A silicon-cored fluoranthene derivative as a fluorescent probe for detecting nitroaromatic compounds

Article abstract of DOI:10.1039/c4tc01183j

Two fluoranthene derivatives, nonsilicon-cored 7,10-diphenylfluoranthene (DF) and silicon-cored bis(7,10-diphenylfluoranthen-8-yl)diphenylsilane (BDS), were synthesized via the Knoevenagel/Diels-Alder method. The thermal properties and fluorescence quench

Full text of DOI:10.1039/c4tc01183j

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Materials Chemistry C
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A silicon-cored fluoranthene derivative as a
fluorescent probe for detecting nitroaromatic
Cite this: J. Mater. Chem. C, 2014, 2,
compounds
9425
Huanling Xie,a Hua Wang,a Zhen Xu,b Ruijing Qiao,a Xuefeng Wang,a Xianming Wang,c
c
a
a
*
*
Lianfeng Wu, Haifeng Lu and Shengyu Feng
Two fluoranthene derivatives, nonsilicon-cored 7,10-diphenylfluoranthene (DF) and silicon-cored bis(7,10-
diphenylfluoranthen-8-yl)diphenylsilane (BDS), were synthesized via the Knoevenagel/Diels–Alder method.
The thermal properties and fluorescence quenching behavior of the derivatives with nitroaromatic
compounds were investigated. Aside from its better thermal properties, BDS also showed lower
detection limit, higher sensitivity, and higher quenching efficiency in detecting nitrobenzene and m-
dinitrobenzene than DF. The detection limits of BDS were 50 and 10 ppm toward nitrobenzene and m-
dinitrobenzene, respectively. Moreover, the Stern–Volmer plot of BDS swiftly curved upward, suggesting
a super amplification effect. This result can be attributed to the special tetrahedral structure of BDS.
Thus, BDS has great potential in the detection of explosives. This work may serve as a basis for designing
new organic materials with great efficiency and sensitivity in fluorescence detection.
Received 5th June 2014
Accepted 14th September 2014
DOI: 10.1039/c4tc01183j
www.rsc.org/MaterialsC
Fluorescence quenching has been recently found to be an
efficient detection method for nitroaromatic explosives because
Introduction
of its high sensitivity, easy visualization, and short response
time.8,13–25 The design and preparation of uorescent materials
are the key factors in this technique. Metal–organic frameworks
(MOFs), particularly luminescent MOF sensors, have been
widely used to detect nitroaromatic compounds because of their
high selectivity and sensitivity.13,26–28 However, the preparation
of MOFs is complicated and expensive, which limits the appli-
cation of these materials.
Organic materials are suitable candidates in uorescence
quenching because of their abundance and exible molecular
design.29–32 Among these organic materials, electron-rich
aromatic compounds have a high quenching efficiency toward
electron-decient nitroaromatic compounds.31,32
However, aromatic compounds have a serious disadvantage.
That is, aromatic molecules demonstrate poor detection
capacity because they easily aggregate and cause uorescence
quenching. The silicon-cored structure can improve the uo-
rescence efficiency of aromatic compounds in organic light-
emitting devices.27,33–38 Silicon-cored aromatic derivatives have
several advantages over common aromatic compounds. These
advantages include well-dened structures, higher glass tran-
sition temperatures, thermal stability, and better uorescent
properties in solid lms. Organic silicon compounds have been
synthesized and applied as uorescent probes. Therefore,
silicon-cored compounds can be used in detecting applications
to solve the uorescence quenching problem of aromatic
compounds.
The serious environmental pollution in recent years has placed
urgency in the design and preparation of chemical sensors for
nitroaromatic compound detection.1–5 Nitrobenzene, dini-
trotoluene (DNT), and trinitrotoluene (TNT) are the primary
nitroaromatic compounds that can cause signicant harm to
humans. Aside from their explosive nature, nitroaromatic
compounds severely pollute the environment and cause head-
aches, anemia, skin irritation, and eye and neurological damage
to humans.6–10 Therefore, nding an efficient detection method
for nitroaromatic compounds is crucial to protect humans and
the environment. Gas chromatography-mass spectrometry, ion
mobility spectroscopy, surface-enhanced Raman spectroscopy,
and other spectroscopic techniques have been used to detect
nitroaromatic explosives.11,12 However, the practical applica-
tions of these instrumental techniques are limited by their high
cost, low selectivity, and low sensitivity. Thus, developing new
techniques with efficient and sensitive detection capabilities is
an important undertaking.
aKey Laboratory of Special Functional Aggregated Materials & Key Laboratory of
Colloid and Interface Chemistry (Shandong University) Ministry of Education,
School of Chemistry and Chemical Engineering, Shandong University, Jinan,
250100, P. R. China. E-mail: fsy@sdu.edu.cn; Fax: +86-531-88564464; Tel: +86-531-
88364866
bCollege of Material Science and Chemical Engineering, Tianjin University of Science
and Technology, Tianjin 300457, P. R. China
cMarine Chemical Research Institute Company Limited and State Key Laboratory of
Marine Coatings, Qingdao, P. R. China
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Accordingly, this study designed and synthesized two
The uoranthene derivatives were synthesized via the
uoranthene derivatives, nonsilicon-cored 7,10-diphenyl- Knoevenagel/Diels–Alder method from acenaphthenequinone
uoranthene (DF) and silicon-cored bis(7,10-diphenyl- and 1,3-diphenylpropan-2-one. The synthesis routes are shown
uoranthene-8-yl)diphenylsilane (BDS). Fluoranthene is an in Scheme 1.
excellent uorescent material that has attracted increasing
attention in recent years. Wudl reported that modifying a DCA was synthesized from acenaphthenequinone and
uoranthene derivative with a phenyl group can effectively 1,3-diphenylpropan-2-one according to a literature method.42
1. 7,9-Diphenyl-8H-cyclopenta[a]acenaphthylen-8-one (DCA).
A
reduce uorescence quenching.39 Meanwhile, Patil et al. three-necked 250 mL round bottom ask was equipped with a
detected nitroaromatics using uoranthene derivatives.40 reux condenser and ethanol (60 mL). Then acenaph-
These derivatives exhibit excellent detection capability for thenequinone (5.47 g, 0.03 mol) and 1,3-diphenylpropan-2-one
nitroaromatic compounds. In the present report, we added a (6.3 g, 0.03 mol) were added, heated and stirred. When the solution
silicon atom into a uoranthene derivative to form a tetra- mixture began to reux, ethanol solution (5 mL) of KOH (0.8 g) was
hedral structure. We previously investigated the optical added dropwise to the slightly boiling solution via a drop funnel.
properties of the silicon-cored derivative in solution and the The reaction mixture immediately became black and formed a
solid state.41 Our results showed that the silicon-cored black precipitate. Aer the dropwise addition of the ethanol
derivative exhibits better uorescent properties than diphe- solution, the reaction was allowed to continue for 2 h. The above
nyluoranthene. In the present study, we explored the uo- solution was cooled to room temperature, and was ltered to
rescence quenching behavior of the silicon-cored derivative obtain the crude product. Then the product was washed with
toward nitrobenzene and m-dinitrobenzene to further eluci- ethanol several times. The pure product was obtained as a purple-
date its uorescent properties and applications. We hope black solid powder with a yield of 90% (10.7 g). 1H NMR (CDCl3,
that this method can retain the excellent uorescent prop- 400 MHz, ppm): d 8.08 (d, 2H), 7.86 (m, 6H), 7.61 (dd, 2H), 7.54 (dd,
erties of uoranthene while improving its thermodynamic 4H), 7.42 (t, 2H). 13C NMR (CDCl3, 100 MHz, ppm): d 154.2, 132.1,
properties, sensitivity, and response time in detecting 131.5, 131.4, 129.0, 128.6, 128.3, 127.8, 121.7, 120.9.
nitroaromatic compounds. The thermodynamic properties
2. (7,10-Diphenyluoranthen-8-yl)trimethylsilane (DFTS).
and uorescence quenching behavior of the derivatives with Under an argon atmosphere, 1.48 g (15 mmol) ethynyl-
nitroaromatic compounds were also investigated. Compared trimethylsilane and 3.44 g (10 mmol) DCA were dissolved in 30
with DF, BDS exhibited better thermal stability and detection mL xylene in a sealed stainless steel reactor, and the reaction
capability. Both showed a special curve relationship between mixture was heated at 230 ꢀC for 20 h. Then xylene was removed
their emission intensity and nitroaromatic compound under reduced pressure. The crude product was precipitated in
concentration, and were sensitive to the presence of nitro- a large amount of methanol and puried by silica gel column
aromatic compounds. BDS showed a lower detection limit to chromatography. Finally, the pure product was obtained as a
nitroaromatic compounds than DF. Compared with DF, BDS yellow solid powder with a yield of 55% (2.32 g). 1H NMR
exhibited better thermal properties, higher sensitivity, and (DMSO, 400 MHz, ppm): d 0.02 (s, 9H), 6.30 (d, 1H), 7.35 (t, 1H),
higher quenching efficiency in detecting nitrobenzene and 7.46–7.68 (m, 13H), 7.82–7.89 (m, 2H). 13C NMR (CDCl3, 100
m-dinitrobenzene. Therefore, BDS has great potential in MHz, ppm): d 1.07 (Si–CH3), 123.2, 123.3, 127.3, 127.8, 128.3,
detecting nitroaromatic compounds.
128.5, 128.7, 129.1, 129.3, 129.4, 129.9, 130.1, 132.4, 135.5,
135.6, 136.4, 136.6, 137.0, 137.2, 138.7, 140.8, 141.4.
3. 7,10-Diphenyluoranthene (DF). 2.00 g (4.6 mmol) DFTS
and concentrated hydrochloric acid (4 mL) were dissolved in 30
mL THF solution. The mixture was reuxed for 10 h. And then
the solvent was removed. The crude product was precipitated in
Experimental section
Materials and methods
Dichloromethane and ethanol were purchased from Tianjin
Fuyu Chemical Engineering Company. Acenaphthenequinone
and 1,3-diphenyl-propan-2-one were purchased from Shanghai
Chemical Reagent Company.
1H, 13C and 29Si NMR spectra were recorded on a Bruker
Avance-400 NMR spectrometer. Elemental analyses (C, H and N)
were carried out on an Elementar Vario MICRO CUBE (Ger-
many) elemental analyzer. The UV-visible spectra were recorded
with a TU-1901 double-beam UV-visible spectrophotometer. The
uorescence spectra were recorded with a Hitachi F-7000
spectrophotometer. Thermal gravimetric analyses (TGA) were
performed with a Mettler Toledo SDTA-854 TGA system in
nitrogen at a heating rate of 10 ꢀC minꢁ1. Differential scanning
calorimetry (DSC) measurement was performed with a Mettler
Toledo DSC-822 system in nitrogen at a heating rate of
ꢁ1
ꢀ
10 C min
.
Scheme 1 The synthesis routes towards the fluoranthene derivatives.
9426 | J. Mater. Chem. C, 2014, 2, 9425–9430
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a large amount of methanol and puried by silica gel column 128.56, 129.26, 129.66, 130.06, 132.87, 133.88, 135.96, 135.99,
chromatography. Finally, the pure product was obtained as a 136.45, 136.57, 136.85, 137.55, 138.39, 139.00, 140.56, 141.13,
yellow crystal with a yield of 90% (1.46 g). 1H NMR (CDCl3, 400 144.43. 29Si NMR (CDCl3, 80 MHz, ppm): d ꢁ14.71. Anal. calcd
MHz, ppm): d 7.24 (d, 2H), 7.29 (s, 2H), 7.37 (t, 2H), 7.52–7.60 for C68H44Si: C 91.85%, H 4.99%. Found: C 91.24%, H 4.87%.
(m, 6H), 7.67 (m, 4H), 7.78 (d, 2H). 13C NMR (CDCl3, 100 MHz,
ppm): d 123.0, 126.7, 127.6, 127.8, 128.7, 129.1, 129.8, 132.8,
136.3, 136.8, 138.0, 141.0. Anal. calcd for C28H18: C 94.88%, H
Results and discussion
5.12%. Found: C 94.83%, H 5.17%.
Optical properties
4. Diethynyldiphenylsilane (DDS). Under an argon atmo-
sphere, 2.4 g (100 mmol) magnesium powder and anhydrous
THF (20 mL) were added to a 100 mL three-necked round bottle.
Under stirring, THF solution (25 mL) of 10.9 g (100 mmol) ethyl
bromide was slowly added dropwise into the ask. Aer all the
magnesium powder disappeared, the reaction mixture was
allowed to boil for 2 h. Aer cooling to room temperature, the
bromoethane Grignard reagent was obtained.
First, the acetylene gas, which was cooled at ꢁ78 ꢀC, was
bubbled into dry 150 mL THF for 1 h to obtain the acetylene
saturated solution. Then the bromoethane Grignard reagent
was added into the acetylene saturated solution. In this process,
acetylene was always kept bubbling into the mixture for 0.5 h.
The reaction was kept for 2 h aer the dropping of the bro-
moethane Grignard reagent was completed. Then the acetylene
Grignard reagent was obtained. A 500 mL three-necked, round
bottom ask was equipped with a reux condenser and a stirrer.
The ask was charged with the acetylene Grignard reagent
obtained in the last step.
The absorption spectra of the two compounds in THF solution
are shown in Fig. 1(a). DF exhibited two absorption peaks
centered at 371 and 326 nm, originating from the p–p* tran-
sitions. The silicon-cored uoranthene derivative showed a
similar absorption spectrum to DF. BDS exhibited two absorp-
tion peaks centered at 372 and 328 nm, and only showed a slight
bathochromic shi compared with DF. In other words, the
silicon-cored structure only slightly inuenced the conjugated
degree and absorption spectra of diphenyluoranthene.
Fig. 1(b) shows the uorescent emission spectra of DF and
BDS in THF solution and in the solid thin lm. The maximum
emission peaks of DF and BDS appeared at 446 and 453 nm in
solution, respectively. The emission spectra of the two
compounds were similar. The uorescence of BDS showed only
a slight bathochromic shi to DF. This phenomenon also
indicated that the silicon-cored structure only slightly inu-
enced the conjugation degree of diphenyluoranthene.
However, the emission spectra of them in the solid thin lm
exhibited red shi compared with those in solution. In contrast,
the uorescent emission spectra of the silicon-cored derivative
showed shorter wavelengths of red shi than that of diphenyl-
uoranthene. It indicated that the silicon-cored structure could
prevent the close-packing of molecules and thus effectively
restrain the intermolecular interactions.
In an ice water bath, 20.26 g (80 mmol) diphenyldi-
chlorosilane and THF (30 mL) were added drop-wise to the well
stirred reaction mixture over 0.5 h. It was quenched by the
addition of methanol (10 mL). The organic layer was washed
with water, dried with anhydrous MgSO4, ltered, and concen-
trated at reduced pressure. The product was puried by silica
gel column chromatography. The pure product was obtained as
a straw yellow crystal with a yield of 70% (13 g) and petroleum
ether as an eluent. 1H NMR (CDCl3, 400 MHz, ppm): d 7.75 (m,
4H, ArH), 7.26–7.50 (m, 6H, ArH), 2.75 (s, 2H, –C^CH).
5. Bis(7,10-diphenyluoranthen-8-yl)diphenylsilane (BDS).
Under an argon atmosphere, a three-necked 100 mL round
bottom ask was equipped with a reux condenser and a
thermometer and charged with 306.5 mg (0.86 mmol) 7,9-
diphenyl-8H-cyclopenta[a]acenaphthylen-8-one and 100 mg
(0.43 mmol) diethynyldiphenylsilane. A minimal amount (7 mL)
of diphenyl ether was added. The reaction mixture was heated at
Thermal properties
The thermal properties of DF and BDS were studied by both
differential scanning calorimetry and thermogravimetric anal-
ysis (Fig. 2 and Table 1).
Table 1 shows that the glass transition temperature (Tg) of
BDS was 250 ꢀC, which was 190 ꢀC higher than that of DF. This
result can be attributed to the molecular tetrahedral congu-
ration formed by the silicon-cored structure. Meanwhile, the
melting temperatures (Tm) of DF and BDS were 165 ꢀC and 350
ꢀC, respectively. The better stability of BDS than DF when they
were prepared into solid lms can be attributed to the higher Tg
and Tm of the former than the latter. BDS also showed higher
ꢀ
230 C for 8 h with vigorous stirring, with a color of heteroge-
neous solution varying from purple-black to homogeneous and
transparent black-red. The reaction mixture was cooled for a
while and poured into a large amount of methanol (150 mL) to
precipitate the crude solid product, which was obtained by
ltration and washed with copious amounts of methanol. What
is more, the above steps were repeated several times and nally
the pure product was obtained as a canary yellow solid powder
with a yield of 30% (114 mg). 1H NMR (CDCl3, 400 MHz, ppm): d
6.04 (d, 2H), 6.94 (d, 8H), 7.08 (t, 4H), 7.15–7.25 (m, 10H), 7.32–
7.40 (m, 4H), 7.50–7.67 (m, 6H), 7.64–7.68 (m, 8H), 7.75 (d, 2H).
13C NMR (CDCl3, 100 MHz, ppm): d 123.19, 123.42, 126.27,
126.96, 127.14, 127.30, 127.41, 127.61, 127.69, 127.96, 128.28, Fig. 1 Absorption and emission spectra of DF and BDS.
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Fig. 4 The fluorescent emission spectra of DF (20 mM) and BDS (10
mM) (upon addition of nitrobenzene in THF solution and the obtained
Stern–Volmer curve with nitrobenzene (0–1500 ppm)).
Fig. 2 The differential thermogravimetric curves of DF and BDS.
Table 1 Thermal properties of DF and BDS; Tg: glass transition; Tm:
melting temperature; Td: decomposition temperature
content. In addition, uorescence quenching was obvious.
When the nitrobenzene content was up to 1500 ppm, the uo-
rescence quenching efficiencies of DF and BDS were 71% and
80%, respectively.
Interestingly, the I0/I–C plots of DF and BDS swily curved
upward, suggesting a super amplication effect. Therefore, DF
Compound
Tg (ꢀC)
Tm (ꢀC)
Td (ꢀC)
DF
BDS
60
250
165
350
298
444
decomposition temperatures (corresponding to 5% weight loss) and BDS had high uorescence sensitivity for nitrobenzene
than DF. This result may be attributed to the H of BDS in the C-8 detection, with detection limits of 100 and 50 ppm, respectively.
position.41
When the nitrobenzene content was up to 200 ppm, the uo-
rescence quenching efficiencies of DF and BDS were 20% and
31.19%, respectively.
Fluorescence quenching of nitroaromatic compounds in
solution
The difference in detection degree and uorescence
quenching efficiency of the two compounds may be attributed
to their molecular structures. DF showed a plane molecular
structure with two phenyl groups twisting out of the core,
whereas BDS possessed a “V” structure that connects two 7,10-
diphenyluoranthene groups.41 The two 7,10-diphenyl-
uoranthene units were signicantly twisted against each other
because of the tetrahedral environment of the central silicon
core, resulting in a noncoplanar conguration.41 This special
tetrahedral structure enhanced the p–p interaction between
BDS and nitrobenzene. As shown in Fig. 5, one nitrobenzene
molecule can intermolecularly interact with one DF molecule
because of the plane structure. However, one nitrobenzene
molecule can simultaneously inuence two uorescent groups
because of the “V” structure of BDS.
We further examined the detection capabilities of DF and
BDS to m-dinitrobenzene. The results are shown in Fig. 6(a) and
(b) for DF and BDS. The I0/I–C plots of the two compounds
swily curved upward, suggesting a super amplication effect.
This trend was similar to that observed in nitrobenzene detec-
tion. Furthermore, the uorescence quenching response of BDS
was observed at a low m-dinitrobenzene concentration of 10
The uorescence spectra of DF and BDS immersed in different
organic solvents, such as acetone, methanol, ethanol, acetoni-
trile, DMF, CH2Cl2, CHCl3, and nitrobenzene, were tested. As
shown in Fig. 3(a) and (b) for DF and BDS, all the emission
spectra of DF and BDS revealed linker-based emission with the
same broad maximum at 446 and 453 nm, respectively. A
signicant uorescence quenching effect was observed for
nitrobenzene (Fig. 3).
This phenomenon can be attributed to the electron transfer
from the benzene rings of DF and BDS to electron-decient
nitrobenzene and their interactions with nitrobenzene mole-
cules. These results demonstrate that DF and BDS exhibit high
selectivity for nitrobenzene compared with other small mole-
cules. Therefore, DF and BDS can be used as uorescent sensors
for nitrobenzene detection.
To examine the sensing ability and monitor the uorescent
response of DF and BDS toward nitrobenzene, the two
compounds were dispersed in THF solution with gradually
increasing nitrobenzene content.
As shown in Fig. 4(a) and (b) for DF and BDS, the emission
intensity gradually decreased with increasing nitrobenzene
Fig. 3 The fluorescent emission spectra of DF and BDS in different Fig.
5
Diagram of DF and BDS with nitrobenzene producing
solvents (DMF ¼ N,N-dimethylformamide).
interaction.
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Fig. 6 The fluorescent emission spectra of DF (20 mM) and BDS (10
mM) upon addition of m-dinitrobenzene in THF solution and the
obtained Stern–Volmer curve with m-dinitrobenzene (0–500 ppm)
(m-DNB ¼ m-dinitrobenzene).
ppm. The silicon-cored derivative had a lower detection degree
than the nonsilicon-cored one. When the m-dinitrobenzene
content was up to 500 ppm, the uorescence quenching effi-
ciencies of DF and BDS were 58% and 68%, respectively. The
silicon-cored derivative also exhibits excellent sensing proper-
ties for compounds that contain multiple nitro groups. There-
fore, BDS had higher sensitivity and higher quenching
efficiency in detecting m-dinitrobenzene than DF.
In summary, DF and BDS showed excellent detection capa-
bilities for nitroaromatic compounds. BDS exhibited lower
detection limit and higher sensitivity than DF, suggesting the
better properties and development potential of the former than
the latter.
Fig. 7 Photographs of the fluorescence quenching (under 365 nm UV
light) of the thin film of DF (up) and BDS (below) upon exposure to the
saturated vapor of nitrobenzene at different times for the visual
detection. (a) Without exposure to nitrobenzene vapor; (b) exposure to
nitrobenzene vapor for 120 s; (c) exposure to nitrobenzene vapor for
180 s.
diffusion of nitrobenzene vapor into the molecules. The pres-
ence of Tg indicated the amorphous fractions of the solid thin
lm. The Tg values of DF and BDS were 60 ꢀC and 250 ꢀC,
respectively. The special tetrahedral structure of BDS can resist
crystallization and form an amorphous thin lm through steric
hindrance. The reduction in uorescence intensity can be
ascribed to the charge transfer between electron-decient
nitrobenzene and electron-rich uorescent molecules,
producing p–p interactions. Energy transfer is a long-range
process, whereas charge transfer is a short-range one.19 There-
fore, the response time of the uorescence probe for nitroben-
zene detection was very short. Overall, the BDS thin lm
exhibited shorter uorescence quenching response time toward
nitroaromatics compared with the DF thin lm.
Fluorescence quenching of nitrobenzene vapor in the solid
state
We further investigated the nitrobenzene detection behavior of
DF and BDS in thin lms.
A solid-state uorescence quenching experiment was per-
formed toward nitrobenzene vapor using thin lms of DF and
BDS. The lms were prepared by dropwise addition of the THF
solutions of DF and BDS onto TLC strips, followed by vacuum
drying.
Then, the TLC strips were placed in a sealed bottle lled with
saturated nitrobenzene vapor. As shown in Fig. 7, the thin lms
of both DF and BDS exhibited strong uorescence without being
Conclusions
exposed to nitrobenzene vapor. Exposure of the DF thin lm to In this study, we synthesized nonsilicon-cored DF and silicon-
saturated nitrobenzene vapor for 120 s partly quenched the cored BDS. The thermal properties and uorescence quenching
uorescence. However, weak uorescence was still observed. behavior of these derivatives with nitroaromatic compounds were
When the exposure time was prolonged to 180 s, the uores- investigated. Aside from its better thermal properties, BDS also
cence was completely quenched. However, the BDS thin lm had higher sensitivity and higher quenching rate in detecting
showed a different phenomenon. The uorescence of the BDS nitroaromatic compounds than DF. Fluorescence quenching can
thin lm was completely quenched aer exposure to saturated be attributed to the electron transfer from the benzene rings of
nitrobenzene vapor for 120 s. This result indicated that the BDS DF and BDS to the electron-decient nitrobenzene and their
thin lm was more efficient and faster in responding to nitro- interactions with nitrobenzene molecules. The detection limits of
benzene vapor compared with DF. Patil et al. also reported that BDS toward nitrobenzene and m-dinitrobenzene were 50 and 10
exposing the thin lms of uoranthene derivatives to saturated ppm, respectively. The special tetrahedral structure of BDS
PA vapor for 210 s decreases the uorescence intensity by 91%.40 enhanced the p–p interaction. Furthermore, the Stern–Volmer
This result may be attributed to the special tetrahedral structure plot curved upward. Thus, BDS has great potential in detecting
of BDS molecules that complicates their aggregation. The explosives. This work may serve as a basis for designing new
nitrobenzene vapor was rapidly diffused into the BDS lm. organic materials with great efficiency and sensitivity in uores-
Meanwhile, the low sensitivity of the DF thin lm can be cence detection. The design and synthesis of high-performance
attributed to the easy aggregation of DF molecules and the poor uorescent probes are still in progress.
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21 Y. H. Xin, G. He, Q. Wang and Y. Fang, Rev. Sci. Instrum.,
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This work was nancially supported by the National Natural
Science Foundation of China (no. 21274080 and 21204043) and
the Key Natural Science Foundation of Shandong Province of
China (no. ZR2011BZ001).
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