Angewandte
Communications
Chemie
Photoluminescent Materials
Redox Switching of Orthoquinone-Containing Aromatic Compounds
with Hydrogen and Oxygen Gas
Kazuki Urakawa, Michinori Sumimoto, Mitsuhiro Arisawa, Masaki Matsuda,* and
Abstract: Unique redox switching of orthoquinone-containing
pentacyclic aromatic compounds with molecular hydrogen and
oxygen in the presence of a palladium nanoparticle catalyst
were interesting candidates for redox switching, because the
orthoquinone could be reduced to the corresponding hydro-
quinone, and the hydroquinone could also be quickly oxidized
[
7]
(
SAPd) is disclosed. These molecules were predicted by in
to the quinone (Scheme 1). Thus, two different states of a p-
silico screening before synthesis. Efficient protocols for the
synthesis of orthoquinone-containing aromatic compounds by
palladium-mediated homocoupling and the benzoin conden-
sation reaction were developed. Clear switching between
orthoquinone and aromatic hydroquinone compounds was
observed on the basis of their photoluminescence properties.
Furthermore, the twist strain of the orthoquinone moiety could
induce dramatic changes in color and emission.
Scheme 1. Proposed redox-switching system.
H
ighly conjugated polyaromatic compounds have been
widely applied in the development of fluorescent materials,
semiconductor materials, organic electroluminescence devi-
ces, and organic solar-cell devices. For this purpose, a wide
variety of polyaromatic organic compounds have been
designed. Various switching technologies of the p-conjugated
conjugated system could be produced by a redox reaction. For
the establishment of a redox system, usually oxidizing and
reducing reagents, such as 2,3-dichloro-5,6-dicyano-p-benzo-
[
6]
quinone (DDQ), NaBH , and Na S O , are required. How-
4
2
2
3
[1]
molecules have also been reported, such as photochromism,
thermochromism, electrochromism, piezochromism, sol-
vatochromism, and halochromism, as well as redox-
mediated chromism induced by electricity or chemical
ever, the side products derived from these reagents are
potential problems for a reversible redox system. For a clean
and reversible redox system, molecular hydrogen and oxygen
would be ideal reagents. Thus, gaseous hydrogen could be
used for the hydrogenation of the orthoquinone to the
hydroquinone in the presence of a metal catalyst. In contrast,
gaseous oxygen could be used for the oxidation of the
[1]
[2]
[3]
[
4]
[5]
[
2]
[
6]
reagents. The key issue for the design of molecules exhibit-
ing redox switching is the introduction of functional groups
that enable interconversion between the oxidized and
reduced states (OFF and ON). We were convinced that
aromatic compounds containing an orthoquinone moiety
[8]
hydroquinone to the orthoquinone. In this proposed envi-
ronmentally friendly redox system based on molecular
hydrogen and oxygen, the main side product is removable
water, and this system could be made reversible without
purification. Furthermore, this technology could possibly be
applied to the development of photoluminescent materials
that respond to switching between hydrogen and oxygen gas
or to gas sensors for the detection of hydrogen and/or oxygen
by the monitoring of fluorescence. To our knowledge, only
one example of the redox switching of a coumarin derivative
as an optical material has been reported, for which a combi-
nation of oxygen and photoenergy were used for oxidation,
and hydrogen was used in the presence of a Pd catalyst for
[
*] K. Urakawa, Prof. Dr. H. Ishikawa
Division of Organic Chemistry, Department of Chemistry
Graduate School of Science and Technology, Kumamoto University
2
-39-1, Kurokami, Chuo-ku, Kumamoto 860-8555 (Japan)
E-mail: ishikawa@sci.kumamoto-u.ac.jp
Homepage: http://www.sci.kumamoto-u.ac.jp/~ishikawa/ishikawa-
lab/Top.html
Prof. Dr. M. Sumimoto
Division of Computational Chemistry
Graduate School of Science and Engineering, Yamaguchi University
2
-16-1, Tokiwadai, Ube, Yamaguchi, 755-8611 (Japan)
[
9]
Prof. Dr. M. Arisawa
Graduate School of Pharmaceutical Sciences, Osaka University
reduction. Herein, we describe a unique redox-switching
system of newly proposed orthoquinone-containing pentacy-
clic aromatic compounds with molecular hydrogen and
oxygen in the presence of a palladium nanoparticle catalyst,
a sulfur-modified gold-supported palladium catalyst (SAPd).
Our ideal molecules for the establishment of a redox-
switching system should show clear switching properties
between fluorescence emission and fluorescence quenching,
and between a colored state and a colorless state. To discover
possible candidates, we screened several orthoquinone-con-
1
-6 Yamada-oka, Suita, Osaka 565-0871 (Japan)
Prof. Dr. M. Matsuda
Division of Physical Chemistry, Department of Chemistry
Graduate School of Science and Technology, Kumamoto University
2
-39-1, Kurokami, Chuo-ku, Kumamoto 860-8555 (Japan)
E-mail: masaki@sci.kumamoto-u.ac.jp
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ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 7432 –7436