Fluorescence quenching of triarylamine functionalized phenanthroline-based probe for detection of picric acid

Article abstract of DOI:10.1016/j.jphotochem.2020.112780

Detection of toxic nitro aromatic compounds (NAC) using a cost-effective fluorescence sensing method have gained global attention. The current work demonstrates the selective sensing of picric acid using imidazo[4,5-f]-1,10-phenanthroline-triarylamines. T

Full text of DOI:10.1016/j.jphotochem.2020.112780

Journal Pre-proof
Fluorescence quenching of triarylamine functionalized
phenanthroline-based probe for detection of picric acid
P.A. Parvathy, R. Dheepika, R. Abhijnakrishna, P.K.M. Imran, S.
Nagarajan
PII:
S1010-6030(20)30579-7
DOI:
https://doi.org/10.1016/j.jphotochem.2020.112780
JPC 112780
Reference:
To appear in:
Journal of Photochemistry & Photobiology, A: Chemistry
Received Date:
Revised Date:
Accepted Date:
6 May 2020
26 June 2020
13 July 2020
Please cite this article as: Parvathy PA, Dheepika R, Abhijnakrishna R, Imran PKM,
Nagarajan S, Fluorescence quenching of triarylamine functionalized phenanthroline-based
probe for detection of picric acid, Journal of Photochemistry and amp; Photobiology, A:
Chemistry (2020), doi: https://doi.org/10.1016/j.jphotochem.2020.112780
This is a PDF file of an article that has undergone enhancements after acceptance, such as
the addition of a cover page and metadata, and formatting for readability, but it is not yet the
definitive version of record. This version will undergo additional copyediting, typesetting and
review before it is published in its final form, but we are providing this version to give early
visibility of the article. 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.
© 2020 Published by Elsevier.

Fluorescence quenching of triarylamine functionalized
phenanthroline-based probe for detection of picric acid
P. A. Parvathy,a R. Dheepika,a R. Abhijnakrishna,a P.K.M. Imran,b S. Nagarajana*
aDepartment of Chemistry, Central University of Tamil Nadu, Thiruvarur-610 005, India.
b Department of Chemistry, Islamiah College, Vaniyambadi- 635 752, India.
*snagarajan@cutn.ac.in
Graphical Abstract
Highlights
 Designed and synthesized new triarylamine based
phenanthroline.
 Molecules act as good sensor for nitro aromatics.

 Picric acid enhanced the absorption and quenched the
fluoresence maxima.
 Selective detection of picric acid at micro mole concentration.

FRET mechanism is observed.
Abstract
Detection of toxic nitro aromatic compounds (NAC) using a cost-effective
fluorescence sensing method have gained global attention. The current work
demonstrates the selective sensing of picric acid using imidazo[4,5-f]-1,10-
phenanthroline-triarylamines. The specific interaction mode of sensor molecules with
NACs is established by absorption and emission spectroscopic methods. Remarkably,
a new band appeared in the range of 420 to 480 nm. This new band increased the
probability of overlap of the absorption with the emission spectra and ensures the
FRET mechanism. The presence of electron rich methoxy group on TAA side arm
improved the interaction with electron deficient picric acid with a binding constant of
1.46 x 105 M-1. The linearity of the Stern-Volmer plot confirms the mechanism is
static quenching.The detection limit was calculated to be at micro molar level for all
the four compounds. Density functional theory was employed to study the HOMO -
LUMO of the compounds and informs that the energy transfer is more feasible from
electron rich sensor molecule to picric acid. These molecules can act as efficient
fluorescence sensor for selective picric acid detection.
Keywords: Quenching; sensing; fluorescence; phenanthroline; triarylamines; picric
acid.
1. Introduction
Sensing of nitro aromatic compounds (NAC) is one of the imperative research topics
due to their toxicity and explosive nature [1]. Among many NACs, picric acid (PA,

2,4,6-trinitrophenol) gained special attention due to its adverse health issues such as
allergy, diarrhoea, and neurological disorders [2]. PA has wide spectrum of
applications in pharmaceutical and dye industries [3]. In addition, high solubility of
PA makes the situation more perilous; leads to ground water and soil pollution.
Considering the wide array of applications and effects, picric acid sensing has been a
mainstream research in the past decades. Various practices such as chromatography
[4], membrane electrode technique [5], and spectrophotometric techniques [6] have
been investigated for sensitive and selective detection of picric acid. However, apart
from spectrophotometry, other techniques have the drawbacks of real-time sample
analysis, costly, and difficulty in handling. As a result of continuous efforts,
fluorescent chemo-sensors have been recognized as an easy, robust alternative method
and applied in many fields like biology, pharmacology, and environmental sciences
[7]. Design of the molecule is the first important strategy to achieve a good sensor.
NACs are electron deficient in nature [8] and hence designing electron-rich molecules
facilitates sensing of picric acid via better interaction.
Different types of sensor molecules are inspected for detection of PA and distinct
mechanisms are proposed [9, 10]. Recently, Sushil Kumar and co-workers [11]
reported palladium-based metal organic frame work as sensor for picric acid. With
one Pd unit, the interaction was through hydrogen bonding and π-electron interaction,
while with two Pd units, picric acid perfectly fits in the cavity of the macrocycle.
Laxmiet al.[12] reported aggregation induced emission probes for the receptor free
detection of picric acid using a copolymer poly(2,7-(9,9- dioctylfluorene)-co-3,4-
diphenyl-2,5-distyrylthiophene) and explained the mechanism through fluorescence
resonance transfer and photoinduced energy transfer processes [13-15]. Gel based
sensor molecules are reported by Bhalla et al. [16] in which pentacene quinone
derivative formed supramolecular aggregates to detect PA in ppb level.
Triarylamines (TAA) are promising candidates for many applications including
organic electronics and sensing [17-20, 22]. They are capable of undergoing two
photon absorption and suitable for biological applications [19, 21]. Structural
modification of the non-planar structure resulted in aggregation induced emission and
utilized in toxic metal ions [23, 24] nitro compounds [25-30] sensing. Palas et al.,

reported a triphenylamine based fluorophore for detection of PA with intramolecular
photoinduced electron transfer mechanism between electron rich triphenylamine and
electron deficient nitroaromatics with detection limit of 449 ppb [31].
Aniketchowdary et al., stated that the PA undergone deprotonation and resonance
energy transfer with the analyte in solution state. In solid state, exciton migration was
observed after analyte binding: as a result, fluorescence quenching was amplified
[32].
In this investigation, we have designed and synthesised new TAA molecules via
focussed microwave assisted synthesis with high purity and yield. The interaction
between the synthesized molecules and the NACs is investigated by absorption and
emission spectroscopic techniques. Density functional theory (DFT) is also employed
to scrutinize the structure and frontier molecular orbitals of the molecules and the
targets to get insight about their interaction. The core objective of this investigation is
to develop fluorescence as an easy and robust technique for NAC sensing.
2. Experimental
2.1 Materials and methods
All the starting materials are purchased from commercial sources and used as
received. Microwave assisted synthesis was performed using CEM microwave
synthesizer. All the reactions and chromatographic separations were monitored by
pre-coated thin layer chromatographic plates. Column chromatography was carried
out with slurry packed activated silica gel (100-200 mesh). UV-Vis absorption spectra
were recorded using Jasco V-670 spectrophotometer. Emission spectra were obtained
using Perkin Elmer LS 55 spectrofluorimeter. FT-IR spectra were recorded using
Perkin Elmer spectrometer. Electron spray ionization (ESI) high resolution mass
spectra were recorded in Thermo scientific Exactiveplus UHPLC mass spectrometer.
The molecules were optimized at the 6-31G basis level of DFT using Gaussian. The
frontier molecular orbital values (HOMO and LUMO) were extracted using
GaussView software.

2.2 Synthesis of compounds
The precursor molecule 1 was synthesized by Vilsmeier Haack reaction of
triphenylamine. It was further subjected to iodination in presence of potassium iodide
and iodate to yield compound 2 (Scheme 1). The compounds were purified by column
chromatography. Phenanthroline was oxidized in vigorous condition (NaBr, H2SO4,
HNO3, 100 °C) to yield phenanthroline dione, 6. The detailed synthetic procedures are
given in the supporting information.
2.3 General procedure for Suzuki coupling, 3-5
Compound 2 (1 eq) was dissolved in THF and Pd(PPh3)4 (0.08 eq) was added under
nitrogen atmosphere. 2 M aqueous Na2CO3 was added and stirred for 20 min at room
temperature. Boronic acid (1.1 eq) was added and refluxed for 7 h. Completion of the
reaction was monitored by TLC. Reaction mixture was cooled to room temperature
filtered over celite to remove Pd. Then it was extracted with DCM/water and dried
over Na2SO4.Solvent was removed under reduced pressure. Purification was done by
liquid column chromatography (Stationary phase: Silica gel (100-200 mesh), eluent:
EtOH/Hexane).
4,4’((4-Phenyl)phenylamino)dibenzaldehyde, 3: Yield: 83%. Yellow solid.1H NMR
(400 MHz, CDCl3, δ in ppm): 9.91 (s, 2H); 7.802 (m, 4H); 7.662 (m, 4H); 7.426 (m,
3H); 7.214 (m, 6H). 13C NMR (100 MHz, CDCl3, δ in ppm): 151.95, 144.68, 139.21,
131.43, 131.37, 128.93, 128.71, 127.10, 126.93, 123.10, 123.02, 122.96.
4,4’-((4’-Methoxy(4-phenyl))phenylamino)dibenzaldehyde, 4: Yield: 66%. Yellow
solid.1H NMR (400 MHz, CDCl3, δ in ppm): 9.906 (s, 2H); 7.795 (d, J=8.4Hz, 3H);
7.553 (m, 4H); 7.232 (m, 7H); 6.998 (d, J=7.2Hz, 2H); 3.866 (s, 3H): 13C NMR (100
MHz, CDCl3, δ in ppm): 190.62, 159.40, 151.97, 144.05, 138.74, 132.45, 131.35,
128.22, 127.98, 127.21, 122.84, 114.37, 55.38.
4,4’((4-(Thiophen-3-yl))phenylamino)dibenzaldehyde 5: Yield: 63%. Yellow
solid.1H NMR (400 MHz, CDCl3, δ in ppm): 9.907 (s, 2H); 7.795 (d, J=8Hz, 4H);

7.617 (d, J=7.6Hz, 2H); 7.434 (m, 3H); 7.224 (m, 6H): 13C NMR (100 MHz, CDCl3, δ
in ppm): 190.61, 151.88, 144.35, 141.16, 133.79, 131.41, 128.10, 127.20, 126.64,
126.09, 122.89, 120.59
2.4
General procedure for microwave assisted synthesis of
imidazo[4,5-f]-1,10- phenanthroline
A mixture 1,10-phenanthroline-5,6- dione (3) (2.5 eq), TPA dialdehyde (1) or Suzuki
coupled compound (4-6) (1 eq), ammonium acetate (30 eq), and glacial acetic acid
o
was heated at 100 C for 20 min under microwave conditions (power: 150, pressure:
270, pre-stirring time: 1min). Completion of the reaction was monitored by TLC and
after completion the reaction mixture was poured to ice-cold water. The solid was
filtered and washed with hot water three times and with ammonia solution. The
product was dried under vacuum.
N,N-Bis(4-1H-imidazo[4,5-f]-1,10-phenanthrolin-2-yl)-[1,1'-biphenyl]-4-amine, 7:
Yield: 80%. Reddish orange solid. m.p: 562°C. 1H NMR (400 MHz, CDCl3, δ in ppm):
13.639 (s, 2H); 9.04 (s, 4H); 8.929 (d, J=7.6 Hz, 4H); 8.255 (d, J=7.6 Hz, 4H); 7.842
(s, 4H); 7.461 (m, 2H); 7.311 (d, J=7.6 Hz, 4H); 7.251 (d, J=6.8 Hz, 3H): 13C NMR
(100 MHz, CDCl3, δ in ppm): 150.92, 148.39, 148.19, 146.75, 144.05, 143.84, 136.25,
130.44, 130.04, 128.11, 126.74, 125.86, 125.05, 124.91, 124.14, 123.84, 123.58. MS
(ESI) m/z calcd for C44H27N9 [M+H]+ 682.2389; found, 682.2451.
N,N-Bis(4-(1H-imidazo[4,5-f]-1,10-phenanthrolin-2-yl)phenyl)-[1,1'-biphenyl]-4-
amine, 8: Yield: 95%. Orange solid. 1H NMR (400 MHz, CDCl3, δ in ppm):9.237 (m,
4H); 8.914 (m, 4H); 8.269 (m, 4H); 7.937 (m, 4H); 7.745 (m, 4H); 7.481 (m, 2H);
7.338 (m, 6H); 7.029 (m, 1H): 13C NMR (100 MHz, CDCl3, δ in ppm): 151.01,
148.23, 147.97, 147.91, 136.30, 130.09, 130.05, 129.47, 128.50, 128.27, 127.75,
126.81, 126.70, 125.70, 125.36, 125.10, 124.38, 124.36, 124.22, 123.67, 123.61. MS
(ESI) m/z calcd for C50H31N9[M-H]- 757.2602; found,756.2633.
N,N-Bis(4-(1H-imidazo[4,5-f]-1,10-phenanthrolin-2-yl)phenyl)-4'-methoxy-[1,1'-
biphenyl]-4-amine, 9: Yield: 93%. Orange solid.1H NMR (400 MHz, CDCl3, δ in

ppm): 13.713 (s, 2H); 9.045 (s, 4H); 8.927 (d, J=6.8 Hz, 4H); 8.271 (d, J=7.2 Hz, 4H);
7.764 (m, 4H); 7.657 (m, 4H); 7.36 (m, 4H); 7.282 (m, 2H); 7.042 (m, 3H); 3.81 (m,
3H): 13C NMR (100 MHz, CDCl3, δ in ppm): 159.32, 150.84, 148.36, 145.54, 144.07,
143.90, 136.37, 136.12, 132.19, 130.05, 128.13, 127.98, 126.74, 126.68, 126.02,
125.08, 124.17, 124.01, 123.55, 119.78, 114.84, 55.35. MS (ESI) m/z calcd for
C51H33N9O[M-H]- 786.2808; found,786.2739.
N,N-Bis(4-(1H-imidazo[4,5-f]-1,10-phenanthrolin-2-yl)phenyl)-4-(thiophen-3-
1
yl)aniline, 10:Yield: 90%, Orange solid. H NMR (400 MHz, CDCl3, δ in ppm):
13.699 (s, 2H); 9.042 (s, 4H); 8.926 (d, J=8Hz, 4H); 8.268 (d, J=8Hz, 4H); 7.805 (m,
7H); 7.671 (s, 1H); 7.594 (d, J=2.4Hz, 1H); 7.355 (d, J=8Hz, 4H); 7.262 (d, J=7.2Hz,
2H): 13C NMR (100 MHz, CDCl3, δ in ppm): 151.15, 151.04, 150.89, 148.28, 148.19,
148.09, 145.61, 143.96, 143.80, 141.49, 141.32, 131.69, 130.11, 128.37, 128.12,
127.99, 127.62, 126.50, 125.86, 125.05, 124.2, 123.99, 123.99, 123.79, 123.71,
121.02. MS (ESI) m/z calcd for C48H29N9S[M+H]+ 764.2266; found, 764.2327.

3. Results and discussions
The sensing molecules are designed with highly conjugated triarylamine -
phenanthroline systems connected via an azole ring. TAA part is further
functionalized with electron rich thiophene and methoxyphenyl groups to improve the
interaction with electron deficient NACs. In addition, the imidazole nitrogen can also
facilitate the interaction through H-bonding. The target molecules 7-10 are obtained
by microwave assisted synthesis (Scheme 1) and characterized using spectroscopic
techniques. Condensation of phenanthrolinedione, 3 with TAA aldehyde in the
presence of acetic acid and ammonium acetate at 100 °C was carried out in CEM
microwave synthesizer and the products were obtained in high purity and good yield.
IR spectra are given in Figures S1 to S4 (supporting information). The peaks in the
range of 1590-1600 cm-1 and 1445-1475 cm-1 corresponds to C=N and C=C
stretching, respectively. ESI-Mass spectrometry analysis confirmed formation of final
compounds 7-10 (Figure S5-S8 in supporting information).

7
8
7
8
10
10
9
9
Scheme 1. Synthetic route and molecular structure of functionalized imidazo[4,5-
f]-1,10- phenanthrolines
The NMR spectra are given in the Figures S9-S22 in supporting information. For
compound 5, the methoxy carbon resonates at 55 ppm. The spectra of the compounds

shows characteristic peak for N-H in highly de-shielded region and aromatic protons
are resonating at 7-9.2 ppm. For the molecule 9, the methoxy protons resonated at 3.8
ppm. The molecular structure of target compounds is shown in Scheme 1.
3.1 Optical properties
To evaluate the photophysical properties of new compounds 7-10, their absorption
and emission spectra are recorded in DMSO at 10-5 M concentration. Spectra are
given in the Figure 1 and the data are represented in Table 1. Absorption spectra
exhibited two prominent peaks around 380 and 285 nm attributed to n-π* and π-π*
transitions, respectively.
Figure1. (a) Absorption and (b) emission spectra of 7-10
Table 1. Photophysical properties of compounds 7-10
C. No
λAbs (nm)
385
λEm (nm)
459.5
Stokes’ shift (nm)
ε (1× 10-4) M-1 cm-1
74.5
74.5
81
5.2
3.8
4.8
4.5
7
381
455.5
8
373
454.0
9
375
453.5
78.5
10

Emission spectra shows single emission peak in the region of 450-460 nm. Among the
four new compounds, compound 10 has higher emission intensity due to the presence
of electron donating thiophene group [33]. Polar medium creates charge separation in
the excited state of the molecule and thereby changes the geometry [34, 35].
Figure 2. Interaction of PA with 7-10 (absorption spectra)
A constant volume of sensor molecule (10-5 M) was titrated against picric acid (10-4
M) and the changes in absorbance were recorded. Significant change was observed in
both transitions. The spectra are depicted in the Figure 2. The absorption spectra
confirms the interaction between the sensor molecule and PA, as there is no indication
of PA’s absorption peak (345 nm) [36]. The absorption spectra of the compounds
tails at around 420 nm and the emission starts at 410 nm and this overlap enables the
possibility of FRET energy transfer [37-41]. Electron rich methoxyphenyl and

thiophene groups in the molecules 9 and 10 have exhibited bathochromic shift of 6
and 4 nm, respectively during PA titration.
Table 2. Thermal properties and computational analysis of compounds 7-10
Computational (DFT) (eV)
C. No.
Td (oC)
HOMO
-5.18
LUMO
-1.70
-1.71
-1.69
-1.73
Band gap
3.48
533
374
447
479
7
-5.16
3.45
8
-5.10
3.41
9
-5.18
3.45
10
The absorbance is slowly increased and the band at 375 nm is red-shifted upon the
addition of PA [42]. Remarkably, one new band appeared in the range of 420 to 480
nm (Figure 2). This new band increased the probability of overlap of the absorption
with the emission spectra and opens the door for FRET mechanism [32]. Change in
the absorption spectra revealed the complex formation/ interaction of picric acid with
probe molecule. The compounds 7-10 show emission maxima at the range of 450-460
nm when excited at their corresponding absorption maxima. Upon the addition of PA
to the sample solution, fluorescence intensity gradually decreased (Figure 3). On
further addition of PA, fluorescence quenching was observed with a slight color
change [43]. The compound 9 shows more quenching effect towards PA addition due
to methoxyphenyl substitution. Pandith et al. reported anthracene carboxamide
fluorescent probe with good response to picric acid over other NACs [44]. Table 2
gives the HOMO-LUMO levels and decomposition temperature.

0 µL
0 µL
1000 µL
1000 µL
0 µL
0 µL
1000 µL
1000 µL
Figure3. Emission spectra of compounds 7-10 with picric acid, excited at 385, 381,
279, and 277 nm respectively
3.2 Stern-Volmer plot
Kinetics of sensing mechanism is explained with Stern-Volmer plot. Linearity of the
plot explains the mechanism of quenching either static or dynamic [45]. The linear
plots obtained for all the four sensing compounds clearly indicated the significance of
[Q]1 dependence in the interaction (Figure 4). The slope of Stern-Volmer plot
indicates that the compound 9 exhibited better interactions with PA and the binding
constant obtained as 1.46 x 105 M-1. This can be substantiated by the presence of
electron rich methoxy group on TAA side arm, which can improve the interaction
with electron deficient picric acid. The compounds 7 and 10 (–H and thienyl
substitution) shows 1.17 x 105 M-1 as the binding constant. Only slight variation in the
binding constants is observed among the four compounds. The binding constant value
of these new TAA functionalized phenanthrolines are ameliorated from the recent

reports. [43, 46] The detection limit was calculated to be at micro molar level for all
the four compounds which is comparable with the similar type of sensor molecules
[47-49].
Figure4.Stern-Volmer plot
3.3 Analyte selectivity studies
It is always important to address the selectivity of sensor molecule. In the present
investigation, the selectivity was analyzed among other NACs such as 4-nitrobenzoic
acid, 4-nitrophenol, 4-nitrobenzaldehyde and, 4-nitrotoluene. The interaction of the
above mentioned nitro aromatic compounds with TAA functionalized phenanthrolines
was scrutinized using UV-vis absorption spectroscopy technique. The responses in
absorption spectra are given in the Figure 5. For the selectivity study, all the NACs

were taken in 10-4 M concentration. The absorption spectra were recorded before and
after adding the NACs at fixed concentration of compounds. Among the NACs, picric
acid shows significant change in the absorption intensity of the sensor molecules,
where as the other NACs have shown negligible effect. This observation is same for
all the four compounds (compounds 7-10). Although, the interaction of the four
compounds with picric acid is appreciable than the others NACs, the difference in the
absorption intensity is small. However, the formation of new band at around 430 nm
(Figure 2) explains the better interaction with picric acid and no such band is
observed with other NACs. Thus, we restricted the emission study for selectivity only
to picric acid.
PA
8
PA
7
Other
NACs
Other
NACs
PA
PA
10
9
Other
NACs
Other
NACs
Figure 5.Interaction of sensors with PA and other NACs

3.4 Thermal properties
Thermal behaviour of the compounds (7-10) was analyzed by thermogravimetric
analysis (TGA). All the compounds exhibited high thermal stability with a single
decomposition in the region of 370-530 °C for 10 % by weight loss. Stepwise
decomposition is not observed and thus the molecules are stable up to 530 °C. Tagare
et al., [50] reported TAAs substituted with phenanthromidazoles in three arms for
OLED application with a decomposition temperature of 450 °C. Hong and co-workers
[51] reported on carbazole-imidazo [4,5-f]-1,10- phenanthroline hybrids for blue LED
application. Those molecules had higher glass transition up to 240 °C but the
decomposition point was less than 400°C. The TGA curves of the compounds 7-10
are shown in Figure 6 and the extracted data are given in Table 2.
Figure6. TGA curves for the compounds 7-10

3.5 Computational studies
The density functional theory (DFT) analysis was performed to get insight about the
energy levels, energy distribution and the interaction between the sensor molecules
and PA. The Frontier molecular orbital energy levels (HOMO and LUMO) were
extracted using GaussView software and represented in the Figures 7. Frontier
molecular energy values of PA (or picrate) and sensor molecules ensure the feasible
charge transfer from sensor molecules to picric acid. Energy transfer is feasible from
the sensor molecules to PA with respect to their HOMO and LUMO levels. LUMO of
picric acid (4.5eV) situated near the HOMO of sensor molecules (5.1eV) which can
provide the possible way for energy transfer.

Figure 7. Qualitative representation of FMOs of molecules 7-10, picric acid and
picrate

4. Conclusion
Four new imidazo[4,5-f]-1,10-phenanthroline-triarylamines were designed for nitro
compounds sensing. The compounds were successfully synthesized via microwave
assisted synthesis with good yield and purity and well characterized using FT-IR,
1
ESI-MS, H and 13C NMR. From the photophysical studies it was established that
among different nitroaromatic compounds picric acid exhibited significant interaction.
Among the molecules synthesized methoxy substituted compound shows high binding
constant. Remarkably, one new band appeared in the range of 420 to 480 nm. This
new band increased the probability of overlap of the absorption with the emission
spectra and opens the door for FRET transfer mechanism. The detection limit was
calculated to be at micro molar level for all the four compounds. These molecules can
act as efficient fluorescence sensor for selective picric acid detection.
Conflicts of Interest Statement
The authors whose names are listed immediately below certify that they
have NO affiliations with or involvement in any organization or entity
with any financial interest (such as honoraria; educational grants;
participation in speakers’ bureaus; membership, employment,
consultancies, stock ownership, or other equity interest; and expert
testimony or patent-licensing arrangements), or non-financial interest
(such as personal or professional relationships, affiliations, knowledge
or beliefs) in the subject matter or materials discussed in this
manuscript. Author names: The authors whose names are listed
immediately below report the following details of affiliation.

References
[1] J. Yang,T.M. Swager., Fluorescent porous polymer films as TNT chemosensorsꢀ:
electronic and structural effects, J. Am. Chem. Soc. (1998) 11864–11873,
https://doi.org/10.1021/ja982293q.
[2] F. Abbasi, A. Akbarinejad, N. Alizadeh., CdS QDs/N-Methylpolypyrrole
Hybrids as Fluorescent Probe for Ultrasensitive and Selective Detection of Picric
Acid. Spectrochim. Acta - Part A Mol. Biomol. Spectrosc.216 (2019) 230–235,
https://doi.org/10.1016/j.saa.2019.03.032.
[3] D. T. Burton,K. R. Cooper,W. L. Goodfellow,D. H. Rosenblattt., Acute toxicity
of picric acid and picramic acid to rainbow trout, salmo gairdneri, and american
oyster, crassostrea virginica, J. Am. Water Resour. Assoc. 19 (1983) 641–648,
https://doi.org/10.1111/j.1752-1688.1983.tb02782.x.
[4] B. Niehus,W. Engewald., Identification and quantification of polar nitroaromatic
compounds in explosive-contaminated waters by means of HPLC-ESI-MS-MS
and
HPLC-UV,
Chromatographia
63
(2006)
1–11,
https://doi.org/10.1365/s10337-005-0703-8.
[5] E. P. Diamandis,T. P. Hadjiioannou., Catalytic determination of selenium with a
picrate-selective electrode, Analytica Chimica Acta 123 (1981)143–150,
https://doi.org/10.1016/S0003-2670(01)83167-6.
[6] S. G. Metcalf, A. A. Okemgbo., A novel picric acid film sensor via combination
of the surface enrichment effect of chitosan films and the aggregation- induced
emission effect of siloles, Abstr. Pap. Am. Chem. Soc 218 (1999) 124,
https://doi.org/10.1039/B906946A.
[7] T. Gunnlaugsson, E. U. Akkaya,J. Yoon,T. D. James., Fluorescent chemosensors:
the past, present and future, Chem. Society Rev. 46 (2017) 7105–7013,
https://doi.org/10.1039/C7CS00240H.
[8] S. Shanmugaraju, P. S. Mukherjee., Pi-Electron rich small molecule sensors for
the recognition of nitroaromatics, Chemcomm. 51 (2015)16014–16032,
https://doi.org/10.1039/C5CC07513K.

[9] P.P. Soufeena, T.A. Nibila, K.K. Aravindakshan., Coumarin Based Yellow
Emissive AIEE Active Probe: A Colorimetric Sensor for Cu2+ and Fluorescent
Sensor for Picric Acid, Spectrochim. Acta - Part A Mol. Biomol. Spectrosc. 223
(2019) 117201, https://doi.org/10.1016/j.saa.2019.117201.
[10]B. Pramanik,N. Singha,D. Das., Sol-, Gel-, and Paper-based detection of picric
acid at femtogram level by a short peptide gelator, ACS Appl. Polym. Mater. 1
(2019) 833–843, https://doi.org/10.1021/acsapm.9b00071.
[11]S. Kumar,R. Kishan,P. Kumar,S. Pachisia,R. Gupta., Size-selective detection of
picric acid by fluorescent palladium macrocycles, Inorg. Chem. 57 (2018)1693–
1697, https://doi.org/10.1021/acs.inorgchem.7b02813.
[12]L. R. Adil,P. Gopikrishna,P. K. Iyer., Receptor-free detection of picric acid: A
structural approach for designing aggregation-induced emission probes,ACS
Appl.
Mater.
Interfaces
10
(2018)
27260–27268,
https://doi.org10.1021/acsami.8b07019.
[13]H. Dong, W. Gao,F. Yan,H. Ji,H. Ju., Fluorescence resonance energy transfer
between quantum dots and graphene oxide for sensing biomolecules,Anal.Chem.
82 (2010) 5511–5517,https://doi.org/10.1021/ac100852z.
[14]T. Kowalczyk, Z. Lin, T. V. Voorhis., Fluorescence quenching by photoinduced
electron transfer in the Zn2+ sensor zinpyr-1ꢀ: A computational investigation,
J.Phys.Chem.A 114 (2010) 10427–10434,https://doi.org/10.1021/jp103153a.
[15]T. M. Swager, The molecular wire approach to sensory signal amplification, Acc.
Chem. Res. 31 (1998) 201–207, https://doi.org/10.1021/ar9600502.
[16]V. Bhalla, A. Gupta, M. Kumar, D. S. S. Rao, S. K. Prasad., Self-assembled
pentacenequinone derivative for trace detection of picric acid, ACS Appl. Mater.
Interfaces 5 (2013) 672–679, https://doi.org /10.1021/am302132h.
[17]M. Hussain,A. Nafady,T. Sherazi,R. Shah,A. Alsalme,M.S. Kalhoro,S.A.
Mahesar,S. Siddiqui., Cefuroxime derived copper nanoparticles and their
application as colorimetric sensor for trace level detection of picric acid, RSC
Adv.6 (2016) 82882-82889, https://doi.org/10.1039/C6RA08571G.

[18] R. Dheepika, R. Abhijnakrishna, P.M. Imran, S. Nagarajan., High performance
p-channel and ambipolar OFETs based on imidazo [4, 5-f]-1, 10-phenanthroline-
triarylamines
RSC
Adv
10,
22
(2020)
13043
https://doi.org/10.1039/D0RA00210K.
[19] R. Dheepika, P.M. Imran, N.S.P Bhuvanesh, S. Nagarajan., Solution-processable
unsymmetrical triarylamines: Towards high mobility and ON/OFF ratio in
bottom-gated
OFET,
Chem.
Eur.
J.
25
(2019)
15155,
https://doi.org/10.1002/chem.201903450.
[20] P. Devibala, R. Dheepika, P. Vadivelu, S. Nagarajan., Synthesis of
aroylbenzoate-based push-pull molecules for OFET Applications,
ChemistrySelect 4 (2019) 2339, https://doi.org/10.1002/slct.201803394.
[21]R. Chennoufi,H. Bougherara,N. Gagey-eilstein,B. Dumat,E. Henry,F. Subra,S.
Bury-moné,F. Mahuteau-betzer,P. Tauc,E. Deprez., Mitochondria-targeted
triphenylamine derivatives activatable by two-photon excitation for triggering
and imaging cell apoptosis,Nat. Publ. Gr. (2016) 1–12, https://doi.org/
10.1038/srep21458.
[22]R. Dheepika, R. A. Shaji, P.M. Imran, S. Nagarajan., Improving device
performance of p-type organic field-effect transistor using butterfly like
triarylamines
Organic
electronics
(2019)
105568
https://doi.org/10.1016/j.orgel.2019.105568
[23]P.P. Kumavata, P.K. Baviskarb, B. R. Sankapal, D. S. Dalal., Facile synthesis of
D-π-A structured dyes and their applications towards cost effective fabrication of
solar cell as well as sensing of hazardous Hg (II), RSC Adv. 6 (2016) 106453–
106464, https://doi.org/10.1039/C6RA18712A.
[24]A.K. Mahapatra, G. Hazra, N.K. Das, S. Goswami., A q highly selective
triphenylamine-based indolylmethane derivatives as colorimetric and turn-off
fluorimetric sensor toward Cu2+ detection by deprotonation of secondary amines,
Sensors
and
Actuators
Bꢀ:
Chemical.
156
(2011)
456–462,
https://doi.org/10.1021/acsomega.9b00970.

[25] J. B. Arockiam, S. Ayyanar., Benzothiazole, Pyridine Functionalized
Triphenylamine Based Fluorophore for Solid State Fluorescence Switching, Fe3+
and Picric Acid Sensing. Sensors Actuators B. Chem. 242 (2016) 535–544.
https://doi.org/10.1016/j.snb.2016.11.086.
[26]E. V. Verbitskiy, Y. A. Kvashnin, A. A. Baranova, K.O. Khokhlov, R. D.
Chuvashov, E. Schapov, Y. A. Yakovleva, E. F. Zhilina, A. V. Shchepochkin, N.
I. Makarova, E. V. Vetrova, A. V. Metelitsa, G. L. Rusinov, O. N. Chupakhin, V.
N. Charushin., Synthesis and Characterization of Linear 1 , 4-Diazine-
Triphenylamine
–
Based Selective Chemosensors for Recognition of
Nitroaromatic Compounds and Aliphatic Amines, Dye. Pigment. 178 (2020) 1–
10. https://doi.org/s://doi.org/10.1016/j.dyepig.2020.108344.
[27]G. Sathiyan, B. Balasubramaniam, S. Ranjan, S. Chatterjee, P. Sen, A. Garg., A
Novel Star-Shaped Triazine-Triphenylamine e Based Fluorescent Chemosensor
for the Selective Detection of Picric Acid, Mater. Today Chem. 12 (2019) 178–
186. https://doi.org/10.1016/j.mtchem.2019.01.002.
[28]X. Q. Yao, G. B. Xiao, H. Xie, D. D. Qin, H. C. Ma, J. C. Liu, P. J. Yan., Two
Triphenylamine-Based Luminescent Metal-Organic Frameworks as a Dual-
Functional Sensor for the Detection of Nitroaromatic Compounds and Ofloxacin
Antibiotic,
CrystEngComm.
21
(2019)
2559–2570.
https://doi.org/10.1039/C8CE02122H.
[29]K. Duraimurugan, R. Balasaravanan, A. Siva., Electron Rich Triphenylamine
Derivatives (D-π-D) for Selective Sensing of Picric Acid in Aqueous Media,
Sensors
Actuators,
B
Chem.
231
(2016)
302–312.
https://doi.org/10.1016/j.snb.2016.03.035.
[30]Wu, H.; Tao, F.; Cui, Y.; Guo, L. Two Triphenylamine-Based AIE Materials for
the Detection of PA in Aqueous Medium. Mater. Chem. Phys.2020, 240 (July
2019), 122141. https://doi.org/10.1016/j.matchemphys.2019.122141.
[31]P.B. Pati, S.S. Zade., Highly emissive triphenylamine based fluorophores for
detection of picric acid, Tetrahedron Lett. 55 (2014) 5290–5293.

[32] A. Chowdhury,P.S. Mukherjee., Electron-rich triphenylamine-based sensors for
picric acid detection, JOC Artic. 80 (2015)
4064−4075,https://doi.org/10.1021/acs.joc.5b00348.
[33] M. Muralisankar, R. Dheepika, J. Haribabu, C. Balachandran, S. Aoki, N.S.P.
Bhuvanesh, S. Nagarajan., Design, Synthesis, DNA/HSA binding, and cytotoxic
activity of halfsandwich Ru(II)-arene complexes containing triarylamine-
thiosemicarbazone
hybrids,
ACS
Omega,
4
(2019)
11712,https://doi.org/10.1021/acsomega.9b01022.
[34] X. Zhang,H. Yu, Y. Xiao., Replacing phenyl ring with thiophene: an approach to
longer wavelength aza-dipyrromethene boron difluoride (Aza-BODIPY) dyes,
jouranl Org. Chem. 77 (2012) 669–673,https://doi.org/10.1021/jo201413b.
[35] R. Dheepika, S. Sonalin, P.M. Imran, S. Nagarajan., Unsymmetrical starburst
triarylamines: synthesis, properties, and characteristics of OFETs, Journal Mater.
Chem. C 6 (2018) 6916–6919,https://doi.org/10.1039/C8TC02017E.
[36] Y. Wu,S. Luo,L. Cao,K. Jiang,L. Wang, J. Xie,Z. Wang., Self-assembled
structures of N -alkylated bisbenzimidazolyl naphthalene in aqueous media for
highly sensitive detection of picric acid, Analytica Chimica Acta. 976 (2017), 74–
83, https://doi.org/10.1016/j.aca.2017.04.022.
[37] H. Fu, L. Yan, N. Wu, L. Ma, S. Zang., Dual-Emission MOF I Dye Sensor for
Ratiometric Fl Uorescence Recognition of RDX and Detection Of a broad class
of nitro-compounds, J. Mater. Chem. A Mater. energy Sustain. 6 (2018) 9183–
9191. https://doi.org/10.1039/C8TA02857E.
[38]D. Dinda, A. Gupta, B. K. Shaw, S. Sadhu, S. K. Saha., Highly Selective
Detection of Trinitrophenol by Luminescent Functionalized Reduced Graphene
Oxide through FRET Mechanism, Appl. Mater. Interfaces 6 (2014) 10722–
10728. https://doi.org/10.1021/am5025676.
[39]M. Kumar, V. Kumar, A. Javed, S. Satapathi., Nano-Structures & Nano-Objects
Graphene Quantum Dots and Carbon Nano Dots for the FRET Based Detection
of Heavy Metal Ions, Nano-Structures & Nano-Objects 19 (2019) 100347.
https://doi.org/10.1016/j.nanoso.2019.100347.

[40]V. Kumar, N. Choudhury, A. Kumar, P. De, S. Satapathi., Poly-Tryptophan /
Carbazole Based FRET-System for Sensitive Detection of Nitroaromatic
Explosives,
Opt.
Mater.
(Amst).
100
(2020)
109710.
https://doi.org/10.1016/j.optmat.2020.109710.
[41]V. V. Koppal, P. G. Patil, R. M. Melavanki, R. A. Kusanur, U. Onumashi, N. R.
Patil., Exploring the in Fl Uence of Silver Nanoparticles on the Mechanism of Fl
Uorescence Quenching of Coumarin Dye Using FRET, J. Mol. Liq. 292 (2019)
111419. https://doi.org/10.1016/j.molliq.2019.111419.
[42] S. Kumari,S. Joshi,T.C. Cordova-sintjago,D.D Pant,R. Sakhuja., Highly
sensitive fluorescent imidazolium-based sensors for nanomolar detection of
explosive picric acid in aqueous medium, Sensors Actuators B. Chem. 229
(2016) 599–608, https://doi.org/10.1016/j.snb.2016.02.019.
[43] B. Roy, A. K. Bar, B. Gole, P.S. Mukherjee., Fluorescent tris-imidazolium
sensors for picric acid explosive,J. Org. Chem. 78 (2013) 1306–
1310,https://doi.org/10.1021/jo302585a.
[44] A. Pandith, A. Kumar, J. Lee, H. Kim., 9-Anthracenecarboxamide fluorescent
probes for selective discrimination of picric acid from mono- and di-nitrophenols
in
ethanol,
Tetrahedron
Lett.
56
(2015)
7094–
7099,https://doi.org/10.1016/j.tetlet.2015.11.017.
[45] J. R. Lakowicz., Principles of fluorescence spectroscopy, Third edit.; (2016)
[46] K. Jiang, S. Luo, C. Pang, B. Wang, H. Wu, Z. Wang., A functionalized
fluorochrome based on quinoline-benzimidazole conjugateꢀ: from facile design to
highly sensitive and selective sensing for picric cid, Dyes and Pigments 162
(2019) 367–376, https://doi.org/10.1016/j.dyepig.2018.10.041.
[47] S. Chaudhary, H. Sharma, M. D. Milton., Novel 2-Arylbenzothiazoles: Selective
Chromogenic and Fluorescent Probes for the Detection of Picric Acid,
ChemistrySelect 3 (2018) 4598–4608. https://doi.org/10.1002/slct.201800645.
[48] S. Nath, S. K. Pathak, B. Pradhan, R. K. Gupta, K. A. Reddy, G.
Krishnamoorthy, A. S. Achalkumar., A Sensitive and Selective Sensor for Picric

Acid Detection with a Fluorescence Switching Response, New J. Chem. 42
(2018) 5382–5394. https://doi.org/10.1039/c7nj05136k.
[49] J. Sahoo, D. S. Lakshmi, E. Suresh, P. S. Subramanian., Selective and Sensitive
Detection of Picric Acid in Aqueous, Sol-Gel and Solid Support Media by Ln(III)
Probes,
Sensors
Actuators,
B
Chem.
250
(2017)
215–223.
https://doi.org/10.1016/j.snb.2017.04.170.
[50] J. Tagare, H. Ulla, B. Kajjam, M.N. Satyanarayan., Star-Shaped
Phenanthroimidazole-Triphenylamine-Based Yellow Organic Emitter for Organic
Light
Emitting
Diodes.
Chem.
Sel.
2
(2017)
2611–2620,
https://doi.org/10.1002/slct.201700056.
[51] H. Huang, Y. Wang, S. Zhuang, X. Yang, L. Wang, C. Yang, Simple
Phenanthroimidazole/Carbazole Hybrid Bipolar Host Materials for Highly E Ffi
Cient Green and Yellow Phosphorescent Organic Light-Emitting Diodes, J. Org.
Chem. 116 (2012) 19458–19466,https://doi.org/10.1021/jp305764b.