Fast and inexpensive synthesis of pentacene with high yield using 6,13-pentacenequinone as precursor

Article abstract of DOI:10.1016/j.molstruc.2017.10.070

Pentacene is an important semiconductor in the field of organic electronics. In this work is presented an alternative synthesis procedure to obtain pentacene from 6,13-pentacenequinone as a precursor. Synthesis of pentacene was performed in two reactions, Diels-Adler cycloaddition of 6,13-pentacenequinone followed by 6,13-pentacenequinone reduction to pentacene, employing LiAlH₄ as reducing agent. The products were characterized by Fourier Transform Infrared Spectroscopy (FTIR), 1H-Nuclear Magnetic Resonance Spectroscopy (1H-NMR), X-Ray Diffraction (XRD), Thermogravimetric Analysis (TGA) and Ultraviolet–Visible Spectroscopy (UV-VIS). In this work, 6,13-pentacenequinone was synthetized with a high yield (55%) using an alternative method. The optimization process resulted in an overall reduction of reaction time while exhibiting high yield. The method presented here provides an affordable pentacene synthesis route with high purity, which can be further applied for research and development of organic electronic applications.

Full text of DOI:10.1016/j.molstruc.2017.10.070

Journal of Molecular Structure 1154 (2018) 511e515
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Fast and inexpensive synthesis of pentacene with high yield using
6
,13-pentacenequinone as precursor
María L. Mota a
,
b
,
*
, Bibiana Rodriguez , Amanda Carrillo , Roberto C. Ambrosio ,
b
b
c
d
e
c
f
Priscy A. Luque , Marcela Mireles , Israel Vivaldo , Manuel A. Quevedo
CONACYT, Universidad Aut oꢀ noma de Ciudad Ju aꢀ rez, C.P 32310, Ciudad Ju aꢀ rez, Chihuahua, Mexico
Instituto de Ingeniería y Tecnología, Universidad Aut oꢀ noma de Ciudad Ju aꢀ rez, Ave. Del Charro 610, C.P 32310, Ciudad Ju aꢀ rez, Chihuahua, Mexico
Faculty of Electronics, Benem ꢀe rita Universidad Aut oꢀ noma de Puebla, C.P 72000, Puebla, Mexico
Universidad Aut oꢀ noma de Baja California FIAD, C.P 22860, Ensenada, B. C, Mexico
a
b
c
d
e
f
Rochester Institute of Technology, 1 Lomb Memorial Dr. Rochester, NY 14623, USA
Universidad de Sonora. Hermosillo, Sonora, C.P. 83000, Mexico
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 2 June 2017
Received in revised form
Pentacene is an important semiconductor in the field of organic electronics. In this work is presented an
alternative synthesis procedure to obtain pentacene from 6,13-pentacenequinone as a precursor. Syn-
thesis of pentacene was performed in two reactions, Diels-Adler cycloaddition of 6,13-pentacenequinone
18 August 2017
4
followed by 6,13-pentacenequinone reduction to pentacene, employing LiAlH as reducing agent. The
Accepted 18 October 2017
products were characterized by Fourier Transform Infrared Spectroscopy (FTIR), 1H-Nuclear Magnetic
Resonance Spectroscopy (1H-NMR), X-Ray Diffraction (XRD), Thermogravimetric Analysis (TGA) and
UltravioleteVisible Spectroscopy (UV-VIS). In this work, 6,13-pentacenequinone was synthetized with a
high yield (55%) using an alternative method. The optimization process resulted in an overall reduction of
reaction time while exhibiting high yield. The method presented here provides an affordable pentacene
synthesis route with high purity, which can be further applied for research and development of organic
electronic applications.
Available online 21 October 2017
Keywords:
Pentacene
Semiconductor
Organic synthesis
©
2017 Elsevier B.V. All rights reserved.
1
. Introduction
organic semiconductors greatly reduces the processing tempera-
tures, hence enabling the use of polymeric substrates which are
applied in flexible electronic devices. In order to further advance
the development of such devices, active organic materials such as
pentacene must be researched through simple and low cost routes.
Cava and collaborators have reported that one of the precursors of
pentacene is 6,13-pentacenequinone, as a byproduct in the syn-
thesis of quinone compounds. The synthesis was conducted using
TBOX as a reactive intermediate that cyclizes spontaneously with
1,4-benzoquinone in the presence of sodium iodide; 6,13-
pentacenequinone was obtained with low yield (7%) [4]. Bruckner
and Tomasz synthetized pentacene by continuous aldol conden-
sations with two equivalents of o-phtalaldehyde and one equiva-
lent of 1,4-ciclohexanodione. A mixture of Al in cyclohexanol or Al/
Pentacene is a well-known p-type semiconductor in the organic
2
-1 -
electronics field. Its high field effect mobility earound 2.2 cm V
s
1
[1] and stability make it a remarkable material in the develop-
ment of organic transistors. The first successful synthesis of pen-
tacene was reported in 1929 by Clar and collaborators. Although,
yield was not reported, pentacene was obtained via dehydrogena-
tion of 6,14-dihydropentacene using phenantraquinone [2]. Since
the implementation of organic semiconductors in large area elec-
tronics, specifically in light switching speed transistors, pentacene
became an alternative to amorphous silicon due to its similar per-
formance to inorganic semiconductors [3]. Moreover, the use of
HgCl
required a long reaction time (48 h) involving toxic reactants
HgCl ) [5]. (see Scheme 1)
Another example is the synthesis of pentacene with 92% yield
reported from 5,14-dihydropentacene in the presence of Pd/C to
produce hydrogenation [6]. Very high yield was obtained at the
2
mixture in cyclohexanol/carbon tetrachloride. This synthesis
*
Corresponding author.
E-mail addresses: mdllmotago@conacyt.mx (M.L. Mota), al131353@alumnos.
(
2
uacj.mx (B. Rodriguez), amanda.carrillo@uacj.mx (A. Carrillo), roberto.ambrosio@
correo.buap.mx (R.C. Ambrosio), pluque@uabc.edu.mx (P.A. Luque), mmrbme@rit.
edu (M. Mireles), israelvivac@gmail.com (I. Vivaldo), mquevedo@utdallas.edu
(
M.A. Quevedo).
https://doi.org/10.1016/j.molstruc.2017.10.070
022-2860/© 2017 Elsevier B.V. All rights reserved.
0

512
M.L. Mota et al. / Journal of Molecular Structure 1154 (2018) 511e515
Scheme 1. Synthesis of pentacene. (a) Synthesis of 6,13-pentacenequinone, (b) 6,13- pentacenequinone reduction to pentacene.
expense of long reaction time (3 days) and use of a toxic catalyst.
Vets and collaborators reported a synthesis route with 6,13-
pentacenquinone using LiAlH for the reduction of the carbonyl
4
group to produce 6,13-pentacenediol followed by acid dehydrations
to produce pentacene with a 54% yield. The procedure was done for
4
each carbonyl group, first with LiAlH to reduce the carbonyl groups
identification of conjugation with two carbonyl (C]O) groups in
the same ring results in delocalization of the electrons of both
unsaturated groups. Conjugation of phenyl groups may cause a
reduction in frequency of C]O band in the 1672 cm region, with
extended conjugation. Steric effects of C]O groups reduces the
coplanarity of the conjugated system.
p
ꢀ1
to alcohol and then with HCl to expel water from the molecule [7].
The syntheses described in this introduction, involve the presence
The common region for carbonyl absorption band shows the
ꢀ
1
two signature peaks; overtone of C]O stretch at 3350 cm and
ꢀ1
of a metallic catalyst (HgCl
2
, PD/C), long reaction time, inaccessible
C]O stretch peak at 1672 cm . Other absorption peaks in the 6,13-
and expensive reactants or equipment. In this manuscript, we
report the results on the synthesis of 6,13-pentacenequinone and
pentacene. As reported by Clar and collaborators, 6,13-
pentacenequinone was prepared from a Diels-Addler adduct;
however, a higher yield (55%) was achieved through he optimiza-
tion of reaction conditions and purification protocol of the final
product. Pentacene was prepared by performing the reduction of
both 6,13-pentacenequinone carbonyl groups in only one step,
avoiding the isolation of a highly unstable intermediate (6,13-
pentacendiol). The final product was obtained with a 51% yield.
The advances presented in this work allow the simple and low cost
production of pentacene enabling research laboratories to advance
the organic and flexible electronics field.
pentacenequinone spectrum are present and associated to a stretch
of CeH aromatic bond at 3054 cm , the C]C stretch corre-
ꢀ
1
ꢀ
1
ꢀ1
sponding to the ring consist of peaks at 1612 cm , 1443 cm and
ꢀ
1
1396 cm . The absorption of bending vibrations in the aromatic
ketones (CeC]OeC) absorb at a higher frequency at 1277 cm
than 1230-1100 cm region as the literature remark and an aro-
matic ring stretch of C]CeC at 758 cm [8,9]. For pentacene H
NMR spectroscopy was utilized to verify the structure and purity of
the synthesized pentacene (see supplementary material). Further-
more, FTIR was also employed and the results can be seen also in
Fig. 1. Pentacene spectrum exhibited bands assigned to vibration of
C]C conjugated bond around 1632 cm , a strong vibration stretch
of aromatic CeH bond at 841 cm , and strong signals corre-
sponding to the aromatic conjugated C]CeC bond from 671 cm
to 601 cm , according to IR peaks identifications previously re-
ꢀ1
ꢀ1
ꢀ
1
1
ꢀ1
ꢀ
1
ꢀ1
ꢀ1
2
. Results and discussions
ꢀ1
ported [10]. A peak for OeH stretching was observed at 3425 cm
due to the presence of moisture in the pentacene sample.
2.1. Chemical characterization
The attenuated total reflection of Fourier Transform Infrared
2.2. Thermal stability
(
FTIR-ATR) spectrums of 6,13-pentacenequinone and pentacene are
shown in Fig. 1. For the 6,13-pentacenequinone the principal
The
TGA
thermograms
corresponding
to
6,13-
pentacenequinone and pentacene are depicted in Fig. 2. Ther-
mogravimetric analysis revealed that the 6,13-pentacenequinone
ꢁ
compound is thermally stable up to 330 C, the latter is due to its
intermolecular p- p stacking arrangement.
Yuan and collaborators reported a commercially available 6,13-
ꢁ
pentacenequinone compound to be thermally stable up to 360 C
[11]. Furthermore, the TGA results for the 6,13-pentacenequinone
compound synthesized in this work showed a singular deflection,
indicating a simple process of decomposition which suggests a high
purity obtained. The TGA thermogram obtained for pentacene in-
dicates a dynamic process of degradation showing two important
deflections. As shown, the pentacene sample starts to decompose
ꢁ
around 150 C with 7 wt% loss associated to CO removal. However,
ꢁ
the pentacene shows to be stable up to 305 C, before thermal
decomposition occurs as a vaporization process [12].
2.3. Structural characterization
The structural analysis of 6,13 pentacenequinone and pentacene
was performed using XRD (Fig. 3).
Fig. 1. FTIR Spectrum of 6,13-pentacenequinone and pentacene.
For 6,13-pentacenequinone (Fig. 3a) the diffraction peaks

M.L. Mota et al. / Journal of Molecular Structure 1154 (2018) 511e515
513
modified synthesis route which avoids diol reduction.
In this work is reported the optical behavior of pentacene in two
different solvents with different polarity. In this way is possible to
observe changes in the maximum absorption according to solvation
process [19]. The main absorption peak found is related to diketone
at 404 nm (marked in Fig. 4a) which disappeared in the synthesis
process to obtain pentacene, and another characteristics peaks are
emerged at 535 and 579 nm and 531 and 575 nm, it is due when the
pentacene is dispersed in 1-2-dichlorobenzene or chloroform
respectively, due to the extended pentacene's
transitions) (Fig. 4b). Furthermore, a strong absorption bands at
26e346 nm and 313e400 nm ranges are present as vibronic
progressions in the same analysis dispersions. In pentacene UVeVis
absorption spectrum a higher absorption assigned to the * is
p
-conjugation (
pꢀ
p*
3
p-p
observed when chloroform is used as a solvent than 1-2 dichloro-
benzene, thus is possible inferred that pentacene in chloroform
provide a better expression in optical studies by UVeVis related to
its behavior reported by others [19]. Similar studies were reported
showing red-shifted or hyperchromic effect in the optical study
with the use of different common solvents [20].
Fig. 2. TGA thermogram for 6,13-pentacenequinone and pentacene.
ꢁ
located at 11.7, 14.6, 23.6, and 27.7 match to the (002) (012), (112),
3. Experimental
and (104) diffraction planes reported in the JCPDS database (JCPDS
no. 47-2123) and [8,13e15]. The XRD pattern of pentacene is shown
3.1. Materials
in Fig. 3b. The diffractogram shows five distinct Bragg diffraction
ꢁ
peaks located at 2
the (001), (020), (003), (004) and (005) diffraction planes respec-
tively [16,17].
q
¼ 5.9, 12.1, 18.9, 23.7, 27.9 that correspond to
Anhydrous solvents were purchased from Sigma-Aldrich and
used without further purification: Tetrahydrofuran and N,N-dime-
0
0
-tetrabromo-o-xylene, p-benzoquinone
thylformamide. A
Sigma-Aldrich) (Aldrich), sodium iodide (Sigma-Aldrich), N,N-
dimethylformamdide (Sigma-Aldrich), lithium aluminum hydride
Aldrich), hydrochloric acid (37%, J.T. Baker), chloroform (Sigma-
a
,
a
,
a
,
a
(
2.4. Optical characterization
(
Aldrich), sodium sulfite (Aldrich) were recently purchased for this
work.
The UVeVis absorbance spectrum for 6,13-pentacenequinone is
shown in Fig. 4a. The 6,13-pentacenequinone was measured in
chloroform. The absorbance peaks observed at 388 and 404 nm
correspond to the
p
ꢀ
p
* and nꢀ
p
* transitions, with a band gap of
3.2. Synthesis procedure
2
.9e2.96 eV respectively. The peak centered at 388 nm is attributed
to an aromatic ring according to reference [11], and the peak
centered at 404 nm is attributed to the carbonyl groups. The po-
sitions of these two peaks have been observed in these range before
The synthesis of 6,13-pentacenequinone (PQ) started by sub-
stitution of hydrogen atoms for charged sodium ions in the p-
0
0
benzoquinone molecule. Subsequently,
a
,a
,
a
,a
-tetrabromo-o-
[
18,19], however the intensity of n-p* is at least one order of
xylene was added in a molar ratio of 2:1 with respect to p-benzo-
quinone. An intermediate compound between Na and iodide
atoms instantly forms as well as double bonds between TBOX and
PQ. Purification and drying of the resulting PQ, was followed by
solubilization and heating of the compound. The reducing agent
þ
magnitude lower than p-p*, the difference observed here with
respect to other reports [17,18] may be due to higher purity of the 6-
1
3 pentacenequinone obtained in this work, as demonstrated by
RMN. The low band gap value reported here can be a result of the
Fig. 3. X-ray diffraction pattern obtained for a) 6,13-pentacenequinone and b) pentacene.

514
M.L. Mota et al. / Journal of Molecular Structure 1154 (2018) 511e515
Fig. 4. UVeVis absorption spectrum for a) 6,13-pentacenequinone and b) pentacene.
LiAlH
4
was chosen for this reaction due to its ability to reduce
Whatman filtering paper #6, and the solid product was washed
with cold acetone and cold water. A deep blue powder was ob-
tained from this synthesis. Powder was dried under vacuum
quinoid compounds. Previous methodologies tried prior to this
reaction were attempted at room temperature and with slow
addition of LiAlH
4
but pentacene was not successfully synthesized
(ꢀ40 kPa) for 48 h. Yield was 51%, 1H-RMN (500 MHz, TDF)
d (ppm)
in measurable weight. Finally, concentrated HCl is added to this
mixture to expel hydroxyl functional groups from the molecules as
water.
8.98 (m, 4H), 8.14 (m, 4H), 7.75 (m, 4H), 7.35 (s, 2H).
3.5. Chemical, thermal, structural and optical analyses
3.3. 6,13-Pentacenequinone
The chemical structure of 6,13-pentacenequinone and penta-
cene were verified by H NMR using a 500 MHz Jeol spectrometer
1
A 500 ml three-necked round-bottom flask (previously cleaned)
3
(JNM-ECO300) and CDCl as solvent. Infrared spectroscopic mea-
equipped with stirring bar and argon atmosphere was used to
dissolve 0.52 g (4.81 mmol) of p-benzoquinone in 150 ml anhy-
drous DMF. The reaction mixture was stirred at 200 rpm until a
surements were carried out using a FTIR Nicolet Is10 infrared
spectrometer with a diamond ATR attachment. The thermal sta-
bility of compounds was determined in vacuum dried samples and
using a thermal analyzer from Dupont Instruments (TGA 951)
homogeneous solution was achieved. After setting heating bath to
ꢁ
ꢁ
7
0 C in a hotplate, 2.88 g of NaI (19.24 mmol) was added to the
connected to a nitrogen vector gas with heating rate of 10 C/min
ꢁ
reaction flask and the mixture was stirred for 2 h. Next, 4.057 g
9.62 mmol) of TBOX were added and the reaction was continued
for 18 h. The reaction mixture was cooled to room temperature and
0 ml of ice cold water were added to the reaction. The content was
from 30 to 800 C. The crystalline structure of 6,13-
(
pentacenequinone and pentacene were analyzed in a Rigaku Ul-
tima III X-ray diffractometer with CuK
a
(
l
) ¼ 1.54 Å, operated at
ꢁ
5
40 kV and 44 mA. The 2W scan rate was 0.5 /min. The optical
properties were studied using a UV/VIS JENWAY 6850 UV/visible
spectrophotometer.
slowly transferred to a Coors Buchner funnel equipped with a
Whatman filter paper #1 and rinsed with 0.5 M sodium sulfite and
DMF. A bright yellow solid is obtained and dried in an oven at
ꢁ
4
0 kPa and 25 C for 24 h. The obtained yield was 28%, 1H-RMN
4. Conclusions
(
300 MHz, TDF
d
¼ ppm): 8.99 (s, 2H), 8.14 (m, 4H), 7.75 (m, 4H),
7.28 (s, 4H).
We have synthesized 6,13 pentacenequinone and pentacene in
two reactions a high final yield (55% and 51% respectively). The
synthesis route reported in this work simplifies the number of steps
by obtaining both 6,13-pentacenequinone and pentacene through a
single reduction reaction.
3
.4. Pentacene
6
,13-pentacenequinone obtained as described in the previous
1
section was reduced to pentacene (PC), this process will be
described next. A 500 mL three-necked round-bottom flask
equipped with stirring and argon atmosphere (previously cleaned)
was used to prepare a suspension of 0.3 g (0.9729 mmol) 6,13-
pentacenequinone and anhydrous THF. A heating bath was uti-
lized at 60 C, under reflux conditions. LiAlH
added to the dropping funnel. THF was then transferred with a
double tipped needle to the dropping funnel to suspend the
reducing agent. The reducing agent was added in a constant streak
to the PQ/THF suspension and stirred for 30 min. The system was
isolated from light and changed to a cooling dry ice/acetone bath.
Cold concentrated HCl (15 ml) (37%) was quickly added to crude
reaction mixture via dropping funnel and stirred for 15 min. Finally,
the crude reaction solution was poured in a Buchner funnel with a
The chemical characterization performed by FTIR and H MNR
showed the main peaks corresponding to 6,13-pentacenequinone
and pentacene, the purity of the obtained compounds was also
confirmed. The XRD pattern allowed determining the phase for
6,13-pentacenequinone and pentacene products and their stability
which is in agreement with the literature. The UveVis showed the
maximum absorption centered at the expected value for each
product. The use of 1-2- chloroform as solvent to disperse penta-
cene improved the obtained UVeVis spectra when compared to the
use of dichlorobenzene. Both solvents and in different solution-
ꢁ
4
(13.1752 mol) was
dispersion UVeVis analysis showed the extended
p-conjugation
like * transitions mechanism. In summary, the results obtained
p p
ꢀ
in this work contribute to the advancement of active organic
electronic materials and their application. Additionally, the

M.L. Mota et al. / Journal of Molecular Structure 1154 (2018) 511e515
7287e7289, https://doi.org/10.1016/j.tetlet.2004.08.011.
515
advantageous synthesis offered in this work represents a valuable
[
8] V.U. Pandit, S.S. Arbuj, U.P. Mulik, B.B. Kale, Novel functionality of organic
alternative route for the production active organic electronic ma-
terials with high yield and high purity at a low cost.
6
,13-pentacenequinone as a photocatalyst for hydrogen production under
solar light, Environ. Sci. Technol. 48 (7) (2014) 4178e4183, https://doi.org/
0.1021/es405150p.
1
[
9] V.U. Pandit, S.S. Arbuj, Y.B. Pandit, S.D. Naik, S.B. Rane, U.P. Mulik, S.W. Gosavi,
Acknowledgments
B.B. Kale, Solar light driven dye degradation using novel organoeinorganic
(
6,13-pentacenequinone/TiO
2 ) nanocomposite, RSC Adv. 5 (14) (2015)
The authors would like to thank CATEDRAS CONACYT M eꢀ xico
for the financial support provided to ML. Mota (1440). We also wish
to thank J. G. Telles ( H RMN) and the University of Texas at Dallas
for its contribution to this work through the valuable character-
ization. This research project was supported by CONACYT & the
UACJ of Chihuahua M eꢀ xico.
10326e10331, https://doi.org/10.1039/C4RA11920G.
[
10] C. Enengl, S. Enengl, M. Havlicek, P. Stadler, E.D. Glowacki, M.C. Scharber,
M. White, K. Hingerl, E. Ehrenfreund, H. Neugebauer, N.S. Sariciftci, The role of
heteroatoms leading to hydrogen bonds in view of extended chemical sta-
bility of organic semiconductors, Adv. Funct. Mater. 25 (42) (2015)
1
6
679e6688, https://doi.org/10.1002/adfm.201503241.
[
[
11] Y. Yuan, Z. Yu, Y. Li, H. Lu, X. Chen, W. Tu, Z. Ji, Z. Zou, A MoS2/6,13-penta-
cenequinone composite catalyst for visible-light-induced hydrogen evolution
in water, Appl. Catal. B Environ. 181 (2016) 16e23, https://doi.org/10.1016/
j.apcatb.2015.07.030.
12] K.Y. Chen, H.H. Hsieh, C.C. Wu, J.J. Hwang, T.J. Chow, A new type of soluble
pentacene precursor for organic thin-film transistors, Chem. Commun. 46 (27)
(2007) 1065e1067, https://doi.org/10.1039/b616511g.
Appendix A. Supplementary data
Supplementary data related to this article can be found at
https://doi.org/10.1016/j.molstruc.2017.10.070.
[13] C.C. Mattheus, A.B. Dros, J. Baas, G.T. Oostergetel, A. Meetsma, J.L. Boer,
T.T.M. Palstra, Identification of polymorphs of pentacene, Synth. Met. 138
(
2003) 475e481, https://doi.org/10.1016/S0379-6779(02)00467-8.
References
[
14] K. Nakayama, Ch Ohashi, Y. Oikawa, T. Motoyama, H. Yamada, Characteriza-
tion and field-effect transistor performance of printed pentacene films pre-
pared by photoconversion of a soluble precursor, J. Mater. Chem. C 1 (2013)
6244e6251, https://doi.org/10.1039/c3tc31083c.
[15] H.J. Nam, Y.J. Kim, D.Y. Jung, Polymorphs of pentacene and 6-13 pentacene-
quinone in solution and vapor phase growths, Bull. Korean Chem. Soc. 31 (8)
(2010) 2413e2415, https://doi.org/10.5012/bkcs.2010.31.8.2413.
[
1] L.B. Roberson, J. Kowalik, L.M. Tolbert, C. Kloc, R. Zeis, X. Chi, R. Fleming,
C. Wilkins, Pentacene disproportionation during sublimation for field-effect
transistors, J. Am. Chem. Soc. 127 (9) (2005) 3069e3075, https://doi.org/
10.1021/ja044586r.
[
2] E. Clar, E.T. John, Polynuclear aromatic hydrocarbons and their derivatives. V.
Naphthoanthracenes, their oxidation products and a new class of deeply
colored hydrocarbons, Ber. Dtsch. Chem. Ges. 62 (1929) 3021e3029, https://
doi.org/10.1002/cber.19290621113.
[16] K.A. Mohamad, F.N. Rusnan, D.M. Husin Seria, I. Saad, A. Alias, U. Katsuhiro,
F.
Hisashi,
Fabrication
and
Characterization
of
6,13
bis(triisopropylsilylethynyl)-Pentacene Active Semiconductor Thin Films
Prepared by Flow-Coating Method, Phys. Mater. Symp. 1674 (2015), https://
doi.org/10.1063/1.4928820, 020003e1e020003-5.
[
[
3] C.D. Dimitrakopoulos, Y.P.R.L. Malefant, Organic thin film transistors for large
area electronics, Adv. Mater. 14 (2) (2002) 99e117, https://doi.org/10.1002/
1521-4095(20020116)14:2<99::AID-ADMA99>3.0.CO;2e9.
[17] W.H. Lee, D.H. Kim, Y. Jang, J.H. Cho, M. Hwang, Y.D. Park, Solution-process-
able pentacene microcrystal arrays for high performance organic field-effect
transistors, Appl. Phys. Lett. 90 (2007), https://doi.org/10.1063/1.2717087,
132106e1-, 132106-3.
[18] T. Itoh, Low- lying electronic states, spectroscopy and photophysics of linear
para acenequinones, Chem. Rev. 95 (1995) 2351e2368, https://doi.org/
10.1021/cr00039a004.
4] M.P. Cava, A.A. Deana, Y.K. Muth, Condensed cyclobutane aromatic com-
pounds. VIII. The mechanism of fomation of 1,2-dibromobenzocyclobuteno; a
new diels-adler synthesis, J. Am. Chem. Soc. 81 (1959) 6458e6460, https://
doi.org/10.1021/ja01533a032.
[5] V. Bruckner, J. Tomasz, Weitere vereinfachung der pentacensynthese, Acta
Chim. Acad. Sci. Hung 28 (1961) 405e408.
[
6] H. Hart, Y.J. Luo, Linear acene derivatives. New routes to pentacene and
naphtacene and the first synthesis of a triptycene with two antracene moi-
eties, J. Org. Chem. 52 (22) (1987) 4833e4836, https://doi.org/10.1021/
jo00231a001.
[19] T.C. Wen, C.J. Tiao, L.C. Hwang, C.Y. Tsai, Synthesis and third-order nonlinear
optical properties of linear p-acenequinones, Synth. Met. 92 (1998) 235e243,
https://doi.org/10.1016/S0379-6779(98)80092-1.
[20] Y. Zhu, A.P. Kulkarni, S.A. Jenekhe, Phenoxazine-based emissive donor-
acceptor materials for efficient organic light-emitting diodes, Chem. Mater.
17 (21) (2005) 5225e5227, https://doi.org/10.1021/cm050743p.
[7] N. Vets, M. Smet, Y.W. Dehaen, Synthesis and thermolysis of a Diels-Adler
adduct of pentacene and thiophosgene, Tetrahedron Lett. 45 (39) (2004)