Diazaboroles with quinone units: Hydrogen bonding network and n-type FETs involving a three-coordinate boron atom

Article abstract of DOI:10.1039/c1jm12650d

A series of monodiazaborole and bis(diazaborole) derivatives with a quinone moiety have been prepared as stable electron acceptors. They show dark colors in the solid states and reversible reduction potentials in the cyclic voltammograms. X-Ray structure analysis of one derivative revealed a π-stacking structure accompanied with a hydrogen-bonding network. Trifluoromethyl substituted derivatives afforded n-type FET characteristics with an electron mobility of 10^-2 cm² V^-1 s ^-1. An ambipolar FET characteristic was also observed in the biphenyl derivative. The planar three-coordinate boron units were used as π-linkers to afford n-type and ambipolar FET characteristics.

Full text of DOI:10.1039/c1jm12650d

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links <
C
Journal of
Materials Chemistry
Cite this: J. Mater. Chem., 2011, 21, 16442
www.rsc.org/materials
PAPER
Diazaboroles with quinone units: hydrogen bonding network and n-type FETs
involving a three-coordinate boron atom†
a
a
b
b
Jun-ichi Nishida, Tomohiro Fujita, Yoshihide Fujisaki, Shizuo Tokito and Yoshiro Yamashita
a
*
Received 9th June 2011, Accepted 22nd August 2011
DOI: 10.1039/c1jm12650d
A series of monodiazaborole and bis(diazaborole) derivatives with a quinone moiety have been
prepared as stable electron acceptors. They show dark colors in the solid states and reversible reduction
potentials in the cyclic voltammograms. X-Ray structure analysis of one derivative revealed a p-
stacking structure accompanied with a hydrogen-bonding network. Trifluoromethyl substituted
derivatives afforded n-type FET characteristics with an electron mobility of 10ꢀ2 cm2 Vꢀ1 sꢀ1. An
ambipolar FET characteristic was also observed in the biphenyl derivative. The planar three-
coordinate boron units were used as p-linkers to afford n-type and ambipolar FET characteristics.
symmetrical structures compared with isoelectronic pyrrole
derivatives. Even in the asymmetrical monodiazaborole deriv-
atives 1 and 2 (Fig. 1), a C2-axis remains along with the
molecular long axis. Third, they contain proton donor and
acceptor units. Well-ordered molecular arrangements through
hydrogen bonds are expected. Fourth, they are easily prepared
by a one-pot condensation reaction and stable enough to handle
in air. The physical properties can be controlled by modification
of boronic acids and quinone moieties as shown in compound 2.
We report here the first examples of n-type and ambipolar
Introduction
Development of organic materials for transporting electrons has
recently attracted much attention because they can be applied
to n-type semiconductors for organic electronic devices such as
field-effect transistors (FETs) and organic photo-voltaic cells
(OPVCs).1,2 In this field, organic p-systems containing a three-
coordinate boron atom are of interest since the boron atom has
a planar geometry with a vacant p-orbital and can connect
p-conjugated systems.3–8 Among them, the derivatives including
boron–nitrogen bonds are known to be stable by a flow of lone-
pair electrons of nitrogen to the vacant p-orbital of boron.5–8
Since they do not need bulky substituents for stabilization,
strong intermolecular interactions helpful for fast carrier
transportation can be expected. However, such p-systems
generally show high HOMO levels8 and have not been applied
to n-type semiconductors for FETs. Bearing this in mind, new
three-coordinate boron derivatives 1–3 based on 1,3-diazabor-
oles7,8 and quinone units9 have been synthesized. They have the
following advantages. First, they have high electron-accepting
properties. Quinone units attract the lone-pair electrons of the
nitrogen, and the empty pz orbital of boron is expected to work
for transporting electrons. Second, they have higher
aDepartment 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
bNHK Science & Technical Research Laboratories, Kinuta, Setagaya-ku,
Tokyo, 157-8510, Japan
† Electronic supplementary information (ESI) available: FT-IR data,
NMR data, X-ray analysis, reflection spectra after K–M
transformation, DPV data, molecular orbital calculations of the
compounds and the tautomeric and dimer forms of 1a, FET, XRD and
AFM data. CCDC reference number 819166. For ESI and
crystallographic data in CIF or other electronic format see DOI:
10.1039/c1jm12650d
Fig. 1 Chemical structures of monodiazaborole derivatives 1 and 2, bis
(diazaborole) derivatives 3, and their amine precursors.
16442 | J. Mater. Chem., 2011, 21, 16442–16447
This journal is ª The Royal Society of Chemistry 2011

View Article Online
Table 1 Optical and electrochemical data
labsa/nm
FETs based on planar crystalline three-coordinate boron
derivatives.10
Compound
(log 3)
Epcb/V
Epab/V
LUMOf
Results and discussion
1a
1b
290, 456
ꢀ0.93, ꢀ1.04c
3.44
3.48
286 (4.64),
471 (3.32)
271, 342, 458
294, 348
274, 321
269, 319
293 (4.62),
353 (4.12),
596 (2.28)
ꢀ0.84c
+1.33d
Synthesis and characterization
2
ꢀ0.66c
ꢀ0.91e
ꢀ0.86e
ꢀ0.91e
ꢀ0.97c
3.71
3.46
3.51
3.46
3.40
Monodiazaborole- and bis(diazaborole)–quinone derivatives
1–3 were prepared by the condensation reaction of dia-
minoquinones 4 and 5 (ref. 11) or tetraaminoquinone 6 with
the corresponding boronic acids 7 in toluene. Compounds 1b
and 3d with tert-butyl groups were prepared to increase the
solubility. These compounds were purified by sublimation
(yields after sublimation: 1a 48%, 1b 54%, 2 35%, 3a 19%, 3b
54%, 3c 4%, 3d 12%), and characterized by MS and elemental
analysis.
3a
3b
3c
3d
+0.83e
+0.91e
+0.85e
+0.86d
a
In DMF. b 0.1 M n-Bu4NPF6 in DMF, Pt electrode, V vs. SCE. c CVs,
reversible waves, half-wave potentials. CV, irreversible wave, peak
d
e
f
DPVs, peak potentials. Calculated from reduction
potential.
potentials.
Photophysical properties
charge-transfer and a hydrogen-bonding network between the
diazaborole and quinone units.
The absorption maxima of monodiazaborole derivatives 1a and
1b were observed at 290, 456 and 286, 471 nm in DMF, respec-
tively (Fig. 2 and Table 1). Compound 2 with a thiadiazole ring
showed a similar absorption spectrum and is pale yellow in
solution. On the other hand, the absorption maxima of bis(dia-
zaborole) derivatives 3a–d were observed at 348, 321, 319 and
353 nm, respectively, which are almost colorless in solution. The
result observed in 3 suggests that p-conjugation based on
1,3-diazaborole rings is not effective for the red-shift of
absorption in solution. On the other hand, in the solid state, these
compounds show dark color (1 and 2: dark red, 3: dark brown).
Reflection spectra of 1a, 2 and 3b in the solid state are collected
by using an integrated sphere and depicted in Fig. 3. While 1a
Electrochemical properties
These compounds have electron-accepting properties attributed
to the quinone units. The reduction potentials were measured by
cyclic voltammograms (CV) and differential pulse voltammo-
grams (DPV) and the results are summarized in Table 1. The
naphthoquinone derivatives 1a and 1b showed reversible reduc-
tion peaks in the CVs (Fig. 4a and b). Replacement of the fused
benzene ring with a thiadiazole one in 2 decreases the LUMO
level, whose reduction potential was observed at ꢀ0.66 V.
Because of the poor solubility of bis(diazaborole) derivatives
3a–c, their reduction potentials were determined by DPVs. A CV
of a compound 3d with tert-butyl groups could be measured and
showed a reversible reduction peak and an irreversible oxidation
peak as depicted in Fig. 4d. Oxidation peaks were observed in all
of derivatives 3 and 1b.
and
2 effectively reflect the light at longer wavelengths
(>600 nm), almost all visible light is absorbed in compound 3b.
These are attributed to the intra- and intermolecular
X-Ray structure analysis
A single crystal of compound 1a was obtained from slow sub-
limation.‡ X-Ray analysis revealed the planar geometry with
a dihedral angle of 4.8ꢁ between the diazaborole and phenyl
rings. Interestingly, an infinite one-dimensional hydrogen-
bonding network was observed between the hydrogen atoms of
‡ X-Ray measurement of single crystal of 1a 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 crystal structure crystallographic software package except for
refinement, which was performed using SHELXL-97.
Crystal data for 1a: C17H10N2O2F3B2, M ¼ 342.08, red platelet, crystal
ꢁ
dimensions 0.70 ꢂ 0.70 ꢂ 0.15 mm, triclinic, space group P1, a ¼ 5.5337
ꢀ
(12), b ¼ 7.9622(19), c ¼ 16.321(3) A, a ¼ 101.835(6), b ¼ 94.236(7), g ¼
93.967(6), V ¼ 699.3(3) A , Z ¼ 2, Dc ¼ 1.625 g cmꢀ3, 6507 reflections
3
ꢀ
collected, 3115 independent (Rint ¼ 0.049), GOF ¼ 1.022, R1 ¼ 0.1265
(I > 2.00s(I)), wR2 ¼ 0.3359 for all reflections. The CCDC reference
number is 819166.
Fig. 2 UV-Vis spectra of (a) monodiazaborole derivatives 1 and 2, and
(b) bis(diazaborole) derivatives 3 in DMF.
This journal is ª The Royal Society of Chemistry 2011
J. Mater. Chem., 2011, 21, 16442–16447 | 16443

View Article Online
Fig. 3 Reflection spectra of 1a, 2 and 3b in the solid state.
Fig. 6 (a) HOMO (left) and LUMO (right) of 1a and 3b calculated from
the B3LYP/6-31G(d) level of theory. (b) Tautomeric forms of 1a-B and
1a-C.
(Fig. S6 and Tables S1 and S2 in the ESI†). Although the
tautomeric forms have high single point energies compared with
1a (1a-B: D38.8 kcal molꢀ1, 1a-C: D80.7 kcal molꢀ1), their small
HOMO–LUMO energies may contribute to the red-shift of the
absorption in the solid state. The similar hydrogen-bonding
networks are observed in compounds 1b and 2 in their FT-IR
data (Fig. S1 in the ESI†).
FET characteristics
The FET devices based on them were fabricated on thermally
oxidized silicon oxide with bottom-contact configuration, and
the measurements were carried out in situ without exposure to
air. A monodiazaborole derivative 1a showed clear n-type FET
characteristics with an electron mobility of 3.9 ꢂ 10ꢀ2 cm2 Vꢀ1 sꢀ1
and a high on/off ratio of 106 (Table 2). Similar n-type charac-
teristics were observed for compound 2 with an electron-
accepting thiadiazole. Unfortunately, in air, the n-type
performances gradually decreased (see ESI†). To improve the air
stability, higher electron accepting heterocycles are necessary. In
the case of symmetrical bis(diazaborole) derivatives 3, 3b with
trifluoromethyl groups exhibited good n-type behavior although
unsubstituted phenyl derivative 3a did not show FET charac-
teristics. This result indicates that the trifluoromethyl group is
necessary to show efficient n-type FET behavior.9d On the other
hand, compound 3c containing biphenyl units provided ambi-
polar FET characteristics.
Fig. 4 Cyclic voltammograms of (a) 1a, (b) 1b, (c) 2, and (d) 3d.
ꢀ
the diazaborole and oxygen atoms of the quinone unit (2.09 A) as
shown in Fig. 5. A p-stacking structure is formed between the
ꢀ
networks with an interplanar distance of 3.41 A, in which a short
ꢀ
contact of 3.15 A between the carbonyl groups was observed.
The p-stacking structure suggests the formation of a channel for
electron transportation through the LUMO. The HOMOs and
LUMOs are estimated by the molecular orbital calculations
based on the B3LYP/6-31G(d) level of theory (Fig. 6a). To
investigate a possibility of hydrogen transfer, tautomeric forms
1a-B, 1a-C (Fig. 6b) and a dimer model were also calculated
Table 2 FET characteristics with bottom contact geometriesa
Tsub
degree
/
Mobility/
cm2 Vꢀ1 sꢀ1
On/
off
Threshold/
V
Compound
1a
20
100
20
20
50
n: 8.8 ꢂ 10ꢀ3
n: 3.9 ꢂ 10ꢀ2
n: 3.7 ꢂ 10ꢀ2
n: 1.5 ꢂ 10ꢀ2
n: 9.2 ꢂ 10ꢀ3
n: 2.3 ꢂ 10ꢀ5
p: 1.5 ꢂ 10ꢀ5
4 ꢂ 106
1 ꢂ 106
6 ꢂ 105
3 ꢂ 103
1 ꢂ 105
7 ꢂ 103
6 ꢂ 10
+49
+53
+38
+43
+39
+53
ꢀ75
2
3b
3c
20
20
a
SiO2 gate dielectric: 300 nm thick. HMDS treated surface.
Interdigitated gold source and drain electrodes, L/W: 25 mm/294 mm.
Fig. 5 (a) Crystal packing of 1a viewed along the a-axis, (b) the
hydrogen-bonding network and (c) overlapping modes.
16444 | J. Mater. Chem., 2011, 21, 16442–16447
This journal is ª The Royal Society of Chemistry 2011

View Article Online
Fig. 7 X-Ray diffractograms of films 1a (Tsub ¼ 100 ꢁC), 2 (20 ꢁC), 3b
(20 ꢁC) and 3c (20 ꢁC) on HMDS treated surfaces.
XRD analysis and AFM measurements
Fig. 9 Top-contact FET characteristics of 1a (Tsub ¼ 20 ꢁC, HMDS
The thin films of 1–3 were examined by X-ray diffraction in
reflection mode (XRD). XRD patterns of films 1a, 2, 3b and 3c
are shown in Fig. 7. In the thin film of 1a, reflections up to the
fifth order were observed, indicating formation of lamellar
ordering and high crystallinity on the substrate. The d-spacing
treated surface): (a) output and (b) transfer characteristics.
AFM measurements and top-contact FET
ꢀ
calculated from the first reflection peak is 16.6 A. Since the
ꢀ
molecular length estimated from the X-ray analysis is 14.4 A, 1a
To further study the film morphology, atomic force microscopy
(AFM) images were measured with the tapping mode. AFM
images of 1a and 3b showed flat surfaces and the surface of 1a
was smoother than that of 3b. In the film 1a, a stair-like layer
with a vertical step size of ca. 1.6 nm corresponding to the
molecular length was observed as depicted in Fig. 8a. This fact
supports that the molecules stand on the substrate. A top-contact
FET device of 1a with a smooth surface was also fabricated.
n-Type characteristics with an electron mobility of 0.04 cm2 Vꢀ1
sꢀ1, on/off ratio of 106 and threshold voltage of +21 V were
obtained. Output and transfer characteristics with small hyster-
esis are shown in Fig. 9.
is considered to stand perpendicularly to the substrate.
Compound 2 also showed similar reflections up to the fifth
order, indicating the perpendicular molecular arrangement
ꢀ
(d-spacing: 15.4 A). On the other hand, in the case of
symmetrical bis(diazaborole) derivatives 3, the d-spacings esti-
mated from the first reflection peaks of films 3a–c were observed
ꢀ
at 13.8, 19.5 and 23.5 A respectively (Fig. 7 and ESI†), which
ꢀ
are not corresponding to calculated molecular lengths (17.7 A
ꢀ
ꢀ
for 3a, 18.6 A for 3b, and 26.3 A for 3c). Therefore, molecules
of 3a–c are considered to stand with declined orientation on the
substrate and they gave more complicated XRD patterns. These
results suggest that the hydrogen-bonding networks in mono-
diazaborole derivatives 1–2 are favorable to afford well-ordered
crystalline films.
Conclusions
In summary, we have developed novel p-systems composed of
diazaboroles and quinones. The three-coordinate boron units
having planar molecular geometries could be used as linkers of
p-systems leading to high electron transportation. Although the
calculated LUMOs are mainly localized on the quinone moieties,
planar boron units effectively assist to afford the n-channels
accompanied with well-ordered molecular arrangements.
Further modifications of the electron-accepting parts are
underway.
Experimental
General information
Melting points were obtained on a SHIMADZU DSC-60. 1H-NMR
spectra were recorded on a JEOL JNM-ECP 300 spectrometer. DI-
MS data were collected on a JEOL JMS-700 mass spectrometer. IR
spectra were recorded using a Smart iTR/ZnSe ATR on the Thermo
SCIENTIFIC Nicolet iS10 FT-IR. UV-Vis spectra were recorded
Fig. 8 AFM images of films (a) 1a (Tsub ¼ 100 ꢁC) and (b) 3b (20 ꢁC) on
HMDS treated surfaces.
This journal is ª The Royal Society of Chemistry 2011
J. Mater. Chem., 2011, 21, 16442–16447 | 16445

View Article Online
on a SHIMADZU Multi Spec-1500 and a JASCO V-650 spectro-
photometer. Reflection spectra in the solid states are collected by
using a JASCO ISV-722 integrated sphere. Cyclic voltammograms
and differential pulse voltammograms were recorded on a HOKU-
TODENKO HZ-5000. Pt disk, Pt wire and SCE were used as
working, counter, and reference electrodes. Tetrabutylammonium
hexafluorophosphate (TBAPF6: 0.1 mol dmꢀ3) was used as sup-
porting electrolyte in dry dimethylformamide (DMF). MO calcu-
lations 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 a CuKa
2,6-Diphenyl-2,3,6,7-tetrahydro-1H,5H-1,3,5,7-tetraaza-2,6-
dibora-s-indacene-4,8-dione (3a). A mixture of phenylboronic
acid 7a (1.20 g, 10.0 mmol) and 2,3,5,6-tetraaminobenzoquinone
6 (504 mg, 3.0 mmol) in toluene (150 mL) was refluxed for 2 d.
The resulting precipitate was filtered off while the solution was
hot. Purification of the crude product by sublimation gave 3a
(194 mg, 19%) as a dark brown solid.
Mp > 400 ꢁC (decomp.). MS/EI (70 eV): m/z 340 (M+, 100%).
IR(KBr) n (cmꢀ1): 3463, 3339, 1621, 1506, 1400, 1247, 1148,
1017, 992, 746, 690. Anal. calcd for C18H14B2N4O2: C, 63.60;
H, 4.15; N, 16.48. Found: C, 63.38; H, 4.21; N, 16.37. HR-MS/
EI: m/z (M+): calcd for C18H14B2N4O2 340.1303. Found
340.1299.
ꢀ
source (l ¼ 1.541A). AFM experiments for films in a tapping mode
were performed using a SII NanoTechnology SPA-400 (DFM)
instrument.
2,6-Bis-(4-trifluoromethylphenyl)-2,3,6,7-tetrahydro-1H,5H-
1,3,5,7-tetraaza-2,6-dibora-s-indacene-4,8-dione (3b). A mixture
of 4-(trifluoromethyl)phenylboronic acid (1.00 g, 5.3 mmol) and
2,3,5,6-tetraaminobenzoquinone 6 (354 mg, 2.1 mmol) in toluene
(150 mL) was refluxed for 36 h. The resulting precipitate was
filtered off while the solution was hot. Purification of the crude
product by sublimation gave compound 3b (544 mg, 54%) as
a dark brown solid.
Mp > 397 ꢁC (decomp.). MS/EI (70 eV): m/z 476 (M+, 100%).
IR(KBr) n (cmꢀ1): 3464, 3326, 1621, 1524, 1406, 1319, 1239, 1133,
1070, 1014, 833, 753, 660. Anal. calcd for C20H12B2F6N4O2: C,
50.47; H, 2.54; N, 11.77. Found: C, 50.24; H, 2.82; N, 11.73. HR-
MS/EI: m/z (M+): calcd for C20H12B2F6N4O2 476.1051. Found
476.1043.
Materials
2-(4-Trifluoromethylphenyl)-2,3-dihydro-1H-1,3-diaza-2-bora-
cyclopenta[b]naphthalene-4,9-dione (1a). A mixture of 4-(tri-
fluoromethyl)phenylboronic acid 7b (221 mg, 1.17 mmol) and
2,3-diaminonaphthoquinone 4 (200 mg, 1.06 mmol) in toluene
(150 mL) was refluxed for 18 h. The resulting precipitate was
filtered off while the solution was hot. Purification of the crude
product by sublimation gave a reddish-brown solid of 1a (174 mg,
48%).
Mp > 295 ꢁC (decomp.). MS/EI (70 eV): m/z 342 (M+, 100%).
IR(KBr) n (cmꢀ1): 3329, 1629, 1584, 1424, 1327, 1261, 1113, 1073,
972, 836, 751. Anal. calcd for C17H10BF3N2O2: C, 59.69; H, 2.95;
N, 8.19. Found: C, 59.74; H, 2.70; N, 8.20.
2,6-Bis-(4-phenylphenyl)-2,3,6,7-tetrahydro-1H,5H-1,3,5,7-tet-
raaza-2,6-dibora-s-indacene-4,8-dione (3c). A mixture of 4-phe-
2-(4-t-Butylphenyl)-2,3-dihydro-1H-1,3-diaza-2-bora-cyclo-
penta[b]naphthalene-4,9-dione (1b). A mixture of 4-tert-butyl-
phenylboronic acid 7d (210 mg, 1.18 mmol) and
2,3-diaminonaphthoquinone 4 (200 mg, 1.06 mmol) in toluene
(150 mL) was refluxed for 18 h. The resulting precipitate was
filtered off while the solution was hot. Purification of the crude
product by sublimation gave a reddish-brown solid of 1b
(190 mg, 54%).
Mp > 362 ꢁC (decomp.). MS/EI (70 eV): m/z 330 (M+, 100%).
1H-NMR (300 MHz, DMSO): d 10.17 (s, 2H, NH), 8.04 (d, 2H, J
¼ 8.0 Hz), 7.99 (dd, 2H, J ¼ 3.5, 3.5 Hz), 7.76 (dd, 2H, J ¼ 3.5,
3.5 Hz), 7.41 (d, 2H, J ¼ 8.0 Hz), 1.30 (s, 9H). IR(KBr) n (cmꢀ1):
3329, 2957, 1634, 1587, 1456, 1425, 1408, 1256, 1200, 1151, 970,
765, 710. Anal. calcd for C20H19BN2O2: C, 72.75; H, 5.80; N,
8.48. Found: C, 72.80; H, 5.29; N, 8.62.
nylphenylboronic
acid
(2.00
g,
10.0
mmol)
and
2,3,5,6-tetraaminobenzoquinone 6 (282 mg, 1.7 mmol) in toluene
(150 ml) was refluxed for 36 h. The resulting precipitate was
filtered off while the solution was hot. Purification of the crude
product by sublimation gave compound 2 (26 mg, 4%) as a dark
brown solid.
Mp > 400 ꢁC (decomp.). MS/EI (70 eV): m/z 492 (M+, 100%).
IR(KBr) n (cmꢀ1): 3459, 3313, 1633, 1523, 1401, 1330, 1244, 1152,
1015, 837, 765, 698, 660. Anal. calcd for C30H22B2N4O2: C,
73.21; H, 4.51; N, 11.38. Found: C, 71.40; H, 4.31; N, 11.04. HR-
MS/EI: m/z (M+): calcd for C30H22B2N4O2 492.1929. Found
492.1938.
2,6-Bis-(4-tert-butylphenyl)-2,3,6,7-tetrahydro-1H,5H-1,3,5,7-
A mixture of
tetraaza-2,6-dibora-s-indacene-4,8-dione (3d).
4-tert-butylphenylboronic acid 7d (250 mg, 1.40 mmol) and
2,3,5,6-tetraaminobenzoquinone 6 (80.0 mg, 0.48 mmol) in
toluene (150 ml) was refluxed for 36 h. The resulting precipitate
was filtered off while the solution was hot. Purification of the
crude product by sublimation gave compound 3d (65.4 mg, 30%)
as a dark brown solid.
Mp > 400 ꢁC (decomp.). MS/EI (70 eV): m/z 452 (M+, 100%).
1H-NMR: (DMSO, ppm) d ¼ 9.68 (s, 2H, NH), 9.66 (s, 2H,
NH), 7.91 (d, 4H, J ¼ 7.8 Hz), 7.34 (d, 2H, J ¼ 7.8 Hz), 1.27 (s,
18H). IR(KBr) n (cmꢀ1): 3467, 3322, 2957, 1619, 1405, 1330,
1241, 1152, 1012, 996, 823, 760, 658. Anal. calcd for
C26H30B2N4O2: C, 69.06; H, 6.69; N, 12.39. Found: C, 68.91; H,
6.04; N, 12.49.
6-(4-Trifluoromethylphenyl)-6,7-dihydro-5H-2-thia-1,3,5,7-tet-
raaza-6-bora-s-indacene-4,8-dione (2).
A mixture of 4-(tri-
fluoromethyl)phenylboronic acid 7b (213 mg, 1.12 mmol) and
2,3-diamino[5,6-c]thiadiazolequinone 5 (200 mg, 1.02 mmol) in
toluene (150 mL) was refluxed for 18 h. The resulting precipitate
was filtered off while the solution was hot. Purification of the
crude product by sublimation gave a reddish-brown solid of 2
(125 mg, 35%).
Mp > 293 ꢁC (decomp.). MS/EI (70 eV): m/z 350 (M+, 100%).
IR(KBr) n (cmꢀ1): 3326, 1645, 1525, 1413, 1324, 1152, 1117, 1072,
1020, 846, 754. Anal. calcd for C13H6F3N4O2S: C, 44.60; H, 1.73;
N, 16.00; S, 9.16. Found: C, 44.55; H, 1.80; N, 15.98; S, 8.98.
16446 | J. Mater. Chem., 2011, 21, 16442–16447
This journal is ª The Royal Society of Chemistry 2011

View Article Online
Device fabrication
Notes and references
Bottom-contact FET. Highly doped n+-Si wafers were used as
substrates, and a layer of 300 nm of silicon dioxide (SiO2: grown
by thermal oxidation) was used as a gate dielectric layer. Cr
(10 nm)/Au (20 nm) was successively evaporated and photo-
lithographically delineated to obtain source and drain electrodes.
The interdigitated structure of the source–drain contacts deter-
mined a channel length of 25 mm and a channel width of 294 mm
(6 mm ꢂ 49). Substrates were cleaned by acetone, 2-propanol
and ozone for 20 min, and immersed in hexamethyldisilazane
(HMDS) at rt for over 12 h to treat the surface. Organic semi-
1 (a) H. Usta, C. Risko, Z. Wang, H. Huang, M. K. Deliomeroglu,
A. Zhukhovitskiy, A. Facchetti and T. J. Marks, J. Am. Chem.
ꢂ
Soc., 2009, 131, 5586; (b) A. R. Murphy and J. M. J. Frechet,
Chem. Rev., 2007, 108, 1066; (c) C. R. Newman, C. D. Frisbie,
ꢂ
D. A. da Silva Filho, J. L. Bredas, P. C. Ewbank and K. R. Mann,
Chem. Mater., 2004, 16, 4436.
2 Y. Shirota, J. Mater. Chem., 2000, 10, 1.
3 (a) S. Yamaguchi, T. Shirasaka, S. Akiyama and K. Tamao, J. Am.
Chem. Soc., 2002, 124, 8816; (b) C. D. Entwistle and T. B. Marder,
Angew. Chem., Int. Ed., 2002, 41, 2927; (c) C. D. Entwistle and
T. B. Marder, Chem. Mater., 2004, 16, 4574; (d) T. Agou,
J. Kobayashi and T. Kawashima, Chem.–Eur. J., 2007, 13,
8051.
4 (a) W. Niu, B. Rambo, M. D. Smith and J. J. Lavigne, Chem.
Commun., 2005, 5166; (b) B. M. Rambo and J. J. Lavigne, Chem.
Mater., 2007, 19, 3732; (c) D. N. Coventry, A. S. Batsanov,
A. E. Goeta, J. A. K. Howard, T. B. Marder and R. N. Perutz,
Chem. Commun., 2005, 2172.
ꢀ
conductor 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.
Top-contact FET. The SiO2 gate dielectric was 200 nm thick.
ꢀ
€
5 (a) F. Jakle, Coord. Chem. Rev., 2006, 250, 1107; (b) N. Matsumi,
K. Kotera, K. Naka and Y. Chujo, Macromolecules, 1998, 31, 3155.
6 (a) H. Noguchi, K. Hojo and M. Suginome, J. Am. Chem. Soc., 2007,
129, 758; (b) S. Yamaguchi and A. Wakamiya, Pure Appl. Chem.,
2006, 78, 1413; (c) T. Kojima, J.-i. Nishida, S. Tokito and
Y. Yamashita, Chem. Lett., 2008, 37, 1122.
7 (a) L. Weber, Coord. Chem. Rev., 2001, 215, 39; (b) L. Weber,
V. Werner, M. A. Fox, T. B. Marder, S. Schwedler, A. Brockhinke,
H.-G. Stammler and B. Neumann, Dalton Trans., 2009, 1339; (c)
S. Maruyama and Y. Kawanishi, J. Mater. Chem., 2002, 12, 2245;
(d) L. Weber, V. Werner, M. A. Fox, T. B. Marder, S. Schwedler,
A. Brockhinke, H.-G. Stammler and B. Neumann, Dalton Trans.,
2009, 2823.
8 (a) I. Yamaguchi, B.-J. Choi, T.-A. Koizumi, K. Kubota and
T. Yamamoto, Macromolecules, 2007, 40, 438; (b) I. Yamaguchi,
T. Tominaga and M. Sato, Polym. Int., 2009, 58, 17; (c) T. Kojima,
D. Kumaki, J.-I. Nishida, S. Tokito and Y. Yamashita, J. Mater.
Chem., 2011, 21, 6607.
9 (a) Q. Tang, Z. Liang, J. Liu, J. Xu and Q. Miao, Chem. Commun.,
2010, 46, 2977; (b) N. Hayashi, T. Yoshikawa, T. Ohnuma,
H. Higuchi, K. Sako and H. Uekusa, Org. Lett., 2007, 9, 5417; (c)
Q. Miao, M. Lefenfeld, T.-Q. Nguyen, T. Siegrist, C. Kloc and
C. Nuckolls, Adv. Mater., 2005, 17, 407; (d) M. Mamada,
D. Kumaki, J.-i. Nishida, S. Tokito and Y. Yamashita, ACS Appl.
Mater. Interfaces, 2010, 2, 1303.
10 n-Type FET materials with four-coordinate borons have recently
reported (a) Y. Sun, D. Rohde, Y. Liu, L. Wan, Y. Wang, W. Wu,
C. Di, G. Yu and D. Zhu, J. Mater. Chem., 2006, 16, 4499; (b)
K. Ono, J. Hashizume, H. Yamaguchi, M. Tomura, J.-i. Nishida
and Y. Yamashita, Org. Lett., 2009, 11, 4326; (c) K. Ono,
A. Nakajima, Y. Tsuji, T. Kinoshita, M. Tomura, J.-i. Nishida and
Y. Yamashita, Chem.–Eur. J., 2010, 16, 13539.
11 T. Suzuki, H. Fujii, Y. Yamashita, C. Kabuto, S. Tanaka,
M. Harasawa, T. Mukai and T. Miyashi, J. Am. Chem. Soc., 1992,
114, 3034.
The organic semiconductor (300 A) was deposited on the SiO2 by
vacuum evaporation at a rate of 0.1–0.2 A sꢀ1 under a pressure of
ꢀ
10ꢀ5 Pa. During the evaporation, the temperature of the
substrate was maintained by heating a copper block on which the
substrate was mounted. Au was used as source and drain elec-
trodes and deposited on the organic semiconductor layer
through a shadow mask with a channel width (W) of 1000 mm
and a channel length (L) of 50 mm. Finally, the FET measure-
ments were carried out at rt in a vacuum chamber (10ꢀ5 Pa)
without exposure to air with Hewlett-Packard 4140A and 4140B
models.
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.
Acknowledgements
This work is supported by a Grant-in-Aid for Scientific Research
(no. 19350092 and 22550162) from the Ministry of Education,
Culture, by Sports, Science and Technology, Japan, and by the
Global COE program ‘‘Education and Research Center for
Emergence of New Molecular Chemistry’’. We thank Center
for Advanced Materials Analysis, Technical Department, TIT
for measurements of elemental analysis and MS.
This journal is ª The Royal Society of Chemistry 2011
J. Mater. Chem., 2011, 21, 16442–16447 | 16447