Bisacenaphthopyrazinoquinoxaline derivatives: Synthesis, physical properties and applications as semiconductors for n-channel field effect transistors

Article abstract of DOI:10.1039/c3ob40982a

Several bisacenaphthopyrazinoquinoxaline (BAPQ) based derivatives 1-3 were synthesized by condensation between the acenaphthenequinones and 1,2,4,5-tetraaminobenzene tetrahydrochloride. Their optical, electrochemical and self-assembling properties are tun

Full text of DOI:10.1039/c3ob40982a

Organic &
Biomolecular Chemistry
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Bisacenaphthopyrazinoquinoxaline derivatives:
synthesis, physical properties and applications as
Cite this: Org. Biomol. Chem., 2013, 11,
5683
semiconductors for n-channel field effect transistors†
Chenhua Tong,a Jingjing Chang,a Jun Min Tan,a Gaole Dai,a Kuo-Wei Huang,b
Hardy Sze On Chan*a and Chunyan Chi*a
Several bisacenaphthopyrazinoquinoxaline (BAPQ) based derivatives 1–3 were synthesized by conden-
sation between the acenaphthenequinones and 1,2,4,5-tetraaminobenzene tetrahydrochloride. Their
optical, electrochemical and self-assembling properties are tuned by different substituents. Among them,
compound 3 possesses a homogeneously distributed low-lying LUMO due to the peripheral substitution
with four cyano groups. The corresponding n-channel field effect transistors showed a field effect elec-
Received 9th May 2013,
Accepted 4th July 2013
DOI: 10.1039/c3ob40982a
www.rsc.org/obc
tron mobility of 5 × 10−3 cm2 V−1 s−1
.
aromatic 4n + 2 stabilization. Furthermore, introduction of a
five-membered ring also causes a two-dimensional fusion,
Introduction
Introduction of an imine nitrogen atom into the framework of which further stabilizes the π-system. Stable and soluble acene
acenes has become an efficient way to stabilize this type of derivatives containing both pyrazine units and five-membered
unstable molecule. At the same time, due to the increased elec- rings are therefore of interest. They can be achieved through
tron affinity,1 they can be used as potential n-type semiconduct-
a
condensation reaction between arene diamine and
ing materials.2–4 Depending on the number and positions of acenaphthenequinone. Herein, we report the development of
nitrogen atoms in the acene framework, different electronic several bisacenaphthopyrazinoquinoxaline (BAPQ) based candi-
structures, stability, solubility, and molecular packing can be dates 1–3 (Fig. 1) and investigate their potential application in
achieved.5 Although many syntheses and theoretical calcu- n-channel OFETs. As an analogue of 5,7,12,14-tetraazapenta-
lations on aza-acenes have been conducted, there are still a cene, BAPQ has a larger area for packing, a slightly lower LUMO
limited number of N-heteroacenes that can be successfully used energy level and a much higher stability,8 but an increased re-
in electronic devices such as organic field effect transistors organization energy in principle.9 Recently, the linear and star-
(OFETs), especially when processed from solutions.2l,m
shaped BAPQ derivatives with imide groups have been syn-
A pyrazine ring is the most widely utilized moiety to con- thesized and proposed as the n-type semiconductors.3d
struct N-heteroacenes owing to its convenient synthesis by con- However, their FET performance has not been reported. In this
densation reactions.6 However, pyrazinacenes with a high paper, three molecules based on BAPQ have been synthesized
pyrazine unit density are hard to obtain because they are very and used for OFET applications by solution processing
sensitive to even weak nucleophiles.7 Incorporation of other techniques. Two types of solubilizing functional groups were
electron-withdrawing groups into a pyrazinacene is therefore adopted to improve the solubility: (i) flexible aliphatic chains
effective for a higher electron affinity.2l,m,3 A fused five-mem- on the naphthalene edges (compound 1) and (ii) the alkyl-
bered ring can lower the LUMO energy level of an acene frame- phenyl group in the middle edges (compounds 2 and 3). The
work due to its tendency to accept an electron through
aDepartment of Chemistry, National University of Singapore, 3 Science Drive 3,
Singapore, 117543, Singapore. E-mail: chmcsoh@nus.edu.sg, chmcc@nus.edu.sg;
Fax: +65 6779 1691; Tel: +65 6516 5375
bKAUST Catalysis Center and Division of Chemical and Life Sciences and
Engineering, 4700 King Abdullah University of Science and Technology, Thuwal
23955-6900, Kingdom of Saudi Arabia
†Electronic supplementary information (ESI) available: Structural characteriz-
ation data for all new compounds; DFT calculation data; additional electro-
chemical data; TGA curves and thin film XRD data. See DOI: 10.1039/c3ob40982a
Fig. 1 Structures of BAPQ derivatives 1–3.
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four strong electron-withdrawing cyano groups in 3 are
expected to further lower the LUMO energy level and reduce
the inner reorganization energy.5 The target compounds have
good stability and solubility, and their photophysical pro-
perties, electrochemical properties, thermal behaviours, and
OFET activities are studied in detail in this work.
Results and discussion
Synthesis
The synthesis of compound 1 started from the protection of
5,6-dibromoacenaphthylene-1,2-dione 410 by ethylene glycol
to give compound 5 in 45% yield (Scheme 1). Subsequent
Hagihara–Sonogashira coupling between 5 and 1-tetradecyne
gave compound 6 in 77% yield. Hydrogenation of the alkyne
groups in compound 6 was then conducted using hydrazine
over Pd/C to afford the dialkylated compound 7 in 34% yield.
Herein, Kumada coupling reaction was also attempted to
directly prepare compound 7 from 5 using saturated aliphatic
Grignard reagent, but resulted in a failure presumably due to
the steric hindrance caused by the two neighbouring bromo
groups. The p-toluenesulfonic acid-catalyzed deprotection of 7
was carried out in a mixed solvent (water, acetonitrile (AN)
and dichloromethane (DCM)) to give 8 in quantitative yield.
BAPQ derivative 1 was finally obtained through the acid-cata-
lyzed condensation between acenaphthenequinone 8 and
the 1,2,4,5-tetraaminobenzene tetrahydrochloride 911 in 70%
yield.
The syntheses of compounds 2–3 started from the Stille
coupling between 4,7-dibromo-5,6-dinitrobenzothiadiazole
1012 and 4-nonylphenyl trimethyl stannane 1113 to give the
dinitrobenzothiadiazole 12 in 71% yield (Scheme 2). Reduction
of 12 by Zn/HOAc led to an air-sensitive intermediate tetra-
amine 13, which reacted with the quinone 14a and 14b14 to
give BAPQ derivatives 2 and 3 in overall 46% and 13% yield,
respectively. Compound 2 can be prepared from 12 in a one-
pot reaction without the purification of intermediate 15.
However, the separation of intermediate 16 was necessary for
further reaction and the reaction yield was low (28%), which is
due to the decomposition of the cyano groups in the presence
of Zn/HOAc and the incomplete reduction of 12. The
Scheme 2 Synthetic route of BAPQ derivatives 2–3.
condensation between 16 and 14b finally gave pure compound
3 in 48% yield.
The chemical structures of compounds 1–3 and intermedi-
ates are identified by NMR, MALDI-TOF mass spectra and
elemental analysis (see ESI†). Because of the strong aggrega-
tion, compound 1 has a poor solubility in most organic sol-
vents at room temperature, but it can be dissolved in hot
toluene. Compound 2 is well dissolved in chlorinated or aro-
matic solvents, and compound 3 shows a good solubility in
chlorobenzene.
Photophysical properties
The UV-Vis absorption and fluorescence spectra recorded in
dilute toluene solution and a thin film are shown in Fig. 2,
and the data are summarized in Table 1. At a concentration of
1.0 × 10−5 M in toluene solution, compound 1 shows a broad
absorption band at room temperature (see Fig. S1 in ESI†)
which is consistent with the spectrum of 1 in a thin film form.
This similarity is caused by the strong tendency of 1 to form
aggregates in solution. If the solution is heated to 80 °C, the
absorption band becomes sharp with an absorption maximum
at 378 nm (Fig. 2a), indicating that the aggregation is reduced
at high temperature. This aggregation effect can be also
1
observed from its H NMR spectrum. At room temperature, no
signal related to aromatic protons can be observed in many
organic solvents such as CDCl3 and CDCl2CDCl2. However, the
sharp peaks appear between 7.7 and 9.1 ppm when the
CDCl2CDCl2 solution is heated to 100 °C. This further con-
firms that the aggregates are suppressed at high temperature.
At room temperature, compounds 2 and 3 just display a
narrow intense absorption band with λmax at 376 nm and
397 nm, respectively, due to the suppressed aggregation by the
Scheme 1 Synthetic route of BAPQ derivative 1.
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Fig. 3 Cyclic voltammograms of BAPQ derivatives 1–3 in chlorobenzene at a
concentration of 1 × 10−3 M (curve of 1 was recorded at 80 °C).
(Fig. 3 and Fig. S2 in ESI†) and the data are summarized in
Table 1. Due to strong aggregation, the voltammogram of com-
pound 1 was recorded at elevated temperature (80 °C), but only
one weak redox wave was observed, with half-wave potential
E1/2 = −1.65 (vs. Fc+/Fc). For compound 2, two pairs of pyra-
zine-based reversible reduction waves at E1/2 = −2.02 and
−1.63 V and one naphthalene-based irreversible oxidization
wave at E1/2 = 1.01 V were observed with a band gap of 2.44 eV.
A small peak at −0.20 V corresponds to the reduction of an
irreversibly oxidized product from compound 2 on the elec-
trode surface. Compound 3, as a structure designed for high
Fig. 2 (a) Normalized UV-Vis absorption and fluorescence spectra of 1–3 in
toluene (the spectra of compound 1 were recorded at 80 °C, all of the fluore-
scence spectra were recorded with excitation wavelength at their absorption
maximum). (b) Normalized UV-Vis absorption spectra of 1–3 in thin films.
electron affinity, exhibits four pairs of reduction waves at E1/2
=
−1.90, −1.70, −1.38 and −1.09 V, respectively. The LUMO
energy levels of these BAPQ derivatives are determined to be
−3.27 eV for 1 and 2, and −3.78 eV for cyanide 3, from the
onset of the first reduction wave. They all exceed the suggested
value (<−3.15 eV) to allow an n-channel operation of OFETs.4a
alkylphenyl substituents. The optical band gap extracted from
the low-energy absorption edge is 2.70, 2.37 and 2.25 eV for
compounds 1–3, respectively. In thin films, the absorption
spectra of compounds 1–3 significantly become broader with
long tails to the near-IR region and show slight hypsochromic
shifts (at λmax) compared to that in solutions, indicating strong
intermolecular associations in the solid state. Compounds 1–3
show sharp fluorescence spectra in toluene (at 1.0 × 10−6 M)
with emission maxima at 499, 538 and 579 nm, respectively. In
the solid state, no fluorescence can be observed for all of these
compounds due to the strong aggregation.
TD DFT calculations
Time-dependent density functional theory (TD DFT at B3LYP/
6-31G*)16 calculations were conducted for compounds 1–3 to
understand their electronic and optical properties by using
Gaussian 0917 (see details in ESI†). All the solubilizing ali-
phatic chains were displaced by ethyl groups to simplify the
calculation. The geometries of these molecules were fully opti-
mized in the gas phase using the default convergence criteria
Electrochemical properties
Cyclic voltammetry (CV) and differential pulse voltammetry without any constraints and confirmed by frequency calcu-
(DPV) measurements were conducted for 1–3 in chlorobenzene lations. The LUMO orbitals of compounds 1–2 are mainly
Table 1 Summary of photophysical and electrochemical properties of 1–3a
E1/2/V
HOMO/eV
LUMO/eV
Eg/eV
Eogpt/eV
λambasxc/nm
ε/cm−1 M−1
λemmaixd/nm
λambasxe/nm
1
2
3
−1.65
−5.97b
−5.71
−3.27
−3.27
−3.78
—
2.44
—
2.70
2.37
2.25
378
376
397
53 000
237 600
155 000
499
538
579
390
366
390
−2.02, −1.63, 1.01
−1.90, −1.70, −1.38, −1.09
−6.03b
a HOMO and LUMO energy levels were determined from the onset of the first oxidation and reduction wave according to the equations: HOMO =
−(4.8 + Eoonx set) eV and LUMO = −(4.8 + Eorendset) eV.15 b Calculated according to the equation: HOMO = LUMO − Eogpt c In dilute toluene solution
.
(1.0 × 10−5 M). d In dilute toluene solution (1.0 × 10−6 M). e In thin film.
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Fig. 4 HOMO (up) and LUMO (down) profiles of BAPQ derivatives (a) 1, (b) 2
and (c) 3.
distributed in the central aza-anthracene moiety (Fig. 4).
Owing to the four strong π electron-withdrawing cyano groups,
the LUMO of 3 is mainly localized in the two side parts of the
central benzene ring, which may enhance intermolecular elec-
tronic coupling in the solid state. The HOMO orbital of mole-
cule 1 is homogeneously distributed, while it is mainly
localized at the central phenyl benzene rings for molecules 2
and 3. The partially separated frontier orbital profiles of mole-
cule 3 indicate significant intramolecular charge transfer
character. This is the reason why the absorption and emission
spectra of compound 3 show an obvious red-shift compared to
that of molecules 1 and 2. Accordingly, compound 2 also has a
weak intramolecular charge transfer character. The calculated
absorption data predicted a major absorption band at 366 nm
(oscillator strength f = 3.1295) for 1, three bands at 462, 365,
276 nm (f = 0.1521, 1.0988, 0.5411, respectively) for 2, and two
bands at 557, 373 nm ( f = 0.2800, 2.6300, respectively) for 3
(Fig. S3–S5 in ESI†). The major π–π* absorption band for these
three compounds between 310 and 420 nm is consistent with
the experimental absorption data in toluene. The weak charge
transfer band between 450 and 600 nm in the calculated data
of compounds 2 and 3 can be also found in the experimental
spectra where it is more like a tail.
Fig. 5 DSC curves of compounds 1 and 2 (at a heating rate of 10 °C min−1 in
N2).
Thermal behaviour
The thermal stability was determined using thermogravimetric
analysis (TGA) in nitrogen gas at a heating rate of 10 °C min−1
.
The decomposition temperatures (Td, corresponding to the 5%
weight loss) for compounds 1, 2, and 3 are 397, 384, and
306 °C, respectively (Fig. S6 in ESI†). Differential scanning
calorimetry (DSC) curves were recorded at a heating rate of
10 °C min−1 and showed endothermic transitions at 240 °C for
1, 300 °C for 2 upon heating (Fig. 5), which have been con-
firmed as melting points by using polarizing optical
Fig. 6 POM image of 2 at 295 °C upon heating.
Field effect transistors
OFETs were fabricated based on thin films of compounds 1–3
from solution, but only the thin films of 3 showed FET activity.
Bottom-gate top-contact FETs were fabricated on p+-Si/SiO2
substrates by casting a solution of 3 in chlorobenzene (0.15 wt%)
onto octadecyltrichlorosilane (OTS) treated substrates. Au
source and drain electrodes (80 nm) were patterned on the
organic layer through a shadow mask. The as-spun thin film
devices were characterized under a N2 atmosphere or in air.
The typical transfer and output curves measured in N2 are
microscopy (POM). Compound
2 also exhibited another
endothermic transition (glass transition) at 260 °C before its
melting point. POM measurements disclosed that 2 entered an
anisotropic phase at ∼290 °C upon heating and a microcrystal-
line texture was observed (Fig. 6). Broad and weak endothermic
transitions (∼96 °C for 1 and ∼108 °C for 2) were observed in
DSC curves; however, the corresponding phase transitions
could not be observed by POM. Compound 3 showed no phase
transition from room temperature to Td.
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Fig. 7 (a) Output and (b) transfer characteristics of FET devices fabricated by
casting
a solution of 3 in chlorobenzene on OTS-treated substrates and
measured in N2.
shown in Fig. 7. The device operated in the n-channel region
and revealed an average charge carrier mobility of 0.005 cm2
V−1 s−1 in the saturation region. The current on/off ratio was
about 104, and the threshold voltage was around 10 V. When
the device was exposed to air, it still showed an electron mobi-
lity of 0.001 cm2 V−1 s−1, indicating a relatively good air stability.
This behaviour may be owing to the cyano groups in 3 which
increase the electron affinity of the molecules and enhance the
intermolecular association in the solid state.5,18 The thin film
morphology and microstructure were characterized by the use
of tapping-mode atomic force microscopy (AFM) and two-
dimensional X-ray diffraction (2D XRD). The thin film exhibited
fibrous crystals but with a scatter of grains with a size larger
than several microns (Fig. 8c, roughness: 18.1 nm). The XRD
pattern (Fig. S7 in ESI†) of the thin film exhibited one major
reflection in the small angle region (2θ = 4.27°, d-value =
20.7 Å), one weak reflection (2θ = 8.53°, d-value = 10.4 Å), and a
halo in the wide angle region (2θ > 25°), indicating a dense
layer-like packing of the molecules on the substrate.
The AFM measurements on the thin film of 1 (casting from
a chlorobenzene solution) displayed an inhomogeneous mor-
phology with a high roughness of 70.5 nm (Fig. 8a). The
reason may be attributed to the poor solubility of 1 at room
temperature, which hinders the generation of a homogeneous
film. XRD pattern of the film only showed one weak reflection
at 2θ = 6.55° (d-value = 13.5 Å) (Fig. S7 in ESI†), indicating a
disordered structure. The AFM image of the thin film of 2 was
much more homogeneous. It exhibited large plate-like crystals
and gave a surface roughness of 5.92 nm (Fig. 8b). However,
the corresponding XRD pattern only showed one reflection
peak at 2θ = 4.80° (d-value = 18.4 Å, Fig. S7 in ESI†) and the
intermolecular packing structure cannot be determined. The
low molecular order in 1 and 2 may explain their FET
inactivity.
Fig. 8 AFM height images of thin films of (a) 1, (b) 2, and (c) 3 on an OTS
modified SiO2 substrate.
were studied in detail. During the synthesis, a new route was
developed for the first time to prepare the dialkylated ace-
naphthenequinone 8. Compared with the reported mono-alkyl-
ated acenaphthenequinone,19 our dialkylated one is symmetric
and hence can control the regularity of the product. The meso-
substitution with alkylphenyl groups is a more efficient way to
improve the solubility of these highly aggregated pyrazinacene
compounds. Owing to the attachment of four cyano groups,
compound 3 shows a very low-lying LUMO and improved
LUMO distribution.5 The field effect electron mobility of
0.005 cm2 V−1 s−1 under a nitrogen atmosphere (0.001 cm2 V−1
s−1 in air) was measured from the solution-cast films of 3. This
also represents one of the few examples of pyrazinacenes
showing FET activity through solution processing.
Conclusions
In summary, three BAPQ based derivatives 1–3 with different
substituents were synthesized and their physical properties
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semiconductor parameter analyzer in the N2 glove box or in
air. To minimize leakage currents, small trenches in the thin
film around the electrodes were created with a needle. The
Experimental section
General
Anhydrous tetrahydrofuran (THF) was obtained by distillation FET mobility was extracted using the following equation in the
with sodium. 5,6-Dibromoacenaphthylene-1,2-dione (4),10 saturation regime from the gate sweep: ID = W/(2L)Ciμ(VG
−
1,2,4,5-tetraaminobenzene tetrahydrochloride (9),11 4,7- VT)2, where ID is the drain current, μ is the field-effect mobility,
dibromo-5,6-dinitrobenzo[c][1,2,5]thiadiazole (10),12 4-nonyl- Ci is the capacitance per unit area of the gate dielectric layer
phenyl(trimethyl)stannane (11)13 and 5,6-dicyano acenaphthene- (SiO2, 200 nm, Ci = 17 nF cm−2), and VG and VT are gate voltage
quinone (14)14 were prepared according to the reported and threshold voltage, respectively. W and L are respectively
methods. All other chemicals were purchased from commer- the channel width and length.
cial supplies and used without further purification. 1H NMR
Synthesis and characterization
and 13C NMR spectra were recorded using
a
Bruker
DRX-300 MHz spectrometer or DRX-500 MHz spectrometer in
1,2-Di(1,3-dioxolan-2-yl)-5,6-dibromoacenaphthylene (5). A
CDCl3 or in CDCl2CDCl2 at 75 °C. All chemical shifts are suspension of 5,6-dibromoacenaphthenequinone 4 (11.8 g,
quoted in ppm, relative to tetramethylsilane. The residual 34.71 mmol), ethylene glycol (30 mL) and 4-methylbenzene-
solvent peak is used as a reference standard. MALDI-TOF mass sulfonic acid (1.20 g, 6.94 mmol) in dry toluene (100 mL) was
spectra were recorded using a Bruker MALDI mass spectro- refluxed for three days. The resulting water was removed from
meter with 1,8,9-trihydroxy anthracene as the matrix. UV-Vis the reaction by means of a water separator. More ethylene
absorption and fluorescence spectra were recorded using a glycol (30 mL) and 4-methylbenzenesulfonic acid (1.20 g,
SHIMADZU UV-1700 UV-Vis spectrometer and a SHIMADZU 6.94 mmol) were added to the reaction system every 24 h. After
RF-5301PC fluorometer, respectively. Cyclic voltammetry was the reaction was completed, the solvent was evaporated and
performed on a CH Instrument 620C electrochemical analyzer the crude product was extracted from the residue using chloro-
with a three-electrode cell in a solution of 0.1 M tetrabutyl- form (50 mL × 6). Chloroform was removed under reduced
ammonium hexafluorophosphate (Bu4NPF6) in HPLC grade pressure to give a crude product, which was washed with
chlorobenzene with a scan rate of 50 mV s−1. A gold electrode ethanol to afford a light brown compound 5 (6.80 g, 45%
1
with a diameter of 2 mm, a Pt wire and an AgCl/Ag electrode yield). H NMR (500 MHz, CDCl3) δ ppm = 8.01 (d, J = 7.6 Hz,
was used as the working electrode, counter electrode and refer- 2H), 7.40 (d, J = 7.6 Hz, 2H), 4.17 (m, 4H), 3.69 (m, 4H); 13C
ence electrode, respectively. The potential was then calibrated NMR (125 MHz, CDCl3) δ ppm = 138.4, 138.1, 136.2, 127.7,
against the ferrocenium/ferrocene couple. TGA and DSC 120.9, 119.3, 97.9, 61.7; Anal. Calcd for C16H12Br2O4: C, 44.89;
measurements were performed at a heating rate of 10 °C H, 2.83; found: C, 44.92; H, 2.73.
min−1 under nitrogen flow on a TA Instruments SDT 2960 and
1,2-Di(1,3-dioxolan-2-yl)-5,6-di(tetradec-1-ynyl)acenaphthyl-
a METTLER TOLEDO DSC1, respectively. The POM platform ene (6). Tetradec-1-yne (3.8 g, 19.62 mmol) was injected into a
was the OLYMPUS BX51, cooperated with a LINKAM TP94 as a suspension of compound 5 (3.5 g, 8.18 mmol), Pd(PPh3)2Cl2
thermal control. Tapping-mode atomic force microscopy (288 mg, 0.41 mmol), CuI (156 mg, 0.82 mmol) and triethyl-
(TM-AFM) was performed on a Nanoscope V microscope amine (4.1 g, 5.7 mL) in dry THF (20 mL) under the protection
(Veeco Inc.). X-ray diffraction (XRD) patterns of the thin film of argon. The mixture was stirred at 75 °C for two days. After
were measured on a Bruker-AXS D8 DISCOVER with a GADDS cooling to room temperature, the mixture was extracted using
X-ray diffractometer. Copper Kα line was used as a radiation ethyl acetate (EA) (50 mL × 3), subsequently washed with de-
source.
ionized water (50 mL × 2) and dried over anhydrous mag-
nesium sulphate. The solvent was removed under reduced
pressure and the residue was purified by silica gel column
Device fabrication
Top-contact, bottom-gate FET devices were prepared on the p+ chromatography (silica gel, hexane : EA = 15 : 1) to give a pure
silicon wafer. A 200 nm thermal SiO2 layer serves as the gate compound 6 (4.1 g, 77% yield) as white crystals. 1H NMR
dielectric. The SiO2/Si substrate was cleaned with acetone and (300 MHz, CDCl3) δ ppm = 7.74 (d, J = 7.2 Hz, 2H), 7.46 (d, J =
isopropanol, then immersed in
a piranha solution for 7.2 Hz, 2H), 4.15 (m, 4H), 3.69 (m, 4H), 2.52 (t, J = 7.1 Hz, 4H),
8 minutes, followed by rinsing with deionized water, and then 1.67 (m, 4H), 1.46 (m, 4H), 1.27 (m, 32H), 0.88 (t, J = 6.9 Hz,
re-immersed in a 3 mM solution of octadecyltrichlorosilane 6H); 13C NMR (75 MHz, CDCl3) δ ppm = 137.1, 135.9, 135.4,
(OTS) in hexadecane at rt for 16 h in N2. It was then rinsed 129.5, 121.5, 119.1, 98.4, 97.4, 79.7, 61.7, 31.9, 29.7, 29.6, 29.3,
with CHCl3, IPA, DI water and then blow dried with nitrogen 29.2, 28.9, 22.7, 20.3, 14.1; Anal. Calcd for C44H62O4: C, 80.69;
gas. The semiconductor layer was deposited on top of the OTS- H, 9.54; found: C, 80.38; H, 9.56; MALDI-TOF MS: 655.340
modified dielectric surface by solution-casting from the solu- [M + H]+; calculated exact mass: 654.465.
tion of compound 3 in chlorobenzene (0.15 wt%). Sub-
5,6-Ditetradecylacenaphthenequinone (7). Palladium (on
sequently, gold source/drain electrodes were deposited by active carbon, 400 mg) was added to a suspension of com-
thermal evaporation through a metal shadow mask to create a pound 6 (2.79 g, 4.26 mmol) in ethanol (250 mL) and hydra-
series of FETs with channel (W = 1 mm, L = 100 nm). The FET zine monohydrate (30 mL). The mixture was then stirred at
devices were then characterized using a Keithley SCS-4200 reflux temperature under the protection of argon for two days.
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After cooling to room temperature, the mixture was filtered with a solution of KF in methanol. The mixture was extracted
through a thin pad of Celite. The organic solvent of the filtrate using EA (15 mL × 3) and then washed with deionized water
was removed under reduced pressure to form an opaque or (30 mL × 2) and dried over anhydrous magnesium sulphate.
suspension of the crude product in hydrazine hydrate. It was After the solvent was removed under reduced pressure, the
extracted using hexane or EA (50 mL × 2) and then washed residue was purified by column chromatography (silica gel,
with water (30 mL × 5). Recrystallization from hexane/EA/ hexane : EA = 20 : 1) to give a pure compound 12 (230 mg, 71%
ethanol gave a pure compound 7 (970 mg, 34% yield) as clear yield) as a yellow solid. 1H NMR (500 MHz, CDCl3) δ ppm =
1
white crystals. H NMR (500 MHz, CDCl3) δ ppm = 7.45 (d, J = 7.49 (d, J = 8.2 Hz, 4H), 7.37 (d, J = 8.2 Hz, 4H), 2.71 (t, J =
7.0 Hz, 2H), 7.39 (d, J = 7.0 Hz, 2H), 4.17 (m, 4H), 3.71 (m, 4H), 7.6 Hz, 4H), 1.69 (m, 4H), 1.40–1.29 (m, 24H), 0.89 (t, J = 7.6
3.09 (t, J = 7.6 Hz, 4H), 1.66 (m, 4H), 1.46 (m, 4H), 1.34–1.26 Hz, 6H); 13C NMR (125 MHz, CDCl3) δ ppm = 153.1, 145.7,
(m, 40H), 0.88 (t, J = 7.0 Hz, 6H); 13C NMR (125 MHz, CDCl3) 142.5, 129.1, 129.0, 128.9, 127.6, 35.9, 31.9, 31.1, 29.5, 29.4,
δ ppm = 140.5, 137.5, 136.0, 130.1, 129.0, 118.8, 98.6, 61.7, 29.3, 22.7, 14.1; Anal. Calcd for C36H46N4O4S: C, 68.54; H, 7.35;
36.1, 33.4, 31.9, 29.8, 29.7, 29.6, 29.5, 29.4, 22.7, 14.1; Anal. N, 8.88; S, 5.08; found: C, 68.44; H, 7.24; N, 8.54; S, 4.94;
Calcd for C44H70O4: C, 79.71; H, 10.64; found: C, 79.34; H, MALDI-TOF MS: 630.401 [M]−; calculated exact mass: 630.324.
10.98; MALDI-TOF MS: 663.424 [M + H]+; calculated exact
mass: 662.527.
BAPQ derivative 2. Zn powder (207 mg, 3.2 mmol) was
added to a suspension of compound 12 (100 mg, 0.16 mmol)
5,6-Ditetradecylacenaphthenequinone (8). A solution of in oxygen free acetic acid (8 mL). The mixture was then stirred
4-methylbenzenesulfonic acid (2.5 g, 14.5 mmol) in aceto- at 65 °C under the protection of argon to generate tetraamine
nitrile (22 mL) and water (7 mL) was added to the solution of 13. After one hour, the reaction mixture became a white sus-
compound 7 (960 mg, 1.45 mmol) in dichloromethane (DCM). pension. It was allowed to be stirred at the same temperature
The mixture was then stirred at 80 °C overnight. After cooling for several more hours until nearly all the Zn powder was con-
to room temperature, the organic solvent was removed under sumed. The suspension was then cooled to room temperature
reduced pressure. Filtration was done to collect the residue, and the acenaphthenequinone 14a (29 mg, 0.16 mmol) was
which was washed with water to give a pure compound 8 in added. The mixture was stirred for 30 min to generate the
1
nearly quantitative yield as a yellow solid. H NMR (500 MHz, intermediate diamine 15. Without further separation or purifi-
CDCl3) δ ppm = 8.01 (d, J = 7.6 Hz, 2H), 7.62 (d, J = 7.6 Hz, 2H), cation, the mixture was charged with another equivalent of 14a
3.24 (t, J = 7.6 Hz, 4H), 1.71 (m, 4H), 1.49 (m, 4H), 1.35–1.26 (29 mg, 0.16 mmol) and then stirred at 60 °C for 3 h. After
(m, 40H), 0.88 (t, J = 6.9 Hz, 6H); 13C NMR (125 MHz, CDCl3) cooling to room temperature, the mixture was filtered off and
δ ppm = 188.8, 148.4, 148.3, 130.6, 129.0, 128.2, 121.8, 37.0, the solid was washed with ethanol. Further purification by
33.0, 31.9, 29.7, 29.6, 29.5, 29.3, 22.7, 14.1; Anal. Calcd for column chromatography (silica gel, hexane : chloroform = 2 : 1)
C40H62O2: C, 83.56; H, 10.87; found: C, 83.32; H, 10.64; MALDI- afforded a pure product 2 (62 mg, 46% yield) as an orange
1
TOF MS: 575.311 [M + H]+; calculated exact mass: 574.475.
solid. H NMR (500 MHz, CDCl3) δ ppm = 8.31 (d, J = 7.0 Hz,
BAPQ derivative 1. 5,6-Ditetradecyl acenaphthenequinone 8 4H), 8.05 (d, J = 7.6 Hz, 4H), 7.85 (d, J = 8.2 Hz, 4H), 7.78 (t, J =
(150 mg, 0.26 mmol) and 1,2,4,5-tetraaminobenzene tetra- 7.6 Hz, 4H), 7.50 (d, J = 7.6 Hz, 4H), 2.89 (t, J = 7.6 Hz, 4H),
hydrochloride 9 (32 mg, 0.11 mmol) were mixed together in 1.89 (m, 4H), 1.50–1.35 (m, 24H), 0.93 (t, J = 7.0 Hz, 6H); 13C
oxygen-free acetic acid (8 mL). The mixture was then stirred at NMR (125 MHz, CDCl3) δ ppm = 153.9, 141.9, 139.3, 138.3,
60 °C for three hours under the protection of argon. After 138.2, 133.8, 132.8, 132.1, 130.1, 129.3, 128.5, 127.1, 122.2,
cooling to room temperature, the reaction mixture was filtered 36.2, 32.0, 31.6, 29.7, 29.4, 22.7, 14.1; Anal. Calcd for
to give a yellow solid which was then washed with chloroform C60H58N4: C, 86.29; H, 7.00; N, 6.71; found: C, 86.23; H, 7.01;
and ethanol. Recrystallization from toluene was carried out to N, 6.63; MALDI-TOF MS: 837.657 [M + 3H]+; calculated exact
afford a pure product 1 (100 mg, 70% yield). 1H NMR mass: 834.466.
(500 MHz, CDCl2CDCl2, 100 °C) δ ppm = 9.07 (s, 2H), 8.47 (d,
Compound 16. Zn powder (100 mg, 1.52 mmol) was added
J = 7.5 Hz, 4H), 7.74 (d, J = 7.5 Hz, 4H), 3.40 (t, J = 7.5 Hz, 8H), to a suspension of compound 12 (40 mg, 0.0634 mmol) in
1.90 (m, 8H), 1.61 (m, 8H), 0.96 (m, 80H), 0.95 (t, J = 6.5 Hz, oxygen-free acetic acid (3 mL). The mixture was then stirred at
12H); 13C NMR (125 MHz, CDCl2CDCl2, 100 °C) δ ppm = 130.6, 65 °C under the protection of argon to generate tetraamine 13.
128.8, 121.5, 36.3, 32.7, 31.6, 29.5, 29.4, 29.3, 29.0, 22.3, 13.6; After 3 h, the suspension was cooled to room temperature and
Anal. Calcd for C86H126N4: C, 84.95; H, 10.44; N, 4.61; found: 0.7 equivalent of 5,6-dicyano acenaphthenequinone 14b
C, 84.73; H, 10.21; N, 4.79; MALDI-TOF MS: 1217.240 (10 mg, 0.0444 mmol) was added and the mixture was then
[M + 2H]+; calculated exact mass: 1214.998.
stirred for 30 min to give the intermediate diamine 16. After
5,6-Dinitro-4,7-bis(4-nonylphenyl)benzo[c][1,2,5] thiadiazole mixing with water, the mixture was filtered off to obtain a
(12). Pb(PPh3)4 (58 mg, 0.051 mmol) was added to a solution solid. The crude product was extracted using chloroform and
of 4,7-dibromo-5,6-dinitrobenzo[c][1,2,5]thiadiazole 10 (197 then purified through column chromatography (silica gel,
mg, 0.51 mmol) and 4-nonylphenyl(trimethyl)stannane 11 chloroform) to give a crude product 16 (13 mg, 28% yield) as a
(754 mg, 2.05 mmol) in dry THF (10 mL) under the protection brown solid. Intermediate 16 was not stable enough to be
of argon. The mixture was stirred at 75 °C for 20 h. After exposed to air for a long time. MALDI-TOF MS: 738.840 [M]−;
cooling to room temperature, the reaction mixture was treated calculated exact mass: 738.441.
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BAPQ derivative 3. A suspension of freshly prepared inter-
Organic & Biomolecular Chemistry
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mediate diamine 16 (13 mg, 0.0176 mmol) and 5,6-dicyano
acenaphthenequinone 14 (4 mg, 0.0176 mmol) in oxygen-free
acetic acid (3 mL) was stirred at 60 °C under the protection of
argon for 3 h. After cooling to room temperature, the mixture
was filtered off. The solid was washed with ethanol and
further purified by column chromatography (silica gel,
chlorobenzene : THF = 100 : 1) to give a pure product 3 (8 mg,
in 48% yield) as a dark red solid. 1H NMR (500 MHz,
CDCl2CDCl2, 75 °C) δ ppm = 8.39 (d, J = 7.5 Hz, 4H), 8.34 (d,
J = 7.5 Hz, 4H), 7.78 (d, J = 7.5 Hz, 4H), 7.52 (d, J = 7.5 Hz, 4H),
2.92 (t, J = 8.0 Hz, 4H), 1.93 (m, 4H), 1.60–1.39 (m, 24H), 0.96
(t, J = 7.0 Hz, 6H); 13C NMR (125 MHz, CDCl2CDCl2, 75 °C)
δ ppm = 152.3, 139.0, 136.9, 133.4, 126.9, 122.3, 115.2, 110.2,
35.9, 31.8, 31.1, 29.5, 29.2, 22.5, 13.9; Anal. Calcd for
C64H54N8: C, 82.20; H, 5.82; N, 11.98; found: C, 82.38; H, 5.73;
N, 11.79; MALDI-TOF MS: 934.935 [M]−; calculated exact mass:
934.447.
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This work was financially supported by the Singapore MOE
AcRF grants R-143-000-510-112 and NUS Start Up grant R-143-
000-486-133 (C. C.) and KAUST (K.-W. H.).
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