Multifunctional radical-doped polyoxometalate-based host-guest material: Photochromism and photocatalytic activity

Article abstract of DOI:10.1021/acs.inorgchem.5b00041

An effective strategy to synthesize multifunctional materials is the incorporation of functional organic moieties and metal oxide clusters via self-assembly. A rare multifunctional radical-doped zinc-based host-guest crystalline material was synthesized with a fast-responsive reversible ultraviolet visible light photochromism, photocontrolled tunable luminescence, and highly selective photocatalytic oxidation of benzylic alcohols as a result of blending of distinctively different functional components, naphthalenediimide tectons, and polyoxometalates (POMs). It is highly unique to link π-electron-deficient organic tectons and POMs by unusual POMs anion-π interactions, which are not only conducive to keeping the independence of each component but also effectively promoting the charge transfer or exchange among the components to realize the fast-responsive photochromism, photocontrolled tunable luminescence, and photocatalytic activity.

Full text of DOI:10.1021/acs.inorgchem.5b00041

Article
pubs.acs.org/IC
Multifunctional Radical-Doped Polyoxometalate-Based Host−Guest
Material: Photochromism and Photocatalytic Activity
Jian-Zhen Liao,† Hai-Long Zhang, Sa-Sa Wang, Jian-Ping Yong, Xiao-Yuan Wu, Rongmin Yu,
,‡
†,‡
†
†
†
†
,†
and Can-Zhong Lu*
†Key Laboratory of Design and Assembly of Functional Nanostructures, Fujian Institute of Research on the Structure of Matter,
Chinese Academy of Sciences, Fuzhou, Fujian 350002, P. R. China
‡
Graduate University of Chinese Academy of Sciences, Beijing 100049, P. R. China
*
S Supporting Information
ABSTRACT: An effective strategy to synthesize multifunctional materials is the
incorporation of functional organic moieties and metal oxide clusters via self-assembly. A
rare multifunctional radical-doped zinc-based host−guest crystalline material was
synthesized with a fast-responsive reversible ultraviolet visible light photochromism,
photocontrolled tunable luminescence, and highly selective photocatalytic oxidation of
benzylic alcohols as a result of blending of distinctively different functional components,
naphthalenediimide tectons, and polyoxometalates (POMs). It is highly unique to link π-
electron-deficient organic tectons and POMs by unusual POMs anion−π interactions, which
are not only conducive to keeping the independence of each component but also effectively
promoting the charge transfer or exchange among the components to realize the fast-
responsive photochromism, photocontrolled tunable luminescence, and photocatalytic
activity.
5
INTRODUCTION
materials. However, only a small number of POM-based host−
■
guest crystalline coordination polymers used as heterogeneous
catalysts have been reported;
materials with both photochromic and photocatalytic properties
have rarely been reported to date, let alone radical-doped
Multifunctional crystalline organic−inorganic hybrid materials,
especially the photochromic and photocatalytic materials, have
attracted considerable interest because of their potential
applications in photomechanics, information storage, optical
2a,6
multifunctional crystalline
7
1
POM-based host−guest multifunctional crystalline solid ma-
switches, green catalysis technologies, etc. By incorporation of
terial.
functional organic moieties and metal oxide clusters via self-
assembly, grafting, or intercalation, such hybrid structures are
formed with multiple functionalities and often new features as a
Taking advantage of electronic complementary effects and
popular anion−π interactions, we previously reported for the
first time that multifunctional electron reservoirs (i.e., POMs)
could be captured by π-electron-deficient NDIs-based coordi-
nation complexes through neoteric POMs anion−π inter-
2
result of blending of distinctively different components. It is of
interest to select the appropriate functional building modules to
effectively construct multifunctional crystalline solid materials
with a suitable structural before researching their properties.
The electrochemical, photophysical, photochemical, and
catalytic multifunctional naphthalenediimide (NDI) dye
derivatives are known to be a class of excellent candidates of
π-electron-deficient organic tectons for construction of multi-
functional crystalline materials or metal−organic frameworks
8
actions. Herein, an extremely rare radical-doped zinc-based
material based on functional linear NDI tectons and POM
molecules was synthesized with a fast-responsive reversible
photochromism, which obviously derived from the coactions of
naphthalene diimide and POMs, as well as excellent photo-
catalytic activity toward the selective oxidation of benzylic
alcohol under ambient conditions irradiated by simulated
sunlight. It should be pointed out that the POMs molecules
were embedded into the coordination polymers through
ingenious anion−π interaction and hydrogen bonds, which
not only effectively immobilize and disperse the POMs but
promote the charge transfer or exchange among NDI center,
coordinated other molecules and POMs surface to realize the
reversible photochromism, photocontrolled tunable lumines-
cence, and maintain efficient photocatalytic performance. To
(
MOFs) due to the controllability of the substituent group on
the diimide nitrogens and the reversibility of the electron
transfer of the naphthalene ring. Polyoxometalates (POMs)
3
are prominent building blocks to design multifunctional
materials owing to their numerous advantageous properties;
for instance, POMs are good electron reservoirs that exhibit
rich redox and photoactivity, which undergo potential photo- or
electron-induced electron- and proton-transfer processes, which
can be used to build photochromic or electrochromic
4
materials. Particularly, some POMs themselves are catalytically
effective and have been used as all-important components
toward design and synthesis of various effective catalytic
Received: January 7, 2015
©
XXXX American Chemical Society
A
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Inorganic Chemistry
Article
the best of our knowledge, this compound is the first radical-
doped polyoxometalate-based host−guest multifunctional
crystalline material with photochromism, photocontrolled
tunable luminescence, and photocatalytic activity.
EXPERIMENTAL SECTION
Synthesis of N,N′-di(4-pyridyl)-1,4,5,8-naphthalenediimide (DPNDI)
tectons. The mixture of 1,4,5,8-naphthalene-tetracarboxylic dianhy-
dride (3 mmol) and 4-aminopyridine (6 mmol) in dimethylformamide
■
(
DMF, 20 mL) was heated under reflux for 8 h. When the reaction
mixture reached room temperature, a crystalline solid precipitated and
was then collected by filtration. The crude product was purified by
recrystallization from DMF to obtain DPNDI as off-white crystalline
8
solids.
Synthesis of compound 1. A solution (1 mL) of N-methyl-2-
pyrrolidone (NMP)/MeCN (1:1, v/v) was carefully layered over an
NMP (2 mL) solution of DPNDI tectons (0.03 mmol, 0.0126 g), and
then the solution of ZnSiF (0.057 mmol, 0.0127g) and H PW O
6
3
12 40
(
0.017 mmol, 0.05g) in MeCN/MeOH (2:1, v/v, 3 mL) mixture was
carefully added as a second layer. Yellow crystals that appeared after
several days were collected and washed with MeCN in ca. 65% yield
(
based on Zn). Crystal data and the structure refinements are
summarized in Table 1S (see the Supporting Information). Elemental
analyses of C, H, and N were performed with a Vario EL III elemental
analyzer. Anal. Calcd for C H F W N O P Zn : C 13.78, H 1.32,
88
100
4
24 16 96
2
3
Figure 1. (a) Coordination environment of the Zn(II) ionic center in
compound 1. Symmetry codes: (i) x, 1.5 − y, 0.5 − z. (b) Anion−π
N 2.92%. Found: C 14.95, H 1.26, N 3.64%. The difference was
probably because of the volatile solvent molecules in the frameworks.
Combined with molecular weight calculator, the result we calculated is
that there are approximately five MeCN molecules. Calcd: C 14.96, H
(
yellow dashed line) interactions between DPNDI and POMs, and C−
H···anion (blue dashed line) interactions among components of 1. Zn
(turquoise), F (yellow-green), C (black), H (gray), O (red), N (blue),
1
.47, N 3.74%. Elemental analyses of Zn and W were performed with
Ultima2 inductively coupled plasma OES spectrometer. Anal. Calcd
P (purple), W (teal), POMs (red and purple polyhedron).
for C H F W N O P Zn : Zn 2.49, W 56.07% (including five
8
8
100
4
24 16 96
2
3
−1
MeCN molecules). Found: Zn 2.53, W 55.98%. IR (cm ): 3438(m),
contiguous network to generate a three-dimensional super-
molecular structure (Figure S3 in the Supporting Information).
In compound 1, the POM anion is located on the line of the
network (Figure S1 in the Supporting Information) rather than
in the void of the two-dimensional (2D) network, which is
much different than common POM-based host−guest 2D
coordination polymer, that is, embedding POMs into the void
of the coordination polymers, which is very sensitive to the
2
8
931(w), 1639(s), 1510(w), 1346(m), 1244(m), 1063(m), 979(s),
22(s), 503(w).
RESULTS AND DISCUSSION
■
Structure of compound 1. Single-crystal X-ray analysis reveals
that compound 1 crystallized in the P4/nnc space group. The
center Zn(II) ion is octahedrally coordinated by two bridging
fluorine atoms (Figure 1a) and four nitrogen atoms from four
functionalized π-electron-deficient DPNDI tectons. The other
nitrogen atoms from the bridging DPNDI tectons coordinated
with neighboring zinc ions to generate a two-dimensional (2D)
grid structure. Additional two Zn(II) ions, which are
perpendicular to the 2D grid network, are linked by the two
bridging fluorine atoms (Figure 1a), respectively, then four
solvent molecules (NMP) and one terminal fluorine atom
occupy other coordination sites of Zn(II) to form a vertical bar,
which looks like a railing. The Keggin polyanions
9
pore size of the network. On the other hand, each π-electron-
deficient naphthalenic ring of DPNDI participates in anion−π
interactions with two POM anions (Figure S2 in the
Supporting Information) to construct a staggered POM-based
host−guest structure, which is conducive to the formation of
the novel railing-type host−guest coordination polymer so as to
stabilize and disperse the trapped POM anions. Furthermore,
these anion−π interactions will boost the electron transfer or
exchange between NDI center and POM surface that helps to
maintain POMs’ efficient catalytic performance. The fraction of
volumes accessible for the inclusion of guest solvent molecules
is 29.3% (calculated by PLATON). Direct evidence for the
inclusion of the guest solvent molecules was obtained by
thermogravimetric analyses (TGA), which showed expected
losses of mass in the range of 30−100 °C. The structure of 1
further demonstrated that electron reservoirs (POMs) can
indeed be captured by π-electron-deficient naphthalenic ring of
the DPNDI through obvious POM anion−π interactions. In a
word, the railing of 2D quadrate network combined with the
anion−π interactions between π-electron-deficient DPNDI
tectons and the intermediate electron reservoirs (POMs) not
only play crucial roles in stabilizing and directing formation of
the novel POM-based host−guest coordination polymer but
also increase the interactions between the components so as to
accelerate the charge transfer and exchange to realize the fast-
3−
([PW O ] ) not merely act as counterions but also serve
12 40
as electron reservoirs; they typically reside directly over the
electron-deficient naphthalenic ring centroid (centroid distance
is ∼3 Å, Figure 1b; Figure S1 in the Supporting Information).
The intermolecular weak C−H···anion interactions (hydrogen-
bond geometry for 1 is available in the Supporting Information,
Table S2) formed between pyridyl-H’s of tectons (or hydrogen
atoms of NMP molecules) and oxygen atoms from the POMs
immobilize the functionalized POMs and enhance the stability
of the structure. The POM anions along with several disordered
solvent molecules filled in the gap of adjacent railings through
obvious POM anion−π interactions.
The POM anion participates in anion−π interactions with
two π-electron-deficient naphthalenic ring centroids (Figure S2
in the Supporting Information) of DPNDI tectons from
B
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responsive photochromism, photocontrolled luminescence, and
photocatalytic activity.
irradiated by ultraviolet visible light (1b, Figure 2b). In
addition, the ESR spectra of compounds 1a and 1b both
have a slightly wide weak peaks with the g value of 1.9278
(Figure 2b), which can be attributed to W(V) ions in the
Powder X-ray diffraction (PXRD) experiments on the bulk
material of 1 show that all major peaks match well with
simulated PXRD, indicating its crystalline phase purity (Figure
S4 in the Supporting Information). TGA revealed that the
weight loss of 2.73% from 30 to 100 °C is attributed to the
desorption of five free MeCN molecules (calculated 2.61%).
The weight loss of 10.2% from 200 °C to ∼400 °C may be
attributed to the desorption of two end-coordinated fluorine
ions and eight coordinated NMP molecules along the vertical
railing (calculated 10.9%). Then the following weight loss from
11
sample. There was an obvious variation of the intensity of
ESR signals of 1a and 1b. This variation most clearly illustrated
that there are more radicals and W(V) ions after being
irradiated by ultraviolet visible light. It is well-known that NDI
derivatives are redox-active and can generate radicals upon light
3
g,12
irradiation.
It also has been known for a long time that
POMs can act as electron reservoirs and be photochemically
reduced to form colored mixed-valence species, and the process
4
a
4
00 °C corresponds to the collapse of coordination polymer
Figure S5 in the Supporting Information). Probably, the
thermal stability of 1 is based on the following considerations:
i) there are some disordered solvent molecules (MeCN) in
the coordination polymer; (ii) low noncovalent bond energy
of formation of mixed-valence species is reversible. Thus, the
photochromic process may mainly arise from photoinduced
radical generation of organic tectons and the changes of valence
state of metal ions of POMs. It must be pointed out that certain
radicals and W(V) ions may occur in 1a under the indoor
natural light illumination; more specifically, the coordination
polymer is a radical-doped material showing an obvious ESR
signal, characteristic of imide radicals (g = 2.0032), which was
present in the yellow crystalline solids without irradiation
(Figure 2b). The Raman spectroscopy was employed to further
probe changes in the vibrational frequencies accompanying
redox state changes in the ligand cores. The Raman spectrum of
1a exhibits one sharp peak at 1731 cm− (Figure S6 in the
Supporting Information), which corresponds to the reported
(
(
(
the anion−π interactions between the POMs and rigid π-
10
conjugated DPNDI tectons); (iii) low bond energy between
the Zn(II) ions and the coordinated solvent (NMP) molecules
(
or end-coordinated fluorine ions); (iv) the certain voids
structure.
Photochromism. Interestingly, compound 1 (1a) is sensitive
to sunlight and undergoes a photochromic transformation from
yellowish to dark (1b) upon irradiation by ultraviolet visible
light (Xenon Lamp, 300W, PLS-SXE 300/300UV, 320−780
nm) for a few seconds (Figure 2a). 1b is stable in air and can
1
−1
value (experiment value: 1726 cm and calculated value: 1785
−1
cm ) of the carbonyl stretching in partially reduced DPNDI
12
(
i.e., DPNDI radical anion).
XPS analysis reveals that the tungstate experiences partial
reduction under natural or ultraviolet visible light. In
compound 1, the main doublets of W 4f peak in 1a (37.8
and 35.6 eV, Figure 2d) and b > 1b (37.4 and 35.2 eV, Figure
2
e) are located between the reported values of W(VI) ions and
13
partial reduction of tungsten that we have attributed to a
partial reduction of tungsten under the natural light or
ultraviolet visible light, which is consistent with the results of
ESR of 1a and 1b. Compared with 1a, the slight low-energy
shifts of the XPS in 1b relative to the reduction of tungsten are
in accord with more W(V) ions in 1b (Figure S7 in the
Supporting Information). Note that, in 1b, the W 4f peak
displayed additional contributions at 36.5 and 34.4 eV (Figure
2
e), which also can be contributed to more reduction of
13
tungsten after ultraviolet light irradiation,
since the
compound is sensitive to light; this is simply a matter of
degree of reduction during light irradiation. Hence, it can be
concluded that the photochromic process may also come from
the changes of valence state of metal ions of POMs. There may
be a charge transfer and exchange process among the
components of this compound by the anion−π interactions
and hydrogen bonds during irradiation.
Figure 2. (a) The photochromic effect of the single crystal from
photographic images. (b) ESR spectra for 1a and 1b. (inset) Enlarged
ESR spectra of 1a. (c) UV−vis spectra of 1a and 1b. (d) Resolved W
UV−vis spectrum of 1a and 1b shows absorption bands at
380 nm, corresponding to the n−π* and π−π* transition of
∼
4
f XPS core-level spectra of 1a. (e) Resolved W 4f XPS core-level
the aromatic organic tectons (Figure 2c). In addition, a weak
shoulder around 500 nm can likewise be observed, which can
be attributed to an intermolecular electron-transfer transition.
The appearance of this band is consistent with the existence of
the anion−π interactions and hydrogen bonds in the structure,
which is considered to be a favorable condition for electron-
transfer interactions. The UV−vis spectrum of 1b displays a
broad absorption band in the region of 600−850 nm, which
may originate from a photoinduced electron-transfer tran-
spectra of 1b.
return to yellow in a dark room for several minutes at ambient
temperature. The analysis of electron spin resonance (ESR)
spectra indicates that compound 1a shows a weak peak radical
signal with the g value of 2.0023 (Figure 2b). Compared with
1
a, 1b exhibits a relatively strong sharp peak ESR signal of
radicals, which suggests that there is a small amount of radicals
in 1a and that 1b will rapidly generate amount of radicals after
3g
sition. Therefore, besides the changes of valence state of
C
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Inorganic Chemistry
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tungsten of POMs, the photochromic process may also arise
from the photoinduced radical generation of organic ligands.
That is to say, there are two reduction-active centers, which
may accept electrons from the solvent molecules.
The cyclic voltammogram (CV) of compound 1a exhibits
one quasi-reversible processes in the cathodic region at E1/2
=
−0.874 V (Figure 3), which correspond to the reported
Figure 4. Photocontrolled tunable luminescence performance of 1 in
the solid under UV−vis light (the spectrum was recorded of the
samples under UV−vis light every 5 s or dark treatment).
Figure 3. Solid-state CV of 1a at 100 mV s− in a 0.1 M nBu NPF /
1
4
6
MeCN electrolyte.
DPNDI]0
/•−
(−0.91 V) redox couples. The reduction
−
12
[
•
potential for DPNDI formation in the coordination polymer
is less negative than that of the DPNDI ligands. On the basis of
Coulombic considerations, one would expect DPNDI reduction
to be easier in MeCN than in the coordination polymer,
because the charged anion radical should be stabilized in a polar
solvent, in contrast to the hydrophobic environment of the
stacked DPNDI molecules in the crystalline coordination
1
4
polymer. Since the opposite was observed, it can be supposed
that DPNDI radical anions are stabilized in the crystalline solid
material by delocalization of the unpaired electron over several
molecules such as NMP molecules, POMs, and DPNDI
molecules through anion−π interactions and hydrogen bonds,
as proposed above for the radical-doped solids.
Luminescence. Considering the luminescence performance
of DPNDI (Figure S8 in the Supporting Information), the d10
Zn(II) metal ion, and the photochromism of 1, the photo-
controlled luminescence of 1 was performed. As shown in
Figure 4, compound 1 shows emission at 450 nm when excited
at 350 nm. Interestingly, photocontrolled tunable luminescence
was observed under the trigger of ultraviolet visible light. The
strength of the emission of 1 was gradually reduced under
ultraviolet visible light irradiation; as expected, the lumines-
cence is almost quenching when the sample changes into dark
after irradiating 15 s, but could be quickly recovered under dark
for several minutes. This distinct behavior indicates that the
photocontrolled tunable luminescence of 1 is reversible, which
further demonstrates that there are electron-transfer inter-
actions among the components of the compound during
irradiation, thus resulting in weaker luminescence and even
quenching.
Figure 5. (a) The estimated energy band gap by the UV−vis diffuse
reflectance spectroscopy based on the Kubelka−Munk Function. (b)
Recycled photocatalytic oxidation of benzyl alcohol over compound 1.
was achieved using this compound as a recyclable and eco-
friendly heterogeneous photocatalyst in acetonitrile under air
using ultraviolet visible light as the sole driving force (Scheme
1).
Experiments on photocatalytic selective oxidation of benzylic
alcohols to corresponding aldehydes started with the reaction
of benzyl alcohol. The time-online photocatalytic results for
benzyl alcohol demonstrated that the high selectivity for
benzaldehyde, ca. 85%, is obtained along with ca. 67%
conversion under irradiating for 11 h (Figure S9 in the
Photocatalytic activity. The estimated band gap of compound
based on Kubelka−Munk Function is 2.83 eV (Figure 5a),
1
which indicates that 1 can be bandgap photoexcited by
simulated sunlight irradiation. As expected, a mild and green
procedure for the photocatalytic oxidation of benzylic alcohols
D
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Scheme 1. Selective Oxidation of Benzylic Alcohols
important role in incorporating functional components to
construct multifunctional crystalline material as well as
facilitating the charge transfer or exchange among internal
components, which might be conducive to effectively
improving the photocatalytic activity of POM-based host−
guest materials in a mild and green experiment condition.
Supporting Information). The control experiments showed that
no reaction occurred in the absence of compound 1 (Table 1,
CONCLUSIONS
■
In conclusion, an extremely rare radical-doped POM-based
host−guest crystalline material was reported for the first time,
which has fast-responsive reversible photochromic properties
varying from yellowish to dark and photocontrolled tunable
luminescence. Moreover, an efficient procedure for the selective
oxidation of benzylic alcohols or substituted benzylic alcohols
has been developed using this POMs-based host−guest
photochromic material as a green and recyclable photocatalyst
under air as the sole catalyst reoxidant. Of particular
importance is that the trapped POM anions connected with
functional DPNDI tectons effectively via directional anion−π
and C−H···anion interactions, which indicate POM anion−π
interactions will not only be applicable to the stabilization and
immobilization of the functional POM anions but also promote
the charge transfer and exchange among components to lead to
the reversible photochromism, photocontrolled tunable lumi-
nescence, and photocatalytic activity. All of these results
indicate that it is a promising way to design and construct
photochromic and photocatalytic crystalline materials based on
multifunctional electron reservoirs (POMs) and π-electron-
deficient NDIs dye derivatives by forming anion−π inter-
actions.
Table 1. Photocatalytic Selective Oxidation of Various
Benzylic Alcohols to the Corresponding Aldehydes with
Compound 1 for 11 h
a
entry
R
catalyst
conversion (%) selectivity (%)
1
2
3
4
5
6
7
8
9
H
H
H
H
1
67
0
85
0
H PW O
87
33
53
76
43
50
63
56
45
40
69
3
12 40
ZnSiF -DPNDI
80
6
p-Me
p-MeO
m-Me
p-F
1
1
1
1
1
1
1
1
>99
>99
>99
83
p-Cl
>99
>99
>99
>99
10
11
12
p-Br
p-iPr
p-tBu
a
Product identification was accomplished by Varian 4000 GC/MS or
GC.
entry 2); therefore, the oxidation of benzyl alcohols is triggered
by compound 1, a photocatalyst. For comparison, a series of
control photocatalysts were employed in the same photo-
catalytic experiments. The homogeneous catalyst H PW O
gave higher conversion (87%) under identical conditions;
however, the selectivity to benzaldehyde was lower (69%)
ASSOCIATED CONTENT
Supporting Information
■
*
S
3
12 40
Experimental materials and physical measurements, crystallo-
graphic data, TGA, PXRD, solid-state Raman spectrum, XPS
core-level spectra of 1, additional figures, TEM images, and
EDS of 1, and hydrogen-bond geometry for compound 1. This
material is available free of charge via the Internet at http://
pubs.acs.org.
(
Table 1, entry 3). Additionally, the recovery and recyclability
of H PW O was difficult. With ZnSiF −DPNDI, although
comparable selectivity can be achieved, the conversion of
3
12 40
6
benzyl alcohol was much lower than that with compound 1
(
Table 1, entry 4). The recycling experiments suggested that
AUTHOR INFORMATION
Corresponding Author
E-mail: czlu@fjirsm.ac.cn. Fax: (+86)591-83714946. Phone:
+86)591-83705794.
Present Addresses
Key Laboratory of Design and Assembly of Functional
Nanostructures, Fujian Institute of Research on the Structure
of Matter, Chinese Academy of Sciences, Fuzhou, Fujian
50002, P. R. China.
■
compound 1 can be recovered easily by filtration. It can be
reused in at least six runs without a significant decrease of
conversion and selectivity (Figure 5b). The results suggest that
compound 1 was more promising than its precursors as a
photocatalyst. The combinations of the two major functional
components not only improve the catalytic efficiency but also
solve the problem of catalyst recycling. It is particularly worth
mentioning that the selective photocatalytic oxidation of
benzylic alcohols was performed at ambient condition using
air as the sole catalyst reoxidant, which further suggests that
compound 1 was an excellent heterogeneous photocatalyst.
Selective oxidation of a variety of ring-substituted benzylic
alcohols to corresponding aldehydes was also performed under
similar reaction conditions; the results are listed in Table 1.
Clearly, compound 1 is also active and highly selective for
oxidation of ring-substituted benzylic alcohols. These results
indicate that compound 1, which combines multiple functional
groups in a single structure, can be used as an excellent
heterogeneous photocatalyst. This greatly improved photo-
catalytic activity may result from the unique structure features
of the railing-type radical-doped host−guest material. The
distinct POMs anion−π and C−H···anion interactions play an
*
(
§
3
⊥
Graduate University of Chinese Academy of Sciences, Beijing
00049, P. R. China.
Notes
1
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the 973 Key Program of the
MOST (2012CB821705), the National Natural Science
Foundation of China (21373221, 21221001, 91122027,
51172232, 21403236), the Chinese Academy of Sciences
(KJCX2-YW-319 and KJCX2-EW-H01), and the Natural
Science Foundation of Fujian Province (2012J06006 and
2006L2005).
E
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(
10) (a) Chifotides, H.; Dunbar, K. R. Acc. Chem. Res. 2013, 46,
REFERENCES
■
8
94−906. (b) Schottel, B. L.; Chifotides, H. T.; Dunbar, K. R. Chem.
Soc. Rev. 2008, 37, 68−83. (c) Jentzsch, A. V.; Henning, A.; Mareda, J.;
Matile, S. Acc. Chem. Res. 2013, 46, 2791−2800. (d) Quinonero, D.;
Garau, C.; Rotger, C.; Frontera, A.; Ballester, P.; Costa, A.; Deya, P. M.
(
6
1) (a) Pardo, R.; Zayat, M.; Levy, D. Chem. Soc. Rev. 2011, 40, 672−
87. (b) Irie, M. Chem. Rev. 2000, 100, 5. (c) Wang, M. S.; Xu, G.;
Zhang, Z. J.; Guo, G. C. Chem. Commun. 2010, 46, 361−376.
d) Zhang, H.; Chen, G.; Bahnemann, D. J. Mater. Chem. 2009, 19,
089−5121. (e) Zhang, T.; Lin, W. Chem. Soc. Rev. 2014, 43, 5982−
993. (f) Wang, C. C.; Li, J. R.; Lv, X. L.; Zhang, Y. Q.; Guo, G. Energy
̃
̀
(
5
5
Angew. Chem., Int. Ed. 2002, 41, 3389−3392. (e) Alkorta, I.; Rozas, I.;
Elguero, J. J. Am. Chem. Soc. 2002, 124, 8593−8598.
(11) (a) Prados, R.; Pope, M. T. Inorg. Chem. 1976, 15, 2547−2553.
Envrion. Sci. 2014, 7, 2831−2867.
2) (a) Zou, C.; Zhang, Z. J.; Xu, X.; Gong, Q.; Li, J.; Wu, C. D. J.
Am. Chem. Soc. 2012, 134, 87−90. (b) Ferey, G.; Mellot-Draznieds, C.;
Serre, C.; Millange, F. Acc. Chem. Res. 2005, 38, 217−225.
(
b) Varga, G. M., JR.; Papaconstantinou, E.; Pope, M. T. Inorg. Chem.
970, 9, 662−667.
12) Leong, C. F.; Chan, B.; Faust, T. B.; D’Alessandro, D. M. Chem.
Sci. 2014, 5, 4724−4728.
13) (a) Mercier, D.; Boujday, S.; Annabi, C.; Villanneau, R.; Pradier,
C. M.; Proust, A. J. Phys. Chem. C 2012, 116, 13217−13224.
b) Legagneux, N.; Basset, J. M.; Thomas, A.; Lefebvre, F.; Goguet, A.;
Sa, J.; Hardacre, C. Dalton Trans. 2009, 2235−2240. (c) Wagner, C.
(
1
(
́
(
3
2
c) Rosseinsky, M. J. Microporous Mesoporous Mater. 2004, 73, 15−
(
0. (d) Rowsell, J. L. C.; Yaghi, O. M. Microporous Mesoporous Mater.
004, 73, 3−14. (e) Maspoch, D.; Ruiz-Molina, D.; Veciana, J. Chem.
(
Soc. Rev. 2007, 36, 770−818. (f) Cheetham, A. K.; Rao, C. N. R.;
Feller, R. K. Chem. Commun. 2006, 4780−4795.
́
D.; Riggs, W. M.; Davis, L. E.; Moulder, J. F.; Muilenberg, G. E.
Handbook of X-ray Photoelectron Spectroscopy; Perkin-Elmer Corpo-
ration, Physical Electronics Division: Waltham, MA, 1979. (d) Nagao-
ka, Y.; Shiratori, S.; Einaga, Y. Chem. Mater. 2008, 20, 4004−4010.
(
3) (a) Dawson, R. E.; Henning, A.; Weimann, D. P.; Emery, D.;
Ravikumar, V.; Montenegro, J.; Takeuchi, T.; Gabutti, S.; Mayor, M.;
Mareda, J.; Schalley, C. A.; Matile, S. Nat. Chem. 2010, 2, 533−538.
(
b) Mareda, J.; Matile, S. Chem.Eur. J. 2009, 15, 28−37. (c) Gorteau,
(
14) (a) Brochsztain, S.; Rodrigues, M. A.; Demets, G. J. F.; Politi, M.
J. J. Mater. Chem. 2002, 12, 1250−1255. (b) Thalacker, C.; Roger, C.;
Wurthner, F. J. Org. Chem. 2006, 71, 8098−8105.
V.; Bollot, G.; Mareda, J.; Perez-Velasco, A.; Matile, S. J. Am. Chem.
Soc. 2006, 128, 14788−14789. (d) Guha, S.; Goodson, F. S.; Corson,
L. J.; Saha, S. J. Am. Chem. Soc. 2012, 134, 13679−13691. (e) Guha, S.;
Saha, S. J. Am. Chem. Soc. 2010, 132, 17674−17677. (f) Zhao, Y.;
Domoto, Y.; Orentas, E.; Beuchat, C.; Emery, D.; Mareda, J.; Sakai, N.;
Matile, S. Angew. Chem., Int. Ed. 2013, 52, 9940−9943. (g) Han, L.;
Qin, L.; Xu, L.; Zhou, Y.; Sun, J.; Zou, X. Chem. Commun. 2013, 49,
̈
̈
4
06−408. (h) Nelson, A. P.; Farha, O. K.; Mulfort, K. L.; Hupp, J. T. J.
Am. Chem. Soc. 2009, 131, 458−460. (i) Mulfort, K. L.; Hupp, J. T. J.
Am. Chem. Soc. 2007, 129, 9604−9605. (j) Bhosale, S. V.; Jani, C. H.;
Langford, S. J. Chem. Soc. Rev. 2008, 37, 331−342. (k) Katz, H. E.;
Lovinger, A. J.; Johnson, J.; Kloc, C.; Siegrist, T.; Li, W.; Lin, Y. Y.;
Dodahalapur, A. Nature 2000, 404, 478−481. (l) Wade, C. R.; Li, M.;
Dinca,
Carthy, B. D.; Hontz, E. R.; Yost, S. R.; Voorhis, T. V.; Dinca,
Phys. Chem. Lett. 2013, 4, 453−458.
̆
M. Angew. Chem., Int. Ed. 2013, 52, 13377−13381. (m) Mc-
̆
M. J.
(
4) (a) Ymamse, T. Chem. Rev. 1998, 98, 307−326. (b) He, T.; Yao,
J. Prog. Mater. Sci. 2006, 51, 810−879. (c) Dolbecq, A.; Dumas, E.;
Mayer, C. R.; Mialane, P. Chem. Rev. 2010, 110, 6009−6048. (d) Liu,
̈
S.; Mohwald, H.; Volkmer, D.; Kurth, D. G. Langmuir 2006, 22,
1
949−1951. (e) Walsh, J. J.; Mallon, C. T.; Bond, A. M.; Keyes, T. E.;
Forster, R. J. Chem. Commun. 2012, 48, 3593−3595.
5) (a) Miras, H. N.; Nadal, L. V.; Cronin, L. Chem. Soc. Rev. 2014,
(
43, 5679−5699. (b) Song, Y. F.; Tsunashima, R. Chem. Soc. Rev. 2012,
41, 7384−7402. (c) Zhou, Y.; Chen, G.; Long, Z.; Wang, J. RSC Adv.
2014, 4, 42092−42113. (d) Du, D. Y.; Qin, J. S.; Li, S. L.; Su, Z. M.;
Lan, Y. Q. Chem. Soc. Rev. 2014, 43, 4615−4632. (e) Nisar, A.; Wang,
X. Dalton Trans. 2012, 41, 9832−9845. (f) Lv, H.; Geletii, Y. V.; Zhao,
C.; Vickers, J. W.; Zhu, G.; Luo, Z.; Song, J.; Lian, T.; Musaev, D. G.;
Hill, C. L. Chem. Soc. Rev. 2012, 41, 7572−7589. (g) Kozhevnikov, I.
V. Chem. Rev. 1998, 98, 171−198. (h) Long, D. L.; Tsunashima, R.;
Cronin, L. Angew. Chem., Int. Ed. 2010, 49, 1736−1758. (i) Han, X. B.;
Zhang, Z. M.; Zhang, T.; Li, Y. G.; Lin, W.; You, W. S.; Su, Z. M.;
Wang, E. B. J. Am. Chem. Soc. 2014, 136, 5359−5366.
(
6) (a) Sun, C. Y.; Liu, S. X.; Liang, D. D.; Shao, K. Z.; Ren, Y. H.;
Su, Z. M. J. Am. Chem. Soc. 2009, 131, 1883−1888. (b) Ma, F. J.; Liu,
S. X.; Sun, C. Y.; Liang, D. D.; Ren, G. J.; Wei, F.; Chen, Y. G.; Su, Z.
M. J. Am. Chem. Soc. 2011, 133, 4178−4181. (c) Song, J.; Luo, Z.;
Britt, D. K.; Furukawa, H.; Yaghi, O. M.; Hardcastle, K. I.; Hill, C. L. J.
Am. Chem. Soc. 2011, 133, 16839−16846. (d) Han, Q.; He, C.; Zhao,
M.; Qi, B.; Niu, J.; Duan, C. J. Am. Chem. Soc. 2013, 135, 10186−
1
0189. (e) Liu, Y.; Liu, S.; Liu, S.; Liang, D.; Li, S.; Tang, Q.; Wang,
X.; Miao, J.; Shi, Z.; Zheng, Z. ChemCatChem 2013, 5, 3086−3091.
7) Lu, J.; Lin, J. X.; Zhao, X. L.; Cao, R. Chem. Commun. 2012, 48,
69−671.
8) Liao, J. Z.; Dui, X. J.; Zhang, H. L.; Wu, X. Y.; Lu, C. Z.
CrystEngComm 2014, 16, 10530−10533.
9) Kong, X. J.; Ren, Y. P.; Zheng, P. Q.; Long, Y. X.; Long, L. S.;
Huang, R. B.; Zheng, L. S. Inorg. Chem. 2006, 45, 10702−10711.
(
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(
̈
(
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DOI: 10.1021/acs.inorgchem.5b00041
Inorg. Chem. XXXX, XXX, XXX−XXX