Dual functional and multiple substituted fluorescent star-shaped POSS for a 1 + 1 > 2 explosive vapour detection

Article abstract of DOI:10.1039/c6ra08686a

A dual functional and multiple substituted fluorescent star-shaped POSS has been designed and synthesized. There is effective FRET between the different functional arms. Compared with a single functional probe, the dual functional POSS showed a much better sensing performance to explosive NG and a comparable performance to TNT vapor.

Full text of DOI:10.1039/c6ra08686a

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Dual functional and multiple substituted fluorescent star-shaped
POSS for a 1+1>2 explosive vapour detection
Received 00th January 20xx,
Accepted 00th January 20xx
a,b
a,b
a,b
a
a
a
a
Yixun Gao, Wei Xu , Xiangtao Zhang ,Yanyan Fu , Defeng Zhu , Qingguo He , Huimin Cao ,
a
and Jiangong Cheng
DOI: 10.1039/x0xx00000x
www.rsc.org/
1
2
A dual functional and multiple substituted fluorescent star-shaped very important explosives in the terrorist activities.
POSS has been designed and synthesized. There is effective FRET Recently, we reported an eight triphenylaminopyrene (PT
)
between the different functional arms. Compared with single substituted polyhedral octavinylsilsesquioxane (POVS) could
1
functional probe, the dual functional POSS showed a much better be applied as high efficient nitrate esters including NG probe.
3
sensing performance to explosive NG and
performance to TNT vapor.
a
comparable Here we also introduce PT as one of the sensing units for
nitrate ester detection. Fluorene is known as a violet-blue light
emitting material, which has a higher LUMO level relative to
Polyhedral oligomeric silsesquioxanes (POSS) with rigid cage-
TNT, and it will emit less short wavelength fluorescence which
may experience effective fluorescence resonance energy
transfer (FRET) to PT upon photo excitation, and hence to
magnify the fluorescence of PT and increase the sensing
like nanostructures consisting of an inorganic Si-O-Si core were
1, 2
commonly used for luminescent material design.
They
possess high thermal and mechanical resistance, together with
a rigid steric configuration, which often act as end group or
connecting groups in macromolecule or polymer to increase
the incorporated stability and regulate the vapor
1
4-16
performance.
Our intension was to excite PT units by
dioctylfluorene (DOF) to maximize the efficient of this
mechanic inside the molecule. We assumed the proportion of
DOF is about 4 or 5 fold PT to acquire enough excitation
3
, 4
permeability.
application of POSS as the core structure of a star-shaped
However, only few groups reported the
energy of PT unit. For comparing their properties, five DOF
s
5
, 6
7, 8
molecule. Several groups introduced pyrene,
10
vinyl benzene, metal complex and other donor-acceptor
fluorene,
and PTs substituted POSS was also designed and synthesized.
9
1
1
emitters on POSS core to obtain hyperbranched molecules
and polymers. These materials could be used as OLED,
microporous materials, cellular imaging etc, and was proved
that the emission wavelength, charge nature, and diameter of
POSS-based fluorescent nanoparticles can be easily tuned via
chemical modification of fluorescent arms on the POSS unit.
But as far as we know, no bifunctional fluorescent branch and
multiple substituted POSS (BFA-POSS) were reported. More
functional unit on POSS will bring about more functionality, we
plan to design and synthesize BFA-POSS for multiple explosives
detection, which is difficult to be actualized with one sensing
material. Here, trinitrotoluene (TNT) and nitroglycerin (NG) Fig. 1 Chemical structure of P5F1PT
.
were chosen as the explosive target due to their two kind of
The syntheses route of the three probes were shown in
Scheme 1, taking the reaction condition reported as a
1
3, 17
reference.
and Suzuki reaction, then coupled relatively with POVS at a
feed ratio of 5:1 in dried dioxane, using Pd (dba) as catalyst,
Cy NMe and P(t-Bu) as ligands. After a column separation,
POSS-5DOF and POSS-5PT were both obtained in a yield of
DOF-Br and PT-Br were obtained by alkylation
2
3
2
3
5
0%. A further reaction of POSS-5DOF with 1 equiv. of PT-Br
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proceeded with same condition provided P5F1PT in a yield of
7%.
Quantum
efficiency
Extinction
coefficient
Absorption Emission
3
POSS-5DOF
POSS-5PT
P5F1PT
329
395
413
512
498
0.82
0.73
0.58
4.80
5.26
4.75
330/395
Table 1 Optical properties of POSS-5DOF, POSS-5PT and P5F1PT.
We can also found that the emission peak of 498 nm is a bit
bluer than that of POSS-5PT. it could be easily interpreted that
in P5F1PT
highly separated to prevent an intermolecular aggregation or
excimer between PT units compared with POSS-5PT
, DOF units dominate the arms, while PT branch was
.
Scheme 1 Synthesis of POSS-5DOF, POSS-5PT and P5F1PT.
MALDI-TOF showed the as-synthesized POSS-5PT contains five,
six and seven substituted substances. POSS-5DOF sample
consisted of both five and six substituted substances, and the
P5F1PT sample contains majority of P5F1PT and minority of
Fig. 3 Schematic of HOMO (left) and LUMO (right) orbit distribution of P5F1PT
1
P6F1PT. The H NMR and mass spectra were shown in Fig. S1
3
Calculation based on Dmol using Materials Studio software
and S2. These results confirmed that by means of precise feed
ratio control, diverse functional units could be introduced onto
POSS by simple Heck coupling reaction with a decent accuracy
and purity for application.
showed that both LUMO and HOMO orbits of P5F1PT were
distributed on PT unit as presented in Fig. 3. This could well
match with the results of fluorescence spectra that energy
would almost entirely transfer from DOF units to PT unit on
the basis of FRET effect. And by the calculation, the diameter
of P5F1PT molecule is
effectively.
̴ 4 nm, enough for FRET to happen
Fig. 2 (a) Absorption and fluorescence spectra of POSS-5DOF (blue) and POSS-5PT
(
green) in thin film state on quartz plates. (b) The absorption spectra (black) and the
emission spectra of P5F1PT under UV light of 330 nm (red) and 395 nm (blue) in thin
films on quartz plates. Both emission spectra were under same condition, and
normalized by the max intensity.
Fig. 4 Quenching efficiency of POSS-5DOF (a) and POSS-5PT (b) in air condition upon
Fig. 2 presented the optical properties of three molecules in exposure to TNT and NG vapor.
thin film state. The spectra in solution state were shown in Fig.
S6. The surface morphology of thin films were shown in Fig. S7
by SEM analysis. Fig. 2a showed that the emission spectrum of
POSS-5DOF well overlapped with the absorption peak of POSS-
5
PT, which ensured the FRET between these two units. Fig. 2b
showed the emission spectra of P5F1PT excited at 330 nm and
95 nm. Upon excitation at 330 nm, FRET between DOF and PT
3
caused the emission peak of DOF units in 413 nm almost
disappeared, and a strong emission band peaked at 498 nm
could be observed. While upon excitation at 395 nm, only a
much lower emission band of PT was witnessed, that proved
the efficient intramolecular FRET inside P5F1PT molecule from
DOF to PT branch.
2
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PleaseRd So Cn oA t da vd aj un s ct ems argins
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P5F1PT is less than that of POSS-5PT in NG. This result
indicated a combination of two quenching mechanisms
occurred for P5F1PT in the explosive detection.
1
00%
91%
8
3%
7
2%
8
6
4
2
0%
0%
0%
0%
69%
45%
In summary, a dual functional and multiple substituted
fluorescent star-shaped POSS has been designed and
synthesized. There is effective FRET between the different
functional arms. Compared with the POSS probe with single
function, the dual functional POSS showed a much better
sensing performance to explosive NG and a comparable
performance to TNT vapor.
25%
0
%
POSS-5DOF
POSS-5PT
P5F1PT
Fig. 5 Quenching efficiencies of P5F1PT in air condition upon exposure to
saturated explosives vapor. The inset picture is the original thin film on quartz It can be seen that POSS structure acts as a crucial role in
plate (left), their fluorescence responses after exposure to TNT (middle) and NG
sensing performance towards multiple functional materials. By
(right) for 300 s relatively. The schematic below shows the comparison of the
sensing performance to TNT (red) and NG (blue).
introducing different functional arm, the functionality will be
enhanced by interchain interaction of different functional arm.
The sensing property of the three probes was investigated as The multi-site skeleton enables multi types of sensing units
shown in Fig. 4 and Fig. 5. The quenching efficiency of POSS- assembled in single molecule, which may find its use in many
5DOF to saturated nitroglycerin (NG) vapor is only ~25%, while fields such sensor, OLEDs and other photoelectronic devices.
it reached 72% to TNT vapor under a same condition implying We thank the research programs from the National Natural
it is more suitable as a TNT sensor. An inverse tendency was Science Foundation of China (Grant Nos. 61325001, 21273267,
found for POSS-5PT, the quenching efficiency of which is 83% 61321492 and 51473182).
in NG vapor and 45% in TNT vapor suggesting it is preferable as
a NG sensor. And when it comes to P5F1PT, an efficiency of
6
9% for TNT and 91% for NG was found as shown in Fig. 5
which is excellent for both explosive sensing. It is noticeable
that compared with POSS-5PT P5F1PT even showed a 8%
,
Notes and references
1
2
3
4
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,
3
enhancement in NG sensing although POSS-5PT has five PT
chains and P5F1PT only have one.
2
This phenomenon may come from the efficient intramolecular
FRET after the photo excitation due to its very small donor-
acceptor distance, followed by an efficient photo induced
charge transfer from P5F1PT to NG molecules (HOMO and
LUMO levels calculated by Materials Studio and cyclic
voltammetry were shown in Fig. S3 and S4). The even better
sensing performance of P5F1PT relative to POSS-5PT may lie in
two aspects. Firstly, for P5F1PT, the FRET between DOF and PT
make the sensing capability towards NG as a whole. The
energy transferred from DOF multiplied the fluorescence
efficiency of PT, making the sensing performance comparable
with multi-PT-substituted POSS. Secondly, from Table 1, the 14
nm red shift relative to P5F1PT suggesting stronger
intermolecular aggregation of POSS-5PT in solid state, which
will decrease the fluorescence efficiency and corresponding
sensing performance of the probe. The low aggregation in
P5F1PT results from the dilution effect of five DOF units, which
make it exhibit a better sensing performance. Such a dual
functionality arm has a 1+1>2 effect for NG sensing due to the
highly efficient intramolecular energy transfer.
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5DOF kept almost unchanged after response to TNT vapor,
while that of POSS-5PT showed a significant decrease upon
contact with NG, which can be proved as static quenching and
collisional quenching, respectively. However, P5F1PT
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A dual functional and multiple substituted fluorescent star-shaped POSS was synthesized, a
highly efficient intramolecular FRET between the branches with different function make it show
excellent sensing performance in both NG and TNT vapor detection.