A silicon-cored tetraphenyl benzene derivative with aggregation-induced emission enhancement as a fluorescent probe for nitroaromatic compounds detection

Article abstract of DOI:10.1016/j.saa.2019.03.050

Two benzene with multiple contiguous phenyl substituent derivatives, namely, 1, 2, 3, 4-tetraphenyl benzene (TPB) and bis(1,2,3,4-tetraphenylbenzene-yl) diphenylsilane (TPB-Si), were synthesized by the Knoevenagel/Diels–Alder method. TPB and TPB-Si both showed aggregation-induced emission enhancement (AIEE) properties in tetrahydrofuran/water mixtures. The fluorescence-quenching behaviors of the two compounds with different nitroaromatic compounds were also investigated. TPB and TPB-Si both showed low detection limit, high sensitivity, and high quenching efficiency in detecting nitroaromatic compounds. Furthermore, the two compounds in aggregate state exhibited much better detection abilities than in THF solution. And TPB-Si exhibited better detection ability than TPB in both solution and aggregate state. The reason could be attributed to the special tetrahedral molecular structure of TPB-Si, which was demonstrated by theoretical calculations and crystal structures. Moreover, TPB-Si in solid film also exhibited excellent detection performance to nitroaromatic explosive vapor. This work may serve as a basis for designing new organic materials with great efficiency and sensitivity in fluorescence detection.

Full text of DOI:10.1016/j.saa.2019.03.050

Accepted Manuscript
A silicon-cored tetraphenyl benzene derivative with aggregation-
induced emission enhancement as a fluorescent probe for
nitroaromatic compounds detection
Yan Liang
PII:
S1386-1425(19)30289-6
https://doi.org/10.1016/j.saa.2019.03.050
SAA 16940
DOI:
Reference:
Spectrochimica Acta Part A: Molecular and Biomolecular
Spectroscopy
To appear in:
Received date: 29 September 2018
Revised date:
Accepted
date:
20 February 2019
1
7 March 2019
Please cite this article as: Y. Liang, A silicon-cored tetraphenyl benzene derivative with
aggregation-induced emission enhancement as a fluorescent probe for nitroaromatic
compounds detection, Spectrochimica Acta Part A: Molecular and Biomolecular
Spectroscopy, https://doi.org/10.1016/j.saa.2019.03.050
This is a PDF file of an unedited manuscript that has been accepted for publication. As
a service to our customers we are providing this early version of the manuscript. The
manuscript will undergo copyediting, typesetting, and review of the resulting proof before
it is published in its final form. Please note that during the production process errors may
be discovered which could affect the content, and all legal disclaimers that apply to the
journal pertain.

ACCEPTED MANUSCRIPT
A Silicon-Cored Tetraphenyl Benzene Derivative with
Aggregation-Induced Emission Enhancement as a
Fluorescent Probe for Nitroaromatic Compounds Detection
Yan Liang*
College of Food Science and Engineering, Qilu University of Technology (Shandong
Academy of Sciences), Jinan, Shandong 250353, People’s Republic of China
*
Corresponding author: liangyan@qlu.edu.cn (Yan Liang)
Abstract
Two benzene with multiple contiguous phenyl substituent derivatives, namely, 1, 2, 3,
-tetraphenyl benzene (TPB) and bis(1,2,3,4-tetraphenylbenzene-yl) diphenylsilane (TPB-Si),
4
were synthesized by the Knoevenagel/Diels–Alder method. TPB and TPB-Si both showed
aggregation-induced emission enhancement (AIEE) properties in tetrahydrofuran/water mixtures.
The fluorescence-quenching behaviors of the two compounds with different nitroaromatic
compounds were also investigated. TPB and TPB-Si both showed low detection limit, high
sensitivity, and high quenching efficiency in detecting nitroaromatic compounds. Furthermore, the
two compounds in aggregate state exhibited much better detection abilities than in THF solution.
And TPB-Si exhibited better detection ability than TPB in both solution and aggregate state. The
reason could be attributed to the special tetrahedral molecular structure of TPB-Si, which was
demonstrated by theoretical calculations and crystal structures. Moreover, TPB-Si in solid film
also exhibited excellent detection performance to nitroaromatic explosive vapor. This work may
serve as a basis for designing new organic materials with great efficiency and sensitivity in
fluorescence detection.
Key words：Silicone-cored structure; aggregation-induced emission enhancement; nanoparticles;
detection; nitroaromatic compounds
1

ACCEPTED MANUSCRIPT
1
. Introduction
In recent years, nitroaromatic compounds, such as nitrobenzene (NB), m-dinitrobenzene
DNB), 2,4,6-trinitrotolune (TNT), and picric acid (PA), have been widely used as explosive
(
components [1]. These nitroaromatic compounds are extremely harmful to the environment and
human bodies [2, 3]. Therefore, the rapid and highly selective, sensitive detection of nitroaromatic
compounds in liquid or vapor has become one of the main concerns of public security, health care,
and environmental pollution [4]. Presently, fluorescence chemical sensors based on organic
compounds have gained much attention because of low cost, their high sensitivity, and flexible
molecular structures, and so on [5-7]. In previous reports, electron-deficient nitroaromatic
compounds were found to efficiently quench the strong fluorescence emission intensities of
electron-rich organic compounds through photo-induced electron transfer [8]. However, traditional
organic compounds are often compromised by the aggregation-caused quenching (ACQ) effect
when dispersed in poor solvent or used as solid film. This effect greatly reduces the efficiency and
sensitivity of the sensors [9].
Recently, Tang and his co-operators found that the fluorescence intensity of an organic
compound is significantly enhanced when it is in aggregate state. This unique phenomenon was
named as aggregation-induced emission enhancement (AIEE) [10, 11]. Therefore, for the strong
fluorescence emission in aggregation, fluorescence materials with AIEE nature was employed to
detect nitroaromatic compounds in the aggregate state [12]. Moreover, in order to meet the
demand of explosive detection in different places, the enhancement of the detection performance
of AIEE molecules will greatly benefit their application in fluorescent chemical sensor fields [13].
As one of the simplest AIEE molecules, dendritic benzene derivatives with multiple
contiguous phenyl substituents are widely used as fluorescence materials for their special
properties [14]. Compared with the planar molecules, phenyl substituents possess the special
ability to rotate around the central benzenes with large twisted angles to form different kind of
configuration. This construction could lead to nonplanar structures, which could efficiently
suppress extensive aromatic π-π interactions in the aggregate state [15]. Therefore, these
compounds typically show high fluorescence emission in solid state. Although the application of
these dendritic benzene derivatives as fluorescence sensors was feasible, the detection efficiency
still needs to be further improved. In our previous work, a silicon-cored structure was introduced
2

ACCEPTED MANUSCRIPT
to the planar fluoranthene molecules. The resulting silicon-cored fluoranthene compound
exhibited better detection performance, such as higher sensitivity, and shorter response time for
the detection of nitroaromatic compounds than planar fluoranthene in both liquid and vapor. In the
paper, we ascribed the results to the unique molecular structure formed by silicon nucleation [16].
In this work, two kinds of dendritic benzene derivatives, named as 1, 2, 3, 4-tetraphenyl
benzene (TPB) and bis(1,2,3,4-tetraphenylbenzene-yl) diphenylsilane (TPB-Si), were designed
and synthesized. Both compounds exhibited excellent AIEE properties. The fluorescence
quenching behaviors of TPB and TPB-Si with respect to nitroaromatic compound detection in
solution and aggregation were further investigated. The compounds showed excellent detection
behaviors to nitroaromatic compounds, especially to picric acid (PA). Compared with TPB,
TPB-Si exhibited better detection capability in aqueous system and solid film state, such as lower
detection limit (LoD), higher sensitivity, and higher quenching efficiency to nitroaromatic
compounds. Hence, TPB-Si has a beneficial potential in detecting nitroaromatic compounds,
which can be attribute to the unique silicon-cored molecular structure. Furthermore, density
functional theory (DFT) calculations and crystal structure analysis were performed to clarify the
conclusion. We hope that this work can serve as a guide for the design of fluorescence molecules
that can be used for the sensitive fluorescence detection of nitroaromatic explosives.
2
. Experimental Section
2.1 Materials and methods
Ethanol, methanol, hydrochloric acid, KOH, magnesium powder and xylene were purchased
from China National Medicines Group and used without further purification. Tetrahydrofuran
THF) was dehydrated by using KOH and sodium. The starting materials, benzil, 1, 3-dibenzyl
(
ketone, ethyl bromide, dichlorodiphenylsilane and trimethylsilylacetylene were purchased from
sigma and used as received.
1
13
H NMR and C NMR (CDCl as the solvent) were recorded on a Bruker-AVANCE 400 NMR
3
spectrometer. Elemental analyses (C, H and N) were carried out on an Elementar Vario MICRO
CUBE (Germany) elemental analyzer. Fluorescence spectrum (excitation and emission) data were
acquired by a HITACHI F-4500 spectrophotometer. The ultraviolet absorption (UV) spectra of
these samples were recorded with a Hitachi U-4100 spectrometer. Thermal stabilities were
performed by TGA Q-600 with heating rate of 10 °C/min from room temperature to 800 °C under
3

ACCEPTED MANUSCRIPT
N (100 mL/min). DSC (α-Al O as reference material) was measured by Mettler Toledo DSC822
2
2
3
series with a heating rate of 10 ºC/ min under nitrogen flow of 26 mL/min from 30 to 400 ºC.
2.2 Synthesis
The two polyphenylbenzene derivatives were synthesized by Knoevenagel and Diels-Alder
reactions with high product yields. The detailed synthesis process is shown in Scheme 1.
Scheme 1. TPB and TPB-Si synthesis
2.2.1 Synthesis of Tetraphenylcyclopentadienone (1)
Benzil (6.3 g, 0.03 mol) and 1, 3-dibenzyl ketone (6.3 g, 0.03mol) were dissolved in 60 mL of
ethanol and then heated with stirring. When the mixture started to reflux, KOH (0.8 g dissolved in
mL of ethanol) was dropped into the mixture and allowed to react for 2 h until black precipitate
8
formed. After the solution was cooled to room temperature, the precipitate was filtered and
washed with ethanol for three times to obtain a black solid product with yield of 90% [17]. Melt
1
point: 219 °C. H NMR (CDCl , 400 MHz, ppm): δ 8.08 (d, 2 H), 7.86 (m, 6 H), 7.61 (dd, 2 H),
3
4

ACCEPTED MANUSCRIPT
1
3
7
1
.54 (dd, 4 H), 7.42 (t, 2 H). C NMR (CDCl , 100 MHz, ppm): δ 154.2, 132.1, 131.5, 131.4,
3
29.0, 128.6, 128.3, 127.8, 121.7, 120.9. ESI-MS spectrometry: m/z calculated for C H O [M +
2
9
20
+
H] : 384.15 ; found: 384.16. Anal. Calcd for C H O: C 90.60%, H 4.16%; found: C 90.66%, H
2
9
20
4
2
.17%.
.2.2 Synthesis of 1, 2, 3, 4-Tetrahydrophenyl trimethyl silane (2)
Trimethylsilylacetylene (1.48 g, 15 mmol) and 1 (3.84 g, 10 mmol) were dissolved in 30 mL of
xylene. Then the mixture was transferred to a poly (tetrafluoroethylene) (Teflon)-lined autoclave
50 mL) and heated at 230 °C for 8 h. Most of the xylene was then removed by distillation in
(
vacuum. Then, 100 mL of methanol was poured into the mixture to form the precipitation. The
precipitation was repeatedly washed by ethanol and purified by silica column chromatography.
1
Finally, a white solid product with yield of 70% was obtained. Melt point: 161 °C. H NMR
(CDCl , 400 MHz, ppm): δ 0.03 (s, 9 H), 6.75 (m, 2 H), 6.85 (m, 5 H), 6.91 (m, 3 H), 7.05-7.20
3
13
(
m, 10 H), 7.75 (s, 1 H). C NMR (CDCl , 100 MHz, ppm): 147.4, 147.1, 146.8, 145.9, 144.6,
3
1
1
44.0, 143.6, 143.4, 142.9, 142.4, 141.5, 140.3, 136.9, 136.4, 136.1, 135.8, 135.4, 135.2, 135.1,
35.0, 134.7, 134.5, 134.2, 133.8, 133.6, 133.2, 132.0, 131.7, 131.3, 130.8, 0.5. Anal. calcd for
C H Si: C 87.17%, H 6.65%; found: C 87.49%, H 6.36%.
3
3
30
2.2.3 Synthesis of 1, 2, 3, 4-Tetraphenyl benzene (TPB)
The mixture of 2 (1 g, 2.2 mmol) and concentrated hydrochloric acid (4 mL) were dissolved in
0 mL of anhydrous THF, and then kept refluxing for 10 h with sharply stir. After removing the
3
solvent by reduced pressure distillation, the crude product was precipitated by pouring into excess
methanol. After that, column chromatography was used to purify the crude product to obtain a
1
white crystal with yield of 92%. Melt point: 189 °C. H NMR (CDCl , 400 MHz, ppm): δ 6.82 (m,
3
1
3
4
1
1
2
H), 6.94 (m, 6 H), 7.12-7.20 (m, 10 H), 7.54 (s, 2 H). C NMR (CDCl , 100 MHz, ppm):
3
42.9, 142.8, 140.1, 138.9, 138.8, 131.8, 131.7, 131.6, 130.6, 130.5, 128.9, 128.7, 127.5, 127.4,
27.2, Anal. calcd for C H : C 94.20%, H 5.80%; found: C 94.31%, H 5.72%.
30
22
.2.4 Synthesis of Diphenyl diacetylene silane (3)
Magnesium powder (2.4 g, 100 mmol) and anhydrous THF (20 mL) were placed into a 100 mL
flask equipped with a reflux condenser, constant pressure dropping funnel, and argon inlet. Ethyl
bromide (10.9 g, 100 mmol) was dissolved in anhydrous THF (25 mL) and then added into the
flask dropwise. The resulting solution was refluxed for 2 h to obtain the Grignard reagent.
5

ACCEPTED MANUSCRIPT
Acetylene gas was aerated into anhydrous THF (150 mL) for 1 h under −78 °C to obtain acetylene
saturated solution. The Grignard reagent was then added into the solution and allowed to react for
2
h under ice water bath. Dichlorodiphenylsilane (20.26 g, 80 mmol) dissolved in anhydrous THF
(30 mL) was dropped into the obtained acetylene Grignard reagent. After reacting for 0.5 h, the
mixture was quenched by 10 mL of methanol. The organic phase was separated and acquired by
separating funnel. After evaporation under reduced pressure, the product was purified by column
chromatography on a silica gel to obtain a pale-yellow solid with 70% yield [18]. Melt point:
1
4
2
5 °C. H NMR (CDCl , 400 MHz, ppm): δ 7.75 (m, 4 H, ArH), 7.26-7.50 (m, 6 H, ArH), 2.75 (s,
3
13
H, －C≡CH). C NMR (CDCl , 100 MHz, ppm): 135.1, 133.2, 132.7, 129.3, 101.7, 83.7. Anal.
3
calcd for C H Si: C 82.71%, H 5.21%; found: C 82.74%, H 5.20%.
16
12
2.2.5 Synthesis of Di-(1, 2, 3, 4- tetrahydrophenyl) diphenyl silane (TPB-Si)
Under N atmosphere, 3 (1.16 g, 5 mmol) and 1 (3.84 g, 10 mmol) dissolved in xylene (30 mL)
2
were sealed in stainless reactor and allowed to react at 230 °C for 10 h. After the evaporation of
the excess solution under reduced pressure, a substantial amount of methanol was poured into the
mixture to precipitate the crude product. The product was purified by column chromatography on
1
silica gel, and a pale-yellow solid with 68% yield was obtained. Melt point: 224 °C. H NMR
(
CDCl , 400 MHz, ppm): δ 6.64 (m, 12 H), 6.77 (m, 12 H), 6.91 (m, 6 H), 7.04 (m, 4 H),
3
1
3
7
1
1
1
.11-7.35 (m, 16 H), 7.75 (s, 2 H). C NMR (CDCl , 100 MHz, ppm): 145.7, 144.2, 144.6, 144.9,
3
43.4, 143.6, 143.1, 142.4, 141.9, 141.4, 139.5, 138.3, 136.9, 136.4, 136.1, 135.7, 135.5, 135.3,
35.0, 134.4, 133.7, 133.5, 132.8, 132.6, 132.1, 131.0, 130.9, 130.7, 129.3, 128.5, 127.6, 127.3,
3.4. Anal. calcd for C H Si: C 91.48%, H 5.54%; found: C 91.65%, H 5.54%.
72
52
3
. Results and Discussion
3.1 Optical Properties
6

ACCEPTED MANUSCRIPT
Fig. 1 PL spectra of the dilute solutions of TPB (20 µM) (a) and TPB–Si (10 µM) (b) in THF
/water mixtures with different water contents (excitation wavelength was 275 nm); Absorption
spectra of TPB (c) and TPB-Si (d) in THF and THF/ water mixture (1:9)
The fluorescence emission spectra (λex = 275 nm) of TPB and TPB-Si in THF/water mixture
solutions with different ratios (from 10:0 to 1:9) were measured. The results are shown in Fig. 1(a,
b). The emission peak of TPB in THF solution was obtained at 343 nm, whereas, that of TPB-Si
showed a slight red shift at 347 nm. Therefore, the existence of silicon-cored structure had no
obvious effect on the conjugated degree of the tetraphenyl benzene. When different amounts water
was added to their THF solutions (with final concentrations constant at 20 µM for TPB, 10 µM
for TPB-Si), the PL intensities of both compounds gradually increased when the water content in
THF increased, which means TPB and TPB-Si exhibited unique AIEE properties. Furthermore,
the water content of 70% is the PL intensity trend transition point of TPB for the water content
affect the aggregation degree. When the water content increased to 90%, the PL peak intensity
increased up to seven-fold. For TPB-Si, the similarly behavior displayed, and its PL peak intensity
increased up to nine-fold when the water content reached 90%. According to the literature, the
7

ACCEPTED MANUSCRIPT
AIEE mechanism of benzene-cored dye is restricted by intramolecular rotation [19, 20]. Similarly,
the AIEE mechanism of TPB and TPB-Si is applicable to this theory. In addition, the absorption
spectra s of TPB in THF and THF/water mixture (1:9) were further investigated to detect the
aggregation-induced emission enhancement properties. As shown in Fig. 1(c), TPB showed the
maximum peak absorption spectrum at 244 nm in the THF solution and 295 nm in THF/water
mixture (1:9). This spectrum can be attributed to the π-π transition of the phenyl group. The
absorption spectra of TPB-Si (Fig. 1d) also exhibited a bathochromic shift of maximum UV
absorption when the water content changed from 0% to 90% (the absorption peak shift from 246
nm to 284 nm). These results indicated that TPB and TPB-Si molecules aggregated at 90% water
content.
3.2 Thermal Properties
The thermal properties of TPB and TPB-Si were investigated by thermogravimetric analysis
and differential scanning calorimetry. The glass transition temperature (T ), melting temperature
g
(
T ), and decomposition temperature (T ) of TPB and TPB-Si are shown in Table 1. Obviously,
m
d
the three thermal parameters of TPB-Si were higher than those of TPB. The reason for this
difference can be assigned to the tetrahedral molecular structure based on the silicon-cored
structure [17].
Table 1 Thermal properties of TPB and TPB-Si
Compound
Tg(ºC)
163
T (ºC)
Td(ºC)
251
m
TPB
189
224
TPB-Si
215
398
T : glass transition; T : melting temperature; T : decomposition temperature (weight loss ratio of
g
m
d
5%).
3.3 Fluorescence quenching of nitroaromatic compounds in solution and aggregation state
8

ACCEPTED MANUSCRIPT
Fig. 2 Fluorescence emission spectra of TPB (a, c and e) and TPB-Si (b, d and f) upon the
addition of nitrobenzene (NB), m-dinitrobenzene (DNB), and picric acid (PA) in the THF
solution; Stern-Volmer curve of TPB and TPB-Si with different nitroaromatic compounds (g) and
partial enlargement (h)
9

ACCEPTED MANUSCRIPT
Nowadays, many researchers are still focused on developing highly sensitive and selective
fluorescent sensors for the detection of nitroaromatic explosive [21, 22]. Because of TPB and
TPB-Si exhibit electro-rich structures and excellent fluorescence properties and can thus be used
as fluorescent sensors for detecting electron-deficient nitroaromatic explosives. In this study,
nitrobenzene (NB), m-dinitrobenzene (DNB) and picric acid (PA) were selected to investigate the
fluorescent response behaviors of TPB and TPB-Si. In this work, TPB and TPB-Si were
dissolved in THF solution (20 µM for TPB and 10 µM for TPB-Si), and the amount of
nitroaromatic compounds was gradually added. As shown in Fig. 2(a–f), all the emission
intensities gradually decreased with the increasing content of nitroaromatic compound. From Fig.
2(a, b), the fluorescence quenching efficiencies of TPB and TPB-Si with 150µM nitrobenzene
were 37.2% and 48.7%, whereas the value reached 74.8% and 79.8% respectively when the
concentration was 400 µM. For m-dinitrobenzene, the fluorescence quenching efficiencies of TPB
and TPB-Si were 65.8% and 75.8% respectively when the concentration was 150 µM, and the
value elevated to 87.3% and 89.3% respectively when the concentration increased to 400 µM
(displayed in Fig. 2(c, d)). Similarly, the PL intensities of the TPB and TPB-Si gradually
decreased when the amount of PA was slightly added into the solution as shown in Fig. 2(e, f).
Relative to the initial intensity, the PL intensities of TPB and TPB-Si decreased to 76.2% and
84.6% respectively when the PA concentration was increased to 150 µM. These results indicated
that TPB and TPB-Si both possess sensitive fluorescence response to nitroaromatic explosive. It is
worthy to note than the fluorescence quenching efficiencies of TPB-Si were higher than those of
TPB when the kind and concentrations of the nitroaromatic explosive were same.
To further investigate the fluorescence response behaviors of TPB-Si and TPB to nitroaromatic
explosive, the Stern–Volmer plots of relative PL intensity (I /I) were thoroughly analyzed. As
0
shown in Fig. 2(g), the I /I-C plots of the two compounds showed upward curves for PA detection,
0
indicating that super amplification effects were exerted in the detection of the PA. Besides, the
plots presented nearly linear relationships when the concentrations of nitroaromatic explosive
were small (displayed in Fig. 2(h)). According to these results, we conclude that TPB and TPB-Si
both exhibit high selectivity to PA in all the nitroaromatic explosives.
10

ACCEPTED MANUSCRIPT
Fig. 3 Fluorescence emission spectra of TPB (a) and TPB-Si (b) upon the addition of PA in
aggregate state; (c) Stern-Volmer curve of TPB and TPB-Si with PA in solution and aggregate
state
In Tang’s work, the compound with AIEE nature showed better detection performance in
aggregation state than in the dilute solution [19, 25, 26]. Herein, the PL variations of TPB and
TPB-Si in aggregation state (THF: water = 1:9) with PA were performed to compare with those in
dilute THF solution. To further investigate the phenomenon, PA was chosen to be the model in this
work. As shown in Fig. 3(a, b), the PL intensities of TPB and TPB-Si gradually decreased when
11

ACCEPTED MANUSCRIPT
the increasing amount of PA added into their aggregate state. The Stern–Volmer plots of relative
PL intensity (I /I) versus PA concentration in aggregation state exhibited curvier bending upward
0
than those in THF solution. This result indicated that TPB and TPB-Si molecules in aggregation
state showed higher sensitive detection response to PA than in dilute THF solution. The reason can
be attributed to the compounds in aggregate state formed a 3D topological structure with a
relatively rigid aromatic scaffold, thus, molecular cavities presenting in the compound
nanoaggregate can capture small PA molecules through electrostatic or charge-transfer interactions
[27]. Thereby, the compound in nanoaggregates phase could bind more PA molecules than in
dilute solution, which means one PA molecule can quench the fluorescence emissions of several
fluorescent molecules in aggregate state. Therefore, TPB and TPB-Si both showed high
sensitivity to PA in aggregate state than those in the THF solution. Furthermore, TPB-Si exhibited
higher sensitive detection response to PA in aggregation state than TPB.
Otherwise, the fluorescence quenching efficiency was calculated by the Stern–Volmer equation
(showed in Eq. 1) to further investigate the comparison between the sensing ability of TPB and
that of TPB-Si towards PA.
퐼0
=
퐾푆푉[푀] + 1
Eq. 1
퐼
where I represents the initial fluorescence intensity without analyte, I is the fluorescence intensity
0
of the solution with the existing of analyte, [M] is the concentration of analyte, and K is the
sv
quenching constant [28, 29].
When a Stern-Volmer plot has a linear trend, the K can be calculated accurately to further
sv
certify the quenching mode [16]. Owing to the formation of static or dynamic quenching within
TPB and TPB-Si in solution and aggregate, both of the Stern-Volmer plots exhibited nearly linear
relationships when the PA concentration was extremely small (as shown in Fig. 3), and the
4
4
corresponding quenching constant were 1.72×10 (TPB in THF), 1.91×10 (TPB-Si in THF),
4
5
6
.82×10 (TPB aggregate), and 1.15×10 (TPB-Si aggregate), respectively. By calculating the
signal-to-noise ration with Eq.2, the LoD of PA in aggregate state has been obtained. For TPB and
-3
TPB-Si, the LoD was found to be 12.8 nM (2.93 ppb, 2.93×10 g/mL) and 7.65 nM (1.75 ppb,
-3
1
.75×10 g/mL), respectively. Compared with other reports in Table 2, TPB and TPB-Si both
exhibit lower LoD, which indicates that TPB and TPB-Si are excellent candidate sensors for the
12

ACCEPTED MANUSCRIPT
detection of nitroaromatic explosive. It means that the introduction of silicon-cored structure could
effective improve the detection ability for the detection of nitroaromatic explosives [18].
푆푑
LoD = 3 ꢀ
Eq. 2
푠푣
where S represents the standard deviation of the blank samples’ fluorescence intensity that was
d
measured 10 times, and k is the quenching constant [30, 31].
sv
Table 2 LoD of sensors for PA detection
Limit of detection
Sensor system
Analyte
Ref.
[32]
(
LoD)
4
-(2,2'-bithiophen-5-yl)-
PA
13 M
5
-phenylpyrimidine derivatives
0
0
.238 M
.836 M
triphenylamine-π-pyrimidines
PA
PA
PA
PA
PA
[33]
[34]
[35]
[36]
[37]
CuS nanoparticles
conjugated polymer with guanidinium side
groups
0.069 M
0.1 M
Fluorescent copper nanoclusters
0.12 M
4
5
.6 nM
.8 nM
Polymer Nanocomposites
Fluorescent metal-organic framework
Nitrogen doped graphene quantum dots
Fluorescent Cellulose Derivatives
PA
PA
PA
PA
2.6 M
0.3 M
[38]
[39]
[1]
0.14 M
0.014 M
Pyrene-Linked PBEMA Microspheres
[40]
1
7
2.8 nM
.65 nM
This work
PA
This work
In summary, TPB and TPB-Si both exhibited high selectivity and high sensitive detection
response to PA in both solution and aggregation state. Moreover, TPB-Si showed better detection
ability for PA detection than TPB in both the solution and aggregation state. The reasons for these
results were deeply discussed according to the theoretical calculations and crystal structures of
13

ACCEPTED MANUSCRIPT
two compounds.
.4 Crystal structures of TPB and TPB-Si
3
Fig. 4 Density functional theory-optimized ground state structures of TPB (a) and TPB-Si (c);
the molecular packing modes of crystal structures of TPB (b) and TPB-Si (d)
DFT calculations were used to characterize the 3D geometries of TPB and TPB-Si at the
B3LYP/6-31G* level by using the Gaussian 03 program [41-43]. The calculated structures of TPB
and TPB-Si in gas phase are shown in Fig. 4 (a, c). For TPB, the four phenyl groups linked to the
benzene core were twisted to form a non-coplanar structure. For TPB-Si, the two tetraphenyl
benzene units were greatly twisted against each other for the tetrahedral environment of the central
silicon core, resulting in “V” molecular structure in each molecule. In our previous work, one
nitroaromatic compound molecule can intermolecularly interact with one fluoranthene molecule
because of the planar structure. However, one nitroaromatic compound molecule can
simultaneously influence two fluorescent fluoranthene groups because of the “V” structure formed
by silicon [16]. In order to clearly demonstrate the theory, the mechanism was detailed interpret in
Fig. 5. As can be seen from Fig.5, one PA molecule can intermolecularly interact with one TPB
molecule, whereas one PA molecule can influence two TPB groups simultaneously because of the
“
V” molecular structure. This unique “V” structure can provide more opportunities for PA
14

ACCEPTED MANUSCRIPT
molecules to influence more TPB groups in TPB-Si and quench more fluorescence. It should be
the reason that the silicon-cored compound TPB-Si exhibited higher sensitivity for the detection
of PA than the non-silicon compound TPB in solution [44-45].
Fig. 5 PA detection process by TPB and TPB-Si in solution and aggregate state
The crystal structures of TPB and TPB-Si were further investigated. As shown in Fig. 4(b), the
molecules of TPB exhibited a symmetry structure, which led to close packing. The distance of the
neighbor TPB molecules was 9 Å. The TPB-Si exhibited a different crystal structure, as shown in
Fig. 4(d). The entire molecule showed a tetrahedral structure, and the two TPB groups that bonded
to the Si atom showed a “V” structure. Owing to this unique molecular structure, the distance of
neighbor molecules was 19 Å, and the TPB-Si molecules showed much looser packing than TPB
and formed more large holes. In aggregate state, TPB-Si nanoaggregates had more cavities than
TPB. These cavities enabled TPB-Si nanoaggregates to capture more PA molecules and enhanced
the possibility of TPB-Si contact with PA, which resulting much more fluorescence quenching.
Therefore, the higher number of cavities in TPB-Si enabled it to achieve higher sensitive
fluorescence response than TPB. Thus, the introduction of silicon-cored structure to AIEE
fluorescent molecules is an effective way to generate nanoaggregates with many cavities, which
can increase sensitive fluorescence response to nitroaromatic explosive [16, 46].
15

ACCEPTED MANUSCRIPT
3.5 Fluorescence quenching of nitrobenzene vapor in solid state
Fig. 6 (a) Photographs of the fluorescence quenching (under a 365 nm UV light) of TPB-Si (up)
and TPB (below) films in nitrobenzene vapor; (b) PL spectra of TPB and TPB-Si films
Solid-state fluorescence quenching experiments were further performed with the thin films of
TPB and TPB-Si in nitrobenzene vapor. As mentioned above, TPB and TPB-Si showed no visible
light emission in the dilute THF solution. However, the thin films of TPB and TPB-Si exhibited
different behaviors. We dropped the THF solution of TPB and TPB-Si on thin-layer
chromatography (TLC) plate to further investigate the solid state fluorescent properties. After the
solvents evaporated, the TLC plates were observed under a UV lamp. As shown in Fig. 6(a), under
the UV lamp (365 nm), the TPB on the TLC plate showed no visible fluorescence emission,
whereas TPB-Si exhibited an obvious strong blue light emission which could be observed by the
naked eye. In Fig. 6(b), the emission peak of TPB-Si film was at 420 nm when that of TPB film
was at 370 nm. The reason can be attributed to the “silicon-cored effect,” which accounted for the
increased rigidity of the tetraphenyl benzene in the aggregate state and for the red-shifted emission.
The quenching process was easily observed because of the visible strong blue emission of TPB-Si,
and thus enabled TPB-Si as a great potential sensor. When the TPB-Si thin film was exposed in
nitrobenzene vapor for 20 s, the fluorescence partly quenched. When the exposure time was up to
42 s, the fluorescence was completely quenched. TPB thin film also showed quenching
phenomenon in nitrobenzene vapor. However, it was hard to observe by naked eyes and the time
16

ACCEPTED MANUSCRIPT
was 57 s when the fluorescence was completely quenched. In our previous work, the fluorescence
emission of silicon-cored fluoranthene film was completely quenched after 120 s in nitrobenzene
vapor. Therefore, TPB-Si film showed extremely short fluorescence response to nitrobenzene
vapor，which indicated that TPB-Si solid film has great potential on the vapor detection of
nitroaromatic compounds. Overall, the TPB-Si exhibited short fluorescence quenching response
time and high sensitivity to nitroaromatic compounds in both liquid and vapor systems.
4
. Conclusion
Two AIEE-active dendritic benzene derivatives, namely, TPB and TPB-Si, were designed and
synthesized. The two organic compounds both exhibited excellent fluorescence properties and
were used as fluorescent probes for nitroaromatic compounds. TPB and TPB-Si exhibited high
selectivity to PA in different nitroaromatic compounds and high sensitive detection response to PA
in both solution and aggregation state. Furthermore, TPB-Si showed better detection ability for
the detection of PA than TPB in the solution and aggregation state. The reasons were further
discussed and attributed to the unique silicon-cored structure. And the results were further
confirmed by the results of the theoretical calculations and single crystal structures. Furthermore,
TPB-Si in solid film also exhibited excellent detection performance to nitroaromatic compound
vapor. This work can serve as a guide for molecular fluorescence design and can be used in the
sensitive fluorescence detection of nitroaromatic explosives.
Acknowledgement
This work was financially supported by Shandong Provincial Natural Science Foundation
(ZR2017BEM046), (ZR2017LB020) and China Postdoctoral Science Foundation (No.
2017M622197).
References
[1] H. Hu, F. Wang, L. Yu, K. Sugimura, J. Zhou, Y. Nishio, Synthesis of Novel Fluorescent
Cellulose Derivatives and Their Applications in Detection of Nitroaromatic Compounds, ACS.
Sustain. Chem. Eng. 6 (2017) 1436-1445.
[2] Z. Hu, B.J. Deibert, J. Li, Luminescent metal-organic frameworks for chemical sensing and
explosive detection, Chem. Soc. Rev. 43 (2014) 5815-5840.
17

ACCEPTED MANUSCRIPT
[3] X. Zhang, W. Wang, Z. Hu, G. Wang, K. Uvdal, Coordination polymers for energy transfer:
Preparations, properties, sensing applications, and perspectives, Coord. Chem. Rev. 284 (2015)
06-235.
4] D. Lin, H. Liu, K. Qian, X. Zhou, L. Yang, J. Liu, Ultrasensitive optical detection of
trinitrotoluene by ethylenediamine-capped gold nanoparticles, Anal. Chim. Acta 744 (2012) 92-98.
5] T. Shu, N. Wang, Y. Li, D. Fu, H. Fan, M. Luo, S. Yue, A New Three-Dimensional Cd(II)
2
[
[
3
+
Metal-Organic Framework for Highly Selective Sensing of Fe as well as Nitroaromatic
Compounds, ChemistrySelect 2 (2017) 12046-12050.
[
6] K. Lin, S. Chen, B. Lu, J. Xu, Hybrid π-conjugated polymers from dibenzo pentacyclic centers:
precursor design, electrosynthesis and electrochromics, Sci. Chi. Chem. 60 (2017) 38-53.
7] B. Lu, S. Zhen, L. Zhao, G. Zhang, D. Mo, J. Xu, A novel solution-processable
[
amino-group-substituted oligopyrene: Synthesis, electropolymerization, properties, and
application in fluorescent chemosensor, Synth. Met. 198 (2014) 155-160.
[
8] Y. Liao, V. Strong, Y. Wang, X.-G. Li, X. Wang, R. Kaner, Oligotriphenylene Nanofiber
Sensors for Detection of Nitro-Based Explosives, Adv. Funct. Mater. 22 (2012) 726-735.
9] D. Li, J.C. Liu, R. T K Kwok, Z. Liang, B. Tang, J. Yu, Supersensitive detection of explosives
by recyclable AIE luminogen-functionalized mesoporous materials, Chem. Commun. 48 (2012)
167-7169.
10] J. Luo, Z. Xie, J.W.Y. Lam, L. Cheng, H. Chen, C. Qiu, H.S. Kwok, X. Zhan, Y. Liu, D. Zhu,
[
7
[
B.Z. Tang, Aggregation-induced emission of 1-methyl-1,2,3,4,5-pentaphenylsilole, Chem.
Commun. (2001) 1740-1741.
[11] J. Liu, Y. Zhong, J.W.Y. Lam, P. Lu, Y. Hong, Y. Yu, Y. Yue, M. Faisal, H.H.Y. Sung, I.D.
Williams, K.S. Wong, B.Z. Tang, Hyperbranched Conjugated Polysiloles: Synthesis, Structure,
Aggregation-Enhanced Emission, Multicolor Fluorescent Photopatterning, and Superamplified
Detection of Explosives, Macromolecules 43 (2010) 4921-4936.
[
12] A. Qin, J.W.Y. Lam, B.Z. Tang, Luminogenic polymers with aggregation-induced emission
characteristics, Prog. Polym. Sci. 37 (2012) 182-209.
13] R. Hu, J.L. Maldonado, M. Rodriguez, C. Deng, C.K.W. Jim, J.W.Y. Lam, M.M.F. Yuen, G.
Ramos-Ortiz, B.Z. Tang, Luminogenic materials constructed from tetraphenylethene building
[
18

ACCEPTED MANUSCRIPT
blocks: Synthesis, aggregation-induced emission, two-photon absorption, light refraction, and
explosive detection, J. Mater. Chem. 22 (2012) 232-240.
[14] H.T. Feng, Y.S. Zheng, Highly sensitive and selective detection of nitrophenolic explosives
by using nanospheres of a tetraphenylethylene macrocycle displaying aggregation-induced
emission, Chemistry 20 (2014) 195-201.
[15] X. Sun, X. Xu, W. Qiu, G. Yu, H. Zhang, X. Gao, S. Chen, Y. Song, Y. Liu, A non-planar
pentaphenylbenzene functionalized benzo[2,1,3]thiadiazole derivative as a novel red molecular
emitter for non-doped organic light-emitting diodes, J. Mater. Chem. 18 (2008) 2709-2715.
[16] H. Xie, H. Wang, Z. Xu, R. Qiao, X. Wang, X. Wang, L. Wu, H. Lu, S. Feng, A silicon-cored
fluoranthene derivative as a fluorescent probe for detecting nitroaromatic compounds, J. Mater.
Chem. C 2 (2014) 9425-9430.
[17] H. Wang, Y. Liang, H. Xie, L. Feng, H. Lu, S. Feng, Emission enhancement and color
adjustment of silicon-cored structure in tetraphenyl benzene with aggregation-enhanced emission,
J. Mater. Chem. C 2 (2014) 5601-5606.
[18] H. Wang, Y. Liang, Y. Wang, H. Xie, L. Feng, H. Lu, S. Feng, The strategy to improve
thermal and optical properties of diphenylfluoranthene based on silicon-cored derivatives, RSC.
Adv. 4 (2014) 17171-17178.
[
19] Y. Hong, J.W.Y. Lam, B.Z. Tang, Aggregation-induced emission: phenomenon, mechanism
and applications, Chem. Commun. (2009) 4332-4353.
20] J. Chen, C. C. W. Law, W. Jacky, Y. Dong, S. M. F. Lo, I. Williams, D.B. Zhu, B. Tang,
Synthesis, Light Emission, Nanoaggregation, and Restricted Intramolecular Rotation of
,1-Substituted 2,3,4,5-Tetraphenylsiloles, Chem. Mater. 15 (2003) 1535-1546.
21] Z.H. Fu, Y.W. Wang, Y. Peng, Two fluorescein-based chemosensors for the fast detection of
,4,6-trinitrophenol (TNP) in water, Chem. Commun. 53 (2017) 10524-10527.
22] A. Kalita, S. Hussain, A.H. Malik, U. Barman, N. Goswami, P.K. Iyer, Anion-Exchange
[
1
[
2
[
Induced Strong π–π Interactions in Single Crystalline Naphthalene Diimide for Nitroexplosive
Sensing: An Electronic Prototype for Visual on-Site Detection, ACS. Appl. Mater. Interfaces 8
(2016) 25326-25336.
19

ACCEPTED MANUSCRIPT
[23] Y. Zhang, S. A, Y. Zou, X. Luo, Z. Li, H. Xia, X. Liu, Y. Mu, Gas uptake, molecular sensing
and organocatalytic performances of a multifunctional carbazole-based conjugated microporous
polymer, J. Mater. Chem. A 2 (2014) 13422-13430.
[24] J. Wang, J. Mei, W.Z. Yuan, P. Lu, A. Qin, J. Sun, Y. Ma, B. Tang, Hyperbranched
polytriazoles with high molecular compressibility: Aggregation-induced emission and
superamplified explosive detection, J. Mater. Chem. 21 (2011) 4056-4059.
[
25] Z. Zhao, Z. Wang, P. Lu, C.Y.K. Chan, D. Liu, J.W.Y. Lam, H.H.Y. Sung, I.D. Williams, Y.
Ma, B.Z. Tang, Structural Modulation of Solid-State Emission of
,5-Bis(trialkylsilylethynyl)-3,4-diphenylsiloles, Angew. Chem. Int. Ed. 48 (2009) 7608-7611.
26] W.Z. Yuan, P. Lu, S. Chen, J.W.Y. Lam, Z. Wang, Y. Liu, H.S. Kwok, Y. Ma, B.Z. Tang,
2
[
Changing the behavior of chromophores from aggregation-caused quenching to
aggregation-induced emission: development of highly efficient light emitters in the solid state,
Adv. Mater. 22 (2010) 2159-2163.
[27] J.C. Liu, Y. Zhong, P. Lu, Y. Hong, W. Jacky, M. Faisal, Y. Yu, K. Sing Wong, B. Tang, A
superamplification effect in the detection of explosives by a fluorescent hyperbranched
poly(silylenephenylene) with aggregation-enhanced emission characteristics, Polym. Chem. 1
(2010) 426-429.
[28] S. Libo, Z. Liang, J. Yu, Octavinylsilsesquioxane-based luminescent nanoporous
inorganic-organic hybrid polymers constructed by Heck coupling reaction, Polym. Chem. 6 (2015)
17-924.
29] J.d.D. Habimana, J. Ji, F. Pi, E. Karangwa, J. Sun, W. Guo, F. Cui, J. Shao, C. Ntakirutimana,
9
[
X. Sun, A class-specific artificial receptor-based on molecularly imprinted polymer-coated
quantum dot centers for the detection of signaling molecules, N-acyl-homoserine lactones present
in gram-negative bacteria, Anal. Chim. Acta 1031 (2018) 134-144.
[30] Y. Ding, Q. Jia, Y. Wen, W. Liu, J. Ge, J. Wu, H. Zhang, P. Wang, New detection method for
nucleoside triphosphates based on carbon dots: The distance-dependent singlet oxygen trapping,
Anal. Chim. Acta 1031 (2018) 145-151.
[31] N.N. Jian, K.W. Lin, B. Guo, G. Zhang, X.M. Liu, L. Zou, B.Y. Lu, J.K. Xu, A reusable
fluorescent sensor from electrosynthesized water-soluble oligo(1-pyrenesulfonic acid) for
3+
effective detection of Fe , New J. Chem. 42 (2018) 19450-19457.
20

ACCEPTED MANUSCRIPT
[32] E. Verbitskiy, E. Cheprakova, A. A. Baranova, K. O. Khokhlov, K. Lugovik, G. L. Rusinov, O.
N.
-(2,2'-bithiophen-5-yl)-5-phenylpyrimidine derivatives as sensors for detection of nitroaromatic
explosives, Chem. Heterocycl. Compds. 52 (2016) 904-909.
33] E.V. Verbitskiy, A.A. Baranova, K.I. Lugovik, M.Z. Shafikov, K.O. Khokhlov, E.M.
Chupakhin,
V.
Charushin,
Microwave-assisted
synthesis
of
4
[
Cheprakova, G.L. Rusinov, O.N. Chupakhin, V.N. Charushin, Detection of nitroaromatic
explosives by new D-π-A sensing fluorophores on the basis of the pyrimidine scaffold, Anal.
Bioanal. Chem. 408 (2016) 4093-4101.
[
34] Y. Wang, W. Cao, L. Wang, Q. Zhuang, Y. Ni, Electrochemical determination of
,4,6-trinitrophenol using a hybrid film composed of a copper-based metal organic framework and
electroreduced graphene oxide, Mikrochim. Acta 185 (2018) 315-323.
35] H.Y. Mi, J.L. Liu, M.M. Guan, Q.W. Liu, Z.Q. Zhang, G.D. Feng, Fluorescence chemical
2
[
sensor for determining trace levels of nitroaromatic explosives in water based on conjugated
polymer with guanidinium side groups, Talanta 187 (2018) 314-320.
[
36] S. Chen, Q. Zhang, J. Zhang, J. Gu, L. Zhang, Synthesis of two conjugated polymers as TNT
chemosensor materials, Sens. Actuators, B 149 (2010) 155-160.
37] P. Dutta, S. Chakravarty, N.S. Sarma, Detection of nitroaromatic explosives using π-electron
rich luminescent polymeric nanocomposites, RSC. Adv. 6 (2016) 3680-3689.
38] S.S. Nagarkar, A.V. Desai, S.K. Ghosh, A fluorescent metal–organic framework for highly
selective detection of nitro explosives in the aqueous phase, Chem. Commun. 50 (2014)
915-8918.
39] L. Lin, M. Rong, S. Lu, X. Song, Y. Zhong, J. Yan, Y. Wang, X. Chen, A facile synthesis of
[
[
8
[
highly luminescent nitrogen-doped graphene quantum dots for the detection of 2,4,6-trinitrophenol
in aqueous solution, Nanoscale 7 (2015) 1872-1878.
[
40] H. Turhan, E. Tukenmez, B. Karagoz, N. Bicak, Highly fluorescent sensing of nitroaromatic
explosives in aqueous media using pyrene-linked PBEMA microspheres, Talanta 179 (2018)
07-114.
41] X. Song, Y. Niu, P. Zhang, C. Zhang, Z. Zhang, Y. Zhu, R. Qu, Removal of Co(II) from fuel
1
[
ethanol by silica-gel supported PAMAM dendrimers: Combined experimental and theoretical
study, Fuel 199 (2017) 91-101.
21

ACCEPTED MANUSCRIPT
[42] S. Ming, S. Zhen, K. Lin, L. Zhao, J. Xu, B. Lu, Thiadiazolo[3,4-c]pyridine as an Acceptor
toward Fast-Switching Green Donor–Acceptor-Type Electrochromic Polymer with Low Bandgap,
ACS Appl. Mater. Interfaces 7 (2015) 11089-11098.
[43] B. Lu, S. Zhen, S. Zhang, J. Xu, G. Zhao, Highly stable hybrid selenophene-3,4-
ethylenedioxythiophene as electrically conducting and electrochromic polymers, Polym. Chem. 5
(2014) 4896-4908.
[44] H. Wang, Y. Liang, H. Xie, H. Lu, S. Zhao, S. Feng, Unexpected SiMe3 effect on
color-tunable and fluorescent probes of dendritic polyphenyl naphthalimides with
aggregation-induced emission enhancement, J. Mater. Chem. C 4 (2016) 745-750.
[45] X.F. Wang, L.C. Xu, D. Mu, H. Wang, S.Y. Feng, Silicon effect of dendritic polyphenyl
derivatives: enhancement of aggregation-induced emission and emission color adjustment, Rsc.
Adv. 6 (2016) 23335-23339.
[46] X.F. Wang, H. Wang, Q. Jiang, Y.I. Lee, S.Y. Feng, H.G. Liu, Highly selective and sensitive
fluorogenic ferric probes based on aggregation-enhanced emission with - SiMe3 substituted
polybenzene, Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 188 (2018) 202-207.
22

ACCEPTED MANUSCRIPT
Graphical abstract
23

ACCEPTED MANUSCRIPT
Highlights:
. Two AIEE-active dendritic benzene derivatives (TPB and TPB-Si) were designed and
synthesized.
. TPB and TPB-Si both showed aggregation-induced emission enhancement (AIEE)
properties.
. Two compounds both shows high detection sensitivity for nitroaromatic
explosives.
. TPB-Si showed better detection ability than TPB because of the unique
silicon-cored structure.
. Theoretical calculations and single crystal structure analysis were used to clarify
the conclusion.
1
2
3
4
5
24