Benzodipyrrole-2,6-dione-3,7-diylidenedimalononitrile Derivatives for Air-Stable n-Type Organic Field-Effect Transistors: Critical Role of N-Alkyl Substituent on Device Performance

Article abstract of DOI:10.1021/acs.joc.9b02207

Benzodipyrrole-2,6-dione-3,7-diylidenedimalononitriles (BDPMs) were synthesized as active materials for the use in air-stable n-type organic field-effect transistors (OFETs), whose optical and electrochemical properties were examined. BDPM-based small molecules exhibit deep lowest unoccupied molecular orbital levels, which are required in air-stable n-type OFETs. An OFET device that was based on BDPM-But and fabricated by vapor deposition provided a maximum electron mobility of 0.131 cm² V^-1 s^-1 under ambient conditions.

Full text of DOI:10.1021/acs.joc.9b02207

Article
pubs.acs.org/joc
Cite This: J. Org. Chem. XXXX, XXX, XXX−XXX
Benzodipyrrole-2,6-dione-3,7-diylidenedimalononitrile Derivatives
for Air-Stable n‑Type Organic Field-Effect Transistors: Critical Role of
N‑Alkyl Substituent on Device Performance
Attrimuni P. Dhondge,† Yi-Xiang Huang,† Ta Lin,† Yu-Hung Hsu,† Shin-Lun Tseng,‡ Yu-Chang Chang,§
Henry J. H. Chen,‡ and Ming-Yu Kuo*,†
†Department of Applied Chemistry and ‡Department of Electrical Engineering, National Chi Nan University, No. 1 University Road,
Puli 54561, Nantou, Taiwan
§Department of Applied Chemistry, Providence University, Taichung 43301, Taiwan
S
* Supporting Information
ABSTRACT: Benzodipyrrole-2,6-dione-3,7-diylidenedimalo-
nonitriles (BDPMs) were synthesized as active materials for
the use in air-stable n‑type organic field-effect transistors
(OFETs), whose optical and electrochemical properties were
examined. BDPM-based small molecules exhibit deep lowest
unoccupied molecular orbital levels, which are required in air-
stable n‑type OFETs. An OFET device that was based on
BDPM-But and fabricated by vapor deposition provided a
maximum electron mobility of 0.131 cm2 V−1 s−1 under
ambient conditions.
sufficient electron affinity for electron injection and transport.
Previous studies have demonstrated that n‑type OFETs that
are based on this core have promising electron mobilities
under ambient conditions.4d Recently, dicyanomethylene-
substituted compounds have attracted much interest as
n‑type OSCs because of the superior electron-withdrawing
characteristics of their cyanovinyl groups, which stabilize their
LUMO levels.5 Certain dicyanomethylene-substituted quinoi-
dal OSCs have shown very promising performance in OFET
devices. To date, the highest electron mobility of furan-
thiophene-based quinoidal OSC (TFT-CN) is 7.7 cm2 V−1 s−1,
based on microsized ribbon transistors.5a For use in solution-
processed transistors, dicyanomethylene-substituted quinoidal
terthiophenes (2DQTT-o-B) have reached an electron
mobility as high as 5.2 cm2 V−1 s−1 under ambient
conditions.5b We recently reported on angular naphthalene
bis(1,5-diamide-2,6-diylidene)malononitriles (NBAMs) with
low-lying LUMO levels and a maximum electron mobility of
0.63 cm2 V−1 s−1 under ambient conditions.5e
Based on the above considerations, dicyanomethylene-
substituted compounds are good candidates for high-perform-
ance air-stable n‑type OSCs. Herein, we present the design and
synthesis of benzodipyrrole-2,6-dione-3,7-diylidenedimalono-
nitrile (BDPM) derivatives for air-stable high-performance n-
type OFETs (Scheme 1). The maximum electron mobility of
an OFET that is based on BDPM-But exhibits a moderate
electron mobility of 0.131 cm2 V−1 s−1 and an on/off ratio of
INTRODUCTION
■
Air-stable p- and n‑type organic field-effect transistors
(OFETs) have received substantial attention during the past
decade in both academia and industry because of their
potential applications in large-area, flexible, and low-cost
complementary circuits.1 The development of n-type organic
semiconductors (OSCs) lags that of their p-type counterparts,
especially regarding performance and ambient stability.2
Therefore, the design of novel high-performance and air-stable
n‑type OSC materials has become an important challenge. To
obtain high-performance air-stable n-type OFET, the material
must have a low-lying lowest unoccupied molecular orbital
(LUMO) close to the work function of the source/drain
electrode and strong intermolecular π−π interaction in the
solid state to facilitate high electron mobility.3 Air-stable n‑type
OFET materials must generally have high electron affinity
(EA), preventing common redox reactions of water and oxygen
that can occur during device operation, causing degradation.
Incorporating strong electron-withdrawing substituents such as
dicarboxylic imides onto rylenes and cyanos onto quinoidal
oligothiophenes and diketopyrrolopyrrole derivatives4−6 has
been proved to be an effective strategy for lowering LUMO
energy levels and strengthening intermolecular π−π inter-
action, supporting the realization of air-stable n-type OFETs.
Rylene diimides, such as pyromelliticdiimide (PyDI),
naphthalene diimides (NDIs), and perylenediimides (PDIs),
have served as some of the most important building blocks in
the construction of OSCs for n‑type OFETs because of their
chemical accessibility, high stability, high electron affinity, and
high electron mobility. PyDI is the smallest rylene core with
Received: August 13, 2019
Published: October 3, 2019
© XXXX American Chemical Society
A
DOI: 10.1021/acs.joc.9b02207
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Scheme 1. Synthetic Routes, Reagents, and Conditions to BDPM Derivatives
4.2 × 103 under ambient conditions. To the best of the
authors’ knowledge, this is the first report of BDPM-based
small molecules in air-stable n‑type OFETs.
RESULTS AND DISCUSSION
■
Synthesis. Scheme 1 describes the synthesis of BDPM
derivatives. 1,4-Dibromo-2,5-diiodo-benzene (1) was prepared
from readily accessible 1,4-dibromobenzene in a good yield.7
Compound 1 was subjected to a Buchwald−Hartwig
amination coupling reaction in the presence of a palladium
catalyst to give the diamine products 2/3. The Sonogashira
coupling reaction of trimethylsilylacetylene with dibromo
Figure 1. DFT-optimized geometries and frontier molecular orbitals
of (a) BDPM-Oct and (b) BDPM-But.
compounds 2/3 in the presence of a palladium(0) catalyst
and a copper(I) cocatalyst yielded alkynylanilines 4/5. The
TMS group was removed from this intermediate using
tetrabutylammonium fluoride, and subsequent treatment of
6/7 with CuI and Et3N in DMF at 90 °C for 2 h led to smooth
cyclization to furnish pyrroloindole derivatives 8/9. The
oxidation of pyrroloindoles 8/9 with I2O5 gave the
corresponding bisisatins 10/11. Finally, the bisisatins 10/11
were treated with malononitrile via the Knoevenagel
condensation reaction to obtain the target compounds
BDPM-Oct and BDPM-But in 67−70% yield. Both BDPM-
Oct and BDPM-But exhibited good solubility in common
organic solvents such as chloroform, THF, and dichloro-
methane (DCM). Both BDPM-Oct and BDPM-But are highly
thermally stable with decomposition temperatures of 326 and
325 °C for 5% weight loss (Figure S1), respectively, as
determined by thermal gravimetric analysis (TGA).
Theoretical Calculations and Optical and Electro-
chemical Properties. To elucidate the electronic structures
and optimized geometries of BDPM derivatives, density
functional theory (DFT) calculations were performed at the
B3LYP/6-31G** level using the GAUSSIAN 09 program. As
presented in Figure 1, the optimized molecular geometries of
BDPM derivatives are completely planar. The electron density
distributions at the HOMO levels are concentrated on the
benzene core, while those at the LUMO levels are widely
delocalized over the entire BDPM core. The calculated LUMO
levels for BDPM-Oct and BDPM-But are −4.42 and −4.44
eV, respectively. The optical and electrochemical properties of
BDPM-Oct and BDPM-But were investigated using UV−vis
absorption spectroscopy and cyclic voltammetry (CV). The
absorption spectra of BDPM-Oct and BDPM-But in DCM
solution were almost identical, as depicted in Figure 2a. The
Figure 2. (a) UV−vis absorption spectra of BDPM derivatives in
DCM (10−5 M) and thin films and (b) cyclic voltammograms of
BDPM derivatives in DCM containing 0.1 M n-Bu4NPF6.
B
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Table 1. Photophysical and Electrochemical Properties of BDPM-Oct and BDPM-But
a
b
c
d
compound
λabs,max solution (nm)
λabs,max thin film (nm)
Eg (eV)
E1/2red1 (V)
Efc (V)
LUMO (eV)
HOMO (eV)
BDPM-Oct
BDPM-But
294, 389, 751
295, 388, 748
299, 420, 751
299, 414, 746
1.30
1.30
0.06
0.07
0.43
0.44
−4.43
−4.42
−5.73
−5.72
a
b
Calculated from λonset of absorption spectra in DCM solution. In DCM (10−3 M), n-Bu4NPF6 (0.1 M), 295 K, scan rate = 100 mV/s, versus Fc+/
c
d
Fc. Determined from ELUMO = −[Ered1/2 − E(Fc+/Fc) + 4.8] eV. Calculated from EHOMO = ELUMO − Eg.
absorption spectra show dual absorption bands, and the high-
energy absorption band, located at 280−430 nm, corresponds
to π−π* transitions; the low-energy band, spanning from 550
to 950 nm, can be attributed to intramolecular charge-transfer
(ICT) transitions. The absorption spectra of the thin films of
BDPM-Oct and BDPM-But were significantly redshifted
relative to those of the solution states, revealing strong π−π
intermolecular interaction and close packing of the conjugated
backbone in the solid state. The energy band gaps (Eg),
estimated from the onsets of the absorption spectra in DCM
solution, were 1.30 eV for both BDPM-Oct and BDPM-But.
The electrochemical behavior of BDPM derivatives was
investigated by cyclic voltammetry (CV) in DCM solution
containing 0.1 M n-tetrabultylammonium hexafluorophosphate
(n-Bu4NPF6) as a supporting electrolyte. The ferrocene/
ferrocenium (Fc+/Fc) redox couple was used as an internal
standard for the calibration of the potentials. The CV spectra
of all compounds revealed well-defined reversible reduction
waves, as shown in Figure 2b. The LUMO levels of BDPM-
Amsterdam density functional (ADF) theory program (Figure
3a,c).8 The maximum t− values of BDPM-Oct and BDPM-But
are 32 and 100 meV, respectively, indicating that the electron
transfer in the devices of BDPM-Oct and BDPM-But is along
the crystallographic b axis (D2) of BDPM-Oct and a axis (D1)
of BDPM-But, respectively. Notably, the t− values of BDPM-
Oct and BDPM-But in the π-column stacking direction (D1)
are 19 and 100 meV, respectively. Figure 4a shows the merger
Oct and BDPM-But estimated using the equation ELUMO
=
−[Ered1/2 − E(Fc+/Fc) + 4.8] eV, were approximately −4.43 and
−4.42 eV, respectively, consistent with the calculated values
that are summarized in Table 1. The deep LUMO levels of
BDPM-Oct and BDPM-But are attributed to the strong
electron-withdrawing character of the dicyanovinylene group,
favoring the injection of electrons from the electrode into the
active layer and improving the stability of n‑type OFETs in air.
Single-Crystal Structures and Electron-Transfer In-
tegrals. Sheet-like single crystals of BDPM derivatives were
obtained using the solvent vapor diffusion method (chloro-
form/isopropanol). The high planarity of the BDPM core was
consistent with the optimized structure. Both BDPM-Oct and
BDPM-But exhibited one-dimensional columnar π-stacking
structures parallel to the crystallographic a axis with very short
π−π distances of 3.28 and 2.92 Å (Figure 3), respectively,
favoring charge transfer between molecules. The electron-
transfer integrals (t−) for BDPM derivatives in different
directions are calculated at the PW91/TZ2P level using the
Figure 4. (a) Merger between D1s of BDPM-Oct and BDPM-But,
(b) electron density distributions for the LUMO of BDPM-But, and
(c) electron density distributions for the LUMOs of D1 dimers of
BDPM derivatives. Side chains in (a, b) were omitted for simplicity.
between D1s of BDPM-Oct and BDPM-But. For clarification,
the backbones of one molecule of BDPM-Oct and BDPM-But
were overlapped as shown in red. Molecular pairs in red and
blue/green represent the D1s of BDPM-Oct/BDPM-But. The
center-to-center distances along D1 directions of BDPM-Oct
and BDPM-But are 8.68 and 9.37 Å, respectively. In BDPM-
Oct, the nitrogen atom of the cyano group of one molecule is
superimposed over the center of the pyrrole ring of the other
molecule where the electron density in the LUMO level is
absent (Figure 4b); likewise, the carbon atom of the carbonyl
group of one molecule is superimposed over the carbon atom
of the cyano group of the other molecule that is a node in the
LUMO level, explaining its small t− value along the D1
direction. The higher t− value of BDPM-But along D1 than
that of BDPM-Oct is probably a result of the different slipped
distances along the molecular long axis and the shorter π−π
distance in BDPM-But (2.92 Å), which is consistent with
stronger bonding character for the LUMO of the D1 dimer of
BDPM-But than that of BDPM-Oct (Figure 4c). Overall,
BDPM-But may have higher electron mobility than BDPM-
Oct, according to the Marcus electron-transfer theory and the
Einstein relation.9 This result indicates that variation of the N-
alkyl chain length may influence the molecular packings and
charge mobilities of BDPM derivatives.
Molecular Packing, Morphology, and Charge Trans-
port Properties. The charge carrier transport properties of
BDPM derivatives were tested using a thin-film transistor with
top-contact bottom-gate architecture. The thin films of
BDPM-Oct and BDPM-But were fabricated by vacuum
Figure 3. Molecular packing viewed along the crystallographic b axis
and schematic illustration of BDPM orientation on the substrate of (a,
b) BDPM-Oct and (c, d) BDPM-But.
C
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deposition on Si/SiO2 substrates that were modified with a
cyclic olefin copolymer (COC) at various substrate temper-
atures (t) to optimize the device performance. Subsequently,
Au drain/source electrodes were vacuum-deposited to yield
OFET devices. The thin films were characterized by atomic
force microscopy (AFM) and X-ray diffraction (XRD) to
elucidate the relationships between molecular structure, film
morphology/crystallinity, and device performance. The X-ray
diffraction (XRD) spectra of BDPM-based films revealed
layered structures with sharp (00l) reflections, as depicted in
Figure 5. The corresponding d-spacings of the thin films of
= 60 °C (Figure 5a), which agrees with device performance.
The maximum electron mobilities of BDPM-But-based
OFETs decrease from 0.131 to 0.055 cm2 V−1 s−1 as the
substrate temperature increases from 40 to 60 °C because of
the low coverage and discontinuous morphology of the
BDPM-But film (Figure 7d). At t = 60 °C, only a few
channels of BDPM-But-based OFET work owing to its
discontinuous morphology. Overall, BDPM-But-based
OFETs showed a highest electron mobility of 0.131 cm2 V−1
s−1, slightly exceeding that of BDPM-Oct devices (0.046 cm2
V−1 s−1). A comparison of BDPM-Oct and BDPM-But with
the same π-conjugated backbone demonstrates that the N-alkyl
chain significantly affects the electron-transporting character-
istics, which are consistent with molecular packing and
electron-transfer integrals. It is noted that the large difference
in the transfer integral and small difference in the electron
mobility between BDPM-Oct and BDPM-But devices may
indicate that the fabrication conditions of BDPM-But are not
optimized yet. The crystallinity of BDPM-But films increases
as substrate temperature raises from 40 to 60 °C (Figure 5b);
however, the maximum electron mobility of BDPM-But-based
OFET decreases at a substrate temperature of 60 °C because
of the low coverage and discontinuous morphology (Figure
7d). Zhu et al. showed that the two-step deposition is an
effective method to improve thin-film uniformity and
continuity.6a The electron mobility of OFET fabricated by
two-step deposition was increased by more than seven times
than that of OFET deposited in one step. Therefore, we
believe that the performance of BDPM-But can be further
improved by two-step deposition.
Molecular Structure−Property Relationship of Isaty-
lidene Malononitrile Analogues. Since angular-shaped
naphthalene bis(1,5-diamide-2,6-diylidene)malononitrile
(NBAM) derivatives have recently been synthesized as
n‑type OSCs for the use in air-stable OFETs,5e the isatylidene
malononitrile analogues provide a series of n‑type OSCs to
investigate the molecular structure−property relationship. Both
NBAM and BDPM derivatives exhibited low-lying LUMO
levels (lower than −4.0 eV) and excellent air stability of n‑type
characteristics due to strong electron-accepting ability of
ketone and dicyanomethylene groups.5e The reorganization
energy (λ−) values for electron transfer of NBAM-EH and
BDPM-But calculated at the B3LYP/6-31G** level are 229
and 256 meV, respectively. The result demonstrates that the
extension of molecular conjugation length of similar com-
pounds reduces the λ− values, consistent with the trend of the
oligoacenes, naphthalene to hexacene.10 Both of NBAM-EH
and BDPM-But display one-dimensional face-to-face stacking
with a short π−π distance of ∼3 Å. The electron-transfer
integral (t−) of linear-shaped BDPM-But (100 meV) along the
π-column stacking direction (D1) is slightly larger than that of
angular-shaped NBAM-EH (80 meV), indicating the linear-
shaped structures may be a benefit to charge transfer.
According to the Marcus electron-transfer theory, reaching a
high charge-transfer rate requires minimizing λ and maximizing
t values. Therefore, linear-shaped NBAM derivatives with a
longer conjugation length compared to BDPM derivatives may
have promising potential for the use in high-performance air-
stable n‑type OFET. The synthesis of linear-shaped NBAM
derivatives is in progress.
Figure 5. XRD patterns of BDPM derivatives films at different
substrate temperatures: (a) BDPM-Oct and (b) BDPM-But.
BDPM-Oct and BDPM-But were 15.43 and 11.45 Å,
respectively, which are consistent with half length of the
crystallographic c axis of BDPM-Oct (15.53 Å) and length of
the crystallographic c axis of BDPM-But (11.32 Å), indicating
that BDPM derivatives have the edge-on molecular orientation
on the substrate, as presented in Figure 3b,d. Notably, this
orientation is advantageous for charge transport in the OFET
geometry. All compounds exhibited typical n‑type responses, as
expected from the low-lying LUMO energy levels. Figure 6 and
Figures S5 and S6 display their transfer characteristics. The
mobility of the OFETs was calculated in the saturation current
regimes. Table 2 presents the device characteristics of BDPM
derivatives, including the electron carrier mobility (μe),
threshold voltage (VT), and current on/off ratios (Ion/Ioff).
At t = 40 °C, BDPM-Oct-based OFETs showed a maximum
electron mobility of 0.046 cm2 V−1 s−1, and when t was further
increased to 60 °C, the maximum electron mobility slightly
drops to 0.036 cm2 V−1 s−1. The atomic force microscopy
(AFM) images of BDPM-Oct films that were deposited at 40
and 60 °C reveal similar polycrystalline morphology with flat
terraces (Figure 7a,b); however, the crystallinity decreases at t
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Figure 6. Output and transfer curves characteristics of OFET devices based on (a, b) BDPM-Oct (t = 40 °C) and (c, d) BDPM-But (t = 40 °C).
lying LUMO levels (−4.4 eV below the vacuum level) that are
suitable for the use in air-stable n-type OFETs. The OFET that
was based on BDPM-But with N-butyl side chains had greater
electron mobility than that was based on BDPM-Oct with N-
octyl side chains under ambient conditions, implying that the
nature of the N-alkyl substituent strongly affected the
performance of OFETs in which BDPM derivatives are used.
Further modifications of the electron-accepting π-units are
underway.
Table 2. Summary of Electrical Characteristics of OFETs
Based on BDPM Derivatives
device
t (°C)
max μe (cm2 V−1 s−1
)
VT (V)
on/off
a
a
BDPM-Oct
40
60
40
60
0.046 (0.040 0.006)
0.036 (0.031 0.005)
0.131 (0.111 0.02)
25−33
28−35
18−22
∼22
102−103
102−103
103−104
∼103
a
BDPM-But
∼0.055
a
Electron (μe) mobilities were obtained from 10 channels.
Experimental Section. General Preparation. All
reagents were purchased from commercial suppliers and used
as received without further purification. All oxygen and
moisture-sensitive reactions were performed under a nitrogen
atmosphere. Toluene, THF, and ethanol were distilled over
sodium and dimethylformamide (DMF) was distilled over
CaH2. Crude product solutions were dried on MgSO4 and
concentrated with a rotary evaporator below 40 °C at 30 Torr.
Silica gel column chromatography was performed employing
1
230−400 mesh silica gels. H and 13C NMR spectra were
recorded using a Bruker Avance II (300 MHz) NMR
spectrometer with TMS as an internal reference; chemical
1
shifts (δ) are reported in parts per million. H NMR data are
presented as follows: chemical shift, multiplicity (s = singlet, br
= broad singlet, d = doublet, t = triplet, m = multiplet and/or
multiple resonances), coupling constant in Hz (Hertz),
integration. High-resolution mass spectra (HRMS) were
determined on a JEOL JMS-700 spectrometer for the EI
mode. Thermogravimetric analyses (TGA) were collected
from 30 to 800 °C at 10 °C min−1 under a dry nitrogen
atmosphere by using a Thermo Cahn Versa TGA. Sample
masses of approximately 5 mg were used. Melting points (Mp)
were recorded with a Fargo (MP-1D) apparatus. The UV−vis
absorption spectra of BDPM derivatives were obtained using a
Figure 7. AFM images (3 μm × 3 μm) of vacuum-deposited films of
BDPM derivatives on COC-modified Si/SiO2 substrates at different
substrate temperatures of (a, b) BDPM-Oct and (c, d) BDPM-But.
White circles in (d) indicate the substrate.
CONCLUSIONS
■
In summary, a new series of BDPM derivatives of n‑type OSCs
were designed and synthesized. BDPM derivatives have low-
E
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1
Scinco S-3100 UV−vis spectrophotometer in dichloromethane
(10−5 M). High-resolution mass spectra were determined on a
JEOL JMS-700 MStation mass spectrometer. The molecular
order of BDPM films was determined by X-ray diffraction
(XRD, Rigaku 18 kW rotating anode X-ray generator) using
Cu Kα radiation (λKα1 = 1.54 Å). Atomic force microscopy
(AFM) images were obtained using a Veeco Dimension 5000
scanning probe microscope. Cyclic voltammograms (CV) were
recorded on a CHI1040B electrochemical work station with a
three-electrode configuration, using a Pt plate as the counter
electrode, a glassy carbon as the working electrode, and an Ag/
AgCl electrode as the reference electrode. Samples were
dissolved in CH2Cl2 (10−3 M) with n-tetrabutylammonium
hexafluorophosphate (n-Bu4NPF6, 0.1 M) as the supporting
electrolyte. The scan speed was 0.1 V s−1. An energy level of
50%) as a pale yellow solid. Mp: 83−84 °C. H NMR (300
MHz, CDCl3): δ = 6.79 (s, 2H), 3.71 (s, 2H), 3.04 (t, J = 7.2
Hz, 4H), 1.58−1.65 (m, 4H), 1.29−1.39 (m, 20H), 0.87−0.90
(m, 6H) ppm.13C{1H} NMR (75 MHz, CDCl3): δ = 137.7,
115.9, 110.0, 44.8, 31.8, 29.3, 29.2, 27.1, 22.6, 14.1 ppm.
LRMS (EI) m/z [M]+ 490. HRMS (EI) m/z [M]+ calcd for
C22H38Br2N2, 490.1381; found, 490.1380.
2,5-Dibromo-N1,N4-dibutylbenzene-1,4-diamine (3).
Compound 3 was synthesized as for compound 2 and
obtained as a pale yellow solid in 45% yield. Mp: 80−83 °C.
1H NMR (300 MHz, CDCl3): δ = 6.80 (s, 2H), 3.71 (s, 2H),
3.05 (t, J = 7.2 Hz, 4H), 1.57−1.64 (m, 4H), 1.40−1.47 (m,
4H), 0.94−0.99 (m, 6H) ppm. 13C{1H} NMR (75 MHz,
CDCl3): δ = 137.6, 115.7, 109.9, 44.3, 31.2, 20.1, 13.7 ppm.
LRMS (EI) m/z [M]+ 378. HRMS (EI) m/z [M]+ calcd for
C14H22Br2N2, 378.0129; found, 378.0122.
−4.8 eV below the vacuum level was used for reference Fc/Fc+.
1/2
N1,N4-Dioctyl-2,5-bis((trimethylsilyl)ethynyl)-
benzene-1,4-diamine (4). To a flame-dried two-necked flask
with a reflux condenser were added compound 2 (1 g, 2.0
mmol) in toluene (10 mL), PdCl2(PPh3)2 (20 mol %), CuI
(20 mol %), and dry Et3N (10 mL) under a nitrogen
atmosphere, and the reaction vessel was evacuated and
backfilled with nitrogen. Finally, trimethylsilylacetylene (0.60
g, 6.1 mmol) was added to the flask via a syringe and the flask
was evacuated and filled with nitrogen once more. The
resulting solution was allowed to stir at 90 °C in an oil bath for
2 h. The reaction mixture was cooled to room temperature,
and 40 mL of water was added slowly, extracted with ethyl
acetate, and washed with brine. The organic phase was dried
over MgSO4, filtered, and evaporated to afford the crude
product. The residue was purified by column chromatography
(eluent: hexane/dichloromethane = 9/1) to obtain 4 (0.69 g,
The LUMO levels estimated from ELUMO = −[Ered
−
E
(Fc+/Fc) + 4.8] eV. Compound 1 was synthesized according to
the literature.7 Single crystals of BDPM derivatives were
successfully obtained using the solvent vapor diffusion method
(chloroform/isopropanol). Single-crystal X-ray diffraction was
performed on a Bruker APEX DUO at 100(2) K. Data were
collected and processed by using an APEX II 4K CCD
detector. Geometry optimization and frontier molecular
orbitals were obtained from the GAUSSIAN 09 program at
the B3LYP/6-31G** level.
Device Fabrication and Evaluation. Cyclic olefin
copolymer (COC, purchased from Polyscience) was used as
received. OFET devices were made using heavily n-doped Si
substrates with 300 nm of thermally oxidized SiO2. The
substrates were successively cleaned with deionized (DI)
water, piranha solution (H2SO4:H2O2 = 7:3), DI water and
finally blown dry with N2 gas. Then, 2.0 wt % solution of COC
in dry toluene were spin-coated at 5000 rpm for 30 s by the on-
the-fly-dispensing spin-coating method.11 Finally, the COC-
modified substrates (capacitance Ci = 4.05 nF cm−2) were
baked at 120 °C in an oven for 1 h to remove the residual
toluene. Thin films (40 nm) of BDPM derivatives were
thermally evaporated onto the COC-modified substrates at a
rate of 0.1−0.2 Å s−1 under a pressure of 5 × 10−6 Torr. The
substrates were maintained at constant temperatures of 40 and
60 °C. Finally, top-contact Au source-drain electrodes (40 nm)
were thermally evaporated onto the active layers with a
channel length (L) and width (W) of 100 and 1000 μm,
respectively. All of the transistors were characterized under
ambient conditions using an Agilent Technologies B1500A
semiconductor device analyzer. The charge mobility (μ) was
calculated from the saturation regime using the formula, Id =
(WCi/2L)μ(Vg − Vth).2
1
65%) as a yellow solid. Mp: 91−92 °C. H NMR (300 MHz,
CDCl3): δ = 6.60 (s, 2H), 4.01 (bs, 2H), 3.07 (t, J = 6.9 Hz,
4H), 1.60−1.63 (m, 4H), 1.28 (m, 20H), 0.88 (m, 6H), 0.26
(s, 18 H) ppm. 13C{1H} NMR (75 MHz, CDCl3): δ = 141.4,
113.6, 109.8, 102.3, 101.1, 44.4, 31.8, 29.4, 29.2, 27.1, 22.6,
14.0, 0.0 ppm. LRMS (EI) m/z [M]+ 524. HRMS (EI) m/z
[M]+ calcd for C32H56N2Si2, 524.3982; found, 524.3981.
N1,N4-Dibutyl-2,5-bis((trimethylsilyl)ethynyl)-
benzene-1,4-diamine (5). Compound 5 was synthesized as
for compound 4 and obtained as a pale yellow solid in 63%
1
yield. Mp: 146−147 °C. H NMR (300 MHz, CDCl3): δ =
6.60 (s, 2H), 4.04 (bs, 2H), 3.07 (m, 4H), 1.58−1.63 (m, 4H),
1.40−1.47 (m, 4H), 0.95 (m, 6H), 0.25 (s, 18 H) ppm.
13C{1H} NMR (75 MHz, CDCl3): δ = 141.2, 113.4, 109.6,
102.2, 100.9, 43.9, 31.3, 20.0, 13.6, −0.1 ppm. LRMS (EI) m/z
[M]+ 412. HRMS (EI) m/z [M]+ calcd for C24H40N2Si2,
412.2730; found, 412.2733.
2,5-Dibromo-N1,N4-dioctylbenzene-1,4-diamine (2). A
two-necked flask was charged under argon with the
corresponding 1,4-dibromo-2,5-diiodobenzene 1 (1.0 g, 2.06
mmol), Pd2(dba)3 (10 mol %), and BINAP (20 mol %),
anhydrous toluene (10 mL), and t-BuONa (0.59 g, 6.1 mmol)
that were added, and the mixture was purged with nitrogen for
20 min. Amine (0.79 g, 6.1 mmol) was added via a syringe and
the mixture is stirred under nitrogen at 110 °C in an oil bath
for 2 h. The reaction mixture was cooled to room temperature,
and 20 mL of water was added slowly, extracted with ethyl
acetate, and washed with brine. The organic phase was dried
over MgSO4, filtered, and evaporated to afford the crude
product. The residue was purified by column chromatography
(eluent: hexane/dichloromethane = 9/1) to obtain 2 (0.5 g,
2,5-Diethynyl-N1,N4-dioctylbenzene-1,4-diamine (6).
The compound 4 (0.8 g, 1.52 mmol) was suspended in dry
THF (10 mL) and cooled in an ice bath. TBAF (1 M in THF,
1 g, 3.81 mmol) was added and the reaction mixture was
stirred at 0 °C in an ice bath for 30 min. The mixture was
concentrated in vacuo, diluted with EtOAc, and washed with
sat aq NH4Cl. The organic layer was concentrated to provide
the crude product 6, which was used directly in the next step
(0.46 g, 80%). 1H NMR (300 MHz, CDCl3): δ = 6.66 (s, 2H),
4.05 (bs, 2H), 3.43 (s, 2H), 3.07 (t, J = 7.2 Hz, 4H), 1.42−
1.64 (m, 4H), 1.27−1.42 (m, 20H), 0.86−0.90 (m, 6H) ppm.
13C{1H} NMR (75 MHz, CDCl3): δ = 141.3, 114.3, 108.9,
83.3, 80.9, 44.44, 31.7, 29.3, 29.3, 29.1, 27.0, 22.6, 14.0 ppm.
F
DOI: 10.1021/acs.joc.9b02207
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The Journal of Organic Chemistry
Article
LRMS (EI) m/z [M]+ 380. HRMS (EI) m/z [M]+ calcd for
C26H40N2, 380.3191; found, 380.3190.
(m, 6H) ppm. 13C{1H} NMR (75 MHz, CDCl3): δ = 183.3,
156.6, 147.3, 123.1, 106.7, 40.5, 29.0, 20.1, 13.5 ppm. LRMS
(EI) m/z [M]+ 328. HRMS (EI) m/z [M]+ calcd for
C18H20N2O4, 328.1423; found, 328.1420.
N1,N4-Dibutyl-2,5-diethynylbenzene-1,4-diamine (7).
Compound 7 was synthesized as for compound 6 and obtained
as a yellow solid in 80% yield, which was used directly in the
next step. 1H NMR (300 MHz, CDCl3): δ = 6.66 (s, 2H), 4.04
(bs, 2H), 3.43 (s, 2 H), 3.08 (m, 4H), 1.56−1.65 (m, 4H),
1.36−1.48 (m, 4H), 0.92−0.97 (m, 6H) ppm. 13C{1H} NMR
(75 MHz, CDCl3): δ = 141.4, 114.3, 108.8, 83.4, 81.0, 44.1,
31.5, 20.2, 13.8 ppm. LRMS (EI) m/z [M]+ 268. HRMS (EI)
m/z [M]+ calcd for C18H24N2, 268.1939; found, 268.1920.
1,5-Dioctyl-1,5-dihydropyrrolo[2,3-f ]indole (8). To a
flame-dried two-necked flask with a reflux condenser were
added crude compound 6 (0.6 g, 1.5 mmol) in DMF (5 mL),
CuI (0.06 g, 0.3 mmol), and Et3N (0.47 g, 4.7 mmol) under a
nitrogen atmosphere, and the mixture was heated to 100 °C in
an oil bath for 2 h. The reaction mixture was cooled to room
temperature, and 40 mL of water was added slowly, extracted
with ethyl acetate, and washed with brine. The organic phase
was dried over MgSO4, filtered, and evaporated to afford the
crude product. The residue was purified by column
chromatography (eluent: hexane/dichloromethane = 9/1) to
2,2′-(1,5-Dioctyl-2,6-dioxo-1,2,5,6-tetrahydropyrrolo-
[2,3-f]indole-3,7-diylidene)dimalononitrile (BDPM-Oct).
In a 50 mL flame-dried two-necked flask with a reflux
condenser was added compound 10 (0.2 g, 0.45 mmol) in
anhydrous EtOH (5 mL) and malononitrile (90 mg, 1.36
mmol) under a nitrogen atmosphere. After that, the mixture
was refluxed in an oil bath for 2 h. Then, the solvent was
evaporated under vacuum and the residue was purified by
column chromatography (eluent: hexane/dichloromethane =
1/1) to afford the corresponding product BDPM-Oct (0.17 g,
1
70%) as a blue solid. Mp: 295−297 °C. H NMR (300 MHz,
CDCl3): δ = 7.64 (s, 2H), 3.75 (t, J = 7.2 Hz, 4H), 1.66−1.71
(m, 4H), 1.26−1.32 (m, 20H), 0.85−0.89 (m, 6H) ppm.
13C{1H} NMR (75 MHz, CDCl3): δ = 161.1, 147.6, 142.7,
124.2, 109.8, 106.7, 86.3, 40.9, 31.5, 28.9, 27.0, 26.8, 22.5, 13.9
ppm. LRMS (EI) m/z [M]+ 536. HRMS (EI) m/z [M]+ calcd
for C32H36N6O2, 536.2900; found, 536.2906.
2 , 2 ′ - ( 1 , 5 - D i b u t y l - 2 , 6 - d i o x o - 1 , 2 , 5 , 6 -
tetrahydropyrrolo[2,3-f ]indole-3,7-diylidene)-
dimalononitrile (BDPM-But). Compound BDPM-But was
synthesized as for compound BDPM-Oct and obtained as a
1
obtain 8 (0.45 g, 75%) as a white solid. Mp: 67−68 °C. H
NMR (300 MHz, CDCl3): δ = 7.53 (s, 2H), 7.14 (d, J = 3.3
Hz, 2 H), 6.54 (d, J = 3 Hz, 2 H), 4.16 (t, J = 7.2 Hz, 4H),
1.88−1.93 (m, 4H), 1.31−1.37 (m, 20H), 0.90−0.94 (m, 6H)
ppm. 13C{1H} NMR (75 MHz, CDCl3): δ = 133.1, 128.5,
126.3, 99.1, 98.5, 46.5, 31.7, 29.8, 29.2, 29.1, 27.0, 22.6, 14.0
ppm. LRMS (EI) m/z [M]+ 380. HRMS (EI) m/z [M]+ calcd
for C26H40N2, 380.3191; found, 380.3195.
1
blue solid in 67% yield. Mp: 319−320 °C. H NMR (300
MHz, CDCl3): δ = 7.65 (s, 2H), 3.76 (t, J = 6.9 Hz, 4H),
1.63−1.70 (m, 4H), 1.35−1.43 (m, 4H), 0.94−0.99 (m, 6H)
ppm. 13C{1H} NMR (75 MHz, CDCl3): δ = 161.1, 147.5,
142.7, 124.2, 111.9, 109.8, 106.7, 86.4, 40.6, 29.0, 20.0, 13.4
ppm. LRMS (EI) m/z [M]+ 424. HRMS (EI) m/z [M]+ calcd
for C24H20N6O2, 424.1648; found, 424.1647.
1,5-Dibutyl-1,5-dihydropyrrolo[2,3-f ]indole (9). Com-
pound 9 was synthesized as for compound 8 and obtained as a
white solid in 72% yield. Mp: 64−65 °C. 1H NMR (300 MHz,
CDCl3): δ = 7.48 (s, 2H), 7.11 (d, J = 3.3 Hz, 2 H), 6.49 (d, J
= 3 Hz, 2 H), 4.14 (t, J = 7.2 Hz, 4H), 1.80−1.90 (m, 4H),
1.30−1.42 (m, 4H), 0.91−0.96 (m, 6H) ppm. 13C{1H} NMR
(75 MHz, CDCl3): δ = 133.1, 128.5, 126.3, 99.1, 98.6, 46.2,
31.9, 20.2, 13.7 ppm. LRMS (EI) m/z [M]+ 268. HRMS (EI)
m/z [M]+ calcd for C18H24N2, 268.1939; found, 268.1938.
1,5-Dioctylpyrrolo[2,3-f ]indole-2,3,6,7(1H,5H)-tet-
raone (10). Pyrroloindole 8 (0.5 g, 1.3 mmol), DMSO (5
mL), and I2O5 (1.7 g, 5.2 mmol) were added into a flask and
vigorously stirred at 90 °C in an oil bath under air. The
reaction was stopped until pyrroloindole was completely
consumed as monitored by TLC analysis. After the completion
of reaction and cooling to room temperature, 40 mL of water
was added slowly, extracted with ethyl acetate, and washed
with brine. The organic phase was dried over MgSO4, filtered,
and evaporated to afford the crude product. The residue was
purified by column chromatography (eluent: hexane/dichloro-
methane = 9/1) to obtain 10 (0.28 g, 50%) as a blue solid.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.joc.9b02207.
Thermogravimetric analyses, computation coordinates,
X-ray crystallographic data (CIF), OFET characteristics,
1
and H/13C NMR spectra (PDF)
X-ray crystallographic data for BDPM-But (CIF)
X-ray crystallographic data for BDPM-Oct (CIF)
AUTHOR INFORMATION
Corresponding Author
■
*E-mail: mykuo@ncnu.edu.tw. Fax: +886-49-2917956. Tel:
+886-49-2910960 ext. 4146.
ORCID
Ming-Yu Kuo: 0000-0002-2787-0554
Notes
The authors declare no competing financial interest.
1
Mp: 183−185 °C. H NMR (300 MHz, CDCl3): δ = 7.16 (s,
2H), 3.72 (t, J = 7.5 Hz, 4H), 1.65−1.70 (m, 4H), 1.25−1.33
(m, 20H), 0.88−0.84 (m, 6H) ppm. 13C{1H} NMR (75 MHz,
CDCl3): δ = 183.3, 156.6, 147.3, 123.1, 106.7, 40.8, 31.6, 29.0,
27.0, 26.8, 22.5, 14.0 ppm. LRMS (EI) m/z [M]+ 440. HRMS
(EI) m/z [M]+ calcd for C26H36N2O4, 440.2675; found,
440.2678.
ACKNOWLEDGMENTS
■
The authors acknowledge the financial support from the
Ministry of Science and Technology of Taiwan under contract
no. NSC 102-2113-M-260-007-MY3 and MOST 105-2119-M-
260-005-MY3. We also thank Prof. S. L. Wang and Ms. P. L.
Chen (National Tsing Hua University, Taiwan) for the X-ray
structure analyses and the National Center for High-Perform-
ance Computing for providing computational resources.
1,5-Dibutylpyrrolo[2,3-f ]indole-2,3,6,7(1H,5H)-tet-
raone (11). Compound 11 was synthesized as for compound
10 and obtained as a blue solid in 48% yield. Mp: 216−218 °C.
1H NMR (300 MHz, CDCl3): δ = 7.16 (s, 2H), 3.74 (t, J = 7.2
Hz, 4H), 1.64−1.67 (m, 4H), 1.38−1.41 (m, 4H), 0.94−0.99
G
DOI: 10.1021/acs.joc.9b02207
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The Journal of Organic Chemistry
Article
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