Bifunctional fluorescent quenching detection of 2,4,6-trinitrophenol (TNP) and acetate ions via 4,4′-(9,9-dimethyl-9H-fluorene-2,7-diyl)dibenzoic acid

Article abstract of DOI:10.1016/j.tetlet.2016.09.089

The 4,4′-(9,9-dimethylfluorene-2,7-diyl)dibenzoic acid (5) was synthesized using commercial fluorene as the starting material followed by processes of bromination, methylation, Suzuki coupling and hydrolysis. We reported it as an exclusive fluorescence sensor for 2,4,6-trinitrophenol (TNP) and acetate ions for the first time. The experimental results suggested a high efficiency for TNP detection with K_SVvalues of 21,215?M^?1, which has achieved to micromolar level (10?μM) of this material. Moreover, the detection limit (1.39?×?10^?6?M) was measured according to the fluorescence intensity changes of Ac^?in CH₃CN.

Full text of DOI:10.1016/j.tetlet.2016.09.089

Accepted Manuscript
Bifunctional fluorescent quenching detection of 2, 4, 6-trinitrophenol (TNP) and
acetate ions via 4,4’-(9,9-dimethyl-9H-fluorene-2,7-diyl)dibenzoic acid
Jue Chen Ni, Jie Yan, Li Jing Zhang, Di Shang, Ning Du, Shuang Li, Jin Xin
Zhao, Yang Wang, Yong Heng Xing
PII:
S0040-4039(16)31271-0
DOI:
http://dx.doi.org/10.1016/j.tetlet.2016.09.089
TETL 48159
Reference:
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
28 July 2016
17 September 2016
27 September 2016
Please cite this article as: Ni, J.C., Yan, J., Zhang, L.J., Shang, D., Du, N., Li, S., Zhao, J.X., Wang, Y., Xing, Y.H.,
Bifunctional fluorescent quenching detection of 2, 4, 6-trinitrophenol (TNP) and acetate ions via 4,4’-(9,9-
dimethyl-9H-fluorene-2,7-diyl)dibenzoic acid, Tetrahedron Letters (2016), doi: http://dx.doi.org/10.1016/j.tetlet.
2
016.09.089
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Graphical Abstract
Bifunctional fluorescent quenching detection
of 2, 4, 6-trinitrophenol (TNP) and acetate
ions via 4,4’-(9,9-dimethyl-9H-fluorene-2,7-
diyl)dibenzoic acid
We reported a compound as an exclusive
fluorescence sensor for TNP and acetate
ions for the first time.
Jue Chen Ni, Jie Yan*, Li Jing Zhang, Di Shang, Ning Du, Shuang Li, Jin Xin Zhao, Yang Wang, Yong Heng
Xing*

1
Tetrahedron Letters
Bifunctional fluorescent quenching detection of 2, 4, 6-trinitrophenol (TNP) and
acetate ions via 4,4’-(9,9-dimethyl-9H-fluorene-2,7-diyl)dibenzoic acid
Jue Chen Ni, Jie Yan*, Li Jing Zhang, Di Shang, Ning Du, Shuang Li, Jin Xin Zhao, Yang Wang, Yong
Heng Xing*
College of Chemistry and Chemical Engineering, Liaoning Normal University, Huanghe Road 850#, Dalian, 116029, P.R. China.
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
The 4,4’-(9,9-dimethylfluorene-2,7-diyl)dibenzoic acid (5) was synthesized using commercial
fluorene as the starting material followed by processes of bromination, methylation, Suzuki
coupling and hydrolysis. We reported it as an exclusive fluorescence sensor for 2, 4, 6-
trinitrophenol (TNP) and acetate ions for the first time. The experimental results suggested a
-
1
Available online
high efficiency for TNP detection with KSV values of 21215 M , which has achieved to
-6
micromolar level (10 μM) of this material. Moreover, the detection limit (1.39 × 10 M) was
Keywords:
Fluorescence sensor
Synthesis
-
measured according to the fluorescence intensity changes of Ac in CH
3
CN.
2
016 Elsevier Ltd. All rights reserved.
Suzuki coupling
Nitroaromatic compounds
Anions
Nitro aromatics, such as nitrobenzene (NB), 4-nitrotoluene (4-
coupling at the 2 and 7 positions, yielding a series of fluorene-
13
NT), 2, 4, 6-trinitrophenol (TNP), and 2, 4, 6-trinitrotoluene
derived compounds. In the past two decades, a large amount of
studies on structure modification of fluorene derivatives have
1
(
TNT) are common ingredients of explosives. Among various
1
4
nitro aromatic compounds, 2, 4, 6-trinitrophenol (TNP) is an
extremely hazardous chemical with strong explosive capacity and
been reported. Recently, fluorene-derived compounds are also
well documented in the literature that they have good
coordination ability, which is due to the electron-rich property
2
a low safety coefficient. It violently explodes when it contacts
3
15
with flames or friction shock. In addition, as a toxicant, the
and conjugate structure.
ingestion of TNP can cause severe poisoning in humans,
including headache, nausea, vomiting, abdominal pain and
destruction of erythrocytes. While all the nitro explosives show
Until now, lots of researchers focused on the synthesis and
16
4
coordination of fluorene derivatives,
but there is little
information for detecting anions and nitro explosives. Here we
explored the selectivity of 4, 4'-(9, 9-dimethylfluorene-2, 7-
diyl)dibenzoic acid (5) for acetate ions and TNP respectively by
the changes of fluorescence intensity. The reason for choosing
fluorene derivatives is due to its strong fluorescence nature as
strong electron affinity, it is very difficult to separate TNP from
5
mixture of other nitro-compounds.
Hence, development of
6
efficient selective sensor for detection TNP is highly desirable.
-
On the other hand, Ac ions plays a significant role in
17
numerous metabolic processes and has been widely investigated
well as the high electron richness. Furthermore, the conjugate
carboxylic fluorene compound has been selected as fluorescent
sensors because of the potential to form an intermolecular
7
in prostate cancer and its metastases. It also plays an important
8
role in industry such as dyes, paper, paints and plastics. Due to
1
8
19
its wide application in many medical and industry, researchers
supramolecular architecture such as π–π interaction and
-
17
pay more attention on the detection method of Ac ions,
hydrogen-bonded in solution.
9
especially in chromogen and fluorescence.
The synthetic routes and detailed procedures of 5 are shown in
Scheme 1. Among them, 2,7-Dibromofluorene (1) and 2,7-
Currently, fluorescent organic materials, for example, pyrene,
styrene and biphenyl have attracted tremendous attention in the
Dibromo -9,9-dimethylfluorene (2) were synthesized by the
10
20
field of technology and science. However, fluorene with the
reported procedures.
Compound 4 (yield 45%) took the
16b
similar conjugated structure to other fluorescent organic
modified literature method,
which was the Suzuki coupling.
11
materials doesn't get enough attention.
Fluorene, a major
Fortunately, we obtained the compound 3 by Suzuki coupling
component of fossil fuels, has unique structural features: two
benzene rings are fused into one plane by a five-member ring,
providing high electron delocalization through increased overlap
reaction, which was not on any literature before.
The X-ray single crystal structural of the compound 2 (Figure
S1A) is the same with that reported on literature before. For the
21
12
of π molecular orbitals between the rings.
Fluorene can be
directly connected to aromatic hydrocarbon via aromatic

2
Tetrahedron Letters
Figure 1. The fluorescence spectra of fluorene and Compounds 1-5
in CH CN
3
Sensing of nitroaromatic compounds
Compound 5 (sensor) is highly soluble in some organic
solvents such as acetonitrile, methanol. We take the acetonitrile
as the solvent for sensing study. The sensor exhibits strong
emission peak at 367 nm (λex = 280 nm).
Scheme 1. Synthetic Routes of compound 5
compound 2, the dihedral angle between two benzene rings (C7,
C8, C9, C10, C11, C12; C7A, C8A, C9A, C10A, C11A, C12A)
and the five-member ring (C7, C12, C13, C12A, C7A) are both
.0 ( 0.0 ) °. X-ray single crystal study shows that compound 3
Figure S1B) is crystallized in a monoclinic system with P2 /c
space group. The dihedral angle between benzene rings (C11,
C12, C13, C14, C15, C16; C18, C19, C23, C20, C21, C22) and
the five-member ring (C14, C15, C17; C19, C18) are 2.1 (0.2) °
and 1.8 (0.2) °, which are larger than compound 2. And the
dihedral angle between benzene ring (C3, C4, C5, C6, C7, C8)
and the fluorene moiety is 43.6 ( 0.1 )°, showing that C-C single
bond distorting between benzene ring and the fluorene moiety is
strong.
The changes in luminescence intensity with the increasing
addition of nitroaromatic compounds (up to 100 ppm) in the
sensor are shown in Figure 2 and Figure S6, respectively. In the
current study, the NACs used are nitrobenzene (NB), 4-
nitrotoluene (4-NT), 4-nitrobenzaldehyde (4-NBA), 1,3-
dinitrobenzene (DNB), 2-nitrophenol (2-NP), 3-nitrophenol (3-
NP), 4-nitrophenol (4-NP), 2,4,6-trinitrophenol (TNP), and 2,4,6-
trinitro toluene (TNT) (Figure 3) to judge the selectivity of
sensing towards nitroaromatic compounds. The most effective
quencher is TNP with QP (quenching percentage = (I − I)/I ×
0
(
1
0
0
100%, I and I are luminescence intensity of sensor before and
0
after exposure to the nitro compound) of 97.91%. Other NACs
can weaken the photo luminescent intensity of sensor to different
level. The order of quenching efficiency is TNP > 2-NP > 4-
NBA ≈ NB ≈ TNT ≈ 4-NP > 3-NP > 4-NT > DNB. In all the
cases, the initial fluorescence intensity of the sensors decreased
considerably upon gradual addition of the NACs. The rate of
quenching, which is essentially related to the Stern - Volmer
constant (KSV), revealed that TNP has faster fluorescence
quenching over the other nitroaromatic compounds. To better
understand this fact, we need to calculate the Stern-Volmer
constants of the quenching process.
Fluorescence measurements
The emission spectra of the fluorene and the compounds 1-5
were shown in Figure 1 and the luminescent spectra of them were
analyzed under excitation wavelength (280 nm) with 400V and
slit width (5:5). For compounds 1 and 2, almost no fluorescence
responds were observed.
wavelength was 313 nm for fluorene, 436 nm for compound 3,
08 nm for compound 4, 380 nm for compound 5. Compared
While, the maximum emission
4
with fluorene, there are fluorescence quenching phenomenon
occurring in compounds 1, 2, 3 and the red shift in the maximum
emission wavelength for compounds 3, 4, 5.
All of compounds 1, 2 and 3 are containing bromine atoms.
22
In this condition of containing halogen atoms, the excited state
of the compounds and heavy atom form the composite in a ratio
of 1:1. The degree of spin orbit coupling in this compound is
much larger than normal compound. This excited state complex
has
a strong charge transfer property, normally is the
fluorescence quenching process. In compounds 3, 4 and 5,
fluorene moiety is conjugated with benzene ring after the Suzuki
coupling reaction of bromination derivatives of fluorene, which
make the fluorescence enhance and a red shift occurs in the
maximum emission wavelength but compound 3 still has the
heavy atom effect. At the same time, the dihedral angle between
two benzene rings and the five-member ring increased, showing
that the fluorene molecular skeleton is distorted by the effect of
benzene rings. Compared with 3, compound 4 has two benzene
rings leading to distorted structure which made the conjugated
effect weak and blue shift. Finally, the compound 4 turned into
compound 5 by hydrolysis reaction, which made the fluorescence
intensity decrease because it contains the carboxyl group which
is an electron-withdrawing group.
Figure 2. Reduction of the fluorescence emission intensity of the
sensor upon gradual addition of TNP

3
Figure 3. Luminescence quenching percentage when sensor was
dispersed in nine different nitro compounds in CH CN (excited and
monitored at 280 nm and 367 nm, respectively). nitrobenzene (NB),
-nitrotoluene (4-NT), 4-nitrobenzaldehyde (4-NBA), 1,3-dinitro
benzene (DNB), 2-nitrophenol (2-NP), 3-nitrophenol (3-NP), 4-
nitrophenol (4-NP), 2,4,6-trinitrophenol (TNP), and 2,4,6-trinitro
toluene (TNT).
Figure 4. (A) Plot of I
analytes in lower concentration ranges of analytes (up to 50 ppm). I
and I are luminescence intensities in the absence and presence of
analyte, respectively. (B) Stern–Volmer plots of analytes in higher
concentration ranges of analytes (up to 100 ppm).
0
/I of sensor (at 367 nm) vs. concentration of
3
0
4
To understand the sensitivity, the Stern-Volmer plots were
used to calculate the quenching constants of the analytes (Figure
4
0 0
) using the SV equation (I /I) = KSV[Q] + 1, where I and I are
the luminescence intensities before and after the addition of the
analyte, [Q] is the molar concentration of the analyte, and KSV is
the quenching constant. As shown in Figure 4A, at low
concentrations (up to 50 ppm) of all nitro analytes, a linear
0
proportional in (I /I-1) was observed. The SV plot diverged from
linearity and began to bend upwards in case of nitroaromatic
compounds with the concentration increasing. The linear
variation at lower concentration is mainly due to static
quenching, whereas the steep curves at higher concentrations are
presumably due to dynamic quenching (Figure 4B). The static
quenching can be attributed to the ground state interaction
between the analytes and the sensor. The dynamic quenching is
mainly due to the energy and electron transfer processes between
the analytes and the sensor. Fitting of linear parts of the plots
allows the determination of the quenching constants (KSV) to be
Figure 5. NMR with addition TNP to sensor in DMSO-d
6
-1
-1
-1
2
1215 M for TNP, 9877 M for 2-NP, 8082 M for 4-NP, 7737
-1 -1 -1 -1
M for 4-NBA, 6377 M for NB, 10584 M for TNT, 5662 M
6
To 50 ppm solution of TNP in DMSO-d was added and the
-1
-1
for 3-NP, 2345 M for 4-NT and 2353 M for DNB. The larger
observed Ksv values revealed extremely high sensitivity, which
made the sensor to be one of the best sensitive luminescence,
based metal–organic detectors of TNP due to the electron
richness and the fluorescent behaviour of the fluorene moiety. In
addition, the determination of the individual Stern-Volmer
constants indicated that the fluorescence quenching mainly
corresponding NMR spectrum was recorded. On addition of
TNP, a significant chemical shift of the protons was observed in
1
the H NMR spectra for the sensor (Figure 5). More importantly,
the fluorene protons are shifted more prominently (by 0.04 ppm)
than the phenyl protons (by 0.01 ppm). This observation clearly
suggests two facts: firstly, the TNP is mainly interacting with the
fluorene moiety of the sensors though π–π interaction. Secondly,
the ability of hydrogen bonds formation between the senior and
TNP is weak. If the sensor forms the hydrogen bonds with the
TNP, the phenyl protons will be affected much more than the
fluorene protons by adding TNP.
occurs through charge transfer.
To further establish the
formation of charge transfer, NMR titration was carried out with
TNP for the sensor. In a typical titration 10 μM of the sensor was
taken in DMSO-d .
6
Sensing properties towards anions
Compound 5 emitted strong blue fluorescence with the
maximum excited wavelength centered at around 390 nm.
Various anions were tested in parallel under the same conditions
for evaluating the specific sensing behavior of the compound 5,
-
-
-
(
Figure 7A), upon the addition of other ions such as F , Cl , Br ,
- - 2- - 2- -
ClO , SCN , HPO , H PO , SO , NO etc. Surprisingly, it is
found that sensor displayed an extremely good selectivity for Ac
only, instead of the other ions examined.
4 2 4 3 3
-
In order to furthermore investigate influence of the
-
luminescent responds of sensor, we tried to add Ac into the
diluted solution of the sensor, and investigated the sensing
-
behavior of 5 towards Ac carefully. As shown in Figure 6,
excitingly, the emission spectra showed significant decrease with

4
Tetrahedron Letters
-
Figure 6. The fluorescence spectra of sensor (10 μM) in the presence of Ac (0～60 equiv.)
(
B)
(
A)
-
Figure 7. (A) The fluorescent response of probe sensor (10 μM) to different species (50 equiv.) (B) Effect of Ac on probe sensor (10 μM)
in the presence of different interferents (50 equiv)
-
-
the increase of Ac . With the increase of the concentration of Ac
Acknowledgments
ions in this system, the emission peak intensity decreased
correspondingly. The peak intensity reached the minimum with
-
We are grateful for support provided by the National Natural
Science Foundation of China (Grant No. 21371086),
Commonweal Research Foundation of Liaoning province in
China (Grant No. 2014003019).
0
the 5.4-fold (I /I) decreasing when 50 equiv. of Ac ions were
added in. However, here no significant difference were observed
-
when the concentration of Ac ions increased from 50 equiv. to
6
0 equiv.. Plotting the normalized fluorescence intensity changes
-
intensity at 390 nm as a function of [Ac ] resulted in a nice linear
relationship (Figure 6), the point at which this line crossed the
ordinate axis is regarded as the detection limit and found to be
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carboxyl group. This compound shows a high fluorescence
5
6
.
.
-
quenching efficiency and low detection limit for TNP and Ac
ions. Then we have a discussion about the fluorescence
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Tetrahedron
Highligths
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We developed a novel pathway to synthesise fluorene derivatives (compound 4).
The single crystal of new intermediate 3 was obtained by Suzuki coupling reaction.
We examined the emission spectrum of the fluorene and compound 1-5 .
New experiment was firstly carried out about sensing of NACs and anions based on 5.
We discussed the quenching mechanism based on the effects of π–π interaction .