Phenanthroimidazole derivatives as a chemosensor for picric acid: A first realistic approach

Article abstract of DOI:10.1039/d0nj03422c

A series of phenanthroimidazole (PI) derivatives (M1-M3): 2-phenyl-1H-phenanthro [9,10-d]imidazole (M1), 2-anthryl-1H-phenanthro[9,10-d]imidazole (M2), and 2-pyrenyl-1H-phenanthro[9,10-d]imidazole (M3) were synthesized and characterized using various spectroscopic techniques. The fluorescence quenching studies or sensing properties of the molecules M1-M3 with picric acid (PA) were studied. The molecules (M1-M3) exhibit strong fluorescence with a peak emission wavelength at 386, 486 and 456 nm. This emission gets quenched with the addition of PA. The mechanism of fluorescence quenching involves proton transfer from PA to M in the ground state, followed by the formation of a complex between the cation (M+) and picrate anion (PA-). The proton transfer breaks the conjugation inside the imidazole ring which in turn leads to loss of fluorescence. The proof of proton transfer was evident from the single X-ray crystal structure of the co-crystals (M1+-PA- and M3+-PA-) and their Hirshfeld surface analysis. Time-resolved fluorescence measurements reveal that quenching is static. The complex formation constant (Ks) and life-time for all the molecules are measured. This journal is

Full text of DOI:10.1039/d0nj03422c

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Phenanthroimidazole derivatives as Chemosensor for Picric Acid: A FirstDROeI:a10l.i1s0t3Vi9ice/Dw0ANrtiJc0le3O4n2l2inCe
Approach
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Ruby Ahmeda, Abid Alia, Musheer Ahmada, Ali Alsalmeb, Rais Ahmad Khan*b, and
Farman Ali*a
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a Department of Applied Chemistry, Zakir Hussain College of Engineering and Technology,
AMU, Aligarh 202002. Email:farmanfrequent@gmail.com, amusheer4@gmail.com,
abidaliamu4@gmail.com, ahmedruby1974@gmail.com
b Department of Chemistry, College of Sciences, King Saud University, P.O. Box 2455, Riyadh,
11451, KSA. Email: aalsalme@ksu.edu.sa and krais@ksu.edu.sa
Abstract:
A series of phenanthroimidazole (PI) derivatives (M1-M3): 2-phenyl-1H-phenanthro [9,10-
d]imidazole (M1), 2-anthryl-1H-phenanthro[9,10-d]imidazole (M2), 2-pyrenyl-1H-
phenanthro[9,10-d]imidazole (M3) were synthesized and characterized using various
spectroscopic techniques. The fluorescence quenching studies or sensing properties of the
molecules M1-M3 with picric acid (PA) were studied. The molecules (M1-M3) exhibit strong
fluorescence with peak emission wavelength at 386, 486 and 456 nm. This emission gets
quenched with the addition of PA. The mechanism of fluorescence quenching involves proton
transfer from PA to M in the ground state, followed by complex formation between cation (M+)
and picrate anion (PA¯). The proton transfer breaks the conjugation inside the imidazole ring
which in turn leads to loss of fluorescence. The proof of proton transfer was evident from single
X-ray crystal structure of the co-crystals (M1+-PA¯ and M3+–PA¯) and their Hirshfeld surface
analysis. Time-resolved fluorescence measurements reveal that quenching is static. The
complex formation constant (Ks) and life-time for are all the molecules is measured.

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DOI: 10.1039/D0NJ03422C
Introduction
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Environmental pollution is a major concern in the present century. The increasing use of
chemicals in our modern life is deteriorating the water bodies and agricultural lands1,2. 2,4,6-
trinitrophenol, also known as picric acid (PA), is also one such chemical used in the dye
industry, pharmaceuticals and chemical industries3,4. It is soluble in water and does not degrade
easily. It affects liver functions, respiratory systems, fertility and also causes anaemia, eye
irritation and cancer5,6. It is also recognized as a more powerful explosive material than its
structural analogous like trinitrotoluene (TNT) and p-dinitrobenzene (p-DNB) etc7. PA can
easily be used by terrorists for unlawful activities. Therefore, its specific and sensitive detection
is desirable.
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The conventional method utilized for PA detection has a long list of techniques such as gas
chromatography-mass spectrometry (GC-MS), electrochemistry, surface-enhanced Raman
spectroscopy, four-probe conductivity measurement and so on7–11. Amongst these, the
fluorescence is more attractive for the following reasons. Firstly, the photomultiplier (PMT)
detectors of fluorimeter are very sensitive therefore; it requires a small sample for signal
detection. Also, the technique is cost-effective and involves fast signal processing. Many
fluorescent sensors of PA have been reported. It includes metal-organic frameworks,
nanoparticles, fluorescence upconversion materials, azo dyes, derivatives of oxadiazoles,
tetrazoles, histidines and squaraines etc8,11–19. The sensing mechanism for PA depends on the
nature of probe20. The sensing mechanism of nitrogen-containing heterocycles like histidine or
oxidazole was mainly ascribed to proton transfer and energy transfer.
To the best of our knowledge, the proof of proton transfer from PA to a nitrogen atom of the
heterocycle has not been demonstrated in the literature. Also, it is the first report of using
phenanthroimidazole for detecting PA. Phenanthroimidazole is a planar and rigid aromatic
system. It exhibits significantly good electron transport and photophysical properties. It also

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has good thermal stability. Due to these properties, phenanthroimidazole derivatives find VtiheweAirrticle Online
DOI: 10.1039/D0NJ03422C
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use as fluorophores for laser dyes, probe for cysteine and homocysteine, component for red,
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green and blue (RGB) emitting systems in organic light-emitting devices (OLEDs) etc21–25
.
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Herein we demonstrate the phenanthroimidazoles as a family of compounds for which
fluorescence get quenched with the addition of PA and also explore the mechanism of
photoluminescence quenching (PLQ) by growing crystal of complex of M1 and PA i.e., M1+–
PA¯ and crystal of complex M3 and PA i.e. M3+–PA¯.
Experimental Section
Chemicals and Instrumentations
Phenanthrene-9,10-dione (Merck), Benzaldehyde (Merck), 9-anthraldehyde (Merck), and 1-
Pyrenecarboxalaldehyde (Merck), Picric acid (Merck), glacial acetic acid (Merck), Ammonium
acetate (Merck) and ethanol (Merck) were used as received. Perkin Elmer IR spectrometer was
used to record Fourier-transform infrared spectra. UV-Vis spectral measurements were carried
out using Perkin Elmer LAMBDA-45 spectrophotometer. The Florescence spectra were
obtained by a HITACHI-F2500 spectrofluorimeter. Melting points were measured in Mel
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Temp device using sealed capillaries. The H and C NMR spectra were recorded at room
temperature using a Bruker 300 MHz NMR spectrometer.
The Single X-ray measurements for Co-crystals (M1+–PA¯) and (M3+–PA¯) were carried out
on a Bruker APEX II Kappa CCD single crystal diffractometer equipped with a graphite
monochromator. MoKα radiation (λ = 0.71073 Å) was used for the collection, which was
controlled by APEX2 with data collected at 100(2)K. Using Olex226 , the structure was solved
with the olex2.solve27 structure solution program using Charge Flipping and refined with the
olex2.refine27 refinement package using Gauss-Newton minimisation. Masking refinement has

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been done in (M3+–PA¯) as the electron densities corresponding to one latDtiOcI:e10.D10M39/SD0ONJ03422C
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molecules are highly diffused.
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Squeezed refinement has been done as the electron densities corresponding to two crystallised
lattice DMSO molecules are highly diffused.
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Results and discussion
General Procedure of the Synthesis of the Compounds
The molecules M1, M2, and M3 were synthesized using the reported procedure as shown in
scheme 124. It involves a one-step condensation reaction between equimolar quantities of
phenanthrene-9,10-dione and aryl aldehyde. 1 mmole of phenanthrene-9,10-dione, 1 mmole of
aryl aldehyde and 5 mmoles of ammonium acetate were added to single-neck 100 ml round-
bottom flask. Then 30 ml of glacial acetic acid was added. The mixture was refluxed on
magnetic stirred for 12 hours under nitrogen. After completion of the reaction, the reaction
mixture was cooled to room temperature and then 50 ml of de-ionized cold water was added.
The product formed precipitates out as pale brown solid. The solid product was filtered under
suction and was washed thrice with de-ionized water. This was dried in a vacuum oven to give
2- aryl-1-H-phenanthro[9,10 d] imidazole as the final product. (See SI, for FTIR spectra, 1H,
13C NMR)
Scheme 1: Synthesis of compounds M1, M2, and M3.
The crystal of complex (M1+-PA¯) was synthesized by mixing M1 (20 mg) and PA (20 mg) in
5 ml ethanol. This solution was left undisturbed and slow evaporation of the solvent leads to

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crystallization. Small crystals were obtained after ten days. The crystal of complexD(OMI: 130+.1–03P9A/D¯0N)J03422C
was synthesized by mixing M3 (100 mg) and PA (300 mg) in 20 ml ethanol and 3 ml DMSO.
The resulting solution was heated at 70 °C. It was left undisturbed and crystals of M3+–PA¯
were obtained by slow evaporation of the solvent. The suitable single crystals of M2+–PA¯ was
not obtained despite of several attempts.
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Photophysical Characterization
Figure 1a shows the absorption spectra of M1, M2, and M3 in ethanol. All the molecules absorb
UV light below 450 nm. The peak absorption wavelengths for M1 are at 260, 310, 343 and 360
nm. The peak absorption wavelengths for M2 are at 249, 275, 303 364 and 384 nm. The peak
absorption wavelengths for molecule M3 are at 253, 274, 304 and 367 nm. The absorption
spectra of M2 and M3 are shifted to longer wavelengths than the absorption of M1. Figure 1b
shows the absorption spectra of M1, PA and complex M1+– PA¯ in ethanol. The absorption of
the M1+-PA¯ complex is not the superposition of the absorption of its constituent M1 and PA.
The peak position and relative intensities are not as expected. This reflects an interaction
between M1 and PA which has been confirmed in the crystal structure of the complex (M1+-
PA¯). The photoluminescence emission spectrum of M1, M2 and M3 in ethanol is shown in
Figure 1c. The samples were excited at 340 nm and the emission was monitored between 370
to 650 nm. The peak emission wavelengths for M1, M2 and M3 are at 386 nm, 486 nm and
456 nm respectively. The redshift in the absorption and emission was observed with the
increase in the size of aryl groups. It shows that the optical band gap decreases with the increase
in π-electrons conjugation.

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DOI: 10.1039/D0NJ03422C
2.0
1.5
1.0
0.5
0.0
2.0
1.5
1.0
0.5
0.0
(b)
(a)
PA
M1
M1-PA
M1
M2
M3
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250 300 350 400 450
Wavelength/nm
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300
350
400
450
Wavelength/nm
(c)
1.0
M1
M2
M3
0.5
0.0
400
500
600
Wavelength/nm
Figure 1(a). The absorption spectra of M1 M2 and M3 recorded in ethanol. (b) Absorption
spectra of M1, PA, and complex (M1+-PA¯). (c) The photoluminescence (PL) emission
spectrum of M1, M2, and M3 recorded in ethanol.
Structural Description of (M1+–PA¯)
Figure 2 shows the molecular structure of the synthesized co-crystal. The space group of the
co-crystal is Triclinic, P-1. This incorporates two molecules of M1, two molecules of picric
acid and one water molecule in an unsymmetrical unit. The process of crystallization begins

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DOI: 10.1039/D0NJ03422C
with proton transfer from the hydroxyl group of picric acid to the nitrogen atom of the
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imidazole ring in M1. The water molecule then assists in the co-crystal formation. One
hydrogen atom of water molecule undergoes hydrogen bond interaction with the oxygen atom
of the hydroxyl group in picric acid and the other hydrogen atom with the oxygen atom from
the nitro group of another picric acid. The oxygen atom of the same water molecule interacts
with N-H of imidazole in M1 via H-bonding. Thus, all atoms of water are engaged in H-
bonding interaction with the two picric acids and one imidazole of M1. A detailed topology of
the complex M1+–PA¯ is also presented in supporting information.
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Figure 2(a)Structure of a single crystal M1+–PA¯.(b) Hydrogen bonding’s in co-
crystals.(c)Crystal packing and (d)supramolecularassembly.
Structural Description of (M3+-PA¯)
Figure 3 shows the molecular structure of the co-crystal M3+–PA¯. The space group of the co-
crystal is monoclinic, P21/c. This incorporates a molecule of M3, a molecule of PA and a
molecule of the solvent DMSO in an unsymmetrical unit. The process of crystallization begins
with the formation of PA anion and M3 cation during proton transfer from hydroxyl of picric

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acid into the nitrogen of 2-pyrenyl-1H-phenanthro[9,10-d]imidazole. Besides hydrogen
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bonding, π-π-interactions play an important role in structure formation. The π-π bonds between
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two M3 cations. Intermolecular contacts M3 – M3 is stronger than DMSO–M3.
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Figure 3(a) Single X-ray Crystal Structure ofM3+-PA¯. (b) Hydrogen bonding in the co-
crystals.(c)Crystal packing and (d)Supramolecular Assembly.
Figure 3 shows the molecular structure of the synthesized co-crystal. The space group of the
co-crystal is Monoclinic, P21/c. This incorporates two molecules of 2-pyrene-1H-
phenanthro[9,10d]imidazole, two molecules of picric acid and one DMSO molecule in an
asymmetric unit.

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Table 1: The Crystal Data for Co-crystals,M1+-PA¯ and M3+-PA¯.
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M3+-PA¯
Parameters
M1+-PA¯
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Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
α (°)
C27H19N5O8
C39H27N5O8S
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541.48
100(2)
Triclinic
P1
7.1550(7)
13.5698(12)
13.6958(13)
115.283(3)
100.531(3)
94.796(3)
1162.41(19)
725.74
100
Monoclinic
P21/c
7.4343(5)
30.238(2)
16.0736 (11)
90
98.342(2)
β (°)
γ (°)
Volume (Å3)
90
3575.1(4)
4
1.348
0.152
Z
2
1.5469
0.117
ρcalc (mg/m3)
μ (mm–1)
1505.3
F(000)
Crystal size (mm3)
Radiation
2Θ range for data collection (°)
Index ranges
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
Final R indexes [I>=2σ (I)]
Largest diff. peak/hole / e Å–3
Final R indexes [all data]
CCDC
560.3
0.38 × 0.28 × 0.16
Mo Kα (λ = 0.71073)
5.76 to 50.1
0.39 × 0.28 × 0.17
Mo Kα (λ = 0.71073)
5.54 to 50.1
–9 ≤ h ≤ 9, –18 ≤ k ≤ 18, –18 ≤ l ≤ 18
18582
4119 (Rint = 0.0904, Rsigma = 0.1035)
4119/0/364
–9 ≤ h ≤ 9, –40 ≤ k ≤ 40, –21 ≤ l ≤21
57453
6312 (Rint = 0.0779, Rsigma = 0.0536)
6312/0/595
1.110
1.091
R1 = 0.0453, wR2 = 0.1100
0.50/–0.42
R1= 0.0611, wR2= 0.1234
1981808
R1 =0.0545, wR2 = 0.1193
0.40/–0.46
R1= 0.0889, wR2= 0.1445
1981809
aGOF is defined as
the number of parameters. bR =
1/ 2 where n denotes the number of data pieces and p
[w(F2  F2 )]/(n  p)}
{

0
c
2
1/ 2
{
F  F /
F , wR { w(F2  F2 )2 / w(F2 ) }




0
c
0
2
0
c
0
The phenanthrene imidazole rings of the molecule of 2-pyrenel-1H-phenanthro[9,10
d]imidazole are planar and bear a torsional angle of 43.39 (N1-C15-C16-C29) with the pyrene
unit of the molecule of 2-pyrene-1H-phenanthro[9,10d]imidazole. The molecule is stabilized
by hydrogen bonds. The prominent ones are between O8-H2 (molecules of DMSO and
imidazole ring H2 of M3), O1---H1(between H1 of imidazole and O1 of PA) and
intramolecular hydrogen bonds between phenolic O1 and ortho nitro groups of PA. These are

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intramolecular hydrogen bonds between (O1-O2, O1-O6 and O1-O6a).A detailedDtOoI:p1o0.l1o03g9y/Do0NfJ03422C
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the complex M3+–PA¯is also presented in supporting information.
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Hirshfeld Surface Analysis
As discussed above in the crystal structure of M1+–PA¯ (Figure 2), it has two
crystallographically inequivalent M1+ cations, i.e. type 1 and type 2. Both of them form
hydrogen bonds with picrate anions (PA¯) and only type 1 is involved in hydrogen-bonding
with the water molecule. Hirshfeld surfaces analysis of type 1 and type 2 is shown in figure 4
and figure 5. Hirshfeld surfaces provide an extended qualitative and quantitative analysis of
the interactions between the constituents of the complex. The analysis of various interactions
in M1+- PA¯ reveals the presence C—H---O, N—H---O and O—H---O hydrogen-bonds
leading to multidirectional interactions to form a three-dimensional complex.
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Figure 4. Hirshfeld surface for M1 (type 1) with dnorm over the range of -0.69 to 2.86.
Neighbouring molecules (water and PA) associated with close contacts are also shown. Pie
chart and FP for overall, other contacts, and percentage contribution from different contacts in
M1.

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The red spots in the Hirshfeld surface of M1 (figure 4) are centered at N1-H1, N2-H2, C11-
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H11, C40-H40, C36-H36, C41-H41, C33-H33, C34-H34. All the atoms of water molecules are
involved in H-bonding interactions. The oxygen atom of water molecule interacts with C-H
bonds of phenyl and phenanthrene and also with the N-H of imidazole ring in M1. The
percentage contributions of H---H and H---O contacts are 32.7% and 23.2% of the total dnorm
surface of M1+ (Figure 4a).
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The N-H---O interaction appears as a sharp spike on the two-dimensional fingerprint plot of
H---O contacts. The percentage contribution of various interactions is shown in the fingerprint
(FP) plot. Analysis of the Hirshfeld surface of M1+ (type 2) is shown in figure 5. The dark red
spot showing strong hydrogen-bonding interaction is centered at N3-H3.
Figure 5. Hirschfeld surface for M1 (type 2) with dnorm over the range of -0.57 to 2.74.
Neighboring molecules (PA) associated with close contacts are also shown. Pie chart and FP
for overall, other contacts and percentage contribution from different contacts in M1.

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The pie chart in figure 5 shows the percentage contribution of various interactions in the
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complex. The percentage contribution of H---H and H---O is 28.1% and 25.1% respectively.
The H---O interaction includes oxygen atoms from the nitro and phenoxide groups in PA¯. The
sharp peak in the FP plot of H---O contacts corresponds to N3-H3---O3 i.e., hydrogen from the
nitrogen of imidazole and oxygen from the phenoxide group in PA¯. Hirshfeld surface analysis
of complex M3+–PA¯ is discussed in supporting information.
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Sensing Studies
Stock solutions of 10 mM concentration were made for different metal ions and nitroaromatic
compounds. The tested metal ions include Na+, Cu2+, Mg2+, Fe2+, Cd2+, and nitroaromatic
compounds include 2-nitrotoluene, trinitrotoluene, dinitrobenzene, and picric acid. The
synthesized molecules M1, M2 and M3, were soluble in chloroform and ethanol. The samples
were excited at 340 nm and emission was monitored. The sensing abilities of M1-M3 in ethanol
were investigated for the above-mentioned metal ions. We find no change in the peak position
and intensity of emission in the fluorescence spectra of M1-M3. Then nitro-aromatics were
tested for their sensing. Among the tested nitroaromatics, only PA showed quenching in the
fluorescence intensity. Phenols and aromatic acids were also found to quench the fluorescence.
Figure 6 shows the photoluminescence quenching of M1, M2 and M3 with the successive
addition of PA as a quencher. The fast and selective quenching was observed for PA among
the tested nitroaromatics. The formation constants (Ks) were calculated using the equation.
F0/F = 1 + Ks[Q]
Where F and F0 are the fluorescence intensity with and without quencher, respectively, Ks is
the ground state complex formation constant (litre/mole) for static quenching and [Q] is the
quencher concentration (mole/litre). The fluorescence intensities were measured at the peak
emission wavelengths. The Ks is calculated from the slope of the linear fit between the

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quenching and quencher concentration (Figure 6). Table 2 summarizes the values of Ks forVMiew1Ar-ticle Online
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M3. The Ks values of M1-M3 are high and nearly similar. We find no correlation between the
size of aryl group and formation constant. As revealed from the Hirschfeld surface analysis of
M1+–PA¯ and M3+–PA¯, the stronger interactions in the complexes are centred on the nitrogen
atoms, terminal carbon of phenanthrene and terminal carbons of aryl groups. The other atoms
in bigger aryl group contribute less with weak Van der waal forces. Therefore, we see less of
effect on the formation constant with the size of aryl groups. The above equation is similar to
the Stern-Volmer equation except that it gives formation constant rather than Stern-Volmer
constant which is related to dynamic quenching. The limit of detection (LOD) for M1-M3 are
0.64, 0.53 and 1.05 ppm respectively. These values are comparable to the values reported in
literature for nitrogen containing compounds like histidines, anthracene bridged poly(N-
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vinylpyrrolidone), substituted oxadiazoles and tetrazoles28–30
.
Table 2: The Ks and LOD of molecules M1-M3.
Molecule
M1
Ks (litre/mole)
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LOD mole/litre , (ppm)
2.8x10-6 , 0.64
M2
1.45x105
2.3 x10-6, 0.53
M3
8.53x104
4.6 x10-6, 1.05
In literature, the quenching with PA is proposed to be because of resonance energy transfer and
proton transfer20–22. Herein we rule out the possibility of resonance energy transfer for the
following reasons. The molecule M1, M2 and M3 have different emission wavelengths and the
overlap of these emissions with the absorption wavelengths is also different. We do not see any
correlation between this overlap and the amount of quenching. Secondly, the quenching of
fluorescence intensity is related to the proton transfer from the hydroxyl group of PA to the

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nitrogen atom of imidazole in phenanthroimidazole derivatives in the ground stateD.OTI:h10e.1p03r9o/tDo0nNJ03422C
transfer is evident from the solved crystal structure complex M1+–PA¯ (Figure 2). The proton
transfer breaks the conjugation in imidazole. The loss of conjugation is evident from the
increasing C=N distance from 1.326 Å in M1 to 1.344 Å in M1+ in the complex. The loss of
conjugation results in fluorescence quenching. Also, the deprotonation of PA leads to a
decrease in C-O distance from 1.344 Å to 1.254 Å (Figure 7). The formation of a non-
fluorescent complex in the ground state is confirmed by doing time-resolved fluorescence
measurements. Figure 8 shows the lifetime decay of M1, M2 and M3. The average lifetime of
excited states of M1, M2 and M3 are measured to be 6.0, 3.9 and 2.0 ns respectively. The
lifetime remains unchanged with the addition of PA. The χ2 value ranges from 0.99 to 1.06 in
all three cases.
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DOI: 10.1039/D0NJ03422C
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600
F0/F
(a)
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Linear fit
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PA; 12.6ppm
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Wavelength/nm
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Concentration/M
Wavelength/nm
Figure 6. Fluorescence quenching and Stern-Volmer plots upon addition of PA to (a) M1, (b)
M2, and (c) M3 respectively.

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M1
M1+ in complex M1+–PA¯ Picric Acid
Picrate with M1+–PA¯
Figure 7. Shows the C=N bond distances in M1, and M1+ and also C-O bond distances in PA
and PA¯. The CO bond length in picric acid (PA) also decreases from 1.344 Å to 1.254 Å
with the formation of the anion (PA¯).
IRF
M1
M1+PA
M2
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Time/ns
Figure 8. Semi-log plots of fluorescence decay versus time for (M1 and M1+–PA¯), (M2 and
M2+–PA¯) and (M3 and M3+–PA¯) in (solvent) at (λex= 397 nm, λem= 505nm).
Conclusion
In summary, a series of phenanthroimidazole (PI) derivatives (M1-M3) were synthesized and
characterized. The synthesized compounds give blue emission in ethanol solution and have
shown sensing of PA with high sensitivity via fluorescence quenching. The mechanism of
quenching involves a proton transfer from the hydroxyl group of PA to Nitrogen atom of

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imidazole, followed by complex formation cation (M1+) and picrate anion (PA¯).DTOhI:e10p.10r3o9t/oDn0N-J03422C
transfer results in loss of conjugation. The complex formation has been demonstrated by
growing the crystal of M1+–PA¯. The selectivity to PA over other tested nitro aromatics is
because of its deprotonation ability. It provides a rational strategy to design nitrogen containing
fluorophores of different colours for the sensing of picric acid. To the best of our knowledge,
this is the first demonstration of fluorescence quenching of PI derivatives with PA. The higher
value of formation constant is suggestive of the potential of these molecules for pollution
control and security applications.
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Supporting Information:
1H NMR, C NMR, FTIR spectra of M1, M2, M3, and Crystallographic data of M1+–PA¯
13
(CCDC No 1981809), M3+–PA¯ (CCDC No 1981808), used in this work.
Corresponding Authors:
Dr. Farman Ali, farmanfrequent@gmail.com,
Phone: - +91-9758304357
ORCID:
Farman Ali: - 0002-5807-3195
Musheer Ahmad: - 0000-0002-7446-0232
Ruby Ahmed: - 0000-0003-0122-1449
Conflicts of interest
“There are no conflicts to declare.”
Acknowledgments
Dr. Farman Ali acknowledges DST for INSPIRE Faculty funding. Chairman of Department
of Applied Chemistry, and Director of Interdisciplinary Nanotechnology Centre, A.M.U. for
allowing the use of fluorimeter. Prof. Ali Alsalme would like to acknowledge the Researchers
Supporting Project (RSP-2020/78), King Saud University, Riyadh, Saudi Arabia.

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References
5
6
7
8
1.
Zhang, Y., Li, F., Zhang, Q., Li, J. & Liu, Q. Science of the Total Environment
Tracing nitrate pollution sources and transformation in surface- and ground-waters
using environmental isotopes. Sci. Total Environ. 490, 213–222 (2014).
Heald, C. L. & Spracklen, D. V. Land Use Change Impacts on Air Quality and
Climate. (2015). doi:10.1021/cr500446g
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2.
3.
4.
S, A. L. Medicinals and Dyes. 18, 1336–1337
Meredith DT, L. C. A Study of Antiseptic Compounds for the Treatment of Burns. Am.
Pharm. Assoc. 28(6), 369–373 (1983).
5.
6.
Blackman, W. C. Basic Hazardous Waste Mangement. (Lewis, CRC Press LLC,
2001).
Wollin, K.-M. & Dieter, H. H. Toxicological Guidelines for Monocyclic Nitro-,
Amino- and Aminonitroaromatics, Nitramines, and Nitrate Esters in Drinking Water.
Arch. Environ. Contam. Toxicol. 49, 18–26 (2005).
7.
8.
Yinon, J. Peer Reviewed: Detection of Explosives by Electronic Noses. Anal. Chem.
75, 98 A-105 A (2003).
Holthoff, E. L., Stratis-Cullum, D. N. & Hankus, M. E. A nanosensor for TNT
detection based on molecularly imprinted polymers and surface enhanced Raman
scattering. Sensors (Basel). 11, 2700–2714 (2011).
9.
Hodyss, R. & Beauchamp, J. L. Multidimensional Detection of Nitroorganic
Explosives by Gas Chromatography-Pyrolysis-Ultraviolet Detection. Anal. Chem. 77,
3607–3610 (2005).
10. Ahmed, S. M., Patil, R. C., Nakayama, M. & Ogura, K. Characterization of picric-
acid-doped poly(o-toluidine) and the picric-acid-doped poly(o-toluidine)-induced
conductive composite of acrylonitrile–butadiene–styrene. Synth. Met. 114, 155–160

New Journal of Chemistry
Page 20 of 24
1
2
3
4
View Article Online
DOI: 10.1039/D0NJ03422C
(2000).
5
6
7
8
11. Pal, A., Sk, M. P. & Chattopadhyay, A. Conducting Carbon Dot–Polypyrrole
Nanocomposite for Sensitive Detection of Picric acid. ACS Appl. Mater. Interfaces 8,
5758–5762 (2016).
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
12. Hirshfeld, F. L. Bonded-Atom Fragments for Describing Molecular Charge Densities.
138, 129–138 (1977).
13. Ahamad, M. N., Shahid, M., Ahmad, M. & Sama, F. Cu(II) MOFs Based on
Bipyridyls: Topology, Magnetism, and Exploring Sensing Ability toward Multiple
Nitroaromatic Explosives. ACS Omega 4, 7738–7749 (2019).
14. Mako, T. L., Racicot, J. M. & Levine, M. Supramolecular Luminescent Sensors.
Chem. Rev. 119, 322–477 (2019).
15. Xu, Y. et al. “ICT-not-quenching” near infrared ratiometric fluorescent detection of
picric acid in aqueous media. Chem. Commun. 49, 4764–4766 (2013).
16. Nagendran, S., Vishnoi, P. & Murugavel, R. Triphenylbenzene Sensor for Selective
Detection of Picric Acid. J. Fluoresc. 27, 1299–1305 (2017).
17. Sanda, S., Parshamoni, S., Biswas, S. & Konar, S. Highly selective detection of
palladium and picric acid by a luminescent MOF: a dual functional fluorescent sensor.
Chem. Commun. 51, 6576–6579 (2015).
18. Mahata, M. K., Bae, H. & Lee, K. T. Upconversion Luminescence Sensitized pH-
Nanoprobes. Molecules 22, 2064 (2017).
19. Mahata, M. K. & Lee, K. T. Development of near-infrared sensitized core–shell–shell
upconverting nanoparticles as pH-responsive probes. Nanoscale Adv. 1, 2372–2381
(2019).
20. Tanwar, A. S., Meher, N., Adil, L. R. & Iyer, P. K. Stepwise elucidation of
fluorescence based sensing mechanisms considering picric acid as a model analyte.

Page 21 of 24
New Journal of Chemistry
1
2
3
4
View Article Online
DOI: 10.1039/D0NJ03422C
Analyst 145, 4753–4767 (2020).
5
6
7
8
21. Tsai, M.-S., Hsu, Y.-C., Lin, J. T., Chen, H.-C. & Hsu, C.-P. Organic Dyes Containing
1H-Phenanthro[9,10-d]imidazole Conjugation for Solar Cells. J. Phys. Chem. C 111,
18785–18793 (2007).
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
22. Ali, F., Periasamy, N., Patankar, M. P. & Narasimhan, K. L. Integrated Organic Blue
LED and Visible−Blind UV Photodetector. J. Phys. Chem. C 115, 2462–2469 (2011).
23. Zhu, J.-J. et al. The structure optimization of phenanthroimidazole based isomers with
external quantum efficiency approaching 7% in non-doped deep-blue OLEDs. J.
Mater. Chem. C 8, 2975–2984 (2020).
24. Kula, S. et al. Phenanthro[9,10-d]imidazole with thiophene rings toward OLEDs
application. Dye. Pigment. 159, 646–654 (2018).
25. Chen, W.-C., Tong, Q.-X. & Lee, C.-S. The Development of Phenanthroimidazole
Derivatives in Blue-Emitting Organic Electroluminescence. Sci. Adv. Mater. 7, (2015).
26. Dolomanov, O. V, Bourhis, L. J., Gildea, R. J., Howard, J. A. K. & Puschmann, H.
OLEX2: a complete structure solution, refinement and analysis program. J. Appl.
Crystallogr. 42, 339–341 (2009).
27. LJ, B., OV, D., RJ, G., JA, H. & H., P. The anatomy of a comprehensive constrained,
restrained refinement program for the modern computing environment - Olex2
dissected. Acta Crystallogr A Found Adv. 71, 59–75 (2015).
28. Singh, R. et al. Highly selective fluorescence ‘turn off’ sensing of picric acid and
efficient cell labelling by water-soluble luminescent anthracene-bridged poly(N-vinyl
pyrrolidone). Analyst 144, 3620–3634 (2019).
29. Nath, S. et al. A sensitive and selective sensor for picric acid detection with a
fluorescence switching response. New J. Chem. 42, 5382–5394 (2018).
30. Patel, R., Bothra, S., Kumar, R. & Sahoo, S. K. Selective turn-off sensing of picric

New Journal of Chemistry
Page 22 of 24
1
2
3
4
View Article Online
DOI: 10.1039/D0NJ03422C
acid and p-nitrophenol using fluorescent histidine. Nano-Structures & Nano-Objects
5
6
19, 100345 (2019).
7
8
9
31. Ponnuvel, K., Banuppriya, G. & Padmini, V. Sensors and Actuators Bꢀ: Chemical
Highly efficient and selective detection of picric acid among other nitroaromatics by
NIR fluorescent organic fluorophores. Sensors Actuators B. Chem. 234, 34–45 (2016).
32. Kumar, M., Reja, S. I. & Bhalla, V. LETTERS A Charge Transfer Amplified
Fluorescent Hg 2 þ Complex for Detection of Picric Acid and Construction of Logic
Functions. 2009–2012 (2012). doi:10.1021/ol3029753
10
11
12
13
14
15
16
17
18
19
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21
22
23
24
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27
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44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
33. Chowdhury, A. & Mukherjee, P. S. Electron-Rich Triphenylamine-Based Sensors for
Picric Acid Detection. J. Org. Chem. 80, 4064–4075 (2015).

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Phenanthreneimidazole derivatives as Chemosensor for Picric Acid: A FirsDtORI: e10a.1l0i3s9t/iDc0NJ03422C
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Approach
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Ruby Ahmeda, Abid Alia, Rais Ahmad Khan*,b, Ali Alsalmeb, Musheer Ahmada, and
Farman Ali*,a
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a.Department of Applied Chemistry, Zakir Hussain College of Engineering and Technology,
AMU, Aligarh 202002. Email:farmanfrequent@gmail.com, amusheer4@gmail.com,
abidaliamu4@gmail.com, ahmedruby1974@gmail.com
bDepartment of Chemistry, College of Sciences, King Saud University, P.O. Box 2455, Riyadh,
11451, KSA. Email: krais@ksu.edu.sa and aalsalme@ksu.edu.sa

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