Synthesis and spectroscopic studies of N,N'-dialkyl derivatives of antisymmetrical 2h,5h-dihydropyrrolo[3,4-c]pyrrole-1,4-diones

Article abstract of DOI:10.1007/s10895-013-1294-7

2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione derivatives (DPP) are chemically stable, fluorescent molecules, known as High Performance Pigments. Preparation of the soluble derivatives of DPPs provides great advantage in designing the optic sensor for new and existing applications and overcoming aggregation problems in solid matrices. For this purpose, the synthesis of antisymmetric DPPs and the formation of new organic dyes through N,N'-dialkylation and their spectroscopic studies have been carried out both in solutions and in solid phase.

Full text of DOI:10.1007/s10895-013-1294-7

J Fluoresc (2014) 24:329–335
DOI 10.1007/s10895-013-1294-7
ORIGINAL ARTICLE
Synthesis and Spectroscopic Studies of N,N’-dialkyl
Derivatives of Antisymmetrical 2H,5H-Dihydropyrrolo
[3,4-c]pyrrole-1,4-diones
Secil Celik Erbas & Serap Alp
Received: 27 May 2013 /Accepted: 21 August 2013 /Published online: 19 September 2013
#
Springer Science+Business Media New York 2013
Abstract 2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione deriva-
tives (DPP) are chemically stable, fluorescent molecules,
known as High Performance Pigments. Preparation of the
soluble derivatives of DPPs provides great advantage in de-
signing the optic sensor for new and existing applications and
overcoming aggregation problems in solid matrices. For this
purpose, the synthesis of antisymmetric DPPs and the forma-
tion of new organic dyes through N,N’-dialkylation and their
spectroscopic studies have been carried out both in solutions
and in solid phase.
organic semiconductors for organic solar cell applications and
have been converted a ‘latent’ pigment [1–13].
When the literature on DPPs is scrutinized, it becomes clear
that the spectroscopic characteristics of DPPs are related to the
3,6-diaryl moieties. The effect of electron-donor and electron-
acceptor groups on the aryl moieties has been investigated
through maximum absorption wavelengths [14].
In this study, six new antisymmetrical DPP derivatives have
been synthesized by base catalyzed condensation reactions using
aromatic nitriles and pyrrolinone esters. Furthermore, structural
analysis, photophysical characteristics and photostabilities of the
newly prepared DPPs in different media are reported.
.
.
Keywords High performance pigments Fluorophores
Thus, antisymmetric 3-phenyl,6-pyridyl-2,5-dimethyl-
pyrrolo[3,4-c]pyrrole-1,4-dione (DPP-1a), Diethyl-2,2’-(1,4-
dioxo-3-phenyl-6-pyridine-4-yl-pyrrolo[3,4-c]pyrrole-2,5-
diyl)diacetate (DPP-1b), 3-tolyl,6-pyridyl-2,5-dimethyl-
pyrrolo[3,4-c]pyrrole-1,4-dione (DPP-2a), Diethyl-2,2’-[1,4-
dioxo-3-(4-methylphenyl)-6-pyridine-4-yl-pyrrolo[3,4-c]pyr-
role-2,5-diyl)diacetate (DPP-2b), 3-methoxyphenyl,6-phenyl-
2,5-dimethylpyrrolo[3,4-c]pyrrole-1,4-dione (DPP-3a) and
Diethyl-2,2’-[1,4-dioxo-3-(4-p-methoxyphenyl)-6-
phenylpyrrolo[3,4-c]pyrrole-2,5-diyl)diacetate (DPP-3b) de-
rivatives have been synthesized and their structural identifica-
tions have been made using FT-IR, NMR and LC-MS spectra.
To determine the photophysical characteristics of the six new-
ly synthesized DPPs, UV–vis absorption and emission spec-
troscopy techniques have been used. The maximum absorp-
tion and emission wavelengths, molar extinction coefficients
(ε), singlet energy levels (Es), Stokes’ shift values (Δλ) and
quantum yields (φF) of DPPs are given. In addition, the
photostabilities of all derivatives have been investigated in
solutions of dimethylformamide (DMF), acetonitrile (ACN),
chloroform (CHCl3), tetrahydrofuran (THF), toluene and in a
solid matrix of PVC.
.
Antisymmetric Diketopyrrolopyrrole
Introduction
Diketopyrrolopyrrole derivatives (DPPs) have been used in plas-
tic coloring, surface coatings, and as colour filters due to their
luminous colours as well as high stability. Today they are widely
used in many optic systems, such as information storage and
monitoring devices. In most of the recent studies, the usages of
DPPs in optic systems have been taken into consideration. For
example Fukuda et al., have developed a thin film ring laser
system using DPP derivatives. DPPs have also been used as
:
S. C. Erbas S. Alp
Department of Chemistry, University of Dokuz Eylul, The Graduate
School of Natural and Applied Sciences, 35160 Izmir, Turkey
S. C. Erbas
e-mail: secil.celik@cbu.edu.tr
S. Alp (*)
Department of Chemistry, University of Dokuz Eylul, Faculty of
Sciences, 35160 Izmir, Tinaztepe, Turkey
e-mail: serap.alp@deu.edu.tr
Figure 1 shows schematic structures of the six different
synthesized antisymmetrical N,N’-dialkyl DPP derivatives.

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Table 2 UV–vis spectroscopic data (λ/nm, ε/Lmol−1 cm−1) and emission
spectroscopic data (Es, kcal/mol; φF) of DPP-1b
Solvent λabs. λex. λfmax
ε
Δλ ES
kcal/mol
φF
Lmol−1 cm−1
(nm)
(nm)
(nm)
DMF
ACN
CHCl3
THF
464 463 526
458 455 523
464 464 525
466 465 525
467 466 529
472 461 525
9,500
20,000
15,333
20,000
20,000
172,413
62 62
65 62
61 62
59 61
62 61
53 61
0,83
Toluen
PVC
Fig. 1 Schematic structures of the antisymmetrical N,N’-dialkyl DPP
derivatives (a) 3-phenyl,6-pyridyl-2,5-dimethyl-pyrrolo[3,4-c]pyrrole-
1,4-dione (DPP-1a) [Ar1: -phenyl, Ar2: -pyridyl, R1:-methyl] (b)
Diethyl-2,2’-(1,4-dioxo-3-phenyl-6-pyridine-4-yl-pyrrolo[3,4-c]pyrrole-
2,5-diyl)diacetate (DPP-1b) [Ar1:-phenyl, Ar2:-pyridyl, R1:-ethylacetate]
(c) 3-tolyl,6-pyridyl-2,5-dimethyl-pyrrolo[3,4-c]pyrrole-1,4-dione (DPP-
2a) [Ar1:-tolyl, Ar2:-pyridyl, R1:-methyl] (d) Diethyl-2,2’-[1,4-dioxo-3-
(4-methylphenyl)-6-pyridine-4-yl-pyrrolo[3,4-c]pyrrole-2,5-
diyl)diacetate (DPP-2b) [Ar1:-tolyl, Ar2:-pyridyl, R1:-ethylacetate] (e) 3-
methoxyphenyl,6-phenyl-2,5-dimethylpyrrolo[3,4-c]pyrrole-1,4-dione
(DPP-3a) [Ar1:methoxyphenyl, Ar2:phenyl, R1:-methyl] (f) Diethyl-
2,2’-[1,4-dioxo-3-(4-p-methoxyphenyl)-6-phenylpyrrolo[3,4-c]pyrrole-
2,5-diyl)diacetate (DPP-3b) [Ar1: methoxyphenyl, Ar2:phenyl, R1:-
ethylacetate]
The DPP derivatives (DPP-1a, 1b, 2a, 2b, 3a, 3b) exhibited
maximum absorption wavelengths between 460–473 nm,
458–467 nm, 470–493 nm, 462–483 nm, 476–485 nm and
466–468 nm respectively in all of the solvents and they
showed maximum absorption wavelengths between 472–
495 nm in the solid matrix of PVC. When all of the absorption
spectrum of the DPP derivatives are analyzed, a bathochromic
shift is observed in toluene relative to the other solvents (see
Fig. 2). This shift can be attributed to the π-π interactions
between the aromatic rings of the DPP derivatives and tolu-
ene. The bathochromic shifts of the absorption wavelength of
the studied DPP derivatives in the PVC matrix are generally
higher than in solvents media. This can be attributed to the
decreasing of the molecular mobility and increasing of
the conjugation. Only the DPP-2b derivative showed a
hypsochromic shift. The ethyl acetate groups which are at-
tached to the nitrogen atoms in DPP-2b, can not be found in
the same plane with the phenyl rings at the 3 and 6 positions of
the DPP core [15, 16].
Results and Discussion
Absorption and Emission Based Studies
The photophysical properties of the DPP derivatives were
characterized in dimethylformamide (DMF), acetonitrile
(ACN), chloroform (CHCl3), tetrahydrofuran (THF) and tol-
uene solvents and in the solid matrix of PVC by means of
UV–vis absorption and emission spectroscopy.
Data related with UV–vis spectroscopy; maximum absorp-
tion wavelengths (λmax; in nm), molar extinction coefficients
(ε; in L mol−1 cm−1), singlet energy levels (Es, kj/mol) of the
DPP derivatives for all the solvents used are shown in Tables 1,
2, 3, 4, 5 and 6 respectively. Quantum yield values were
calculated in THF only because it was found to be an appro-
priate solvent which has the same characteristics with the
standard used.
The molar absorption coefficient values of all DPPs were
found to be quite enough for different applications. Especially
in PVC matrix, this value was found to be the highest one
which can be attributed to the rigidity of the immobilized phase.
The emission spectroscopic data of the fluorescent DPP
derivatives are shown in Tables 1, 2, 3, 4, 5 and 6.
DPP-1a, 1b, 2a, 2b, 3a, 3b exhibited maximum emission
wavelengths between 528–532 nm, 523–529 nm, 542–
Table 1 UV–vis spectroscopic data (λ/nm, ε/Lmol−1 cm−1) and emission
spectroscopic data (Es, kcal/mol; φF) of DPP-1a
Table 3 UV–vis spectroscopic data (λ/nm, ε/Lmol−1 cm−1) and emission
spectroscopic data (Es, kcal/mol; φF) of DPP-2a
Solvent λabs. λex. λfmax
ε
Δλ ES
kcal/mol
φF
Solvent λabs. λex. λfmax
ε
Δλ ES
kcal/mol
φF
Lmol−1 cm−1
Lmol−1 cm−1
(nm)
(nm)
(nm)
(nm)
(nm)
(nm)
DMF
ACN
CHCl3
THF
467 467 530
460 460 528
468 468 530
468 466 529
473 469 532
477 473 528
13,667
14,000
13,667
14,333
5,167
63 61
68 62
62 61
61 61
59 60
51 60
DMF
ACN
CHCl3
THF
470 483 548
477 475 538
474 484 545
470 484 542
493 482 542
491 477 544
5,667
6,667
78 61
61 61
71 60
72 61
49 58
53 58
6,667
0,76
4,167
0,73
Toluen
PVC
Toluen
PVC
18,000
32,787
37,140

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331
Table 4 UV–vis spectroscopic data (λ/nm, ε/Lmol−1 cm−1) and emission
spectroscopic data (Es, kcal/mol; φF) of DPP-2b
Table 6 UV–vis spectroscopic data (λ/nm, ε/Lmol−1 cm−1) and emission
spectroscopic data (Es, kcal/mol; φF) of DPP-3b
Solvent λabs. λex. λfmax
ε
Δλ ES
kcal/mol
φF
Solvent λabs. λex. λfmax
ε
Δλ ES
kcal/mol
φF
Lmol−1 cm−1
Lmol−1 cm−1
(nm)
(nm)
(nm)
(nm)
(nm)
(nm)
DMF
ACN
CHCl3
THF
469 468 530
462 462 528
470 466 530
469 467 530
483 467 533
480 466 529
13,000
35,000
33,333
40,000
23,333
50,000
61 61
66 62
60 61
61 61
50 59
49 59
DMF
ACN
CHCl3
THF
467 472 521
462 460 518
466 466 522
466 466 520
468 473 523
473 466 525
10,000
3,667
54 61
56 62
56 61
54 61
50 61
52 60
14,333
14,167
29,000
37,941
0,79
0,99
Toluen
PVC
Toluen
PVC
548 nm, 528–533 nm, 525–531 nm and 520–523 nm respec-
tively in all of the solvents used and significiant bathofluoric
shifts in the maximum emission wavelenghts were observed
in toluen relative to the other solvents (see Fig. 3). In PVC
matrices, maximum emission wavelengths are between 525–
544 nm as in toluene. In a similar way, the DPP core which has
phenyl rings at the 3 and 6 positions exhibited a bathofluoric
shift but the other aromatic moieties didn’t show any
significiant shift. This result can be attributed to the difference
between the HOMO-LUMO energy levels of different aryl
groups.
The singlet energy levels (Es) of these derivatives were
estimated to be about 58–62 kcal/mol. These values are small-
er in the PVC matrix with respect to the studied solvents.
The Stokes’ shift values are in the range 44–78 nm in
solutions. When doped into PVC, this value is between 37
and 53 nm. A large Stokes’ shift is often highly desirable for
fluorescence measurements in sensor studies.
obtained at their maximum emission wavelengths for one hour
of monitoring. The acquired data of DPP-2b is shown in
Fig. 4. These results are compatible with 3,6-diphenyl-2,5-
dihexyl-1,4-diketopyrrolo[3,4-c]pyrrole-1,4-dione’s photo-
stability results (see Fig. 5) which has been published before
[17].
Fluorescence Quantum Yield Calculations
Fluorescence Quantum Yield values (φF) of the DPP deriva-
tives were measured using the comparative William’s method
[18], which involves the use of standards with known φF
values. For this purpose, the UV–vis absorbance and corrected
emission spectra of five different concentrations of DPP de-
rivatives and reference standards (Perylenediimide N, N-
didodecyl λex=470 nm) were recorded. The integrated fluo-
rescence intensities of the DPP dyes were plotted as a function
of absorbance values. The quantum yield of the studied mol-
ecules was proportional to the gradients of the plots. To protect
from the inner filter effect; the optical densities of the stan-
dards and unknown were kept constant at less than 0.1 at the
excitation wavelength. Unknown and standard solutions
which were used in the measurement of quantum yields have
the same optical density. For this reason, the actual quantum
efficiencies of the standards and samples were compared. The
formula is applied to correct the differences arising from the
Photostability Studies
The photostabilities of the DPP derivatives were measured in
DMF, ACN, CHCl3, THF, toluene and PVC (see Fig. 4).
Photostability tests of DPP derivatives were performed by
using a steady state spectrofluorimeter in the mode of “Time
Based Measurements” employing a xenon arc lamp. All of the
fluorophores were excited at around 470 nm and the data were
Table 5 UV–vis spectroscopic data (λ/nm, ε/Lmol−1 cm−1) and emission
spectroscopic data (Es, kcal/mol; φF) of DPP-3a
THF
ACN
CHCl3
Toluene
DMF
Solvent λabs.
(nm)
λex.
(nm)
λfmax
(nm)
ε
Δλ ES kcal/ φF
Lmol−1 cm−1
mol
DMF
ACN
481
476
476
470
476
477
479
482
529
525
528
528
531
532
11,833
9,333
48 59
49 60
47 59
CHCl3 481
THF 484
Toluen 485
PVC 495
9,000
9,000
44 59
46 59
37 58
0,96
7,833
128,000
Fig. 2 Absorption spectrum of DPP-2b in different solvents

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THF
ACN
CHCl3
Toluene
DMF
Fig. 5 Photostability results of 3,6-diphenyl-2,5-dihexyl-1,4-
diketopyrrolo[3,4-c]pyrrole-1,4-dione in all studied solvents [17]
Fig. 3 Emission and excitation spectrum of DPP-2b in different solvents
were prepared and used on a Perkin-Elmer Spectrum BX
FTIR spectrometer for IR spectra. NMR spectra were
recorded on a Unity Inova 500 (Varian) Instrument and chem-
ical shifts are expressed in ppm downfield from SiMe4. An
Agilent 1260 Infinity Liquid Chromatography- Agilent 6420
Triple Quadrupole Mass Spectrometry was used for mass
spectra. A Shimadzu 1601 UV-Visible spectrophotometer
was used for absorption spectra. AVarian Cary Eclipse Spec-
trofluorimeter with a Xenon flash lamp as the light source was
used to measure steady state fluorescence emission and exci-
tation spectra.
refractive index of the matrices. Quantum yield (φF) values
were evaluated according to the following equation where ST
and X denote standard and sample respectively, Grad is the
gradient from the plot and n is the refractive index of the
solvent [19].
ꢀ
.
ꢁꢀ
.
ꢁ
2
2
ΦSample ¼ ΦST Gradx GradST ηx ηST
The quantum yield value of DPP-3 is higher than DPP-1
and DPP-2. This increase can be attributed to the rich electron
donation of the methoxy group which is connected to the
phenyl ring.
All the experiments were carried out at room temperature;
25 1 °C. Perylenediimide N,N-didodecyl was used as a ref-
erence standard for fluorescence quantum yield calculations of
the DPP.
Experimental
Reagents
Instrumental
All reagents were obtained from Merck and Fluka. Chromato-
graphic grade solvents were used in chromatographic separation
and crystallization processes. Solvents used in spectroscopic
A Bamstead Electrothermal 9,100 apparatus was used for
determining melting points. KBr pellets of three derivatives
Fig. 4 Photostability results of
DPP-2b in all studied solvents
and solid matrix (PVC)

J Fluoresc (2014) 24:329–335
333
Fig. 6 The 1H-NMR spectrum of the DPP-1b
studies were of analytical grade and used without a purification
process.
A suspension of sodium hydride (60 % suspension in
paraffine oil, 330 mmol) in diethyl carbonate was heated to
100 °C. During 4 h, acetophenone derivative (acetophenone,
4’-methyl acetophenone) (300 mmol) dissolved in diethyl
carbonate was added under vigorous stirring. Stirring was
continued for 30 min at the same temperature, then the solu-
tion was allowed to cool to r.t. After adding water and acetic
acid, the solution was stirred overnight. The aqueous phase
was extracted twice with diethyleter. The combined organic
layers were washed with saturated aqueous solutions of
NaHCO3 and NaCl. After drying (MgSO4), the solvent was
evaporated under reduced pressure. The residue was used for
the next step without further purification.
Synthesis
The intermediate product pyrrolinone ester derivatives were
prepared in three steps by following the literature
procedure[20].
DPP derivatives were synthesized by base catalyzed con-
densation of equivalent numbers of an aromatic nitrile e.g. 4-
pyridiylcarbonitrile, p-methoxybenzonitrile with a pyrro-
linone ester i.e. ethyl-4,5-dihydro-5-oxo-2-phenyl(1H)-
pyrrole-3-carboxylate, ethyl-4,5-dihydro-5-oxo-2-tolyl(1H)-
pyrrole-3-carboxylate [21].
Alkylation of DPP derivatives was carried out in the pres-
ence of sodium hydride as a base in 1-methyl-2-pyrrolidone.
Ethylbromoacetate and dimethylsulphate were used as
alkylating agents.
2-(4-arylbenzoyl)Maleic Acid Diethyl Ester
The procedure used for the synthesis of 2-(4-arylbenzoyl)maleic
acid diethyl ester:
A mixture of 2-(4-arylbenzoyl)acetic acid ethyl ester
(44 mmol), ethyl-2-bromoacetate (53 mmol) and potassium
carbonate (51 mmol) in acetone was heated under reflux for
20 h. After cooling to r.t., the suspension was filtered and the
salts were washed with diethylether. The organic layers were
2-(4-arylbenzoyl)Acetic Acid Ethyl Ester
The procedure used for the synthesis of 2-(4-arylbenzoyl)acetic
acid ethyl ester:

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J Fluoresc (2014) 24:329–335
Table 7 Structural analyses values of DPP derivatives
DPP-1a
as red-orange crystal (yield; 3.6 %) mp 148,7–149,5 °C. FT-IR [KBr, eν max (cm−1)]: 3036 (=CHstretch), 2851-2921
(C-Hstretch), 1684 (lactam C=Ostretch). 1H-NMR [DMSO-d6, δH (ppm)]: 2.480 s (6H), 7.400 d (2H), 7.700 m (5H),
8.800 d (2H). LC-MS: MW=317 Da; m/z 318 (M+H)
as red-crystal (yield; 10 %) mp 133,3–133,5 °C. FT-IR [KBr, eν max (cm−1)]: 3047–3075 (=CHstretch), 2923–2985
(C-Hstretch), 1739 (ester C=Ostretch), 1662 (lactam C=Ostretch). 1H-NMR [DMSO-d6, δH (ppm)]: 1.095 t (6H), 4.069
q (4H), 4.587 s (2H), 4.619 s (2H), 7.606–7.624 d, dd (3H), 7.722–7.737 d (2H), 7.797–7.819 dd (2H), 8.808–8.823 d
(2H). LC-MS: MW=461 Da; m/z 462 (M+H)
DPP-1b
DPP-2a
DPP-2b
as red-orange crystal (yield; 35 %) mp 255–257 °C. FT-IR [KBr, eν max (cm−1)]: 3035 (=CHstretch), 2924–2952
(C-Hstretch), 1673 (lactam C=Ostretch). 1H-NMR [CDCl3, δH (ppm)]: 2.450 s (3H), 3.350 s (6H), 7.360 d (2H), 7.760
d (2H), 7.830 d (2H), 8.810 d (2H). LC-MS: MW=331 Da; m/z 332 (M+H)
as orange-crystal (yield; 26 %) mp 118–120 °C. FT-IR [KBr, eν max (cm−1)]: 3030 (=CHstretch), 2929–2989 (C-Hstretch),
1732 (ester C=Ostretch), 1683 (lactam C=Ostretch). 1H-NMR [DMSO-d6, δH (ppm)]: 1.087 t (3H), 1.075 t (3H), 2.393 s
(3H), 4.047 q (2H), 4.059 q (2H), 4.564 s (2H), 4.596 s (2H), 7.391–7.412 d (2H), 7.691–7.715 d, d (4H), 8.800 d (2H).
LC-MS: MW=475 Da; m/z 476 (M+H)
DPP-3a
DPP-3b
as red-orange crystal (yield; 40 %) mp 184–185 °C. FT-IR [KBr, eν max (cm−1)]: 3053 (=CHstretch), 2952–2985
(C-Hstretch), 1680 (lactam C=Ostretch). 1H-NMR [DMSO-d6, δH (ppm)]: 3.240–3.260 s (6H), 3.880 s (3H),
7.150 d (2H), 7.585 d (3H), 7.925 d (2H), 7.990 d (2H). LC-MS: MW=346 Da; m/z 347 (M+H)
as orange-yellow crystal (yield; 55 %) mp 168–170 °C. FT-IR [KBr, eν max (cm−1)]: 3072 (=CHstretch), 2939–2971
(C-Hstretch), 1739 (ester C=Ostretch), 1680 (lactam C=Ostretch). 1H-NMR [CDCl3, δH (ppm)]: 1.200 t (6H), 3.870 s (3H),
4.190 q (4H), 4.500 s (4H), 7.000 d (2H), 7.500 dd (3H), 7.770 d (4H). 13C NMR (DMSO-d6, ppm): 14.53; 14.56; 43.88;
44.07; 56.28; 61.98 (2xC); 108.08; 109.17; 115.30 (2xC); 119.94; 127.85; 129.11(2xC); 129.72 (2xC); 131.31(2xC);
132.13; 147.27; 148.95; 161.90; 162.21; 162.65; 169.09; 169.12. LC-MS: MW=490 Da; m/z 491 (M+H)
combined, the solvent was evaporated off under reduced
pressure, and the residue was used for the next step without
further purification.
portionwise at 100 °C above 30 s. The mixture was stirred
for 1 h at 100 °C and 24 h at r.t. Finally, the mixture was poured
into cold water. T-amyl alcohol was evaporated and the residue
was filtered off, washed with methanol and dried under
vacuum.
2-(4-aryl)-3-ethoxycarbonyl-2-pyrroline-5-on
The procedure used for the synthesis of 2-(4-aryl)-3-
ethoxycarbonyl-2-pyrroline-5-on:
3-phenyl-6-methoxyphenyl-2,
5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione
Ammonium acetate (600 mmol) and 2-(4-aryl)-3-
ethoxycarbonyl-2-pyrroline-5-on (55 mmol) were refluxed
in acetic acid for 3 h (oil-bath temperature: 125 °C). After
cooling to r.t., ice water was added to the dark green solution
with rapid stirring. The residue was filtered, dried under
vacuum and re-crystallization was performed from methanol
for all derivatives.
This derivative was prepared by the same procedure using the
appropriate starting materials.
N,N’-dialkylation of DPP
The procedure used for synthesis of N,N’-dialkyl derivatives
of antisymmetric DPPs:
3-phenyl-6-pyridine-2,5-dihydropyrrolo
[3,4-c]pyrrole-1,4-dione
and 3-tolyl-6-pyridine-2,5-dihydropyrrolo
[3,4-c]pyrrole-1,4-dione
DPP derivative was stirred in 1-methyl-2-pyrrolidone at
room temperature. Sodium hydride was added under a nitro-
gen atmosphere. After that, n-alkyl halide (dimethylsulphate,
ethylbromo acetate) was added and stirred for 18 h. The
mixture was poured into water. The precipitate was filtered
off and the crude product was re-crystallized from methanol
for all derivatives.
The procedure used for the synthesis of 3-tolyl-6-pyridine-
2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione:
Pyridine-4-carbonitrile (20 mmol) was added, under stir-
ring and a nitrogen atmosphere, to a solution of sodium t-amyl
oxide [from sodium metal (60 mmol)] in dry t-amyl alcohol.
Natrium was dissolved under reflux in the catalytic presence
of FeCl3 (it takes approximately 2 h). 2-(4-phenyl)-3-
etoxycarbonyl-2-pyrroline-5-on and 2-(4-tolyl)-3-
ethoxycarbonyl-2-pyrroline-5-on (10 mmol) was added
Structural Analysis
The NMR spectra of the DPP-1b were indicated in Fig. 6. All
structural analysis results are reported in Table 7.

J Fluoresc (2014) 24:329–335
335
Acknowledgements We thank Dokuz Eylul University for support of
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