Structural and electronic properties of crystalline, isomerically pure anthradithiophene derivatives

Article abstract of DOI:10.1002/adfm.201502440

Anthradithiophene chromophores are found in many current high-performance organic semiconductors, even though these materials are typically synthesized as an inseparable mixture of syn and anti isomers. Recent syntheses of pure syn anthradithiophenes have shown no improvement in performance for the more homogeneous system, but similar studies on the pure anti isomer have not been reported. In this work, a simple protocol is described to prepare the pure anti isomer of fluorinated, functionalized anthradithiophenes, and perform detailed analysis of the intermolecular interactions in the crystal that yield increased density and closer chromophore contacts. Studies of the charge-transport properties of these pure isomers, compared to the isomeric mixtures, suggest that the benefit of isomer purity is not consistent; in the syn case, there was minimal difference between the pure isomer and the mixture, while for the anti isomer mobility improved nearly twofold. Analysis of disorder in the crystals suggests a reason for this difference in performance. Isolation of pure anti anthradithiophene derivatives sheds light on the intermolecular interactions that increase order in these materials. Strong hydrogen-fluorine interactions, along with an inversion center in the pure anti isomer, reduces disorder and decrease intermolecular spacing in these derivatives, yielding field-effect mobility higher than 6 cm² V^-1 s^-1 in spin-cast films.

Full text of DOI:10.1002/adfm.201502440

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Structural and Electronic Properties of Crystalline,
Isomerically Pure Anthradithiophene Derivatives
Rawad K. Hallani, Karl J. Thorley, Yaochuan Mei, Sean R. Parkin, Oana D. Jurchescu,
and John E. Anthony*
considering that the majority of devices
based on ADTs reported to date have been
Anthradithiophene chromophores are found in many current high-perfor-
mance organic semiconductors, even though these materials are typically
synthesized as an inseparable mixture of syn and anti isomers. Recent
syntheses of pure syn anthradithiophenes have shown no improvement in
performance for the more homogeneous system, but similar studies on the
pure anti isomer have not been reported. In this work, a simple protocol
is described to prepare the pure anti isomer of fluorinated, functionalized
anthradithiophenes, and perform detailed analysis of the intermolecular inter-
actions in the crystal that yield increased density and closer chromophore
contacts. Studies of the charge-transport properties of these pure isomers,
compared to the isomeric mixtures, suggest that the benefit of isomer purity
is not consistent; in the syn case, there was minimal difference between the
pure isomer and the mixture, while for the anti isomer mobility improved
nearly twofold. Analysis of disorder in the crystals suggests a reason for this
difference in performance.
formed from a material consisting of a
mixture of isomers. Typically, isomeric
mixtures are expected to offer decreased
electronic performance, due to the inho-
mogeneities in intermolecular order that
[6]
arise in the crystalline state.
The isomer mixtures (mix ADTs) arise
due to the nonregiospecific aldol condensa-
tion used in the most common synthesis of
[7]
the ADT chromophore. Even in the case of
highly soluble ADT derivatives, separation
of the syn and anti isomers after synthesis
has proven impossible. Thus the chemical
community has adopted much lengthier
synthetic approaches to synthesize each
pure isomer directly. Geerts and co-workers
were the first to explore pure ADT isomers,
developing an elegant synthesis of pure anti
dihexyl ADT with an overall chemical yield
of ≈3% in 2011.[8] Unfortunately, there have been no reports of
the device performance/hole transport property measurement
for this material. In 2012, the Tykwinski group demonstrated
the first synthesis of pure syn diF TES ADT, in an overall yield
1
. Introduction
Anthradithiophene (ADTs, Figure 1) semiconductors, intro-
duced by Katz and co-workers,[ have become a common
core in both small-molecule and polymeric semiconductor
systems.[ Incorporated into polymer backbones, ADTs have
yielded materials with hole mobility extracted from field-effect
transistor (FET) devices on the order of 0.1 cm V s . The
solubilized small-molecule versions of this chromophore fare
significantly better in this application, exhibiting impressive
1]
[9]
of 9% from commercial starting materials. Single-crystal studies
by Jurchescu and co-workers showed no significant difference in
charge transport properties between the mix and syn materials.
More recently, Takimiya and co-workers prepared the parent
ADT in isomerically pure anti form in six synthetic steps and
2]
2
−1 −1 [3]
[
10]
43% overall yield, and found that the transistor performance
was several times higher than that of the isomeric mixture
2
−1 −1 [4]
[1]
hole mobilities as high as 6 cm V s , and have proven
amenable to a vast array of different processing conditions.
reported by Katz (although some of this improvement may
[
5]
arise due to improved modern device fabrication protocols).
These impressive charge transport properties are surprising,
Mamada and co-workers prepared both isomeric forms of the
parent ADT, in 12% overall yield for anti and 7% yield for syn.
[
11]
In vacuum-deposited devices, the anti isomer showed substan-
2
−1 −1
tially higher performance than the syn isomer; 0.18 cm V
s
R. K. Hallani, Dr. K. J. Thorley, Dr. S. R. Parkin,
Prof. J. E. Anthony
Department of Chemistry
University of Kentucky
Lexington, KY 40506-0055, USA
E-mail: anthony@uky.edu
2
−1 −1
compared to 0.017 cm V
s
for syn. Similarly, Takimiya and
co-workers also observed an order-of-magnitude difference in
hole transport efficiency between alkylated isomerically pure
anti- and syn-naphthodithiophenes, with the anti derivative
again exhibiting better performance. These results strongly
suggest that a detailed understanding of the impact of isomer
mixtures in the solution-processable, ethyne-substituted ADTs
will not be complete without side-by-side analysis of the mix,
syn, and heretofore-elusive pure anti isomers.
[
12]
Y. Mei, Prof. O. D. Jurchescu
Department of Physics
Wake Forest University
Winston-Salem, NC 27109, USA
DOI: 10.1002/adfm.201502440
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chromatographic environment. We thus chose the mono-
silylated diethynyl anthradithiophenes 1(a–c) as our synthetic
target. The isomeric mixture of this ADT molecule is prepared
in two synthetic steps in 41% yield as outlined in Scheme 1, and
although slightly unstable in concentrated solution, these iso-
mers are easily separated by silica gel column chromatography
using an automated system (eluting with hexanes). Crystallo-
graphic characterization of these stable molecules did indeed
show the separation of the three expected isomers as shown in
the scheme (thermal-ellipsoid plots confirming isomer struc-
tures are shown in the Supporting Information).
The isolated isomers were then quickly converted to the final
semiconductors as shown in Scheme 1. Each isomer of 1 was
first fully desilylated, then the desired alkyne cap was installed
by stirring the poorly soluble diethynyl ADT in a solution of
silyl (or germyl) chloride and the non-nucleophilic base lithium
bis(trimethylsilyl)amide. The anti isomer in this case was
formed in an overall 14% yield from commercially available
starting materials. The syn isomer was also formed, in overall
≈
4% isolated yield.
2
.2. Structural Characterization
X-ray crystallographic analysis of anti diF TES ADT and anti
diF TEG ADT showed that both isomers adopted solid-state
arrangements nearly identical to those observed from the corre-
sponding isomeric mixtures. However, in both cases there were
small decreases in interatomic spacing in structures acquired
at the same temperature—and in the case of diF TEG ADT,
we observed a small but significant increase in density of the
crystal that suggests tighter overall intermolecular interactions.
To determine whether these changes alter the electronic
coupling between chromophores in the solid, we performed
charge-transfer integral calculations based on the obtained
crystal structures. To achieve this, we used the localized mon-
Figure 1. Structures of the anthradithiophene derivatives discussed in
this study.
[14]
[15]
omer approach
with Gaussian09,
using the B3LYP/
Because the direct synthesis of isomerically pure ADTs is
lengthy and typically exhibits low product yield,[13] we were
curious whether a chromatographic separation might be pos-
sible. While the maximum yield of any particular isomer is
6–31G(d) functional and basis set. As a 2D π-stacked material,
each ADT chromophore interacts with two symmetry-related
pairs of molecules in the solid state. Figure 2 shows the appro-
priate stacking partners, consisting of one strongly interacting
(dark oval) and one weakly interacting (light oval) ADT molecule.
The calculated electronic couplings derived from the crystal
structures of both the anti and mix ADT isomers (as well as the
syn diF TES ADT) show that in both the TES and TEG case, the
electronic coupling is stronger for the anti ADT—and in the case
of the TEG compound, the difference is substantial. It should be
noted that even in the isomerically pure materials, some posi-
tional disorder of the thiophene rings exists (as described below);
the couplings listed in Figure 2 correspond to those for the crys-
tallographically most common arrangement of molecules.
5
0% by this route (assuming syn and anti are formed in sim-
ilar amounts during the regio-random synthesis), the smaller
number of higher-yielding synthetic steps in this route allow for
scaling of the reactions, and should provide an overall increased
throughput in synthesis. Additionally, pure syn isomer will also
be produced by this method as a byproduct, allowing side-by-
side comparison of anti, syn, and mix ADT systems.
[9]
2
. Results and Discussion
2
.1. Synthesis
2
.3. Device Studies: Hole Transport Properties
Recent efforts in the Anthony group toward the synthesis
of highly desymmetrized silylethyne ADTs suggested that
such molecules do indeed allow the separation of iso-
mers by standard silica-based chromatographic methods,
due to the better exposure of the polar sulfur atoms to the
To investigate the impact of isomer purity on device perfor-
mance and hole transport properties, we fabricated organic thin-
film transistors (OTFTs) based on both the isomeric mixture,
the syn and anti isomers of TES and TEG, respectively. To
2
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Scheme 1. Synthesis of pure syn and anti diF ADT isomers by chromatographic separation.
accurately compare device performance across all compounds,
all devices investigated here maintained a similar structure
tive mix diF TES ADT (a), syn diF TES ADT (b), anti diF TES
ADT (c), mix diF TEG ADT (d), syn diF TEG ADT (e), anti diF
TES ADT (f) devices. These measurements were taken in the
saturation regime of OTFT operation (source–drain voltage
(Figure 3). Bottom contact, top gate OTFTs were fabricated by
spin-coating the organic semiconductor on gold source-drain
electrodes chemically modified with pentafluorobenzenethiol
VDS = −40 V). On the right axis we show the drain current I , as
D
[
16]
(
PFBT) to improve injection and film crystallization.
amorphous fluoropolymer gate dielectric known as Cytop
Asahi Glass) was used as the dielectric, with Al top gate elec-
An
a function of source–gate voltage, VGS, and on the left axis the
square root of I , which was used in mobility calculations. Note
D
(
that these curves show close to zero threshold voltages, sharp
turn-on and a well-defined linear dependence of the square root
trode. For comparison, the pure syn isomer was studied along
with the mixture of isomers and the pure anti isomer.
of I with VGS, suggesting that our measurements do not suffer
D
The devices were measured in the dark under air, using an
Agilent 4155 C semiconductor parameter analyzer. Figure 4
illustrates typical current–voltage characteristics for representa-
from large contact or trapping effects. Similar current–voltage
Figure 2. Electronic coupling between π-stacked pairs of mix and anti diF
TES and diF TEG ADTs.
Figure 3. Schematic representation of the bottom-contact, top-gate
structure used in this study.
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Figure 4. Transfer characteristics of ADT devices: a) mix diF TES ADT, b) syn diF TES ADT, c) anti diF TES ADT, d) mix diF TEG ADT, e) syn diF TEG
ADT, f) anti diF TES ADT. The device geometry and mobility are included in the inset.
characteristics for devices of identical geometry are illustrated
in Figure S2 of the Supporting Information.
cases the anti isomer outperforms both the isomeric mixture
and the syn isomer, while the syn isomer, as suggested by prior
studies, exhibited device performance generally on par with
Table 1 shows the average field-effect mobility, μ, of the best
six samples studied, as well as the average mobility over all
samples studied (>20 for each type of ADT). These mobilities
were calculated in the saturation regime of device operation,
[
8]
that of the mixture of isomers. The performance of the TEG
compounds is consistently superior to that of the TES, which is
related to the optimized crystalline packing in this compound,
–2
[17]
and the areal capacitance of the dielectric was C = 1.30 nF cm .
as we have shown in an earlier study. While the increase in
i
To minimize the effects of microstructure on the resulting
mobilities, we restricted our analysis to devices with channels
fully covered with large grains, which in this case consisted of
performance arising from anti diF TES ADT is only margin-
ally better than that observed in the isomeric mixture, anti diF
TEG ADT showed a substantial improvement in performance,
yielding spin-cast devices performing at the level of the best
single-crystal devices fabricated from mix diF TES ADT. This
improvement, however, may partially come from the use of
Cytop dielectric, which is free of surface-states characteristic to
[16]
5
µm ≤ L ≤ 50 µm. We note that the short channel devices
(L = 5 µm) exhibit lower mobility values due to significant
contributions from the contact resistance. Nevertheless, in all
the SiO dielectric used in previous studies on both the TES
and TEG compounds.
2
Table 1. Device performance of anti, mix, and syn ADTs.
Material
Avg. mobility best six samples Avg. mobility all samples
2
−1 −1 a)
2
−1 −1
[
cm V
s
]
[cm V
s ]
2
.4. Discussion
Mix diF TES ADT
Syn diF TES
2.7 ± 0.7
3.0 ± 0.4
4.3 ± 0.8
2.4 ± 0.3
2.8 ± 0.3
6.2 ± 0.4
1.5 ± 0.8
1.9 ± 0.9
2.2 ± 1.1
1.7 ± 0.6
2.2 ± 0.5
3.4 ± 1.6
The ability to compare crystal structures of the mix, syn,
and anti diF ADTs allows us to understand several impor-
tant issues related to the fine-tuning of crystal packing in
these heteroaromatic systems, along with the impact of
these subtle changes on charge transport properties. Fore-
most among these issues is the disordering of the thiophene
rings in the syn, anti, and mix cases. For example, in the diF
TES ADT series, both isomers and the mix crystallize with
Anti diF TES ADT
Mix diF TEG ADT
Syn diF TEG ADT
Anti diF TEG ADT
a)Dependence of mobility on gate voltage sweep rate is included in the Supporting
Information.
2
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space group P1 with half a molecule in the
asymmetric unit. For the pure syn mol-
ecule, which itself has no inversion center,
the presence of an inversion center in the
crystal structure at the center of the middle
benzene ring forces the disorder fractions
for the thiophene rings to be exactly 50:50.
In the reported structure, syn diF TES
ADT[ the disorder fraction was treated
as a variable, which refined to 0.506(2)
and 0.494(2). Since any deviation from
8]
0
.5 would have indicated contamination by
the anti-isomer, it should have been fixed
at exactly 0.5. Since the pure anti molecule
itself has an inversion center, there is no
constraint on the thiophene-flip disorder
fractions. In the refined model for the anti Figure 5. Pairwise interaction energy decomposition analysis for in-plane interactions between
isomer, the fractions refine to 0.891(2) and the ends of diF ADT dimers interacting through strictly HF coupling (top), a mixture of HF and
SF couplings (middle), and exclusive SF couplings (bottom).
0
.109(2). For the mix, the refined thiophene
disorder fractions were intermediate, at
.688(4) and 0.312(4). For comparison, the anti diF TEG ADT
fractions refined to 0.944(2):0.056(2) while the mix yielded
.706(6):0.294(6). These models do not address the question
0
stronger electronic coupling and higher charge carrier mobility
in the anti systems.
0
Device studies harmonize with our assessments of the
crystal structures of the mix and anti isomers. For the TES com-
pound, the similar values computed for the transfer integral
are accompanied by comparable charge transport properties
for the devices based on the anti TES compared with the mix-
of whether disorder of the ADT core occurs at the individual
molecule level or whether it occurs as misoriented clusters
of well-ordered molecules. Either way, since the pure anti is
predominantly (i.e., ≈90% for TES, ≈95% for TEG) in a single
orientation, it is clear that the pure anti is on the whole sub-
stantially more ordered than either the pure syn or the mix,
and that the degree of ordering trends with improvement in
charge transport properties.
2
−1 −1
ture (μanti-TE S2 = 4.3 ± 0.8 cm V
s
compared with μmix-TES =
−1
−1
2.7 ± 0.7 cm V s ). For the TEG devices, on the other hand,
the average mobility for the anti isomer is more than double
2
−1 −1
the value of the mix sample (μanti-TEG = 6.2 ± 0.4 cm V
s
2
−1 −1
Along with issues of improved overall order in the anti
isomer, the fact that we see increased density for the pure anti
isomer suggests that there is some form of intermolecular inter-
action in the anti isomer that is weakened or frustrated in the
mix or syn forms. We investigated intermolecular interactions
found in the crystal structure by pairwise interaction energy
compared with μmix-TEG = 2.4 ± 0.3 cm V s ), in agreement
with the larger value obtained for the transfer integral. It is pos-
sible that these differences in mobility are even larger, but our
measurements on the polycrystalline samples have precluded
us from accessing only the strongly interacting π–π stacking
direction, which we considered for our calculations. The reduc-
tion in mobility for the mix-compounds may also originate from
the fact that the presence of the disruptive syn isomer leads to
trapping states for the injected charges. Nevertheless, the small
values of the subthreshold slopes recorded in our devices based
on mix-isomers suggest that this effect, if present, is minor.
Another point is that both diF ADTs investigated here form a
decomposition analysis[ using the GAMESS software at the
MP2 level. This analysis breaks down the van der Waals inter-
action energies between two molecules into different energy
terms to highlight the driving forces stabilizing the interaction.
In this case, the in-plane diF ADT dimer was analyzed in three
different alignments, with the fluorine atom interacting either
with protons or sulfur atoms on the neighboring molecule
18]
[19]
differential microstructure on the Au and SiO in the presence
2
(Figure 5). While the S–F interaction—often
cited as an important interaction in many
organic semiconductors[ —is stabilizing,
the H–F interaction is three times stronger,
and is the major interaction seen in the pure
anti structure. Assuming the strongest inter-
action between molecules, the anti isomer
can form a similar contact with a third mole-
cule, whereas a syn isomer must necessarily
form a weaker interaction involving sulfur
20]
(Figure 6). Therefore, the H–F interaction
can contribute to the increased order seen in
the pure anti isomers, as well as decreasing
intermolecular distances and giving denser
Figure 6. Regular intermolecular F...H interactions (highlighted by black arrows) in the pure
anti diF ADTs (top) and the loss of one such interaction (gray arrow) required to incorporate
molecular packing, which may explain the the syn isomer in mix ADTs (bottom).
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1
3
of PFBT-treated contacts, consisting of large grains of highly
oriented molecules bridging narrow contacts and small grains
of mixed orientations in the middle of long channels.
In this work, however, we only focused on the short-channel
devices (L < 50 µm), to exclude the microstructure effects from
our analysis.
J = 6.94 Hz, 6H), 0.95 (d, J = 6.94 Hz, 6H). C NMR (100 MHz, CDCl3,
δ): 167.28, 167.22, 164.31, 164.25, 163.11, 136.41, 136.33, 136.29,
136.22, 133.75, 133.61, 129.69, 129.56, 129.41, 129.31, 129.27, 120.56,
[
13a,b,d]
1
1
20.47, 120.19, 120.08, 119.98, 119.73, 117.49, 115.15, 108.45, 103.49,
02.50, 102.40, 102.29, 90.16, 80.60, 67.94, 26.51, 25.38, 25.29.
1
1
b: H NMR (400 MHz, CDCl , δ): 8.69 (s, 2H), 8.63 (s, 1H), 6.67
3
(s, 2H), 4.04 (s, 1H), 2.16 (m, 3H), 1.19 (d, J = 6.61 Hz, 18H), 0.95
1
3
(
d, J = 6.93 Hz, 6H). C NMR (100 MHz, CDCl , δ): 167.29, 164.32,
3
1
1
8
63.12, 136.31, 136.24, 133.67, 129.77, 129.15, 129.12, 120.48, 120.40,
19.76, 114.48, 108.65, 103.61, 102.40, 102.29, 102.26, 102.25, 89.89,
3
. Conclusion
0.51, 67.94, 26.53, 25.33.
1
1
c: H NMR (400 MHz, CDCl , δ): 8.88 (s, 2H), 8.70 (s, 2H), 6.75
3
We have demonstrated that chromatographic separation of
ADT isomers is a convenient approach to the preparation of the
pure materials, providing both pure isomers in a single, short
synthetic route. Our results from device studies support prior
observations that in ethyne-functionalized ADTs, obtaining the
pure syn isomer offers no substantial benefits to device perfor-
mance. In this first reported study of the pure anti isomers,
benefits to device performance rely heavily on the particulars of
the system studied. In common with the work by Mamada, the
extra steps and decreased yield involved in the preparation of
pure anti diF TES ADT is not warranted by the small increase
in performance of the pure isomer. However, in the case of
anti diF TEG ADT, the substantial performance enhancement
may justify the added effort required to separate the highest-
performing compound. More importantly, the ability to study in
detail the crystalline motif of each isomer, along with the struc-
ture of the corresponding mixture, combined with careful meas-
urement of charge transport properties under identical process
conditions, shed light on the precise intermolecular interac-
tions guiding the dense packing of the electronic chromophore.
This information will allow refinement of models for crystal
packing in this class of heteroacene, assisting development of
new design rules for high-performance chromophore design.
(
(
s, 2H), 4.17 (s, 1H), 2.13 (m, 3H), 1.16 (d, J = 6.61 Hz, 18H), 0.92
13
d, J = 6.93 Hz, 6H). C NMR (100 MHz, CDCl , δ): 167.29, 164.32,
3
163.12, 136.31, 136.24, 133.67, 129.77, 129.15, 129.12, 120.39, 120.15,
120.06, 114.48, 108.65, 103.61, 102.40, 102.29, 102.26, 102.25, 89.89,
8
0.51, 67.94, 26.53, 25.33.
General Procedure for the Synthesis of 2a: in a 100 mL round bottom
flask 1a (290 mg, 0.53 mmol) was dissolved in 5 mL THF and 10 mL
methanol. 1 mL of 15% KOH solution was added and the mixture was
stirred for 2 h until the solution turned into an orange suspension. The
reaction mixture was then filtered and the solid washed with methanol,
and dried under high vacuum to yield 160 mg 2a (80%) as an orange
powder. The product was immediately taken to the next step without any
further purification.
General Procedure for the Synthesis of Anti diF ADT s: In a flame dried
round bottom flask equipped with a stir bar, 160 mg of 2a was dissolved
in 10 mL of dry THF under nitrogen. LiHMDS (1 M in hexane, 0.9 mL,
0.9 mmol) was added dropwise followed by chlorotriethyl silane or
chlorotrigermyl silane (1.28 mmol) and the reaction was left to stir for
h. After quenching with water and extraction with dichloromethane,
the solution was dried (MgSO ) and concentrated under vacuum. The
crude product was then purified by silica gel chromatography with
hexanes as the eluent, followed by recrystallization from hexanes to yield
the pure ADT.
1
4
1
Anti diF TES ADT: H NMR (400 MHz, CDCl , δ): 8.92(s, 2H), 8.84(s,
3
2H), 6.80(d, J = 2.51Hz, 2H), 1.22(t, J = 15.71Hz, 18H), 0.87–0.93 (m,
FH
1
3
12H). C NMR (100 MHz, CDCl3, δ): 167.29, 164.33, 163.10, 136.55,
1
1
36.48, 133.86, 130.10, 129.56, 129.52, 121.23, 120.81, 120.56, 120.42,
20.32, 117.46, 107.35, 103.17, 102.68, 102.57, 7.94, 4.80. MS (EI 70 eV)
m/z 602 (100%, M ). Elemental analysis calculated for C H S Si: %C
7.73, %H 6.02, %F 6.30, %S 10.63, Si 9.32. Found: %C 68.32, %H 6.39.
Anti diF TEG ADT: H NMR (400 MHz, CDCl3, δ): 8.95(s, 2H), 8.87(s,
2H), 6.79(d, JFH = 2.37 Hz, 2H), 1.29–1.34(m, 18H), 1.11–1.17 (m, 12H). C
NMR (100 MHz, CDCl3, δ): 167.49, 164.52, 163.45, 136.70, 136.63, 133.95,
130.21, 129.89, 129.86, 121.25, 120.80, 120.72, 120.63, 119.98, 117.43,
107.83, 102.94, 102.77, 102.74, 9.73, 6.56. MS (EI 70 eV) m/z 692 (100%,
M ). Elemental analysis calculated for C32H36S2Si: %C 59.01, %H 5.24, %F
5.49, %S 9.27, %Ge 20.99. Found: %C 60.15, %H 5.31.
+
32
36 2
4
. Experimental Section
6
1
ADT Synthesis: Solvents were purchased in bulk from Pharmco-Aaper.
Tri-iso-butylsilylacetylene was prepared by literature methods.[ All other
chemicals were used as supplied from Sigma-Aldrich. NMR spectra were
measured on a Varian (Unity 400 MHz) spectrometer, chemical shifts
reported in ppm relative to CDCl3.
21]
13
+
Synthesis of 1(a–c): To a nitrogen purged round-bottom flask was
added diethyl ether (15 mL), followed by tri-iso-butylsilylacetylene
(
2
510 mg, 2.275 mmol). n-Butyllithium (1.6 M in hexanes, 1.3 mL,
X-Ray Crystallographic Analysis: X-ray diffraction data were collected
at low temperature on either a Nonius kappaCCD (MoKα) or a Bruker
X8 Proteum (CuKα) diffractometer. Raw data were integrated, scaled,
merged, and corrected for Lorentz-polarization effects using either
.1 mmol) was added dropwise at 0 °C and the mixture was stirred for 1 h
[22]
while allowing it to reach room temperature. FADT quinone (560 mg,
.75 mmol) was added to the flask followed by 40 mL of diethyl ether
1
Denzo-SMN[ or the APEX2 package. The structures were solved by
23]
[24]
and the reaction was left to stir for 48 h at room temperature. Ethynyl
magnesium bromide (0.5 M in THF, 6.8 mL, 3.41 mmol) was added to
the reaction mixture, which was stirred for another 2 h. Deoxygenation
proceeded by the addition of 5 mL of 10% aqueous H SO , and stannous
either SHELXS[ or SHELXT, and refined with SHELXL. Hydrogen
atoms were found in difference maps but subsequently placed at
calculated positions and refined using a riding model. Nonhydrogen
atoms were refined with anisotropic displacement parameters.
Atomic scattering factors were taken from the International Tables for
25]
[26]
[25]
2
4
chloride dihydrate (2 g, 8.75 mmol) and the mixture was stirred for
0 min. The mixture was then quenched with water and extracted with
3
[27]
[28]
ethyl acetate, then dried with magnesium sulfate. The solution was then
filtered and the solvent was evaporated. The crude product was purified
by chromatography on silica using hexanes as the eluent to yield 41%
of isomers 1a, 1b, and 1c. The three isomers were recrystallized by
slow evaporation from dichloromethane to yield red colored crystals. In
general, these poorly stable materials were best kept in dilute solution
Crystallography. Final models were checked using Platon and by an
R-tensor.[ The CCDC contains the supplementary crystallographic data
for the new materials described in this work, including anti diF TES ADT
(1406651), anti diF TEG ADT (1406649), 1a (1406647), 1b (1406648),
and 1c (1406650). These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
29]
under nitrogen in the dark.
1
1
a: H NMR (400 MHz, CDCl , δ): 8.81(s,1H), 8.68 (s,1H), 8.67
Calculations: Electronic coupling calculations were performed with
3
Gaussian09,[ using the B3LYP functional with the 6–31G(d) basis
15]
(s,1H), 8.51 (s, 1H), 6.67 (s, 2H), 4.08 (s, 1H), 2.16 (m, 3H), 1.19 (d,
2
346 wileyonlinelibrary.com
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Adv. Funct. Mater. 2016, 26, 2341–2348

www.afm-journal.de
www.MaterialsViews.com
set. The localized monomer orbital approach was used to account for
any site energy differences between interacting molecules. The major
molecular alignments observed in the crystal structures were considered.
Data for the disordered molecules are available in the Supporting
Information. Molecular interaction energy decomposition analysis was
performed with GAMESS[ at the MP2 level using the cc-pVDZ basis
set. Atomic coordinates for all input files were taken directly from the
crystal structures, including the disordered atoms when considering the
minor interactions.
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Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
Acknowledgements
R.K.H., K.J.T., and J.E.A. thank the NSF (DMR-1035257 and CMMI-
1
255494) for support of the synthesis of organic semiconductors.
Y.M. and O.D.J. thank the NSF (ECCS-1254757 and ECCS-1338012) for
supporting their device studies.
Received: June 15, 2015
Revised: August 5, 2015
Published online: November 10, 2015
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