Published on Web 01/10/2006
Organization of Acenes with a Cruciform Assembly Motif
Qian Miao,† Xiaoliu Chi,‡,§ Shengxiong Xiao,† Roswitha Zeis,‡ Michael Lefenfeld,†
Theo Siegrist,‡ Michael L. Steigerwald,† and Colin Nuckolls*,†
Contributions from the Department of Chemistry and The Nanoscience Center, Columbia
UniVersity, New York, New York 10027 and Bell Laboratories, Lucent Technologies,
600 Mountain AVenue, Murray Hill, New Jersey 07974
Received October 18, 2005; E-mail: cn37@columbia.edu
Abstract: This study explores the assembly in the crystalline state of a class of pentacenes that are
substituted along their long edges with aromatic rings forming rigid, cruciform molecules. The crystals were
grown from the gas phase, and their structures were compared with DFT-optimized geometries. Both
crystallographic and computed structures show that a planar acene core is the exception rather than the
rule. In the assembly of these molecules, the phenyl groups block the herringbone motif and further guide
the arrangement of the acene core into higher order structures. The packing for the phenyl-substituted
derivatives is dictated by close contacts between the C-H’s of the pendant aromatic rings and the carbons
at the fusions in the acene backbone. Using thiophene substituents instead of phenyls creates cofacially
stacked acenes. In thin films, the thiophene-substituted derivative forms devices with good electrical
properties: relatively high mobility, high ON/OFF ratios, and low threshold voltage for device activation.
An unusual result is obtained for the decaphenyl pentacene when devices are fabricated on its crystalline
surface. Although its acene cores are well isolated from each other, this material still exhibits good electrical
properties.
Introduction
Controlling the assembly of linear acenes is an important
problem with promise in improving many materials in applica-
This study explores the assembly of a class of pentacenes
that are substituted along their long edges with aromatic rings
forming rigid, cruciform1 shaped molecules. This work was
driven, in part, by curiosity as to how these unusually shaped
molecules arrange themselves in the solid state. Despite diphe-
nylpentacene, 2a, and tetraphenylpentacene, 3, having been
known for over 60 years2 and even though they have shown
promise in light-emitting diodes,3 their structures in the solid
state have not been reported, and very few other derivatives of
the phenylated pentacenes have been synthesized.4,5 Our inten-
tion in expanding this class of compounds was to use the
sterically encumbered phenyl groups to block the herringbone
motif that is typical of many acenes. Given the importance of
edge-to-face interactions in π-electron-rich aromatics, we are
exploring whether these phenyls could provide a guide to direct
the arrangement of the acene core into higher order structures.
tions involving intermolecular charge transport.6 The important
finding of this work is that the cruciform acenes have rich
diversity in the solid state, including layered, columnar, and
cage-like superstructures formed through edge-to-face contacts
between the aryl hydrogens and specific atoms in the pentacene
backbone. Understanding these assembly characteristics allows
the intermolecular contacts to be tuned at the molecular level
to adjust the electrical properties.
Results and Discussion
Synthesis. The approach used here successively substitutes
the acene core with phenyl rings and studies their structures in
the solid state. Figure 1 shows a subset of the phenylated acenes
that were synthesized and studied below. 2a and 3 were
synthesized by published procedures,7 which were adapted to
yield the 6,13-di(2′-thienyl)pentacene (2b). During the course
of this work a paper detailing a preparation of 2b similar to the
present one was reported;8 compounds 1, 4, and 5 (shown below)
have not been reported heretofore. 1 was synthesized by addition
† Columbia University.
‡ Bell Laboratories, Lucent Technologies.
§ Present address: Department of Chemistry, Texas A & M University-
Kingsville, MSC 161, 920 W. Santa Gertrudis, Kingsville, TX, 78363.
(1) (a) Klare, J. E.; Tulevski, G. S.; de Picciotto, A.; White, K.; Nuckolls, C.
J. Am. Chem. Soc. 2003, 125, 6030-6031. (b) Klare, J. E.; Tulevski, G.
S.; Nuckolls, C. Langmuir 2004, 20, 10068-10072.
(6) (a) Moon, H.; Zeis, R.; Borkent, E.-J.; Besnard, C.; Lovinger, A. J.; Siegrist,
T.; Kloc, C.; Bao, Z. J. Am. Chem. Soc. 2004, 126, 15322-15323. (b)
Anthony, J. E.; Brooks, J. S.; Eaton, D. L.; Parkin, S. R. J. Am. Chem.
Soc. 2001, 123, 9482-9483. (c) Payne, M. M.; Parkin, S. R.; Anthony, J.
E.; Kuo, C.-C.; Jackson, T. N. J. Am. Chem. Soc. 2005, 127, 4986-4987.
(d) Miao, Q.; Lefenfeld, M.; Nguyen, T.-Q.; Siegrist, T.; Kloc, C.; Nuckolls,
C. AdV. Mater. 2005, 17, 407-412. (e) Swartz, C. R.; Parkin, S. R.; Bullock,
J. E.; Anthony, J. E.; Mayer, A. C.; Malliaras, G. G. Org. Lett. 2005, 7,
3163-3166.
(2) (a) Allen, C. F. H.; Bell, A. J. Am. Chem. Soc. 1942, 64, 1253-1260. (b)
Bendikov, M.; Wudl, F.; Perepichka, D. F. Chem. ReV. 2004, 104, 4891-
4945. (c) Miller, G. P.; Mack, J.; Briggs, J. Org. Lett. 2000, 2, 3983-
3986.
(3) (a) Picciolo, L. C.; Murata, H.; Kafafi, Z. H. Appl. Phys. Lett. 2001, 78,
2378-2380. (b) Wolak, M. A.; Jang, B.-B.; Palilis, L. C.; Kafafi, Z. H. J.
Phys. Chem. B 2004, 108, 5492-5499.
(4) Miller, G. P.; Briggs, J. Org. Lett. 2003, 5, 4203-4206.
(5) Duong, H. M.; Bendikov, M.; Steiger, D.; Zhang, Q.; Sonmez, G.; Yamada,
J.; Wudl, F. Org. Lett. 2003, 5, 4433-4436.
(7) 2a and 3 were synthesized by phenylation of the corresponding pentacene
quinones followed by reduction in acidic conditions, similar to ref 2a.
(8) Vets, N.; Smet, M.; Dehaen, W. Synlett 2005, 2, 217-222.
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J. AM. CHEM. SOC. 2006, 128, 1340-1345
10.1021/ja0570786 CCC: $33.50 © 2006 American Chemical Society