Controlled doping in thin-film transistors of large contorted aromatic compounds

Article abstract of DOI:10.1002/anie.201300209

Bigger and better: The new thin-film organic material octabenzcircumbiphenyl (OBCB; see scheme) forms an active layer in a field effect transistor, which can be switched simultaneously with two different inputs, that is, electrical bias and protonation. C

Full text of DOI:10.1002/anie.201300209

Angewandte
Chemie
DOI: 10.1002/anie.201300209
Materials Chemistry
Controlled Doping in Thin-Film Transistors of Large Contorted
Aromatic Compounds**
Shengxiong Xiao, Seok Ju Kang, Yu Zhong, Shengguo Zhang, Amy M. Scott, Alberto Moscatelli,
Nicholas J. Turro, Michael L. Steigerwald, Hexing Li,* and Colin Nuckolls*
Dedicated to Sandra Turro
+
ꢀ
Herein, we describe a new thin-film organic material that
forms the active layer in an organic field-effect transistor
(OFET)[1–6] and can be switched simultaneously by using two
different inputs, that is, electrical bias and protonation. The
thin materials are formed from a new contorted aromatic
compound (c-OBCB 1) that has an expanded central core
(Scheme 1). This polycyclic aromatic hydrocarbon (PAH) can
be protonated by exposure to acid and the resulting cations
are stable under ambient conditions. In thin-film transistors,
the PAH H formed acts as a chemical oxidant that positions
carriers at the interface of the dielectric layer by a series of
electron transfers. In the protonated films with no applied
gate bias, the device is in the on state, and the carriers can be
depleted from the channel by applying an electrical gate bias
to switch the transistor to the off state. In this way the two
inputs, protonation and electrical bias, can work synergist-
ically in this new type of multimode transistor. The effect is
reversible, and removing the dopants (i.e., protons) restores
the transistors to a typical OFEToperation where the carriers
are accumulated in the channel with a gate bias. The
advantage of molecular-based electronic materials is that
they can be tailored by chemical synthesis to have functions
beyond simply carrying current.[7–15] This approach provides
new information processing strategies with the capacity to
switch,[16] actuate, and sense to modulate conductivity[10,12,13,16]
and a design strategy for organic switches[17,18] employing
chemical inputs.
The dodecyloxy-substituted contorted octabenzocircum-
biphenyl (c-OBCB; 1; Scheme 1) is a ring-expanded version
of a class of electronic materials formed from contorted
aromatics known as contorted hexabenzocoronene (c-HBC;
2).[9] Typical derivatives of c-HBC form hole-transporting
semiconducting thin films and have shown field-effect hole
mobility as high as 1 cm2 Vꢀ1 s.[10,11] The c-OBCB skeleton can
be protonated when exposed to acid, and the resulting
conjugate acids are persistent; they do not degrade or
undergo subsequent irreversible rearrangements.
The design of the ring-expanded c-OBCB 1 was based on
that of c-HBC (2), which when substituted with four
dodecyloxy groups forms a columnar liquid crystalline
phase where the columns align parallel to the substrate.[9]
To synthesize the extremely crowded tris-olefin 5, we use
a Barton–Kellogg olefination,[19–21] which joins the two
pentacene fragments 3 and 4 (Scheme 2). We cyclize 5 by
using a Katz-modified Mallory photocyclization[22,23] to yield
1 (see the Supporting Information for full details of the
synthesis and characterization).
c-OBCB 1 forms a rectangular arrangement of molecular
columns, as seen in the powder X-ray diffractogram (see the
Supporting Information, Figure S1). In a related study, we
have shown that films of the c-OBCB act as the p-type organic
semiconductor in an OFET, and they can serve as a donor
material in an organic photovoltaic device when mixed with
fullerenes. The HOMO (ꢀ5.4 ev) and LUMO (ꢀ3.0 eV) were
measured by using cyclic voltammetry with a ferrocene
standard.[24]
Scheme 1. Dodecyloxy-substituted contorted aromatic compounds,
ring-expanded octabenzocircumbiphenyl (c-OBCB 1) and hexabenzo-
coronene (c-HBC 2).
[*] Dr. S. Xiao, Prof. H. Li, Prof. C. Nuckolls
Department of Chemistry
Optoelectronic Nano Materials and Devices Institute
Shanghai Normal University, Shanghai (China)
E-mail: hexing-Li@shnu.edu.cn
Dr. S. Xiao, Dr. S. J. Kang, Y. Zhong, S. Zhang, Dr. A. M. Scott,
Dr. A. Moscatelli, Prof. N. J. Turro, Dr. M. L. Steigerwald,
Prof. C. Nuckolls
Department of Chemistry
Columbia University, New York, NY 10027 (USA)
E-mail: cn37@columbia.edu
[**] This work was supported through the Center for Re-Defining
Photovoltaic Efficiency Through Molecular-Scale Control, an Energy
Frontier Research Center (EFRC) funded by the U.S. Department of
Energy (DOE), Office of Science, Office of Basic Energy Sciences
under award number DE-SC0001085. This material is also based
upon work supported by the Center on Functional Engineered Nano
Architectonics (FENA) under award number 2009-NT-2048, suba-
ward UCLA 0160 S MB 959 and by the Camille and Henry Dreyfus
Foundation’s Postdoctoral Program in Environmental Chemistry
under award number DRFSCHU CU11-2626. C.N. would like to
thank Ying Wu for supplying material for Figure S2.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201300209.
Angew. Chem. Int. Ed. 2013, 52, 1 – 6
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1
These are not the final page numbers!

.
Angewandte
Communications
exposed to trifluoroacetic acid (Figure S2C in the Supporting
Information), but we detected the protonation through OFET
measurements described below.
The films and solutions containing these cations are stable
in an ambient atmosphere. We have not been able to obtain
a crystal structure to determine the site or sites of protonation
on the c-OBCB. We speculate that the protonation sites are in
the core of the c-OBCB (the red region of 1 in Scheme 1)
because the exterior phenyl groups provide an insulating
sheath around the outside of the molecule.[32] The band at
550 nm in the spectrum of the unprotonated solution and that
of the film of 1 is attributed to the absorbance of the triplet
band in UV/Vis.[32] It is difficult to assign this band in the
protonated spectra owing to the multitude of long-wavelength
absorbances.
Scheme 2. Synthesis of the dodecyloxy-substituted c-OBCB 1. Reaction
conditions: a) PPh3; b) hn, I2, propylene oxide, anhydrous benzene.
In the films exposed to triflic acid, the long-wavelength
absorbance (ca. 700 nm, marked cation in Figure 1B) char-
+
ꢀ
The property that we exploit here is the well-known
ability of coronenes to act as Brønsted bases.[25–30] Our
hypothesis is that c-OBCB would be more easily protonated
because it has an expanded core, and would produce a more
stable, delocalized cation than its smaller aromatic analogues.
Figure 1 and Figure S2 (see the Supporting Information)
show the UV/Vis spectra of solutions (dichloromethane) and
films c-OBCB treated with triflic acid (CF3SO3H). Upon
treatment with acid, the solutions change color from yellow to
deep blue. After exposure to triflic acid, long-wavelength
absorbance is seen in the UV/Vis spectra of both the solution
in dichloromethane and the film (25 nm thick; Figure 1 and
Figure S2B in the Supporting Information). This absorption is
similar to that seen for the aromatic radical cation of
dicoronylene.[31] We see similar long-wavelength features
when trifluoroacetic acid (Figure S2A in the Supporting
Information) or HBr gas are used in solution. We did not
detect these long-wavelength absorbances in films that were
acteristic of the cation, c-OBCB H , is clearly present. The
change in intensity of this absorption with exposure over time
is shown in Figure S2C (see the Supporting Information). The
band at approximately 500 nm, which is indicative of the
unprotonated c-OBCB, is still present, thus implying that only
a fraction of the material is protonated in the films. By
exposing the films to triflic acid at higher temperatures, we
confirmed that only a fraction of the material is protonated;
the spectra of the resulting films contained a more intense
band corresponding to the cation (Figure S2C in the Support-
ing Information). The films do not have sufficient porosity to
allow penetration of the proton and the corresponding
counterions into the bulk of the film. When we neutralize
solutions of the protonated compound the long-wavelength
absorbance disappears, and the original spectrum of the
unprotonated c-OBCB is recovered. When the acid-treated
films are placed in a vacuum, the long-wavelength absorbance
disappears as the acid is removed, thus indicating that the
protonation is reversible and does not chemically degrade the
sample. We were able to repeat this at least ten times.
When protonated through intermolecular electron trans-
fer, coronene and other aromatic compounds form radicals
that can serve as one-electron oxidants in both solution and
the solid state.[25–27,33,34] To confirm the presence of the radical
cation, c-OBCB+C, the EPR spectrum of c-OBCB 1 was
recorded, in the absence of oxygen, both in dichloromethane
and in the solid state, before and after exposure to triflic acid.
The steady-state spectrum is shown in Figure S3 (see the
Supporting Information), and in both protonated cases
a strong, featureless resonance at ca. 3480 G is observed
that is typical of carbon-centered radicals. We do not observe
any hyperfine coupling in these spectra at room temperature
under these conditions; however, the resolution of the EPR
spectrum and the intensity of hyperfine couplings are
sensitive to the environment and influenced by sample
concentration, temperature, and the physical properties of
the solvent, therefore varying these parameters empirically
may result in a more resolved EPR profile.[25–27,33,34] Treat-
ment of c-OBCB 1 with either triflic acid or trifluoroacetic
acid results in qualitatively similar EPR spectra, however, the
magnitude of the EPR signal is greater in the triflic acid case
(when equivalent molar amounts of the acids were used).
Figure 1. A) Comparison of the UV/Vis spectra of c-OBCB 1 in solution
(1ꢀ10ꢀ5 m in CH2Cl2, 1 cm path length) before (red curve) and after
(green curve) addition of triflic acid (15 mL to 3 mL of solution).
B) UV/Vis of a thin film of c-OBCB 1 on quartz before (red curve) and
after (green curve) exposure to triflic acid vapor.
2
www.angewandte.org
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2013, 52, 1 – 6
These are not the final page numbers!

Angewandte
Chemie
Triflic acid itself is not an oxidant, but in the presence of an
oxidizing agent, or in the presence of UV radiation and
oxygen, the radical cations of dibenzo-p-dioxins have been
observed.[34] In this case and in several other examples, in the
absence of oxygen the radical cation still persists.[33] The
level as the unprotonated device at Vg = 0 V in Figure 2B. As
a positive gate bias is applied, the holes are depleted and the
device can be converted into the off state. The mobility, on/off
ratio, and threshold voltage are 7 ꢀ 10ꢀ4 cm2 Vꢀ1 sꢀ1, 1.5 ꢀ 103,
and 88 V, respectively. Importantly, the device is in the on
state after exposure to trifluoroacetic acid, and the gate
electrode can deplete the carriers in the channel. This is
opposite from the operation of typical organic field-effect
transistors in which carriers are introduced by application of
a gate bias voltage. The reversibility with respect to acid
treatment and removal, which we observed in the optical
behavior of c-OBCB (see above), is observed in the electrical
behavior of these devices. After the acid-treated devices are
placed in a vacuum for a few hours, the device behaves
qualitatively as it did before treatment with acid. The carriers
are now no longer in the channel and the device operates as
a standard OFET where a bias introduces the carriers. There
are some quantitative differences in the absolute current
levels and mobility in the devices. This data is shown in
Figure S4 in the Supporting Information. We were able to
repeat this process four times.
When triflic acid, the stronger acid, is used the device is
also very conductive. Figure 3 shows the performance of
a device after it has been exposed to triflic acid vapor for
5 min. In the case of triflic acid the device is so heavily doped
that it cannot be turned off with a gate bias. The resistance of
the treated film is six orders of magnitude lower than that of
the untreated film (VG = 0 V). We can also reverse this
process by applying a vacuum to the sample.
The origin of the effect of the doping process with acid is
twofold. 1) As is shown in Figure 2A, the layer of protonated
material is on the surface of the film and in an OFET
configuration with the source and drain
mechanism for oxidation in the presence of triflic acid as
+
ꢀ
a Brønsted acid, to form c-OBCB H C is shown by the
following equations:
c-OBCB þ CF3SO3H Ð c-OBCBꢀHþ þ CF3SO3
ð1Þ
ð2Þ
ꢀ
c-OBCBꢀHþ þ c-OBCB Ð c-OBCBꢀH þ c-OBCB
C
þC
To determine how the layer of protonated PAH in the thin
film influences electrical properties, we fabricated OFETs
with c-OBCB 1 and then subjected the devices to acid vapor
(Figure 2A). Before it is exposed to acid, the device exhibits
characteristics of a typical OFET (Figure 2B and C). The
c-OBCB is a p-type, hole-transporting semiconductor. The
mobility, threshold voltage, and on/off ratio for this device are
2.4 ꢀ 10ꢀ3 cm2 Vꢀ1 sꢀ1, ꢀ5.0 V, and 6.7 ꢀ 103, respectively. The
1/2
mobility is calculated by plotting j IDS
j
versus j VG j and
using the equation: IDS = (mWCi/2L)(VGꢀV0)2 with W (elec-
trode width) = 2 mm and L (channel length) = 100 mm; the
source-drain voltage is fixed at ꢀ100 V, in the saturation
regime of the current–voltage curves (Figure 2B).
The electrical characteristics change dramatically when
the OFETs made from c-OBCB are exposed to trifluoroacetic
acid. This change is shown in Figure 2D and Figure 2E. The
transistor can now be operated in depletion or “turn-off”
mode. It is important to note that at zero gate bias the
protonated device already shows essentially the same current
electrodes. The originally formed cation,
+
ꢀ
c-OBCB H , is not the carrier in the
films, as if it were, at minimum, the
movement of protons would be required
for conduction to occur. The carriers
must be the electrons/holes represented
by the radical cations[35] and produced
through charge transfer as described by
equations (1) and (2).[36] The charge
transport is then the thermoneutral
charge transfer between c-OBCB+C and
c-OBCB. As with the cation, the radical
is not the carrier because then the
movement of a hydrogen atom would
be required for conduction to occur. We
see evidence in the EPR spectra (Fig-
ure S3) in films for the formation of c-
OBCB+C upon protonation. 2) Impor-
tantly, the counterion, trifluoroacetate,
will be localized at the top of the film,
thus creating a dipole layer. We do not
Figure 2. A) Schematic of a thin-film field-effect transistor made from c-OBCB 1 after its
exposure to triflic acid. Electrode width W=2 mm and channel length L=100 mm. B) Transistor
output before treatment with acid. VG =0 and ꢀ100 V in ꢀ20 V steps. C) Transfer characteristics
before treatment with acid. VDS =ꢀ100 V. D) Transistor output after treatment with trifluoro-
acetic acid. VG =0 and 100 V in 20 V steps. E) Transfer characteristics after treatment with acid.
anticipate that the counterions will be
able to penetrate the entire film, based
on the UV/Vis data in Figure 1B, thus
creating a dipole field into the channel in
the same way that a gate bias introduces
VDS =ꢀ100 V.
Angew. Chem. Int. Ed. 2013, 52, 1 – 6
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
3
These are not the final page numbers!

.
Angewandte
Communications
switch the device on. The device can be switched off by
applying a gate bias. These studies open the way for the
development of other types of multimode switching based on
a variety of recognition and binding phenomenon.
Received: January 9, 2013
Revised: February 20, 2013
Published online: && &&, &&&&
Keywords: doping · organic electronic materials ·
.
polycyclic aromatic hydrocarbons · switching · thin films
[1] K. Takimiya, S. Shinamura, I. Osaka, E. Miyazaki, Adv. Mater.
2011, 23, 4347 – 4370.
[2] A. Facchetti, Chem. Mater. 2011, 23, 733 – 758.
[3] Y. Liu, Y. Liu, X. Zhan, Macromol. Chem. Phys. 2011, 212, 428 –
443.
[4] H. Usta, A. Facchetti, T. Marks, Acc. Chem. Res. 2011, 44, 501 –
510.
[5] M. Mas-Torrent, C. Rovira, Chem. Rev. 2011, 111, 4833 – 4856.
[6] C.-a. Di, Y. Liu, D. Zhu, Acc. Chem. Res. 2009, 42, 1573 – 1583.
[7] A. Operamolla, G. M. Farinola, Eur. J. Org. Chem. 2011, 423 –
450.
[8] J. Janata, M. Josowicz, J. Solid State Electrochem. 2009, 13, 41 –
49.
Figure 3. Performance of a thin-film field-effect transistor made from c-
OBCB 1 after its exposure to triflic acid. Electrode width W=2 mm
and channel length L=100 mm (A) S-D bias at 0 gate voltage after
exposure to triflic acid vapor. B) Transfer characteristics after exposure
to triflic acid vapor. VDS =ꢀ100 V.
[9] S. X. Xiao, M. Myers, Q. Miao, S. Sanaur, K. L. Pang, M. L.
Steigerwald, C. Nuckolls, Angew. Chem. 2005, 117, 7556 – 7560;
Angew. Chem. Int. Ed. 2005, 44, 7390 – 7394.
[10] X. Guo, M. Myers, S. Xiao, M. Lefenfeld, R. Steiner, G. S.
Tulevski, J. Tang, J. Baumert, F. Leibfarth, J. T. Yardley, M. L.
Steigerwald, P. Kim, C. Nuckolls, Proc. Natl. Acad. Sci. USA
2006, 103, 11452 – 11456.
[11] S. X. Xiao, J. Y. Tang, T. Beetz, X. F. Guo, N. Tremblay, T.
Siegrist, Y. M. Zhu, M. Steigerwald, C. Nuckolls, J. Am. Chem.
Soc. 2006, 128, 10700 – 10701.
[12] X. F. Guo, S. X. Xiao, M. Myers, Q. Miao, M. L. Steigerwald, C.
Nuckolls, Proc. Natl. Acad. Sci. USA 2009, 106, 691 – 696.
[13] J. Wu, W. Pisula, K. Mꢁllen, Chem. Rev. 2007, 107, 718 – 747.
[14] C. Klinke, A. Afzali, P. Avouris, Chem. Phys. Lett. 2006, 430, 75 –
79.
a field in the channel of a transistor. This field, and the
associated electron transfers, position the carriers at the
interface with the gate dielectric to turn the device on, thus
creating a chemical capacitor on top of the unprotonated
material. To test this theory we made OFET devices where we
spin cast films from acidic solution. This method should
randomly distribute cations and cation radicals in the film but
the films will lack the dipole layer. Although the films have
spectroscopic signatures of the cations, we see only degraded
electrical characteristics.
Herein, we have presented is a new chemical method for
controlling the doping levels in organic semiconductor films.
In contrast to polymer-based electronics, there are few ways
to controllably dope molecular semiconductors. Previously,
doping techniques of OFETs were limited to doping of
thiophene-based polymer semiconductors, mostly poly(3-
hexylthiophene) (P3HT), with electrochemical dopants of
such as tetraethylammonium perchlorate,[37,38] 2,3,5,6-tetra-
fluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ),[39,40]
and 4-ethyl-benzenesulfonic acid (EBSA) acid.[41,42] Doping
of pentacene-based OFETs with F4-TCNQ forms a charge
transfer complex.[43,44] In each case, the material goes from an
off state when undoped to an on state when doped. In each of
these cases, however, the materials have not been switchable
with a gate field. Our study represents a new method for
doping of molecular semiconductors that produces films that
can be turned off with an applied gate field.
[15] J. H. Back, M. Shim, J. Phys. Chem. B 2006, 110, 23736 – 23741.
[16] P. Lutsyk, K. Janus, J. Sworakowski, G. Generali, R. Capelli, M.
Muccini, J. Phys. Chem. C 2011, 115, 3106 – 3114.
[17] S. Huettner, M. Sommer, J. Hodgkiss, P. Kohn, T. Thurn-
Albrecht, R. H. Friend, U. Steiner, M. Thelakkat, ACS Nano
2011, 5, 3506 – 3515.
[18] W. Takashima, T. Murasaki, S. Nagamatsu, T. Morita, K. Kaneto,
Appl. Phys. Lett. 2007, 91, 071905 – 071908.
[19] R. M. Kellogg, Tetrahedron 1976, 32, 2165 – 2184.
[20] D. H. R. Barton, J. Willis, J. Chem. Soc. D 1970, 1225 – 1226.
[21] B. L. Feringa, Acc. Chem. Res. 2001, 34, 504 – 513.
[22] F. B. Mallory, C. S. Wood, J. T. Gordon, L. C. Lindquist, M. L.
Savitz, J. Am. Chem. Soc. 1962, 84, 4361 – 4362.
[23] L. Liu, B. Yang, T. Katz, M. K. Poindexter, J. Org. Chem. 1991,
56, 3769 – 3775.
[24] S. Xiao, S. J. Kang, Y. Wu, S. Ahn, J. B. Kim, Y.-L. Loo, T.
Siegrist, M. L. Steigerwald, H. Li, C. Nuckolls, Chem. Sci., DOI:
10.1039/c3sc50374g.
[25] K. K. Laali, J. J. Houser, M. Zander, J. Chem. Soc. Perkin Trans.
2 1996, 1265 – 1269.
[26] K. K. Laali, J. J. Houser, J. Chem. Soc. Perkin Trans. 2 1994,
1303 – 1308.
[27] K. K. Laali, Chem. Rev. 1996, 96, 1873 – 1906.
[28] J. R. Bolton, A. Carrington, Mol. Phys. 1961, 4, 271 – 272.
[29] H. van Willigen, J. Chem. Phys. 1968, 49, 1190 – 1190.
This study centers on the discovery that Brønsted acids
protonate the contorted OBCB and the resulting cations are
stable. The protonated PAH, in the absence of oxygen,
initiates charge-transfer reactions, resulting in the doping of
the semiconducting film. The counterions localized at the
surface of the film act as a chemical version of a capacitor to
4
www.angewandte.org
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2013, 52, 1 – 6
These are not the final page numbers!

Angewandte
Chemie
[30] H. Ohya-Nishiguchi, H. Ide, N. Hirota, Chem. Phys. Lett. 1979,
66, 581 – 583.
[31] F. Cataldo, S. Iglesias-Groth, A. Manchado, Spectrochim. Acta
Part A 2010, 77, 998 – 1004.
[32] Y. S. Cohen, S. Xiao, M. L. Steigerwald, C. Nuckolls, C. R.
Kagan, Nano Lett. 2006, 6, 2838 – 2841.
[33] R. Rathore, C. Zhu, S. V. Lindeman, J. K. Kochi, J. Chem. Soc.
Perkin Trans. 2 2000, 1837 – 1840.
[34] G. C. Yang, A. E. Pohland in Advances in Chemistry (Ed.: E.
Blair), American Chemical Society, Washington, 1973.
[35] E. de Boer, S. I. Weissman, J. Am. Chem. Soc. 1958, 80, 4549 –
4555.
[36] S. M. Hubig, S. V. Lindeman, J. K. Kochi, Coord. Chem. Rev.
2000, 200 – 202, 831 – 873.
[38] V. I. Arkhipov, P. Heremans, E. V. Emelianova, G. J. Adriaens-
sens, H. Bassler, Appl. Phys. Lett. 2003, 82, 3245 – 3247.
[39] E. Lim, B. J. Jung, M. Chikamatsu, R. Azumi, Y. Yoshida, K.
Yase, L. M. Do, H. K. Shim, J. Mater. Chem. 2007, 17, 1416 –
1420.
[40] L. Ma, W. H. Lee, Y. D. Park, J. S. Kim, H. S. Lee, K. Choa, Appl.
Phys. Lett. 2008, 92, 063310 – 063313.
[41] S. Nam, J. Kim, H. Lee, H. Kim, C.-S. Ha, Y. Kim, ACS Appl.
Mater. Interfaces 2012, 4, 1281 – 1288.
[42] S. Nam, M. Shin, H. Kim, C.-S. Ha, M. Ree, Y. Kim, Adv. Funct.
Mater. 2011, 21, 4527 – 4534.
[43] Y. Abe, T. Hasegawa, Y. Takahashi, T. Yamada, Y. Tokura, Appl.
Phys. Lett. 2005, 87, 153506.
[44] T. Minari, T. Miyadera, K. Tsukagoshi, Y. Aoyagi, H. Ito, Appl.
Phys. Lett. 2007, 91, 053508.
[37] X. Jiang, Y. Harima, K. Yamashita, Y. Tada, J. Ohshita, A.
Kunai, Chem. Phys. Lett. 2002, 364, 616 – 620.
Angew. Chem. Int. Ed. 2013, 52, 1 – 6
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
These are not the final page numbers!

.
Angewandte
Communications
Communications
Materials Chemistry
Bigger and better: The new thin-film
organic material octabenzcircumbiphenyl
(OBCB; see scheme) forms an active
layer in a field effect transistor, which can
be switched simultaneously with two
different inputs, that is, electrical bias and
protonation.
S. Xiao, S. J. Kang, Y. Zhong, S. Zhang,
A. M. Scott, A. Moscatelli, N. J. Turro,
M. L. Steigerwald, H. Li,*
C. Nuckolls*
&&&& — &&&&
Controlled Doping in Thin-Film
Transistors of Large Contorted Aromatic
Compounds
6
www.angewandte.org
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2013, 52, 1 – 6
These are not the final page numbers!