A novel ultrasound-sensitive mechanofluorochromic AIE-compound with remarkable blue-shifting and enhanced emission

Article abstract of DOI:10.1039/c4tc00553h

A novel ultrasonic-sensitive mechanofluorochromic AIE-compound (ITPADA) has been designed and synthesized. The fluorescent properties of the ITPADA suspensions were greatly affected by the ultrasonic treatment and extremely sensitive to its power, which s

Full text of DOI:10.1039/c4tc00553h

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Materials Chemistry C
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A novel ultrasound-sensitive
mechanofluorochromic AIE-compound with
Cite this: J. Mater. Chem. C, 2014, 2,
remarkable blue-shifting and enhanced emission†
5812
*
Huawei Sun, Yi Zhang, Wei Yan, Wenxin Chen, Qi Lan, Siwei Liu, Long Jiang,
*
Zhenguo Chi, Xudong Chen and Jiarui Xu
Received 20th March 2014
Accepted 3rd May 2014
A novel ultrasonic-sensitive mechanofluorochromic AIE-compound (ITPADA) has been designed and
synthesized. The fluorescent properties of the ITPADA suspensions were greatly affected by the ultrasonic
treatment and extremely sensitive to its power, which show remarkable blue-shifting and enhanced
emission. Moreover, perfect ITPADA nano-sheets could be obtained by facile ultrasonic treatment.
DOI: 10.1039/c4tc00553h
www.rsc.org/MaterialsC
some mechanochromic luminescent molecules might show
distinct responses to the mechanical grinding (anisotropic) and
Introduction
hydrostatic pressure (isotropic), which accelerated and enriched
the chemistry of the mechanochromism. However, the applica-
tion of hydrostatic pressure is limited in practical applications
because of the requirement of high pressure.
Stimuli-responsive materials have been considered to be the
fourth generation of materials aer natural materials,
synthetic polymer materials and articial design materials.1 It
is one of the important developing trends in high-tech new
materials and will support the development of modern high
technology. Among them, mechanouorochromic materials
are rather rare and have aroused tremendous interest in recent
years.2 These materials show photoluminescence and colour
change under external forces such as grinding,3 crushing,4
shearing,5 rubbing6 and stretching,7 and have attractive
application prospects in the eld of uorescence switches and
probes, mechanosensors, optoelectronic devices, data storage,
indicators of mechanohistory, and so on.8 However, most of the
reported studies are usually conned to the description of the
phenomenon. The quantitative study of the applied force to the
assembled structure and the uorescent properties of the
mechanouorochromic materials, such as color change and
uorescent intensity, is still pending as an important and tough
topic due to the lack of effective research methods. Tian9 used
hydrostatic pressure to study the inuence and mechanism of
applied pressure on the luminescence of a piezochromic mate-
rial BP2VA, which gives a clear picture of the structure–property
relationship and is very important for the development of pie-
zochromic materials. Immediately aerwards, Saito10 found that
Ultrasonication is a special way of energy input and widely
used in various applications such as in industry, medical
diagnosis, medicine, preparation of nano-materials, etc.11
Recently, ultrasound was reported as an effective trigger for
the formation of organogels12 or to create defects5a in uo-
rescent crystal materials. Compared with the reported external
stimuli, ultrasonication has overriding advantages such as
high energy efficiency and quantitative controlling effects.
Thus, ultrasound is likely to become a convenient, highly
efficient and controllable external stimulus applied in
mechanouorochromic materials. But until now, it is
extremely rarely reported in the eld.
Herein, we report a novel ultrasonic-sensitive mechano-
uoro-chromic aggregation-induced emission (AIE)-compound,
named ITPADA. The uorescent properties of the ITPADA
suspensions (such as multicolour change, blue-shiing and
intensity enhancement) and the aggregation morphologies were
found to be greatly affected by the ultrasonic treatment and
extremely sensitive to its power. In other words, the lumines-
cent properties are tunable through controlling of the molec-
ular packing mode. ITPADA nano-sheets with perfect crystalline
structure and high purity could be obtained simply by a facile
ultrasonic process with an appropriate power supply. Such
interesting phenomena promote us to carry out systematic
studies on the structure–property relationships. An effective
mechanism of the ultrasonic-sensitive mechanouorochromic
phenomenon on the basis of the molecular packing patterns
was thus proposed, which might provide a theoretical basis for
the molecular design strategies of a new generation of
controllable mechanouorochromic materials. Such ultrasonic-
MOE Key Laboratory of Polymeric Composite and Functional Materials, Design and
Synthesis of New Polymer Materials and Application Laboratory, State Key
Laboratory of Optoelectronic Materials and Technologies, School of Chemistry and
Chemical Engineering, Sun Yat-sen University, Guangzhou 510275, P.R. China.
E-mail: ceszy@mail.sysu.edu.cn; xjr@mail.sysu.edu.cn; Fax: +86 20 84112222; Tel:
+86 20 84112222
† Electronic supplementary information (ESI) available: Experimental section,
spectroscopic data, thermal properties and crystallographic data of ITPADA.
CCDC 985149. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c4tc00553h
5812 | J. Mater. Chem. C, 2014, 2, 5812–5817
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sensitive materials may provide a suitable system for the study
of the mechanism of mechanouorochromic behaviours using
ultrasound as a convenient and highly efficient external stim-
ulus, which would be very important for the development and
new application of stimuli-responsive materials.
Results and discussion
Synthesis and characterization
The designed molecule ITPADA was synthesized from diphe-
nylamine (DPA), which reacted with para-nitrobenzoyl chlo-
ride (NBFC) using pyridine as the catalyst to afford 4-nitro-
N,N-diphenyl-benzamide (IP-NO2), followed by the reduction
reaction to obtain 4-amino-N,N-diphenyl-benzamide (IP-
NH2). 4-(Bis(4-nitrophenyl)-amino)-N,N-diphenylbenzamide
(ITPADN) was synthesized from IP-NH2 and 4-uoroni-
trobenzene under alkaline conditions. And nally, the
reduction of ITPADN by hydrazine hydrate and the palladium/
C catalyst gave the target molecule ITPADA. The detailed
synthetic procedure is shown in Scheme 1. The chemical
1
structure of the nal product was conrmed by H NMR, 13C
NMR (H-H COSY, C-H QC and C-H BC) spectra, HRMS, FT-IR
and elemental analysis, respectively. The characterization of
ITPADA is described in the Experimental section and shown
in Fig. S1 in the ESI.† The original ITPADA powder showed
good thermal stability. The 5% and 10% weight-loss temper-
atures (Td) of ITPADA in nitrogen were 399 and 419 ꢀC,
respectively, and the glass transition temperature (Tg) was
ꢀ
117 C (Fig. S2 and S3 in the ESI†).
Fig. 1 PL spectra and pictures of ITPADA in the THF–H2O mixtures
with different water fractions. (a) Non-ultrasonic conditions; (b)
ultrasonic conduction.
Ultrasonic-sensitive luminescent behaviours
ITPADA showed interesting ultrasonic sensitivity when we
studied the luminescence behaviour of ITPADA. The experi-
ments were carried out in the diluted mixed solvent system of
THF–H2O with different volume contents of water under
different mixing conditions. As shown in Fig. 1a, ITPADA
showed non-luminescent behaviour when it was molecularly
dissolved in pure THF (1 Â 10À5 mol LÀ1). Addition of a large
amount of water (poor solvent of ITPADA) into its dilute THF
solution (like 90% or more) caused the ITPADA molecules to
aggregate and luminesce. It showed a yellow uorescence with
em
max
the maximum emission wavelength (l ) at about 540 nm. The
uorescence quantum yield (FF) of the THF solution of ITPADA
was virtually nil, and the FF value of its aggregates suspended in
the THF–H2O mixture is obviously enhanced, which is 4.74%
when the water content reached 92%. Clearly, the photo-
luminescence (PL) behaviour of ITPADA in the mixed solvent of
THF–H2O is typical of an AIE luminogen.
The uorescent characteristics of the ITPADA aggregates
suspended in the THF–H2O mixture were greatly changed when
treated by ultrasonication, as shown in Fig. 1b. It showed a blue
em
max
uorescence with the l
at about 470 nm. The maximum
emission wavelength was remarkably blue-shied by approxi-
mately 70 nm as compared with that determined without
ultrasonic treatment. More importantly, the uorescence
intensity was greatly enhanced by the ultrasonic treatment. The
suspended system began to luminesce strongly when the water
content reached 80%, and the FF value was as high as 50.2%
(red column in Fig. 2). Aer that, the uorescence quantum
yield of the mixture maintained at a high level, which was 52.4%
when the water content reached 92%. The ITPADA aggregated
suspensions show notable and interesting ultrasonic sensitive
mechanouorochromic behaviours, which is abnormal as the
Scheme 1 Synthesis routes towards the ITPADA.
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uorescent intensity and the blue-shied effect. When the power
reached 200 W, the intensity of the mixture was enhanced by 25
times, and the maximum wavelength was blue-shied by about
70 nm, as compared with that without being treated with ultra-
sonication. Moreover, before and aer the ultrasonic treatment,
the chemical structure of the ITPADA remained the same, as
conrmed and shown in Fig. S6 in the ESI.†
Aggregated morphology and crystalline structures
The above interesting ultrasonic sensitive uorescence behav-
iours of ITPADA suspensions motivated us to look into their
aggregated morphology and crystalline structures before and
aer ultrasonic treatment. The ITPADA aggregates obtained
under general mixing conditions revealed to be spherical
Fig. 2 Influence of ultrasonic treatment on the fluorescence quantum
yield of ITPADA in the THF–H2O mixtures with different water
fractions.
particles with an average diameter of about 350 nm, which
em
max
showed a yellow uorescence with the l
at 540 nm, as shown
stimuli-induced emission of the most reported mechano-
uorochromic compounds was found to be red-shied and the
intensity tended to be decreased or even quenching upon
grinding.2g,3e,5c,6b,9,13 Such phenomena have not yet been repor-
ted in the literature to the best of our knowledge.
We also tried other solvent/non-solvent combinations, such
as the THF/n-hexane system (where n-hexane is a non-polar
solvent and a poor solvent of ITPADA) and the DMF–H2O
system. The results are shown in Fig. S4 and S5 in the ESI.† As
can be seen, the uorescent properties of the ITPADA suspen-
sions also showed similar ultrasonic-sensitive behaviour, such
as remarkable blue-shiing and enhanced emission. The
interesting ultrasonic-sensitive phenomenon of the ITPADA
suspensions does not seem to be solvent dependent.
The uorescence behaviours of the ITPADA aggregated
suspensions also show a strong ultrasonic power-dependent
behaviour, as shown in Fig. 3. Before being treated with ultra-
sonication, ITPADA aggregates in the mixture solvent of THF–
H2O (90% content of water) showed very weak uorescence with
the maximum wavelength at about 540 nm. When ultrasonic
treatment was performed, at a power of 80 W and a frequency of
40 kHz, the uorescent intensity was enhanced by almost 10
times and the maximum wavelength was blue-shied to 513 nm.
Further increase of the ultrasonic power strengthened the
in Fig. 4a. Such spherical precipitates turned amorphous as
revealed by powder XRD (blue pattern in Fig. 5). When an
ultrasonic power of 80 W was used, the spherical particles of
ITPADA changed into regular four-side prism crystals, and the
uorescent color of the suspension changed into green (Fig. 4b).
When the ultrasonic power was increased to 120 W, the thick-
ness of the four-side prism became thinner, most of them
turned into thin slices, and the suspension color changed into
em
max
bluish green, with the l
at about 480 nm (Fig. 4c). On further
increasing the ultrasonic power, such as 160 W or 200 W, the
ITPADA slices thinned down to transparent rhombic nano-
sheets, and the uorescent color was further blue-shied to
pure blue (Fig. 4d and e). The XRD results showed that the
ITPADA nano-sheet possessed very perfect crystal structures
(red pattern in Fig. 5), which is almost the same as its single
crystalline structure, as shown in the black pattern of Fig. 5. The
ITPADA single crystal was transparent and emitted blue uo-
rescence (picture in Fig. 5), which is similar to the nano-sheets
of ITPADA. In other words, it is applicable to get highly puried
single crystals of ITPADA by a facile ultrasonic process, which
should be extremely important to the practical application as
purication of the as-synthesized compounds is generally a
choke point for the luminescent materials.
The SEM studies revealed that the uorescent properties of
the ITPADA aggregates were mainly affected by their aggregated
Fig. 4 Influence of the ultrasonic power on the morphology and
fluorescence color of ITPADA suspensions in the THF–H2O mixtures
Fig. 3 PL spectra of ITPADA in the THF–H2O mixtures (90% of water), (90% content of water) with a frequency of 40 kHz. (a) Non-ultrasonic;
with a frequency of 40 kHz and different ultrasonic powers.
(b) 80 W; (c) 120 W; (d) 160 W; (e) 200 W.
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results showed that ITPADA molecules were crystallized in the
ꢀ
triclinic system space group P1. The basic unit of the single
crystal was formed by four ITPADA molecules through three
kinds of strong hydrogen bond interactions, that is, the N3–
˚
H3B/N7 hydrogen bond interaction with a distance of 2.37 A,
the N3–H3A/O2 hydrogen bond interaction with a distance of
˚
2.14 A and the N4–H4B/N8 hydrogen bond interaction with a
˚
distance of 2.21 A. The four molecules could be divided into two
types, which are Type 1 (gray) and Type 2 (red) shown in Fig. 6a.
The crystals were grown along the x-axis through a short contact
˚
interaction of C47–C48/H54 with distances of 2.776 A and
˚
2.882 A (Fig. 6b and e). Along the y-axis, the crystals were grown
Fig. 5 Powder XRD patterns of ITPADA with and without ultrasonic
treatment; simulated powder XRD pattern of the single crystal. The
inset pictures are the corresponding photos under 365 nm UV light.
˚
through a weak hydrogen bond of N8–H8B/O1 (2.48 A) and
N4–H4A/O1 (2.54 A), as well as short contact interactions of
˚
˚
˚
˚
C5–H4A/O1 (2.54 A and 2.828 A), C31–H8B/H31 (2.39 A and
˚
˚
˚
2.619 A), C30–H2 (2.886 A), C31–H3 (2.795 A) and C3–H25 (2.858
morphology, that is to say, it is able to control the aggregated
structures and uorescent properties of ITPADA by adjusting
the ultrasonic power. The improvement in the crystallinity and
especially the formation of the ITPADA nano-sheet crystalline
structure greatly enhanced its uorescent properties, such as
the uorescence quantum yield and the blue-shi effect.
To thoroughly understand the mechanism of the ultrasonic
effects on the formation of nano-sheets of ITPADA, systematic
X-ray diffraction studies were performed on the single crystal of
ITPADA to determine the growth process of the crystals. All
structures were solved by a combination of direct methods and
˚
A), as shown in Fig. 6c. The growth of the crystals along the x
and y axes formed the basic planar structures of the nano-
sheets, as shown in Fig. 6f. Outside the plane, the crystals were
grown along the z-axis through short contact interactions such
˚
˚
˚
as C18–H8A/H18 (2.216 A and 2.784 A), C12–H7A–N3 (2.448 A
˚
˚
and 2.871 A) and H53–H41 (2.375 A), as shown in Fig. 6d. Such a
layer-by-layer growth pattern nally formed the four-side prism
crystalline structure of the ITPADA single crystals (Fig. 6g).
Discussion
difference Fourier syntheses and rened against F2 by the full- Based on the above analysis, it now is clear why the ultrasonic
matrix least-squares technique (Tables S1–S3 in the ESI†). The treatment would have such an obvious effect on the
Fig. 6 Crystal packing of ITPADA single crystals. (a) Basic unit of the single crystals; (b) interactions along the x-axis; (c) interactions along the y-
axis; (d) interactions along the z-axis; (e) ITPADA molecules grown along the x-axis; (f) the in-plane assembly of the ITPADA molecules; (g) the
lattice structure of the ITPADA crystals.
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morphologies of the ITPADA aggregates. Under general mixing
conditions, the precipitates of ITPADA tended to form spherical
aggregates because of the surface tension to obtain the minimal
specic area and surface energy. Due to the special chemical
structure and the polar molecular nature of ITPADA (imide and
amino groups in one molecule), the spherical structure seems
to be destroyed and the ITPADA molecules underwent a self-
assembled process through the mentioned intermolecular
forces (ve kinds of hydrogen bonds and some other short
contact interactions) by the application of a low energy ultra-
sonic power such as 80 W. The ITPADA molecules nally formed
the regular prism through the mentioned x, y and z axis growing
processes.
Compared with the interaction strength among the x, y and z
axes directions, one can see that because of the existence of
hydrogen bond interactions along the x and y axes, that is, the
interaction in plane is much stronger than that along the z axis,
which is aggregated only by short contact interactions. So when
the ultrasonic power was increased, the layer-by-layer structure
would be easily peeled off. So the four-side prism became
thinner and thinner with the increase of the ultrasonic power,
and nally turned into a rhombic nano-sheet structure, as
shown in Fig. 7.
To obtain further insight into the mechanism of the ultra-
sonic effect on the uorescent properties of ITPADA at the
molecular level, DFT calculations were performed by using
Gaussian 09w at the B3LYP/6-31G(d) level. Fig. 8 shows the
optimization geometry structure, the spatial electron distribu-
tions and the orbital energies of the HOMO and LUMO of
ITPADA in free and in single crystals by Gauss calculation. The
optimization geometry structure in free crystals can be used to
estimate the geometry structure of ITPADA in its diluted solu-
tion or in its amorphous form. Compared with these two situ-
ations, the molecules in the single crystals (Type 1 and Type 2)
turned more tortuous and non-coplanar due to the existence of
the strong intermolecular interactions. Thus the band gaps of
the molecules in single crystals (DEg, 4.192 eV and 4.544 eV)
were much higher than that in free crystals (3.765 eV). Higher
energy was thus needed for electronic transitions; as a result,
the maximum uorescent wavelength of the crystals was obvi-
ously blue-shied than that in diluted solution or in its amor-
phous aggregates. On the other hand, compared with the
Fig. 8 The optimization geometry structure, the spatial electron
distributions and the orbital energy of the HOMO and LUMO of
ITPADA in free and in single crystals by Gauss calculation.
ITPADA molecules in amorphous form, like the spherical
particles, the intramolecular rotation of ITPADA molecules in
the crystal lattice was greatly restricted, which would greatly
reduce the energy relaxation of the excited state. Thus, the
uorescence intensity and the uorescent quantum yield were
greatly enhanced.
Conclusions
In conclusion, a novel ultrasonic sensitive mechanouoro-
chromic AIE-compound (ITPADA) has been designed and
synthesized. The uorescent properties of the ITPADA suspen-
sions and its aggregation morphologies were greatly affected by
the ultrasonic treatment and extremely sensitive to its power.
The maximum uorescent wavelength of ITPADA suspensions
was abnormally blue-shied, the uorescent quantum yield was
greatly enhanced, and the aggregation structure was changed
from an amorphous form into regular crystals by sonication.
Moreover, the ITPADA nano-sheets with perfect crystalline
structure could be obtained simply by a facile ultrasonic process
with an appropriate power supply. The theoretical studies by
systematic X-ray diffraction and DFT calculations at the
molecular level showed that in the ITPADA molecule, the imide
and the amino groups play a signicant role. The special
intermolecular interactions among them and the crystalline
growth mode made the ITPADA molecules extremely sensitive
to the external forces, like ultrasound. Such strong interactions
would affect the geometry structure and spatial electron distri-
butions of ITPADA molecules, and thus inuence their uo-
rescent properties. Based on the above mechanism, we are
using this strategy to exploit more ultrasonic-sensitive mecha-
nouoro-chromic compounds in our lab.
Acknowledgements
The nancial support by the National 973 Program of China
Fig. 7 (a) SEM image of the ITPADA crystal obtained by ultrasonic
treatment; (b) molecular packing of ITPADA in the single crystal.
(2014CB643605 and 2011CB606100), the National Natural
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Science Foundation of China (51373204, 51173214, 51233008,
J1103305), the Doctoral Fund of the Ministry of Education of
China (20120171130001), Department of Education of Guang-
dong Province (2012KJCX0005), and the Science and Tech-
nology Bureau of Guangzhou (12C52051577) is gratefully
acknowledged.
S. Yoon, J. W. Chung, J. Gierschner, K. S. Kim, M. Choi,
D. Kim and S. Y. Park, J. Am. Chem. Soc., 2010, 132, 13675.
6 (a) H. T. Baytekin, A. Z. Patashinski, M. Branicki, B. Baytekin,
S. Soh and B. A. Grzybowski, Science, 2011, 15, 308; (b)
G. Zhang, J. Lu, M. Sabat and C. L. Fraser, J. Am. Chem.
Soc., 2010, 132, 2160; (c) S. Kato and C. Pac, Chem. Mater.,
2001, 3, 711.
7 (a) S. Y. Cho, J. G. Kim and C. M. Chung, Sens. Actuators, B,
2008, 134, 822; (b) J. Kunzelman, B. R. Crenshaw,
M. Kinami and C. Weder, Macromol. Rapid Commun., 2006,
27, 1981; (c) A. Pucci, R. Bizzarri and G. Ruggeri, So
Matter, 2011, 7, 3689.
8 (a) E. Graugnard, D. L. Kellis, H. Bui, S. Barnes, W. Kuang,
J. Lee, W. L. Hughes, W. B. Knowlton and B. Yurke, Nano
Lett., 2012, 12, 2117; (b) L. Luo, D. Bozyigit, V. Wood and
M. Niederberger, Chem. Mater., 2013, 25, 4901; (c) C. Mayer
and Y. L. Janin, Chem. Rev., 2013, 114, 2313; (d) A. Pucci
and G. J. Ruggeri, Mater. Chem., 2011, 21, 8282; (e)
K. Ariga, T. Mori and J. P. Hill, Adv. Mater., 2012, 24, 158.
9 Y. Dong, B. Xu, J. Zhang, X. Tan, L. Wang, J. Chen, H. Lv,
S. Wen, B. Li, L. Ye, B. Zou and W. Tian, Angew. Chem., Int.
Ed., 2012, 51, 10782.
Notes and references
1 (a) D. Roy, J. N. Cambre and B. S. Sumerlin, Prog. Polym. Sci.,
2010, 35, 278; (b) P. Theatoa, B. S. Sumerlinb, R. K. O'Reillyc
and T. H. Epps, Chem. Soc. Rev., 2013, 42, 7055; (c)
K. M. Wiggins, J. N. Brantley and C. W. Bielawski, Chem.
Soc. Rev., 2013, 42, 7130; (d) G. Armstrong, S. Davey,
R. Johnson and A. Pichon, Nat. Chem., 2013, 5, 809; (e)
M. Nakahata, Y. Takashima, H. Yamaguchi and A. Harada,
Nat. Commun., 2011, 2, 511; (f) S. Mura, J. Nicolas and
P. Couvreur, Nat. Mater., 2013, 12, 991.
2 (a) Z. G. Chi, X. Q. Zhang, B. J. Xu, X. Zhou, C. P. Ma,
Y. Zhang, S. W. Liu and J. R. Xu, Chem. Soc. Rev., 2012, 41,
3878; (b) Y. Sagara1 and T. Kato, Nat. Chem., 2009, 1, 605;
(c) J. W. Chung, Y. You, H. S. Huh, B. K. An, S. J. Yoon,
S. H. Kim, S. W. Lee and S. Y. Park, J. Am. Chem. Soc.,
2009, 131, 8163; (d) H. Ito, M. Muromoto, S. Kurenuma,
S. Ishizaka, N. Kitamura, H. Sato and T. Seki, Nat.
Commun., 2013, 4, 2009; (e) T. Seki, K. Sakurada and H. Ito,
Angew. Chem., Int. Ed., 2013, 52, 12828; (f) S. Kim,
S. J. Yoon and S. Y. Park, J. Am. Chem. Soc., 2012, 134,
12091; (g) X. L. Luo, J. N. Li, C. L. Li, L. P. Heng,
Y. Q. Dong, Z. P. Liu, Z. S. Bo and B. Z. Tang, Adv. Mater.,
2011, 23, 3261.
10 K. Nagura, S. Saito, H. Yusa, H. Yamawaki, H. Fujihisa,
H. Sato, Y. Shimoikeda and S. Yamaguchi, J. Am. Chem.
Soc., 2013, 135, 10322.
ˇ
´
´
´
11 (a) V. Andruch, M. Burdel, L. Kocurova, J. Sandrejova and
I. S. Balogh, TrAC, Trends Anal. Chem., 2013, 49, 1; (b)
B. Bao, Y. Wang, H. Hu, H. Yao, Y. Li, S. Tang, L. Zheng,
Y. Xu and Z. Liang, Int. J. Biol. Sci., 2013, 9, 463; (c)
J. H. Bang and K. S. Suslick, Adv. Mater., 2010, 22, 1039; (d)
W. Chen and J. Du, Sci. Rep., 2013, 3, 2162.
12 (a) N. Komiya, T. Muraoka, M. Iida, M. Miyanaga,
K. Takahashi and T. Naota, J. Am. Chem. Soc., 2011, 133,
16054; (b) K. Isozaki, H. Takaya and T. Naota, Angew.
Chem., Int. Ed., 2007, 46, 2855; (c) C. D. Dou, D. Li,
H. Y. Zhang, H. Z. Gao, J. Y. Zhang and Y. Wang, Sci.
China: Chem., 2011, 54, 641; (d) C. Dou, D. Chen, J. Iqbal,
Y. Yuan, H. Zhang and Y. Wang, Langmuir, 2011, 27, 6323.
13 (a) J. Kunzelman, M. Kinami, B. R. Crenshaw,
J. D. Protasiewicz and C. Weder, Adv. Mater., 2008, 20, 119;
(b) B. J. Xu, Z. G. Chi, X. Q. Zhang, H. Y. Li, C. J. Chen,
S. W. Liu, Y. Zhang and J. R. Xu, Chem. Commun., 2011, 47,
11080; (c) C. Dou, L. Han, S. Zhao, H. Zhang and Y. Wang,
J. Phys. Chem. Lett., 2011, 2, 666; (d) H. Y. Li, X. Q. Zhang,
Z. G. Chi, B. J. Xu, W. Zhou, S. W. Liu, Y. Zhang and
J. R. Xu, Org. Lett., 2011, 13, 556; (e) F. Wang, M. Y. Han,
K. Y. Mya, Y. Wang and Y. H. Lai, J. Am. Chem. Soc., 2005,
127, 10350.
3 (a) Z. Ma, M. Teng, Z. Wang, S. Yang and X. Jia, Angew. Chem.,
Int. Ed., 2013, 52, 12268; (b) M. Teng, X. Jia, X. Chen, Z. Ma
and Y. Wei, Chem. Commun., 2011, 47, 6078; (c)
X. Q. Zhang, Z. G. Chi, J. Y. Zhang, H. Y. Li, B. J. Xu,
X. F. Li, S. W. Liu, Y. Zhang and J. R. Xu, J. Phys. Chem. B,
2011, 115, 7606; (d) K. Mizuguchi, H. Kageyama and
H. Nakano, Mater. Lett., 2011, 65, 2658; (e) H. Y. Li,
Z. G. Chi, B. J. Xu, X. Q. Zhang, X. F. Li, S. W. Liu,
Y. Zhang and J. R. Xu, J. Mater. Chem., 2011, 21, 3760.
4 (a) X. Q. Zhang, Z. G. Chi, H. Y. Li, B. J. Xu, X. F. Li, W. Zhou,
S. W. Liu, Y. Zhang and J. R. Xu, Chem.–Asian J., 2011, 6, 808;
(b) G. G. Shan, H. B. Li, H. T. Cao, D. X. Zhu, P. Li, Z. M. Su
and Y. Liao, Chem. Commun., 2012, 14, 2000.
5 (a) T. Han, Y. Hong, N. Xie, S. Chen, N. Zhao, E. Zhao,
J. W. Y. Lam, H. H. Y. Sung, Y. Dong, B. Tong and
B. Z. Tang, J. Mater. Chem. C, 2013, 1, 7314; (b) Y. Sagara
and T. Kato, Angew. Chem., Int. Ed., 2011, 50, 9128; (c)
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