2H, m, H-ortho); 7.08 (4H, m, H-meta); 3.86 (4H,
t, NCH2); 3.43 (8H, m, –CH2 CH2CH2N); 1.65 (12H, m, -CH2CH2 CH2N
and –CH2CH2CH2N); 1.55 (2H, m, CH2); 1.26 (2H, m, CH2); 0.87 (3H,
t, CH3).
rate 7 dm3 minꢁ1
, nebulizer gas pressure 60 psi, drying gas
temperature 350 ꢃC, nebulizer gas temperature 350 ꢃC.
The samples were dissolved in a mixture of DMSO/acetonitrile
and methanol in various ratios. All the samples were analyzed by
means of direct infusion into LC/MS.
3.5.2. Elemental analysis
VIII: Calculated: C (76.29), H (8.18), N (9.89). Found: C (76.08), H
(8.09), N (9.84). MW ¼ 566 Da; Pozitive-ion APCI-MS: m/z 567
[M þ H]þ (100%). 1H chemical shifts: 7.84 (4H, m); 7.1 (4H, m); 3.81
(4H, t, NCH2); 3.40 (8H, m, -CH2 CH2CH2N); 1.65 (12H, m, -CH2CH2
CH2N and –CH2CH2CH2N) 1.50 (4H, m, CH2); 1.25 (4H, m, CH2); 0.86
(6H, t, CH3).
Perkin Elmer PE 2400 SERIES II CHNS/O and EA 1108 FISONS
instruments were used for elemental analyses.
3.5.3. Nuclear magnetic resonance
Bruker AVANCE 500 NMR spectrometer operating at
500.13 MHz for 1H was used for measurements of the 1H NMR
spectra and A Bruker AMX 360 NMR spectrometer, operating at
360.13 MHz for 1H and 90,56 MHz for 13C, was used for
measurements of 1H and 13C NMR spectra. The compounds were
dissolved in hexadeuteriodimethyl sulfoxide. The 1H and 13C
chemical shifts were referred to the central signal of the solvent
3.4.5. Syntheses of 3,6-bis-(4-chloro-phenyl))-2-butyl-2,5–
dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione (IX) and 3,6-bis-(4-chloro-
phenyl))-2,5-butyl-2,5–dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione (X)
The starting 3,6-Bis-(4-chloro-phenyl)-2,5–dihydro-pyrrolo-
[3,4-c]pyrrole-1,4-dione was purchased from Synthesia as the
commercial pigment Versal Red DP3G. The sample was refluxed in
2-propanol before for 1 h and the ensuing hot suspension was
filtered, washed with 2-propanol and hot water. 46.6 g (0.13 mol) of
this intermediate and 500 ml of dry DMF were charged into an
evaporating flask and stirred. Subsequently, a methanolic solution
of sodium methylate prepared from 6 g (0.26 mol) of sodium metal
and 50 ml of methanol was added. The fine slurry of the sodium salt
of I was stirred for 20 min, methanol was distilled under vacuum
(t < 40 ꢃC, p ¼ 40 mbar) and then 100 g (0.735 mol) of n-butyl
bromide was added. The mixture was heated to 60 ꢃC and stirred
for 20 h, after which time the temperature was increased to 100 ꢃC
and maintained at this temperature for a further 2 h with stirring.
(
d
¼ 2.55 (1H) and 39.60 (13C)). Positive values of chemical shifts
denote shifts to higher frequencies.
3.5.4. IR spectrometry
IR spectra were determined by FT-IR spectrometer Nicolet
Magna-IR 760. Samples were measured by KBr pellet technique.
KBr pellet (diameter 13 mm) was prepared from 1 mg sample and
300 mg KBr.
4. Conclusions
Novel diphenyl-diketo-pyrrolopyrroles with electron-donating
or withdrawing groups were prepared. To increase their solubility,

182
M. Vala et al. / Dyes and Pigments 84 (2010) 176–182
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The research was supported by the Ministry of Industry and
Trade of the Czech Republic via Tandem project No FT-TA3/048 and
by the Grant Agency of the Academy of Sciences of the Czech
Republic via project A401770601. The access to the METACentrum
supercomputing facilities provided under the research intent
MSM6383917201 as well as the computer time on the servers Luna/
Apollo in the Institute of Physics of the AS CR, v.v.i., Prague is highly
appreciated.
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