Angewandte
Chemie
DOI: 10.1002/anie.201408862
Photochromism Hot Paper
Photochromic Metal–Organic Frameworks: Reversible Control of
Singlet Oxygen Generation**
Jihye Park, Dawei Feng, Shuai Yuan, and Hong-Cai Zhou*
Abstract: The controlled generation of singlet oxygen is of
great interest owing to its potential applications including
industrial wastewater treatment, photochemistry, and photo-
dynamic therapy. Two photochromic metal–organic frame-
works, PC-PCN and SO-PCN, have been developed. A
photochromic reaction has been successfully realized in PC-
PCN while maintaining its single crystallinity. In particular, as
a solid-state material which inherently integrates the photo-
because of their thermal stability, rapid response, and fatigue
[
4a,5]
resistance.
By employing the DTE photochromic switch
and a porphyrinic photosensitizer in a homogeneous bicom-
ponent system, Feringa et al. have recently demonstrated
[
6]
reversible control of singlet oxygen generation.
Attachment of the catalyst onto solid support materials,
such as silica or metal oxides, has shown the potential to
integrate distinctive attributes of both homogeneous and
[7]
chromic switch and photosensitizer, SO-PCN has demon-
heterogeneous catalysis. For instance, a heterogeneous
system of two or more incompatible components could be
of great value because of the ability to accommodate various
functionalities as well as efficient recovery and recyclability.
Along these lines, researchers have strived to design a photo-
sensitizer in a hybrid material form to incorporate these
1
strated reversible control of O generation. Additionally, SO-
2
PCN shows catalytic activity towards photooxidation of 1,5-
dihydroxynaphthalene.
1
S
inglet oxygen ( O ) is a reactive oxygen species (ROS)
2
[
8]
which can be generated by cellular metabolism, redox
chemistry, or photosensitization between a photosensitizer
and molecular oxygen ( O ) upon irradiation. The develop-
features into one system for photocatalysis. However, most
of the approaches suffer from synthetic difficulty, leaching,
3
[1]
[7a,9]
and improper spatial arrangement.
2
ment of a photosensitizer for the generation of singlet oxygen
is of great interest owing to potential applications including
industrial wastewater, photochemical synthesis, and photo-
Metal–organic frameworks (MOFs) are an emerging class
of porous materials and have captured widespread research
interest because of their design flexibility and viability in
potential applications such as gas storage/separation, sensing,
[
2]
dynamic therapy (PDT). While progress has been made to
advance photosensitizers, more recently the design of
a system in which the production of singlet oxygen is can be
controlled or activated, upon environmental changes or
interaction with biomolecules or nanomaterials, has attracted
[
10,11]
and catalysis.
as light-harvesting platforms.
More recently, MOFs have been explored
[12]
Because MOFs provide
highly ordered structures in proximity to each other but not
in direct contact, incorporation of chromophores as linkers to
construct MOFs gives rise to an efficient platform for energy
transfer. As a result of the structural diversity and tunability
of MOFs, it is very convenient to introduce multiple func-
tional moieties into the framework, thus making MOFs as
ideal candidates for realizing cooperative functionalities
[
2a,3]
growing attention.
However, such methods often involve
irreversible or passive interaction, which may lead to
1
imprecise control over O2 generation. In this sense,
a system which inherently bears a photosensitizer and control
functionality could be ideal to achieve controlled generation
of singlet oxygen.
[
13]
based on periodic arrangement on a molecular scale.
Photochromic molecules, which upon photoirradiation
exhibit a reversible transformation between isomers having
different properties, hold considerable promise for optical
switches as a control unit in smart materials. Of the many
photochromic compounds, dithienylethene (DTE) deriva-
tives are one of the most promising class of compounds
Meanwhile, leaching of each component can be alleviated
on account of the strong coordination bond. Moreover, the
porous feature of MOFs allows all the functionalities within
the framework to be accessible by incoming reactants
regardless of their solubility.
Herein, we present two MOFs, namely PC-PCN (photo-
chromic porous coordination network) and SO-PCN (singlet
oxygen-generating porous coordination network) which con-
[
4]
[
*] J. Park, D. Feng, S. Yuan, Prof. Dr. H.-C. Zhou
Department of Chemistry, Texas A&M University
College Station, TX 77843 (USA)
tain
1,2-bis(2-methyl-5-(pyridin-4-yl)thiophen-3-yl)cyclo-
pent-1-ene (BPDTE) as a photochromic switch. Notably,
a molecular dyad system which contains a photochromic
E-mail: zhou@chem.tamu.edu
Homepage: http://www.chem.tamu.edu/rgroup/zhou/
switch and photosensitizer was well established with SO-PCN.
[
**] The project was supported by the Office of Naval Research under
N000141310753 and as part of the Center for Gas Separations
Relevant to Clean Energy Technologies, an Energy Frontier Research
Center funded by the U.S. Department of Energy (DOE), Office of
Science, Office of Basic Energy Sciences under Award Number DE-
SC0001015.
1
The reversible control over O generation through a compe-
2
tition of energy transfer pathways upon irradiation at specific
wavelengths in SO-PCN was studied. Also, SO-PCN was
demonstrated as a heterogeneous catalyst for photooxidation
of 1,5-dihydroxynaphthalene (DHN).
Porphyrin derivatives have been widely used for 1O2
generation because of their well-known photochemistry and
Angew. Chem. Int. Ed. 2014, 53, 1 – 6
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1
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