Functionalized tetrathienoanthracene: Enhancing π-π Interactions through expansion of the π-conjugated framework

Article abstract of DOI:10.1021/cg201521w

The functionalization of tetrathienoanthracene (TTA) with bromine and 2-hexylthiophene moieties is described, and their influence at both the molecular and solid-state level has been investigated. Comparative optical and electrochemical studies indicate a

Full text of DOI:10.1021/cg201521w

Article
pubs.acs.org/crystal
Functionalized Tetrathienoanthracene: Enhancing π−π Interactions
Through Expansion of the π-Conjugated Framework
Alicea A. Leitch,†,‡ Aya Mansour,†,‡ Kimberly A. Stobo,†,‡ Ilia Korobkov,† and Jaclyn L. Brusso*,†,‡
‡
†Department of Chemistry and Centre for Catalysis Research and Innovation, University of Ottawa, Ottawa, Ontario K1N 6N5,
Canada
S
* Supporting Information
ABSTRACT: The functionalization of tetrathienoanthracene (TTA) with
bromine and 2-hexylthiophene moieties is described, and their influence at both
the molecular and solid-state level has been investigated. Comparative optical
and electrochemical studies indicate an increase in conjugation for the thiophene
derivative compared to the parent TTA. In the solid state, these materials form
slipped π-stack structures with a number of close intermolecular contacts.
Comparison of the two structures reveals a more steeply inclined slipped π-stack
for the thiophene derivative resulting in a closer interplanar separation. This,
coupled with the extended molecular framework, leads to an enhanced number
of π−π interactions within the stack. The combination of increased conjugation
at the molecular level, and π-stacked structures with strong intermolecular communication at the solid-state level, augurs well for the use
of TTA materials in optoelectronic applications.
When the oligothiophene arms are attached to a rigid core (e.g.,
trithienothiophene, 2), tight π-stacking interactions are
observed, and, in thin films, the molecules are oriented parallel
to the surface of the substrate, maximizing the absorbance of
incident light (sought-after properties for photovoltaic
applications).15 In that regard, tetrathienoanthracene (TTA, 3)
represents an ideal structure for a central core unit in star-shaped
conjugated materials. Not only does it possess a planar, de-
localized π-electron system, it has been shown to form a highly
organized 2D thin film network and possesses high thermal
stability in air.16 Herein we report the preparation and char-
acterization of TTA functionalized with halogens (3c) and
thiophenes (3d). It is anticipated that extending the conjugation
in 2D, through the attachment of thiophene moieties, will favor
close π-stacking interactions and, hence, enhance charge
transport. Comparative studies with the alkylated parent com-
pound (3b) by cyclic voltammetry, UV−vis, and fluorescence
spectroscopy were performed to investigate the effect that
“expanding” the conjugation of the TTA core has on the
INTRODUCTION
■
Organic semiconductors (OSC), both molecular and poly-
meric, have seen significant development over the past two
decades owing to their potential use in next-generation
electronic devices. With regard to polymeric materials, most
consist of one-dimensional (1D) chains in which delocalization
occurs through the polymer backbone, facilitating efficient
movement of charge carriers and excitons along the chain.
Unfortunately, polymer films tend to be disordered in the bulk,
resulting in a decrease in the effective conjugation due to
twisting of the polymer backbone. Since the charge mobility is
largely anisotropic in 1D conjugated polymers, this disorder
limits the total electronic communication. In the case of
molecular materials, a particularly important requirement for
the realization of high performance thin film optoelectronic
devices is tight π-stacking interactions, which provide a pathway
for charge transport. For example, field effect transistors
(FETs) based on small molecules (e.g., pentacene)1 generally
attain higher mobilities compared to polymer-based devices
owing to the crystallinity and, hence, morphology of the OSC. It is
anticipated that expanding the dimensionality of conjugated
systems should increase the degree of intermolecular communi-
cation and enhance the carrier mobility while diminishing the
anisotropy associated with polymeric systems.2,3
Chart 1
The development of “star-shaped” conjugated molecules,
where the dimensionality is extended in two or three dimen-
sions through a central core unit, leads to materials with physical
properties that can be markedly different from their simple, linearly
conjugated analogues.4 In recent years, a great deal of effort has
been dedicated to the development of two- and three-dimensional
(2D and 3D) conjugated molecules where oligothiophenes are
covalently linked to a central benzenic core (1, Chart 1).5−14
Received: November 17, 2011
Revised: December 22, 2011
Published: January 3, 2012
© 2012 American Chemical Society
1416
dx.doi.org/10.1021/cg201521w | Cryst. Growth Des. 2012, 12, 1416−1421

Crystal Growth & Design
Article
situated at the inversion center, and all non-hydrogen atoms were
refined anisotropically with satisfactory thermal parameter values.
Solution of the structure for 3d revealed the positional disorder for
one of the alkyl chains. Disordered fragments are located in general
positions and are not related by any symmetry elements. Occupational
factors for the disordered fragments were successfully modeled with a
1:1 ratio with stable refinement results. However, in order to obtain
satisfactory thermal parameters, and due to the low data to parameter
ratio of the collected data set, a set of SIMU restraints was used in the
refinement of the disordered moiety. Positions of all hydrogen atoms
were obtained from the Fourier map analysis; nonetheless, all
hydrogen atoms were treated as idealized contributions. All scattering
factors are contained in several versions of the SHELXTL program
library with the latest version (v.6.12) being used.20 Crystallographic
data and selected data collection parameters are reported in Table S1,
Supporting Information.
optoelectronic properties. The solid-state structures were studied
by X-ray crystallography and revealed a number of close π−π
contacts in 3d compared to the brominated derivative 3c.
EXPERIMENTAL SECTION
■
General Procedures and Starting Materials. The reagents
palladium chloride and triphenylphosphine were obtained commer-
cially and used as received. Compounds 4b and 3b were prepared as
outlined in the literature.16 All reactions were performed under an
atmosphere of dry nitrogen. Melting points are uncorrected. 1H NMR
spectra were run in CDCl3 solutions at 50 °C on a Bruker Avance 500
MHz Wide Bore spectrometer. Infrared spectra were recorded on a
Nicolet Avatar FTIR spectrometer at 2 cm−1 resolution using KBr
optics and a nujol mull. UV−vis spectra were measured with a Varian
Cary-100 spectrophotometer, and the fluorescence spectra were
obtained using a Photon Technology International (PTI) spectro-
fluorimeter. Both UV−vis and fluorescence spectra were measured on
dichloromethane solutions with a 1 cm precision quartz cuvette. Sub-
limation of 3c was carried out on an ATS series 3210 three-zone tube
furnace, mounted horizontally, and linked to a series 1400 temperature
control system.
Preparation of 3c. Compound 3c was prepared as outlined in the
literature.16 Purification of the crude yellow-green powder involved
washes with 10% aq. HCl, saturated aq. sodium bicarbonate solution,
and MeOH followed by fractional sublimation at 10−4 Torr along a
temperature gradient of 420−300−260 °C. The resulting yellow
needles were suitable for X-ray analysis; mp > 350 °C. IR: 1546.11
(m), 1482.93 (s), 1457.41 (s), 1429.82 (w), 1406.58 (w), 1392.24 (w),
1377.11 (m), 1304.20 (w), 1297.96 (m), 1262.48 (w), 1185.63 (w),
1128.94 (w), 978.63 (w), 971.77 (w), 960.91 (m), 913.36 (s), 860.06
(s), 816.64 (m), 800.24 (s), 722.01 (w), 697.16 (w), 655.41 (w),
613.36 (m), 559.32 (m), 494.10 (s), 434.07 (s) cm−1. Anal. Calcd for
C22H6S4Br4: C, 36.79; H, 0.84. Found: C, 36.75; H, 1.00. Given the
Electrochemistry. Cyclic voltammetry was performed using a
Princeton Applied Research (PAR) VersaSTAT 3 potentiostat/
galvanostat/frequency response analyzer and V3-Studio electro-
chemical software (V 1.0.281 (c) 2008 PAR) employing a glass cell
fitted with platinum electrodes. The measurements were carried out
on dichloromethane solutions (dried by distillation over CaH2)
containing 0.1 M tetrabutylammonium hexafluorophosphate (Aldrich)
as supporting electrolyte with a scan rate of 100 mV/s. The experi-
ments were referenced to the Fc/Fc+ couple of ferrocene at +0.48 V vs
SCE.17
Crystal Growth. Because of its virtual insolubility in organic
solvents, compound 3c was purified by zone sublimation at 10−4 Torr
along a temperature gradient of 420−300−260 °C using an ATS series
3210 three-zone tube furnace, mounted horizontally, and linked to a
series 1400 temperature control system. The resulting yellow needles
were suitable for X-ray analysis. Yellow needles of 3d suitable for X-ray
analysis were grown by slowly cooling a saturated dichloroethane solu-
tion. Compound 3d is soluble in most chlorinated solvents; however,
attempts to grow crystals suitable for X-ray analysis were only successful
from dichloroethane; other chlorinated solvents provided microcrystal-
line material.
1
low solubility of this compound, H and 13C NMR spectroscopy was
not possible. The identity of this compound was confirmed by
elemental analysis and X-ray crystallography.
Preparation of 3d. 4b (0.764 g, 1.67 mmol) was added to a slurry
of 3c (0.200 g, 0.278 mmol), PdCl2 (10 mg, 0.0564 mmol), and PPh3
(30 mg, 0.114 mmol) in degassed DMF (0.45 mL) and the reaction
mixture was set to heat at 130 °C under N2. After 16 h, hexanes were
added to the reaction flask and the crude product was filtered off
and washed with hexanes, crude yield 0.218 g (0.204 mmol, 73%).
The crude material was washed with hot EtOAc and recrystallized
from DCE to afford yellow needles (0.155 g, 0.145 mmol, 71%);
1
dec > 200 °C. H NMR (δ, CDCl3, 50 °C): 7.88 (2H, s), 7.16 (4H, s),
7.00 (4H, d, J = 3.2 Hz), 6.65 (4H, d, J = 3.4 Hz), 2.82 (8H, t, J =
7.5 Hz), 1.76 (8H, m, J = 7.6 Hz), 1.52−1.33 (24H, m), 0.96 (12H, t, J =
7.1 Hz). Anal. Calcd for C62H66S8: C, 69.74; H, 6.23. Found: C, 69.54; H,
6.04. Given the low solubility of this compound, 13C NMR spectroscopy
Crystallography. Compounds 3c and 3d consistently produced
very small crystals. The presented results are the best from a series of
data collection attempts. Crystals of 3c were mounted on thin glass
fibers using epoxy glue and the data were collected at room tem-
perature (25 °C). A crystal of 3d was mounted on a thin glass fiber
with oil and cooled to −73 °C prior to data collection.
1
was not possible. The identity of this compound was confirmed by H
NMR spectroscopy, elemental analysis, and X-ray crystallography.
RESULTS AND DISCUSSION
■
Synthesis. Our first attempts to prepare 3d were focused on
4-fold Stille coupling of tetrabromobenzene with 5-hexyl-5′-
tributylstannyl-2,2′-bithiophene followed by oxidative cyclo-
dehydrogenation with FeCl3, analogous to the synthesis of the
parent compound 3b.16,21 Unfortunately, an uncharacterizable
solid was isolated, which may be attributed to side reactions of
the β-thienyl positions generating a complicated mixture of
materials.22 To circumvent these challenges, focus shifted to
preparation of the TTA core prior to functionalization.
Following the route outlined in Scheme 1, 5a was prepared
via Stille coupling of 4a with tetrabromobenzene. Subsequent
treatment with NBS followed by oxidative cyclization with
FeCl3 afforded the brominated derivative 3c.23 Although 3c is
essentially insoluble, coupling reactions with solubilizing
alkylthiophenes is possible, as 4-fold Stille coupling of 3c
with 4b proved successful, providing a general procedure to the
functionalization of TTA. We are currently exploring the versatility
of this route via the attachment of longer oligothiophenes. Using
this approach, the peripheral substituent may be easily altered, and
Data acquisition was carried out on a Bruker AXS KAPPA single
crystal diffractometer equipped with a sealed Mo tube source
(wavelength 0.71073 Å) and APEX II CCD detector. Raw data
collection and processing were performed with APEX II software
package from BRUKER AXS.18 Diffraction data for 3c were collected
with a sequence of 0.5° ω scans at 0°, 120°, and 240° in ϕ. Initial unit
cell parameters were determined from 60 data frames collected at the
different sections of the Ewald sphere. The significantly weaker dif-
fraction of 3d required a considerable increase in the exposure time as
well as the collection of thinner 0.3° ω scans at 0°, 90°, 180°, 270° in
ϕ. Initial unit cell parameters were determined from 320 data frames of
the original data set positioned at the different sections of the Ewald
sphere. Semiempirical absorption corrections based on equivalent
reflections were applied.19 Systematic absences in the diffraction data
set and unit-cell parameters for both 3c and 3d were consistent with
monoclinic P21/n (alternative setting of P21/c No. 14) space group.
Solutions in this centrosymmetric space group yielded chemically
reasonable and computationally stable results of refinement. The
structures were solved by direct methods, completed with difference
Fourier synthesis, and refined with full-matrix least-squares procedures
based on F2. In both crystal structures molecules of the compounds are
1417
dx.doi.org/10.1021/cg201521w | Cryst. Growth Des. 2012, 12, 1416−1421

Crystal Growth & Design
Article
a
Scheme 1. Synthesis of Functionalized Thienoanthracenes
a
Reagents and Conditions: (a) 1,2,4,5-tetrabromobenzene,
PdCl2(PPh3)2, DMF, 130 °C; (b) NBS, THF, RT; (c) FeCl3,
MeNO2/chlorobenzene, RT; (d) 4b, PdCl2(PPh3)2, DMF, 130 °C.
Figure 1. Absorption (solid line) and emission spectra (dotted line) of
3b (green) and 3d (blue).
a
b
c
Table 1. Theoretical, Electrochemical, and Photophysical
Properties for 3b and 3d
are similar to that of 3b; however, a much less defined vibronic
structure is observed. This may be attributed to a less rigid
structure due to the flexibility of the periphery thiophene
moieties.22 Comparison of the Stokes shifts reveals a slightly
larger energy for 3d and may also be explained by molecular
flexibility; however, the difference is minimal and, when compared
to fused thienoacenes (e.g., 0.28 eV for pentathienoacene),26 is
indicative of little structural distortion upon excitation. This also
strongly suggests that the reorganization energy of the charge
carrier (polaron or radical cation), which limits the intrinsic
mobility of OSCs, will be low.
3b
3d
calcd
EHOMO
(eV)
(eV)
−5.21
3.35
1.15
−5.33
431
−5.12
2.95
0.94
−5.11
475
calcd
Egap
Eox (V)
d
expt
EHOMO (eV)
abs
λmax (nm)
abs
λedge (nm)
440
493
e
opt
Egap (eV)
2.83
435
2.52
490
f
PL
λmax (nm)
Stokes shift (eV)
0.03
0.08
X-ray Crystallography. Long-range molecular ordering is
of paramount importance to obtain high charge carrier
mobilities in OSCs.27 In particular, the degree of π-orbital
overlap is expected to strongly influence the mobility, as has
been illustrated in structurally related pentacene derivatives.28
To shed light on supramolecular organization and the effect of
“widening” the π-conjugated core, single crystals of 3c and 3d
a
b
DFT/B3LYP/6-311G(d,p) level of theory where R = Me. In DCM,
0.1 M nBu4NPF6 as supporting electrolyte, referenced to the Fc/Fc+
couple of ferrocene at +0.48 V vs SCE.17 Measurements performed in
c
d
e
DCM. Derived using expression from ref 25. Calculated from λedge
.
f
In DCM, upon excitation at 320 nm for 3b and 380 nm for 3d.
thus the electronic characteristics and solid-state properties of
target molecules can be tuned.
Electrochemical and Spectroscopic Studies. To inves-
tigate the influence additional thiophene moieties have on the
optoelectronic properties of TTA, electrochemical and optical
spectroscopy studies were performed on dichloromethane solu-
tions of 3b and 3d; the results are summarized in Table 1.24
Cyclic voltammetry (CV) of 3d revealed a single quasi-reversible
redox process corresponding to the formation of the radical cation
(Supporting Information Figure S2). Unlike the behavior of the
parent compound 3b, 3d does not exhibit a second oxidation
process under the conditions used. The oxidation potential of
3d is shifted in the cathodic direction by 0.21 V with respect to
3b resulting from the increase in conjugation length, which has
been observed in other star-shaped conjugated molecules with
extended oligothiophene arms.15 This behavior is supported by
DFT calculations on the R = Me derivatives of 3b and 3d at the
B3LYP/6-311G(d,p) level. Comparison of the two molecules
demonstrates that the energy of the HOMO of 3d (R = Me) is
raised by 0.09 eV due to the extension of conjugation into 2D
(Table 1).
Optical spectroscopy provides further evidence of increased
effective π-conjugation through the attachment of thiophene
units to the TTA core. A bathochromic shift of ∼55 nm is
observed in the absorption and emission spectra for 3d with
respect to 3b (see Table 1 and Figure 1). On the basis of the
onset of UV−vis absorption, the addition of thiophene moieties
leads to a decrease in the optical band gap of 0.31 eV (3b →
3d). Furthermore, the absorption and emission profiles for 3d
Table 2. Crystal Data for 3c and 3d
3c
3d
formula
C22H6Br4S4
718.15
C31H33S4
533.81
fw
crystal system
space group
a (Å)
monoclinic
P21/n
monoclinic
P21/n
13.9674(6)
3.9096(2)
19.9845(9)
106.906(3)
1044.13(8)
2
5.9663(6)
25.007(3)
18.1843(15)
95.154(3)
2702.1(4)
4
b (Å)
c (Å)
β (deg)
V (Å3)
Z
Dcalc (mg/m3)
2.284
1.312
T (K)
298
200
μ (mm−1)
2θmax (deg)
no. of total reflections
no. of unique reflections
Rint
8.119
0.371
56.62
37.70
10037
13041
2536
2119
0.0306
0.0540
R1, wR2 (on F2)
0.0474, 0.1270
65.48(2)
3.557(1)
0.0494, 0.1217
34.34(2)
a
τ (deg)
b
δ (Å)
3.365(2)
a
b
τ is the tilt angle between the mean molecular plane and the stacking axis. δ is
the mean interplanar separation between molecules along the π-stack.
have been analyzed by X-ray diffraction (Table 2). Similar to
the protonated parent compound 3a,16 crystals of 3c and 3d
1418
dx.doi.org/10.1021/cg201521w | Cryst. Growth Des. 2012, 12, 1416−1421

Crystal Growth & Design
Article
Figure 2. Unit cell (top) and slipped π-stack (bottom) drawings of 3c (left) and 3d (right). In the π-stacked structure of 3d the hexyl chains are
omitted for clarity. For 3c (left), close intermolecular contacts between stacks are shown; Br---Br′ contacts are shown in brown; Br---S′ are in purple;
S---S′ are in red.
belong to the monoclinic space group P21/n and consist of
slipped π-stacks (along y and x) which are aligned in
herringbone arrays running along the z- and y-directions, res-
pectively. Two views of the crystal structures, showing the unit-
cell packing and the slipped π-stacked structure, are provided in
Figure 2. These molecules are essentially planar as the core
atoms show minimal displacement from the mean plane
(0.0211 Å and 0.0213 Å for 3c and 3d, respectively) formed by
the 26-atom TTA core. In the case of the brominated derivative
3c, close S---S′ (3.669(2) Å), Br---Br′ (3.676(1) Å), and S---Br′
(3.660(1) Å) contacts exist laterally between the herringbone
ribbons, as shown in Figure 2. Such Br---Br′ and S---Br interac-
tions have been observed in other bromo-substituted π-conjugated
organic molecules.29−33 Their influence on the packing arrange-
ment of these types of materials is difficult to assess as the
solid-state structure results from a balance between π−π and
dipole−dipole interactions, among other factors.32,34 Similar
interactions were also observed in 2D arrays of 3c when
measured at the liquid/solid interface, although when confined
to a graphite surface the monolayers form a more tightly packed
structure (i.e., shorter contacts).35 Additional S---C′ interactions
also exist along the slipped π-stacks (see Figure 3).
the TTA core and the substituents, only a slight propeller-like
distortion with dihedral angles of 4.3(4)° and 7.8(3)° from the
mean plane for the two unique thiophene moieties is observed
in the crystal structure of 3d. Furthermore, as is apparent from
Figure 2, the hexyl substituents in 3d form an interdigitated
network along the herringbone array, and, consequently, the
degree of lateral communication is diminished in 3d compared
to 3c. A similar motif was observed in thin films of the parent
compound 3b where the molecules formed monolayers con-
sisting of a highly oriented 2D structure held together by
interactions between the interdigitated hexyl chains.16 Inter-
digitation or alkyl−alkyl interactions are commonly observed in
the solid state for alkyllated π-conjugated molecules;36−38
however, whether the packing arrangement is dominated by the
alkyl−alkyl or π−π interactions is very difficult to determine
and is dependent on many factors (e.g., the size and shape of
the conjugated core, length and number of alkyl substituents,
etc). For example, Wang et al. attributed the packing arrange-
ment of a dodecyl functionalized pyrazinoquinoxaline to the
alkyl−alkyl interactions rather than the stacking of π-planes due
to the lack of π−π interactions between the conjugated cores
and the completely parallel and overlapped dodecyl chains
which maximizes the alkyl−alkyl interactions.37 Conversely, a
“layer-by-layer” structure with alternating alkyl chains and arene
cores was observed with strong intermolecular π−π inter-
Interestingly, although the replacement of bromine sub-
stituents with hexylthiophene moieties introduces the potential
for distortion through the flexibility of the C−C bond between
1419
dx.doi.org/10.1021/cg201521w | Cryst. Growth Des. 2012, 12, 1416−1421

Crystal Growth & Design
Article
CONCLUSIONS
■
To summarize, a general route for the synthesis of thiophene
functionalized tetrathienoanthracenes has been developed. The
effect of “widening” the conjugation of the thienoacene core on
the optoelectronic properties and solid-state structure was
investigated by cyclic voltammetry, UV−vis and fluorescence
spectroscopy, and X-ray crystallography. On the basis of these
studies, we can conclude that attachment of thiophene moieties
to the periphery of TTA leads to an increase in the effective
conjugation as evidenced by the bathochromic shift in the
absorption profile and reduced oxidation potential compared to
the alkylated derivative 3b, and is supported by DFT calcula-
tions. Along with the relatively small Stokes shift, which implies
that little structural reorganization occurs upon excitation, these
results augur well for enhanced charge transport. X-ray
crystallography reveals a less superimposed π-stack for 3d com-
pared to 3c, and an interplanar separation between molecules
less than the sum of van der Waals radii of carbon (3.4 Å).
Since the planar molecular framework of 3d is extended out to
the peripheral thiophene moieties, a number of close contacts
within the π-stacks exist. The favorable intermolecular inter-
actions observed in the solid state, coupled with the extended
π-conjugation, bode well for the use of this material in device
applications. To that end, further studies are needed to investigate
the thin film morphology of the thiophene functionalized TTA,
and implementation into FET devices is required to determine the
hole mobility; such investigations are currently being pursued.
Figure 3. Crystal structure of (a) 3c and (b) 3d showing atom
numbering and close intermolecular contacts along the π-stacks. S---S′
contacts are shown in red; S---C′ are in green; C---C′ are in blue. Hexyl
chains omitted for clarity in (b).
actions when n-propyl substituents were attached to a fused
thienoacene core.36 In the case of 3d, the packing arrangement
appears to result from a delicate balance between the alkyl−
alkyl interactions coupled with π−π orbital overlap (vide infra).
The inclusion of hexylthiophene moieties at the periphery of
the TTA core results in more steeply inclined π-stacks
compared to the brominated derivative (Table 2; Figures S3
and S4). The larger degree of inclination, quantified in terms of
the slippage angle τ  a smaller angle value of τ indicates a
higher degree of slippage  leads to a decrease in the
interplanar separation between molecules (δ3c > δ3d). Recently,
a report on seven-ring-fused dibenzothienotetrathiophenes
functionalized with ethyl and hexyl substituents found a similar
observation of a greater degree of slippage and decrease in
interplanar separation with increase in alkyl chain length.39
The diminishing of the interplanar separation, coupled with
the larger molecular framework, results in an increase in the
number of close contacts within the slipped π-stacks for 3d
which are within or nominally larger than the van der Waals
separation, as shown in Figure 3.40 Interestingly, 3d, the
compound with the flexible substituents, has a slippage angle
and interplanar distance that is more comparable to the parent
ASSOCIATED CONTENT
■
S
* Supporting Information
1H NMR spectrum of 3d; CVs and DFT archival files for 3b
and 3d; CIF files and illustrations of τ and δ for 3c and 3d.
This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*Tel: +1 (613) 562 5800 ext 7091; fax: +1 (613) 562 5170;
e-mail: jbrusso@uottawa.ca.
ACKNOWLEDGMENTS
■
The authors are grateful to NSERC for funding this work.
A.A.L. acknowledges support through an NSERC postdoctoral
fellowship.
REFERENCES
■
(1) Kelley, T. W.; Boardman, L. D.; Dunbar, T. D.; Muyres, D. V.;
Pellerite, M. J.; Smith, T. Y. P. J. Phys. Chem. B 2003, 107, 5877−5881.
(2) Perepichka, D. F.; Rosei, F. Science 2009, 323, 216−217.
(3) He, F.; Wang, W.; Chen, W.; Xu, T.; Darling, S. B.; Strzalka, J.;
Liu, Y.; Yu, L. J. Am. Chem. Soc. 2011, 133, 3284−3287.
(4) Kanibolotsky, A. L.; Perepichka, I. F.; Skabara, P. J. Chem. Soc.
Rev. 2010, 39, 2695−2728.
(5) Ponomarenko, S. A.; Kirchmeyer, S.; Elschner, A.; Huisman,
B. H.; Karbach, A.; Drechsler, D. Adv. Funct. Mater. 2003, 13, 591−596.
(6) Fischer, M. K. R.; Ma, C. Q.; Janssen, R. A. J.; Debaerdemaeker,
compound 3a than the brominated derivative 3c (δ3a
=
3.354(3) Å, τ3a = 41.79(1)°).16 The observation of a number of
π−π contacts in 3d, even though the molecules are more
steeply inclined than 3a and 3c, may be attributed to the
extended π-conjugated core; that is, the potential for π−π
interactions is increased due to the larger molecular framework.
Similar results were observed by He et al. when they compared
the crystal packing arrangement of decyl substituted linearly
fused tetrathienoacene and pentathienoacene.38 In both
structures the alkyl−alkyl interactions dominate the crystal
packing motif; however, the larger conjugated framework of
pentathienoacene afforded π−π interactions, whereas very little
π-orbital overlap was reported for tetrathienoacene.
T.; Bauerle, P. J. Mater. Chem. 2009, 19, 4784−4795.
̈
(7) Roncali, J.; Leriche, P.; Cravino, A. Adv. Mater. 2007, 19, 2045−
2060.
(8) Wong, W. W. H.; Ma, C. Q.; Pisula, W.; Yan, C.; Feng, X. L.;
Jones, D. J.; Mullen, K.; Janssen, R. A. J.; Bauerle, P.; Holmes, A. B.
̈
̈
Chem. Mater. 2010, 22, 457−466.
1420
dx.doi.org/10.1021/cg201521w | Cryst. Growth Des. 2012, 12, 1416−1421

Crystal Growth & Design
Article
(9) Sun, X. B.; Zhou, Y. H.; Wu, W. C.; Liu, Y. Q.; Tian, W. J.; Yu,
G.; Qiu, W. F.; Chen, S. Y.; Zhu, D. B. J. Phys. Chem. B 2006, 110,
7702−7707.
́ ̂ ̀
(10) Roquet, S.; Cravino, A.; Leriche, P.; Aleveque, O.; Frere, P.;
Roncali, J. J. Am. Chem. Soc. 2006, 128, 3459−3466.
(11) He, C.; He, Q. G.; Yi, Y. P.; Wu, G. L.; Bai, F. L.; Shuai, Z. G.;
Li, Y. F. J. Mater. Chem. 2008, 18, 4085−4090.
(12) Zhang, J.; Yang, Y.; He, C.; He, Y. J.; Zhao, G. J.; Li, Y. F.
Macromolecules 2009, 42, 7619−7622.
(13) Shang, H. X. S. H. X.; Fan, H. J.; Liu, Y.; Hu, W. P.; Li, Y. F.;
Zhan, X. W. Adv. Mater. 2011, 23, 1554−1557.
(14) Li, W. W.; Du, C.; Li, F. H.; Zhou, Y.; Fahlman, M.; Bo, Z. S.;
Zhang, F. L. Chem. Mater. 2009, 21, 5327−5334.
(15) Nicolas, Y.; Blanchard, P.; Levillain, E.; Allain, M.; Mercier, N.;
Roncali, J. Org. Lett. 2004, 6, 273−276.
(16) Brusso, J. L.; Hirst, O. D.; Dadvand, A.; Ganesan, S.; Cicoira, F.;
Robertson, C. M.; Oakley, R. T.; Rosei, F.; Perepichka, D. F. Chem.
Mater. 2008, 20, 2484−2494.
́
(17) Boere, R. T.; Moock, K. H.; Parvez, M. Anorg. Allg. Chem. 1994,
620, 1589−1598.
(18) APEX Software Suite v.2010; Bruker AXS: Madison, WI, 2005.
(19) Blessing, R. H. Acta Crystallogr., Sect. A 1995, 51, 33−38.
(20) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112−122.
(21) Liu, W.-J.; Zhou, Y.; Ma, Y.; Cao, Y.; Wang, J.; Pei, J. Org. Lett.
2007, 9, 4187−4190.
(22) Zophel, L.; Enkelmann, V.; Rieger, R.; Mullen, K. Org. Lett.
̈
̈
2011, 13, 4506−4509.
(23) Mitchell, W. J.; Kopidakis, N.; Rumbles, G.; Ginley, D. S.;
Shaheen, S. E. J. Mater. Chem. 2005, 15, 4518−4528.
(24) Electrochemical and optical spectroscopy of 3b has been
performed elsewhere;16 however, it was repeated here for direct
comparison with 3d.
(25) He, Y.; Wu, W.; Zhao, G.; Liu, Y.; Li, Y. Macromolecules 2008,
41, 9760−9766.
(26) Zhang, X. N.; Matzger, A. J. J. Org. Chem. 2003, 68, 9813−9815.
(27) Coropceanu, V.; Cornil, J.; da Silva, D. A.; Olivier, Y.; Silbey, R.;
́
Bredas, J. L. Chem. Rev. 2007, 107, 926−952.
(28) Sheraw, C. D.; Jackson, T. N.; Eaton, D. L.; Anthony, J. E. Adv.
Mater. 2003, 15, 2009−2011.
(29) Okamoto, T.; Reese, C.; Senatore, M. L.; Tang, M. L.; Jiang, Y.;
Parkin, S. R.; Bao, Z. Synth. Met. 2010, 160, 2447−2451.
(30) Bosch, E.; Barnes, C. L. Cryst. Growth Des. 2002, 2, 299−302.
(31) Skabara, P. J.; Berridge, R.; McInnes, E. J. L.; West, D. P.; Coles,
S. J.; Hursthouse, M. B.; Mullen, K. J. Mater. Chem. 2004, 14, 1964−
̈
1969.
(32) Felsmann, M.; Eissmann, F.; Schwarzer, A.; Weber, E. Cryst.
Growth Des. 2011, 11, 982−989.
(33) Meng, H.; Perepichka, D. F.; Wudl, F. Angew. Chem., Int. Ed.
2003, 42, 658−661.
(34) Pigge, F. C.; Vangala, V. R.; Swenson, D. C.; Rath, N. P. Cryst.
Growth Des. 2010, 10, 224−231.
(35) Gutzler, R.; Ivasenko, O.; Fu, C.; Brusso, J. L.; Rosei, F.;
Perepichka, D. F. Chem. Commun. 2011, 47, 9453−9455.
(36) Wang, J. Y.; Zhou, Y.; Yan, J.; Ding, L.; Ma, Y. G.; Cao, Y.;
Wang, J.; Pei, J. Chem. Mater. 2009, 21, 2595−2597.
(37) Wang, X.; Zhou, Y.; Lei, T.; Hu, N.; Chen, E.-Q.; Pei, J. Chem.
Mater. 2010, 22, 3735−3745.
(38) He, M.; Zhang, F. J. Org. Chem. 2007, 72, 442−451.
(39) Wang, J.; Xu, H.; Li, B.; Cao, X.-P.; Zhang, H.-L. Tetrahedron
2012, 68, 1192−1197.
(40) Zefirov, Y. V.; Zorkii, P. M. Zh. Strukt. Khim. 1976, 17, 745−
756.
1421
dx.doi.org/10.1021/cg201521w | Cryst. Growth Des. 2012, 12, 1416−1421