Heptagon-embedded pentacene: Synthesis, structures, and thin-film transistors of dibenzo[d,d′]benzo[1,2-a:4,5-a′]dicycloheptenes

Article abstract of DOI:10.1002/anie.201403509

This study presents a new class of conjugated polycyclic molecules that contain seven-membered rings, detailing their synthesis, crystal structures and semiconductor properties. These molecules have a nearly flat C ₆-C₇-C₆-C₇-C₆ polycyclic framework with a p-quinodimethane core. With field-effect mobilities of up to 0.76cm²V^-1s^-1 as measured from solution-processed thin-film transistors, these molecules are alternatives to the well-studied pentacene analogues for applications in organic electronic devices. All sixes and sevens: A new class of conjugated polycyclic molecules have a nearly flat C₆-C₇-C₆-C ₇-C₆ polycyclic framework with a p-quinodimethane core. With a field-effect mobility of up to 0.76cm²V^-1s ^-1 as measured from solution-processed thin-film transistors, these molecules are alternatives to the pentacene analogues for application in organic electronic devices.

Full text of DOI:10.1002/anie.201403509

Angewandte
Chemie
DOI: 10.1002/anie.201403509
Conjugated Polycycles
Heptagon-Embedded Pentacene: Synthesis, Structures, and Thin-Film
Transistors of Dibenzo[d,d’]benzo[1,2-a:4,5-a’]dicycloheptenes**
Xuejin Yang, Danqing Liu, and Qian Miao*
Abstract: This study presents a new class of conjugated
polycyclic molecules that contain seven-membered rings,
detailing their synthesis, crystal structures and semiconductor
properties. These molecules have a nearly flat C6-C7-C6-C7-C6
polycyclic framework with a p-quinodimethane core. With
field-effect mobilities of up to 0.76 cm2 VÀ1 sÀ1 as measured
from solution-processed thin-film transistors, these molecules
are alternatives to the well-studied pentacene analogues for
applications in organic electronic devices.
C
onjugated polycyclic hydrocarbons containing non-hexag-
onal carbocycles[1] have received considerable attention in
organic chemistry and materials science because of their
novel properties and potential applications. The most widely
studied subgroup of these conjugated polycyclic hydrocar-
bons contains five-membered rings. This group of molecules
include curved p-conjugated molecules known as aromatic
bowls[2,3] (or buckybowls[4]) and electron acceptors[5] as
applied in organic electronics, since the five-membered
rings can not only introduce positive curvature but also
stabilize injected electrons by forming the aromatic cyclo-
pentadienyl anion. Unlike five-membered rings, seven-mem-
bered rings can give rise to saddle-shaped p-molecules with
negative curvature[6] and stabilize holes injected into p-type
organic semiconductors by forming the aromatic cyclohepta-
trienyl cation.[7] However, conjugated polycyclic hydrocar-
bons containing seven-membered rings have been rarely
explored. Herein, we report dibenzo[d,d’]benzo[1,2-a:4,5-
a’]dicycloheptene derivatives (1a–c, Figure 1),[8] which have
an unprecedented pentacyclic conjugated backbone contain-
ing two seven-membered carbocycles.[9] Unlike the recently
reported indenofluorenes (3a,b and 4, Figure 1),[10] 1a–c have
seven-membered rings rather than five-membered rings
replacing two benzene rings in pentacene, a benchmark
Figure 1. Structures of ethynylated dibenzo[d,d’]benzo[1,2-a:4,5-a’]-
dicycloheptenes (1a–c) and related molecules.
organic semiconductor for applications in organic thin-film
transistors (OTFTs). The synthesis, X-ray crystal structures
and OTFTs containing compounds 1a–c are described.
Scheme 1 details the synthesis of molecules 1a–c starting
from compound 5,[11] which was prepared from p-xylene in
four steps by modification of reported methods.[12] Cyanation
of compound 5 was achieved by heating with CuCN to reflux
in DMF to form 6 as a mixture of isomers, which were used in
the subsequent catalytic hydrogenation without separation. In
contrast, lithiation of molecule 5 followed by reaction with
CO2 afforded the corresponding diacid in very poor yield, and
subsequent catalytic hydrogenation of 5 led to debromina-
tion. Hydrolysis of dicyanide 7 resulted in the diacid 8. The
total yield of 8 from p-xylene in seven steps was 49%. In
comparison to this synthesis, the earlier reported preparation
of 8 from phenylacetic acid and pyromellitic dianhydride
required fewer steps but had a much lower total yield (14%),
and involved a byproduct that could lead to explosion.[13]
Double cyclization of diacid 8 with polyphosphonic acid at
elevated temperature and subsequent dehydrogenation
yielded dione 10, which was first reported 40 years ago[13]
but almost neglected afterwards. Addition of various acety-
lide compounds to 10 produced diols 11a–c. Subsequent
reduction of the intermediate diol 11a in THF with a solution
of 37% HCl that was saturated with SnCl2 led to the
formation of a deep purple solution, from which 1a was
isolated as a stable compound in good yield. The same
[*] X. Yang, D. Liu, Prof. Q. Miao
Department of Chemistry,
The Chinese University of Hong Kong
Shatin, New Territories, Hong Kong (China)
E-mail: miaoqian@cuhk.edu.hk
Prof. Q. Miao
Institute of Molecular Functional Materials
(Areas of Excellence Scheme, University Grants Committee)
Hong Kong (China)
[**] We thank Hoi Shan Chan (the Chinese University of Hong Kong) for
the single-crystal X-ray crystallography. This work was supported by
the Research Grants Council of Hong Kong (project number:
GRF402412) and the University Grants Committee of Hong Kong
(project number: AoE/P-03/08).
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201403509.
Angew. Chem. Int. Ed. 2014, 53, 1 – 6
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1
These are not the final page numbers!

.
Angewandte
Communications
Scheme 1. Synthesis of 1a–c. NBS=N-bromosuccinimide. DBN=1,5-
diazabicyclo[4.3.0]non-5-ene.
method was used to prepare 1b and 1c from diols 11b and
11c, respectively, with lower yields.
Figure 2. a) The pentacyclic backbone of 1a in the crystal structure
with partial carbon-atom labeling and some highlighted bond lengths;
b) p-stacking between 1a molecules in the single crystal; c) molecular
packing of 1b as viewed along the c-axis of the unit cell. (Hydrogen
atoms are removed for clarity. Thermal ellipsoids set at 50% proba-
bility, silylethynyl substituents are shown as capped sticks, and
disordered triethyl groups of 1b are shown as dots.)
Two findings related to the stability of 1a–c should be
noted. First, 1a–c appeared unstable on common silica gel or
neutral alumina for unknown reasons. However, these com-
pounds were successfully purified with column chromatog-
raphy using silica gel or neutral alumina that were deactivated
with 6% of water (detailed in the Supporting Information).
Second, it was necessary to keep the concentration of 11b,c at
2 mm or lower to achieve a good yield of 1b,c. When the
concentration of 11b,c in THF was higher, the yield of 1b,c
decreased dramatically and the 1H NMR spectra of the crude
products exhibited broad signals, which suggested polymer-
ization of 1b,c under the acidic conditions. To further
investigate this observation, the stability of 1a–c in solution
(concentration 0.02m) was monitored with 1H NMR spectros-
copy. It was found that after storage of the solutions under
ambient conditions for six days, no changes were apparent in
Crystals of 1a and 1b suitable for single-crystal X-ray
analysis were grown from solutions in hexane and ethyl
acetate.[14] Figure 2a shows the pentacyclic backbone of 1a,
which is essentially flat. Examination of the bond lengths
À
indicates that the central six-membered ring has two short C
À
À
À
C bonds (C6 C6a and C14 C14a: 1.37 ꢀ) and four long C C
À
À
À
À
bonds (C5a C6 and C13a C14: 1.43 ꢀ; C5a C14a and C6a
C13a: 1.45 ꢀ) and is bonded to C5 and C13 by relatively short
À
À
bonds (C5 C5a and C13 C13a: 1.40 ꢀ). These bond lengths
are similar to the corresponding bond lengths in the crystal
structure of 3b,[10a] and are in agreement with a p-quinodi-
1
the H NMR spectra of the solutions of 1a and 1b in CDCl3
(Supporting Information). In contrast, the solution of 1c in
À
CDCl3 turned dark red and exhibited a broad signal in the
aromatic region of the H NMR spectra after storage under
the same conditions for one day. The instability of 1c may be
methane structure. The seven-membered ring contains a C C
1
À
double bond (C15 C16) which measures 1.33 ꢀ, a typical
À
À
bond length for alkenes. In comparison, the C5 C4a, C14a
C15, and C16 C16a bonds in the seven-membered ring
À
À
related to polymerization of the reactive C C double bonds in
the p-conjugated backbone. In contrast, compounds 1a and
1b are more stable, likely because their larger substituents
can hinder polymerization by blocking overlap of the reactive
measure 1.44–1.48 ꢀ and resemble single bonds between two
sp2-hybridized carbon atoms.[15] Unlike its pentacene ana-
logue 2 (Figure 1),[16] which stacks in a two-dimensional face-
to-face p-stacking arrangement, compound 1a forms one-
À
C C double bonds.
2
www.angewandte.org
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2014, 53, 1 – 6
These are not the final page numbers!

Angewandte
Chemie
dimensional offset p-stacks (Figure 2b). In each stack, two
parallel neighbors have roughly two rings overlapped with
a p-to-p distance of 3.47 ꢀ. The non-overlapped space above
and below the pentacyclic backbone is occupied by the
triisopropylsilyl groups of neighboring stacks. The fact that 1a
forms one-dimensional p-stacks rather than two-dimensional
p-stacks is likely related to the substitution position of bulky
triisopropylsilyl groups. With a smaller substituting group, 1b
exhibits a special herringbone-type arrangement (shown in
Figure 2c), where one molecule of 1b has the edge of its
termini contacted with the p-face of a neighboring molecule.
This packing motif involves much less intermolecular overlap
of p-orbitals than the established herringbone packing of
pentacene.
oxidized than the benzene ring in 2 and the five-membered
ring in 3a by forming an aromatic cycloheptatrienyl cation.
To test the semiconductor properties of 1a–c, thin-film
transistors of 1a–c were fabricated by dip-coating or drop-
casting a solution onto an oxidized silicon substrate. High-
quality films of 1a were formed by immersing a SiO2/Si
substrate in a solution of 1a (2 mgmLÀ1) in a solvent mixture
of dichloromethane and acetone (1:1 by volume) and then
pulling it up with a constant speed of 5.4 mmsÀ1. The films of
1a deposited on the SiO2 surface were composed of aligned
crystalline fibers, as shown in the polarized-light micrograph
of Figure 4a. X-ray diffraction patterns from the films of 1a
(Supporting Information) exhibited one peak at a d-spacing
of 11.19 ꢀ (2q = 7.908) and three higher-order peaks at d-
spacings of 5.59 ꢀ, 3.72 ꢀ, and 2.79 ꢀ. These peaks do not
correspond to any diffractions derived from the single-crystal
structure of 1a, and thus indicate a polymorph different from
Molecules 1a–c are deep purple and nonfluorescent in
solution when excited with UV light, and exhibit almost
identical UV/Vis absorption spectra. The UV/Vis absorption
spectra of compounds 1a and 2 are shown in Figure 3 for
comparison. In the visible-light region, 1a exhibits more
Figure 4. a) Reflection polarized-light micrograph of a film of 1a as
dip-coated on SiO2 at a substrate temperature of room temperature.
b) Drain current (IDS) versus gate voltage (VG) with drain voltage (VDS
)
Figure 3. UV/Vis absorption spectra of 0.05 mm solutions of 1a and 2
in dichloromethane.
at À50 V for the best-performing OTFT of 1a measured in air with an
active channel of W=1 mm and L=50 mm.
intense absorption than 2. The longest wavelength absorption
maxima of 1a occurs at l = 587 nm, which is blue-shifted by
55 nm relative to that of 2. To determine the energy levels of
the highest occupied molecular orbital (HOMO) and the
lowest unoccupied molecular orbital (LUMO), the redox
behavior of compound 1a in solution in dichloromethane was
investigated with cyclic voltammetry. The cyclic voltammo-
gram of 1a (Supporting Information) exhibited a reversible
reduction wave and a reversible oxidation wave with half-
wave potentials of À1.66 V and 0.12 V versus ferrocene/
ferrocenium, respectively. Based on these electrochemical
potentials, the HOMO and LUMO energy levels of 1a are
estimated as À4.92 eV and À3.14 eV, respectively.[17] These
energy levels lead to a HOMO–LUMO energy gap of 1.78 eV,
which is in good agreement with the absorption edge at
approximately l = 649 nm (1.91 eV). In comparison, the
HOMO and LUMO energy levels of 2, also estimated from
electrochemical potentials, are À5.17 eV and À3.30 eV,
respectively,[18] and the HOMO and LUMO energy levels of
3a are À5.88 eV and À4.00 eV, respectively.[10b] The higher
HOMO and LUMO energy levels of 1a correspond to the
fact that the seven-membered ring in 1a is more easily
its bulk crystals. The device fabrication was completed by
depositing a layer of gold on the film of 1a through a shadow
mask to form top-contact source and drain electrodes. As
measured in air from these devices, 1a functioned as a p-type
semiconductor with a field-effect mobility in the range of
0.19–0.76 cm2 VÀ1 sÀ1. The highest mobility was extracted from
the transfer I–V curves shown in Figure 4b using the
equation: IDS = (mWCi/2L)(VGÀVT)2, where IDS is the drain
current, m is field-effect mobility, Ci is the capacitance per unit
area (11 nFcmÀ2) for the 300 nm-thick dielectric layer of SiO2,
W is the channel width, L is the channel length, and VG and VT
are the gate and threshold voltage, respectively. It was found
that the mobility of 0.76 cm2 VÀ1 sÀ1 decreased to
0.57 cm2 VÀ1 sÀ1 and 0.39 cm2 VÀ1 sÀ1 after the device was
stored in air for one week and one month, respectively.
Such degradation of mobility can be attributed to the fact that
the thin-film phase gradually changes to the more stable bulk-
crystal phase. This is shown by the X-ray diffractions from the
film stored for one week (Supporting Information), which
indicate the existence of both the thin-film phase and the
bulk-crystal phase of 1a. The thin-film transistors of 1b and
1c exhibited field-effect mobilities of 6 ꢁ 10À4 and 5 ꢁ
10À5 cm2 VÀ1 sÀ1, respectively, for holes. The low mobility of
Angew. Chem. Int. Ed. 2014, 53, 1 – 6
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
3
These are not the final page numbers!

.
Angewandte
Communications
Spain, P. Rempała, M. R. Chin, B. T. King, Angew. Chem. 2010,
122, 409 – 412; Angew. Chem. Int. Ed. 2010, 49, 399 – 402; b) C.-
N. Feng, M.-Y. Kuo, Y.-T. Wu, Angew. Chem. 2013, 125, 7945 –
7948; Angew. Chem. Int. Ed. 2013, 52, 7791 – 7794.
1b is in agreement with its molecular packing, which only has
poor edge-to-face interactions between the p-backbone of
neighboring molecules.
The device exhibits a positive threshold voltage of
approximately 10 V and a large drain current of circa 1 ꢁ
10À5 A at zero gate bias (Figure 4b). The drain current is
suppressed by a positive gate voltage of 12 V to approx-
imately 1 ꢁ 10À9 A, which corresponds to an on/off ratio of
greater than 105 when compared with the on-current obtained
at a gate voltage of À50 V. The large drain current at zero gate
bias and the positive threshold voltage of 1a are similar to
those of the solution-processed OTFTs of 2 reported ear-
lier,[19] and indicate that the film of 1a is already p-doped at
zero gate bias. This observation is in agreement with the fact
that molecule 1a has an even higher HOMO energy level
than 2. To identify the possible dopants, the thin-film
transistors of 1a were then tested under vacuum. It was
found that under vacuum the transistor of 1a exhibited
[2] a) Y. T. Wu, J. S. Siegel, Chem. Rev. 2006, 106, 4843 – 4867;
b) L. T. Scott, Polycyclic Aromat. Compd. 2010, 30, 247 – 259.
[3] For recent examples, see: a) B. D. Steinberg, E. A. Jackson, A. S.
Filatov, A. Wakamiya, M. A. Petrukhina, L. T. Scott, J. Am.
Chem. Soc. 2009, 131, 10537 – 10545; b) T. Amaya, T. Nakata, T.
Hirao, J. Am. Chem. Soc. 2009, 131, 10810 – 10811; c) A. C.
Whalley, K. N. Plunkett, A. A. Gorodetsky, C. L. Schenck, C.-Y.
Chiu, M. L. Steigerwald, C. Nuckolls, Chem. Sci. 2011, 2, 132;
d) T. Amaya, T. Hirao, Chem. Commun. 2011, 47, 10524 – 10535;
e) T.-C. Wu, M.-K. Chen, Y.-W. Lee, M.-Yu. Kuo, Y.-T. Wu,
Angew. Chem. 2013, 125, 1327 – 1331; Angew. Chem. Int. Ed.
2013, 52, 1289 – 1293.
[4] P. W. Rabideau, A. Sygula, Acc. Chem. Res. 1996, 29, 235 – 242.
[5] a) F. G. Brunetti, X. Gong, M. Tong, A. J. Heeger, F. Wudl,
Angew. Chem. 2010, 122, 542 – 546; Angew. Chem. Int. Ed. 2010,
49, 532 – 536; b) D. T. Chase, A. G. Fix, S. J. Kang, B. D. Rose,
C. D. Weber, Y. Zhong, L. N. Zakharov, M. C. Lonergan, C.
Nuckolls, H. M. Haley, J. Am. Chem. Soc. 2012, 134, 10349 –
10352; c) J. Nishida, S. Tsukaguchi, Y. Yamashita, Chem. Eur. J.
2012, 18, 8964 – 8970; d) J. D. Wood, J. L. Jellison, A. D. Finke, L.
Wang, K. N. Plunkett, J. Am. Chem. Soc. 2012, 134, 15783 –
15789; e) J. L. Jellison, C.-H. Lee, X. Zhu, J. D. Wood, K. N.
Plunkett, Angew. Chem. 2012, 124, 12487 – 12490; Angew. Chem.
Int. Ed. 2012, 51, 12321 – 12324; f) H. Xia, D. Liu, X. Xu, Q.
Miao, Chem. Commun. 2013, 49, 4301 – 4303.
[6] a) K. Yamamoto, T. Harada, M. Nakazaki, J. Am. Chem. Soc.
1983, 105, 7171 – 7172; b) K. Yamamoto, T. Harada, Y. Okamoto,
H. Chikamatsu, M. Nakazaki, Y. Kai, T. Nakao, M. Tanaka, S.
Harada, N. Kasai, J. Am. Chem. Soc. 1988, 110, 3578 – 3584; c) K.
Yamamoto, Y. Saitho, D. Iwaki, T. Ooka, Angew. Chem. 1991,
103, 1202 – 1203; Angew. Chem. Int. Ed. Engl. 1991, 30, 1173 –
1174; d) J. Luo, X. Xu, R. Mao, Q. Miao, J. Am. Chem. Soc. 2012,
134, 13796 – 13803; e) K. Kawasumi, Q. Zhang, Y. Segawa, L. T.
Scott, K. Itami, Nat. Chem. 2013, 5, 739 – 744.
[7] H. Xia, D. Liu, K. Song, Q. Miao, Chem. Sci. 2011, 2, 2402 – 2406.
[8] Dibenzo[d,d’]benzo[1,2-a:4,5-a’]dicycloheptene is the name rec-
ommended by the ACS. According to recent IUPAC nomencla-
ture (1998), it should be named as dibenzo[d,d’]benzo[1,2-a:4,5-
a’]di[7]annulene.
essentially the same drain current of approximately 1 ꢁ 10À5
A
at zero gate bias, suggesting that the film is doped not by
oxygen from the air but likely by oxygen species on the SiO2
dielectric surface. To test this hypothesis, the SiO2 surface was
pretreated with a self-assembled monolayer (SAM) of
organosilane. As shown in the Supporting Information,
when the SiO2 surface was modified with phenyltrichlorosi-
lane,[20] the drain current at zero gate bias was reduced to circa
1 ꢁ 10À8 A and the threshold voltage shifted to approximately
3 V. This change is probably because the oxygen species on
the SiO2 were passivated by the SAM of phenyltrichlorosi-
lane. When the SiO2 was modified with 3-(aminopropyl)trie-
thoxysilane,[21] the drain current at zero gate bias was further
reduced to approximately 1 ꢁ 10À10 A and the threshold
voltage shifted to À26 V. This change occurs because the
surface amino groups are known to cause a shift in threshold
voltage to more negative values, presumably by electron
transfer into organic semiconductors.
In summary, this study puts forth a new class of conjugated
polycyclic molecules that contain a linearly annulated C6-C7-
C6-C7-C6 polycyclic framework. The crystal structures of 1a
and 1b indicate that their pentacyclic p-backbone is nearly
flat with a p-quinodimethane core. With bulky substituents,
1a and 1b exhibit robust environmental stability in solution.
It is found that 1a–c function as p-type organic semiconduc-
tors in solution-processed OTFTs with field-effect mobilities
of up to 0.76 cm2 VÀ1 sÀ. These results suggest that heptagon-
embedded conjugated polycyclic hydrocarbons are promising
candidates for organic electronic materials.
[9] A similar pentacyclic conjugated backbone of boron-substituted
heteroarenes has two fewer p-electrons than molecules 1a – c.
See: A. J. Caruso, M. A. Siegler, J. D. Tovar, Angew. Chem. 2010,
122, 4309 – 4313; Angew. Chem. Int. Ed. 2010, 49, 4213 – 4217.
[10] a) D. T. Chase, B. D. Rose, S. P. McClintock, L. N. Zakharov,
M. M. Haley, Angew. Chem. 2011, 123, 1159 – 1162; Angew.
Chem. Int. Ed. 2011, 50, 1127 – 1130; b) D. T. Chase, A. G. Fix,
B. D. Rose, C. D. Weber, S. Nobusue, C. E. Stockwell, L. N.
Zakharov, M. C. Lonergan, M. M. Haley, Angew. Chem. 2011,
123, 11299 – 11302; Angew. Chem. Int. Ed. 2011, 50, 11103 –
11106; c) A. Shimizu, Y. Tobe, Angew. Chem. 2011, 123, 7038 –
7042; Angew. Chem. Int. Ed. 2011, 50, 6906 – 6910.
Received: March 20, 2014
Published online: && &&, &&&&
[11] R. Umeda, S. Miyake, Y. Nishiyama, Chem. Lett. 2012, 41, 215 –
217.
Keywords: conjugation · organic electronics ·
polycyclic aromatic hydrocarbons · semiconductors ·
seven-membered ring
[12] a) M. C. Bonifacio, C. R. Robertson, J.-J. Jung, B. T. King, J. Org.
Chem. 2005, 70, 8522 – 8526; b) Z. Shi, X. Zhang, G. Yang, Z. Su,
Z. Cui, Tetrahedron 2011, 67, 4110 – 4117.
[13] I. Agranat, D. Avnir, J. Chem. Soc. Perkin Trans. 1 1974, 1155 –
1161.
.
[14] CCDC 992241 (1a) and 992242 (1b) contain 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.
[1] For recent examples of conjugated polycyclic hydrocarbons
containing four- and eight-membered rings, see: a) Bharat, R.
´
Bhola, T. Bally, A. Valente, M. K. Cyranski, Ł. Dobrzycki, S. M.
4
www.angewandte.org
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2014, 53, 1 – 6
These are not the final page numbers!

Angewandte
Chemie
[15] The typical bond length for a single bond between two sp2-
hybridized carbon atoms is 1.45 – 1.46 ꢀ. See: E. V. Anslyn,
D. A. Dougherty, Modern Physical Organic Chemistry, Univer-
sity Science Books, Sausalito, 2004, chap. 1, p. 22.
[16] a) J. E. Anthony, J. S. Brooks, D. L. Eaton, S. R. Parkin, J. Am.
Chem. Soc. 2001, 123, 9482 – 9483.
[17] The commonly used HOMO energy level of ferrocene is
À4.80 eV, which is calculated on the basis of an approximation,
neglecting solvent effects, using a work function of 4.6 eV for the
standard hydrogen electrode (SHE) and an electrochemical
potential of 0.2 V for the ferrocene/ferrocenium couple versus
SHE. See: a) J. Pommerehne, H. Vestweber, W. Guss, R. F.
Mahrt, H. Bꢂssler, M. Porsch, J. Daub, Adv. Mater. 1995, 7, 551 –
554; b) B. W. DꢃAndrade, S. Datta, S. R. Forrest, P. Djurovich, E.
Polikarpov, M. E. Thompson, Org. Electron. 2005, 6, 11 – 20.
[18] Z. Liang, Q. Tang, J. Xu, Q. Miao, Adv. Mater. 2011, 23, 1535 –
1539.
[19] a) M. M. Payne, S. R. Parkin, J. E. Anthony, C.-C. Kuo, T. N. J.
Jackson, J. Am. Chem. Soc. 2005, 127, 4986 – 4987; b) S. K. Park,
T. N. Jackson, J. E. Anthony, D. A. Mourey, Appl. Phys. Lett.
2007, 91, 063514.
[20] G. Giri, E. Verploegen, S. C. B. Mannsfeld, S. Atahan-Evrenk,
D. H. Kim, S. Y. Lee, H. A. Becerril, A. Aspuru-Guzik, M. F.
Toney, Z. Bao, Nature 2011, 480, 504 – 508.
[21] S. Kobayashi, T. Nishikawa, T. Takenobu, S. Mori, T. Shimoda, T.
Mitani, H. Shimotani, N. Yoshimoto, S. Ogawa, Y. Iwasa, Nat.
Mater. 2004, 3, 317 – 322.
Angew. Chem. Int. Ed. 2014, 53, 1 – 6
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
These are not the final page numbers!

.
Angewandte
Communications
Communications
Conjugated Polycycles
All sixes and sevens: A new class of
conjugated polycyclic molecules have
a nearly flat C6-C7-C6-C7-C6 polycyclic
framework with a p-quinodimethane core.
With a field-effect mobility of up to
0.76 cm2 VÀ1 sÀ1 as measured from solu-
tion-processed thin-film transistors,
these molecules are alternatives to the
pentacene analogues for application in
organic electronic devices.
X. Yang, D. Liu, Q. Miao*
&&&& — &&&&
Heptagon-Embedded Pentacene:
Synthesis, Structures, and Thin-Film
Transistors of Dibenzo[d,d’]benzo[1,2-
a:4,5-a’]dicycloheptenes
6
www.angewandte.org
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2014, 53, 1 – 6
These are not the final page numbers!