Preparation, physical properties and n-type FET characteristics of substituted diindenopyrazinediones and bis(dicyanomethylene) derivatives

Article abstract of DOI:10.1039/c2jm14955a

A series of halogen and alkyl substituted diindenopyrazinediones and bis(dicyanomethylene) derivatives have been synthesized as new n-type organic semiconductors based on nitrogen-containing heterocycles. Halogen groups were introduced to improve the electron injection. Their crystal structures and solid physical properties are discussed. Alkyl groups were introduced to increase the solubility in organic solvents. Furthermore, hexanoyl groups were introduced by oxidation of alkyl groups to increase the solubility and electron affinity. Dicyanomethylene groups were also introduced to further enhance the electron-accepting properties. Drop-cast as well as vapour deposited thin films showed n-type FET properties.

Full text of DOI:10.1039/c2jm14955a

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PAPER
Preparation, physical properties and n-type FET characteristics of substituted
diindenopyrazinediones and bis(dicyanomethylene) derivatives†‡
*
Jun-ichi Nishida, Hironori Deno, Satoru Ichimura, Tomohiro Nakagawa and Yoshiro Yamashita
*
Received 3rd October 2011, Accepted 22nd November 2011
DOI: 10.1039/c2jm14955a
A series of halogen and alkyl substituted diindenopyrazinediones and bis(dicyanomethylene)
derivatives have been synthesized as new n-type organic semiconductors based on nitrogen-containing
heterocycles. Halogen groups were introduced to improve the electron injection. Their crystal
structures and solid physical properties are discussed. Alkyl groups were introduced to increase the
solubility in organic solvents. Furthermore, hexanoyl groups were introduced by oxidation of alkyl
groups to increase the solubility and electron affinity. Dicyanomethylene groups were also introduced
to further enhance the electron-accepting properties. Drop-cast as well as vapour deposited thin films
showed n-type FET properties.
n-type organic semiconductors, nitrogen-containing heterocycles
are used as important components to construct the p-units.3
They can be prepared by a simple reaction and have strong
electron-accepting properties with planar geometries. Introduc-
tion of nitrogen-heterocycles such as pyrazine,4 thiazole,5
pyrimidine,6 and benzothiadiazole7 provides high performance
n-type semiconductors as well as stable p-type semiconductors.8,9
Recently, indenofluorenedione derivatives 1 have attracted
attention as a core unit affording n-type semiconductors.10,11 We
have replaced the central benzene ring with pyrazine to give
diindeno[1,2-b;10,20-e]pyrazine-6,12-dione derivatives 2a,b.11
Compared with indenofluorenediones, they have lower LUMO
levels (ca. 0.3 eV) than 1.11 As a result, 2a exhibited n-type FET
performances in contrast to 1a (R]H) which showed no
FET behaviour. Introduction of fluoro substituents improved
FET performances and the derivative 2b showed a high electron
mobility of 0.17 cm2 Vꢀ1 sꢀ1 and a low threshold voltage of
+17 V.11 As an extension of this work, chloro and bromo
derivatives were also prepared and their crystal structures and
solid physical properties are discussed here. On the other hand,
the halogen substituted derivatives 2a–d are hardly dissolved in
organic solvents. To improve the solubility, alkyl substituted
derivatives 2e and 2f have now been prepared. Furthermore, acyl
substituents and dicyanomethylene groups were introduced to
increase the electron-accepting properties. We report their
preparation, physical properties and FET characteristics (Fig. 1).
Introduction
Organic field-effect transistors (OFETs) have attracted much
attention in recent years owing to advantages such as large-area
fabrication and mechanical flexibility leading to their possible
applications in electronic devices.1 Development of new organic
semiconductors is very important for progress in this field.
Compared with hole-transporting materials, the numbers of
n-type materials are still limited and their development is
strongly required.2 As a promising approach to obtain new
Department of Electronic Chemistry, Interdisciplinary Graduate School of
Science and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta,
Midori-ku, Yokohama, 226-8502, Japan. E-mail: yoshiro@echem.titech.
ac.jp; Fax: +81-45-924-5489; Tel: +81-45-924-5571
† Electronic supplementary information (ESI) available: UV-Vis spectra,
FET characteristics, XRD data and AFM images. CCDC reference
numbers 846545 and 846546. For ESI and crystallographic data in CIF
or other electronic format see DOI: 10.1039/c2jm14955a.
‡ X-Ray measurement of single crystals of 2c and 2d was carried out
using a RAXIS-RAPID imaging plate diffractometer with Mo-Ka
ꢁ
ꢀ
radiation (l ¼ 0.71075 A) at ꢀ180.0 C. The structure was solved by the
direct method (SIR2004) and refined by the full-matrix least-squares
method on F2. The non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were refined using the riding model. Absorption
correction was applied using an empirical procedure. All calculations
were performed using the CrystalStructure crystallographic software
package except for refinement, which was performed using SHELXL-97.
Crystal data for 2c: C18H6Cl2N2O2, M ¼ 353.16, red block, crystal
dimensions 0.50 ꢂ 0.30 ꢂ 0.10 mm, monoclinic, space group P21/n, a ¼
ꢁ
3
ꢀ
ꢀ
6.73 (1), b ¼ 7.65 (2), c ¼ 13.37 (2) A, b ¼ 94.23 (6) , V ¼ 687 (2) A , Z ¼
2, Dc ¼ 1.708 g cmꢀ3, 6347 reflections collected, 1560 independent (Rint
¼
0.0761), GOF ¼ 1.064, R1 ¼ 0.0572 (I > 2.00 s (I)), wR2 ¼ 0.1448 for all
reflections. Crystal data for 2d: C18H6Br2N2O2, M ¼ 442.07, red block,
crystal dimensions 0.20 ꢂ 0.10 ꢂ 0.05 mm, monoclinic, space group
Results and discussion
Synthesis and characterization
ꢁ
ꢀ
P21/n, a ¼ 6.838 (8), b ¼ 7.76 (1), c ¼ 13.38 (2) A, b ¼ 92.92 (5) , V ¼ 709
3
(2) A , Z ¼ 2, Dc ¼ 2.070 g cmꢀ3, 6693 reflections collected, 1624 inde-
ꢀ
Chloro and bromo substituted diindenopyrazinediones 2c and 2d
were prepared for comparisons with 2a,b. Alkyl substituted
diindenopyrazinediones 2e and 2f were also synthesized by
pendent (Rint ¼ 0.0877), GOF ¼ 0.873, R1 ¼ 0.0364 (I > 2.00 s (I)), wR2
¼ 0.0650 for all reflections. The CCDC reference numbers are 846545 and
846546.
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X-Ray crystal structure analysis
X-Ray single crystal analysis of halogen substituted compounds
2b,11 2c and 2d was carried out to investigate the intermolecular
interactions (Fig. 2). These compounds are completely planar and
form p-stacking structures. Fluoro derivative 2b shows a poly-
morphism and afforded two kinds of crystals, black and red ones.
These were prepared by multiple sublimation. The overlap
patterns of molecules are different as shown in Fig. 2a and b. In the
black crystal, the whole molecule is involved with close contacts
between the carbon of the carbonyl group and the oxygen of
adjacent molecules, whereas in the red crystal, only a half of the
molecule is overlapped with close contacts between the carbon of
the carbonyl group and the halogens of adjacent molecules
ꢀ
(3.21 A). Chlorineand brominederivatives 2c and2d affordedonly
ꢀ
redcrystals with similar carbonyl andhalogen contacts (2c: 3.37A,
ꢀ
2d: 3.44 A) and the same space group (P21/n) as depicted in Fig. 2c
and d. Interplanar distances are different depending on the
Fig. 1 Chemical structures of indenofluorendiones 1, diindenopyr-
azinediones 2 and bis(dicyanomethylene) derivatives 3.
ꢀ
ꢀ
ꢀ
halogen size (2b red: 3.22 A, 2c: 3.36 A, 2d: 3.42 A).
Photophysical properties
a similar method as 2a.12 The procedure is shown in Scheme 1.
Hexanoyl substituted derivative 2g was synthesized by oxidation
reaction of intermediate 9e with an excess amount of
sodium dichromate in 19% yield. Since 2g is dissolved in organic
solvents, purification was carried out by using column chroma-
tography and sublimation. Bis(dicyanomethylene) derivatives
3 were prepared by condensation reaction with malononitrile
in DMSO in a microwave reactor. Since hexyl derivative 3e
was not dissolved in organic solvents, tert-butyl derivative 3f
was also prepared. These compounds were purified by
sublimation.
The compounds prepared here are almost colourless in solution.
UV-Vis spectra of the alkyl substituted compounds are described
in Fig. 3. In compound 2e with hexyl groups, the absorption
maxima were observed at 325 and 376 nm and a weak intra-
molecular charge-transfer (CT) band was observed at 476 nm.
The weak CT band is blue-shifted in 2g with hexanoyl groups
(Fig. S1, ESI†). On the other hand, bis(dicyanomethylene)
derivatives 3e and 3f showed red-shifted end-absorptions in
dichloromethane or DMF.
In contrast to the solution spectra, in the solid state, these
compounds showed dark colours (2b: black and red, 2c: red,
2d: red, 2e: dark red, 2g: orange and 3e: green). Reflection spectra
in the solid state were measured by using an integrated sphere
and the spectra were transformed to the corresponding absorp-
tion spectra (K–M transformation) (Fig. 4). The difference in the
crystal colour is obvious in Fig. 4a. An end-absorption of red
crystals is observed at 600 nm, whereas that of the black crystal is
red-shifted to 700 nm. This large shift (100 nm) provides a small
HOMO–LUMO energy gap. On the other hand, the solid colour
Scheme 1 Synthetic procedures of diindenopyrazinedione derivatives.
Reagents: (i) AlCl3, CH2Cl2; (ii) conc. H2SO4; (iii) isoamyl nitrite, conc.
HCl, benzene; (iv) Na2S2O4, EtOH, NH3 aq.; (v) Na2Cr2O7, AcOH,
Ac2O; (vi) Na2Cr2O7, AcOH, Ac2O; (vii) CH2(CN)2, DMSO.
Fig. 2 Overlap modes in (a) black and (b) red crystals of 2b. Crystal
structures of (c) 2c and (d) 2d.
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measured as shown in Fig. 5b. The HOMOs and LUMOs are
estimated by the DFT calculations based on the B3LYP/6-31G(d)
level (Fig. 6) (calculated HOMO of 2e: 6.11 eV, 2g: 6.71 eV, 3e:
6.46 eV; LUMO of 2e: 3.09 eV, 2g: 3.54 eV, 3e: 4.01 eV).
FET characteristics
The FET devices based on compounds 2 and 3 were fabricated on
SiO2/Si wafers by vapour-deposition with bottom contact geom-
etry. The SiO2 gate dielectric surface was treated with hexame-
thyldisilazane (HMDS). The FET measurements were carried out
at room temperature in a high vacuum chamber (10ꢀ5 Pa). The
FET performances are summarized in Table 2. Chloro and bromo
substituted derivatives 2c,d showed lower electron mobilities than
the fluoro derivative 2b. This may be attributed to the longer
interplanar distances in p-stacks of 2c,d as revealed by X-ray
analysis. Compound 2e with hexyl groups showed an electron
mobility of 1.6 ꢂ 10ꢀ5 cm2 Vꢀ1 sꢀ1, when the wafer was kept at
100 ꢁC. Introduction of hexanoyl groups improved the mobility to
9.2 ꢂ 10ꢀ3 cm2 Vꢀ1 sꢀ1 in 2g, which is 500 times higher than that of
2e. The mobility was almost similar to that of the fluorine deriv-
ative 2b. This result suggests that terminal carbonyl groups are
effective in increasing electron mobility. Introduction of bis
(dicyanomethylene) groups also improved the electron mobility in
compound 3e. The highest mobility of 1.1 ꢂ 10ꢀ2 cm2 Vꢀ1 sꢀ1 was
obtained (Fig. 7). After exposure to air, FETs based on 2g grad-
ually deteriorated. The air-stability was improved in dicyano-
methylene compounds 3. Thus, compound 3e exhibited an
electron mobility of 1.7 ꢂ 10ꢀ3 cm2 Vꢀ1 sꢀ1 and a high on/off ratio
(105) in air (after 3 h). The stability can be ascribed to the lower
LUMO level and the high crystallinity of the thin film (vide infra).
Since some of these compounds can be dissolved in organic
solvents, a drop-cast method was applied for fabrication of
FETs. After chloroform solutions of 2g and 3f were drop-cast on
Fig. 3 UV-Vis spectra of indenopyrazinedione derivatives 2e, 2f and 2g
and bis(dicyanomethylene) derivatives 3f in CH2Cl2.
ꢁ
a channel, the devices were annealed at 100 C in vacuo for 20
Fig. 4 Reflection spectra of compounds (a) 2b (black and red solids) and
2c and (b) 2c, 2g and 3e in solid state after K-M transformation.
min. Their films showed n-type FET characteristics and the
results are summarized in Table 3. The film 2g on an untreated
surface afforded an electron mobility of 1.7 ꢂ 10ꢀ5 cm2 Vꢀ1 sꢀ1
and the film 3f exhibited a mobility of 5.3 ꢂ 10ꢀ5 cm2 Vꢀ1 sꢀ1. The
low mobility in 2g compared with those of vapour-deposited
films in Table 2 may be ascribed to the large grain boundary as
detected by atomic force microscopy (AFM), which is caused by
the large grains with vertical interval maxima of ca. 73 nm on the
untreated surface and ca. 116 nm on the HMDS treated surface
(Fig. S1–S4 in ESI†). The low mobility in 3f may be attributed to
the amorphous-type structures.
reflects the molecular arrangements. In turn, replacement of
hexyl groups with hexanoyl groups in 2g afforded a blue-shift of
the end-absorption as shown in Fig. 4b. Since the blue-shift was
also observed in the solution spectra (Fig. 3), the shift is
considered to be related to an intramolecular charge transfer
(CT) band. A large red-shift of the end-absorption was observed
in 3e with strong electron-withdrawing groups. These results may
be explained by considering the intra- and intermolecular CTs
from the outside benzene ring to the pyrazine core.
Electrochemical properties
XRD analysis and AFM measurements
Compounds 2 and 3 have electron-accepting properties attributed
to the pyrazine and fused cyclopentadienone units. Their reduc-
tion potentials were measured by cyclic voltammetry (CV) and the
results are summarized in Table 1. In hexyl substituted compound
2e, two reversible reduction peaks were observed as shown in
Fig. 5a. The introduction of hexanoyl groups in 2g led to 0.2 V
positive shifts of the reduction potentials. tert-Butyl substituted
compound 2f showed similar reduction potentials as 2e. While bis
(dicyanomethylene) derivative 3e was not dissolved in any
solvents, the reduction potentials of tert-butyl derivative 3f were
The thin films of 2 and 3 were examined by X-ray diffraction
(XRD) in reflection mode. The XRD patterns of films are shown
in Fig. 8. In the thin film 2e, a sharp first reflection was observed
ꢁ
ꢀ
at 2q ¼ 4.8 (d-space: 18.3 A), when the SiO2/Si wafer was kept at
ꢁ
room temperature. When the wafer was kept at 100 C, a new
peak was observed at 5.5ꢁ (d-space: 16.1 A), indicating the
ꢀ
presence of two patterns of molecular arrangements in the film.
ꢀ
Since the calculated molecular length of 2e is 26.7 A, the mole-
cules are considered to take declined orientation or telescope-
type arrangements. In the film 2g, similar first reflection peaks
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Table 1 Optical and electrochemical data
Compd
labs/nm (log 3)
Epc/Vc
LUMOe
2a
2b
2c
2d
2e
2f
2g
3e
3f
268, 317, 367, 455a
ꢀ0.52, ꢀ1.08ac
3.85
3.96
267, 311, 361, 469a
ꢀ0.41, ꢀ0.99ac
267, 316, 356, 372, 456a
—
—
—
—
d
d
267, 319, 357, 374, 416a
d
d
239 (4.55), 326 (4.51), 376 (4.46), 476 (2.95)b
239 (4.62), 326 (4.55), 377 (4.53)b
244 (4.60), 323 (4.58), 381 (4.66), 440 (3.16)b
249, 305, 346, 358, 581a
ꢀ0.63, ꢀ1.07bc
ꢀ0.62bc
3.74
3.75
3.93
ꢀ0.43, ꢀ0.90bc
d
—
d
—
4.15
249 (4.51), 306 (4.62), 346 (4.68)b
ꢀ0.22, ꢀ0.56bc
a
In DMF. b In CH2Cl2. c 0.1 M n-Bu4NPF6, Pt electrode, V vs. SCE. Half-wave potentials. d Low solubility. e Calculated from reduction potentials.
considered to have an ca. 35ꢁ declining orientation on the
substrate. In contrast to the reflection peaks, the FET properties
were dependent on the surface conditions and temperatures.
To further study the film morphology, the surface of the thin
film 3e was investigated by using atomic force microscopy
(AFM) with the tapping mode. As the substrate temperature
increased up to 100 ꢁC, the grain size and grain boundaries
became larger (Fig. 9). The large grain boundary is considered to
result in the decrease of the mobility at high substrate
temperatures.
Conclusions
In summary, we have developed new halogen and alkyl
substituted diindenopyrazinediones and the bis(dicyano-
methylene) derivatives, and applied them to FETs. Halogen
groups were effective in enhancing the electron-accepting abili-
ties of the compounds and improved the FET performances. On
the other hand, alkyl groups were effective in enhancing the
solubility in organic solvents. Introduction of hexanoyl groups
increased the electron affinity leading to improved FET prop-
erties. Bis(dicyanomethylene) derivatives showed strong elec-
tron-accepting properties and the FETs exhibited air stability.
Further modifications of the electron-accepting p-units and
terminal groups are under way.
Fig. 5 Cyclic voltammograms of (a) compounds 2e and 2g and (b) tert-
butyl substituted 2f and 3f.
Experimental
General information
Melting points were obtained using a SHIMADZU DSC-60. 1H-
NMR spectra were recorded on a JEOL JNM-ECP 300 spec-
trometer. DI-MS data were collected on a JEOL JMS-700 mass
spectrometer. IR spectra were recorded using a JASCO FT/IR-
4100 Fourier Transform Infrared Spectrometer. UV-Vis spectra
were recorded on a JASCO V-650 spectrophotometer. Reflection
spectra in the solid states were collected using a JASCO ISV-722
integrated sphere. Cyclic voltammograms and differential pulse
voltammograms were recorded on a HOKUTODENKO HZ-
5000. Pt disk, Pt wire and SCE were used as working, counter,
and reference electrodes. Tetrabutylammonium hexa-
fluorophosphate (TBAPF6: 0.1 mol dmꢀ3) was used as a sup-
porting electrolyte in dry DMF or dichloromethane. MO
calculations were carried out by DFT methods at the B3LYP/6-
31G(d) level using the Gaussian program 03. X-Ray diffraction
(XRD) measurements were carried out on a Rigaku RINT with
Fig. 6 DFT calculations of HOMOs (left) and LUMOs (right) of (a) 2e,
(b) 2g and (c) 3e.
were observed at 4.6ꢁ at room temperature and 5.1ꢁ at 100 ꢁC. In
theꢁdrop-cast film 2g, the first reflection peak was observed at
ꢀ
5.2 (d-space: 16.1 A) accompanied by two other peaks. In the
case of bis(dicyanomethꢁylene) derivative 3e, a sharp reflection
ꢀ
peak was observed at 5.6 (d-space: 15.6 A), and the peak did not
change against the surface conditions and the substrate temper-
atures. Since the molecular length is 27.5 A, the molecules are
4486 | J. Mater. Chem., 2012, 22, 4483–4490
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Table 2 FET characteristics based on vapour deposited filmsa
Compd
Surface
Tsub (degree)
Mobility/(cm2 Vꢀ1 sꢀ1
)
On/off
Threshold/V
2b (black)b
HMDS
HMDS
HMDS
HMDS
HMDS
HMDS
HMDS
Bare
HMDS
Bare
HMDS
Bare
HMDS
Bare
HMDS
Bare
HMDS
HMDS
20
20
20
20
20
100
20
20
20
60
60
100
100
20
1.1 ꢂ 10ꢀ2
8.7 ꢂ 10ꢀ3
2.2 ꢂ 10ꢀ4
1.4 ꢂ 10ꢀ6
1.1 ꢂ 10ꢀ6
1.6 ꢂ 10ꢀ5
7.4 ꢂ 10ꢀ8
4.3 ꢂ 10ꢀ4
1.3 ꢂ 10ꢀ3
9.4 ꢂ 10ꢀ4
5.6 ꢂ 10ꢀ3
9.2 ꢂ 10ꢀ3
1.1 ꢂ 10ꢀ3
1.1 ꢂ 10ꢀ2
2.7 ꢂ 10ꢀ3
4.6 ꢂ 10ꢀ5
3.3 ꢂ 10ꢀ4
1.2 ꢂ 10ꢀ4
1 ꢂ 106
9 ꢂ 105
8 ꢂ 105
2 ꢂ 102
2 ꢂ 102
2 ꢂ 103
9 ꢂ 10
8 ꢂ 105
1 ꢂ 106
1 ꢂ 106
1 ꢂ 106
2 ꢂ 106
1 ꢂ 106
1 ꢂ 106
1 ꢂ 104
3 ꢂ 103
3 ꢂ 103
1 ꢂ 104
+27
+27
+35
+14
+52
+25
+15
+21
+36
+36
+45
+46
+17
+25
+20
+6
2b (red)b
2c
2d
2e
2f
2g
3e
20
100
100
20
+16
+31
3f
a
Bottom contact configuration. b Ref. 11. Polymorphism.
Fig. 7 (a) Output and (b) transfer characteristics of FET 3e.
ꢀ
a CuKa source (l ¼ 1.541 A). AFM experiments for films in
a tapping mode were performed using a SII NanoTechnology
SPA-400 (DFM) instrument.
Fig. 8 X-Ray diffractograms of films of (a) 2e at Tsub ¼ 20 ꢁC on
untreated surface, (b) 2e at 100 ꢁC on HMDS treated surface, (c) 2g at
20 ꢁC on HMDS treated surface, (d) 2g deposited by drop-cast method
on untreated surface, and (e) 3e at 20 ꢁC on untreated surface.
Materials
(10 mL) was added slowly. After the reaction mixture was stirred
for 15 min at room temperature, a solution of hexylbenzene (5e)
(10.2 g, 62.9 mmol) in CH2Cl2 (10 mL) was added slowly, and the
3-Chloro-1-(4-hexylphenyl)propanone (6e). To a suspension of
AlCl3 (9.07 g, 68.0 mmol) in dry CH2Cl2 (20 mL), a solution of
3-chloropropionylchloride (9.77 g, 76.9 mmol) in CH2Cl2
Table 3 FET characteristics based on the solution processa
Compd
2g
Method
Surface
Mobility/cm2 Vꢀ1 sꢀ1
On/off
Threshold/V
Solution
Solution
Solution
Solution
Bare
1.7 ꢂ 10ꢀ5
2.9 ꢂ 10ꢀ6
3.9 ꢂ 10ꢀ5
5.3 ꢂ 10ꢀ5
8 ꢂ 102
1 ꢂ 102
5 ꢂ 10
1 ꢂ 102
+36
+22
>0
HMDS
Bare
HMDS
3f
>0
a
Bottom contact configuration.
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2,8-Di-tert-butyldiindeno[1,2-b;10,20-e]pyrazine (9f). A mixture
of 5-tert-butyl-2-nitroso-1-indanone (8f)13 (3.02 g, 13.9 mmol),
sodium dithionite (7.57 g, 57.9 mmol), ethanol (13 mL) and aq.
NH3 (28%, 26 mL) was refluxed for 24 h under Ar. The reaction
mixture was extracted with CH2Cl2, and the organic layer was
washed with brine, and dried over Na2SO4. Purification by SiO2
column chromatography (eluent: CH2Cl2) gave a colorless solid
of 9f (591 mg, 23%).
Mp: 304.2–308.5 ꢁC. 1H-NMR (CDCl3): d 8.04 (d, J ¼ 8.4 Hz,
2H), 7.68 (s, 2H), 7.56 (dd, J ¼ 8.4, 2.1 Hz, 2H), 4.05 (s, 4H), 1.40
(s, 18H). IR (KBr) n (cmꢀ1): 3073, 2950, 2921, 1616, 1457, 1370,
1248, 1136, 1126, 831, 663, 434.
Fig. 9 AFM images of films of 3e at Tsub ¼ (a) 20 ꢁC and (b) 100 ꢁC on
untreated SiO2 surfaces.
resulting mixture was stirred for 24 h at room temperature. The
mixture was poured onto ice, and was extracted with CH2Cl2.
The organic layer was washed with aq. NaHCO3 and brine, and
dried over Na2SO4. The organic solvent was removed, and the
crude product was purified by column chromatography (SiO2:
CH2Cl2) to give a colourless solid of 6e (15.8 g, 99%).
1H-NMR (300 MHz: CDCl3): d 7.89 (dd, J ¼ 8.1, 1.8 Hz, 2H),
7.28 (dd, J ¼ 8.1, 1.8 Hz, 2H), 3.92 (t, J ¼ 7.5 Hz, 2H), 3.45 (t, J ¼
7.5 Hz, 2H), 2.67 (t, J ¼ 7.8 Hz, 2H), 1.58–1.68 (m, 2H), 1.27–
1.35 (m, 6H), 0.88 (t, J ¼ 7.2, 3H).
2,8-Dihexyldiindeno[1,2-b;10,20-e]pyrazine-6,12-dione (2e).
A
mixture of 9e (140 mg, 0.33 mmol), Na2Cr2O7/2H2O (290 mg,
0.97 mmol), acetic acid (9 mL) and acetic anhydride (1 mL) was
refluxed under Ar for 24 h. After addition of water at room
temperature, the resulting precipitate was collected by suction.
Purification by SiO2 column chromatography (eluent: CH2Cl2)
followed by sublimation gave a red solid of 2e (35.4 mg, 24%).
Mp: >271 ꢁC (sublimation). 1H-NMR (CDCl3): d 7.88 (d, J ¼
8.1 Hz, 2H), 7.65 (br. s, 1H), 7.50 (br. d, J ¼ 8.1 Hz, 2H), 2.70
(t, J ¼ 7.5 Hz, 4H), 1.70–1.60 (m, 4H), 1.35–1.25 (m, 12H), 0.93–
0.85 (br. t, 6H). IR (KBr) n (cmꢀ1): 2953, 2924, 2855, 1726, 1605,
1463, 1382, 1216, 1154, 1131, 418. MS/FAB: m/z 453 (M+ + 1).
Anal. Calcd for C30H32N2O2: C, 79.61; H, 7.13; N, 6.19. Found:
C, 79.38; H, 7.23; N, 6.01%.
5-Hexyl-1-indanone (7e). A mixture of 6e (4.38 g, 17.3 mmol)
andconc. H2SO4 (60mL)wasstirredat120ꢁCfor2h. Theresulting
mixture was poured onto ice and was extracted with CH2Cl2. The
organic layer was neutralized with aq. NaHCO3, washedwith brine
and dried over Na2SO4. After the organic solvent was removed, the
crude product was purified by column chromatography (SiO2:
CH2Cl2) to give yellow oil of 7e (2.24 g, 60%).
1H-NMR (CDCl3): d 7.67 (d, J ¼ 7.8 Hz, 1H), 7.39 (s, 1H),
7.19 (d, J ¼ 7.8 Hz, 1H), 3.11 (t, J ¼ 5.4 Hz, 2H), 2.71–2.66 (m,
4H), 1.66–1.60 (m, 2H), 1.32–1.31 (m, 6H), 0.89 (br. t, 3H).
2,8-Di-tert-butyldiindeno[1,2-b;10,20-e]pyrazine-6,12-dione (2f).
A mixture of 9f (997 mg, 2.71 mmol), Na2Cr2O7/2H2O (2.42 g,
8.12 mmol), acetic acid (50 mL) and acetic anhydride (5 mL) was
refluxed under Ar for 24 h. After addition of water at room
temperature, the resulting precipitate was collected by suction.
Purification of the crude product by SiO2 column chromatog-
raphy (eluent: CH2Cl2) gave a red solid of 2f (246 mg, 23%).
Mp: 366.5–368.2 ꢁC. 1H-NMR (CDCl3): d 7.91 (d, J ¼ 8.1 Hz,
2H), 7.89 (d, J ¼ 2.1 Hz, 2H), 7.73 (dd, J ¼ 8.1, 2.1 Hz, 2H), 1.39
(s, 18H). IR (KBr) n (cmꢀ1): 2958, 2867, 1736, 1608, 1473, 1454,
1364, 1215, 1176, 1151, 839, 430. MS/FAB: m/z 397 (M+ + 1).
Anal. Calcd for C26H24N2O2: C, 78.76; H, 6.10; N, 7.07. Found:
C, 78.45; H, 6.00; N, 6.97%.
5-Hexyl-2-nitroso-1-indanone (8e). To a solution of 7e (987 mg,
4.56 mmol) in benzene (6 mL), a solution of isoamyl nitrite
(558 mg, 4.76 mmol) in conc. HCl (2 mL) was added dropwise at
40 ꢁC. The reaction mixture was stirred at 40 ꢁC for 3 h and 3 d at
room temperature. The reaction mixture was extracted with
CH2Cl2, and the organic layer was neutralized with aq.
NaHCO3, washed with brine, and dried over Na2SO4. Purifica-
tion by SiO2 column chromatography (eluent: CH2Cl2/ethyl
acetate) gave a colourless solid of 8e (670 mg, 60%).
1H-NMR (DMSO): d 7.66 (d, J ¼ 8.1 Hz, 1H), 7.45 (br. s, 1H),
7.31 (br. d, J ¼ 8.1 Hz, 1H), 3.74 (s, 2H), 2.69 (t, J ¼ 7.2 Hz, 2H),
1.62–1.58 (m, 2H), 1.35–1.25 (m, 6H), 0.86 (t, J ¼ 7.2 Hz, 3H).
2,8-Dihexanoyldiindeno[1,2-b;10,20-e]pyrazine-6,12-dione (2g).
A mixture of 9e (291 mg, 0.68 mmol), Na2Cr2O7/2H2O (2.05 g,
6.86 mmol), acetic acid (25 mL) and acetic anhydride (5 mL) was
stirred at 40 ꢁC for 3 d. After addition of water and aq. NaHCO3,
the resulting precipitate was collected by suction. Purification by
SiO2 column chromatography (eluent: CH2Cl2) followed by
sublimation gave a reddish-orange solid of 2g (67.4 mg, 20%).
2,8-Dihexyldiindeno[1,2-b;10,20-e]pyrazine (9e). A mixture of 8e
(3.05 g, 12.4 mmol), sodium dithionite (7.24 g, 41.6 mmol),
ethanol (13 mL) and aq. NH3 (28%, 26 mL) was refluxed for 24 h
under Ar. The reaction mixture was extracted with CH2Cl2, and
the organic layer was washed with brine, and dried over Na2SO4.
Purification by SiO2 column chromatography (eluent: CH2Cl2)
gave a colorless solid of 9e (532 mg, 20%).
Mp: 185.2–188.3 ꢁC. 1H-NMR (CDCl3): d 8.01 (d, J ¼ 8.1 Hz,
2H), 7.45 (s, 2H), 7.32 (d, J ¼ 8.1 Hz, 2H), 4.02 (s, 4H), 2.72
(t, J ¼ 7.5 Hz, 4H), 1.70–1.63 (m, 4H), 1.35–1.31 (m, 12H), 0.89
(t, J ¼ 6.3 Hz, 6H). IR (KBr) n (cmꢀ1): 2999, 2928, 2852, 1618,
1466, 1362, 1243, 1162, 1119, 826, 656, 431.
ꢁ
1
Mp: >310 C (sublimation). H-NMR (CDCl3): d 8.41 (br. s,
2H), 8.37 (br. d, J ¼ 7.8 Hz, 2H), 8.15 (d, J ¼ 7.8 Hz, 2H), 3.02
(t, J ¼ 7.2 Hz, 4H), 1.80–1.75 (m, 4H), 1.45–1.35 (m, 12H), 0.93
(br. t, 6H). IR (KBr) n (cmꢀ1): 3093, 2932, 2864, 1731, 1685, 1606,
1500, 1213, 1159, 1140, 1108, 437. MS/EI (70 eV): m/z 409
(M+ ꢀ C5H11, 100), 480 (M+, 19). Anal. Calcd for C30H28N2O4:
C, 74.98; H, 5.87; N, 5.83. Found: C, 74.93; H, 5.73; N, 5.84%.
2,20-(2,8-Dihexyldiindeno[1,2-b;10,20-e]pyrazine-6,12-diylidene)
dimalononitrile (3e). A mixture of 2e (96.6 mg, 0.21 mmol),
4488 | J. Mater. Chem., 2012, 22, 4483–4490
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malononitrile (164 mg, 2.48 mmol) and DMSO (10 mL) was
stirred in a microwave reactor (350 W) for 90 s. After addition of
water at room temperature, the resulting precipitate was
collected by suction. Purification of crude product by sublima-
tion afforded a dark green solid of 3e (28.1 mg, 24%).
Mp: >276 ꢁC (sublimation). MS/EI (70 eV): m/z 548 (M+, 100).
Anal. Calcd for C36H32N6: C, 78.80; H, 5.88; N, 15.32. Found: C,
78.96; H, 6.06; N, 15.10%. IR (KBr) n (cmꢀ1): 2950, 2927, 2847,
2229, 1463, 1245, 1174, 1136, 850.
(HMDS) at rt for 12 h to treat the surface. Organic semiconductor
ꢀ
layers (500 A) were deposited on the channel region by vacuum
evaporation at a rate of 0.2–0.3 A sꢀ1 under a pressure of 10ꢀ5 Pa.
ꢀ
Mobilities (m) were calculated in the saturation regime by the
relationship: msat ¼ (2IDSL)/[WCox(VG ꢀ Vth)2] where IDS is the
source–drain saturation current. Cox is the oxide capacitance. VG
is the gate voltage and Vth is the threshold voltage. The latter can
be estimated as the intercept of the linear section of the plot
of (IDS)
1/2 vs. VG.
2,20-(2,8-Di-tert-butyldiindeno[1,2-b;10,20-e]pyrazine-6,12-diyli-
dene)dimalononitrile (3f). A mixture of 2f (246 mg, 0.620 mmol),
malononitrile (456 mg, 6.91 mmol) and DMSO (15 mL) was
stirred in a microwave reactor (350 W) for 90 s. After addition of
water at room temperature, the resulting precipitate was
collected by suction. Purification of the crude product by SiO2
column chromatography (eluents: CH2Cl2 : toluene ¼ 1 : 1) gave
a red solid of 3f (126 mg, 41%).
Acknowledgements
This work was supported by a Grant-in-Aid for Scientific
Research (no. 19350092 and 22550162) from the Ministry of
Education, Culture, Sports, Science and Technology, Japan, and
by the Global COE program ‘‘Education and Research Center
for Emergence of New Molecular Chemistry’’. We thank the
Center for Advanced Materials Analysis, Technical Department,
TIT for measurements of elemental analysis and MS.
ꢁ
1
Mp: 360.6–363.8 C. H-NMR (CDCl3): d 8.26 (s, 2H), 7.92
(br. d, 2H), 7.82 (br. d, 2H), 1.35 (s, 18H). IR (KBr) n (cmꢀ1);
2967, 2872, 2225, 1615, 1581, 1478, 1368, 1233, 1166, 848. MS/
FAB: m/z 493 (M+ + 1). Anal. Calcd for C32H24N6: C, 78.03; H,
4.91; N, 17.06. Found: C, 78.04; H, 4.78; N, 17.08%.
Notes and references
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that of 9c with Na2Cr2O7/2H2O and purified by sublimation.
2c: a red solid (49% yield), mp: >403.3 ꢁC (sublimation).
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C18H6Cl2N2O2: C, 61.22; H, 1.71; N, 7.93. Found: C, 61.10; H,
1.52; N, 7.95%.
2,8-Dibromodiindeno[1,2-b;10,20-e]pyrazine-6,12-dione
(2d).
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with Na2Cr2O7/2H2O and purified by suꢁblimation.
2d: a red solid (66% yield), mp: >450 C. MS/EI (70 eV): m/z
442 (M+, 100). Anal. Calcd for C18H6Br2N2O2: C, 48.91; H, 1.37;
N, 6.34. Found: C, 48.81; H, 1.23; N, 6.37%.
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