Synthesis and cofacial π-stacked packing arrangement of 6,13-bis(alkylthio)pentacene

Article abstract of DOI:10.1021/ol060679x

6,13-Bis(alkylthio)pentacenes directed toward organic field-effect transistors (OFETs) were synthesized by the Znl₂-mediated reaction of trans-6,13-dihydroxy-6,13-dihydropentacene with alkylthiols, followed by the dehydrogenative aromatization

Full text of DOI:10.1021/ol060679x

ORGANIC
LETTERS
2006
Vol. 8, No. 11
2385-2388
Synthesis and Cofacial
Packing Arrangement of
π-Stacked
6,13-Bis(alkylthio)pentacene
Kenji Kobayashi,*,†,‡ Reishi Shimaoka,† Masatoshi Kawahata,§
Masamichi Yamanaka,† and Kentaro Yamaguchi§
Department of Chemistry, Faculty of Science, Shizuoka UniVersity, 836 Ohya,
Suruga-ku, Shizuoka 422-8529, Japan, PRESTO, JST, 4-1-8 Honcho Kawaguchi,
Saitama 332-0012, Japan, and Faculty of Pharmaceutical Sciences at Kagawa
Campus, Tokushima Bunri UniVersity, Shido, Sanuki, Kagawa 769-2193, Japan
skkobay@ipc.shizuoka.ac.jp
Received March 19, 2006
ABSTRACT
6,13-Bis(alkylthio)pentacenes directed toward organic field-effect transistors (OFETs) were synthesized by the ZnI2-mediated reaction of trans-
6,13-dihydroxy-6,13-dihydropentacene with alkylthiols, followed by the dehydrogenative aromatization of the resulting trans-6,13-bis(alkylthio)-
6,13-dihydropentacenes with p-chloranil. The X-ray crystallographic analysis of 6,13-bis(methylthio)pentacene reveals that this compound is
arranged as a result of cofacial
π-stacking with S−S and S−π interactions.
Sulfur-containing aromatics are attractive candidates for
organic semiconductors.1,2 Pentacene is another promising
candidate for organic semiconductors, especially organic
field-effect transistors (OFETs).3 It is generally recognized
that the charge-carrier mobility in organic semiconductors
depends on π-π interactions between molecules. Acenes
such as pentacene, however, tend to be susceptible to
herringbone packing arrangements with minimal π-stacking,4
although the herringbone-packed pentacene still holds the
highest hole mobility among organic semiconductors.3,5
Realization of a 2-D cofacial π-stacked packing arrangement
of acenes may achieve greater charge-carrier transport
(2) For other sulfur-containing aromatics, see: (a) Laquindanum, J. G.;
Katz, H. E.; Lovinger, A. J. J. Am. Chem. Soc. 1998, 120, 664-672. (b)
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,
2206-2207. (c) Mas-Torrent, M.; Durkut, M.; Hadley, P.; Ribas, X.; Rovira,
C. J. Am. Chem. Soc. 2004, 126, 984-985. (d) Takimiya, K.; Kunugi, Y.;
Konda, Y.; Niihara, N.; Otsubo, T. J. Am. Chem. Soc. 2004, 126, 5084-
5085. (e) Meng, H.; Sun, F.; Goldfinger, M. B.; Jaycox, G. D.; Li, Z.;
Marshall, W. J.; Blackman, G. S. J. Am. Chem. Soc. 2005, 127, 2406-
2407. (f) Naraso; Nishida, J.; Ando, S.; Yamaguchi, J.; Itaka, K.; Koinuma,
H.; Tada, H.; Tokito, S.; Yamashita, Y. J. Am. Chem. Soc. 2005, 127,
10142-10143. (g) 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, 13281-13286.
† Shizuoka University.
‡ PRESTO.
§ Tokushima Bunri University.
(1) For oligothiophenens, see: (a) Sirringhaus, H.; Brown, P. J.; Friend,
R. H.; Nielsen, M. M.; Bechgaard, K.; Langeveld-Voss, B. M. W.; Spiering,
A. J. H.; Janssen, R. A. J.; Meijer, E. W.; Herwig, P.; de Leeuw, D. M.
Nature 1999, 401, 685-688. (b) Facchetti, A.; Deng, Y.; Wang, A.; Koide,
Y.; Sirringhaus, H.; Marks, T. J.; Friend, R. H. Angew. Chem., Int. Ed.
2000, 39, 4547-4551. (c) Facchetti, A.; Letizia, J.; Yoon, M.-H.; Mushrush,
M.; Katz, H. E.; Marks, T. J. Chem. Mater. 2004, 16, 4715-4727. (d)
Janzen, D. E.; Burand, M. W.; Ewbank, P. C.; Pappenfus, T. M.; Higuchi,
H.; da Silva Filho, D. A.; Young, V. G.; Bre´das, J. L.; Mann, K. R. J. Am.
Chem. Soc. 2004, 126, 15295-15308.
(3) (a) Katz, H. E.; Bao, Z.; Gilat, S. L. Acc. Chem. Res. 2001, 34, 359-
369. (b) Wu¨rthner, F. Angew. Chem., Int. Ed. 2001, 40, 1037-1039. (c)
Bendikov, M.; Wudl, F.; Perepichka, D. F. Chem. ReV. 2004, 104, 4891-
4945. (d) Reichmanis, E.; Katz, H.; Kloc, C.; Maliakal, A. Bell Lab. Tech.
J. 2005, 10(3), 87-105.
10.1021/ol060679x CCC: $33.50
© 2006 American Chemical Society
Published on Web 04/26/2006

efficiency because this molecular ordering would permit good
overlapping of the intermolecular π-orbitals.3c,d,6 Thus,
control of molecular orientation and arrangement is a very
important subject for OFETs. Several groups have reported
strategies for molecular design to achieve the cofacial
π-stacked packing arrangement of acenes,7-9 in which the
introduction of aryl,7c,d bulky trialkylsilylethynyl,8 or halogen
groups9 into acenes at the appropriate positions changes the
packing structure from a herringbone to a cofacial π-stacking
motif. Recently, we have demonstrated that S-S interactions
assist a cofacial π-stacking of 9,10-bis(methylthio)an-
thracene.10,11 Here, we report the synthesis of 6,13-bis-
(alkylthio)pentacenes (3) and the X-ray crystal packing
structure of 6,13-bis(methylthio)pentacene (3a), wherein 3a
is arranged by cofacial π-stacking with S-S and S-π
interactions.
Scheme 1. Formation of 2 by a ZnI2-Mediated Reaction of 1
with Thiols
(2e), respectively, in good yields (Scheme 1). These com-
pounds are freely soluble in CHCl3. This reaction is
applicable to a variety of thiols14 and scarcely produces any
of the cis isomer of 2. In contrast, reaction of the dimesylate
of 1 with n-C8H17SNa (4 equiv) in CH2Cl2-DMF gave a
mixture of 2c and cis-2c in a 2:1 ratio (total 57% yield).
The final step in the synthesis of 6,13-bis(alkylthio)-
pentacenes (3) is dehydrogenative aromatization of 2. The
results are summarized in Table 1. With the goal of
The direct method for the synthesis of 3 may be the
reaction of 6,13-dilithiopentacene with a dialkyl disulfide.
However, 6,13-dilithiopentacene cannot be prepared. The
reaction of 6,13-dihydropentacene with n-BuLi in the pres-
ence of TMEDA also did not generate 6,13-dilithio-6,13-
dihydropentacene. We devised a general synthetic route to
3, the key step of which utilizes the ZnI2-mediated reaction
of a benzylic alcohol with alkylthiol to provide a benzylic
alkyl sulfide.12
Table 1. Formation of 3 by Dehydrogenative Aromatization of
2 with p-Chloranil
The reduction of 6,13-pentacenequinone with NaBH4 (4
equiv) in MeOH at room temperature gave trans-6,13-
dihydroxy-6,13-dihydropentacene (1) in 77% yield.13 The
reaction of 1 with alkylthiols or thiophenol (2.2 equiv) in
the presence of ZnI2 (1 equiv) in CH2Cl2 at room temperature
produced trans-6,13-bis(alkylthio)-6,13-dihydropentacenes
(2a-d) or trans-6,13-bis(phenylthio)-6,13-dihydropentacene
temp/time
(°C/days)
K2CO3
(10 equiv)
yield of 3
entry
R
solvent
(%)
1
2
3
4
5
6
7
a
b
c
c
c
d
e
C6H6
C6H6
CHCl3
C6H6
C6H6
C6H6
CHCl3
60/3
60/2
40/3
60/2
60/2
60/2
40/2
yes
yes
no
66
85
40
10
68
45
79
no
(4) (a) Desiraju, G. R. Crystal Engineering: The Design of Organic
Solids; Elsevier: Amsterdam, 1989; Chapter 4. (b) Holmes, D.; Kuma-
raswamy, S.; Matzger, A. J.; Vollhardt, K. P. C. Chem.-Eur. J. 1999, 5,
3399-3412. (c) Cornil, J.; Calbert, J. P.; Bre´das, J. L. J. Am. Chem. Soc.
2001, 123, 1250-1251. (d) Fritz, S. E.; Martin, S. M.; Frisbie, C. D.; Ward,
M. D.; Toney, M. F. J. Am. Chem. Soc. 2004, 126, 4084-4085.
(5) (a) Klauk, H.; Halik, M.; Zschieschang, U.; Schmid, G.; Radlik, W.;
Weber, W. J. Appl. Phys. 2002, 92, 5259-5263. (b) 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. (c) Butko, V. Y.; Chi, X.;
Lang, D. V.; Ramirez, A. P. Appl. Phys. Lett. 2003, 83, 4773-4775. (d)
Jurchescu, O. D.; Baas, J.; Palstra, T. T. M. Appl. Phys. Lett. 2004, 84,
3061-3063.
(6) (a) Swenberg, C. E.; Pope, M. Electronic Processes of Organic
Crystals and Polymers; Oxford University Press: Oxford, NY, 1999. (b)
Curtis, M. D.; Cao, J.; Kampf, J. W. J. Am. Chem. Soc. 2004, 126, 4318-
4328. (c) Bre´das, J. L.; Beljonne, D.; Coropceanu, V.; Cornil, J. Chem.
ReV. 2004, 104, 4971-5003.
(7) (a) Meng, H.; Bendikov, M.; Mitchell, G.; Helgeson, R.; Wudl, F.;
Bao, Z.; Siegrist, T.; Kloc, C.; Chen, C.-H. AdV. Mater. 2003, 15, 1090-
1093. (b) Tulevski, G. S.; Miao, Q.; Fukuto, M.; Abram, R.; Ocko, B.;
Pindak, R.; Steigerwald, M. L.; Kagan, C. R.; Nuckolls, C. J. Am. Chem.
Soc. 2004, 126, 15048-15050. (c) Sundar, V. C.; Zaumeil, J.; Podzorov,
V.; Menard, E.; Willett, R. L.; Someya, T.; Gershenson, M. E.; Rogers, J.
A. Science 2004, 303, 1644-1646. (d) 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.
yes
yes
no
establishing the optimum conditions, 2c (R ) n-C8H17) was
chosen as a test substrate (entries 3-5). All reactions were
(8) (a) Anthony, J. E.; Brooks, J. S.; Eaton, D. L.; Parkin, S. R. J. Am.
Chem. Soc. 2001, 123, 9482-9483. (b) Anthony, J. E.; Eaton, D. L.; Parkin,
S. R. Org. Lett. 2002, 4, 15-18. (c) Sheraw, C. D.; Jackson, T. N.; Eaton,
D. L.; Anthony, J. E. AdV. Mater. 2003, 15, 2009-2011. (d) Payne, M.
M.; Delcamp, J. H.; Parkin, S. R.; Anthony, J. E. Org. Lett. 2004, 6, 1609-
1612. (e) Payne, M. M.; Odom, S. A.; Parkin, S. R.; Anthony, J. E. Org.
Lett. 2004, 6, 3325-3328. (f) Swartz, C. R.; Parkin, S. R.; Bullock, J. E.;
Anthony, J. E.; Mayer, A. C.; Malliaras, G. G. Org. Lett. 2005, 7, 3163-
3166. (g) Payne, M. M.; Parkin, S. R.; Anthony, J. E.; Kuo, C.-C.; Jackson,
T. N. J. Am. Chem. Soc. 2005, 127, 4986-4987. (h) Payne, M. M.; Parkin,
S. R.; Anthony, J. E. J. Am. Chem. Soc. 2005, 127, 8028-8029.
(9) (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) Sakamoto, Y.; Suzuki, T.; Kobayashi, M.; Gao, Y.; Fukai, Y.; Inoue,
Y.; Sato, F.; Tokito, S. J. Am. Chem. Soc. 2004, 126, 8138-8140. (c) Chen,
Z.; Mu¨ller, P.; Swager, T. M. Org. Lett. 2006, 8, 273-276.
2386
Org. Lett., Vol. 8, No. 11, 2006

carried out under an argon atmosphere in the dark. p-
Chloranil (2 equiv) was the best dehydrogenative aromati-
zation reagent for 2c.15 In entry 3, the reaction of 2c with
p-chloranil in CHCl3 at 40 °C for 3 days gave 3c in 40%
yield, along with 6,13-dihydro-13,13-bis(n-octylthio)penta-
cen-6-one (4c: 42% yield) as a rearrangement product16 and
the Diels-Alder adduct of 3c with p-chloranil at the 6,13-
positions (5c: 16% yield). In benzene at 60 °C for 2 days
(entry 4), although overreactions toward 4c and 5c were
almost inhibited, the reaction gave 3c in 10% yield, together
with cis-2c and recovered 2c, wherein cis-2c had no reactivity
with respect to p-chloranil. The use of K2CO3 as an additive
was effective in inhibiting the formation of undesirable cis-
2c.17 Thus, the best result for the synthesis of 3c (entry 5:
68% yield) was obtained under the conditions of 2c,
p-chloranil (2 equiv), and K2CO3 (10 equiv) in benzene at
60 °C for 2 days. On the basis of this procedure, 2a, 2b,
and 2d were transformed into 3a (entry 1: R ) CH3, 66%
yield), 3b (entry 2: R ) n-C5H11, 85% yield), and 3d (entry
6: R ) (CH2)2Si(CH3)3, 45% yield), respectively. The
transformation of 2e into 3e (entry 7: R ) Ph, 79% yield)
was carried out in CHCl3 because hardly any 4e and 5e were
produced. Compounds 3a and 3e are less soluble in CHCl3
and benzene (ca. 0.3 mg/mL at room temperature), whereas
3b-d are freely soluble in these solvents. The UV-vis
spectrum of 3c in CH2Cl2 showed λmax ) 617 nm, which is
red-shifted by 39 nm relative to λmax of pentacene.8d,18 Under
both air and room light, 3a-e in solution gradually decom-
posed to 6,13-pentacenequinone. In contrast to pentacene,18
without lights, 3a-e can be handled and purified under air.19
The X-ray crystal packing structure of 3a reveals that 3a is
arranged by cofacial π-stacking along the a axis with S-S
and S-π interactions (Figures 1 and 2).
Figure 1. 2-D network sheet of 3a in the crystal structure: (a)
front and (b) top views.
Figure 1 shows one 2-D network sheet of 3a. The
pentacene ring of 3a forms the pentacene column through a
slipped-cofacial π-stacking motif along the a axis,8b,10 with
a face-to-face pentacene-pentacene distance of 3.39 Å. The
pentacene rings in one column are slipped relative to each
other along the long molecular axis by 3.64 Å and along the
short molecular axis by 1.19 Å. This molecular ordering
would permit good overlapping of the intermolecular π-or-
bitals of the pentacene rings. There is no S-S interaction
(5.128 Å) in the pentacene column. Instead, there are weak
intermolecular S-π interactions between the sulfur atom and
the neighboring pentacene ring in the pentacene column, with
the interatomic distances of S‚‚‚C3′ ) 3.610, S‚‚‚C4′ )
3.611, and S‚‚‚C5′ ) 3.652 Å.20 The intermolecular S‚‚‚S′
closest distance between the neighboring pentacene columns
in 3a is 4.297 Å (the second closest distance is 4.563 Å).
Although this intermolecular S‚‚‚S′ distance is 16% longer
Single crystals of 6,13-bis(methylthio)pentacene (3a) suit-
able for X-ray diffraction analysis were obtained by allowing
a hot solution of 3a in 1,2,4-trichlorobenzene under an argon
atmosphere in the dark to slowly cool to room temperature.
(10) Kobayashi, K.; Masu, H.; Shuto, A.; Yamaguchi, K. Chem. Mater.
2005, 17, 6666-6673.
(11) For S-S interactions for molecular ordering, see: (a) Werz, D. B.;
Gleiter, R.; Rominger, F. J. Am. Chem. Soc. 2002, 124, 10638-10639. (b)
Gleiter, R.; Werz, D. B. Chem. Lett. 2005, 34, 126-131.
(12) Guindon, Y.; Frenette, R.; Fortin, R.; Rokach, J. J. Org. Chem. 1983,
48, 1357-1359.
(13) The reduction of 6,13-pentacenequinone with NaBH4 in refluxing
THF gives the trans and cis isomers of 1 in a 65:35 ratio. Vets, N.; Smet,
M.; Dehaen, W. Tetrahedron Lett. 2004, 45, 7287-7289.
(14) For the synthesis of 2a, a 1:1 mixture of CH3SNa and acetic acid
in CH2Cl2 was used as CH3SH without any purification.
(15) The reaction of 2c with DDQ in CHCl3 gave 3c in very low yield,
wherein the main product was 4c.
(16) For an anthracene analogue of 4c, see: Koyama, E.; Kobayashi,
K.; Horn, E.; Furukawa, N. Tetrahedron Lett. 1999, 40, 8833-8836.
(17) A 1:1 mixture of 3c with tetrachlorohydroquinone in C6D6 at 60
°C for 2 days remained intact. The isomerization of 2c to cis-2c could occur
at the back reaction of a 6,13-bis(n-octylthio)-6-hydropentacene radical with
a phenoxy radical of tetrachlorohydroquinone as intermediates in the reaction
of 2c with p-chloranil. K2CO3 as an additive would be effective in trapping
of the hydroquinone or its phenoxy radical.
Figure 2. 3-D packing structure of 3a: perspective views looking
down (a) the a axis and (b) the c axis.
Org. Lett., Vol. 8, No. 11, 2006
2387

than the van der Waals distance,20 this value is still
sufficiently in the range of van der Waals interactions.11,21
The contact angles of S‚‚‚S′-Cpentacene and S‚‚‚S′-CMe are
119.88 and 70.92°, respectively. Thus, the pentacene columns
of 3a formed by slipped-cofacial π-stacking and S-π
interactions are parallel to each other and are linked by the
S-S interactions to self-assemble into a 2-D network sheet
(Figure 1). Figure 2 shows the 3-D packing structure of 3a.
The 3a molecules in one 2-D network sheet and in the
neighboring 2-D network sheets are packed relative to each
other with a large tilt angle of 84.4°, in what is called the
γ-motif.4a
In summary, we have developed a general method for the
synthesis of 6,13-bis(alkylthio)pentacenes (3) and demon-
strated that the intermolecular S-S and S-π interactions
assist the cofacial π-stacked packing arrangement of the
pentacene rings of 3a. It is noted that the introduction of a
small methylthio group into pentacene at the 6,13-positions
changes the packing structure from a herringbone to a
cofacial π-stacking motif. Studies on the preparation of thin
films and OFET properties of 3 are currently in progress.
(18) Maliakal, A.; Raghavachari, K.; Katz, H.; Chandross, E.; Siegrist,
T. Chem. Mater. 2004, 16, 4980-4986.
(19) Decomposition of 3c to 6,13-pentacenequinone in air-saturated
CDCl3 in the dark at room temperature was monitored by 1H NMR, wherein
3c survived in 93, 88, 82, and 66% yields after 13, 25, 48, and 168 h,
respectively.
(20) Pauling, L. The Nature of the Chemical Bond, 3rd ed.; Cornell
University Press: Ithaca, NY, 1973. The sum of van der Waals radii of
two atoms is as follows: S‚‚‚S ) 3.70 Å; S‚‚‚C ) 3.55 Å.
(21) Maitland, G. C.; Rigby, M.; Smith, E. B.; Wakeham, W. A.
Intermolecular Forces; Clarendon Press: Oxford, 1981.
Supporting Information Available: Synthetic procedures
and spectral data for 1-3, 4c, and 5c and ORTEP drawing
and CIF file of 3a. This material is available free of charge
via the Internet at http://pubs.acs.org.
OL060679X
2388
Org. Lett., Vol. 8, No. 11, 2006