The novel anthracene decorated dendrimeric cyclophosphazenes for highly selective sensing of 2,4,6-trinitrotoluene (TNT)

Article abstract of DOI:10.1016/j.saa.2019.05.020

Novel fluorescent anthracene-decorated cyclotri- and cyclotetraphosphazenes (5 and 6) are designed and synthesized, and their chemosensor behaviors against nitroaromatic compounds are examined by UV/Vis and fluorescence spectroscopies for addressing the s

Full text of DOI:10.1016/j.saa.2019.05.020

Accepted Manuscript
The novel anthracene decorated dendrimeric cyclophosphazenes
for highly selective sensing of 2,4,6-trinitrotoluene (TNT)
Emrah Özcan, Süreyya Oğuz Tümay, Gürkan Keşan, Serkan
Yeşilot, Bünyemin Çoşut
PII:
S1386-1425(19)30496-2
https://doi.org/10.1016/j.saa.2019.05.020
SAA 17115
DOI:
Reference:
Spectrochimica Acta Part A: Molecular and Biomolecular
Spectroscopy
To appear in:
Received date: 31 December 2018
Revised date:
Accepted
date:
9 May 2019
1
0 May 2019
Please cite this article as: E. Özcan, S.O. Tümay, G. Keşan, et al., The novel anthracene
decorated dendrimeric cyclophosphazenes for highly selective sensing of
2
,4,6-trinitrotoluene (TNT), Spectrochimica Acta Part A: Molecular and Biomolecular
Spectroscopy, https://doi.org/10.1016/j.saa.2019.05.020
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ACCEPTED MANUSCRIPT
The Novel Anthracene Decorated Dendrimeric Cyclophosphazenes for
Highly Selective Sensing of 2,4,6-Trinitrotoluene (TNT)
Emrah Özcan, Süreyya Oğuz Tümay, Gürkan Keşan, Serkan Yeşilot, Bünyemin Çoşut*
Department of Chemistry, Faculty of Science, Gebze Technical University, Gebze, Kocaeli,
Turkey
*
Corresponding author: Department of Chemistry, Faculty of Science, Gebze Technical
University, Gebze, Kocaeli, Turkey, Phone: +902626053015, e-mail: bc@gtu.edu.tr

ACCEPTED MANUSCRIPT
Abstract
Novel fluorescent anthracene-decorated cyclotri- and cyclotetraphosphazenes (5 and 6) are
designed and synthesized, and their chemosensor behaviors against nitroaromatic compounds
are examined by UV/Vis and fluorescence spectroscopies for addressing the sensors with
cyclophosphazenes for 2,4,6-trinitrotoluene detection. The fluorescence intensities of (5 and
6
) are found to be selectively quenched by only 2,4,6-trinitrotoluene through the non-covalent
π⋯π stacking interactions between anthracene-substituted cyclophosphazenes and 2,4,6-
trinitrotoluene. In addition, cyclic voltammetry and theoretical calculation of novel sensor
systems are studied. The proposed fluorescent sensor systems are critical in terms of practical
detection of 2,4,6-trinitrotoluene.
Keywords: Phosphazenes, Explosive, TNT, Fluorescence, Nitroaromatic, Chemosensor,
Detection limit

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1
. Introduction
The sensing of nitroaromatic compounds (NACs) such as picric acid and 2,4,6-
trinitrotoluene (TNT) by novel fluorescent chemosensors in order to increase the selectivity and
sensitivity of previously reported systems have been one of the issues of the supramolecular
chemistry [1]. TNT is one of the most widely used NACs and detection of TNT is critical in
owing to concerns on environmental protection and global security [2]. Various analytical
techniques such as chromatographic techniques [3], electrochemical detection [4],
chemiluminescence detection [5], fluorescent monitoring [6], gas chromatography [7] and high-
performance liquid chromatography [8] have been used for detection and determination of
NACs. Although instrumental techniques are selective and sensitive, most of these devices are
rather bulky, expensive, time consuming and requiring laboratory conditions with expert users.
Thus, fluorescence-based sensing which is highly sensitive, convenient, and cost effective has
been attracted academy and industry. Hence, a wide variety of fluorescent sensor such as
organic/inorganic polymeric materials [9, 10], metal organic materials [11, 12], covalent
organic polymers and dendrimers [13-15] and quantum dots [4, 16] have been prepared recently
and screened for detection of NACs. In addition to these detection systems, π-electron-rich
small molecules have become alternative fluorescent sensors for detection of NACs [17, 18].
Small molecules as a fluorescent sensor are attractive because of their high quantum yield,
straightforward synthesis, better reproducibility and easy purification. Therefore, the design and
preparation of the conformationally strict π-electron-rich systems have fascinated considerable
attention in recent years due to their strong π⋯π piling interactions resulting in mainly
fluorescent quenching process [19].
Cyclophosphazenes are important compounds for preparation of novel
fluorescent systems as substituted groups on phosphorus atoms can be used as various terminal
groups for fluorescence detection [20, 21]. In addition, optical properties of cyclophosphazene

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derivatives could be tuned by substituents on phosphorus, as the cyclophosphazenes scaffold is
optically inert in UV–Vis region which is playing an important role in the design of
cyclophosphazene-based
detection
Cl
systems
[22].
Commercially
available
Cl , are
hexachlorocyclotriphosphazene, N
3
P
3
6
, and octachlorocyclotetraphosphazene, N
4
P
4
8
fascinating compounds. They exhibit high thermal stability and are extremely sensible to
nucleophilic reactions under basic conditions. Thus, those compounds allow the preparation of
a variety of cyclophosphazene-based materials. Also, hexakis- and octakis-cyclophosphazenes
display intramolecular excimer emission through the non-covalent π⋯π piling interactions
between the anthracene moieties [23-28].
According to previous reports on detection of NACs, strong π⋯π stacking interactions
between electron-rich cyclophosphazene-based systems and NACs led to non-selective
detection of NACs [29]. In the present study, we provide strong π⋯π interactions between the
TNT and anthracene through cyclophosphazene platform. We chose anthracene as a
chromophore to provide strong π⋯π interactions. We synthesized hexakis(4-
hydroxyphenylanthracene-9-carboxylate) cyclotriphophazene (compound 5), octakis(4-
hydroxyphenylanthracene-9-carboxylate) cyclotetraphophazene (compound 6) (Figure 1) and
1
13
31
characterized those compounds by standard spectroscopic techniques such as H, C and P
NMR, and mass spectrometry (MALDI-TOF). In addition, to understand the effect of
cyclophosphazene core on sensor properties of compounds 5 and 6, phenyl anthracene 9-
carboxylate (precursor) was synthesis according to the literature [30] and its molecular structure
was determined by X-ray crystallography. All the characterization data for synthesized
compounds are given in Supporting information (Figure S1-S9). After synthesis and
characterization, we tested the sensor properties of novel compounds to sense TNT and showed
the important potential of the compounds on the sensing of TNT.

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Figure 1. The molecular structures of compound 5, compound 6 and the precursor.
2
. Materials and Methods
All chemicals were reagent grade quality and obtained from commercial suppliers. While
the deuterated solvents CDCl and (CD CO, cyclohexene, ethanol, 4-benzyloxyphenol,
Pd(OH) , 4-Dimethylaminopyridine (DMAP), N,N'-Dicyclohexylcarbodiimide (DCC),
Cs CO , acetonitrile, silica gel 60, 9-Anthracenecarboxylic acid and tetrahydrofuran was
3
)
3 2
2
2
3
purchased from Merck, 1,8,9-Anthracenetriol (for MALDI analysis) was obtained from Fluka.
Hexachlorocyclotriphosphazene (trimer) and octachlorocyclotetraphosphazene (tetramer;
Otsuka Chemical Co. Ltd) were purged by using by fractional crystallization with n-hexane.
2
.1. Equipments
Electronic absorption in the UV-visible region, fluorescence excitation and emission
spectra were measured by Shimadzu 2101 and Varian Eclipse spectrofluorometer, respectively,
using 1 cm pathlength cuvettes at room temperature. Horiba-Jobin-Yvon-SPEX Fluorolog 3-
2
iHR instrument with Fluoro Hub-B Single Photon Counting Controller were used to calculate
fluorescence life time for excitation at 390 nm. Signal acquisition was carried out TCSPC
module. Mass spectra were obtained by Bruker Daltonics Microflex mass spectrometer

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(Bremen, Germany) equipped with a nitrogen UV-Laser operating at 337 nm in linear modes
1
13
31
with average of 50 shots. H, C and P NMR spectra were setted in CDCl or deuterated
3
acetone solutions down with a Varian 500 MHz spectrometer. Analytical thin layer
chromatography (TLC) was implemented on silica gel plates (Merck, Kieselgel 60A, 0.25 mm
thickness) with F254 indicator. Column chromatography was applied on silica gel (Merck,
Kieselgel 60A, 230-400 mesh).
2
.2. X-ray data collection and structure refinement
The X-Ray data were obtained with Bruker APEX II QUAZAR three-circle
diffractometer. Indexing was performed by using APEX [31]. Data integration and reduction
were achived with SAINT V8.34A [32]. Absorption correction was executed by multi-scan
method implemented in SADABS V2014/5 [33]. The structures were elucidated and clarified
by Bruker SHELXTL Software Package [34]. The final geometrical parameters and the
molecular drawings were completed using with Platon (version 1.17) and Mercury CSD
(version 3.5.1) programs [35, 36]. Structural determination has been stored to the Cambridge
Crystallographic Data Centre with references CCDC 1541931 for structure precursor.
2
2
.3. Synthesis
.3.1. Synthesis of compounds 1-4 and precursor
The compounds 1-4 and precursor were synthesized and purified according to the
literature procedure (Scheme S1 in SI) [25-27, 30, 37].
2
.3.2. Synthesis of compound
5
(hexakis(4-hydroxyphenylanthracene-9-
carboxylate) cyclotriphophazene)

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A mixture of 2,2,4,4,6,6 hexakis-(hydroxyphenoxy) cyclotriphosphazatriene (2; 31 mg,
0
.04 mmol), 9-Anthracenecarboxylic acid (71 mg, 0.32 mmol), DMAP (129 mg, 1.064 mmol)
and DCC (156 mg, 0.76 mmol) in dry acetonitrile (15 mL) in a sealed tube was stirred for 48 h
at room temperature; then, refluxed for 2 days under an argon atmosphere. The reaction mixture
filtered off and the volatile materials were evaporated under vacuum. The residue was purified
by silica-gel column chromatography with n-hexane/DCM (gradient 1/2, v/v) as the eluent. The
desired material was obtained as a yellow solid (yield 80%). IR (ATR, room temp.): 1187 cm-
1
-1
31
1
(
P=N); 949 cm (P-O). P NMR (500 MHz, CDCI
MHz, CDCI ) δ 8.43 (s, 1H), 8.12 (d, J =8.8 Hz, 2H), 7.90 (d, J =8.3 Hz, 2H), 7.50 (d, J =7.7
Hz, 2H), 7.31 (d, J= 7.4 Hz, 2H), 7.24-7.18 (m, 4H) ppm; C NMR (125 MHz, CDCI
3
) δ 9.52 (s, 3P, N
3
P ring); H NMR (500
3
3
13
3
) δ
1
1
2
50.50, 142.50, 141.62, 135.78, 130.75, 130.72, 129.97, 128.55, 128.25, 127.20, 125.50,
25.32, 124.61, 123.96, 123.03, 122.34 ppm; MALDI TOF (m/z) calc. 2015.740, found:
015.776 m/z.
2
.3.3. Synthesis of compound
6
(octakis(4-hydroxyphenylanthracene-9-
carboxylate) cyclotetraphophazene)
A mixture of 2,2,4,4,6,6,8, 8-octakis (hydroxyphenoxy) cyclotetraphosphazatetraene (4;
50 mg, 0.237 mmol), 9-Anthracenecarboxylic acid (527 mg, 2.37 mmol), DMAP (404 mg,
.31 mmol) and DCC (585 mg, 2.84 mmol) in dry acetonitrile (15 mL) in a sealed tube was
2
3
stirred for 48 h at room temperature; then, refluxed for 2 days under an argon atmosphere. The
reaction mixture filtered off and the volatile materials were evaporated under vacuum. The
residue was purified by silica-gel column chromatography with n-hexane/DCM (gradient 1/3,
v/v) as the eluent. The desired material was obtained as a yellow solid (yield 79%). IR (ATR,
-1
-1
31
room temp.): 1187 cm (P=N); 949 cm (P-O). P NMR (500 MHz, CDCI ) δ -11.29 (s, 4P,
3
1
N
4
P
4
ring); H NMR (500 MHz, CDCI
3
) δ 8.42 (s, 1H), 8.12 (d, J = 8.5 Hz, 2H), 7.87 (d, J =

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1
3
8
.1 Hz, 2H), 7.52 (d, J =8.8 Hz, 2H), 7.37 (d, J =8.4 Hz, 2H), 7.24-7.12 (m, 4H) ppm; C NMR
(
125 MHz, CDCI ) δ 151.55, 142.72, 139.93, 135.81, 130.73, 128.35, 128.28, 127.64, 127.19,
3
1
2
26.80, 126.07, 125.55, 125.32, 124.91, 124.70, 122.30 ppm; MALDI TOF (m/z) calc.
687.650, found: 2687.166 m/z.
3
. Results and Discussions
The compounds 1-4 and precursor were obtained according to literature [25-27, 30, 37].
They were characterized by standard spectroscopic techniques and X-ray crystallography. The
target compounds 5 and 6 were synthesized by esterification reaction of 2 and 4 with 9-
anthracene carboxylic acid, respectively (Scheme S1 and Figure 1). The esterification reactions
were carried out by using DMAP and DCC as an acyl transfer reagent and dehydrating agent in
acetonitrile. After filtration of reaction mixture, compound 5 and 6 were obtained by column
chromatography with using n-hexane/DCM (v/v) as eluent and silica gel as stationary phase.
1
13
31
Characterization of all synthesized compounds were performed by H, C and P NMR, and
mass spectrometry (MALDI-TOF) and obtained result in a good agreement with predicted
1
structures. For instances, H NMR of -OH of benzene moieties of compound 2 and 4 were
observed at =8.33 and =8.38 ppm which were disappeared after esterification reactions as
expected (Figure S2 and S6) [25, 37]. In addition, the integration of aromatic proton signals of
1
anthracene group to the benzene group in H NMR spectrum of compound 5 and 6 nearly 9:4
3
1
which demonstrated predicted structure as shown in Figure 1. P NMR of compound 5 and 6
showed only singlet peaks at =9.52 ppm and =-11.29 ppm, respectively (Figure S1 and S5).
3
.1. Thermal Properties
The thermal stability of the compounds 5 and 6 were followed by thermogravimetric
analysis (TGA) and differential scanning calorimetry (DSC) which are given at Figure S10 and

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S11. According to the TGA thermograms of compounds 5 and 6, the compounds exhibit very
high thermal stability with decomposition temperatures (T
d
) in the range of 300–350 °C. The
decomposition onset temperatures (Ton) are 310 °C for compound 5 and 300 °C for compound
6
. Also, the glass transition temperatures (T ) of compounds are 161 °C for compound 5 and
g
1
83°C for compound 6.
3
.2. Optical and Chemosensor Properties
Optical and chemosensor behaviors of compound 5, 6 and precursor were studied in THF
with UV/vis and fluorescence spectroscopies. UV/Vis absorption and fluorescence signals of
-5
the concentration of 5x10 M for compounds 5, 6 and precursor are shown in Figure 2 and
Stokes shifts are given at Figure S12. The major absorption features of compounds 5 and 6 are
same with their precursor. It is well known that phosphazene cores (N
3
P
3
Cl
6
or N
4
P
4
Cl ) are
8
optically inactive in UV/vis region, therefore they do not affect the ground state absorption
properties of the attached dyes [38]. It can be seen form Figure 2b, emission of compounds 5,
6
and precursor demonstrated broad emission bands which centered at 475 nm (λex=365 nm).
In addition to the emission band of compound 5 is slightly broader than that of compound 6
because of reflection of emission of the excimer anthracene units which are originated from
intramolecular π⋯π interactions of the narrower cyclotriphosphazene platform. Fluorescence
quantum yields (Φ
f
) of the target compounds were calculated with comparative method (Eq.
(1)) where 0.1 M H
2
SO solution of quinine sulfate as a standard [39, 40]. The concentration of
4
-5
each solution were fixed at 1x10 M. Fluorescence quantum yields (Φ ) of compound 5 and 6
f
were calculated as 0.18 and 0.07, respectively.
2
F.AStd.n
ΦF
 Φ (Std)
F
(1)
2
Std
FStd.A.n

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-5
Figure 2. (a) UV/vis absorption and (b) fluorescence spectra of 5x10 M 5, 6 and precursor.
(THF, λex=365 nm.)
Anthracene and its derivatives have extensively been used as fluorescence probes for
explosive detection thanks to strong photoluminescence characteristics and π-electron-richness
[
41]. Chemosensor behaviors of compounds 5, 6 and precursor were examined by fluorescence
spectroscopy with nitrobenzene, nitrophenol, TNT, picric acid and RDX which are commonly
use NACs. When compared the structure of TNT and other NACs, it can be seen that the
quenching efficiency of TNT could be more effective than NACs. This observation may exist
because of the three nitro-groups on its structure, which making the structure have lowest
electron density [42, 43]. According to results, only TNT changed the fluorescence emission
which observed at 475 nm (anthracene emission) as shown in Figure 3a and Figure 3b where
other common analytes did not cause any significant changes in fluorescence emission. Also,
there have not been any changes in fluorescence emissions of precursor upon addition of 500
ppm of TNT, Figure 3c. In addition, spectrofluorometric titration was performed to understand
the interactions of the compounds 5 and 6 with TNT. As can be seen from Figure 4, compounds
5
(Figure 4a) and 6 (Figure 4b) with gradually increased concentration of TNT showed linear
range of TNT. According to obtained data from fluorescence signals, the limit of detection
-5
(
LOD) of compounds 5 and 6 for TNT were determined as 8.35 ppm (3.67x10 M) and 6.43
-5
ppm (2.83x10 M), respectively, pointing a high detection sensitivity. LODs were calculated

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based on 3σ/K, σ is the deviation of blank solution signal, K is slope of the calibration curve
(Figure 4a and Figure 4b) [44-46]. Stoichiometry of compounds 5, 6 with TNT were
investigated with the method of continuous variation (Job’s plot analyses, Figure S13). As can
be seen from Job’s analyses which obtained according to emission data change, 1:1
complexation was observed for compounds 5, 6 with TNT. In addition, association constants
4
4
-
for complexation of compounds 5, 6 with TNT were determined as 4.39x10 and 4.73x10 M
1,
respectively, with using Benesi–Hildebrand equation (Figure S14) [47]. In addition, precision
of 5 and 6 were evaluated for TNT detection. Therefore, ten measurements were performed for
00 ppm and 250 ppm TNT under the same experimental conditions and relative standard
deviations (RSDs %) were calculated as 1.04 % and 2.05 %.
5
-5
-5
-5
Figure 3. The selectivity of 5x10 M 5 (a), 5x10 M 6 (b) and 1x10 M precursor (c) (THF,
λex=365 nm).

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-5
-5
Figure 4. Spectrofluorometric titration of 5x10 M 5 (a), and 5x10 M 6 (b) with increased
amount of TNT in THF solution. Excitation wavelength is 365 nm. The insets; linear range of
5
and 6 versus TNT.
3
.3. Quenching Mechanism
Fluorescence quenching can occur in two different ways: static and dynamic quenching
mechanism, which are completely different processes from each other. In static quenching, non-
fluorescent fluorophore-quencher complex form by fluorophore and quencher in ground state.
This non-fluorescent complex causes to quench of the fluorescence signal. On the other hand,
in dynamic quenching process, the excited molecules of quencher and fluorophore collides and
signal of the fluorophore quenches with this collision [48]. Therefore, it can be said that
dynamic quenching is a diffusion-controlled process. For these reasons, fluorescence lifetime
of dyes does not affect in static quenching process. However, this is completely different in the
dynamic quenching process and fluorescence lifetime of fluorophore tend to decrease. In
addition, concentration of quencher can give information about quenching process via
fluorescence intensity changing [22]. Based on these informations, fluorescence lifetime and
intensity changing of fluorophore with quencher (TNT) were measured in different
concentration. To calculate those values, Stern-Volmer relationship were used [49] (2).
퐼0
=
퐾푆푉[푄] + 1
(2)
퐼

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Quencher (Q) is TNT for our detection method and in this equation, fluorescence signal of
compounds 5 and 6 are shown as ꢀ (in absence of TNT) and ꢀ (in presence of TNT). Also, 퐾푆푉
ꢁ
and 푄 represent the Stern-Volmer constant and concentration of TNT, respectively. According
to Stern-Volmer equation, a plot of ꢀ /ꢀ - [TNT] gave linear graph where y-axis intercept=1
ꢁ
(Figure S15). Therefore, it can be said that static quenching is effective in quenching of
fluorescence signal [50]. In addition, fluorescence lifetime measurements in the absence and
presence of TNT for compounds 5 and 6 were performed and illustrated in Figure S15.
Fluorescence lifetimes were calculated as 1.998±0.001 ns and 1.740±0.002 ns for compound 5
and compound 5 + TNT, respectively, and 1.317±0.004 ns, 1.284±0.006 ns for compound 6
and compound 6 + TNT, respectively (Figure 5 and Figure S16). It is clear the fluorescence
lifetimes of compounds 5 and 6 do not change obviously by the addition of 500 ppm and 250
ppm of TNT for compounds 5 and 6, respectively and 휏 /휏 are approximately equal to 1. This
ꢁ
result showed that quenching of fluorescence signal occurred by the static quenching in a
ground-state with non-fluorescent complex formation (compound 5 + TNT and compound 6 +
TNT).
Figure 5. Fluorescence lifetime decay profiles of a) compound 5 and compound 5 + TNT, b)
compound 6 and compound 6 + TNT using laser excitation source of 390 nm.

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It is well-known that fluorescence detection can be achieved using the relatively the
lowest unoccupied molecular orbitals (LUMO) energies of the explosive material. Because,
LUMO of explosive materials can accept an excited electron from the fluorophore [51, 52]. In
other words, when NACs interact with a fluorophore, the excited electron in the fluorophore
can be transferred to the LUMO of the NACs instead of relaxing back to the ground state,
resulting the emission changes. We assumed that there is a close relationship between the
LUMO energy levels of compound 5, 6 and TNT, causing fluorescence emission to remarkably
be quenched by only TNT, even in the presence of other competing analogues, such as
nitrobenzene, nitrophenol, picric acid, toluene or benzene. To confirm this assumption, HOMO
and LUMO energy levels of compounds 5 and 6 were measured by the cyclic voltammetry. The
cyclic voltammetry studies of compounds 5 and 6 (given in the SI as Figure S17) showed that
the lowest unoccupied molecular orbital energy (LUMO) is -3.51 eV for compound 5 and -3.67
eV for compound 6. Their LUMO energies differ only 0.16 eV. Thus, it seems there is a
relationship between sensitivity and LUMO energy level of the analytes. Secondly, since TNT
has a lower LUMO orbital energy, -3.7 eV [42], it can accept an electron from excited state of
those compounds. LUMO of fluorophores (compound 5 and 6) and TNT LUMO band gap were
much closed to each other as expected because of phosphazene compounds known as optically
inert in UV/vis radiation as mentioned.
3
.4. Theoretical Calculations
Even absorption (Figure 2a) and fluorescence spectra (Figure 2b) of compounds 5 and 6
were very similar to their precursor, their sensor properties are fully different (Figure 3). This
situation can be explained by that the anthracene groups are projected above and below the
cyclophosphazene plane, producing the non-covalent π⋯π interaction between anthracene and
TNT. Hence, we carried out quantum chemical calculations to obtain equilibrium structures of

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compounds 5 and 6 with TNT and to estimate their HOMO-LUMO energies. All calculations
were completed in the gas phase with standard density functional theory (DFT) the level of
B3LYP using 6-31G (d,p) and performed with the Gaussian09 [53] package. The optimized
geometries of compounds 5 and 6 with TNT, 5-TNT and 6-TNT, respectively, are shown in
Figure 6. The optimized structures showed that the space between the anthracene and TNT
molecule in the 6–TNT complex structure is smaller and more planer than that of the 5–TNT.
This conformational change for donor-acceptor systems may reflect disparities in the charge-
transfer quenching properties [54]. As one can see from the frontier orbitals given in Figure 7,
the highest occupied molecular orbitals (HOMO) are located on the anthracene for both
complex structures.
Figure 6. Optimized geometries of compound 5 and 6 with TNT.

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Figure 7. Frontier orbitals of 5-TNT (left) and 6-TNT (right) with B3LYP level of theory.
Although, their provided HOMO energies are almost similar (-5.44 eV for 5-TNT and -
.40 eV for 6-TNT), LUMO are different (-2.39 eV for 5-TNT and -2.09 eV for 6-TNT) from
5
each other. This result indicates that there is an intermolecular π⋯π interaction between the
anthracene and TNT molecule on the complex structures, which is influenced by position of the
TNT molecule. Moreover, the order of the orbitals on the complex structures predicted by DFT
confirms the experimental findings that the LUMO orbital for TNT is lower than anthracene.
Thus, there is an energy transfer from LUMO of anthracene to LUMO of TNT. The energy gap
between these two orbitals are 1.11 eV for 5-TNT and 1.41 eV for 6-TNT.
Table 1: The comparison of developed chemosensors with some previously TNT reports
Sensing System
Linear Range (M) LOD (M)
RSD% Ref.
−
5
−4
1.0x10−5
1.3x10-7
cross-linking electropolymerized films
PPV functionalized mesoporous silica
nanoparticles with graphene oxide
pyrimidine derivatives
CdSe quantum dots
MIPs@CDs
1.0x10 -1.0x10
-2.4x10-6
N.r
N.r
[55]
[56]
0
-
1
-4
-3
1.26x10 -5.61x10
2.77x10
2.0x10
N.r
3.4
3.4-5.0
[57]
[58]
[59]
-
7
-5
-8
1.0x10 –5.0x10
-
7
-5
-8
5.0x10 -2.0x10
1.7x10
1
7
.0×10−5
.0x10-5
conjugated polymer nanoparticles
N.r
N.r
[60]
-
6
-3
-3
-5
5
6
2.2x10 -2.2x10
8.8x10 -1.1x10
3.67x10
2.83x10
1.04
2.05
PW
PW
-
7
-5
*N.r: not reported; PW: present work

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4
. Conclusion
Newly synthesized fluorescent anthracene-decorated dendrimeric cyclophosphazenes by
esterification reaction compounds are highly soluble in common organic solvents, have high
thermal stability and high glass transition temperatures (T ). Considering the spectroscopic
g
findings described above, those compounds exhibit high binding affinity and selectivity
towards TNT, but not for other NACs such as nitrobenzene, nitrophenol, picric acid, toluene or
benzene. The predicted computational results support experimental findings that there is a close
relationship between anthracene and TNT molecule in the complex. Moreover, our novel
system has moderate LOD, low RSD %, high selectivity, low cost, simple and time friendly
compared to the reports focusing on TNT detection with similar approach in the (Table 1).
According to obtained results, it is worthy of note that synthetic cyclophosphazenes based on
dendrimeric materials can be designed and developed to get more efficient new fluorescence
sensor systems for not only TNT but also other NACs, which are known as environmental
pollutant and toxic to living organisms.
Acknowledgment
The research was supported by the TÜBİTAK grant 214Z259. The numerical calculations
reported in this paper were fully performed at TUBITAK ULAKBIM, High Performance and
Grid Computing Center (TRUBA resources).
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Graphical abstract

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Highlights
►
A new type of fluorescent chemosensors based on anthracene-decorated cyclotri- and cyclotetraphosphazenes
have been synthesized.► The photophysical properties of the compounds have been studied in THF ► The
Fluorescence Sensing properties of the compounds have been studied in THF ►Very selective and sensitive
fluorescence sensors for detection of TNT have been obtained.