Angular-shaped naphthodifurans, naphtho[1,2-b;5,6-b′]- and naphtho[2,1-b;6,5-b′]-difuran: Are they isoelectronic with chrysene?

Article abstract of DOI:10.1039/c2cc31546g

Although angular-shaped naphthodifurans, naphtho[1,2-b;5,6-b′]- and naphtho[2,1-b;6,5-b′]-difuran, are formally isoelectronic with chrysene as their thiophene counterparts, naphtho[1,2-b;5,6-b′]- and naphtho[2,1-b;6,5-b′]-dithiophene, the HOMO energy leve

Full text of DOI:10.1039/c2cc31546g

View Article Online / Journal Homepage / Table of Contents for this issue
This article is part of the
Aromaticity
web themed issue
Guest editors: Nazario Martín, Michael Haley and
Rik Tykwinski
All articles in this issue will be gathered together
online at
www.rsc.org/cc/aroma

Dynamic Article Links
ChemComm
Cite this: Chem. Commun., 2012, 48, 5671–5673
www.rsc.org/chemcomm
COMMUNICATION
Angular-shaped naphthodifurans, naphtho[1,2-b;5,6-b0]- and
naphtho[2,1-b;6,5-b0]-difuran: are they isoelectronic with chrysene?wz
Masahiro Nakano,y Shoji Shinamura,y Yoshinobu Houchin, Itaru Osaka, Eigo Miyazaki and
Kazuo Takimiya*
Received 29th February 2012, Accepted 16th April 2012
DOI: 10.1039/c2cc31546g
Although angular-shaped naphthodifurans, naphtho[1,2-b;5,6-b0]-
and naphtho[2,1-b;6,5-b0]-difuran, are formally isoelectronic
with chrysene as their thiophene counterparts, naphtho[1,2-b;5,6-b0]-
and naphtho[2,1-b;6,5-b0]-dithiophene, the HOMO energy level
of naphthodifurans is much higher than those of naphthodithio-
phenes and chrysene. The difference in electronic structure in the
ground state can be explained by distinct electronic perturbation
from the outermost aromatic rings.
semiconductors, e.g., diphenyl derivatives (DPh-NDTns),
the linear-shaped NDT1 gave the best mobility of up to
1.5 cm2 Vꢀ1 sꢀ1 9
,
whereas in the polymer semiconductors,
i.e., PNDTn-BTs, the angular-shaped NDT3 gave the highest
mobility of up to 0.8 cm2 Vꢀ1 sꢀ1 10
These results on NDTn
.
isomers indicate that the core electronic structure is one of the
key properties in the development of heteroacenes and their
application to organic semiconducting materials.
We have also recently reported the linear-shaped naphtho-
[2,3-b;5,6-b0]difuran (NDF1) and found that its electronic
structure is much influenced by the poor aromaticity of furan
rings compared to that of the thiophene, resulting in a
relatively low-lying HOMO energy level (EHOMO B ꢀ5.5 eV)
compared to those of NDT1.11 This result poses an interesting
viewpoint: the aromaticity of constituent chalcogenophene
rings influences the whole electronic structure of the fused
aromatic ring system, which then prompts us to elucidate the
electronic structure of angular-shaped naphthodifurans, naphtho-
[1,2-b;5,6-b0]difuran (NDF3)12 and naphtho[2,1-b;6,5-b0]difuran
(NDF4).13 In the present contribution, we discuss the electronic
structures of NDF3 and NDF4 in comparison with corre-
sponding NDT3/NDT4 and also the linear-shaped NDF1
and NDT1.
Acenedithiophenes (AcDTs), such as benzo[1,2-b:4,5-b0]dithiophene
(BDT)1 and anthra[2,3-b:6,7(7,6)-b0]dithiophene (ADT),2 are
prototypical heteroacenes and have been widely utilized as
important p-cores for the development of not only molecular
organic semiconductors but also polymer semiconductors for
organic field-effect transistors (OFETs)3,4 and organic photo-
voltaics (OPVs).5,6 Among the AcDT family including larger
AcDTs, such as tetracenodithiophenes (TDTs) and pentaceno-
dithiophenes (PDTs),7 naphthodithiophenes (NDTs) had been
long missing members owing to the lack of practical methods
for their syntheses. Recently, we have successfully established
efficient and selective syntheses of four isomeric naphtho-
dithiophenes (NDTn, n = 1–4, Fig. 1)8,9 and reported their
properties. Despite the structural similarity, their electronic
structures are significantly different and depend largely on the
molecular shapes; the linear-shaped NDT1 and NDT2
are naphthacene-like with high-lying HOMO energy levels
(EHOMO B ꢀ5.3 eV), whereas the angular-shaped NDT3
and NDT4 are chrysene-like with deep EHOMO of B ꢀ5.8 eV.9
Not just the difference in the electronic features of the NDTns
at the molecular level, the molecular- and polymer- semiconductors
consisting of the NDTn cores showed diverse device charac-
teristics depending on the NDT isomers. Among the molecular
The reported synthesis of NDF3 involves a polyphosphoric
acid-mediated cyclization reaction of 1,5-bis(o-dimethyloxyl-
ethyloxo)naphthalene,14 often resulting in a blackish tar
containing NDF3. To obtain pure NDF3, therefore, a tedious
purification step is usually required. For this reason, we have
Department of Applied Chemistry, Graduate School of Engineering,
Hiroshima University, Higashi-Hiroshima 739-8527, Japan.
E-mail: ktakimi@hiroshima-u.ac.jp; Fax: +81-82-424-5494;
Tel: +81-82-424-7734
w This article is part of the ChemComm ‘Aromaticity’ web themed
issue.
z Electronic supplementary information (ESI) available: Synthetic
details of NDF3 and NDF4, cyclic voltammogram of NDF1/NDT1
and 2,6-dimethoxynaphthalene, energy diagrams of NDT1/3/4 and
NDF1/3/4 based on the DFT-MO calculations. See DOI: 10.1039/
c2cc31546g
Fig. 1 Molecular structures of naphthodithiophenes (NDTns),
naphthodifurans (NDFns), and related hydrocarbons.8
y These authors contributed equally to this work.
c
This journal is The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 5671–5673 5671

angular NDT3/4, the HOMO energy level shifts downwards
and the LUMO level is almost constant, resulting in a larger
HOMO–LUMO gap for NDT3/4 than that of NDT1. In
contrast, for the NDF series, the HOMO energy levels are
not changed so much. As a result, the HOMO energy levels
of NDF3/NDF4 are higher than that of NDT3/NDT4 by
ca. 0.2 eV, whereas HOMO–LUMO gaps estimated from the
absorption edges are almost constant, resulting in high-lying
LUMO energy levels for NDF3/NDF4 than for NDT3/NDT4
(Fig. 3).16
It is somewhat surprising that the tendency of HOMO
energy levels for the NDF- and NDT-series is quite different.
To explain these results, we consider that the overall electronic
structures of acenedichalcogenophenes should be affected by
the aromaticity of outermost chalcogenophene rings. The
ground state structure of NDF3/NDT3 and NDF4/NDT4
can be expressed by two canonical resonance structures, a
chrysene-like or a substituted naphthalene-like structure
(Fig. 4). We speculate that the chrysene-like structure is
dominant over the substituted naphthalene-like structure for
NDT3/NDT4 owing to higher aromaticity of thiophene than
furan. This is in good agreement with the HOMO energy level
of chrysene (5.9 eV below the vacuum level) determined by an
identical method.9 On the other hand, the lower aromaticity of
furan rings makes NDF3/NDF4 (even NDF1) a substituted
naphthalene-like structure, which could make the fused
position of furan rings less influential on their ground state
electronic structures. This consideration is consistent with the
fact that NDF1 and NDF3/NDF4 have similar HOMO
energy levels (ꢀ5.5 to ꢀ5.6 eV). Furthermore, cyclic voltammo-
grams of 1,5-dimethoxynaphthalene and 2,6-dimethoxy-
naphthalene were measured (Fig. S1, ESIz) as model
compounds for ‘‘substituted naphthalenes’’ with oxygen func-
tionalities, and their HOMO energy level was estimated to be
within ꢀ5.5 to ꢀ5.6 eV, which qualitatively supports this
speculation.
Fig. 2 Cyclic voltammograms (a) and absorption spectra (in dichloro-
methane) (b) of NDF3/NDT3 and NDF4/NDT4.
developed an improved synthesis of NDF3 from 2,6-dibromo-
1,5-naphthalenediol via a base-mediated cyclization reaction
of 1,5-diacetoxy-2,6-bis[(trimethylsilyl)ethynyl]naphthalene.15
Analogously, NDF4 was also synthesized from 1,5-dibromo-
2,6-naphthalenediol (see ESIz).14
Cyclic voltammograms of NDF3/NDT3 and NDF4/NDT4
are depicted in Fig. 2(a). Similar to NDT3 and NDT4, the
oxidation waves of NDF3 and NDF4 are irreversible, but the
oxidation of NDFs occurs at a lower potential than that of
NDTs by ca. 0.2 V, which is in sharp contrast to those
of the linear-shaped naphtho[2,3-b;6,7-b0]dichalcogenophenes
(NDF1/NDT1), where the furan analogue (NDF1) shows
much higher oxidation potential (+1.11 V) than the thiophene
analogue (NDT1, +0.96 V) (Fig. S2, ESIz).9b,11 The HOMO
energy levels expected from the oxidation onsets are ꢀ5.6 eV
for NDF3, ꢀ5.8 eV for NDT3, ꢀ5.6 eV for NDF4, and
ꢀ5.7 eV for NDT4. Absorption spectra depicted in
Fig. 2(b), on the other hand, indicate that the HOMO–LUMO
energy gaps estimated from the absorption edge are not quite
different for all the systems (3.4–3.6 eV).
Depicted in Fig. 3 is a schematic representation of HOMO
and LUMO energy levels of NDT1/NDT3/NDT4 (blue lines)
and NDF1/NDF3/NDT4 (red lines). From linear NDT1 to
To get further insight into the electronic structure of the
angular-shaped naphthodichalcogenophenes, we calculate
nucleus-independent chemical sifts (NICSs) for the central
naphthalene part in chrysene, NDF3/NDF4, and NDT3/
NDT4.17 The NICS for the central naphthalene in chrysene
was calculated to be ꢀ7.7 ppm, which is much larger than that
of naphthalene (ꢀ10.0 ppm), clearly indicating that the
aromatic nature of the central naphthalene part in chrysene
is quite reduced, and the aromatic stabilization is indeed
Fig. 3 Schematic representation of the frontier orbitals energy levels
of NDF1/NDT1, NDF3/NDT3 and NDF4/NDT4. The HOMO
energy levels (EHOMO) and HOMO–LUMO energy gaps (DE) were
estimated from oxidation onset in cyclic voltammograms and absorption
edges in the UV-vis absorption spectra. The LUMO energy levels
(ELUMO) were calculated from: ELUMO = EHOMO + DE.
Fig. 4 Two resonance structures of NDF3/NDT3 and NDF4/NDT4.
c
5672 Chem. Commun., 2012, 48, 5671–5673
This journal is The Royal Society of Chemistry 2012

localized in the outermost benzene rings. In sharp contrast, the
NICS for the naphthalene part in NDF3/NDF4 (ꢀ10.5 and
ꢀ10.4 ppm, respectively) is very close to that of naphthalene,
strongly implying the localized aromatic nature on the
naphthalene part in the NDF3 structure. In the case of
NDT3/NDT4, the NICS was calculated to be ꢀ9.3 ppm,
which is in between the two extremes, chrysene and naphthalene.
The value, however, is slightly larger than that of naphthalene,
indicating that reduced aromaticity in the naphthalene part in
NDT3/NDT4 is most likely.
(b) K. C. Dickey, J. E. Anthony and Y. L. Loo, Adv. Mater.,
2006, 18, 1721–1726; (c) J. E. Anthony, Chem. Rev., 2006, 106,
5028–5048; (d) J. E. Anthony, Angew. Chem. Int., Ed., 2008, 47,
452–483; (e) S. Subramanian, S. K. Park, S. R. Parkin,
V. Podzorov, T. N. Jackson and J. E. Anthony, J. Am. Chem.
Soc., 2008, 130, 2706–2707; (f) M.-C. Chen, C. Kim, S.-Y. Chen,
Y.-J. Chiang, M.-C. Chung, A. Facchetti and T. J. Marks,
J. Mater. Chem., 2008, 18, 1029–1036.
5 (a) Y. Liang, Y. Wu, D. Feng, S.-T. Tsai, H.-J. Son, G. Li and
L. Yu, J. Am. Chem. Soc., 2009, 131, 56–57; (b) Y. Liang, D. Feng,
Y. Wu, S.-T. Tsai, G. Li, C. Ray and L. Yu, J. Am. Chem. Soc.,
2009, 131, 7792–7799; (c) L. Huo, J. Hou, S. Zhang, H. Y. Chen
and Y. Yang, Angew. Chem., Int. Ed., 2010, 49, 1500–1503;
(d) Y. Liang, Z. Xu, J. Xia, S.-T. Tsai, Y. Wu, G. Li, C. Ray
and L. Yu, Adv. Mater., 2010, 22, E135–E138; (e) C. Piliego,
T. W. Holcombe, J. D. Douglas, C. H. Woo, P. M. Beaujuge and
J. M. J. Frechet, J. Am. Chem. Soc., 2010, 132, 7595–7597;
(f) Y. Zhang, S. K. Hau, H.-L. Yip, Y. Sun, O. Acton and
A. K. Y. Jen, Chem. Mater., 2010, 22, 2696–2698; (g) Y. Zou,
A. Najari, P. Berrouard, S. Beaupre, B. Reda Aich, Y. Tao and
M. Leclerc, J. Am. Chem. Soc., 2010, 132, 5330–5331; (h) P.-L. T.
Boudreault, A. Najari and M. Leclerc, Chem. Mater., 2011, 23,
456–469.
In summary, we experimentally demonstrated that the
electronic structures of the angular-shaped NDFs are signifi-
cantly different from those of their corresponding NDTs, and
the origin of the difference can be boiled down to the distinct
aromaticity between furan and thiophene that strongly affects
the overall electronic structure of naphthodichalcogenophenes.
As a result, the angular-shaped NDFs should not be iso-
electronic with chrysene and are totally different p-electronic
systems from the thiophene counterparts. Although the
angular-shaped NDF3/NDF4 has not so far been exploited
as the building units for optoelectronic materials,18 their
characteristic features including relatively high-lying HOMO
energy levels make it an interesting ingredient for the
development of new functional p-materials.
This work was financially supported by Grants-in-Aid for
Scientific Research (No. 23245041) from MEXT, Japan, The
Strategic Promotion of Innovative Research and Development
from the Japan Science and Technology Agency, and a
Founding Program for World-Leading R&D on Science and
Technology (FIRST), Japan. One of the authors (SS) is grate-
ful for the research fellowship for young scientists from JSPS.
6 (a) M. T. Lloyd, A. C. Mayer, S. Subramanian, D. A. Mourey,
D. J. Herman, A. V. Bapat, J. E. Anthony and G. G. Malliaras,
J. Am. Chem. Soc., 2007, 129, 9144–9149; (b) Z. Li, Y.-F. Lim,
J. B. Kim, S. R. Parkin, Y.-L. Loo, G. G. Malliaras and
J. E. Anthony, Chem. Commun., 2011, 47, 7617–7619.
7 M. M. Payne, S. A. Odom, S. R. Parkin and J. E. Anthony, Org.
Lett., 2004, 6, 3325–3328.
8 The present numbering of NDT isomers, i.e., NDT1 for
naphtho[2,3-b;6,7-b0]dithiophene, NDT2 for naphtho[2,3-b;7,6-b0]-
dithiophene, NDT3 for naphtho[1,2-b;5,6-b0]dithiophene, and
NDT4 for naphtho[2,1-b;6,5-b0]dithiophene, is just for convenience
without any scientific significance, which follows our recent
publications (ref. 9b and 10b). The same numbering is used for
naphthodifuran (NDF) isomers in this article.
9 (a) S. Shinamura, E. Miyazaki and K. Takimiya, J. Org. Chem.,
2010, 75, 1228–1234; (b) S. Shinamura, I. Osaka, E. Miyazaki,
A. Nakao, M. Yamagishi, J. Takeya and K. Takimiya, J. Am.
Chem. Soc., 2011, 133, 5024–5035.
10 (a) I. Osaka, T. Abe, S. Shinamura, E. Miyazaki and K. Takimiya,
J. Am. Chem. Soc., 2010, 132, 5000–5001; (b) I. Osaka, T. Abe,
S. Shinamura and K. Takimiya, J. Am. Chem. Soc., 2011, 133,
6852–6860; (c) I. Osaka, T. Abe, M. Shimawaki, T. Koganezawa
and K. Takimiya, ACS Macro Lett., 2012, 1, 437–440.
11 M. Nakano, H. Mori, S. Shinamura and K. Takimiya, Chem.
Mater., 2012, 24, 190–198.
Notes and references
1 (a) P. Beimling and G. Kossmehl, Chem. Ber., 1986, 119,
3198–3203; (b) K. Takimiya, Y. Konda, H. Ebata, N. Niihara
and T. Otsubo, J. Org. Chem., 2005, 70, 10569–10571;
(c) T. Kashiki, S. Shinamura, M. Kohara, E. Miyazaki,
K. Takimiya, M. Ikeda and H. Kuwabara, Org. Lett., 2009, 11,
2473–2475.
12 P. R. Dingankar, T. S. Gore and V. N. Gogte, Indian J. Chem.,
1971, 9, 24–30.
13 A. P. Kuriakose and S. Sethna, J. Indian Chem. Soc., 1966, 43, 435–439.
14 A. S. Wheeler and D. R. Ergle, J. Am. Chem. Soc., 1930, 52,
4872–4880.
15 (a) W.-M. Dai and K. W. Lai, Tetrahedron Lett., 2002, 43,
9377–9380; (b) N. Hayashi, Y. Saito, H. Higuchi and K. Suzuki,
J. Phys. Chem. A, 2009, 113, 5342–5347.
2 (a) J. G. Laquindanum, H. E. Katz and A. J. Lovinger, J. Am.
Chem. Soc., 1998, 120, 664–672; (b) B. Tylleman, C. M. L. Vande
Velde, J.-Y. Balandier, S. Stas, S. Sergeyev and Y. H. Geerts, Org.
Lett., 2011, 13, 5208–5211.
3 (a) J. G. Laquindanum, H. E. Katz, A. J. Lovinger and
A. Dodabalapur, Adv. Mater., 1997, 9, 36–39; (b) K. Takimiya,
Y. Kunugi, Y. Konda, N. Niihara and T. Otsubo, J. Am. Chem.
Soc., 2004, 126, 5084–5085; (c) T. Kashiki, E. Miyazaki and
K. Takimiya, Chem. Lett., 2008, 284–285; (d) Q. Meng, L. Jiang,
Z. Wei, C. Wang, H. Zhao, H. Li, W. Xu and W. Hu, J. Mater.
Chem., 2010, 20, 10931–10935; (e) H. Pan, Y. Li, Y. Wu, P. Liu,
B. S. Ong, S. Zhu and G. Xu, Chem. Mater., 2006, 18, 3237–3241;
(f) H. Pan, Y. Wu, Y. Li, P. Liu, B. S. Ong, S. Zhu and G. Xu, Adv.
Funct. Mater., 2007, 17, 3574–3579; (g) H. Pan, Y. Li, Y. Wu,
P. Liu, B. S. Ong, S. Zhu and G. Xu, J. Am. Chem. Soc., 2007, 129,
4112–4113.
16 Theoretical MO calculations also reproduced a similar trend of
HOMO and LUMO energy levels for NDF1/NDT1 NDF3/NDT3
and NDF4/NDT4 (See Fig. S2, ESIz).
17 P. v. R. Schleyer, C. Maerker, A. Dransfeld, H. Jiao and N. J. R. v. E.
Hommes, J. Am. Chem. Soc., 1996, 118, 6317–6318.
18 After submission of this manuscript, synthesis and transistor
characteristics of diphenyl and di(p-octylphenyl) derivatives of
NDF4 were reported; see C. Mitsui, J. Soeda, K. Miwa,
H. Tsuji, J. Takeya and E. Nakamura, J. Am. Chem. Soc., 2012,
134, 5448–5451.
4 (a) M. M. Payne, S. R. Parkin, J. E. Anthony, C. C. Kuo and
T. N. Jackson, J. Am. Chem. Soc., 2005, 127, 4986–4987;
c
This journal is The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 5671–5673 5673