New 3,6-bis(biphenyl)diketopyrrolopyrrole dyes and pigments via Suzuki-Miyaura coupling

Article abstract of DOI:10.1016/j.dyepig.2012.11.011

New soluble dyes and insoluble organic pigments based on the diketopyrrolopyrrole skeleton have been prepared via Suzuki-Miyaura coupling on 3,6-bis(4-bromophenyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione. Boc protection of the amidic functions was advantageously used to solubilize the starting diketopyrrolopyrrole prior to the introduction of substituents. Absorption, fluorescence emission and optical features of these new diketopyrrolopyrroles dyes are presented.

Full text of DOI:10.1016/j.dyepig.2012.11.011

Dyes and Pigments 96 (2013) 679e685
Contents lists available at SciVerse ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
New 3,6-bis(biphenyl)diketopyrrolopyrrole dyes and pigments via
SuzukieMiyaura coupling
,
a
a
b
Riccardo Beninatto b, Giuseppe Borsato a , Ottorino De Lucchi , Fabrizio Fabris , Vittorio Lucchini ,
*
Elisabetta Zendri b
a Dipartimento di Scienze Molecolari e Nanosistemi, Università Ca’ Foscari, Dorsoduro 2137, I-30123, Venezia, Italy
b Dipartimento di Scienze Ambientali, Informatica e Statistica, Università Ca’ Foscari, Dorsoduro 2137, I-30123 Venezia. Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
New soluble dyes and insoluble organic pigments based on the diketopyrrolopyrrole skeleton have been
prepared via SuzukieMiyaura coupling on 3,6-bis(4-bromophenyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-
dione. Boc protection of the amidic functions was advantageously used to solubilize the starting dike-
topyrrolopyrrole prior to the introduction of substituents. Absorption, fluorescence emission and optical
features of these new diketopyrrolopyrroles dyes are presented.
Received 7 September 2012
Received in revised form
5 November 2012
Accepted 6 November 2012
Available online 20 November 2012
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
DPP
Diketopyrrolopyrrole
SuzukieMiyaura coupling
Pigment
Dye
Photophysical property
1. Introduction
gives high physical and chemical stability but makes any chemical
transformation of these compounds rather difficult. In other words,
The color red in daily life is present in all objects that need urgent
visibility, such as those representing emergency or danger situa-
tions. At the present time, the red pigment used in almost all paint
formulations belongs to the class of the diketopyrrolopyrroles (DPP),
the most common of which is known as “Ferrari Red” (C.I. Pigment
Red 254). The reason for such widespread use and prominence is
due to DPP’s high mechanical and thermal stabilities, bright shades
and high color strength. The DPP has been occasionally synthesized
in the early of ‘70s [1], but only in the ‘80s the industrial synthesis
was developed by Ciba researchers via a pseudo Stobbe condensation
[2]. Other different approaches have also been described by Gomp-
per [3] and Langhals [4], and more recently non-symmetrical DPPs
were synthesized by two-step reactions [5]. Nowadays, the scientific
interest around the DPPs molecules is focused on its optoelectronic
properties [6], in particular for the O- and N-alkylated derivatives of
DPPs [7]. In this paper we present the design and synthesis of new
DPPs with different biphenyl moieties, shown in Fig. 1.
it is almost impossible to use the original DPP scaffold to prepare
new organic pigments, attaching auxochromic groups and func-
tionalities. To circumvent this problem, we thought to combine the
“latent pigment” [8] approach with the SuzukieMiyaura cross-
coupling [9] in order to produce both soluble dyes 1 and insol-
uble pigments 2. The choice of this type of coupling is due to the
mild basic conditions and temperatures employed in this reaction.
This approach allows to obtain several new DPPs with electron-
donating groups (EDG) in the para position, which are difficult to
synthesize in good yield by other routes [10]. The product 1g with
the electron-withdrawing (EWG) methylsulfonyl group in para
position was synthesized by direct oxidation of 1e.
A comprehensive study of the effect of peripheral substituents
around the DPP core on the optical properties was carried out for all
soluble compounds 1. The knowledge of these features is essential
for potential application of these dyes in fields such as organic
photovoltaic (OPV) [6d,11], organic field effect transistor (OFET)
[12] dye-sensitized solar cells devices (DSSC) [13], solid state
laser [10a,14], and polymeric light-emitting diodes (PLED) [15].
Moreover, DPPs have been used as chemosensors [16] and as dyes
for Near Infrared Spectroscopy [10b,17]. The insoluble products 2
with biphenyl functionalities have the same structure of the
One of the main physical properties of DPP pigments is their low
solubility (<110 mg/L in DMF solution at 25 ꢀC) [2c]. This feature
* Corresponding author. Tel.: þ39 041 2348537; fax: þ39 041 2348940.
E-mail address: gborsato@unive.it (G. Borsato).
0143-7208/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2012.11.011

680
R. Beninatto et al. / Dyes and Pigments 96 (2013) 679e685
Fig. 1. Dyes 1 and pigments 2.
common Color Index P.R. 264, which is presently used in many
different applications, especially for metallic like finishes. The
stability of these pigments makes them suitable for food packaging
and toy materials [2c]
the reaction mixture was heated at 95 ꢀC and then a solution of
di-isopropyl succinate (1.667 g, 8.24 mmol) in t-AmOH (10 mL) was
added dropwise in 7 h. The resulting red suspension was stirred at
95 ꢀC for 17 h, cooled to 60 ꢀC and then a solution of water (100 mL)
and acetic acid (7 mL) was slowly added. The mixture was filtered
and the cake was washed with water and methanol until the mother
liquor are colorless. The product was dried under vacuum at 60 ꢀC for
24 h to give 3 (2.138 g, yield: 58%) as dark-red pigment. EA (calcu-
lated): C (48.46), H (2.26), N (6.28)/(found): C(48.23), H (2.09), N
2. Experimental section
2.1. Materials and instrumentation
(6.32). 1H NMR ((CD3)2SO, 400 MHz),
d
(ppm): 8.40 (4H, d, J ¼ 8.1 Hz),
All chemicals were purchased from Aldrich and were used
without further purification unless otherwise noted. The solvents
were of analytical grade and freshly distilled before use according
to literature procedures [18]. Tetrahydrofuran (THF) was dried over
Na and benzophenone and freshly distilled before use. Toluene was
degassed with argon in an ultrasound bath for 15 min before use in
SuzukieMiyaura cross-coupling reactions.
7.82 (4H, d, J ¼ 8.1 Hz). 13C chemical shifts were not determined due
to a very low solubility of the sample. IR (KBr), cmꢁ1: 3434, 3131,
3075, 3025, 2969, 2829, 1636, 1600, 1552, 1490, 1437, 1390, 1317,
1275, 1191, 1135, 1071, 1029, 1006, 833, 816, 746, 69, 620, 469.
2.2.2. Di-tert-butyl 3,6-bis(4-bromophenyl)-1,4-dioxopyrrolo[3,4-
c]pyrrole-2,5(1H,4H)-dicarboxylate (4)
1H NMR and 13C NMR spectra were recorded on a Varian Unity
400 MHz Spectrometer. IR spectra were recorded on a Perkin Elmer
Spectrum One FT-IR Spectrometer. Melting points were determined
on a Stuart Scientific Melting Point Apparatus SMP3 and are
uncorrected. UVeVis and fluorescence spectra were recorded in
dichloromethane or dimethylsulfoxide solutions on a Perkin Elmer
Lambda 40 UV/VIS Spectrometer with a Perkin Elmer PTP 6 Peltier
temperature programmer set at 25 ꢀC and on a Perkin Elmer LS55
Fluorescence Spectrometer, respectively. Fluorescence quantum
yields were determined according to the literature method [19], by
using fluorescein solution in 0.1 M aqueous NaOH for compounds
1a, 1b, 1d, 1e, 1f, 1g and rhodamine 101 solution in EtOH as stan-
dards for product 1c, taking Ffluorescein ¼ 0.79 and Frhodamine ¼ 1.00,
respectively. In order to minimize re-absorption effects, concen-
trations of the analyzed samples were properly chosen to ensure
absorbance values never exceeding 0.1 at the excitation wave-
length. The fluorescence quantum yield calculations were obtained
via the main equation:
Compound 4 was prepared according to the literature procedure
[8a]. A solution of 3 (0.748 g, 1.68 mmol) and a catalytic amount of
4-(dimethylamino)pyridine (DMAP) in dry THF (120 mL) was stir-
red at room temperature under argon atmosphere. After 15 min,
di-tert-butyl dicarbonate (Boc2O) (1.50 mL, 1.54 mmol) was added.
The green yellow fluorescent solution was stirred at 35 ꢀC over-
night, and then the solvent and excess of Boc2O were removed
under reduced pressure at 45 ꢀC to give 4 (1.083 g, yield: 99%) as
yellow solid. EA (calculated): C (52.03), H (4.05), N (4.33)/(found):
C(51.89), H (3.87), N (4.28). 1H NMR (CDCl3, 400 MHz),
d
(ppm):
(ppm):
7.64-7.59 (8H, m), 1.44 (18H, s). 13C NMR (CDCl3, 100 MHz),
d
159.2, 148.1,145.4,131.9, 130.0, 127.1,126.4, 112.7, 85.9, 27.7. IR (KBr),
cmꢁ1: 3434, 2985, 2929, 1753, 1714, 1625, 1583, 1482, 1474, 1457,
1398, 1370, 1325, 1289, 1261, 1211, 1144, 1104, 1057, 1006, 892, 875,
847, 822, 800, 760, 735, 713, 685, 646, 615, 489. MW
(C28H26Br2N2O6): 646.32 g/mol. MS (ESI) m/z: 669 (MþþNaþ, 100%).
2.3. General procedure for SuzukieMiyaura cross-coupling
derivatives (1a-f)
!
hX2
hS2
If
FXA
S ØS
FSAX
Øf
¼
¼
Iabs
To a suspension of degassed toluene (30.0 mL) and K2CO3
(9.2 mL of a 2 M solution) were added, under argon atmosphere, 4
(0.200 g, 0.31 mmol), boronic acid 5 (0.93 mmol, 3 equiv.) and
a catalytic amount (1% m/m) of Pd(PPh3)4. The resulting mixture
was heated at 90 ꢀC overnight, then cooled down to room
temperature, and solvents were removed under reduced pressure
at 80 ꢀC. The products 1 was purified from the crude reaction by
precipitation with acetonitrile, and the solid was washed with
water. All new compounds 1 were shown to be homogeneous by
their TLC examination with different polarity elution mixtures (see
Supporting Information e Part II).
2.2. Synthesis of precursors 3 and 4
2.2.1. 3,6-bis(4-bromophenyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-
dione (3)
Compound 3 was prepared according to the literature procedure
[8a], with some modifications. Sodium (0.758 g, 32.96 mmol) was
dissolved in tert-amyl alcohol (40 mL) under argon atmosphere at
80 ꢀC with a catalytic amount of anhydrous FeCl3. After the addition
of 4-bromo-benzonitrile (3.00 g, 16.48 mmol) at room temperature,

R. Beninatto et al. / Dyes and Pigments 96 (2013) 679e685
681
2.3.1. Di-tert-butyl 3,6-bis(4’-methoxybiphenyl-4-yl)-1,4-
dioxopyrrolo[3,4-c]pyrrole-2,5(1H,4H)-dicarboxylate (1a)
(with decomposition). EA (calculated): C (76.28), H (5.82), N
(4.04)/(found): C (76.04), H (5.69), N (4.01). 1H NMR (CDCl3,
It was prepared according to general procedure,1a was obtained
as a brilliant red solid (216 mg, yield: 99%). Mp: 190e192 ꢀC (with
decomposition). EA (calculated): C (71.98), H (5.75), N (4.00)/
(found): C (71.76), H (5.62), N (4.06). 1H NMR (CDCl3, 400 MHz),
400 MHz),
d
(ppm): 7.79 (4H, d, J ¼ 8.4 Hz), 7.62 (4H, d, J ¼ 8.4 Hz),
7.55 (4H, d, J ¼ 7.3 Hz), 7.39 (4H, t, J ¼ 7.5 Hz), 7.30 (2H, t, J ¼ 7.3 Hz),
7.18 (2H, d, J ¼ 16.4 Hz), 7.14 (2H, d, J ¼ 16.4 Hz), 1.46 (18H, s). 13C
NMR (CDCl3, 100 MHz),
d (ppm): 187.6, 182.5, 159.7, 152.1, 148.6,
d
(ppm): 7.83 (4H, d, J ¼ 8.4 Hz), 7.68 (4H, d, J ¼ 8.4 Hz), 7.60 (4H, d,
141.0, 137.2, 129.3, 129.0, 127.5, 127.0, 126.5, 123.4, 112.6, 85.5, 46.6,
27.9. IR (KBr), cmꢁ1: 3422, 3025, 2980, 2924, 1734, 1717, 1611, 1600,
1544,1507,1490,1448,1393,1370,1337,1278,1255,1202,1141,1046,
1006, 973, 895, 869, 830, 819, 774, 752, 696, 665, 640, 623, 587, 520.
MW (C44H40N2O6): 692.80 g/mol. MS (ESI) m/z: 693 (Mþ, 100%).
J ¼ 8.8 Hz), 7.00 (4H, d, J ¼ 8.8 Hz), 3.87 (6H, s), 1.46 (18H, s). 13C
NMR (CDCl3, 100 MHz),
d (ppm): 160.1, 159.8, 148.5, 145.9, 144.1,
143.1,136.2,132.5,129.3,128.4,126.5,114.6,112.3, 85.4, 55.5, 27.8. IR
(KBr), cmꢁ1: 3400, 3193, 2974, 2834, 1765, 1742, 1706, 1600, 1496,
1476, 1448, 1370, 1283, 1250, 1205, 1177, 1144, 1060, 1037, 998, 878,
822, 797, 772, 704, 671, 601. MW (C42H40N2O8): 700.78 g/mol. MS
(ESI) m/z: 701 (Mþ, 100%).
2.3.5. Di-tert-butyl 3,6-bis(4’-(methylthio)biphenyl-4-yl)-1,4-
dioxopyrrolo[3,4-c]pyrrole-2,5(1H,4H)-dicarboxylate (1e)
It was prepared according to general procedure,1e was obtained
as brownish solid (225 mg, yield: 99%). Mp: 190e192 ꢀC (with
decomposition). EA (calculated): C (68.83), H (5.50), N (3.82)/
(found): C (68.70), H (5.38), N (3.87). 1H NMR (CDCl3, 400 MHz),
2.3.2. Di-tert-butyl 3,6-bis(30,40-dimethoxybiphenyl-4-yl)-1,4-
dioxopyrrolo[3,4-c]pyrrole-2,5(1H,4H)-dicarboxylate (1b)
It was prepared according to general procedure, 1b was obtained
as a reddish solid (198 mg, yield: 84%). Mp: 184e186 ꢀC (with
decomposition). EA (calculated): C (69.46), H (5.83), N (3.68)/(found):
d
(ppm): 7.84 (4H, d, J ¼ 8.5 Hz), 7.69 (4H, d, J ¼ 8.5 Hz), 7.58 (4H, d,
J ¼ 8.5 Hz), 7.34 (4H, d, J ¼ 8.5 Hz), 2.54 (6H, s), 1.46 (18H, s). 13C
C (69.31), H (5.98), N (3.64). 1H NMR (CDCl3, 400 MHz),
d
(ppm): 7.84
NMR (CDCl3, 100 MHz), d (ppm): 162.2, 159.7, 157.7, 148.5, 145.9,
(4H, d, J ¼ 8.5 Hz), 7.68 (4H, d, J ¼ 8.5 Hz), 7.22 (2H, dd, J ¼ 8.4 Hz), 7.16
143.8, 139.2, 136.7, 129.3, 127.6, 126.7, 112.5, 109.6, 85.5, 27.8, 15.8. IR
(KBr), cmꢁ1: 3434, 2980, 2918, 1737, 1714, 1619, 1591, 1482, 1454,
1429, 1393, 1365, 1337, 1317, 1286, 1272, 1255, 1208, 1141, 1096,
1060, 1001, 967, 892, 872, 844, 813, 777, 758, 727, 707, 671, 651, 492.
MW (C42H40N2O6S2): 732.91 g/mol. MS (ESI) m/z: 733 (Mþ, 100%).
(2H, s), 6.98 (2H, d, J ¼ 8.4 Hz), 3.98 (6H, s), 3.95 (6H, s), 1.48 (18H, s).
13C NMR (CDCl3, 100 MHz),
d (ppm): 159.7, 149.6, 148.6, 145.9, 144.3,
140.2, 133.0, 132.0, 129.2, 126.7, 119.9, 112.4, 111.7, 110.5, 85.5, 56.2,
27.8. IR (KBr), cmꢁ1: 3422, 3215, 2974, 2929, 2834, 1751, 1700, 1613,
1597, 1524, 1502, 1462, 1398, 1367, 1331, 1289, 1275, 1253, 1219, 1174,
1144, 1060, 1026, 881, 833, 802, 766, 741, 704, 651, 618. MW
(C44H44N2O10): 760.83 g/mol. MS (ESI) m/z: 762 (Mþ þ Hþ, 100%).
2.3.6. Di-tert-butyl 3,6-bis(4’-tert-butylbiphenyl-4-yl)-1,4-
dioxopyrrolo[3,4-c]pyrrole-2,5(1H,4H)-dicarboxylate (1f)
It was prepared according to general procedure, 1f was obtained
as a deep red solid (147 mg, yield: 63%). Mp: 189e191 ꢀC (with
decomposition). EA (calculated): C (76.57), H (6.96), N (3.72)/
(found): C (76.39), H (6.90), N (3.65). 1H NMR (CDCl3, 400 MHz),
2.3.3. Di-tert-butyl 3,6-bis(4’-(dimethylamino)biphenyl-4-yl)-1,4-
dioxopyrrolo[3,4-c]pyrrole-2,5(1H,4H)-dicarboxylate (1c)
It was prepared according to general procedure, 1c was obtained
as a dark violet solid (224 mg, yield: 99%). Mp: 188e190 ꢀC (with
decomposition). EA (calculated): C (72.71), H (6.38), N (7.71)/
(found): C (72.75), H (6.29), N (7.66). 1H NMR (CDCl3, 400 MHz),
d
(ppm): 7.84 (4H, d, J ¼ 8.6 Hz), 7.72 (4H, d, J ¼ 8.6 Hz), 7.60 (4H, d,
J ¼ 8.6 Hz), 7.50 (4H, d, J ¼ 8.6 Hz), 1.45 (18H, s), 1.37 (18H, s). 13C
NMR (CDCl3, 100 MHz),
d (ppm): 159.8, 151.6, 148.5, 146.0, 144.3,
d
(ppm): 7.81 (4H, d, J ¼ 8.5 Hz), 7.67 (4H, d, J ¼ 8.5 Hz), 7.58 (4H, d,
141.8, 137.2, 129.2, 127.0, 126.9, 126.1, 112.4, 85.4, 34.8, 31.5, 27.7. IR
(KBr), cmꢁ1: 3434, 2963, 2868, 1748, 1714, 1616, 1605, 1496, 1474,
1457, 1393, 1367, 1334,1289,1278, 1255,1205,1146, 1110,1057,1001,
897, 872, 822, 772, 758, 732, 699, 570. MW (C48H52N2O6):
752.94 g/mol. MS (ESI) m/z: 754 (Mþ þ Hþ, 100%).
J ¼ 8.8 Hz), 6.80 (4H, d, J ¼ 8.8 Hz), 3.03 (12H, s), 1.46 (18H, s). 13C
NMR (CDCl3, 100 MHz),
d (ppm): 159.9, 150.7, 148.7, 145.8, 144.4,
129.3, 128.0, 127.6, 125.8, 122.6, 112.8, 112.0, 89.5, 85.3, 40.6, 27.7. IR
(KBr), cmꢁ1: 3437, 3019, 2952, 2829, 1597, 1586, 1485, 1460, 1437,
1412, 1345, 1325, 1295, 1208, 1163, 1088, 1071, 1048, 1018, 984, 970,
872, 808, 744, 707, 654, 573, 537. MW (C44H46N4O6): 726.86 g/mol.
MS (ESI) m/z: 727 (Mþ, 21%), 364 (Mþ/2 þ Hþ, 79%).
2.4. Oxidation of compound 1e to methylsulfonyl 1g
2.4.1. Di-tert-butyl 3,6-bis(4’-(methylsulfonyl)biphenyl-4-yl)-1,4-
dioxopyrrolo[3,4-c]pyrrole-2,5(1H,4H)-dicarboxylate (1g)
To a suspension of 1e (101 mg, 0.14 mmol) and Na2CO3 (73 mg,
0.69 mmol) in CH2Cl2 (25 mL), a solution of 3-chloroperbenzoic
acid 70% (mCPBA) (136 mg, 0.55 mmol) in CH2Cl2 (25 mL) was
2.3.4. Di-tert-butyl 1,4-dioxo-3,6-bis(4-styrylphenyl)pyrrolo[3,4-c]
pyrrole-2,5(1H,4H)-dicarboxylate (1d)
It was prepared according to general procedure, 1d was obtained
as deep red solid (138 mg, yield: 65%). Mp: 167e169 ꢀC
Scheme 1. Synthesis of compounds 1 and 2.

682
R. Beninatto et al. / Dyes and Pigments 96 (2013) 679e685
Table 2
added dropwise over 15 min at room temperature. After 20 min,
the crude reaction was washed twice with water, the organic layer
dried over MgSO4 and the solvent was removed under reduced
pressure. The product was purified by washing the crude with
acetonitrile and water to give 1g afford as a yellow solid (55 mg,
yield: 50%). Mp: 182e184 ꢀC (with decomposition). EA (calculated):
C (63.30), H (5.06), N (3.52)/(found): C (63.08), H (4.92), N (3.55). 1H
Substituent effects on the absorption (lmax) and fluorescence spectra (Fmax) of the
synthesized dyes 1 determined in CH2Cl2.
Compound lmax (nm)
no.
ε (L∙molꢁ1∙cmꢁ1
)
Fmax (nm) Stokes
emission shift (nm)
F
absorption
1a
1b
1c
1d
1e
1f
468
472
518
479
469
463
451
17,400
18,500
15,400
17,400
28,700
34,200
23,300
539
545
642
554
544
531
528
71
73
124
75
75
68
0.389
0.333
0.005
0.172
0.388
0.482
0.484
NMR (CDCl3, 400 MHz),
J ¼ 8.5 Hz), 7.83 (4H, d, J ¼ 8.5 Hz), 7.75 (4H, d, J ¼ 8.5 Hz), 3.11 (6H,
s), 1.49 (18H, s). 13C NMR (CDCl3, 100 MHz),
(ppm): 159.4, 148.4,
d
(ppm): 8.05 (4H, d, J ¼ 8.5 Hz), 7.89 (4H, d,
d
1g
77
145.8, 145.4, 142.2, 140.2, 129.5, 128.5, 128.3, 128.2, 127.5, 113.0,
109.6, 85.8, 44.8, 27.8. IR (KBr), cmꢁ1: 3428, 2980, 2924, 1745, 1703,
1613, 1594, 1516, 1488, 1393, 1367, 1339, 1306, 1261, 1213, 1149, 1110,
1065,1004, 956, 948, 875, 830, 777, 744, 721, 676, 556, 539, 517, 492,
447. MW (C42H40N2O10S2): 796.90 g/mol. MS (ESI) m/z: 797
(Mþ, 100%).
2.5.2. 3,6-bis(30,40-dimethoxybiphenyl-4-yl)pyrrolo[3,4-c]pyrrole-
1,4(2H,5H)-dione (2b)
It was prepared according to general procedure, 2b as fine deep-
red pigment. EA (calculated): C (72.84), H (5.03), N (5.00)/(found): C
(72.93), H (4.91), N (5.06). IR (KBr), cmꢁ1: 3406, 1639, 1602, 1502,
1404, 1253, 1219, 1200, 1141, 1051, 1023, 1006, 878, 830, 813, 763,
707, 612.
2.5. General procedure for deprotection of DPP 1
Reagents 1 (60 mg) was dissolved in the smallest volume of pure
acetone and immediately removed under reduced pressure, in
order to obtain a thin film on the surface of a one neck round flask.
The compound was brought to 180 ꢀC without stirring for 20 min,
then cooled to room temperature and connected to a high vacuum
pump for 30 min. All products 2 are obtained in quantitative yields.
The great insolubility of 2 made the NMR characterization of these
substrates not possible. Only the elemental analysis and IR are re-
ported. Melting points of 2 are higher than 350 ꢀC.
2.5.3. 3,6-bis(4’-(dimethylamino)biphenyl-4-yl)pyrrolo[3,4-c]
pyrrole-1,4(2H,5H)-dione (2c)
It was prepared according to general procedure, 2c was obtained
as fine deep-red pigment. EA (calculated): C (77.54), H (5.74), N
(10.64)/(found): C (77.31), H (5.61), N (10.48). IR (KBr), cmꢁ1: 3400,
1636, 1588, 1538, 1502, 1437, 1401, 1365, 1295, 1197, 1166, 1141, 1060,
1043, 1006, 945, 847, 811, 769, 746, 699, 632, 581.
2.5.4. 3,6-bis(4-styrylphenyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-
dione (2d)
2.5.1. 3,6-bis(4’-methoxybiphenyl-4-yl)pyrrolo[3,4-c]pyrrole-
1,4(2H,5H)-dione (2a)
It was prepared according to general procedure, 2d was ob-
tained as fine deep-red pigment. EA (calculated): C (82.91), H
It was prepared according to general procedure, 2a was obtained
as dark-red pigment. EA (calculated): C (76.78), H (4.83), N (5.60)/
(found): C (76.53), H (4.68), N (5.64). IR (KBr), cmꢁ1: 3422, 3126,
1641, 1600, 1499, 1437, 1418, 1250, 1197, 1177, 1144, 1032, 998, 850,
825, 797, 746, 710, 632, 595.
(4.91), N (5.69)/(found): C (82.99), H (4.84), N (5.77). IR (KBr), cmꢁ1
:
3434, 3131, 3025, 2840, 1636, 1597, 1546, 1513, 1490, 1448, 1406,
1331, 1194, 1141, 1068, 1034, 962, 951, 864, 822, 800, 755, 688, 660,
626, 573, 525, 436.
Table 1
2.5.5. 3,6-bis(4’-(methylthio)biphenyl-4-yl)pyrrolo[3,4-c]pyrrole-
1,4(2H,5H)-dione (2e)
Boronic acids used in SuzukieMiyaura cross-coupling.
It was prepared according to general procedure, 2e was obtained
as fine deep-red pigment. EA (calculated): C (72.15), H (4.54), N
(5.26)/(found): C (71.93), H (4.42), N (5.17). IR (KBr), cmꢁ1: 3428,
3120, 2974, 2840,1639, 1602, 1516, 1482, 1437, 1406, 1317, 1197, 1141,
1093, 1040, 998, 850, 813, 758, 744, 721, 674, 632, 520, 433.
Products 1
Boronic acid 5
Yield (%)
99
1a
1b
1c
84
99
2.5.6. 3,6-bis(4’-tert-butylbiphenyl-4-yl)pyrrolo[3,4-c]pyrrole-
1,4(2H,5H)-dione (2f)
It was prepared according to general procedure, 2f was obtained
as a fine deep-red pigment. EA (calculated): C (82.58), H (6.57), N
(5.07)/(found): C (82.39), H (6.35), N (5.00). IR (KBr), cmꢁ1: 3434,
3137, 2957, 2901, 2862, 1639, 1602, 1499, 1446, 1409, 1384, 1362,
1d
1e
65
98
Table 3
Substituent effects on the absorption (lmax) and fluorescence spectra (Fmax) of the
synthesized pigments 2 determined in DMSO. *The ε values of 2a and 2e could not
be determined because of their low solubility.
ε (L∙molꢁ1∙cmꢁ1
)
Fmax (nm)
emission
Stokes
shift (nm)
*
Compound
no.
lmax (nm)
absorption
2a
2b
2c
2d
2e
2f
541
543
566
564
544
536
540
/
554
557
629
574
558
550
557
13
14
63
10
14
14
17
1f
63
15,300
31,200
35,800
/
47,600
46,400
1h
e
2g

R. Beninatto et al. / Dyes and Pigments 96 (2013) 679e685
683
used in organic synthesis. This type of reaction affords 4 in quan-
titative yield. Furthermore the Boc residue, established as a basic
condition protecting group [20], is suitable for SuzukieMiyaura
cross-coupling conditions on compound 4. The boronic acids used
to obtain the products 1 are summarized in Table 1. Six soluble dyes
1a-f and six insoluble pigments 2a-f bearing electron-donating
groups (EDG) were obtained via direct cross-coupling from the
corresponding boronic acids, followed by the thermal deprotection
of the BOC groups. 2d was already synthesized trough another
route, and its spectral properties are consistent with our data [21].
In order to achieve an exhaustive study on the effects of the
substituent in para position on the optical properties of the DPP
core, the series 1 and 2 were completed with the introduction of an
EWG. Unfortunately, the direct introduction with the Suzukie
Miyaura coupling of an EWG, such as the nitro group (e.g. boronic
acid 5h, with slight changes of the original literature procedures:
Pd2(dba)3 with different ligands such as t-Bu3PþBF4, JohnPhos,
Cy-JohnPhos, XPhos, PhCy2P and K3PO4 as base) [22], proved not
possible. In this case, the only product detected in the crude reac-
tion mixture was the 4,40-dinitrobiphenyl compound, derived by
the homo-coupling of 1h as previously reported in similar cases
[23]. However the electron withdrawing sulfonyl group was
introduced in good yield via oxidation of 1e with meta-chlor-
operbenzoic acid under basic conditions.
3.2. Photophysical characterization of compounds 1 and 2
The effect of substituent on photophysical properties for soluble
compounds 1 are summarized in Table 2. All measurements were
obtained in solution of 1 in CH2Cl2. The lmax for all products 1 are
bathochromically shifted in respect to the maximum of 424 nm
[5a] of DPP 2,5-bis-(t-butoxycarbonyl) derivative, and the largest
effect was obtained for the product 1c. The observed Stokes shifts
for dyes 1 were on average in the range of 70e80 nm, except
compound 1c, that shows a Stokes shift equal to 124 nm. This data
for 1c indicated its smaller difference of energy between the
lowest vibrational level of the excited state S1 and vibrational
levels of the ground state comparing to other dyes. In Table 2 are
Fig. 2. (a) UVeVis spectra of all BOC-protected products 1; (b) UVeVis spectra of all
deprotected products 2.
1323, 1267, 1194, 1141, 1110, 1043, 1001, 853, 819, 755, 682, 626, 567,
514, 467.
also shown the fluorescence quantum yield (F). In this case, the
higher values of quantum yield were obtained for substrate 1g,
with the sulfonyl electron withdrawing group, and for 1f, with the
2.5.7. 3,6-bis(4’-(methylsulfonyl)biphenyl-4-yl)pyrrolo[3,4-c]
pyrrole-1,4(2H,5H)-dione (2g)
tert-butyl group, that prevent the
pep interactions between
It was prepared according to general procedure, 2g was ob-
tained as a fine deep-red pigment. EA (calculated): C (64.41), H
different molecules [24].
The photophysical properties of new pigments 2 in DMSO
solution are presented in Table 3. Relative to the Boc protected
molecules 1, the lmax of all of products 2 are bathochromically
shifted in respect to the maximum of 496 nm of the P.R. 255. Also in
this case, the largest difference between 3 and series of products 2
was observed for the molecule 2c with the electron donating group
dimethylamino, and the same compound gives a value of Stokes
shift equal to 63 nm. For 2a and 2e the molar extinction coefficients
were not calculated, due to the severe insolubility of these
pigments in the solvent. Finally in Fig. 2 are shown the UVeVis
Spectra of protected compounds 1 and corresponding pigments 2.
In Fig. 3 are shown the vials of resulting solutions of the dyes 1
in dichloromethane, lighted with visible (A) and UV light (B).
(4.05), N (4.69)/(found): C (64.53), H (3.96), N (4.71). IR (KBr), cmꢁ1
:
3434, 3131, 3014, 2924, 2845, 1641, 1605, 1572, 1521, 1488, 1446,
1409, 1300, 1200, 1146, 1090, 1040, 1001, 965, 822, 780, 744, 674,
629, 562, 545, 514, 483.
3. Results and discussion
3.1. Design and synthesis of products 1 and 2
The synthetic path to access DPP’s 1 and 2 is shown in Scheme 1.
Initially the approach involves the derivation of 3 with Boc moieties
[8b], in order to solubilize the starting material in common solvents
Fig. 3. Vials with the solution of dyes 1 in dichloromethane, lighted with visible (A) and UV light (B).

684
R. Beninatto et al. / Dyes and Pigments 96 (2013) 679e685
heterojunction solar cells. Chem Mater 2011;23:470e82;
4. Conclusions
(d) Qu S, Tian H. Diketopyrrolopyrrole (DPP)-based materials for organic
photovoltaics. Chem Commun 2012;48:3039.
The synthetic protocol reported herein allows for the homolo-
gation/functionalization of the para position of the aromatic rings
in the DPP scaffold via SuzukieMiyaura cross-coupling, as shown
with the preparation of seven different DPP-based soluble dyes 1.
Such dyes, after simple thermal removal of t-BOC residues, are
transformed into a new class of insoluble DPP pigments 2 in high
yields and purity. All dyes 1 showed a bathochromic shift compared
to the original DPP core, regardless of the nature of substituent. The
high Stokes shifts measured make the fluorophore emission bath-
ochromically shifted, so an easy discrimination of the fluorescence
signal from Rayleigh scattering is possible and the signal-to-noise
ratio is increased [25]. These results are important for the poten-
tial application of these compounds as molecular probes in imaging
techniques.
ꢀ
ꢀ
ꢀ ꢀ
[7] (a) Lunák S, Vala M, Vynuchal J, Ouzzane I, Horáková P, Mozísková P, et al.
Absorption and fluorescence of soluble polar diketo-pyrrolo-pyrroles. Dyes
Pigm 2011;91:269e78;
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
(b) Frebort S, Eliás Z, Lycka A, Lunák Jr S, Vynuchal J, Kubác L, et al. O- and
N-alkylated diketopyrrolopyrrole derivatives. Tetrahedron Lett 2011;52:
5769e73;
(c) Qian G, Qi J, Davey JA, Wright JS, Wang ZY. Family of Diazapentalene
chromophores and narrow-band-gap polymers: synthesis, halochromism,
halofluorism, and visibleenear infrared photodetectivity. Chem Mater 2012;
24:2364e72.
[8] (a) Zambounis JS, Hao Z. Iqbal A Pyrrolo[3,4-c]pyrroles. EP0648770; 1995;
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pigments as laser-active media for a solid-state dye laser. Dyes Pigm 2004;63:
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The Stokes shifts of all compounds were higher than the typical
value required, indeed, in the case of laser dyes applications
(50 nm), and a good mirror-type shape of the absorption and
luminescence bands has been also detected (see Supporting Infor-
mation e Part II).
[11] (a) Lee W-H, Son SK, Kim K, Lee SK, Shin WS, Moon S-J, et al. Synthesis
and characterization of new selenophene-based DonoreAcceptor low-
bandgap polymers for organic photovoltaic cells. Macromolecules 2012;45:
1303e12;
The changing of the emission maxima of the reagent 1e
(544 nm) compared to the product 1g (528 nm), during the
oxidation process, after appropriate modifications to increase
solubility, makes this substrate useful as chemosensor for the
detection of S-oxidizing agents. We are currently investigating such
a possibility.
(b) Bronstein H, Chen Z, Ashraf RS, Zhang W, Du J, Durrant JR, et al. Thieno 3,2-
b thiophene-diketopyrrolopyrrole-containing polymers for high-performance
organic field-effect transistors and organic photovoltaic devices. J Am Chem
Soc 2011;133:3272e5;
(c) Karsten BP, Bijleveld JC, Janssen RAJ. Diketopyrrolopyrroles as
acceptor materials in organic photovoltaics. Macromol Rapid Commun 2010;
31:1554e9;
(d) Ripaud E, Demeter D, Rousseau T, Boucard-Cétol E, Allain M, Po R, et al.
Structureeproperties relationships in conjugated molecules based on dike-
topyrrolopyrrole for organic photovoltaics. Dyes Pigm 2012;95:126e33.
[12] (a) Zhang Y, Kim C, Lin J, Nguyen TQ. Solution-processed ambipolar field-
effect transistor based on diketopyrrolopyrrole functionalized with benzo-
thiadiazole. Adv Funct Mater 2012;22:97e105;
Acknowledgments
This work was funded by MIUR within the PRIN national project.
Appendix A. Supplementary data
(b) Wang X, Luo H, Sun Y, Zhang M, Li X, Yu G, et al. Narrow band gap D-A
copolymer of indacenodithiophene and diketopyrrolopyrrole with deep
HOMO level: synthesis and application in field-effect transistors and polymer
solar cells. J Polym Sci Part A: Polym Chem 2012;50:371e7;
(c) Qiao Y, Guo Y, Yu C, Zhang F, Xu W, Liu Y, et al. Diketopyrrolopyrrole-
containing quinoidal small molecules for high-performance, air-stable, and
solution-processable n-channel organic field-effect transistors. J Am Chem Soc
2012;134:4084e7;
(d) Chen Z, Lee MJ, Shahid Ashraf R, Gu Y, Albert-Seifried S, Meedom
Nielsen M, et al. High-performance ambipolar diketopyrrolopyrrole-thieno
3,2-b thiophene copolymer field-effect transistors with balanced hole and
electron mobilities. Adv Mater 2012;24:647e52.
Supplementary data related to this article can be found at
http://dx.doi.org/10.1016/j.dyepig.2012.11.011
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