1,7-Dinitroperylene bisimides: Facile synthesis and characterization as n-type organic semiconductors

Article abstract of DOI:10.1016/j.tetlet.2010.09.029

1,7-Dinitroperylene bisimides (1a-1b) and 1-nitroperylene bisimides (2a-2b) were synthesized under mild condition in high yields, and were characterized by FT-IR, ¹H NMR, UV-vis, HRMS spectra, cyclic voltammetry, and thermogravimetric analyses.

Full text of DOI:10.1016/j.tetlet.2010.09.029

Tetrahedron Letters 51 (2010) 5959–5963
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
1,7-Dinitroperylene bisimides: facile synthesis and characterization
as n-type organic semiconductors
Kew-Yu Chen a, , Tahsin J. Chow b,
⇑
⇑
a Department of Chemical Engineering, Feng Chia University, 40724 Taichung, Taiwan, ROC
b Institute of Chemistry, Academia Sinica, 115 Taipei, Taiwan, ROC
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 24 July 2010
Revised 8 September 2010
Accepted 10 September 2010
Available online 16 September 2010
1,7-Dinitroperylene bisimides (1a–1b) and 1-nitroperylene bisimides (2a–2b) were synthesized under
mild condition in high yields, and were characterized by FT-IR, 1H NMR, UV–vis, HRMS spectra, cyclic vol-
tammetry, and thermogravimetric analyses. These compounds are stable up to 260 °C according to ther-
mogravimetric analyses. They undergo two quasi-reversible one-electron reductions in THF at modest
potentials. The nitro functionalities provide stability of n-type charge carriers by lowering the LUMO
to resist ambient oxidation.
Keywords:
Ó 2010 Elsevier Ltd. All rights reserved.
Organic field-effect transistors
Charge carrier mobility
1,7-Dinitroperylene bisimides
1-Nitroperylene bisimides
Derivatives of perylene-3,4:9,10-tetracarboxylic acid bisimides
have attracted much attention due to their applications in molecular
electronic devices, such as organic field-effect transistors (OFETs),1
photovoltaic cells,2 light-emitting diodes,3 and light-harvesting ar-
rays.4 The advantages of organic materials rely on their structural
diversity and tunability through molecular design. Although organic
thin film transistors (OTFTs) have been investigated for many years,
most studies have been focused on developing p-type semiconduc-
tors, such as pentacene5,6 and oligothiophenes derivatives.7 For the
applications on organic complementary metal-oxide semiconductor
(CMOS) circuits, both n- and p-type semiconductors are required.8
However, there are some major drawbacks in most organic n-type
materials, such as their low charge carrier mobility, low on/off cur-
rent ratio, instability in air, large barriers to electron injection,9
and poor solubility which hampers processes of film-casting. Many
n-type organic semiconductors with high electron mobility have
been reported in the literatures, for example, (a) naphthalene and
perylene bisimides derivatives,10 (b) fullerene (C60) and its deriva-
tives,11 (c) perfluorohexyl oligothiophenes (DFH-nT),12 (d) tetracya-
noquinodimethane (TCNQ), and 11,11,12,12-tetracyanonaphtho-
2,6-quinodimethane (TCNNQ),13 etc. The OTFT devices fabricated
with some of the previous n-type materials without strong elec-
tron-withdrawing substituents were air sensitive. The electron
charge carriers were easily trapped by oxygen, leadingto device deg-
radation upon exposure to air. The development of new n-type or-
ganic semiconductors with both high mobility and good stability
in air is a current challenge. A promising strategy is to introduce
strong electron-withdrawing substituents onto the main p-chromo-
phore by lowering its potential energy level, so that the electron
charge carriers are less susceptible to oxidation. Several air-stable
n-type organic semiconductors based on this concept have been re-
ported.14 More recently, cyano-substituted perylene bisimides
(PDI-CN2 and PDI-FCN2, Fig. 1) were prepared with an electron
mobility of 0.1–0.6 cm2/V s in air.15 In this study, a series of n-type
organic semiconductors based on perylene bisimides modified with
strong electron-withdrawing nitro groups are prepared. By chang-
ing the number of the nitro substituents, the trend of molecular en-
ergy level can be investigated.
The chemical structures of compounds 1a, 1b, 2a, 2b and their
synthetic routes are shown in Scheme 1. By controlling the reac-
tion time, both mono- and di-substituted nitroperylene bisimides
CN
O
N
O
O
N
O
R
R
NC
PDI-CN2 : R = cyclohexyl
PDI-FCN2 : R = n-CH2C3F7
⇑
Tel.: +886 4 24517250x3683; fax: +886 4 24510890 (K.-Y.C.); tel.: +886 2
27898552; fax: +886 2 27884179 (T.J.C.).
E-mail addresses: kyuchen@fcu.edu.tw (K.-Y. Chen), tjchow@chem.sinica.edu.tw
(T.J. Chow).
Figure 1. The structures of PDI-CN2 and PDI-FCN2.
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.09.029

5960
K.-Y. Chen, T. J. Chow / Tetrahedron Letters 51 (2010) 5959–5963
R
N
spectrum, corresponding to an asymmetrical stretching of the nitro
group (Fig. 2).18
O
O
O
O
O
Further nitration of 2a–2b using the same reagents at ambient
temperature for 48 h gave 1a–1b (1,7-dinitro) in 60% yield.19
Among the products, a 3:1 mixture of regioisomers (nitrated at
the 1,7- or 1,6-positions) were observed by 1H NMR spectroscopy,
a situation analogous to the result of bromination described previ-
ously by Rybtchinski and co-workers.20 Pure 1,7-regioisomer (1a or
1b) can be obtained through repetitive crystallizations.
The steady state absorption spectra of 1a–3a in THF are shown
in Figure 3, where those of 1b–3b can be found in the Supplemen-
tary data. The longest wavelength absorption bands of 1a–3a ap-
pear at 515, 518, and 520 nm, respectively. These peaks are
RNH2
NMP, HOAc
O
O
4
O
O
N
R
O
3
3a: R = cyclohexyl
3b: R = octyl
assigned to the
p–p
* transitions localized on the perylene core
(Fig. 4).21 The vibronic progressions at 450–525 nm diminish grad-
ually with an increasing number of the nitro groups (Supplemen-
tary data). The phenomenon can be explained by the decrease of
molecular rigidity due to enhanced steric hindrance induced by
the nitro groups.
CAN, HNO3
CH2Cl2, 2 h
R
N
R
N
O
O
O
O
To gain insight into the electronic properties of 1a–3a, 1b–3b,
and PDI-CN2, quantum mechanical calculations were performed
22
**
using density functional theory (DFT) at the B3LYP/6-31G level.
NO2
NO2
CAN, HNO3
CH2Cl2, 48 h
The highest occupied molecular orbital (HOMO) and the lowest
unoccupied molecular orbital (LUMO) of 1a are shown in Figure
4. The HOMO in 1a is delocalized mainly on the perylene core,
while the LUMO is extended from the central perylene core to
the peripheral nitro and the bisimide groups. The calculated and
experimental parameters are summarized in Table 1. The results
indicate that both the HOMO and LUMO energy levels decrease
as the number of nitro groups increase. The calculated LUMO en-
ergy levels of 1a are similar to those of PDI-CN2. It is believed that
these nitro-substituted derivatives should be air-stable n-type or-
ganic semiconductors, quite like their cyano-counterparts, that is,
PDI-CN2 and PDI-FCN2.
The cyclic voltammograms of 3a, 2a, and 1a with no, mono and
di-nitro substituents are illustrated in Figure 5. These chromoph-
ores undergo two quasi-reversible one-electron reductions in
THF at modest potentials. Table 2 summarizes the optical absorp-
tion peaks obtained in THF solutions and the LUMO energy levels
estimated from cyclic voltammetry (CV) for 1a–3a, 1b–3b, and
PDI-CN2.22 It appears that the first reduction potential is shifted to-
ward more positive values with increasing number of substituted
nitro groups, while the LUMO energy level decreases along the
trend. The LUMO levels of compounds 3a (3b), 2a (2b), and 1a
(1b) are estimated to be À3.98 (À3.99), À4.25 (À4.26), and À4.35
O2N
O
N
R
O
O
N
R
O
2
1
1a: R = cyclohexyl
2a: R = cyclohexyl
2b: R = octyl
1b: R = octyl
Scheme 1. The synthetic routes of 2a–2b and 1a–1b.
can be obtained. The synthesis starts from an imidization of pery-
lene bisanhydride (4) by reacting with either cyclohexylamine or
octylamine. The cyclohexyl end-capping groups increase the steric
bulkiness to the periphery of molecule, so that the solubility can be
improved without inducing a detrimental effect on the packing of
molecules during the formation of solid thin films.16 The mono-
nitration can be achieved by a reaction of perylene bisimides
(3a–3b) with cerium (IV) ammonium nitrate (CAN) and HNO3 (or
H2SO4) under ambient temperature for 2 h,17 giving 2a–2b in high
yields of ca. 90%. The presence of a single nitro substituent can be
verified by the presence of seven signals at d 8.1–8.8 ppm in 1H
NMR spectrum and the strong absorption at 1539 cmÀ1 in FT-IR
1.0
0.8
0.6
0.4
0.2
0.0
100
80
60
40
20
0
300
350
400
450
500
550
600
650
700
1800
1700
1600
1500
1400
1300
1200
Wavelength (nm)
Wave number (cm-1)
Figure 3. Normalized absorption spectra of 3a (black line), 2a (blue line) and 1a
(red line) in THF solution (2 Â 10À4 M).
Figure 2. FT-IR spectra of 3a (dashed line) and 2a (solid line).

K.-Y. Chen, T. J. Chow / Tetrahedron Letters 51 (2010) 5959–5963
5961
Table 2
Summary of optical absorption wavelengths, reduction potentials, and LUMO energy
levels for perylene bisimide derivatives
(MÀ1 cmÀ1))
E(1) (V)
E(2) (V)
LUMOc (eV)
a
b
b
Compound
kabs (nm)/(
e
3a
3b
2a
2b
1a
1b
520 (68600)
519 (66000)
518 (62400)
518 (58000)
515 (54200)
514 (51000)
530
À0.46
À0.45
À0.19
À0.18
À0.09
À0.09
À0.07
À0.76
À0.73
À0.51
À0.49
À0.34
À0.33
À0.40
À3.98
À3.99
À4.25
À4.26
À4.35
À4.35
À4.37
d
PDI-CN2
a
Measured in THF (2 Â 10À5 M).
b
Measured in a solution of 0.1 M tetrabutylammonium hexafluorophosphate
(TBAPF6) in THF versus SCE.
c
23
Estimated versus vacuum level from ELUMO = À4.44 eV À E(1)
.
d
Ref. 15.
100
90
80
70
60
Figure 4. The HOMO (bottom) and LUMO (top) of 1a calculated at by DFT at B3LYP/
6-31G** level.
Table 1
Calculated and experimental parameters for perylene bisimide derivatives 1a–3a, 1b–
3b, and PDI-CN2
a
b
Compound
HOMOa (eV)
LUMOa (eV)
Eg (eV)
Eg (eV)
3a
3b
2a
2b
1a
1b
À5.94
À5.97
À6.25
À6.29
À6.57
À6.61
À6.52
À3.46
À3.49
À3.84
À3.84
À4.11
À4.13
À4.09
2.48
2.48
2.41
2.45
2.46
2.48
2.43
2.38
2.39
2.39
2.39
2.40
2.41
2.34
100
200
300
T (ºC)
400
500
600
Figure 6. Thermogravimetric analysis graphs for 1a (solid line) and 2a (dashed line)
in nitrogen atmosphere at normal pressure. Heating rate, 10 °C/min.
c
PDI-CN2
a
b
c
Calculated by DFT/B3LYP.
At absorption maxima (Eg = 1240/kmax).
Ref. 15.
absorption maximum of 1a are similar to the corresponding
parameters of PDI-CN2, that is, À4.37 eV and 530 nm. It is apparent
that the electrochemical as well as the photophysical properties of
1a and 1b are a close resemblance to those of PDI-CN2. The lower-
ing of the LUMOs by multiple nitration suggests an increase of an-
ion stability against oxidation along with an increased number of
nitro groups.
1.0x10-5
5.0x10-6
0.0
Thermogravimetric analysis of compounds 1a and 2a are pre-
sented in Figure 6. The decomposition temperature of 1a is
260 °C and that of 2a is 300 °C, yet both are lower than that of
3a (ꢀ400 °C).24 The weight loss of about 7% for both 1a and 2a is
in good agreement with the theoretical calculations of 7.1% and
7.7%, respectively, and is plausibly ascribed to the fragmentation
of nitro group. The decomposition of 2a was further confirmed
by FT-IR spectrum. The strong absorption peak at 1539 cmÀ1, cor-
responding to the nitro stretching of 2a, disappeared completely
upon heating. The most probable mechanism of fragmentation at
high temperature should have started at a C–NO2 bond scission,
because this step has been predicted as the most feasible pathway
in a series of nitro-substituted compounds.25 It also complies well
with the relative stability of 3a > 2a > 1a.
-5.0x10-6
-1.0x10-5
0.0
-0.2
-0.4
-0.6
-0.8
-1.0
Potential (V)
In summary, we have successfully synthesized a new series of
nitro-substituted perylene bisimides, that is, 1-nitroperylene bisi-
mides (2a–2b) and 1,7-dinitroperylene bisimides (1a–1b). These
molecules undergo two quasi-reversible one-electron reductions
in THF at modest potentials. Their first reduction potential is
shifted toward more positive values with an increasing number
of substituted nitro groups, and consequently the LUMO energy
Figure 5. The cyclic voltammograms of 3a (black line), 2a (blue line), and 1a (red
line) measured in THF solution, at 200 mV/s.
(À4.35) eV, respectively. Compared to the unsubstituted perylene
bisimides 3a, the LUMO of 2a is lowered by an amount of
0.27 eV and that of 1a by 0.37 eV. Both the LUMO and the longest

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Acknowledgment
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Financial support from the National Science Council of the Rep.
of China is gratefully acknowledged.
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18. General procedure for nitration: 3a (or 3b) (1.8 mmol), cerium (IV) ammonium
nitrate (CAN) (1.2 g, 2.2 mmol), nitric acid (2.0 g, 31.7 mmol) and
dichloromethane (150 ml) were stirred at 25 °C under N2 for 2 h. The
mixture was neutralized with 10% KOH and extracted with CH2Cl2. After the
solvent was removed, the crude product was purified by silica gel column
chromatography with the eluent CH2Cl2 to afford 2a (or 2b) in 95% yield.
Characterization data: 2a: 1H NMR (500 MHz, CDCl3) d 8.74 (d, J = 7.6 Hz, 1H),
8.62–8.69 (m, 4H), 8.55 (d, J = 8.5 Hz, 1H), 8.18 (d, J = 7.6 Hz, 1H), 5.00 (m, 2H),
2.54 (m, 4H), 1.91 (m, 4H), 1.76 (m, 6H), 1.47 (m, 4H), 1.34 (m, 2H); 13C NMR
(125 MHz, CDCl3) d 163.40, 163.10, 163.00, 162.11, 147.60, 135.32, 132.78,
132.68, 131.20, 131.01, 129.25, 129.21, 128.87, 127.81, 127.40, 126.44, 126.40,
126.34, 126.19, 125.32, 124.59, 124.35, 123.89, 123.52, 54.46, 54.21, 29.06,
29.00, 26.45, 26.41, 25.34, 25.29; IR (KBr): 2928, 2851, 1700, 1659, 1596, 1539,
1401, 1336, 1262, 1245, 1190, 809, 743 cmÀ1
; MS (FAB): m/z (relative
intensity) 600 (M+H+, 100); HRMS calcd for C36H30O6N3 600.2135, found
600.2141. Selected data for 2b: 1H NMR (500 MHz, CDCl3) d 8.79 (d, J = 8.0 Hz,
1H), 8.73–8.67 (m, 4H), 8.60 (d, J = 8.0 Hz, 1H), 8.23 (d, J = 8.5 Hz, 1H), 4.19 (m,
4H), 1.76 (m, 4H), 1.26–1.54 (m, 20H), 0.87 (t, J = 6.5, 6H); MS (FAB): m/z
(relative intensity) 660 (M+H+, 100); HRMS calcd for C40H42O6N3 660.3074,
found 660.3076.
4. (a) Wood, T. E.; Thompson, A. Chem. Rev. 2007, 107, 1831–1861; (b) Loewe, R.
S.; Tomizaki, K.; Youngblood, W. J.; Bo, Z.; Lindsey, J. S. J. Mater. Chem. 2002, 12,
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19. General procedure for nitration: 2a (or 2b) (1.7 mmol), cerium (IV) ammonium
nitrate (CAN) (4.8 g, 8.8 mmol), nitric acid (8.0 g, 131.1 mmol), and
dichloromethane (250 ml) were stirred at 25 °C under N2 for 48 h. The
mixture was neutralized with 10% KOH and extracted with CH2Cl2. After the
solvent was removed, the crude product was purified by silica gel column
chromatography with the eluent CH2Cl2 to afford a mixture of 1,7- and -1,6-
dinitroperylene bisimides, and 1H NMR (500 MHz) analysis revealed a 3:1
ratio. The regioisomeric 1,7- and 1,6-dinitroperylene bisimides could not be
separated by column chromatography. Regioisomerically pure 1,7-
dinitroperylene bisimides was obtained by repetitive crystallization.
Characterization data: 1a: 1H NMR (500 MHz, CDCl3) d 8.78 (s, 2H), 8.67 (d,
J = 8.5 Hz, 2H), 8.28 (d, J = 8.5 Hz, 2H), 4.99 (m, 2H), 2.51 (m, 4H), 1.92 (m, 4H),
1.74 (m, 6H), 1.46 (m, 4H), 1.36 (m, 2H); MS (FAB): m/z (relative intensity) 645
(M+H+, 100); HRMS calcd for C36H29O8N4 645.1985, found 645.1981. Selected
data for 1b: 1H NMR (500 MHz, CDCl3) d 8.82 (s, 2H), 8.71 (d, J = 8.0 Hz, 2H),
8.30 (d, J = 8.0 Hz, 2H), 4.20 (m, 4H), 1.75 (m, 4H), 1.26–1.53 (m, 20H), 0.87 (t,
J = 6.5, 6H); 13C NMR (125 MHz, CDCl3) d 161.97, 161.46, 148.29, 132.57,
130.36, 129.60, 128.67, 127.56, 126.30, 125.58, 124.53, 124.44, 41.06, 31.72,
29.19, 29.10, 27.96, 26.98, 22.55, 13.99; MS (FAB): m/z (relative intensity) 705
(M+H+, 100); HRMS calcd for C40H41O8N4 705.2924, found 705.2923.
20. Rajasingh, P.; Cohen, R.; Shirman, E.; Shimon, J. W.; Rybtchinski, B. J. Org. Chem.
2007, 72, 5973–5979.

K.-Y. Chen, T. J. Chow / Tetrahedron Letters 51 (2010) 5959–5963
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