1259
Table 4. Physicochemical properties of [6]phenacenes 6a-6d
opt
Eonset
/Va
EHOMO
/eVb
ELUMO
/eVc
Eg
-
/nm
EHOMO
/eVe
ELUMO
/eVe
Eg
/eVe
edge
[6]Phenacenes
/eVd
6a
6b
6c
6d
+0.84
+0.81
+0.36
+0.76
¹5.76
¹5.73
¹5.29
¹5.68
¹2.57
¹2.58
¹2.17
¹2.56
3.19
3.15
3.12
3.12
389
393
397
397
¹5.41
¹5.39
¹5.02
¹5.36
¹1.39
¹1.39
¹1.22
¹1.34
4.02
4.00
3.80
4.02
aObtained from cyclic voltammograms in CH2Cl2. V vs. Ag/Ag+. bAll the potentials were calibrated with the Fc/Fc+ (E1/2 = ¹0.12 V
measured under identical conditions). Estimated with a following equation: EHOMO (eV) = ¹4.92 ¹ Eonset. cCalculated according to the
formula ELUMO = EHOMO + Egopt. dOptical band gap calculated from -edge, Egopt = 1240/-edge. eObtained from theoretical calculations.
Y. Kubozono, H. Okamoto, A. Fujiwara, M. Yamaji, Appl. Phys.
Okamoto, T. Kambe, N. Ikeda, A. Fujiwara, M. Yamaji, K.
Kawasaki, X. Lee, H. Okamoto, Y. Sugawara, S. Oikawa, A. Ito,
H. Okazaki, T. Yokoya, A. Fujiwara, Y. Kubozono, Appl. Phys.
Kaji, R. Mitsuhashi, H. Okamoto, Y. Sugawara, A. Fujiwara, Y.
Kaji, K. Ogawa, R. Eguchi, H. Goto, Y. Sugawara, T. Kambe, K.
a) N. Komura, H. Goto, X. He, H. Mitamura, R. Eguchi, Y. Kaji,
H. Okamoto, Y. Sugawara, S. Gohda, K. Sato, Y. Kubozono,
Goto, E. Uesugi, S. Hamao, Y. Takabayashi, Y. Kubozono, Org.
a) F. B. Mallory, K. E. Butler, A. C. Evans, E. J. Brondyke, C. W.
2119. b) F. B. Mallory, K. E. Butler, A. Bérubé, E. D. Luzik, Jr.,
C. W. Mallory, E. J. Brondyke, R. Hiremath, P. Ngo, P. J. Carroll,
C. K. Regan, R. J. Aspden, A. B. Ricks, J. M. Racowski, A. I.
R. G. Harvey, J. Pataki, C. Cortez, P. D. Raddo, C. Yang, J. Org.
H. Okamoto, M. Yamaji, S. Gohda, K. Sato, H. Sugino, K.
N.-H. Chang, X.-C. Chen, H. Nonobe, Y. Okuda, H. Mori, K.
C. J. O’Brien, E. A. B. Kantchev, C. Valente, N. Hadei, G. A.
Chass, A. Lough, A. C. Hopkinson, M. G. Organ, Chem.®Eur. J.
[6]Phenacenes 6b and 6d bearing substituents at the 3-
position have similar HOMO energy levels and slightly
narrower optical band gaps than those of 6a. These results
indicate that the effect of substituents at the 3-position of the
[6]phenacene core is rather small. In sharp contrast, the
methoxy-substituted [6]phenacene 6c has almost the same
optical energy gaps (ca. 3.12 eV), but a higher HOMO energy
level than those of 6a.
In order to understand the differences among the electronic
structures, the molecular geometries of 6a-6d were optimized
using density functional theory at the B3LYP/6-31G(d) level,
using Gaussian 09, Revision A. 02. The results are listed in
Table 4. The frontier molecular orbitals of the optimized
molecules were also calculated (Figure S3). All the HOMOs
and LUMOs of the [6]phenacenes, except 6c, are evenly
delocalized over the entire molecular ³-frameworks. The
HOMO coefficient of [6]phenacenes at the 3-position is
relatively small, implying a small inductive effect of alkyl and
TMS groups. In contrast, the HOMO coefficient is strongly
located at the 2,4-positions of the [6]phenacene core of 6c. In
fact, the HOMOs of 6c partially delocalized to the peripheral
groups, whereas the LUMOs were mainly localized on the core.
These results are clearly consistent with the similarities-
differences among the energy levels of the frontier orbitals, as
well as the molecular electronic structures, of 6a-6d, as is
evident from their physicochemical properties.
3
4
5
6
7
8
9
In summary, we synthesized a new family of unsymmetrically
substituted [6]phenacenes via the sequential Suzuki-Miyaura
coupling and intramolecular cyclization. The introduction of
methoxy and alkyl groups into the [6]phenacene framework
increased the solubilities of the [6]phenacenes. Further elucida-
tion of the physical properties, in particular the FET character-
istics, of the obtained [6]phenacenes is currently underway.
10 With [PdCl2(dppf)] the reaction of 3 with 4a resulted in a lower
yield of 5a (55%). In addition, the reaction of 1 with an equimolar
amount of 4 in place of 2 gave a mixture of monocoupled and
dicoupled products. This result strongly indicates that the
sequence of the reagent addition is very critical.
11 a) K. Kamikawa, I. Takemoto, S. Takemoto, H. Matsuzaka,
The authors gratefully thank Ms. Megumi Kosaka and Mr.
Motonari Kobayashi at the Department of Instrumental Analysis,
Advanced Science Research Center, Okayama University for the
measurements of elemental analyses, and the SC-NMR Labo-
ratory of Okayama University for the NMR spectral measure-
ments. Y.N. is grateful to the JNC Petrochemical Corporation for
the generous donation of trimethylsilylacetylene.
12 The main by-product in the cyclization step is the protodechlori-
nated compound.
13 Supporting Information is available electronically on the CSJ-
b) K. Suzuki, A. Kobayashi, S. Kaneko, K. Takehira, T.
Yoshihara, H. Ishida, Y. Shiina, S. Oishi, S. Tobita, Phys. Chem.
References and Notes
1
F. B. Mallory, K. E. Butler, A. C. Evans, C. W. Mallory,
2
a) H. Okamoto, N. Kawasaki, Y. Kaji, Y. Kubozono, A. Fujiwara,
Chem. Lett. 2013, 42, 1257-1259
© 2013 The Chemical Society of Japan