Easily reducible materials from the reactions of diselenopheno[3,2-b: 2′,3′-d]pyrrole and dithieno[3,2-b:2′,3′-d ]pyrrole with tetracyanoethylene

Article abstract of DOI:10.1021/jo3020006

A new core, 4H-diselenopheno[3,2-b:2′,3′-d]pyrrole (DSP), was reacted with tetracyanoethylene, and three products, mono-tricyanovinyl, bis-tricyanovinyl, and quinoidal, were isolated and compared with the respective 4H-dithieno[3,2-b:2′,3′-d]pyrrole (DTP) derivatives using cyclic voltammetry, UVa-vis absorption, and differential scanning calorimetry analyses. Organic field-effect transistors were fabricated using solution-processed films, and only one derivative, bis-tricyanovinyl-DSP, exhibited transistor behavior with μ_e reaching 8.7 × 10^a-4 cm ²/V·s. This enhancement of the electron-transporting properties in comparison with DTP derivative is attributed to stronger LUMOa-LUMO interaction due to a larger size of selenium atom, which in the case of the bis-tricyanovinyl derivative, has wave function density on the chalcogen.

Full text of DOI:10.1021/jo3020006

Note
pubs.acs.org/joc
Easily Reducible Materials from the Reactions of
Diselenopheno[3,2‑b:2′,3′-d]pyrrole and
Dithieno[3,2‑b:2′,3′‑d]pyrrole with Tetracyanoethylene
Yulia A. Getmanenko,† Thomas A. Purcell,‡ Do Kyung Hwang,§,∥ Bernard Kippelen,§
and Seth R. Marder*,†
†Department of Chemistry & Biochemistry, Center for Organic Photonics and Electronics, Georgia Institute of Technology, 901
Atlantic Drive NW, Atlanta, Georgia 30332-0400, United States
‡New York University, 100 Washington Square East, New York, New York 10003, United States
§School of Electrical and Computer Engineering, Center for Organic Photonics and Electronics, Georgia Institute of Technology, 777
Atlantic Drive NW, Atlanta, Georgia 30332-0250, United States
∥Interface Control Research Center, Future Convergence Research Division, Korea Institute of Science and Technology (KIST),
Hwarangno 14-gil 5, Seongbuk-gu, Seoul 136-791, Korea
S
* Supporting Information
ABSTRACT: A new core, 4H-diselenopheno[3,2-b:2′,3′-d]-
pyrrole (DSP), was reacted with tetracyanoethylene, and three
products, mono-tricyanovinyl, bis-tricyanovinyl, and quinoidal,
were isolated and compared with the respective 4H-dithieno-
[3,2-b:2′,3′-d]pyrrole (DTP) derivatives using cyclic voltam-
metry, UV−vis absorption, and differential scanning calorim-
etry analyses. Organic field-effect transistors were fabricated using solution-processed films, and only one derivative, bis-
tricyanovinyl-DSP, exhibited transistor behavior with μe reaching 8.7 × 10−4 cm2/V·s. This enhancement of the electron-
transporting properties in comparison with DTP derivative is attributed to stronger LUMO−LUMO interaction due to a larger
size of selenium atom, which in the case of the bis-tricyanovinyl derivative, has wave function density on the chalcogen.
he development of solution-processable electron-trans-
The influence of the nature of chalcogen on the charge
Tporting (ET) organic semiconductors for use in organic transport behavior of the related cores was reported by Handa
field-effect transistors (OFETs) that exhibit high mobility
values and high current on−off ratios and stability in air and
under electrical stress remains a challenging task; however,
substantial progress in this field had been achieved in recent
years.1,2 The design of such materials typically includes planar
aromatic cores functionalized with strong electron-withdrawing
groups to increase the electron affinity (EA), thus facilitating
charge injection. The tricyanovinyl (TCV) and dicyanovinylene
(DCV) groups were explored in combination with various π-
systems3−10 to achieve high EA (which is often probed
indirectly by electrochemistry). Rasmussen’s group11 reported
the isolation of three products from the reaction of N-(p-
hexylphenyl)-substituted 4H-dithieno[3,2-b:2′,3′-d]pyrrole
(DTP) with tetracyanoethylene (TCNE), with two minor
products, bis-TCV and quinoidal material, possessing large EA.
The materials isolated were not particularly soluble, and no
characterization in OFET devices was reported. Taking into
consideration the ease of the first reduction of these
compounds, the possibility for modification of the group at
the nitrogen atom to improve the solubility and availability of
the selenium analogue of DTP, 4H-diselenopheno[3,2-b:2′,3′-
d]pyrrole (DSP),12 we decided to investigate the products of
reaction of TCNE with DTP and DSP as potential ET
materials.
et al., wherein they examined dicyanomethylene quinoidal
derivatives with terthiophene13 and mixed14 skeleton in
solution-processed OFETs. It was found that substitution of
sulfur with selenium led to one order magnitude decrease in
electron mobility μe and enhanced hole mobility μh, which was
attributed to the wave function distribution (chalcogen has a
very little contribution to LUMOs and substantial contribution
to HOMOs, and as a result larger size of selenium can only
enhance the hole transport).
SYNTHESIS
■
Starting materials 2 were obtained from their respective 2,7-bis-
trimethylsilyl derivatives12 1 by the reaction with tetra-n-
butylammonium fluoride (TBAF) in 69% and 85% yield,
respectively (Scheme 1). Material 2a was also prepared in 60%
yield using modified literature procedures12,15 starting from
3,3′-dibromo-2,2′-dithiophene, which was prepared by the
CuCl2-oxidative coupling of 2-lithio-3-bromothiophene16 gen-
erated from 3-bromothiophene by the lithiation with lithium
diisopropylamide at −78 °C. The reaction of 2a with excess of
Received: September 17, 2012
Published: October 25, 2012
© 2012 American Chemical Society
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Note
Scheme 1. Reaction DTP (2a) and DSP (2b) with TCNE
2. ELECTRONIC, ELECTROCHEMICAL, AND
ELECTRICAL PROPERTIES OF 3−5
Solution UV−vis absorption spectra of DTP and DSP
derivatives in dichloromethane have similar band structure;
for 3b and 4b, absorption maxima are bathochromically shifted
in comparison with the respective DTP derivatives (Figure 1,
Table 1), while for quinoidal products 5 the position and the
shape of the absorption band are strikingly similar. For all
products, substitution of sulfur with selenium leads to increase
of the extinction coefficient (by ∼8% for 3b and 5b, and by
∼13% for 4b).
The film absorption spectra of 3 are quite similar, and the
λmax is hypsochromically shifted for both materials in
comparison with their solution spectra. A much larger
difference between the film absorption spectra of the DTP
and DSP derivatives is observed for bis-TCV materials 4 and
quinoidal products 5. While the film absorption spectrum of 4a
shows a band with one maximum, a broader band with two
maxima is observed for 4b suggesting stronger intramolecular
interaction. Band broadening is also observed upon the
substitution of sulfur with selenium in quinoidal products 5.
Electrochemical properties were examined by the cyclic
voltammetry (CV) in two different solvents (Figure 2, Table 1).
For mono-TCV derivatives 3 the first reduction potentials in
dichloromethane are very similar, while in less polar solvent,
tetrahydrofuran, both first and second reduction potentials for
the DSP derivative 3b are more negative (harder to reduce) (by
0.03 and 0.07 V, respectively) in comparison with the DTP
derivative 3a. For bis-TCV derivatives, DSP derivative 4b is
slightly more easy to reduce in dichloromethane with both first
and second reduction potentials being more positive in
comparison with 4a (by 0.02 and 0.03 V, respectively), while
in THF the first reduction potentials for 4a and 4b are
identical, and the second reduction is easier for DTP derivative
(by 0.04 V). For the quinoidal products 5 a somewhat similar
trend is observed, when in dichloromethane the DSP derivative
is easier to reduce (by 0.05 V), while in THF both first and
second reduction potentials are more negative (harder to
reduce) for both first and second reductions (by 0.07 and 0.08
V, respectively).
TCNE in DMF at 80 °C resulted in a mono-TCV product 3a
as a major material, and desired bis-TCV product 4a and
quinoidal product 5a as two minor materials, as it was observed
by Rasmussen’s group.11 Use of the excess of TCNE and/or
increase of the reaction temperature (up to 110 °C) or time did
not substantially improve the yield of 4a. Surprisingly, the
reaction of 2b resulted in a different product distribution, and
desired bis-TCV product 4b was isolated as a major compound,
while both mono- and quinoidal materials were obtained as
minor products. It is not clear what accounts for such increased
reactivity of the mono-TCV derivative with the second
molecule of TCNE. While 1b is somewhat easier to oxidize
in comparison with 1a,12 which suggests that the DSP core is
more electron-rich in comparison with DTP, the oxidation
potentials of mono-TCV derivatives of DTP and DSP are quite
similar (Table 1) with DSP derivative being the one that is
slightly more difficult to oxidize. The reaction mechanism,11
proposed for the formation of both mono- and bis-TCV DTP
products, involves the electron-transfer reaction as a first step,
and experimental results with DSP suggest that this step is
more favorable for the selenium-containing core.
In comparison with the respective thiophene-based quinoidal
material, 2,2′-(thiophene-2,5-diylidene)dimalononitrile,17 and
Table 1. Summary of UV−vis Absorption and CV Analyses
λmax, nm (ε × 10−3
,
λmax (film),
solvent for
CV
E
,
E
,
E1/2
,
E1/21−/2−-E1/2
,
E1/20/1−, V1 (vs
0/1+
0/1−
1−/2−
0/1−
1/2a
1/2 a
a
b
c
entry
M−1cm−1) (CH2Cl2)
nm
V
V
V
V
SCE)
EA, eV
3a
284 (15.5), 536 (49.0)
519
CH2Cl2
THF
+0.90
n/a
−0.96
−0.96
−0.97
−1.00
−0.51
−0.54
−0.49
−0.54
−0.66
−0.62
−0.61
−0.69
−1.63
−1.73
−1.62
−1.80
−0.81
−0.85
−0.78
−0.89
−0.96
−1.02
−0.96
−1.10
0.67
0.77
0.65
0.80
0.30
0.31
0.29
0.35
0.30
0.40
0.34
0.41
−0.50
−0.40
−0.51
−0.44
−0.05
+0.02
−0.03
+0.02
−0.20
−0.06
−0.13
−0.09
−3.84
3b 363 (13.4), 549 (52.8)
4a 267 (17.1), 374 (10.5), 576 (78.7)
4b 276 (17.8), 383 (10.4), 596 (88.7)
5a 375 (8.96), 509 (75.2), 546 (96.4)
512
CH2Cl2
THF
+0.92
n/a
−3.83
−4.29
−4.31
−4.14
−4.11
550
CH2Cl2
THF
n/a
n/a
d
529, 610
514
CH2Cl2
THF
+1.02
n/a
CH2Cl2
THF
+1.06
n/a
5b 276 (10.5), 510 (79.5), 547 (104.0)
549
CH2Cl2
THF
+1.06
n/a
a
b
n
0.1 M Bu4NPF6, in the specified solvent, Cp2Fe internal standard at 0 V, 50 mV·s−1 scan rate. Potentials were estimated vs SCE using the
following formula: E1/20/1−(vs SCE) = E1/20/1−(vs Cp2Fe) + 0.56 (V) (for THF); E1/20/1−(vs SCE) = E1/20/1−(vs Cp2Fe) + 0.46 (V) (for CH2Cl2).18
c
19 d
0/−
Electron affinity EA was estimated as follows: EA = −(eE1/2 + 4.8 eV). For 4b oxidation at +1.02 V is not reversible (large error).
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HOMOs of 3 are delocalized over the π-system with the node
on nitrogen and no contribution from trialkoxyphenyl
substituent or chalcogen. This wave function distribution
suggests that substitution of sulfur with selenium might lead
to improved electron transport, but no benefit of having
selenium is expected for the hole charge transport. For bis-TCV
derivatives 4, LUMOs are delocalized over the π-system with
some coefficients on chalcogens, and the larger size of the
selenium atom might contribute to improved electron charge
transport in DSP derivative 4b (vide infra). For quinoidal
products 5 both HOMOs and LUMOs are delocalized over the
π-system and dicyanomethylene groups, and while there is
some chalcogen contribution observed for the HOMOs, there
is no such contribution to the LUMOs, and enhancement of
the electron transport due to larger selenium atom is not to be
expected.
Differential scanning calorimetry (DSC) analysis of 3 and 4
showed two transitions (during both heating and cooling on
the second cycle), while quinoidal products 5 showed more
complex thermal behavior with three transitions observed for
5a and four transitions observed for 5b (Figure 3). For all DSP
derivatives the temperatures for transition to isotropic liquid is
Figure 1. UV−vis absorption spectra of 3−5: (a) in dichloromethane;
(b, c) as neat films.
Figure 2. Cyclic voltammetry analyses (0.1 M of nBu4PF6 in
dichloromethane, Cp2Fe0/+ as internal reference at 0 V, 50 mV·s−1
scan rate).
selenophene-based quinoidal material, 2,2′-(selenophene-2,5-
diylidene)dimalononitrile,17 the difference between the first and
second reduction potentials for quinoidal derivatives 5 is
smaller (0.30−0.40 V (5a) vs 0.60 V;17 and 0.34−0.41 V (5b)
vs 0.51 V17), indicating reduced Coulombic repulsion in
dianions due to delocalization over a larger (in comparison with
thiophene and selenophene) π-systems of DTP and DSP.
DFT calculations (B3LYP/6-31G**) were performed to
investigate the electronic structure of DTP and DSP derivatives.
As it was observed for mono-TCV derivative of quaterthio-
phene,20 the LUMOs of 3 are more localized on the TCV
group with some coefficients on one of the chalcogens (closer
to TCV-group) (Figure S4, Supporting Information), while
Figure 3. DSC analysis (second heating−cooling cycle, 10 °C/min
heating and cooling rate): (a) mono-TCV derivatives 3; (b) bis-TCV
derivatives 4; (c) quinoidal derivatives 5.
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higher than that of DTP derivatives, providing further evidence
for enhanced intermolecular interaction in the solid state.
Polarized optical microscopy (POM) analysis of 3b showed
the formation of a mesophase with the texture characteristic for
Colh phase followed by the transition to crystalline phase
(Figure 4b), while 3a formed the crystalline phase directly from
the isotropic liquid (Figure 4a).
Figure 7. (Left) Transfer and (right) output characteristics of n-
channel bottom-contact top-gate OFET of 4b as active layer and
CYTOP (45 nm)/Al2O3 (50 nm) dielectric layer with Au source/drain
electrodes.
configuration using CYTOP (45 nm)/Al2O3 (50 nm) dielectric
and gold electrodes,9 and slight improvement in the device
characteristics was observed with μe reaching 8.7 × 10−4 cm2/
V·s (Vth = 10.4 V, Ion/Ioff = 50).
The device was exposed to ambient conditions for 9 months,
and its characteristics (μe = 7.8 ( 1.6) × 10−4 cm2/V·s, Vth =
10.3 0.9 V, Ion/Ioff = 50) remained almost the same providing
some evidence for good device stability.
Figure 4. (a) Micrograph of 3a, transition from isotropic liquid to
crystalline phase, 149.7 °C. (b) POM micrograph of 3b, spherulitic
texture with maltese crosses of the mesophase formed from the
isotropic liquid at 180.3 °C (image size ∼870 × 650 μm).
Material 4a forms an unidentified transient liquid crystalline
phase (Figure 5a), followed by crystallization (Figure 5b). DSC
In conclusion, we have tested 4-(3,4,5-tris(dodecyloxy)-
phenyl)-4H-diselenopheno[3,2-b:2′,3′-d]pyrrole in the reaction
with TCNE, and this core was found to have increased
reactivity in comparison with dithieno[3,2-b:2′,3′-d]pyrrole,
which resulted in the formation of the bis-tricyanovinyl
derivative as a major product. This product was the only
material with measurable electron mobility in n-channel OFET,
suggesting that substitution of sulfur with selenium might lead
to stronger intermolecular interaction and improved charge
transport without significant change in the electrochemical and
optical properties.
Figure 5. POM micrographs of 4a: (a) 144.9 °C, not identified LC
phase; (b) 143.0 °C, transition from unidentified LC to crystal phase
(image size ∼870 × 650 μm).
EXPERIMENTAL SECTION
analysis of 4b suggested formation of the possibly liquid
crystalline phase for wider temperature range, but it was
difficult to obtain a good quality micrograph to identify the
phase that forms from the isotropic liquid.
While product 5b shows formation of the liquid crystalline
phase from the isotropic liquid (Figure 6(b), the nature of the
first phase that forms from the isotropic liquid of 5a is less clear,
and the grainy texture was observed by the POM (Figure 6a).
■
General Methods. Anhydrous N,N-dimethylformamide (DMF)
was used as received, and TCNE was sublimed prior to use.
Tetrahydrofuran (THF) was distilled from sodium benzophenone
ketyl. 1H and 13C{1H} and DEPT-135 NMR spectra were acquired in
CDCl3 (peaks in 1H NMR were referenced to solvent peak or
tetramethylsilane at δ 0.00 ppm). UV−vis absorption spectra were
recorded in 1 cm quarts cells. The solid-state UV−vis absorption was
measured for the films prepared on the glass substrates using
chlorobenzene solutions with concentration of ∼10 mg/mL. DSP
derivatives 3b and 5b were not completely dissolved at this
concentration at room temperature, and the solutions were heated
prior to filtration through 0.2 μm filter (for 5b precipitation started
before the spin-coating). Cyclic voltammetry (CV) experiments were
carried out under nitrogen on dry deoxygenated dichloromethane or
THF solutions ca. 10−4 M of analyte and 0.1 M solution of tetra-n-
butylammonium hexafluorophosphate at scan rates of 50 mV·s−1 using
a potentiostat, a platinum auxiliary electrode, a glassy carbon working
electrode, and a silver wire anodized in 1 M aqueous potassium
chloride (a pseudoreference electrode). Potentials were referenced to
ferrocenium/ferrocene (Cp2Fe0/1+) as an internal standard at 0 V.
Polarizing microscope equipped with the CCD camera and the hot
stage was used for microscopy analysis (200× magnification).
Figure 6. POM micrograph: (a) 5a, 156.6 °C, not identified LC phase;
(b) 5b, 190.8 °C, formation of unidentified LC from the isotropic
liquid (image size ∼870 × 650 μm).
Fabrication and Characterization of Organic Field-Effect
Transistors (OFETs). For bottom gate and top contact geometry,
OFETs were fabricated on heavily n-doped silicon substrates (n+-Si, as
the gate electrode) with 200-nm-thick thermally grown SiO2 as the
gate dielectric. Ti/Au (10 nm/100 nm) metalization on the backside
of the substrate was used to enhance the gate electrical contact. Prior
to surface modification, the substrates were treated by O2 plasma for 3
min to increase hydrophilicity of the SiO2 surface. SiO2 dielectric
Materials 3−5 were tested in the n-channel OFETs (bottom
gate, top contact configuration with Ca/Au electrodes) using
solution-processed films, and devices fabricated with material
4b were the only ones to show field-effect behavior (μe = 3.1
3.6 V, Ion/Ioff = 10)
(Figure 7, Table S1, Supporting Information). This material
was then tested in the top gate bottom contact device
( 1.2) × 10−5 cm2/V·s, Vth = −4.5
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surface was then coated with a thin buffer layer of BCB (Cyclotene,
Dow Chemicals) to provide a high-quality hydroxyl-free interface (the
solution of BCB in trimethylbenzene (TMB) with a ratio of 1:20 was
spin coated at 3000 rpm for 60 s to provide a very thin uniform layer;
thickness was not measured, final capacitance density was measured).
The samples were cross-linked at 250 °C on a hot plate for 1 h in a N2-
filled glovebox. The total capacitance density (Ci) measured from
parallel-plate capacitors was ∼13.8 nF/cm2. The organic semi-
conductor layer of compound 4b was formed on the substrates by
spin coating a solution prepared from chlorobenzene (10 mg/mL) at
500 rpm for 10 s and at 2000 rpm for 20 s. Finally, Ca/Au source/
drain electrodes were deposited by thermal evaporation through a
shadow mask. Devices were never exposed to normal ambient during
the process.
For top gate and bottom contact geometry, OFETs were fabricated
on glass substrates (Corning Eagle2000). Au (50 nm) bottom contact
source/drain electrodes were deposited by thermal evaporation
through a shadow mask. The organic semiconductor layer of 4b
compound was formed on the substrates by spin coating a solution
prepared from chlorobenzene (30 mg/mL) at 500 rpm for 10 s and at
2000 rpm for 20 s. A CYTOP (45 nm)/Al2O3 (50 nm) bilayer9 was
used as top gate dielectric. The CYTOP solution (CTL-809M) was
purchased from Asahi Glass with a concentration of 9 wt %. To
deposit the 45-nm-thick CYTOP layer, the original solution was
diluted with solvent (CT-solv.180) to have a solution:solvent volume
ratio of 1:3.5. The CYTOP layers were then deposited by spin coating
at 3000 rpm for 60 s. Samples were annealed at 100 °C for 10 min.
Al2O3 (50 nm) films were deposited on CYTOP layers by atomic layer
deposition (ALD) at 110 °C using alternating exposures of trimethyl
aluminum and H2O vapor at a deposition rate of approximately 0.1 nm
per cycle. All spin-coating and annealing processes were carried out in
a N2-filled drybox. Finally, Al (150 nm) gate electrodes were deposited
by thermal evaporation through a shadow mask.
LDA solution was added dropwise to a solution of 3-bromothiophene
(0.100 mol, 16.30 g) in 100 mL of anhydrous THF cooled in acetone/
dry ice bath (nitrogen atmosphere). After the solution was stirred for 5
min, precipitation was observed. The reaction mixture was stirred for 1
h, and CuCl2 (1.05 equiv, 0.105 mol, 14.11 g) was added in one
portion (exothermic reaction). The mixture became very dark (with
blue hue) and then orange-brown with precipitation. The reaction
mixture was allowed to warm to room temperature and treated with
aqueous HCl, and the organic phase was removed. The aqueous phase
was extracted with diethyl ether several times, the combined organic
phases were dried over MgSO4, the drying agent was filtered off, and
the solvents were removed by rotary evaporation. Crude product was
obtained as dark tan or brown solid (∼100% yield), and this material
was purified by Kugelrohr distillation (200−215 °C/0.5−0.8 mmHg)
to give off-white solid in 70−80% yields (11.3 g (70.0% yield); 13.13 g
(81.1%); lower purified yield of the product (52.3%) was observed on
a larger scale (200 mmol) with the workup that involved the filtration
of the reaction mixture diluted with hexanes through silica gel pad
1
using hexanes and then dichloromethane as eluant). H NMR (400
MHz, CHCl3): δ 7.42 (d, J = 5.4 Hz, 2H), 7.09 (d, J = 5.4 Hz, 2H)
(this analysis is in agreement with the literature data21).
Reaction of 2a with TCNE. 4-(3,4,5-Tris(dodecyloxy)phenyl)-4H-
dithieno[3,2-b:2′,3′-d]pyrrole (2a) (3.0 mmol, 2.42 g) was dissolved
in anhydrous DMF (30 mL), and TCNE (4.0 equiv, 12.0 mmol, 1.54
g) was added (nitrogen atmosphere). The solution changed color from
colorless to yellow-brown, then reddish-brown, and then dark red-
wine. After the solution was stirred for 20 min at room temperature, a
purple-red suspension formed. TLC analysis (chloroform as eluant)
showed consumption of the starting material, formation of
monotricyanovinyl product 3a as a major product, quinoidal product
5a as minor product and trace amount of bis-tricyanovinyl product 4a.
An additional amount of anhydrous DMF (20 mL) was added to the
thick suspension, and the reaction mixture was heated at 72 °C (bath
temperature) for ∼1 h, then at 55 °C (bath temperature) for 15 h, and
then at 100 °C (bath temperature), and then heating was extended for
2 more weeks (no significant progress was observed, and additional
byproducts were detected upon reaction time extension). The reaction
mixture was cooled to room temperature and treated with water, and
the dark solid was separated by vacuum filtration, washed with water,
and dried. This solid was dissolved in chloroform−dichloromethane
mixture and dried over anhydrous magnesium sulfate, the drying agent
was filtered off, and the solvents were removed to give crude product,
which was column chromatographed (silica gel, chloroform as eluant).
First fractions containing 3a were combined, the solvent was removed
by rotary evaporation, and the product 3a was obtained as dark solid
(1.57 g, 35% yield). This material can be recrystallized from 2-
propanol. Next fractions (hot-pink) containing quinoidal product 5a
were combined, the solvent was removed, and dark solid was obtained
(0.82 g, 29%). Fractions containing 4a (slightly contaminated with 5a)
were collected next, the solvent was removed, and 4a was obtained
(0.29 g, 9.7%).
Purification of 4a. Material 4a (0.29 g) isolated from the crude
reaction mixture was further purified by column chromatography
(silica gel, dichloromethane; in dichloromethane 4a comes out first
followed by 5a). Fractions containing 4a with very minor
contamination were subjected to rotary evaporation, and the residue
was purified by column chromatography two more times (silica gel,
dichloromethane as eluant). Pure material was obtained as very dark
solid (0.11 g, 39% recovery). This material can be recrystallized from
2-propanol.
Purification of 5a. Material 5a (0.82 g) obtained from the crude
reaction mixture after the first column chromatography was further
purified (silica gel, dichloromethane as eluant). Major fractions
containing 5a were combined, the solvent was removed and dark
solid was obtained (0.60 g, 73% recovery; contaminated fractions were
kept separately). This material was further purified for mobility
measurement by three successive column chromatographies (silica gel,
dichloromethane as eluant). The solvent was removed from combined
fractions, and the residue was recrystallized from distilled 2-propanol
twice (0.114 g, 13.9% recovery).
All current−voltage (I−V) and capacitance−voltage (C−V)
characteristics were measured in a N2-filled glovebox (O2, H2O <
0.1 ppm) with an Agilent E5272A source/monitor unit and an Agilent
4284A LCR meter.
4-(3,4,5-Tris(dodecyloxy)phenyl)-4H-dithieno[3,2-b:2′,3′-d]-
pyrrole (2a). 2,6-Bis(trimethylsilyl)-4-(3,4,5-tris(dodecyloxy)phenyl)-
4H-dithieno[3,2-b:2′,3′-d]pyrrole (1a) (3.00 mmol, 2.85 g) was
dissolved in THF (40 mL), and tetra-n-butylammonium fluoride
(TBAF) (1.0 M in THF, 6.00 mmol, 6.0 mL) was added dropwise at
room temperature under nitrogen atmosphere. The reaction mixture
was stirred for ∼0.5 h, and the reaction completion was confirmed by
TLC analysis (hexanes/dichloromethane (1:1) as eluant). Reaction
mixture was treated with water, the organic phase was separated, and
the aqueous phase was extracted with hexanes two times. The
combined organic phases were dried over anhydrous magnesium
sulfate, the drying agent was filtered off, and the organic solvents were
removed by rotary evaporation. Crude product was purified by column
chromatography (silica gel dichloromethane/hexanes (2:1), and then
dichloromethane/ethyl acetate (10:1) as eluants). Combined fractions
were subjected to rotary evaporation, the residue was dried under
vacuum, and the product (2a) was obtained as yellowish solid (1.68 g,
69.2% yield). 1H NMR (400 MHz, CDCl3): δ 7.18 (appears as s, 4H),
6.78 (s, 2H), 4.02 (m, 6H), 1.85 (m, 6H), 1.63 (m, (6H), 1.45−1.20
(m, 48H), 0.91 (m, 9H). 13C{1H} NMR (400 MHz, CDCl3): δ 153.7,
144.1, 136.4, 135.2, 123.3 (CH), 116.5, 112.2 (CH), 101.7 (CH), 73.6
(CH2), 69.3 (CH2), 31.9 (CH2), 31.9 (CH2), 30.4 (CH2), 29.8 (CH2),
29.7 (CH2), 29.64 (CH2), 29.6 (CH2), 29.4 (CH2), 29.36 (CH2),
29.32 (CH2), 26.2 (CH2), 26.1 (CH2), 22.7 (CH2), 14.1 (CH3)
(expected number of alkyl carbon resonances is 24; only 16 resonances
were observed presumably due to overlap) (assignment of the CH,
CH2 and CH3 carbons was made based on DEPT-135 experiment)
(1H and 13C{1H} NMR recorded in CDCl3 are in good agreement
with the literature analyses reported in CD2Cl2).15
3,3′-Dibromo-2,2′-dithiophene. Lithium diisopropylamide (LDA)
was prepared by the addition of n-butyllithium (2.89 M in hexanes,
0.100 mol, 84 mL) to a solution of diisopropylamine (0.110 mol, 11.1
g) in 50 mL of anhydrous THF (−78 °C to room temperature). This
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The Journal of Organic Chemistry
Note
1
3a. H NMR (400 MHz, CDCl3): δ 8.04 (s, 1H), 7.66 (d, J = 5.4
TCNE (4.00 mmol, 1.03 g) were mixed in a flask under nitrogen
atmosphere. Anhydrous DMF (25 mL) was added, and the solution
became purple within 1 min. The reaction mixture was initially heated
to 117 °C and then stirred at 102 °C overnight. The reaction was
monitored by TLC in hexanes/dichloromethane (1:1), and after
consumption of the starting material the dark blue mixture was cooled
to room temperature and treated with water (50 mL). The organic
matter was extracted with dichloromethane (four times) and then with
chloroform, and combined organic phases were dried over anhydrous
magnesium sulfate. The drying agent was filtered off, the organic
solvents were removed by rotary evaporation, and the crude product
was column chromatographed (silica gel, hexanes:dichloromethane
(2:1) as eluant). First fractions containing monosubstituted product
3b were combined, the solvents were removed by rotary evaporation,
and the residue was further purified using prepacked Biotage columns
(chloroform as eluant) (0.29 g, 14.6% yield). The next fractions
containing disubstituted product 4b came out with dichloromethane as
eluant. The dark blue pure fractions were combined, and the solvents
were removed by rotary evaporation to give product as dark blue film,
which was further purified using prepacked Biotage columns
(chloroform as eluant) (0.99 g, 44%). The next fractions containing
slightly contaminated 5b (dichloromethane as eluant) were combined,
the solvents were removed by rotary evaporation, and the residue was
further purified by Biotage column chromatography (chloroform as
eluant) (0.14 g, 6.9% yield).
Hz, 1H), 7.14 (d, J = 5.4 Hz, 1H), 6.69 (s, 2H), 4.05 (t, J = 6.5 Hz,
2H), 4.00 (t, J = 6.3 Hz, 4H), 1.83 (m, 6H), 1.53 (m, 6H), 1.40−1.20
(m, 48H), 0.90 (m, 9H). 13C{1H} NMR (400 MHz, CDCl3): δ 154.2,
152.6, 145.4, 137.9, 134.5 (CH), 132.6, 132.05, 131.9, 129.8, 121.7
(broad, CH), 116.7, 113.5, 113.3, 112.9, 112.4 (CH), 102.1 (CH),
73.7 (CH2), 69.5 (CH2), 31.92 (CH2), 31.89 (CH2), 30.4 (CH2),
29.75 (CH2), 29.73 CH2, 29.68 (CH2), 29.63 (CH2), 29.60 (CH2),
29.37 (CH2), 29.34 (CH2), 29.26 (CH2), 26.1 (CH2), 26.0 (CH2),
22.7 (CH2), 14.1 (CH3) (expected number of alkyl carbon resonances
is 24; only 17 resonances were observed presumably due to overlap)
(assignment of the CH, CH2 and CH3 carbons was made based on
DEPT-135 experiment). HRMS (MALDI-TOF): calcd for
C55H80N4O3S2 908.5672, found 908.5626. Anal. Calcd for
C55H80N4O3S2: C, 72.64; H, 8.87; N, 6.16. Found: C, 72.89; H,
8.71; N, 6.13.
4a. 1H NMR (400 MHz, CDCl3): δ 8.09 (s, 2H), 6.64 (s, 2H), 4.06
(t, J = 6.6 Hz, 2H), 3.99 (t, J = 6.4 Hz, 4H), 1.86 (m, 6H), 1.49 (m,
6H), 1.27 (s, 48H), 0.89 (m, 9H). 13C{1H} NMR (400 MHz, CDCl3):
δ 154.6, 149.2, 138.8, 137.2, 132.9, 131.2, 125.3, 121.1 (CH), 112.6,
112.1, 111.6, 102.2 (CH), 84.9, 73.8 (CH2), 69.6 (CH2), 31.93 (CH2),
31.91 (CH2), 30.4 (CH2), 29.76 (CH2), 29.74 (CH2), 29.69 (CH2),
29.65 (CH2), 29.61 (CH2), 29.39 (CH2), 29.36 (CH2), 29.24 (CH2),
26.09 (CH2), 26.02 (CH2), 22.7 (CH2), 14.1 (CH3) (expected
number of alkyl carbon resonances is 24; only 17 resonances were
observed presumably due to overlap) (assignment of the CH, CH2 and
CH3 carbons was made based on DEPT-135 experiment). HRMS
(MALDI-TOF): calcd for C60H79N7O3S2 1009.5686; found
1009.5707. Anal. Calcd for C60H79N7O3S2: C, 71.32; H, 7.88; N,
9.70. Found: C, 71.49; H, 7.86; N, 9.57.
3b: 1H NMR (400 MHz, CDCl3): δ 8.23 (m, 2H), 7.35 (d, J = 5.9
Hz, 1H), 6.64 (s, 2H), 4.06 (t, J = 6.5 Hz, 2H), 3.98 (t, J = 6.4 Hz,
4H), 1.84 (m, 6H), 1.49 (m, 6H), 1.26 (m, 48H), 0.90 (m, 9H).
13C{1H} NMR (400 MHz, CDCl3): δ 154.2, 153.8, 145.8, 138.3 (CH),
134.1, 133.5, 132.7, 126.4 (CH), 118.7, 115.5 (CH), 114.0, 113.1,
103.1 (CH), 76.2, 73.8 (CH2), 69.5 (CH2), 31.96 (CH2), 31.93
(CH2), 30.4 (CH2), 29.79 (CH2), 29.77 (CH2), 29.71 (CH2), 29.67
(CH2), 29.64 (CH2), 29.40 (CH2), 29.38 (CH2), 29.3 (CH2), 26.13
(CH2), 26.07 (CH2), 22.7 (CH2), 14.1 (CH3) (assignment of the CH,
CH2 and CH3 carbons was made based on DEPT-135 experiment).
HRMS (MALDI-TOF): calcd for (C55H80N4O3Se2 + H) 1005.4639,
found 1005.4592. Anal. Calcd for C55H80N4O3Se2: C, 65.85; H, 8.04;
N, 5.58. Found: C, 66.02; H, 8.14; N, 5.43.
5a. 1H NMR(400 MHz, CDCl3): δ 6.52 (s, 2H), 6.50 (s, 2H), 4.03
(t, J = 6.6 Hz, 4H), 3.98 (t, J = 6.4 Hz, 4H), 1.86 (m, 7H), 1.49 (m,
7H), 1.27 (s, 56H), 0.90 (t, J = 6.5 Hz, 9H). 13C{1H} NMR (400
MHz, CDCl3): δ 174.1, 163.7, 154.5, 139.5, 129.5, 129.2, 112.6, 112.4,
104.4 (CH), 102.8 (CH), 73.9 (CH2), 73.5, 69.7 (CH2), 31.9 (CH2),
30.4 (CH2), 29.78 (CH2), 29.72 (CH2), 29.67 (CH2), 29.63 (CH2),
29.41 (CH2), 29.38 (CH2), 29.3 (CH2), 26.1 (CH2), 22.7 (CH2), 14.1
(CH3) (expected number of alkyl carbon resonances is 24; only 14
resonances were observed presumably due to overlap). MS (MALDI-
TOF): calcd for (C56H79N5O3S2 + H) 934.6, found 934.6. Anal. Calcd
for C56H79N5O3S2: C, 71.98; H, 8.52; N, 7.50. Found: C, 72.00; H,
8.56; N, 7.39.
4-(3,4,5-Tris(dodecyloxy)phenyl)-4H-diselenopheno[3,2-b:2′,3′-
d]pyrrole (2b). 2,6-Bis(trimethylsilyl)-4-(3,4,5-tris(dodecyloxy)-
phenyl)-4H-diselenopheno[3,2-b:2′,3′-d]pyrrole (1b) (5.22 mmol,
5.46 g) was dissolved in 25 mL of anhydrous THF and TBAF (1.0
M in THF, 2.2 equiv, 11.48 mmol, 11.5 mL) was added dropwise. The
yellow-orange reaction mixture became darker in color. The mixture
was stirred for 25 min, analyzed by TLC (hexanes:dichloromethane
(2:1) as eluant, consumption of the starting material was confirmed),
and the mixture was treated with water (∼20 mL). The dark brown
organic phase was separated, the aqueous phase was extracted with
hexanes (3 × 15 mL), the combined organic phases were dried over
anhydrous magnesium sulfate, and the drying agent was filtered off.
The solvent was removed, and the brownish oil was obtained as a
crude product (4.01 g, solidified on standing, 85.1% yield, only trace
amount of impurity was detected by TLC). This material was purified
by column chromatography (silica gel, hexanes:CH2Cl2 (2:1), and the
yellowish oil was obtained after solvent removal (solidified on standing
4b. 1H NMR (400 MHz, CDCl3): δ 8.28 (s, 2H), 6.63 (s, 2H), 4.08
(t, J = 6.6 Hz, 2H), 3.98 (t, J = 6.4 Hz, 4H), 1.82 (m, 6H), 1.50 (m,
6H), 1.27 (48H), 0.90 (m, 9H). 13C{1H} NMR (400 MHz, CDCl3): δ
154.6, 149.8, 139.5, 139.1, 135.1, 131.3, 128.9, 125.8 (CH), 112.7,
112.5, 111.8, 103.1 (CH), 83.9, 77.4, 77.0, 76.7, 73.9 (CH2), 69.7
(CH2), 31.96 (CH2), 31.93 (CH2), 30.4 (CH2), 29.77 (CH2), 29.72
(CH2), 29.68 (CH2), 29.65 (CH2), 29.41 (CH2), 29.39 (CH2), 29.27
(CH2), 26.12 (CH2), 26.06 (CH2), 22.7 (CH2), 14.1 (CH3). HRMS
(MALDI-TOF): calcd for (C60H79N7O3Se2 + H) 1106.4653, found
1106.4667. Anal. Calcd for C60H79N7O3Se2: C, 65.26; H, 7.21; N, 8.88.
Found: C, 65.34; H, 7.20; N, 8.82 (for material prior to the
purification by Biotage column chromatography). Found: C, 65.20; H,
7.12; N, 8.72 (for material after the purification by the Biotage column
chromatography).
5b. 1H NMR (400 MHz, CDCl3): δ 6.53 (s, 2H), 6.48 (s, 2H), 4.05
(t, J = 6.6 Hz, 2H), 3.96 (t, J = 6.4 Hz, 4H), 1.82 (m, 6H) 1.49 (m,
6H), 1.27 (m, 48H), 0.89 (t, J = 6.7 Hz, 9H). 13C{1H} NMR (400
MHz, CDCl3): δ 174.5, 165.8, 154.4, 139.5, 131.5, 129.4, 113.7, 112.4,
105.5 (CH), 103.4 (CH), 76.0, 73.8 (CH2), 69.6 (CH2), 31.9 (CH2),
30.4 (CH2), 29.76 (CH2), 29.72 (CH2), 29.69 (CH2), 29.65 (CH2),
29.61 (CH2), 29.38 (CH2), 29.36 (CH2), 29.2 (CH2), 26.0 (CH2),
22.7 (CH2), 14.1 (CH3) (12 alkyl carbon signals are missing due to
overlap) (assignment of the CH, CH2 and CH3 carbons was made
based on DEPT-135 experiment). HRMS (MALDI-TOF): calcd for
(C56H79N5O3Se2 + H) 1030.4592, found 1030.4478. Anal. Calcd for
C56H79N5O3Se2: C, 65.42; H, 7.74; N, 6.81. Found: C, 65.55; H, 7.58;
N, 6.76.
1
to give off-white solid). H NMR (400 MHz, CDCl3): δ 7.72 (d, J =
5.8 Hz, 2H), 7.40 (d, J = 5.8 Hz, 2H), 6.71 (s, 2H), 4.03 (t, J = 6.6 Hz,
2H), 3.98 (t, J = 6.5 Hz, 4H), 1.81 (m, 6H), 1.49 (m, 6H), 1.40−1.20
(m, 48H), 0.89 (m, 9H). 13C{1H} NMR (400 MHz, CDCl3): δ 153.6,
144.7, 136.8, 135.1, 126.2, 117.9, 115.6, 102.9, 73.6, 69.3, 31.94, 31.92,
30.4, 29.8, 29.69, 29.65, 29.63, 29.40, 29.36, 29.31, 26.14, 26.08, 22.7,
14.1. MS (MALDI-TOF): calcd for C50H81NO3Se2 902.5, found 903.5.
Anal. Calcd for C50H81NO3Se2: C, 66.57; H, 9.05; N, 1.55. Found: C,
66.78; H, 9.22; N, 1.60.
Reaction of 2b with TCNE. 4-(3,4,5-Tris(dodecyloxy)phenyl)-4H-
diselenopheno[3,2-b:2′,3′-d]pyrrole (2b) (2.00 mmol, 1.80 g) and
10936
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The Journal of Organic Chemistry
Note
(20) Burand, M. W.; Mcgee, K. A.; Cai, X. Y.; Da Silva, D. A.; Bredas,
J. L.; Frisbie, C. D.; Mann, K. R. Chem. Phys. Lett. 2006, 425, 251−256.
(21) Faid, K.; Cloutier, R.; Leclerc, M. Macromolecules 1993, 26,
2501−2507.
ASSOCIATED CONTENT
* Supporting Information
■
S
Computational methodology, table with the summary of the
device characterization of 4b, DSC graphs for the first heating−
cooling cycle, HOMO and LUMO (3−5), and HOMO-1 (3
and 4) wave function illustrations, additional micrographs, and
tables of atom coordinates and absolute energies for 3−5. This
material is available free of charge via the Internet at http://
pubs.acs.org
AUTHOR INFORMATION
Corresponding Author
*E-mail: seth.marder@chemistry.gatech.edu.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported in part by Solvay S.A., by the STC
Program of the National Science Foundation under Agreement
No. DMR-0120967. Y.A.G. thanks Benjamin Wunsch for the
DSC analyses, Timothy Parker for providing help with the DFT
calculations, and Professor John Reynolds for providing access
to the microscope equipped with the hot stage.
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