Conjugated thiophene-containing oligoacenes through photocyclization: Bent acenedithiophenes and a thiahelicene

Article abstract of DOI:10.1021/jo900590u

(Graph Presented) The preparation of bent anthradithiophenes (BADTs) using an oxidative photocyclization-based synthetic strategy is reported. The optical properties of the new compounds were characterized by UV-vis and fluorescence spectroscopies, and the redox properties were probed by cyclic voltammetry. Structural studies using single crystal X-ray crystallography show that the unsubstituted BADT adopts a slipped cofacial stacking arrangement in the solid state with π-π interactions along the intermolecular stacking axis. The dialkylated derivatives adopt similar packing motifs with varying degrees of slipping along their long and short molecular axes while the diphenyl derivative packs into an edge-to-face herringbone arrangement. Powder diffraction data show that in thin films prepared by vacuum evaporation, molecules of the unsubstituted BADT are oriented nearly perpendicular to the substrate surface whereas the dialkylated derivatives adopt either multiple phases or new polymorphs. A thiahelicene prepared from the oxidative photocyclization of two isomers of 2,5-dithienyl-1,4-distyrylbenzene is described and the crystal structure reported.

Full text of DOI:10.1021/jo900590u

Conjugated Thiophene-Containing Oligoacenes Through
Photocyclization: Bent Acenedithiophenes and a Thiahelicene
Agostino Pietrangelo, Brian O. Patrick, Mark J. MacLachlan,* and Michael O. Wolf*
Department of Chemistry, UniVersity of British Columbia, VancouVer, BC, Canada V6T 1Z1
mmaclach@chem.ubc.ca; mwolf@chem.ubc.ca
ReceiVed March 18, 2009
The preparation of bent anthradithiophenes (BADTs) using an oxidative photocyclization-based synthetic
strategy is reported. The optical properties of the new compounds were characterized by UV-vis and
fluorescence spectroscopies, and the redox properties were probed by cyclic voltammetry. Structural
studies using single crystal X-ray crystallography show that the unsubstituted BADT adopts a slipped
cofacial stacking arrangement in the solid state with π-π interactions along the intermolecular stacking
axis. The dialkylated derivatives adopt similar packing motifs with varying degrees of slipping along
their long and short molecular axes while the diphenyl derivative packs into an edge-to-face herringbone
arrangement. Powder diffraction data show that in thin films prepared by vacuum evaporation, molecules
of the unsubstituted BADT are oriented nearly perpendicular to the substrate surface whereas the dialkylated
derivatives adopt either multiple phases or new polymorphs. A thiahelicene prepared from the oxidative
photocyclization of two isomers of 2,5-dithienyl-1,4-distyrylbenzene is described and the crystal structure
reported.
Introduction
properties, oligoacenes are typically insoluble and chemically
unstable making large scale solution-processing difficult, a clear
drawback if these compounds are to be deposited using inkjet
or pad printing processes. Recently, several researchers have
developed strategies to improve the solubility of oligoacenes
through chemical functionalization, while maintaining or im-
proving both chemical stability and charge carrier mobility.3
For example, thin films prepared from 6,13-bis(trialkylsilyl-
π-Conjugated organic compounds based on extended aromatic
systems have attracted considerable attention over the past
decade for their potential use as semiconductors in organic field-
effect transistors (OFETs), organic light-emitting diodes (OLE-
Ds), and photovoltaic cells.1 Among the many classes that have
been studied to date, oligoacenes are promising candidates for
device applications since their linearly fused benzenoid struc-
tures give rise to a substantial increase in conjugation compared
to their oligophenylene analogues.2 Pentacene, for instance, is
one of the most extensively studied oligoacenes as it exhibits
superior charge carrier mobilities that make it suitable for
application in OFETs.3 Despite of their attractive electronic
ethynyl)pentacenes are stable toward oxidation and exhibit hole
4
mobilities up to 1.0 cm2 V-1 s-1
,
and 2,7-dialkyl[1] ben-
zothieno[3,2-b][1]benzothiophenes have field effect mobilities
5
of up to 2.7 cm2 V-1 s-1
.
Incorporating thiophene into oligoacene frameworks is an
alternative strategy in the development of new organic semi-
(1) Murphy, A. R.; Fre´chet, J. M. J. Chem. ReV. 2007, 107, 1066–1096. (b)
Kovac, J.; Peternai, L.; Lengyel, O. Thin Solid Films 2003, 433, 22–26.
(2) Bendikov, M.; Wudl, F.; Perepichka, D. F. Chem. ReV. 2004, 104, 4891–
4946.
(4) Payne, M. M.; Parkin, S. R.; Anthony, J. E.; Kuo, C.-C.; Jackson, T. N.
J. Am. Chem. Soc. 2005, 127, 4986–4987.
(5) Ebata, H.; Izawa, T.; Miyazaki, E.; Takimiya, K.; Ikeda, M.; Kuwabara,
H.; Yui, T. J. Am. Chem. Soc. 2007, 129, 15732–15733.
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4918 J. Org. Chem. 2009, 74, 4918–4926
10.1021/jo900590u CCC: $40.75  2009 American Chemical Society
Published on Web 05/26/2009

Bent Acenedithiophenes and a Thiahelicene
CHART 1
SCHEME 1
product resulting from oxidative photocyclization of the novel
cis,cis- and trans,trans-2,5-dithienyl-1,4-distyrylbenzenes is
discussed.
conductors since thiophene moieties can improve the extent of
intermolecular π-π overlap in the solid state, a feature that is
intimately related to charge carrier mobility; see Chart 1 for
some examples of known thiophene-based acenes.5,6 Moreover,
the site-selective reactivity of thiophene makes these molecules
amenable to derivatization, leading to improved solubility,
environmental stability, and processability. For instance, linear
anthradithiophene (1),6a-c and benzo[1,2-b:4,5-b′]bis[1]ben-
zothiophene (2),6i have hole mobilities that approach that of
pentacene while showing improved oxidative stability and
solubility. Recent efforts have shown that pentaceno[2,3-b]-
thiophene is useful for application in OFETs.6m This is the most
conjugated acene-based system to be used in a device applica-
tion, overcoming the instability of hexacene that renders it
impractical for application in thin-film transistors.
Recently, we communicated the synthesis of bent anthra-
dithiophenes (BADTs) that are structurally analogous to di-
benz[a,h]anthracene, a structural isomer of pentacene.7 These
compounds are soluble at room temperature, enabling their facile
purification and processing. In this paper, the synthesis and
spectroscopy of five BADTs and their thiophene-phenylene
oligomer precursors are discussed in detail. The packing
structures of the BADTs as single-crystals and thermally
evaporated thin films are examined and compared, and the major
Results and Discussion
Synthesis, Characterization, and Spectroscopic Studies.
The synthetic approach used to prepare BADTs 5a-e is outlined
in Scheme 1. Compounds 3a-e were prepared via a 2-fold Stille
cross-coupling reaction between 2,5-dibromoterephthalaldehyde
and the appropriate 2-tributylstannylthiophene. The products
were isolated as bright yellow solids after purification.
1
The H NMR spectrum of 3b is typical for the dialkylated
derivatives. Singlets at δ 10.25 and 8.05 are assigned to the
aldehyde CHO and aryl CH protons, respectively. Resonances
at δ 6.94 and 6.86 are assigned to the thienyl CH protons and
the singlet at δ 2.57 is assigned to the aliphatic CH3 protons.
The IR spectra of compounds 3a-e exhibit strong stretching
bands at 1680-1685 cm-1 confirming the integrity of the
aldehydes after purification. The solution-phase UV-vis absorp-
tion spectra of 3a-e in CH2Cl2 (see Supporting Information)
contain three distinct absorption bands that are assigned to π-π*
and n-π* electronic transitions. Introduction of alkyl-substit-
uents to the thiophene moieties results in a small bathochromic
shift of the absorption bands while the large shift observed for
3e is attributed to an extension in conjugation that is imparted
by the phenyl substituents. Compounds 3a-e all exhibit green
luminescence in solution with emission maxima between 490
and 548 nm, and quantum yields (ΦF) of 0.39-0.92.
(6) (a) Lovinger, A. J.; Davis, D. D.; Ruel, R.; Torsi, L.; Dodabalapur, A.;
Katz, H. E. J. Mater. Res. 1995, 10, 2958–2962. (b) Servet, B.; Horowitz, G.;
Ries, S.; Lagorsse, O.; Alnot, P.; Yassar, A.; Deloffre, F.; Srivastava, P.; Hajlaoui,
R. Chem. Mater. 1994, 6, 1809–1815. (c) Laquindanum, J. G.; Katz, H. E.;
Lovinger, A. J. J. Am. Chem. Soc. 1998, 120, 664–672. (d) Cornil, J.; Beljonne,
D.; Calbert, J.-P.; Bre´das, J.-L. AdV. Mater. 2001, 13, 1053–1067. (e) Wex, B.;
Kaafarani, B. R.; Schroeder, R.; Majewski, L. A.; Burckel, P.; Grell, M.; Neckers,
D. C. J. Mater. Chem. 2006, 16, 1121–1124. (f) Yamamoto, T.; Takimiya, K.
J. Am. Chem. Soc. 2007, 129, 2224–2225. (g) Gao, J.; Li, R.; Li, L.; Meng, Q.;
Jiang, H.; Li, H.; Hu, W. AdV. Mater. 2007, 19, 3008–3011. (h) Kim, E.-G.;
Coropceanu, V.; Gruhn, N. E.; Sa´nchez-Carrera, R. S.; Snoeberger, R.; Matzger,
A. J.; Bre´das, J.-L. J. Am. Chem. Soc. 2007, 129, 13072–13081. (i) Gao, P.;
Beckmann, D.; Tsao, H. N.; Feng, X.; Enkelmann, V.; Pisula, W.; Mu¨llen, K.
Chem. Commun. 2008, 1548–1550. (j) Izawa, T.; Miyazaki, E.; Takimiya, K.
AdV. Mater. 2008, 20, 3388–3392. (k) Kashiki, T.; Miyazaki, E.; Takimiya, K.
Chem. Lett. 2008, 37, 284–285. (l) Du, C.; Guo, Y.; Liu, Y.; Qiu, W.; Zhang,
H.; Gao, X.; Liu, Y.; Qi, T.; Lu, K.; Yu, G. Chem. Mater. 2008, 20, 4188–
4190. (m) Tang, M. L.; Mannsfeld, S. C. B.; Sun, Y.-S.; Becerril, H. A.; Bao,
Z. J. Am. Chem. Soc. 2009, 131, 882–883.
Wittig olefination of 3a-e using methyltriphenylphospho-
nium bromide afforded compounds 4a-e as white or yellow
1
solids. The H NMR spectra of 4a-e show three distinct sets
of doublet of doublets in the regions δ 7.00, 5.74, and 5.28 that
are characteristic of the two-bond and three-bond coupling of
the vinylic protons. All solution phase UV-vis absorption
spectra in CH2Cl2 (see Supporting Information) show absorption
maxima at 276-280 nm that are assigned to a π-π* transition
involving the vinylic CdC chromophores. The lower energy
shoulders are assigned to a π-π* transition involving the
thiophene-phenylene oligomer.
BADTs 5a-e were prepared by irradiating dilute benzene
(or xylenes) solutions of 4a-e with UV light (ca. 300 nm) in
the presence of iodine. The reactions were monitored by
UV-vis absorption spectroscopy and terminated when the
(7) Pietrangelo, A.; MacLachlan, M. J.; Wolf, M. O.; Patrick, B. O. Org.
Lett. 2007, 9, 3571–3573.
J. Org. Chem. Vol. 74, No. 14, 2009 4919

Pietrangelo et al.
FIGURE 1. UV-vis absorption spectra of 5e recorded at 30 s intervals
during photolysis in benzene containing dissolved iodine at ca. 25 °C.
FIGURE 2. Cyclic voltammetry of 5a in CH2Cl2 containing 0.1 M
[(n-Bu)4N]ClO4. Scanned from +0.4 to + 1.3 V vs SCE for 10 cycles,
scan rate ) 100 mV s-1
.
TABLE 1. UV-Vis Absorption and Emission Data for 5a-e
proton of the central phenyl ring of the anthracenyl moiety and
the doublets at δ 7.86 and 7.72 are assigned to the remaining
aromatic CH protons.
solution absorptiona
max/nm
(ε/102 M-1cm-1
solution solid-state
λ
emissiona emission
quantum
compound
)
λmax/nm
λ
max/nm
yielda (Φf)
Electrochemical Studies. The redox properties of BADTs
5a-d were probed by cyclic voltammetry (CV). The parent
BADT 5a shows a single irreversible anodic wave at +1.2 V
vs SCE that increases upon successive sweeps (Figure 2). The
formation of a film on the working electrode suggests that radical
cation species are generated during repeated cycling followed
by polymerization affording poly-5a. Similar results have been
observed for anthratetrathiophenes as well.9
5a
5b
5c
5d
5e
304 (1429), 292 (600)
309 (2179), 296 (963)
311 (1295), 298 (529)
311 (1620), 298 (670)
324 (894), 339 (1560),
400 (180)
408
425
425
427
439
413
447
453
480
-
0.36
0.56
0.60
0.56
0.96
a CH2Cl2.
To investigate the optical properties of the polymer, films of
poly-5a were deposited on indium tin oxide (ITO) substrates.
The UV-vis absorption spectrum of a poly-5a film on ITO
exhibits a λmax at 319 nm, only 15 nm red-shifted from the
monomer (5a) suggesting that there is limited delocalization
between monomeric units. In the cyclic voltammograms of
dialkyl derivatives 5b-d, all exhibit a single quasi-reversible
redox wave that does not increase in intensity upon successive
sweeps indicating that the alkyl substituents prevent polymer-
ization and that the oxidative coupling of 5a likely occurs
through the R-positions of the thienyl groups.
intensity of product absorption bands no longer increased with
further irradiation. Figure 1 illustrates the conversion of 4e to
5e through a series of UV-vis absorption spectra taken at 30 s
intervals during a typical photolysis experiment. Comparison
with the absorption spectrum of pure 5e (Supporting Informa-
tion) confirms that this is the major product of the photolysis.
Unlike the linear anthradithiophene (1, Chart 1) and its alkylated
derivatives, compounds 5a-d are synthesized as single isomers
that are readily soluble in common organic solvents at room tem-
perature enabling solution-based processing and purification. The
diphenyl-derivative 5e, however, was poorly soluble and
therefore was best purified by sublimation. Compounds 5a-e
were all isolated as pale-yellow solids.
Oxidative Photocyclization of 2,5-Dithienyl-1,4-distyryl-
benzenes. To elucidate the scope of the synthetic approach, the
oxidative photocyclization of 2,5-dithienyl-1,4-distyrylbenzenes
6 and 7 was investigated. The cis,cis-isomer 6 was prepared
via a synthetic strategy also used to prepare the all-phenyl
analogue cis,cis-2,5-diphenyl-1,4-distyrylbenzene.10 This isomer
was converted to the trans,trans-isomer 7 by heating 6 to reflux
in p-xylene with catalytic iodine. These two isomers are
unambiguously characterized as either cis,cis or trans,trans by
The solution phase UV-vis spectra of 5a-e (Table 1) have
nearly identical features and exhibit a vibronic structure that is
similar to that of the all-phenyl analogue dibenz[a,h]anthracene.8
These compounds exhibit blue fluorescence in solution (emission
maxima ) 408 - 439 nm; quantum yields (Φf) of 0.36-0.96)
and green/blue fluorescence in the solid state.
1
The H NMR spectrum of the dimethyl derivative 5b has a
1
both H NMR and UV-vis absorption spectroscopy, and by
resonance pattern that is consistent with BADTs functionalized
at the R-position of the thiophene groups. A singlet at δ 8.59 is
assigned to the thienyl ꢀ-hydrogens, which are shifted upfield
from those of 5e by 0.75 ppm. This is likely due to an extension
of π-electron delocalization over the thienyl and the phenyl
moieties in the latter. A singlet at δ 7.17 is assigned to the CH
comparison to the spectra of the all-cis and all-trans isomers
of 2,5-diphenyl-1,4-distyrylbenzene.10
Irradiation of 7 in the presence of iodine was anticipated to
afford a BADT with phenyl substituents extending from the
(9) 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.
(10) Xie, Z.; Yang, B.; Liu, L.; Li, M.; Lin, D.; Ma, Y.; Cheng, G.; Liu, S.
J. Phys. Org. Chem. 2005, 18, 962–973.
(8) Karcher, W.; Fordham, R. J.; Dubois, J. J.; Glaude, P. G. J. M.; Ligthart,
J. A. M. Spectral Atlas of Polycyclic Aromatic Compounds; D. Reidel Publishing
Company: Dordrecht, The Netherlands, 1985.
4920 J. Org. Chem. Vol. 74, No. 14, 2009

Bent Acenedithiophenes and a Thiahelicene
FIGURE 3. (a) Thermal ellipsoid plot of 8. Thermal ellipsoids are drawn at 50% probability. The hydrogen atoms are omitted for clarity. (b)
Packing diagram of 8.
CHART 2
shown in Figure 3b. The S · · ·S distance (ca. 3.29 Å) between
alternating P and M enantiomers (i.e., i-ii and iii-iV) is shorter
than the sum of their van der Waals radii (1.80 Å for S),
suggesting the presence of intermolecular interactions that give
rise to a one-dimensional chain-like structure. This stacking
arrangement is unique since both thiophene moieties in 8
participate in intermolecular interactions, a feature that may be
an attractive approach to self-assembly of thiahelicenes. In
addition, a short intermolecular distance of 3.33 Å is observed
between adjacent enantiomers, ii and iii, suggesting that π-π
interactions also contribute to the intimate contact between P
and M isomers in the single crystal.
Solid-State Crystal Structures and Packing. Elucidating
the solid-state packing of BADTs in both single crystals and
films grown by thermal evaporation is essential in understanding
how the molecular assembly is influenced by substituents and,
ultimately, to best optimize the solid-state arrangement for
device applications.6j For the BADT derivatives that adopt a
cofacial stacking arrangement, translational displacements be-
tween adjacent molecules were quantified using a method
developed by Curtis and co-workers where slipping along the
long and short molecular axis is described by pitch (P) and roll
(R) angles (Figure 4).15
central anthracenyl group. To our surprise, irradiation of either
6 or 7 afforded a racemic mixture of the novel thiahelicene 8.
This product is formed through cyclization with the central aryl
ring on one side, and with thiophene on the other. In contrast,
the all-aryl analogue, 2,5-diphenyl-1,4-distyrylbenzene, under-
goes cyclization exclusively at the central aryl ring to give 7,14-
diphenyl-dibenz[a,h]anthracene.11 Thiahelicenes are an emerging
class of compounds that are interesting due to the site-selective
reactivity of the thiophene group(s) that can be exploited to tune
their electronic and chiroptical properties.12
Compound 8 was identified only after a single crystal X-ray
diffraction (SCXRD) study. The thermal ellipsoid plot of 8 is
shown in Figure 3. The thiahelicene 8 possesses C1 symmetry
and crystallizes as a racemate. Aromatic rings B-E all deviate
from planarity while the thienyl ring A remains planar. A
dihedral angle of 51° between the mean planes of A and E
illustrates the large degree of twisting in the heterohelicene. For
comparison, the dihedral angle between the terminal aromatic
rings in trithia[5]heterohelicene13 and [5]carbohelicene14 are 37°
and 49°, respectively. This large dihedral angle is somewhat
surprising since a lower degree of steric crowding would be
expected due to the orientation of the thiophene moiety A with
its R and ꢀ-hydrogen atoms located on the periphery of the
thiahelicene framework. The dihedral angles between the
remaining mean planes of 8 are as follows: A-B: 11°, B-C:
15°, C-D: 12°, and D-E: 14°. The crystal packing of 8 is
Crystals of 5a and 5b suitable for SCXRD studies were grown
from cold CH2Cl2. Both compounds crystallize in the monoclinic
P21/n space group with two molecules in the unit cell. The rigid
conjugated molecules are planar and show a small extent of
cofacial overlap between adjacent molecules (Figure 5).
The pitch and roll angles of 5a (see Table 2 for selected bond
lengths) are 13° and 28°, respectively. An interplanar distance
of 3.46 Å indicates the presence of π-π interactions along the
intermolecular stacking axis. For comparison, dibenz[a,h]an-
thracene crystallizes into a herringbone arrangement (P21 or Pcab
)
with no intermolecular cofacial interactions.16 Thus, the incor-
poration of thienyl groups appears to enhance π-stacking in the
crystal lattice, a feature that is highly desirable in molecular
organic semiconductors. In addition, the π-slipped stacks are
aligned into edge-to-face herringbone arrays where four inter-
molecular close-contacts are observed between each molecule
of 5a and four others in adjacent stacks (Figure 5c). For instance,
the distance between the sulfur atoms in a molecule of 5a (i.e.,
(11) Xie, Z.; Yang, B.; Cheng, G.; Liu, L.; He, F.; Shen, F.; Shen, F.; Ma,
Y.; Liu, S. Chem. Mater. 2005, 17, 1287–1289.
(12) Collins, S. K.; Vachon, M. P. Org. Biomol. Chem. 2006, 4, 2518–2524.
(13) Nakagawa, H.; Yamada, K.; Kawazura, H.; Miyamae, H. Acta Cryst,
Sect. C: Cryst. Struct. Commun. 1984, C40, 1039–1041.
(15) Curtis, M. D.; Cao, J.; Kampf, J. W. J. Am. Chem. Soc. 2004, 126,
4318–4328.
(14) Goedicke, C.; Stegemeyer, H. Tetrahedron Lett. 1970, 11, 937–940.
J. Org. Chem. Vol. 74, No. 14, 2009 4921

Pietrangelo et al.
substituents, a phenomenon that has also been observed in a
dihexyloxy-derivatized fluorinated tetracene.19
The didodecyl derivatized BADT 5d crystallizes into the
triclinic P-1 space group with a single molecule in the unit cell
(graphic is shown in ref 7). Functionalizing the thienyl R-posi-
tions with dodecyl chains regenerates the cofacial stacking
arrangement with pitch and roll angles of 19° and 48°,
respectively. In the crystal lattice, both dodecyl chains are in a
conformation that extends above and below the aromatic plane
of the BADT framework at 46° angles. The interplanar stacking
distance of 3.49 Å is indicative of π-π interactions along the
stacking axis. In the solid state, the molecules are organized
into a lamellar packing arrangement with the stacks separated
by insulating dodecyl chains. The lack of contact between the
π-stacks suggests a one-dimensional electronic structure in the
crystal.
Single crystals of the diphenyl-derivatized BADT 5e were
grown from a solution of 5e in p-xylene that was heated to reflux
and subsequently cooled to room temperature; the structure
determined by SCXRD is shown in Figure 7. The rigid
conjugated structure is slightly twisted with the pendant phenyl
rings rotated out of the plane of the thiophene groups at an angle
of 21°. In the solid state, 5e adopts an edge-to-face herringbone
packing motif where the tilt angle between two mean planes of
the BADT framework is 33°, compared to 45° in the all-carbon
analog dibenz[a,h]anthracene16 and 52° in pentacene.17 There
are eight intermolecular close-contacts in these edge-to-
face structures that link a molecule of 5e with four others in
the lattice. The two types of contacts are shown in Figure 7b.
The closest intermolecular C-C distances are 3.29 and 3.33
Å. These distances are shorter than the closest intermolecular
C-C distances observed in pentacene,17 phenyl-substituted
pentacenes,20 and dibenz[a,h]anthracene,16 and may lead to
strong electronic coupling between adjacent molecules in the
crystalline lattice.
Powder X-Ray Diffraction (PXRD) Analyses of BADT
Films. The PXRD pattern of a film of 5a prepared by vacuum
evaporation exhibits two strong reflections corresponding to the
(10-1) and (20-2) planes assigned from the diffraction pattern
calculated from the SCXRD data. The thin film is highly
crystalline, with reflections indicating that the molecules are
oriented with their long molecular axes nearly perpendicular
(ca. 77°) to the substrate surface, a phenomenon seen in
oligothiophenes as well as in the linear anthradithiophenes
prepared by Katz and co-workers.6a,c This packing orientation
is favorable for electronic device applications as the direction
of the π-orbital overlap is parallel to the substrate surface and
coincides with the plane in which a current must flow.
The XRD pattern of a film of 5d prepared by vacuum
evaporation exhibits six strong reflections that correspond to
the (001) through (006) planes (Figure 8b). The molecules are
oriented with their long molecular axes inclined approximately
47° with respect to the (001) plane that is parallel to the substrate
surface. These reflections are consistent with those observed in
films prepared from the didodecyl derivative of 1, suggesting
that this compound packs into a similar arrangement.6c
The XRD pattern of a film of 5b suggests that there are two
phases present (Figure 8c). The two sharp reflections at 2θ )
11.4 and 23.0° correspond to the (10-1) and (20-2) planes of
the P21/n space group. These assignments are supported by the
SCXRD data and are consistent with the diffraction pattern
FIGURE 4. (a) Pitch angle (P) describing intermolecular slipping along
the long molecular axis (view down short molecular axis). (b) Roll
angle (R) describing intermolecular slipping along the short molecular
axis (view down long molecular axis). (c) Long and short molecular
axes of 5a.
S1 and S1*) and a single C9 atom from two adjacent molecules
is 3.47 Å, a distance shorter than the sum of their van der Waals
radii (3.55 Å). This same distance is observed between the C9
and C9* atoms of each molecule and the sulfur atoms of two
additional molecules. Interestingly, this contact distance is
shorter than those observed between close-carbon contacts in
adjacent molecules of pentacene (3.6-3.8 Å),17 and suggests
that a single crystal of 5a may have a two-dimensional electronic
structure.
An interplanar distance of 3.28 Å between adjacent molecules
of 5b (Figure 5d) indicates the presence of π-π interactions
along the intermolecular stacking axis. The pitch and roll angles
are 45 and 44°, respectively; hence, it appears that the methyl
substituents induce a large degree of slipping along both the
short and long molecular axes compared to the parent. In
addition, there is no evidence of close contacts between adjacent
stacks. This packing feature has been observed in 218 and
suggests that a single crystal of 5b may have a one-dimensional
electronic structure.
Single crystals of the dihexyl (5c) and didodecyl (5d)
derivatives were grown from cold chloroform and their struc-
tures determined by SCXRD. Compound 5c crystallizes into
the monoclinic P21/c space group with two molecules in the
unit cell. In the crystal lattice, both hexyl chains are in a
conformation that extends above and below the aromatic plane
of the BADT framework at 39° angles (Figure 6).
Unlike 5a and 5b, there is no evidence of cofacial π-π
interactions in the crystalline phase of 5c due to the large degree
of slipping (pitch angle, 15°; roll angle, 72°) between adjacent
coplanar molecules along their short molecular axis (Figure 6).
This could be due to steric effects imparted by the hexyl
(16) (a) Iball, J. Nature 1936, 137, 361. (b) Iball, J.; Morgan, C. H.; Zacharias,
D. E. J. Chem. Soc., Perkin Trans. 2: Phys. Org. Chem. 1975, 1271–1272. (c)
Krishnan, K. S.; Banerjee, S. Z. Kristallogr. 1935, 91, 170–172. (d) Robertson,
J. M.; White, J. G. J. Chem. Soc. 1947, 1001–1010. (e) Robertson, J. M.; White,
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(17) (a) Campbell, R. B.; Robertson, J. M.; Trotter, J. Acta Crystallogr. 1962,
15, 289–90. (b) Holmes, D.; Kumaraswamy, S.; Matzger, A. J.; Vollhardt,
K. P. C. Chem.sEur. J. 1999, 5, 3399–3412. (c) Siegrist, T.; Kloc, C.; Scho¨n,
J. H.; Batlogg, B.; Haddon, R. C.; Berg, S.; Thomas, G. A. Angew. Chem., Int.
Ed. 2001, 40, 1732–1736. (d) Mattheus, C. C.; Dros, A. B.; Baas, J.; Meetsma,
A.; de Boer, J. L.; Palstra, T. T. M. Acta Cryst., Sect. C: Cryst. Struct. Commun.
2001, C57, 939–941.
(18) Ebata, H.; Miyazaki, E.; Yamamoto, T.; Takimiya, K. Org. Lett. 2007,
9, 4499–4502.
(19) Chen, Z.; Mu¨ller, P.; Swager, T. M. Org. Lett. 2006, 8, 273–276.
4922 J. Org. Chem. Vol. 74, No. 14, 2009

Bent Acenedithiophenes and a Thiahelicene
FIGURE 5. (a) Thermal ellipsoid plot of 5a. The hydrogen atoms are omitted for clarity. Thermal ellipsoids are drawn at 50% probability. (b)
View down the stacking axis of two cofacial molecules of 5a. (c) Crystal packing of 5a. Dashed lines illustrate short contacts (ca. 3.47 Å). (d) View
down the stacking axis of two cofacial molecules of 5b.
TABLE 2. Selected Bond Lengths of BADT 5a
bond length /Å bond length / Å
C(1)-C(2)
tive, the dihexyl derivative also adopts a lamellar packing
arrangement in the film.
Solid-State Absorption and Luminescence Properties of
Films. The solid-state UV-vis absorption spectra of drop-cast
films of 5a-d exhibit nearly identical features with λmax ranging
between 280 and 311 nm. Representative spectra of 5a and 5d
are shown in Figure 9. The high energy peaks in the solid-state
emission spectrum of 5a and 5d are similar to those found in
the solution phase spectrum. At longer wavelengths, however,
the emission intensity from the thin film is greater and a new
peak is present at 486 nm. The solid-state emission spectrum
of 5d is red-shifted relative to solution, a feature that is attributed
to intermolecular interactions in the microcrystalline film,22
where π-stacking has been observed in the solid-state structures.
1.347(3)
1.715(2)
1.452(3)
1.388(3)
1.429(3)
1.432(3)
C(4)-S1
1.725(2)
1.351(3)
1.436(3)
1.394(3)
1.435(3)
1.389(3)
C(1)-S(1)
C(2)-C(3)
C(3)-C(4)
C(3)-C(5)
C(4)-C(8)
C(5)-C(6)
C(6)-C(7)
C(7)-C(9)
C(7)-C(8)
C(8)-C(9)
obtained from crystals of 5b. The molecules are inclined
approximately 35° with respect to the (10-1) plane that is
parallel to the substrate surface. The additional reflections
observed at 2θ ) 10.8 and 22.4° are absent in both the calculated
and experimental diffraction patterns and are shifted ap-
proximately 0.6° from the reflections assigned to the (10-1)
and (20-2) planes. Similar features have been observed in the
XRD analysis of a pentacene thin-film grown onto a silica
substrate using molecular beam deposition techniques.21 These
features have been attributed to the coexistence of two phases,
a “thin-film” phase and a “single-crystal” phase that form under
certain deposition conditions.
The diffraction pattern obtained from a film of 5c exhibits
four sharp reflections at 2θ ) 5, 10, 15, and 20° (Figure 8d).
These reflections are inconsistent with those calculated from
the SCXRD data and those obtained experimentally from
crystals of 5c suggesting that the dihexyl-derivatized BADT
adopts a different packing motif in the evaporated film.
Interestingly, this diffraction pattern is very similar to that
obtained from a film of 5d (Figure 8b). The similarities between
the diffraction patterns suggests that, like the didodecyl deriva-
Conclusions
A new series of bent anthradithiophenes (BADTs) 5a-e has
been prepared via photochemical cyclization of 4a-e using
iodine as the oxidant. Apart from the diphenyl derivative 5e,
all the new BADTs are soluble in common organic solvents
including hexanes, CH2Cl2, and chloroform. Cyclic voltammetry
revealed that 5a polymerizes electrochemically upon successive
potential sweeps to afford thin films while the dialkyl derivatized
BADTs 5b-d exhibit a similar quasi-reversible redox wave but
do not electropolymerize, supporting the conclusion that 5a
polymerizes through the R-carbon of the thienyl groups. In order
to extend the scope of the synthetic strategy used here, oxidative
photocyclization reactions were carried out on the cis,cis- and
trans,trans-2,5-dithienyl-1,4-distyrylbenzenes 6 and 7. Both
reactions yielded a racemic mixture of the thiahelicene 8 which
(20) Miao, Q.; Chi, X.; Xiao, S.; Zeis, R.; Lefenfeld, M.; Siegrist, T.;
Steigerwald, M. L.; Nuckolls, C. J. Am. Chem. Soc. 2006, 128, 1340–1345.
(21) Dimitrakopoulos, C. D.; Brown, A. R.; Pomp, A. J. Appl. Phys. 1996,
80, 2501–2508.
(22) Dabestani, R.; Ivanov, I. N. Photochem. Photobiol. 1999, 70, 10–34.
(23) Xia, C.; Advincula, R. C. Macromolecules 2001, 34, 6922–6928.
J. Org. Chem. Vol. 74, No. 14, 2009 4923

Pietrangelo et al.
FIGURE 6. Packing diagram of 5c. (a) View along short molecular axis. The hydrogen atoms are omitted for clarity. Thermal ellipsoids are drawn
at 50% probability. (b) View perpendicular to the molecular plane of the stacking axis. (c) Space-filling diagram of 5c. Sulfur atoms are yellow,
sp3-hybridized carbon atoms are gray, and sp2-hybridized carbon atoms are purple.
FIGURE 7. (a) View down the short molecular axis of 5e. The
FIGURE 8. X-ray diffractograms and schematic representations of the
structural orientation of (a) 5a, (b) 5d, (c) 5b, and (d) 5c on glass
substrates (parallel to the x-axes) deposited by vacuum evaporation.
hydrogen atoms are omitted for clarity. Thermal ellipsoids are drawn
at 50% probability. (b) Crystal structure of 5e showing two of the eight
close contacts between the edge of one acene and the face of another.
Single-crystal and powder XRD studies demonstrated that
films prepared via vacuum evaporation are highly crystalline
with a preferred specific orientation relative to the substrate
surface. Films of 5a and 5d possess reflections that are consistent
with the single crystal data suggesting that packing in the film
is similar to packing in the single crystal. In addition, molecules
of 5a are oriented nearly perpendicular to the substrate surface,
a feature that is highly desirable for application in thin-film
OFETs. Films of the dimethyl derivative showed some reflec-
tions that were consistent with the single-crystal data and others
that could not be attributed to this structure, suggesting the
presence of two phases in the film. Films of the dihexyl
derivative 5c showed a set of reflections that were inconsistent
has been characterized by a variety of spectroscopic techniques
and SCXRD studies.
The solid-state packing motif of crystalline BADT 5a shows
a slipped cofacial stacking arrangement with π-π interactions
along the intermolecular stacking axis. This motif was not
observed in the all-carbon analog, dibenz[a,h]anthracene, sug-
gesting that the thiophene units enhance π-stacking in the crystal
lattice. The dialkyl derivatized BADTs 5b-d adopt similar
packing motifs with varying degrees of slipping along their long
and short molecular axes. The diphenyl derivative, 5e, packs
into an edge-to-face herringbone arrangement that is common
in many phenyl-substituted and unsubstituted oligoacenes.
4924 J. Org. Chem. Vol. 74, No. 14, 2009

Bent Acenedithiophenes and a Thiahelicene
553, 532 cm-1. Mp > 230 °C. Anal. Calcd for C28H18O2S2: C, 74.64;
H, 4.03. Found: C, 74.24; H, 4.04.
2,5-Bis(5-phenyl-2-thienyl)-1,4-divinylbenzene (4e). A suspen-
sion of methyltriphenylphosphonium bromide (0.30 g, 0.84 mmol)
and 60 mL of anhydrous THF in a 250 mL round-bottom Schlenk
flask was cooled to 0 °C, then 0.62 mL of n-BuLi (1.6 M in
hexanes; 0.99 mmol) was added dropwise. After 30 min of stirring,
a solution of 3e (0.15 g, 0.33 mmol) dissolved in 30 mL of
anhydrous THF was added. The combined solution was then
warmed to room temperature and left to stir for 24 h. Solvent was
then removed under reduced pressure and the product purified by
column chromatography using CH2Cl2 as the eluent (Rf ) 1.00).
The product was isolated as a white solid in 84% yield (0.125 g,
0.280 mmol).1H NMR (CD2Cl2, 400 MHz) δ 7.74 (2H, s), 7.67
3
3
(4H, d, JHH ) 7.40 Hz), 7.42 (4H, t, JHH ) 7.44 Hz), 7.36 (2H,
d, 3JHH ) 3.67 Hz), 7.32 (2H, t, 3JHH ) 7.37 Hz), 7.13 (2H, d, 3JHH
3
3
) 3.67 Hz), 7.08 (2H, dd, JHH ) 17.47 Hz, JHH ) 11.03 Hz),
5.82 (2H, d, 3JHH ) 17.42 Hz), 5.35 (2H, d, 3JHH ) 11.53 Hz). 13
C
FIGURE 9. (a) Solid-state UV-vis absorption spectrum of 5a (s).
Emission spectrum of 5a in solution (---, λex ) 304 nm) and as a thin
film (· · ·, λex ) 300 nm). (b) Solid-state UV-vis absorption spectrum
of 5d (s). Emission spectrum of 5d in solution (---, λex ) 311 nm)
and as a thin film (· · ·, λex ) 281 nm). All spectra were obtained at ca.
25 °C.
NMR (CD2Cl2, 100 MHz) δ 145.4, 141.5, 136.4, 135.8, 134.7,
133.2, 129.54, 129.49, 128.88, 128.23, 126.2, 124.0, 116.6. EI-
MS: m/z ) 446.1 (M+, 100%). UV-vis (CH2Cl2): λmax (ꢀ) ) 344
nm (25300), 291 nm (20400) (L mol-1 cm-1). IR (neat): ν ) 1592,
1485, 1460, 1444, 1408, 1379, 1337, 1254, 1159, 1099, 1075, 982,
940, 920, 897, 889, 842, 812, 753, 686, 615 cm-1. Mp 209 °C.
Anal. Calcd for C30H22S2: C, 80.68; H, 4.96. Found: C, 80.41; H,
5.07.
with those calculated from the single-crystal data suggesting
the presence of a new polymorph in the thin film.
Anthra(1,2-b:5,6-b′)di-5-phenylthiophene (5e). A 500 mL
quartz flask was charged with 4e (0.080 g, 0.18 mmol), iodine (0.25
g, 1.0 mmol), and 200 mL of xylenes sparged with dinitrogen gas.
The flask was irradiated in a photoreactor (300 nm lamps) for 72 h,
and UV-vis spectroscopy confirmed that the reaction was complete.
For workup, the organic solution was washed with aqueous sodium
dithionite solution and the solvent removed under vacuum. Benzene
(60 mL) was added to the brown solid that remained, and the
product was isolated by filtration and washed with hexanes. The
product was sublimed under vacuum for further purification,
Experimental Section
General. Chromium trioxide, 2-tributylstannylthiophene, meth-
yltriphenylphosphonium bromide, anhydrous DMF, Pd(PPh3)4, and
benzyltriphenylphosphonium chloride were purchased from standard
suppliers. THF was distilled from sodium and benzophenone under
N2. 2,5-Dibromoterephthalaldehyde,23 5-methyl-2-tributylstannylth-
iophene,24 5-hexyl-2-tributylstannylthiophene,25 5-dodecyl-2-tribu-
tylstannylthiophene,26 and 5-phenyl-2-tributylstannylthiophene27
were prepared according to literature procedures. The syntheses of
3a-d, 4a-d and 5a-d were reported in a previous communica-
tion.7 All reactions were carried out under a dinitrogen atmosphere
unless otherwise noted.
Synthesis. 2,5-Bis(5-phenyl-2-thienyl)terephthalaldehyde (3e).
A round-bottom Schlenk flask was charged with 2,5-dibromot-
erephthalaldehyde (0.300 g, 1.03 mmol), Pd(PPh3)4 (0.12 g, 0.010
mmol), 2-tributylstannyl-5-phenylthiophene (1.4 g, 3.1 mmol) and
anhydrous DMF (30 mL) and heated to 80 °C with stirring for
36 h. The reaction mixture was then cooled to room temperature,
diluted with Et2O, and filtered through Celite. The organic phase
was washed with brine and water, then dried over Na2SO4. After
filtration, the solvent was removed to yield the crude product, which
was chromatographed on silica using a hexanes/CH2Cl2 (1:1) solvent
mixture as the eluent (Rf ) 0.70). The orange product was isolated
in 43% yield (0.20 g, 0.44 mmol). 1H NMR (CD2Cl2, 400 MHz) δ
10.36 (2H, s), 8.19 (2H, s), 7.70 (4H, m), 7.44 (6H, m), 7.36 (2H,
t, 3JHH ) 7.39 Hz), 7.16 (2H, d, 3JHH ) 3.72 Hz). 13C NMR (CD2Cl2,
100 MHz) δ 191.5, 148.0, 137.42, 137.26, 134.2, 131.29, 131.26,
129.7, 128.8, 126.4, 124.7. EI-MS: m/z ) 450 (M+, 100%). UV-vis
(CH2Cl2): λmax (ꢀ) ) 270 (22400), 333 (29300), 413 (11400) nm
(L mol-1 cm-1). IR (neat): ν ) 1681, 1476, 1444, 1379, 1325,
1270, 1251, 1146, 1079, 903, 822, 812, 759, 689, 644, 634, 586,
1
yielding a yellow solid (32 mg, 40%). H NMR (DMSO-d6, 400
3
MHz) δ 8.89 (2H, s), 8.13 (2H, d, JHH ) 8.74 Hz), 8.08 (2H, s),
3
3
7.95 (2H, d, JHH ) 8.73 Hz), 7.89 (4H, d, JHH ) 7.46 Hz), 7.54
(4H, t, 3JHH ) 7.50 Hz), 7.43 (2H, t, 3JHH ) 7.24 Hz). EI-MS: m/z
) 442 (M+, 100%). HRMS (EI): Calcd for C30H18S2: 442.08499;
Found: 442.08404. UV-vis (CH2Cl2): λmax (ꢀ) ) 324 (89400), 339
(156200), 400 (17500) nm (L mol-1 cm-1). IR (neat): ν ) 1071,
1025, 879, 835, 801, 757, 745, 689, 608 cm-1. Mp > 230 °C.
Cis,cis-2, 5-bis(2-thienyl)-1,4-distyrylbenzene (6). A suspension
of benzyltriphenylphosphonium chloride (0.313 g, 0.805 mmol) and
30 mL of anhydrous THF in a 250 mL round-bottom Schlenk flask
was cooled to 0 °C and left to stir for 30 min. With stirring, 0.46
mL of n-BuLi (1.6 M in hexanes) was added dropwise. After an
additional 30 min of stirring, a solution of 2,5-di(2-thienyl)-
terephthalaldehyde 3a (0.100 g, 0.335 mmol) dissolved in 30 mL
of anhydrous THF was added. The combined solution was warmed
to room temperature and left to stir for 24 h. Solvent was then
removed under reduced pressure and the product purified by column
chromatography using CH2Cl2 as the eluent (Rf ) 0.97). The cis,cis-
isomer was isolated as a white solid (0.12 g, yield 80%). 1H NMR
(CD2Cl2, 400 MHz) δ 7.43 (2H, s), 7.30 (12H, m), 7.05 (2H, d,
3
3
3JHH ) 3.55 Hz), 7.00 (2H, dd, JHH ) 5.02 Hz, JHH ) 3.67 Hz),
6.71 (2H, d, 3JHH ) 12.09 Hz), 6.67 (2H, d, 3JHH ) 12.09 Hz). 13
C
NMR (CD2Cl2, 100 MHz) δ 142.4, 137.5, 135.2, 133.0, 132.2,
132.1, 130.2, 129.5, 128.8, 127.86, 127.83, 127.6, 126.5. EI-MS:
m/z ) 446 (M+, 100%). UV-vis (CH2Cl2): λmax (ꢀ) ) 311 nm
(27400) (L mol-1 cm-1). IR (KBr): ν ) 1481, 1438, 1400, 1382,
1241, 1241, 1213, 1072, 1056, 919, 904, 846, 831, 773, 744, 735,
690, 538, 505, 471, 445 cm-1. Mp 175-177 °C. Anal. Calcd for
C30H22S2: C, 80.68; H, 4.96. Found: C, 80.79, H, 5.17.
(24) Berridge, R.; Wright, S. P.; Skabara, P. J.; Dyer, A.; Steckler, T.; Argun,
A. A.; Reynolds, J. R.; Harrington, R. W.; Clegg, W. J. Mater. Chem. 2007, 17,
225–231.
(25) Jousselme, B.; Blanchard, P.; Gallego-Planas, N.; Levillain, E.; Delaunay,
J.; Allain, M.; Richomme, P.; Roncali, J. Chem.sEur. J. 2003, 9, 5297–5306.
(26) Wilson, P.; Lacey, D.; Sharma, S.; Worthington, B. Mol. Cryst. Liq.
Cryst. Sci. Tech. 2001, 368, 279–292.
(27) Li, J. J.; Carson, K. G.; Trivedi, B. K.; Yue, W. S.; Ye, Q.; Glynn,
R. A.; Miller, S. R.; Connor, D. T.; Roth, B. D.; Luly, J. R.; Low, J. E.; Heilig,
D. J.; Yang, W.; Qin, S.; Hunt, S. Bioorg. Med. Chem. 2003, 11, 3777–3790.
Trans,trans-2, 5-bis(2-thienyl)-1,4-distyrylbenzene (7). Com-
pound 6 (0.12 g, 0.27 mmol) was dissolved in 10 mL of xylenes
with a catalytic amount of I2 and heated to reflux for 12 h. After
J. Org. Chem. Vol. 74, No. 14, 2009 4925

Pietrangelo et al.
cooling, the product was precipitated upon addition to methanol
and isolated on a Bu¨chner funnel (0.10 g, 83%). 1H NMR (CD2Cl2,
400 MHz) δ 7.85 (2H, s), 7.47 (6H, m), 7.40 (2H, d, 3JHH ) 16.24
The structures were solved using direct methods30 and refined using
the SHELXTL crystallographic software package.31 For each
structure, all non-hydrogen atoms were refined anisotropically and
all hydrogen atoms were included in calculated positions but were
not refined. Compounds 5b-d crystallize with one-half-molecule
residing on an inversion center.
3
Hz), 7.35 (4H, m, aromatic CH), 7.22 (2H, dd, JHH ) 3.51 Hz,
3
3
3JHH ) 1.17 Hz), 7.18 (2H, dd, JHH ) 5.06 Hz, JHH ) 3.57 Hz),
3
7.14 (2H, d, JHH ) 16.23 Hz). 13C NMR (CD2Cl2, 100 MHz) δ
142.3, 138.0, 135.8, 133.8, 131.1, 129.3, 129.0, 128.44, 128.33,
128.07, 127.29, 127.21, 126.8. EI-MS: m/z ) 446 (M+, 100%).
UV-vis (CH2Cl2): λmax (ꢀ) ) 312 (43600), 348 (43700) nm (L
mol-1 cm-1). IR (KBr): ν ) 1594, 1493, 1446, 1390, 1315, 1235,
1207, 983, 946, 897, 854, 840, 755, 710, 731, 689, 669, 590, 513,
484 cm-1. Mp > 220 °C. Anal. Calcd for C30H22S2: C, 80.68; H,
4.96. Found: C, 80.31; H, 5.30.
Crystals of 5e were too thin for structural determination with a
standard diffractometer, so synchrotron radiation was used. Suitable
crystals of 5e were mounted on a glass fiber and the data collected
at 150 K on a D8 goniostat equipped with a CCD detector at
Beamline 11.3.1 at the Advanced Light Source (Lawrence Berkeley
National Laboratory) using synchrotron radiation tuned to λ )
0.7749 Å. A series of 3 s data frames measured at 0.2° increments
of ω were collected to calculate a unit cell. For data collection, 3 s
frames were measured at 0.3° intervals of ω and φ. The data frames
were collected using the program APEX2 and processed using the
program SAINT.28
Thiahelicene (8). A 500 mL quartz flask was charged with 7
(0.080 g, 0.18 mmol), iodine (0.090 g, 0.36 mmol), and 250 mL of
benzene sparged with dinitrogen gas. The flask was irradiated in a
photoreactor (300 nm lamps) for 2 weeks. After purification by
flash column chromatography (1:1 hexanes:CH2Cl2), side products
of lower solubility that eluted with the helicene were separated by
precipitation from cold hexanes/ CH2Cl2 (1:1) solutions. The final
product is a gray solid (yield 20%) that decomposes in solution at
Data were corrected for absorption effects using
the multiscan technique (SADABS).29 The structure was solved
using direct methods and refined using the SHELXTL31 crystal-
lographic software package. Compound 5e crystallizes with one-
half molecule residing on an inversion center.
1
room temperature. Rf ) 0.80 (hexanes/ CH2Cl2 (1:1)). H NMR
Electrochemistry. Cyclic voltammetry (CV) experiments were
conducted using a potentiostat. The working electrode was either
a Pt disk or an indium tin oxide (ITO) thin film on glass. The
counter electrode was a Pt mesh and the reference electrode a silver
wire. An internal reference, decamethylferrocene, was added to
correct the measured potentials with respect to saturated calomel
electrode (SCE). All experiments were carried out using a scan
rate of 100 mV/s. CH2Cl2 used for CV experiments was purified
by passing the solvent through an activated alumina tower.
3
(CD2Cl2, 400 MHz) δ 8.85 (1H, d, JHH ) 8.44 Hz), 8.20 (1H, d,
3JHH ) 8.84 Hz), 8.10 (1H, s), 8.05 (1H, d, 3JHH ) 7.85) 7.95 (2H,
3
3
m), 7.78 (2H, d, JHH ) 6.94 Hz), 7.68 (1H, t, JHH ) 6.91 Hz),
3
3
7.58 (2H, t, JHH ) 7.24 Hz), 7.50 (4H, m), 7.35 (1H, d, JHH
)
3
3
5.57 Hz), 7.32 (1H, dd, JHH ) 3.49 Hz, JHH ) 1.17 Hz), 7.25
(1H, dd, 3JHH ) 5.15 Hz, 3JHH ) 3.50 Hz). 13C NMR (CD2Cl2, 100
MHz) δ 141.8, 141.0, 139.3, 139.1, 137.9, 133.2, 131.42, 131.37,
130.76, 130.72, 130.3, 129.9, 129.2, 128.82, 128.67, 128.33, 128.23,
128.05, 128.01, 127.9, 127.7, 126.6, 125.43, 125.36, 125.03, 124.83,
124.15, 123.89. EI-MS: m/z ) 442 (M+, 100%). HRMS (EI): Calcd
for C30H18S2: 442.08499; Found: 442.08444. UV-vis (CH2Cl2):
λmax (ꢀ) ) 319 (33917), 269 (20785), 243 (30345) nm (L mol-1
cm-1). IR (neat): ν ) 1495, 1434, 1386, 1243, 1219, 1081, 1026,
905, 853, 838, 820, 798, 770, 760, 748, 722, 711, 694, 666, 643,
612, 591, 554, 521, 504 cm-1. Mp 195 °C.
Acknowledgment. We thank the Canadian Space Agency
and the Natural Sciences and Engineering Research Council of
Canada for funding. Samples for crystallographic analysis at
the synchrotron were submitted through the SCrALS (Service
Crystallography at Advanced Light Source) program. Crystal-
lographic data were collected at the Small-Crystal Crystal-
lography Beamline 11.3.1 at the Advanced Light Source (ALS).
The ALS is supported by the U.S. Department of Energy, Office
of Energy Sciences Materials Sciences Division, under contract
DE-AC03-76SF00098 at Lawrence Berkeley National Laboratory.
X-Ray Crystallographic Analysis. Crystallographic data for 3b,
5b-e, and 8 are included in the Supporting Information. Data for
5a are available in ref 7.
Single crystals of 3b, 5b-d, and 8 were grown from cold CH2Cl2
or chloroform. Crystals were mounted on glass fibers and the data
collected at 173(1) K on a diffractometer with graphite monochro-
mated Mo KR radiation. Data were collected in a series of φ and
ω scans in 0.50° oscillations with 10-30 s exposures, and collected
and integrated using the SAINT software package.28 Data were
corrected for absorption effects using the multiscan technique
(SADABS)29 and corrected for Lorentz and polarization effects.
Supporting Information Available: General experimental
1
details, H and 13C NMR spectra, and CIF files. This material
is available free of charge via the Internet at http://pubs.acs.org.
JO900590U
(30) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A. J. Appl.
Crystallogr. 1994, 27, 1045–1050.
(31) SHELXTL, Version 5.1; Bruker AXS Inc.: Madison, WI, 1997.
(28) SAINT, Version 7.23A; Bruker AXS Inc.: Madison, WI, 1997-2003.
(29) SADABS, V.2.10; Bruker AXS Inc.: Madison, WI, 2003.
4926 J. Org. Chem. Vol. 74, No. 14, 2009