Facile synthesis of picene from 1,2-Di(1-naphthyl)ethane by 9-fluorenone-sensitized photolysis

Article abstract of DOI:10.1021/ol200874q

A facile formation of picene was achieved by photosensitization of 1,2-di(1-naphthyl)ethane using 9-fluorenone as a sensitizer. This sensitized photoreaction is the first photochemical cyclization of ethylene-bridged naphthalene moieties to afford the picene skeleton. 5,8-Dibromopicene, prepared by this procedure using 1,2-di[1-(4-bromonaphthyl)]ethane as the substrate, was readily converted to novel functionalized picenes by conventional substitution and cross-coupling reactions.

Full text of DOI:10.1021/ol200874q

ORGANIC
LETTERS
2011
Vol. 13, No. 10
2758–2761
Facile Synthesis of Picene from
1,2-Di(1-naphthyl)ethane by
9-Fluorenone-Sensitized Photolysis
Hideki Okamoto,*,† Minoru Yamaji,*,‡ Shin Gohda,§ Yoshihiro Kubozono,†
Noriko Komura,† Kaori Sato,§ Hisako Sugino,§ and Kyosuke Satake†
Division of Chemistry and Biochemistry, Graduate School of Natural Science and
Technology, Okayama University, Tsushima-Naka 3-1-1, Okayama 700-8350, Japan,
Department of Chemistry and Chemical Biology, Graduate School of Engineering,
Gunma University, Kiryu, Gunma 376-8515, Japan, Material Science Research Group,
NARD Institute, Ltd., Nishinagasu-cho 2-6-1, Amagasaki, Hyogo 660-0805, Japan
hokamoto@cc.okayama-u.ac.jp; yamaji@gunma-u.ac.jp
Received April 4, 2011
ABSTRACT
A facile formation of picene was achieved by photosensitization of 1,2-di(1-naphthyl)ethane using 9-fluorenone as a sensitizer. This sensitized
photoreaction is the first photochemical cyclization of ethylene-bridged naphthalene moieties to afford the picene skeleton. 5,8-Dibromopicene,
prepared by this procedure using 1,2-di[1-(4-bromonaphthyl)]ethane as the substrate, was readily converted to novel functionalized picenes by
conventional substitution and cross-coupling reactions.
Aromatic compounds possessing extended π-conjuga-
tion have attracted significant attention because of their
potential for use as organic electronic materials.1 In the
past decade, pentacene 1 has been widely used as an active
layer in organic thin-film field-effect transistors (FETs).
However, because pentacene is quite unstable upon ex-
posure to light and air, a number of issues arise, which need
to be resolved for its practical application in devices.
Picene 2, an isomer of pentacene 1 (Figure 1), has been
known as a stable compound in which the benzene rings
are fused in a zigzag phenacene structure. However,
phenacenes have attracted less attention as organic elec-
tronic materials than acenes, typified by pentacene 1.
Figure 1. Structures of pentacene 1 and picene 2.
† Okayama University.
In a previous report by the current authors, it was shown
that picene 2 could serve as an active layer of a high-
performance p-channel organic thin film FET with a very
highfield-effectmobility:μ ∼ 5 cm2 VÀ1 sÀ1.2 Additionally,
the reportedpicene thin film FET was remarkablysensitive
to O2; thus, the FET device responded to O2 at pressures as
low as 10 ppm of O2 gas.2a The picene thin film FET also
displayed appreciable hysteresis in the forward and reverse
transfer curves under high humidity.2a That study, there-
fore, demonstrated that picene thin film FETs were po-
tentialy applicable to practical organic electronic devices
‡ Gunma University.
§ NARD Institute, Ltd.
(1) Yamashita, Y. Sci. Technol. Adv. Mater. 2009, 10, 024313.
(2) (a) Okamoto, H.; Kawasaki, N.; Kaji, Y.; Kubozono, Y.;
Fujiwara, A.; Yamaji, M. J. Am. Chem. Soc. 2008, 130, 10470. (b)
Kawasaki, N.; Kubozono, Y.; Okamoto, H.; Fujiwara, A.; Yamaji, M.
Appl. Phys. Lett. 2009, 94, 043310. (c) Kaji, Y.; Mitsuhashi, R.; Lee, X.;
Okamoto, H.; Kambe, T.; Ikeda, N.; Fujiwara, A.; Yamaji, M.; Omote,
K.; Kubozono, Y. Org. Electron. 2009, 10, 432. (d) Kaji, Y.; Kawasaki,
N.; Lee, X.; Okamoto, H.; Sugawara, Y.; Oikawa, S.; Ito, A.; Okazaki,
H.; Yokoya, T.; Fujiwara, A.; Kubozono, Y. Appl. Phys. Lett. 2009, 95,
183302. (e) Lee, X.; Sugawara, Y.; Ito, A.; Oikawa, S.; Kawasaki, N.;
Kaji, Y.; Mitsuhashi, R.; Okamoto, H.; Fujiwara, A.; Omote, K.;
Kambe, T.; Ikeda, N.; Kubozono, Y. Org. Electron. 2010, 11, 1394.
r
10.1021/ol200874q
Published on Web 04/22/2011
2011 American Chemical Society

such as gas sensors.2 Furthermore, picene 2 showed super-
conductivity with a high superconducting transition tem-
perature, Tc = 18 K, upon being doped with alkaline
metals such as potassium.3 The potassium-doped picene is
the first hydrocarbon-based superconductor3 illustrating
that picene 2 and its derivatives represent a novel and
promising class of materials for organic electronics,
although picene has rarely been applied to practical elec-
tronic devices.
The conventional synthetic methods employed in the
preparation of picene involve the use of multistep
procedures.4 Therefore, a simple and convenient strategy
for the synthesis of picene 2 is highly desirable in order to
promote further investigations into its use in organic
electronics.
In the course of our synthetic study of picene 2, we have
found that sensitized photolysis of 1,2-di(1-naphthyl)-
ethane 3 unexpectedly produced picene 2 in one step.
Herein, we report the photochemical formation of picene
2 as a new and convenient methodology for picene synth-
esis. Additionally, the preparation of novel functionalized
picenes, with the aim of developing a new phenacene for
potential use as an organic electronic material, is also
described.
The initial investigations were performed using direct
irradiationofdinaphthylethane3. Whendinaphthylethane
3 was irradiated (>280 nm) in degassed acetonitrile
(MeCN), no appreciable product formation was observed.
In contrast, photolysis of the same in aerated MeCN
resulted in the formation of 1-naphthaldehyde, instead of
the desired picene 2, as observed in the absorption spectra
of the photolysate (Figure S1, Supporting Information). It
can be concluded that upon direct photolysis, homolytic
cleavage of the CÀC bond of the ethylene bridge of
dinaphthylethane 3 occurred to afford the 1-naphthyl-
methyl radical A which was trapped with the dissolved
O2 and finally produced 1-naphthaldehyde (Scheme 1).5
(DCA) as sensitizers. Primary screening was carried out by
monitoring the progress of the photoreactions (irradiated
at 350 nm) by H NMR spectroscopy. The ratio of 3/
1
sensitizer was set to 1:3. Typical 1H NMR spectral changes
during the photolysis are shown in Figure S2 (Supporting
Information). Figure 2 shows the time course of consump-
tion of the starting dinaphthylethane 3 and formation of
picene 2. For XT-sensitized irradiation, neither significant
consumption of dinaphthylethane 3 nor formation of
picene 2 was observed. In the case of DCA-sensitized
irradiation, 32% of the starting dinaphthylethane 3 was
consumed, whereas a trace amount of picene 2 was ob-
served (<3%) after 44 h of irradiation. It was found that,
among the sensitized photolyses investigated, the photo-
lysis of dinaphthylethane 3 in the presence of 9F resulted in
the highest yield of picene, with a yield of 25% accompa-
nied by 53% consumption of dinaphthylethane 3, after 44
h of irradiation. Prolonged irradiation was not effective for
enhancing the yield (27% after 90 h). In the case of BP
sensitization, conversion of dinaphthylethane 3 (61%) was
the highest among the sensitized phtolyses investigated,
however, the yield of picene 2 (11%) was lower than
that for the 9F sensitization. Therefore, 9F was selected
for use asthe sensitizer in subsequent preparative studies of
picene 2.
Scheme 1. Direct Photolysis of Dinaphthylethane 3
Figure 2. Time course of photolysis (350 nm, CDCl3) of di-
naphthylethane 3 sensitized with 9F (9), BP (b), XT ((), and
DCA (1). The solid and dotted lines show the yield of picene 2
and consumption of dinaphthylethane 3, respectively.
In a small-scale preparation, a mixture of dinaphthy-
lethane 3 (0.25 mmol) and 9F (0.50 mmol) in CHCl3 (50
mL) was irradiated with 350-nm fluorescent lamps for 38.5
h. After chromatographic separation, picene 2 was isolated
in 14% yield. (Since 51% of dinaphthylethane 3 was
recovered, the product yield based on consumed starting
material was 28%.) Larger scale preparation was also
conducted using typical experimental procedures outlined
as follows. A solution of dinaphthylethane 3 (9.7 mmol)
and 9F (29 mmol) in CHCl3 (450 mL) was irradiated with a
450-W high-pressure mercury arc lamp under N2 atmo-
sphere. After 48 h of irradiation, the solvent was removed
under reduced pressure and the residue was washed with
Subsequently, the sensitized photolysis of dinaphthy-
lethane 3 was performed using xanthone (XT), benzophe-
none (BP), 9-fluorenone (9F), and 9,10-dicyanoantharacene
(3) Mitsuhashi, R.; Suzuki, Y.; Yamanari, Y.; Mitamura, H.;
Kambe, T.; Ikeda, N.; Okamoto, H.; Fujiwara, A.; Yamaji, M.;
Kawasaki, N.; Maniwa, Y.; Kubozono, Y. Nature 2010, 464, 76.
(4) For some reported picene syntheses, see: (a) Mallory, F. B.;
Mallory, C. W. Org. React. 1984, 30, 1. (b) Harvey, R. G.; Pataki, J.;
Cortez, C.; Di Raddo, P.; Yang, C. X. J. Org. Chem. 1991, 56, 1210. (c)
Minuti, L.; Taticchi, A.; Gacs-Baitz, E.; Marrocchi, A. Tetrahedron
1998, 54, 10891. (d) Some, S.; Dutta, B.; Ray, J. K. Tetrahedron Lett.
2006, 47, 1221. (e) Nakano, Y.; Saito, M.; Nakamura, H. WO
2010016511 A1 20100211, 2010; Chem. Abstr. 2010, 152, 276730.
(5) Slocum, G. H.; Schuster, G. B. J. Org. Chem. 1984, 49, 2177.
Org. Lett., Vol. 13, No. 10, 2011
2759

CHCl3 to afford picene 2 (15À20% yield based on the
dinaphthylethane 3 used). It is worth noting that no
appreciable impurity was detected using 1H NMR spectro-
scopy in the crude product 2 obtained by the above workup
procedure (Figure S3, Supporting Information). It can be
concluded that the 9F-sensitized photolysis of dinaphthy-
lethane 3 provides a simple and convenient procedure for
the synthesis of picene 2. Higher purity samples of picene 2
suitable for use in the fabrication of organic electronic
devices could be obtained by sublimation of the crude
product under reduced pressure.6
Because the yield of picene 2 from the 9F-sensitized
photolysis of dinaphthylethane 3 was not affected by the
amount of dissolved oxygen (data not shown), any con-
tribution of the triplet state of 9Ftothe formation of picene
2 can be excluded. In order to gain mechanistic insight into
the photoinduced formation of picene, transient absorp-
tion spectra were measured for dinaphthylethane 3 in the
presence of 9F (Figure 3). An intense transient absorption
band with the absorption maximum at 425 nm, assigned to
triplet 9F,7 was seen upon 355-nm laser photolysis of 9F in
CCl4. In contrast, in CHCl3, the intensity of the triplet
absorption of 9F decreased compared to that in CCl4, and
the intensity was not affected by the amount of dinaphthy-
lethane 3. When the 9F-sensitized photolysis of dinaphthy-
lethane 3 was performed in CCl4 as the solvent, only a trace
amount of picene 2 was detected in the photolysate. These
observations indicate the existence of a chemical interac-
tion between the excited singlet state of 9F and CHCl3.
Because picene formation unambiguously proceeds from
dinaphthylethane 3 upon photosensitization with 9F in
CHCl3, chemical intermediates generated from the inter-
action between the excited singlet state of 9F and CHCl3
may play a key role in promoting the pertinent cyclization.
been used to modify both the electronic properties and the
orientations of pentacene cores in the solid state.8 In
addition, sulfur-containing groups9 and cyano gorups10
have been used to enhance the stability of the pentacene
core against exposure to air and light. For benzothieno-
benzothiophene-based organic FETs, long alkyl chains
could be used to modify aggregation of the aromatic nuclei
in the crystalline state.11 It has recently been suggested that
appropriately substituted picenes are also applicable to the
active layer of organic FETs.4e Therefore, derivatization of
picene 2 is ardently desired for elucidation of the electronic
properties of picene-derived materials. However, systema-
tic functionalization of the picene core has rarely been
reported. We have found that functionalized picenes can
be readily prepared in moderate to good yields by conven-
tional substitution and cross-coupling reactions starting
with brominated picene 2-Br (Schemes 2 and 3).
Scheme 2. Preparation of Dibromopicene 2-Br
Subjection of di(bromonaphthyl)ethane 3-Br to the 9F-
sensitized photolysis yielded dibromopicene 2-Br in a 25%
yield. The dibromopicene 2-Br could also be prepared by
direct bromination of picene 2 (Scheme 2). The bromine
atoms were replaced with CN groups using CuCN to afford
2-CN in 70% yield. Palladium-catalyzed cross coupling of
dibromopicene 2-Br with thiophenol12 produced 2-SPh
(53%). The Sonogashira reaction13 using triisopropylsily-
lacetylene and SuzukiÀMiyaura cross-coupling14 using
phenylboronic acid resulted in the formation of 2-TIPS
(86%) and 2-Ph (26%), respectively. Alkyl substituents can
be introduced into an aromatic nucleus by means of the
KumadaÀTamao cross-coupling reaction.15 Thus, dibro-
mopicene 2-Br was reacted with tridecylmagnesium bromide
in the presence of a Pd catalyst to afford the alkyl-sub-
stituted picene, 2-C13 (69%). All of the new functionalized
picenes obtained were characterized by NMR and IR
spectroscopic analyses as well as mass spectrometry.
Figure 3. Transient absorption spectra obtained at 100 ns upon
355-nm laser pulsing in 9F in CCl4 (black line), and in the
absence (blue line) and presence (red line) of dinaphthylethane 3
in CHCl3.
(8) Payne, M. M.; Parkin, S. R.; Anthony, J. E.; Kuo, C.-C.; Jackson,
T. N. J. Am. Chem. Soc. 2005, 127, 4986.
(9) Kaur, I.; Jia, W.; Kopreski, R. P.; Selvarasah, S.; Dokmeci,
M. R.; Pramanik, C.; McGruer, N. E.; Miller, G. P. J. Am. Chem.
Soc. 2008, 130, 16274.
(10) Kuo, M.-Y.; Chen, H.-Y.; Chao, I. Chem.;Eur. J. 2007, 13,
4750.
(11) Ebata, H.; Izawa, T.; Miyazaki, E.; Takimiya, K.; Ikeda, M.;
Kuwabara, H.; Yui, T. J. Am. Chem. Soc. 2007, 129, 15732.
(12) Migita, T.; Shimizu, T.; Asami, Y.; Shiobara, J.; Kato, Y.;
Kosugi, M. Bull. Chem. Soc. Jpn. 1980, 53, 1385.
A large number of functionalized aromatic hydrocar-
bons, namely pentacene-derived ones, have been synthe-
sized withthe aim ofdevelopingnovelmaterials for organic
electronic devices.1 Trialkysilylethynyl functionalities have
(6) Okamoto, H.; Kubozono, Y.; Yamaji, M.; Goda, M. Jpn. Kokai
Tokkyo Koho JP 2010143895, 2010; Chem. Abstr. 2010, 153, 115918.
(7) Carmichael, I.; Hug, G. L. J. Phys. Chem. Ref. Data 1986, 15, 1.
(13) Sonogashira, K. J. Organomet. Chem. 2002, 653, 46.
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ethylene-linked naphthalene chromophores to afford the
picene framework 2. In the 9F-sensitized photolysis of
naphthylphenylethane 4, production of chrysene 5;a
lower phenacene;was confirmed although its yield was
low (∼3%, Scheme 4). Thus, the 9F-sensitized ring-closure
of 1,2-diaryl-substituted ethane would provide a novel and
powerful strategy for construction of phenacene skeletons.
Detailed photophysical studies are underway to clarify the
photoreaction mechanisms. Various functionalized pi-
cenes could be systematically obtained by conventional
substitution and cross-coupling reactions using dibromo-
picene 2-Br as the precursor. Currently, the characteristics
of the new picenes as organic electronics are under
investigation.
Scheme 3. Preparation of Functionalized Picenes
Scheme 4. 9F-Sensitized Irradiation of Naphthylphenylethane 4
Acknowledgment. Part of this work was performed
under the Cooperative Research Program of the “Network
Joint Research Center for Materials and Devices.” H.O.
and M.Y. are grateful for the financial support through
Grants-in-Aid for Scientific Research (KAKENHI) from
JSPS (Nos. 21550134 and 23350059). We are grateful to
the SC-NMR Laboratory of Okayama University for the
NMR spectral measurements. Mr. Takaaki Mikoshiba at
Gunma University is acknowledged for his assistance in
this work.
In summary, the present 9F-sensitized photolysis of
dinaphthylethane 3 providesa simpleand convenient route
to the facile synthesis of picene 2. To the best of our
knowledge, this is the first photochemical cyclization of
Supporting Information Available. Details of experi-
mental procedures; 1H and 13C NMR spectra of the new
compounds. This material is available free of charge via
the Internet at http://pubs.acs.org
(14) Suzuki, A. Acc. Chem. Res. 1982, 15, 178.
(15) Minato, A.; Tamao, K.; Hayashi, T.; Suzuki, K.; Kumada, M.
Tetrahedron Lett. 1980, 21, 845.
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