Sensitive detection of hazardous explosives via highly
fluorescent crystalline porous aromatic frameworks
Author
Yuan, Ye, Ren, Hao, Sun, Fuxing, Jing, Xiaofei, Cai, Kun, Zhao, Xiaojun, Wang, Yue, Wei, Yen,
Zhu, Guangshan
Published
2012
Journal Title
Journal of Materials Chemistry
DOI
https://doi.org/10.1039/c2jm35341e
Copyright Statement
© 2012 Royal Society of Chemistry. This is the author-manuscript version of this paper.
Reproduced in accordance with the copyright policy of the publisher. Please refer to the journal
website for access to the definitive, published version.
Downloaded from
http://hdl.handle.net/10072/52021
Griffith Research Online
https://research-repository.griffith.edu.au
Sensitive Detection of Hazardous Explosives via Highly Fluorescent
Crystalline Porous Aromatic Frameworks
Ye Yuan,
a
Hao Ren,
a
Fuxing Sun,
a
Xiaofei Jing,
a
Kun Cai,
a
Xiaojun Zhao,
a
Yue Wang,
b
Yen Wei
c
and
Guangshan Zhu
*a
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
A three-dimensional (3D) porous aromatic frameworks (PAF-14) with high fluorescence quantum yield
was synthesized through synthesizing the luminescent monomer of tetra(4-
dihydroxyborylphenyl)germanium (TBPGe) as the building blocks. The powder X-ray diffraction
(PXRD) analysis of the experimental and simulated patterns display the high crystallinity of PAF-14 with
ctn topology. The Argon sorption measurement indicates that PAF-14 possesses high surface area
(Brunauer Emmet Teller surface area: 1288 m
2
g
-1
). Significantly, the introduction of germanium into
PAF-14 skeletons may bring about a low-lying Lowest Unoccupied Molecular Orbital (LUMO) and the
crystalline polymeric backbones enhance the sensitivity of electron delocalization. Therefore the designed
PAF-14 is exhibiting high fluorescence quenching ability for hazardous explosives, such as nitrobenzene,
2,4-DNT (2,4-dinitrotoluene) and TNT (2,4,6-trinitrotoluene).
Introduction
Porous materials have experienced rapid progress in the past few
decades and have been widely explored for various applications,
particularly in gas storage, separation and catalysis.
1
Besides the
well-investigated inorganic porous materials
2
and hybrid metal-
organic frameworks,
3
porous organic frameworks (POFs)
4,5
recently emerged as a new class of porous materials attracting
escalating interests. A number of different types of POFs, such as
covalent organic frameworks (COFs),
6-15
conjugated microporous
polymers (CMPs),
16-21
polymers of intrinsic microporsity
(PIMs),
22-25
element organic frameworks (EOFs),
26-27
triazine-
based organic frameworks (CTFs),
28-31
benzimidazole-linked
polymers (BILP)
32
, Porous Polymer Networks (PPN)
33
, covalent
organic polymers (COP)
34
and porous aromatic frameworks
(PAFs),
35-40
have been reported. Owing to the robust covalent
bonds, high stability and adjustable pore sizes, POFs afford
themselves as novel functional materials with great potential for
different applications. One possibility is the detection of
explosive molecules, which is very important in tackling national
security and environmental pollution.
41-43
As current detection of
explosives exclusively relies on the instruments that are either
quite expensive or difficult to operate.
41
Fluorescence quenching
used for sensing is a much simpler yet very sensitive technique,
which has been investigated in the field of fluorescent MOFs.
45-47
It is well-known that commercial explosives, such as 2,4-DNT
and TNT, possess electronegative group of –NO
2
. It is expected
that electron donating POFs could attract the electronegative -
NO
2
group through coulombic interactions and the crystalline
polymeric skeletons of POFs may facilitate efficient exciton
migration to enhance quenching sensitivity.
48
All these features
should make POFs promising candidates for the detection of the
hazardous explosives. However, this possibility has rarely been
explored due to the difficulty to achieve high fluorescence
quantum yield in crystalline POFs materials for quenching.
On the basis of our previous success of designing highly
porous PAFs,
37,40
we selected the luminescent monomer,
49,50
tetra(4-dihydroxyborylphenyl)germanium, as the building block
to construct the highly fluorescent PAF-14 (Fig. 1). Introduction
of germanium into the PAFs skeletons may bring about a low
reduction potential and low-lying LUMO, due to σ*-π*
conjugation arising from the interaction between σ* orbital of
germanium and π* orbital of phenyl rings.
51,52
Electron
delocalization in the crystalline polymeric backbones provides
one means of amplification, because interaction of an analyte
molecule at any position might quench an excited state or exciton
delocalized along the frameworks.
53
Fig. 1 TBPGe was chosen as the building unit (a). Condensation reaction
of boronic acids afforded PAF-14 (b), with model structure of crystalline
products PAF-14 (c)
Experimental
Materials.
All starting materials were purchased from commercial suppliers
and used without further purification unless otherwise noted.
tetra(4-dihydroxyborylphenyl)germanium was prepared
according to the previously reported method. All reactions were
performed under a purified nitrogen atmosphere.
Synthesis of PAF-14.
Tetra(4-(dihydroxy)borylphenyl)germanium (56.1 mg, 0.10
mmol) and 1.0 mL of a 1:1 v:v solution of mesitylene/dioxane
was mixed in a pyrex tube. Then the tube was flash frozen at 77
K (Liquid N
2
bath), evacuated to an internal pressure of 150
mTorr and flame sealed. The reaction mixture was heated at
85 °C for 72 h to afford a white precipitate which was isolated by
filtration over a medium glass frit and washed with anhydrous
tetrahydrofuran (10 mL). The product was immersed in
anhydrous tetrahydrofuran (10 mL) for 4 h, during which the
activation solvent was decanted and freshly replenished four
times. The solvent was removed under vacuum at room
temperature to afford PAF-14 as a white powder (29.1 mg, 65 %).
Physical measurements.
TG analysis was performed using a Netzch Sta 449c thermal
analyzer system at the heating rate of 10 °C min
-1
in air
atmosphere. Fourier Transform Infrared Spectroscopy (FTIR)
spectra (film) was measured using a Nicolet Impact 410 Fourier
transform infrared spectrometer. The Ar adsorption isotherm was
measured on a Quantachrome Autosorb-iQ. PXRD was
performed by a Riguku D/MAX2550 diffractometer using CuKα
radiation, 40 kV, 200 mA with scanning rate of 0.3 °/min (2θ).
SEM and energy-dispersive X-ray spectroscopy (EDS) analyses
were performed on a JEOS JSM 6700. The solid-state
13
C and
11
B
cross polarization magic angle spinning nuclear magnetic
resonance (CP MAS NMR) spectra were recorded on a Bruker
AVANCE III 400 WB spectrometer. The absolute quantum yield
of fluorescence (Φ
FL
) was recorded on a Edinburgh FLSP920.
Results and discussion
Fourier Transform Infrared Spectroscopy (FTIR) and cross
polarization magic angle spinning nuclear magnetic resonance
(CP MAS NMR) were employed to confirm the bonding and
structural features in polymeric materials. The condensation
reaction for PAF-14 can be evaluated by FTIR spectra. The
appearance of the expected B
3
O
3
boroxine [B
3
O
3
(707 cm
-1
)] (Fig.
2), confirmed the almost completeness of the cross-coupling
reaction. The structural assignments of PAF-14 was revealed by
CP MAS NMR spectroscopic studies. The solid-state
11
B CP
MAS NMR spectra of the activated product is highly sensitive to
the immediate bonding environment of boron. In addition,
13
C
solid-state NMR experiment was also performed to reveal the
local structures of PAF-14, which strongly indicate the
environments of respective atoms. As shown in Fig. 3, all the
expected signals are matched with the predicted chemical shift
values.
Fig. 2 FT-IR spectrum of PAF-14 (red) and TBPGe (black).
Fig. 3 Solid-state
13
C and
11
B NMR spectras for PAF-14 (a and b).
The experimentally PXRD pattern displays narrow line widths,
indicative of the high crystallinity of PAF-14 (Fig. 4). According
to the criteria by O’Keeffe, fitting tetrahedral and triangular
building units can expediently generate ctn or bor nets.
54
The
consistence between the experimental PXRD pattern and
simulated ones based on the ctn topology validates the structural
models for PAF-14. The optimal simulation reveals the space
group of I-43d with the cell parameters of a = 28.69 Å. The
topology of PAF-14 is the same as that of COF-102 and COF-
105.
6
Fig. 4 PXRD profiles for PAF-14 including patterns calculated with the
use of Material Studio 5.0, with observed profiles in black, calculated
patterns in red.
Scanning electron microscopy (SEM) was performed to probe
the shape of PAF-14. As shown in Fig. S2a, PAF-14 is
agglomerated nanoparticles with size around 100 nm. In addition,
energy-dispersive X-ray spectroscopy (EDS) analysis of the
various elements confirmed the compositions of PAF-14 derived
from modelled structure (Fig. S2b) and the result was
corresponded to formulations predicted from modeling. The
thermal stability of PAF-14 was assessed by thermogravimetric
analysis (TGA), which reveals it can stabilize up to 230 ℃ (Fig.
S3).
To characterize the nature of the pores, a fresh PAF-14 sample
was fully activated at 100
o
C under dynamic vacuum for 24 h to
remove the guest solvent molecules, and Argon sorption of PAF-
14 (110 mg) was measured at 87 K from 0 to 760 torr. It exhibits
a typical type I isotherm featured by a sharp uptake at the low-
pressure region between P/P
0
= 1 × 10
−5
to 1 × 10
−2
, where P is
gas pressure and P
0
is saturation pressure (Fig. 5). The apparent
surface area is 1288 m
2
g
-1
from BET model and the apparent
surface area calculated from Langmuir model is 1345 m
2
g
-1
. The
pore size distribution (PSD) obtained from non-local density
functional theory (NLDFT) gave a narrow distribution in
microporous region.
Fig. 5 Reversible argon gas adsorption isotherms for PAF-14 measured at
87 K. STP, standard temperature and pressure. Pore size distribution for
PAF-14 (insert) calculated by NLDFT method.
The absolute quantum yield of fluorescence (Φ
FL
) value of
PAF-14 was as high as 37.53 % in CH
2
Cl
2
at 25 °C was evaluated
using the integrating sphere method.
55
The delocalized π electrons
in the systems increased the electrostatic interaction between
PAF-14 and analytes. The photoluminescence (PL) spectra of
PAF-14 uniformly dispersed in CHCl
3
showed maximum
emission at 371 nm (excited at 250 nm). As expected, the
addition of 150 ppm common aromatic compounds such as
benzene, toluene, chlorobenzene, bromobenzene, phenol and
aniline basically does not affect the luminescence intensity (Fig.
6). However, quenching effect with different levels could be
observed upon the addition of nitroaromatics such as
nitrobenzene, 2,4-DNT (2,4-dinitrotoluene) and TNT (2,4,6-
trinitrotoluene) when dispersed PAF-14 in CHCl
3
.
Fig. 6 PL spectra of the CHCl
3
solutions of PAF-14 with different
analytes (excited at 250 nm). Benzene, toluene, chlorobenzene,
bromobenzene, phenol, aniline, nitrobenzene, 2,4-DNT, and TNT are
represented as red, green, blue, cyan, magenta, yellow, navy, purple and
wine, respectively.
As shown in Fig. 7, after the addition of nitrobenzene, 2,4-
DNT and TNT with different concentrations in the samples
respectively, high luminescence quenching ability can be observe
for PAF-14, which is much more significant than the MOF-1
56
and Zn(II)-MOF
57
. The strong quenching might be explained by
the interaction between the host and guest interaction that the
great amount of electron donor conjugated groups with
delocalized π electrons facilitate the electrostatic interaction
between PAF-14 and electron deficient compounds.
58,59
It is
worth noting that detection limit among the best for porous
materials-based sensors, high-light its potential as a new type of
sensor materials.
60
Fig. 7 PL spectra of the CHCl
3
solutions of PAF-14 (a, b and c) with
different analytes concentration (excited at 250 nm).
Conclusions
In summary, we have selected the luminescent monomer,
tetra(4-dihydroxyborylphenyl)germanium (TBPGe), as the
building block to construct new PAFs. The three-dimensional
(3D) crystalline PAFs material, PAF-14, was successfully
designed and synthesized with high fluorescence quantum yield.
Experimental results indicate that PAF-14 is highly crystalline
with ctn topology. Particularly, owing to the introduction of
germanium into the crystalline skeletons, PAF-14 exhibits high
luminescence quenching ability for nitroaromatics compounds,
making this PAF materials promising for the detection of
hazardous explosive compounds.
Acknowledgements
We are grateful for the financial support of National Basic
Research Program of China (973 Program, grant nos.
2012CB821700), Major International (Regional) Joint Research
Project of NSFC (grant nos.21120102034) and NSFC (grant nos.
20831002).
Notes and references
a
State Key Laboratory of Inorganic Synthesis and Preparative Chemistry,
College of Chemistry, Jilin University, Changchun, China (130012), Fax:
86 0431 85168331; Tel: 86 0431 85168887; E-mail: zhugs@jlu.edu.cn.
b
State Key Laboratory of Supramolecular Structure and Materials,
College of Chemistry, Jilin University, Changchun, China (130012)
C
.Department of Chemistry, Tsinghua University, Beijing, China (100084)
† Electronic Supplementary Information (ESI) available: Details of the
study and characterization data are provided.
See DOI: 10.1039/b000000x
1. M. E. Davis, Nature, 2002, 417, 813-821.
2. C. S. Cundy, P. A. Cox, Micropor. Mesopor. Mat., 2005, 82, 1.
3. N. Brun, S. Ungureanu, H. Deleuze, R. Backov, Chem. Soc. Rev.,
2011, 40, 771.
4. A. Thomas, P. Kuhn, J. Weber, M. M. Titirici, M. Antonietti,
Macromol Rapid Comm., 2009, 30, 221.
5. N. B. McKeown, P. M. Budd, Macromolecules, 2010, 43, 5163.
6. H. M. El-Kaderi, J. R. Hunt, J. L. Mendoza-Cortes, A. P. Cote, R. E.
Taylor, M. O'Keeffe, O. M. Yaghi, Science, 2007, 316, 268.
7. A. P. Cote, A. I. Benin, N. W. Ockwig, M. O'Keeffe, A. J. Matzger,
O. M. Yaghi, Science, 2005, 310, 1166.
8. H. Furukawa, O. M. Yaghi, J. Am. Chem. Soc., 2009, 131, 8875.
9. A. P. Cote, H. M. El-Kaderi, H. Furukawa, J. R. Hunt, O. M. Yaghi,
J. Am. Chem. Soc., 2007, 129, 12914.
10. X. S. Ding, J. Guo, X. A. Feng, Y. Honsho, J. D. Guo, S. Seki, P.
Maitarad, A. Saeki, S. Nagase, D. L. Jiang, Angew. Chem. Int. Edit., 2011,
50, 1289.
11. S. Wan, J. Guo, J. Kim, H. Ihee, D. L. Jiang, Angew. Chem. Int.
Edit., 2008, 47, 8826.
12. S. Wan, J. Guo, J. Kim, H. Ihee, D. L. Jiang, Angew. Chem. Int.
Edit., 2009, 48, 5439.
13. L. Chen, Y. Honsho, S. Seki, D. L. Jiang, J. Am. Chem. Soc., 2010,
132, 6742.
14. R. W. Tilford, S. J. Mugavero, P. J. Pellechia, J. J. Lavigne, Adv.
Mater., 2008, 20, 2741.
15. R. W. Tilford, W. R. Gemmill, H. C. zur Loye, J. J. Lavigne, Chem.
Mater., 2006, 18, 5296-5301.
16. J. X. Jiang, F. Su, A. Trewin, C. D. Wood, N. L. Campbell, H. Niu,
C. Dickinson, A. Y. Ganin, M. J. Rosseinsky, Y. Z. Khimyak, A. I.
Cooper, Angew. Chem. Int. Edit., 2007, 46, 8574.
17. J. X. Jiang, F. Su, H. Niu, C. D. Wood, N. L. Campbell, Y. Z.
Khimyak, A. I. Cooper, Chem. Commun., 2008, 4, 486.
18. E. Stockel, X. F. Wu, A. Trewin, C. D. Wood, R. Clowes, N. L.
Campbell, J. T. A. Jones, Y. Z. Khimyak, D. J. Adams, A. I. Cooper,
Chem. Commun., 2009, 2, 212.
19. C. D. Wood, B. Tan, A. Trewin, H. J. Niu, D. Bradshaw, M. J.
Rosseinsky, Y. Z. Khimyak, N. L. Campbell, R. Kirk, E. Stockel, A. I.
Cooper, Chem. Mater., 2007, 19, 2034.
20. R. Dawson, A. Laybourn, R. Clowes, Y. Z. Khimyak, D. J. Adams,
A. I. Cooper, Macromolecules, 2009, 42, 8809.
21. R. Dawson, D. J. Adams, A. I. Cooper, Chem. Sci., 2011, 2, 1173.
22. P. M. Budd, B. S. Ghanem, S. Makhseed, N. B. McKeown, K. J.
Msayib, C. E. Tattershall, Chem. Commun., 2004, 2, 230.
23. P. M. Budd, N. B. McKeown, D. Fritsch, J. Mater. Chem., 2005, 15,
1977.
24. N. B. McKeown, P. M. Budd, Chem. Soc. Rev., 2006, 35, 675.
25. B. S. Ghanem, N. B. McKeown, P. M. Budd, J. D. Selbie, D. Fritsch,
Adv. Mater., 2008, 20, 2766.
26. M. Rose, W. Bohlmann, M. Sabo, S. Kaskel, Chem. Commun., 2008,
21, 2462.
27. M. Rose, N. Klein, W. Bohlmann, B. Bohringer, S. Fichtner, S.
Kaskel, Soft Matter, 2010, 6, 3918.
28. P. Kuhn, M. Antonietti, A. Thomas, Angew. Chem. Int. Edit., 2008,
47, 3450.
29. J. Weber, M. Antonietti, A. Thomas, Macromolecules, 2008, 41,
2880.
30. J. Weber, A. Thomas, J. Am. Chem. Soc., 2008, 130, 6334.
31. P. Kuhn, A. Thomas, M. Antonietti, Macromolecules, 2009, 42, 319.
32. M. G. Rabbani, T. E. Reich, R. M. Kassab, K. T. Jackson, H. M. El-
Kaderi, Chem. Commun., 2012, 48, 1141.
33. D. Q. Yuan, W. G. Lu, D. Zhao, H. C. Zhou, Adv. Mater., 2011, 23,
3723.
34. H. A. Patel, F. Karadas, A. Canlier, J. Park, E. Deniz, Y. S. Jung, M.
Atilhan, C. T. Yavuz, J. Mater. Chem., 2012, 22, 8431.
35. T. Ben, C. Y. Pei, D. L. Zhang, J. Xu, F. Deng, X. F. Jing, S. L. Qiu,
Energ. Environ. Sci., 2011, 4, 3991.
36. H. Ren, T. Ben, E. S. Wang, X. F. Jing, M. Xue, B. B. Liu, Y. Cui,
S. L. Qiu, G. S. Zhu, Chem. Commun., 2010, 46, 291.
