Synthesis of substituted picenes through Pd-catalyzed cross-coupling reaction/annulation sequences and their physicochemical properties

Article abstract of DOI:10.1021/ol401375n

A novel and versatile synthetic method for picene derivatives is developed using the Pd-catalyzed intramolecular double cyclization of the corresponding 2,3-bis[(1Z)-2-phenylethenyl]-1,4-dichlorobenzenes, which are readily prepared by Suzuki-Miyaura cross-coupling reactions of polyhalobenzenes with (Z)-arylethenylboronates. The physical properties of the obtained picenes can be modified via introducing a variety of functional groups to the picene framework. All compounds are investigated by UV-vis and fluorescence spectroscopic measurements, CV, and DFT calculations as well as X-ray diffraction analysis.

Full text of DOI:10.1021/ol401375n

ORGANIC
LETTERS
XXXX
Vol. XX, No. XX
000–000
Synthesis of Substituted Picenes through
Pd-Catalyzed Cross-Coupling Reaction/
Annulation Sequences and Their
Physicochemical Properties
Ning-hui Chang,† Xi-chao Chen,† Hikaru Nonobe,† Yasuhiro Okuda,† Hiroki Mori,†
Kiyohiko Nakajima,‡ and Yasushi Nishihara*,†,§
Division of Earth, Life, and Molecular Sciences, Graduate School of Natural Science and
Technology, Okayama University, 3-1-1 Tsushimanaka, Kita-ku, Okayama 700-8530,
Japan, Japan Science and Technology Agency, ACT-C, 4-1-8 Honcho, Kawaguchi,
Saitama 332-0012, Japan, and Department of Chemistry, Aichi University of Education,
1 Hirosawa, Igaya-cho, Kariya, Aichi 448-8542, Japan
ynishiha@okayama-u.ac.jp
Received May 16, 2013
ABSTRACT
A novel and versatile synthetic method for picene derivatives is developed using the Pd-catalyzed intramolecular double cyclization of the corresponding
2,3-bis[(1Z)-2-phenylethenyl]-1,4-dichlorobenzenes, which are readily prepared by SuzukiꢀMiyaura cross-coupling reactions of polyhalobenzenes with
(Z)-arylethenylboronates. The physical properties of the obtained picenes can be modified via introducing a variety of functional groups to the picene frame-
work. All compounds are investigated by UVꢀvis and fluorescence spectroscopic measurements, CV, and DFT calculations as well as X-ray diffraction analysis.
Among the fused polycyclic compounds, [n]phenacenes,
arm-chair edged benzenoid compounds possessing ex-
tended π-conjugation, have attracted a great deal of
attention as an active layer in organic field-effect transis-
tors (OFETs)1 because of their mechanical flexibility,
lightweight, large-area coverage, ambipolar property,
and low-cost/low-temperature fabrication process. Picene
([5]phenacene; Figure 1) represents a novel and promising
class of materials for organic electronics.2 However, the
systematic modification of a picene core has rarely been
reported,3 although the development of methods to pre-
parevariouspicenederivativesisof great interestbecauseit
may adjust their optical and electronic properties as well
as their solubility and packing structures in the crystals.4
In addition, there are several critical drawbacks for the
† Okayama University.
‡ Japan Science and Technology Agency.
§ Aichi University of Education.
(1) (a) Sugawara, Y.; Kaji, Y.; Ogawa, K.; Eguchi, R.; Oikawa, S.;
Gohda, H.; Fujiwara, A.; Kubozono, Y. Appl. Phys. Lett. 2011, 98,
013303. (b) Komura, N.; Goto, H.; He, X.; Mitamura, H.; Eguchi, R.;
Kaji, Y.; Okamoto, H.; Sugawara, Y.; Gohda, S.; Sato, K.; Kubozono,
Y. Appl. Phys. Lett. 2012, 101, 083301.
(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) 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. (d) Wang,
Y.; Motta, S. D.; Negri, F.; Friedlein, R. J. Am. Chem. Soc. 2011, 133,
10054. (e) Kawai, N.; Eguchi, R.; Goto, H.; Akaike, K.; Kaji, Y.; Kambe,
T.; Fujiwara, A.; Kubozono, Y. J. Phys. Chem. C 2012, 116, 7983.
(3) (a) Okamoto, H.; Yamaji, M.; Gohda, S.; Kubozono, Y.; Komura,
N.; Sato, K.; Sugino, H.; Satake, K. Org. Lett. 2011, 13, 2758. (b) Kitazawa,
K.;Kochi, T.; Nitani, M.; Ie, Y.;Aso, Y.; Kakiuchi, F.Chem. Lett. 2011, 40,
300. (c) Xia, Y.; Liu, Z.; Xiao, Q.; Qu, P.; Ge, R.; Zhang, Y.; Wang, J.
Angew. Chem., Int. Ed. 2012, 51, 5714. (d) Mallory, F. B.; Mallory, C. W.;
Regan, C. K.; Aspden, R. J.; Ricks, A. B.; Racowski, J. M.; Nash, A. I.;
Gibbons, A. V.; Carroll, P. J.; Bohen, J. M. J. Org. Chem. 2013, 78, 2040.
(4) For examples of pentacene, see: (a) Takahashi, T.; Kitamura, M.;
Shen, B.; Nakajima, K. J. Am. Chem. Soc. 2000, 122, 12876. (b) Payne,
M. M.; Parkin, S. R.; Anthony, J. E.; Kuo, C.-C.; Jackson, T. N. J. Am.
Chem. Soc. 2005, 127, 4986.
r
10.1021/ol401375n
XXXX American Chemical Society

established synthetic methods for picenes, such as limitation
of irradiation for large scale,3a,d multiple steps for their
preparation,3b,d and a requirement of unstable precursors.3c
Therefore, a simple and convenient strategy for the synthesis
of various substituted picene derivatives is highly desirable
in order to promote further investigations into its use in
organic electronics. Herein we report the synthesis, char-
acterization, and physicochemical properties of a series of
novel substituted picenes.
Table 1. Synthesis of the Picene Precursors 3 through
SuzukiꢀMiyaura Coupling Reactions of 1 with 2
entry
2
3
yield (%)
1
2
3
4
5
2a
2b
2c
2d
2e
(R1 = R2 = H)
3a
3b
3c
3d
3e
57
68
67
38
67
(R1 = 3-SiMe3, R2 = H)
(R1 = 3-OMe, R2 = H)
(R1 = 2,4-OMe, R2 = H)
(R1 = H, R2 = Et)
found to be the best. Encouraged by an identical 1H NMR
spectrum of the isolated 4a to that of the commercial
source, a series of picene derivatives 4bꢀe were synthesized
in moderate yields under optimized reaction conditions
(Scheme 2).9
Figure 1. Structure of picene.
An outline for the synthesis of the substituted picene
derivatives 4 is shown in Scheme 1. Although there have
been no examples of the application of Pd-catalyzed CꢀH
arylation to the picene synthesis, to the best of our knowl-
edge, itwouldbe a powerful method for the construction of
the desired framework.5 In order to obtain picene precur-
sors 3, SuzukiꢀMiyaura coupling reaction of 1,4-dichloro-
2,3-diiodobenzene (1) with the stereodefined (Z)-alkenyl-
boronates 2 bearing various substituents was designed.
A series of (Z)-alkenylboronates 2aꢀe were successfully
preparedbyRh-catalyzedstereoselective hydroboration of
terminal alkynes6 or the zirconium-mediated synthesis
from alkynylboronate.7 SuzukiꢀMiyaura coupling reac-
tions of 1 with 2aꢀe catalyzed by PEPPSI-IPr8 gave the
corresponding 3aꢀe in moderate to high yields (Table 1).
Scheme 2. Synthesis of Picenes 4aꢀe
Scheme 1. Retrosynthetic Route to Picene Derivatives 4
It is noteworthy that the structure of compound 4c is
different from our initial expectation that two methoxy
groups would locate in the 3,10-positions by the CꢀH
bond functionalization to avoid a steric congestion. How-
ever, as shown in Figure 2, X-ray structural analysis suc-
cessfully clarified the structure of 4c, in which two OMe
groups are situated at the 1,12-positions.10 Moreover, the
1H NMR measurement of 4c showed a characteristic
singlet at δ 9.92 ppm.
The optical properties of 4aꢀe were studied by UVꢀvis
and steady-state fluorescence spectroscopy. The observed
optical properties are listed in Table 2. As shown in Figure 3(A),
the wavelengths of maximum absorptions (λmaxabs) of 4aꢀe
are ca. 290 nm. The substituted picenes 4bꢀe exhibited
absorption peaks at longer wavelengths, but their molar
Next, we investigated the Pd-catalyzed double cycliza-
tion of 3a through the CꢀH functionalization toward the
synthesis of picene (4a). Among the different catalyst
systems, the in situ generated PdCl2(PCy3)2 from PdCl2-
(NCPh)2 and PCy3 and pivalic acid as the additive was
ꢀ
(5) For reviews, see: (a) Echavarren, A. M.; Gomez-Lor, B.;
ꢀ
ꢀ
Gonzalez, J. J.; Frutos, O. D. Synlett 2003, 585. (b) Alberico, D.; Scott,
M. E.; Lautens, M. Chem. Rev. 2007, 107, 174. (c) Lyons, T. W.; Sanford,
M. S. Chem. Rev. 2010, 110, 1147.
(9) Although the picene precursor 3 from a (Z)-arylethenylboronate
bearing an electron-withdrawing CF3 group in the 3-position was
successfully synthesized, Pd-catalyzed double cyclization resulted in
the formation of a mixture of structural isomers in a ratio of 46:54.
(10) CCDC-932531 (4c) contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge from the
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
(6) Ohmura, T.; Yamamoto, Y.; Miyaura, N. J. Am. Chem. Soc.
2000, 122, 4990.
(7) Nishihara, Y.; Miyasaka, M.; Okamoto, M.; Takahashi, H.; Inoue,
E.; Tanemura, K.; Takagi, K. J. Am. Chem. Soc. 2007, 129, 12634.
(8) O’Brien, C. J.; Kantchev, E. A. B.; Valente, C.; Hadei, N.; Chass,
G. A.; Lough, A.; Hopkinson, A. C.; Organ, M. G. Chem.;Eur. J. 2006,
12, 4743.
B
Org. Lett., Vol. XX, No. XX, XXXX

Figure 2. ORTEP drawing of 4c determined by X-ray crystal-
lography with 30% thermal ellipsoidal plotting. Hydrogen
atoms are omitted for simplicity.
extinction coefficient ε values are smaller compared to that
of 4a. These results indicate that an introduction of the
substituents into a picene framework can affect the physi-
cal properties, since no concentration influence was ob-
served when UVꢀvis spectra of 4aꢀe in different con-
centrations were measured.3,11 The absorption spectra of
the either edged- (as 4b) or side- (as 4c and 4e) substituents
are similar in shape, possessing the main transition around
290 nm and at higher wavelengths the other transitions
appeared as a shoulder.
Figure 3. (A) Absorption spectra (1 ꢁ 10ꢀ5 M) and (B) fluores-
(5 ꢁ 10ꢀ7 M) of 4aꢀe in CH2Cl2.
abs
cence emission spectra with excitation wavelength at λmax
Table 2. UVꢀvisa and Fluorescenceb Data of Picenes 4aꢀe
from 1240/λonset are summarized in Table 3. The electro-
chemical properties of 4aꢀe were also investigated by
cyclic voltammetry (CV). The CV curves were recorded
versus the potential of the Ag/Agþ, which was calibrated
by the ferroceneꢀferrocenium (Fc/Fcþ) redox couple
(ꢀ4.8 eV below the vacuum level).14 The electrochemical
data are also summarized in Table 3. The highest occupied
molecular orbital (HOMO) energy levels were calculated
abs
emc
λmax
ε
λmax
Stokes shift
picenes
(nm)
(Mꢀ1cmꢀ1
)
(nm)
(cmꢀ1
)
Φfd
4a
4b
4c
4d
4e
285
293
290
290
290
94300
56800
49700
55100
43700
378
384
388
391
385
212
274
201
331
273
0.07
0.10
0.06
0.18
0.13
a 1 ꢁ 10ꢀ5 M in CH2Cl2. b 5 ꢁ 10ꢀ7 M in CH2Cl2. c Wavelength of
maximum fluorescence emission. d p-Terphenyl was used as a standard
sample.
from the CV data and the corresponding LUMO levels
opt
were estimated from formula ELUMO = EHOMO þ Eg
.
The observed oxidation waves and no reduction waves in
the CV measurement suggest that all compounds are
p-type semiconductors, which have potent applications
in organic electronics. Moreover, all picene derivatives
exhibited quasi-reversible oxidation wave,15 reflecting that
they possess an excellent electrochemical stability.
Since all the compounds 4aꢀeare fluorescent, we performed
the fluorescence spectral measurements by using the diluted
CH2Cl2 solution (5 ꢁ 10ꢀ7 M), as shown in Figure 3(B). The
abs
results are also summarized in Table 2. Using the λmax
values of picenes as the 0ꢀ0 transition wavelength, the emis-
sion maxima (λmaxem) displayed Stokes shifts by approxi-
mately 4 nm.12 The relative fluorescence quantum yields (Φf)
of 4aꢀe were estimated with Williams’ relative method.13
The substituents in the picene framework can signifi-
cantly affect the Φf values. The Φf values of 4d and 4e were
0.18 and 0.13, respectively. An introduction of the meth-
oxy group decreased the Φf values for 4c. It is uncertain at
present why the Φf value was changed by an introduction
of these substituents.
Picene derivative 4b bearing the substituents in the 3,10-
positions have the similar HOMO energy levels and
slightly narrow optical band gaps than that of a parent
picene4a. These results indicatethatasubstitution effectof
a picene core in the 3,10-positions is rather small. In sharp
contrast, other substituted picenes, 4c, 4d, and 4e, have
lower HOMO energy levels and smaller optical band gaps
than that of 4a. Furthermore, their HOMO levels signifi-
cantly elevate with increasing the number of the substitu-
ents. In these cases, alkyl and methoxy groups introduced
into the picene framework in the 1,12-, 2,11-, and 4,9-
positions act as strong electron-donating groups. New five
picenes 4bꢀe could show better electron transfer capability
in electronic devices since they showed relatively smaller
the band gaps of than picene (3.23 eV).16 Thus we calculated
The absorption band edges (λonset) of picenes 4aꢀe
and the corresponding optical band gaps (Egopt) calculated
(11) Kato, S.; Noguchi, H.; Kobayashi, A.; Yoshihara, T.; Tobita, S.;
Nakamura, Y. J. Org. Chem. 2012, 77, 9120.
(12) Okamoto, H.; Yamaji, M.; Gohda, S.; Sato, K.; Sugino, H.;
Satake, K. Res. Chem. Intermed. 2013, 39, 147.
(13) (a) Fery-Forgues, S.; Lavabre, D. J. Chem. Educ. 1999, 76, 1260.
(b) Suzuki, K.; Kobayashi, A.; Kaneko, S.; Takehira, K.; Yoshihara, T.;
Ishida, H.; Shiina, Y.; Oishi, S.; Tobita, S. Phys. Chem. Chem. Phys.
2009, 11, 9850.
(14) Liu, S.-Y.; Shi, M.-M.; Huang, J.-C.; Jin, Z.-N.; Hu, X.-L.; Pan,
J.-Y.; Li, H.-Y.; Jen, A. K.-Y.; Chen, H.-Z. J. Mater. Chem. A 2013, 1, 2795.
(15) See the Supporting Information.
Org. Lett., Vol. XX, No. XX, XXXX
C

Table 3. Physicochemical Properties of Picenes 4aꢀe
compd
Eonseta (V)
EHOMO (eV)b
ELUMO (eV)c
Egopt/λonset[(eV)d/nm]
EHOMO (eV)e
ELUMO (eV)e
Eg (eV)e
4a
4b
4c
4d
4e
þ0.88
þ0.86
þ0.59
þ0.37
þ0.74
ꢀ5.80
ꢀ5.78
ꢀ5.51
ꢀ5.29
ꢀ5.67
ꢀ2.57
ꢀ2.60
ꢀ2.38
ꢀ2.21
ꢀ2.52
3.23/384
3.18/390
3.13/396
3.08/402
3.15/393
ꢀ5.48
ꢀ5.45
ꢀ5.12
ꢀ4.80
ꢀ5.33
ꢀ1.27
ꢀ1.25
ꢀ1.02
ꢀ0.84
ꢀ1.19
4.21
4.20
4.10
3.96
4.14
a Obtained from cyclic voltammograms in CH2Cl2. Reference electrode: Ag/Agþ. b All of the potentials were calibrated with the Fc/Fcþ
(E1/2 = ꢀ0.12 V measured under identical conditions). Estimated with the following equation: EHOMO (eV) = ꢀ4.92 ꢀ Eonset
.
c Calculated according
. .
d Optical band gap, Egopt = 1240/λonset e Obtained from theoretical calculations.
opt
to the formula ELUMO = EHOMO þ Eg
molecular reorganization energy (λ), which may poten-
tially affect the transport properties.17 From the results of
λh, 4c should be advantageous for efficient carrier trans-
port. However, the calculated transfer integrals (tHOMOs)
of 4c were found to be fairly small, because packing structure
of 4c is less effective for carrier transport, which was quite
different from 4a with high field-effect mobility.18
Electronic structures of novel picenes 4aꢀe are theore-
tically investigated through calculation. The molecular
geometries of 4aꢀe were optimized using density func-
tional theory (DFT) at the B3LYP/6-31G(d) level using
Gaussian 09, Revision A. 02.19 The results are also listed in
Table 3. The frontier molecular orbitals of the optimized
molecules were also calculated, as shown in Figure 4. The
theoretically calculated HOMOꢀLUMO gaps are higher
than those obtained in the UVꢀvis spectroscopic measure-
ments (Egopt) by ca. 1.0 eV. All the HOMOs and LUMOs
of picenes 4aꢀe are evenly delocalized over the entire
molecular π-frameworks. In addition, coefficients of pi-
cenes 4cꢀe reside on the 1,12-, 2,11-, and 4,9-methoxy and
5,8-alkyl groups in the HOMO. On the other hand, the
carbon atoms in the 3,10-position in 4b have nodal planes
in the HOMO. These results clearly support the similarity/
difference of the energylevelsof the frontier orbitals aswell
as the molecular electronic structures among 4aꢀe.
Figure 4. Wave functions for the HOMO and LUMO of 4aꢀe.
intramolecular CꢀH bond functionalization. This methodol-
ogy might also be used for the synthesis of other picene
analogues, for instance, heteroatom-containing picenes
and unsymmetric fused aromatic compounds such as [6]-
phenacene. On the basis of this study, the effects of the
structural variations of substituents on their electronic and
electrochemical properties have emerged. A further elucida-
tion of their physical properties involving the FET characters
is underway in our laboratories.
In summary, we have developed a novel and versatile syn-
thetic method for the synthesis of various picene derivatives
by sequential SuzukiꢀMiyaura coupling and cyclization via
(16) Li, G.; Wu, Y.; Gao, J.; Wang, C.; Li, J.; Zhang, H.; Zhao, Y.;
Zhao, Y.; Zhang, Q. J. Am. Chem. Soc. 2012, 134, 20298.
(17) (a) Bredas, J.-L.; Beljonne, D.; Coropceanu, V.; Cornil, J. Chem.
Rev. 2004, 104, 4971. (b) Sakanoue, K.; Motoda, M.; Sugimoto, M.;
Sakaki, S. J. Phys. Chem. A 1999, 103, 5551.
Acknowledgment. We gratefully thank Profs. Koichi
Mitsudo and Seiji Suga (Okayama University) for the
measurements of CV and Ms. M. Kosaka and Mr. M.
Kobayashi at the Department of Instrumental Analysis,
Advanced Science Research Center, Okayama University,
for the measurements of elemental analyses, respectively.
The SC-NMR Laboratory of Okayama University for the
NMR spectral measurements is gratefully acknowledged.
(18) Takimiya, K.; Shinamura, S.; Osaka, I.; Miyazaki, E. Adv.
Mater. 2011, 23, 4347.
(19) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson,
G. A.;Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.;
Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.;
Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.;
Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.;
Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.;
Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.;
Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.;
Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.;
Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.;
Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth,
G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas,
Supporting Information Available. Copies of 1H NMR
and 13C{1H} NMR spectra for all the new compounds, as
well as details on experimental procedures and character-
ization data. This material is available free of charge via
the Internet at http://pubs.acs.org.
€
O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian, Inc.,
Wallingford, CT, 2009.
The authors declare no competing financial interest.
D
Org. Lett., Vol. XX, No. XX, XXXX