Synthesis and structures of novel luminescent bent acenedithiophenes

Article abstract of DOI:10.1021/ol071387e

1,4-Dithienyl-2,5-divinylbenzenes are readily available compounds that undergo oxidative photocyclization to afford bent anthradithiophenes (BADTs). The new parent and didodecyl-functionalized derivatives have been structurally characterized, and their absorption and emission spectra are reported.

Full text of DOI:10.1021/ol071387e

ORGANIC
LETTERS
2007
Vol. 9, No. 18
3571-3573
Synthesis and Structures of Novel
Luminescent Bent Acenedithiophenes
Agostino Pietrangelo, Mark J. MacLachlan,* Michael O. Wolf,* and
Brian O. Patrick
Department of Chemistry, UniVersity of British Columbia, 2036 Main Mall,
VancouVer, British Columbia, Canada, V6T 1Z1
mmaclach@chem.ubc.ca; mwolf@chem.ubc.ca
Received June 12, 2007
ABSTRACT
1,4-Dithienyl-2,5-divinylbenzenes are readily available compounds that undergo oxidative photocyclization to afford bent anthradithiophenes
(BADTs). The new parent and didodecyl-functionalized derivatives have been structurally characterized, and their absorption and emission
spectra are reported.
Acenes have optical and electronic properties that are
desirable for application in organic-based electronic devices
such as organic field-effect transistors (OFETs) and light-
emitting diodes (OLEDs).1 Incorporating heteroarenes such
as thiophene into these frameworks has been part of an
ongoing effort to prepare new materials with improved device
performances.2
of LADTs approach that of pentacene while showing
improved oxidative stability. In addition, theoretical studies
have suggested that increasing the cofacial interactions
between adjacent LADT molecules could lead to improved
Linear anthradithiophenes (LADTs, Figure 1) have been
prepared for use as semiconductors in OFETs.3 LADTs are
of particular interest because they possess a rigid conjugated
framework that is structurally analogous to pentacene, an
organic semiconductor.4 These heteroacenes are prepared as
a mixture of syn and anti isomers that form highly ordered
polycrystalline films by vacuum evaporation. Hole mobilities
Figure 1. LADTs.
(1) Anthony, J. E. Chem. ReV. 2006, 106, 5028.
device performances.5 Anthony and co-workers have pre-
pared a series of silylethynyl-functionalized LADTs that have
improved solubilities and favorable solid-state packing
motifs.6 More importantly, thin films of these compounds
are processable from solution and exhibit good hole mobili-
ties that can be further improved by annealing the films with
solvent vapor.7
(2) (a) Yamamoto, T.; Takimiya, K. J. Am. Chem. Soc. 2007, 129, 2224.
(b) Wex, B.; Kaafarani, B. R.; Schroeder, R.; Majewski, L. A.; Burckel,
P.; Grell, M.; Neckers, D. C. J. Mater. Chem. 2006, 16, 1121. (c) Cicoira,
F.; Santato, C.; Melucci, M.; Favaretto, L.; Gazzano, M.; Muccini, M.;
Barbarella, G. AdV. Mater. 2006, 18, 169. (d) Xiao, K.; Liu, Y.; Qi, T.;
Zhang, W.; Wang, F.; Gao, J.; Qiu, W.; Ma, Y.; Cui, G.; Chen, S.; Zhan,
X.; Yu, G.; Qin, J.; Hu, W.; Zhu, D. J. Am. Chem. Soc. 2005, 127, 13281.
(e) Takimiya, K.; Kunugi, Y.; Konda, Y.; Niihara, N.; Otsubo, T. J. Am.
Chem. Soc. 2004, 126, 5084. (f) Iosip, M. D.; Destri, S.; Pasini, M.; Porzio,
W.; Pernstich, K. P.; Batlogg, B. Synth. Met. 2004, 146, 251. (g) Li, X.-C.;
Sirringhaus, H.; Garnier, F.; Holmes, A. B.; Moratti, S. C.; Feeder, N.;
Clegg, W.; Teat, S. J.; Friend, R. H. J. Am. Chem. Soc. 1998, 120, 2206.
(h) Laquindanum, J. G.; Katz, H. E.; Lovinger, A. J.; Dodabalapur, A. AdV.
Mater. 1997, 9, 36.
(4) Laquindanum, J. G.; Katz, H. E.; Lovinger, A. J.; Dodabalapur, A.
Chem. Mater. 1996, 8, 2542.
(5) Kwon, O.; Coropceanu, V.; Gruhn, N. E.; Durivage, J. C.; Laquin-
danum, J. G.; Katz, H. E.; Cornil, J.; Bre´das, J. L. J. Chem. Phys. 2004,
120, 8186.
(3) Laquindanum, J. G.; Katz, H. E.; Lovinger, A. J. J. Am. Chem. Soc.
1998, 120, 664.
10.1021/ol071387e CCC: $37.00
© 2007 American Chemical Society
Published on Web 08/09/2007

In this work, we were motivated by the hypothesis that
bent anthradithiophenes (BADTs), structurally analogous to
dibenz[a,h]anthracene, a structural isomer of pentacene, may
also be of interest for organic electronics applications.
BADTs are virtually unexplored8 and there is no reported
route to the parent unsubstituted compound. Swager and co-
workers have developed aryl-functionalized derivatives using
a chemical cyclization strategy; however, this is limited in
scope.9
parent BADT is planar and shows a small extent of cofacial
overlap between adjacent molecules (Figure 2). An inter-
Here we report a new route to luminescent BADTs using
an oxidative photocyclization-based synthetic strategy. This
route also enables access to dialkyl-functionalized BADTs,
with the alkyl groups modifying both the solubility and
structural organization of the rigid BADT framework.
The synthetic route to 1,4-di(2-thienyl)-2,5-divinylbenzene
4a and its alkylated derivatives 4b-d is outlined in Scheme
1. Compounds 3a-d were prepared via a Pd(0)-catalyzed
Figure 2. (a) Thermal ellipsoid plot of 5a. (b) View down the
short molecular axis of 5a; the stacking axis is vertical. (c) View
down the long molecular axis of 5a; the stacking axis is vertical.
(d) View down the stacking axis of two cofacial molecules of 5a.
Scheme 1
planar distance of 3.46 Å indicates the presence of π-π
interactions along the intermolecular stacking axis. For
comparison, dibenz[a,h]anthracene crystallizes into a her-
ringbone arrangement (P21 or Pcab) with no intermolecular
cofacial interactions.10 Thus, the incorporation of thienyl
groups appears to enhance π-stacking in the crystal lattice.
The XRD pattern of a thin film of 5a prepared by vacuum
evaporation (Figure 3a) exhibits two strong reflections
corresponding to the (1,0,-1) and (2,0,-2) planes assigned
from the diffraction pattern calculated from the single-crystal
XRD data. The thin film is highly crystalline, with reflections
indicating that the molecules in the thin film are oriented
with their long molecular axes nearly perpendicular to the
substrate surface, a phenomenon seen in oligothiophenes as
well as in LADTs.3,11
Single crystals of 5d were grown from cold chloroform
and the structure was determined by XRD (Figure 4a).
Functionalizing the thienyl R-positions with dodecyl chains
imparts a larger degree of cofacial slipping along both the
short and long molecular axes (Figure 4b). 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 rigid central motif
separated by dodecyl chains (Figure 4c). The XRD pattern
of a thin film of 5d prepared by vacuum evaporation exhibits
six strong reflections that correspond to the (0,0,1) through
(0,0,6) planes. The molecules are oriented with the long
molecular axes inclined approximately 45° with respect to
Stille cross-coupling reaction between 2 and the appropriate
2-(tributylstannyl)thiophene. Wittig olefination of the di-
aldehyde species with methyltriphenylphosphonium bromide
offered compounds 4a-d in good yield. The BADTs 5a-d
were prepared by irradiating dilute benzene solutions of
4a-d with UV light. Unlike the parent LADT and its
alkylated derivatives, compounds 5a-d are formed as single
isomers and are readily soluble in common organic solvents
at room temperature, thus enabling purification by column
chromatography.
Crystals of 5a suitable for single-crystal X-ray diffraction
(XRD) studies were grown from cold dichloromethane. The
(6) (a) Payne, M. M.; Odom, S. A.; Parkin, S. R.; Anthony, J. E. Org.
Lett. 2004, 6, 3325. (b) Payne, M. M.; Parkin, S. R.; Anthony, J. E.; Kuo,
C.-C.; Jackson, T. N. J. Am. Chem. Soc. 2005, 127, 4986.
(7) Dickey, K. C.; Anthony, J. E.; Loo, Y.-L. AdV. Mater. 2006, 18,
1721.
(8) A different isomer than described here has been prepared; see: Shen,
H.-C.; Tang, J.-M.; Chang, H.-K.; Yang, C.-W.; Liu, R.-S. J. Org. Chem.
2005, 70, 10113.
(10) (a) Iball, J.; Morgan, C. H.; Zacharias, D. E. J. Chem. Soc., Perkin
Trans. 2 1975, 1271. (b) Iball, J. Nature 1936, 137, 361. (c) Krishnan, K.
S.; Banerjee, S. Z. Kristallogr. 1935, 91, 173. (d) Robertson, J. M.; White,
J. G. J. Chem. Soc. 1947, 1001. (e) Robertson, J. M.; White, J. G. J. Chem.
Soc. 1956, 925.
(11) (a) Lovinger, A. J.; Davis, D. D.; Ruel, R.; Torsi, L.; Dodabalapur,
A.; Katz, H. E. J. Mater. Res. 1995, 10, 2958. (b) Servet, B.; Horowitz, G.;
Ries, S.; Lagorsse, O.; Alnot, P.; Yassar, A.; Deloffre, F.; Srivastava, P.;
Hajlaoui, R.; Lang, P.; Garnier, F. Chem. Mater. 1994, 6, 1809.
(9) (a) Tovar, J. D.; Swager, T. M. J. Organomet. Chem. 2002, 653,
215. (b) Goldfinger, M. B.; Crawford, K. B.; Swager, T. M. J. Am. Chem.
Soc. 1997, 119, 4578.
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Org. Lett., Vol. 9, No. 18, 2007

The higher energy peaks in the solid-state emission
spectrum of the thin film of 5a are similar to those found in
the solution-phase spectrum of this compound (Figure 5a).
Figure 3. X-ray diffractograms of films of (a) 5a and (b) 5d on
glass substrates deposited by vacuum evaporation.
Figure 5. (a) Excitation spectrum of 5a in solution (black).
Emission spectrum of 5a in solution (blue) and as a thin film (red).
(b) Excitation spectrum of 5d in solution (black). Emission spectrum
of 5d in solution (blue) and as a thin film (red).
the (0,0,1) plane that is parallel to the substrate surface. These
reflections are consistent with those observed in films
prepared from the didodecyl derivative of LADT,3 suggesting
that this compound packs into a similar arrangement as 5d.
At longer wavelengths, however, the emission intensity from
the thin film is greater and a new peak is present at 486 nm.
The emission spectrum of 5d (thin film) is also red-shifted
relative to solution. The broad red-shifted emission features
are attributed to intermolecular interactions in the micro-
crystalline film,13 and are possibly related to the π-π
stacking observed in the solid-state structures.
In summary, we report here a new family of acene-
dithiophenes, the dithienyl[a,h]anthracenes, prepared via
double oxidative photocyclization of precursors 4a-d.
Single-crystal and powder XRD studies demonstrate that
films prepared via vacuum evaporation are highly crystalline
with a preferred specific orientation relative to the substrate
surface. Compounds 5a and 5d adopt packing motifs in the
crystalline phase displaying different degrees of cofacial π-π
interactions, and show red-shifted emission spectra in the
thin films relative to solution. The incorporation of these
luminescent compounds into OLEDs and OFETs is being
investigated.
Figure 4. (a) Thermal ellipsoid plot of 5d. View down the a-axis.
(b) View down the “stacking axis” of two cofacial molecules of
5d with dodecyl chains omitted. (c) Space-filling diagram of 5d
illustrating packing structure. Sulfur atoms are yellow, sp3-
hybridized carbon atoms are gray, and sp2-hybridized carbons atoms
are purple.
Acknowledgment. The authors would like to thank the
Canadian Space Agency (CSA) and the Natural Sciences and
Engineering Research Council of Canada (NSERC) for
financial support.
Supporting Information Available: Experimental pro-
1
cedures, spectroscopic data, and H and 13C spectra for all
new compounds, as well as crystallographic data presented
in CIF format. This material is available free of charge via
the Internet at http://pubs.acs.org.
The solution-phase UV/vis absorption spectra of com-
pounds 5a-d (see Supporting Information) exhibit nearly
identical features (λmax between 304 and 311 nm), and are
similar to the absorption spectrum of dibenz[a,h]anthracene,12
although slightly red-shifted. Compounds 5a-d exhibit blue
luminescence in solution with emission maxima between 408
and 427 nm, and quantum yields (Φf) of 0.36-0.66 (see
Scheme 1).
OL071387E
(12) 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.
(13) Dabestani, R.; Ivanov, I. N. Photochem. Photobiol. 1999, 70, 10.
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