Benzophenone based fluorophore for selective detection of Sn2?+ ion: Experimental and theoretical study

Article abstract of DOI:10.1016/j.saa.2016.11.051

Synthesis of novel benzophenone-based chemosensor is presented for the selective sensing of Sn^2?+ ion. Screening of competitive metal ions was performed by competitive experiments. The specific cation recognition ability of chemosensor towards

Full text of DOI:10.1016/j.saa.2016.11.051

Accepted Manuscript
Benzophenone based fluorophore for selective detection of Sn2+
ion: Experimental and theoretical study
Amol G. Jadhav, Suvidha S. Shinde, Sandip K. Lanke, Nagaiyan
Sekar
PII:
DOI:
Reference:
S1386-1425(16)30714-4
doi: 10.1016/j.saa.2016.11.051
SAA 14811
Spectrochimica Acta Part A: Molecular and Biomolecular
Spectroscopy
To appear in:
Received date:
Revised date:
Accepted date:
28 July 2016
25 November 2016
30 November 2016
Please cite this article as: Amol G. Jadhav, Suvidha S. Shinde, Sandip K. Lanke, Nagaiyan
Sekar , Benzophenone based fluorophore for selective detection of Sn2+ ion: Experimental
and theoretical study. The address for the corresponding author was captured as affiliation
for all authors. Please check if appropriate. Saa(2016), doi: 10.1016/j.saa.2016.11.051
This is a PDF file of an unedited manuscript that has been accepted for publication. As
a service to our customers we are providing this early version of the manuscript. The
manuscript will undergo copyediting, typesetting, and review of the resulting proof before
it is published in its final form. Please note that during the production process errors may
be discovered which could affect the content, and all legal disclaimers that apply to the
journal pertain.

ACCEPTED MANUSCRIPT
Benzophenone based fluorophore for selective detection of Sn2+ ion:
experimental and theoretical study
Amol G. Jadhav, Suvidha S. Shinde, Sandip K. Lanke, Nagaiyan Sekar*
Department of Intermediate and Dyestuff Technology
Institute of Chemical Technology (Formerly UDCT),
N. P. Marg, Matunga, Mumbai - 400 019.
Maharashtra, India.
Email: n.sekar@ictmumbai.edu.in, nethi.sekar@gmail.com
Tel.: +22 3361 1111/ 2707; Fax: +22 3361 1020
Mumbai-400 019
Abstract:
Synthesis of novel benzophenone-based chemosensor is presented for the selective sensing of
Sn2+ ion. Screening of competitive metal ions was performed by competitive experiments. The specific
cation recognition ability of chemosensor towards Sn2+ was investigated by experimental
1
13
(UV–visible, fluorescence spectroscopy, H NMR, C NMR, FTIR and HRMS) methods and
further supported by Density Functional Theory study. The stoichiometric binding ratio and
binding constant (Ka) for complex is found to be 1:1 and 1.50 x 104, respectively. The detection
limit of Sn2+ towards chemosensor was found to be 0.3898 ppb. Specific selectivity and
superiority of chemosensor over another recently reported chemosensor is presented.
Keywords: Benzophenone, Schiff base, Chemosensor, ESIPT, Sn2+.
1. Introduction:
Chemosensors provide a powerful method for the efficient detection of trace metal ions
and thus they have wide applications in biological [1], environmental [1], clinical [2],
industrial [2] and chemical processes [1,2]. Among the various sensing techniques [3],
fluorescence chemosensors [4] have been a focus of utmost importance in recent years due to
their high sensitivity and selectivity [5], operational simplicity [6], rapid response time [7], and
for their potential application [8] in environmental and medicinal research [9–11]. Also
fluorescence chemosensing technique is more cost efficient than traditional methods such as
1

ACCEPTED MANUSCRIPT
atomic absorption spectroscopy [12], inductively coupled plasma-mass spectrometry and
inductively coupled plasma-atomic emission spectrometry [13].
Tin is involved in most of reactions during preparation of important molecules of PGF
derivatives [14], coumarin derivatives [15], indole derivatives [16] and graphene sheets [17]. Tin
is an essential trace mineral for humans and is found in the greatest amounts in most of the
organs [18]. Some toxic effects of tin which are limited mostly to gastrointestinal is reported
[19]. There are some evidences that tin is involved in cancer prevention [20]. Therefore, the
development of more selective and sensitive fluorescent sensors for detection of Sn2+ is urgent.
Structure analogs of L [21] is reported having sensitivity to Al3+ ion is reported. However, there
are very few reports which include Sn2+ complexation affecting optical properties of 4-arylvinyl-
2,6-di(pyridine-2yl)pyrimidines [22] and detection of Sn2+ ion along with Al3+ [23], but our
sensor (L) is only selective for Sn2+ ion without any interference of other competitive ions.
Schiff bases (imines) and their derivatives containing fluorescent scaffold are claimed to be
encouraging tools for optical sensing of metal ions [24–28]. Benzophenone derivatives have
been widely used as an important chemical entity in developing materials such as photoreactive
micro particles [29], hybrid photoreactive silica nanoparticles [30,31] and efficient pH sensors
[32]. Some of Schiff base chemosensor showed one or more drawbacks in terms of real
applicability including synthetic difficulties, fluorescence quenching, and cross-sensitivities with
other competitive metal ions [33]. Hence, it is worthwhile to overcome for a practical fluorescent
sensor for selective detection of metal ions like Sn2+.
In this study, we report the synthesis of a new turn-on fluorescent sensor (L) that can
selectively detect Sn2+ ion. The sensing behavior of L to various metal ions (Ba2+, Cu2+, Pb2+,
Hg2+, Mn2+, Ni2+, Fe3+, Na+, Al3+, Ca2+ and Mg2+) was studied by absorption and fluorescence
spectra. Moreover, sensing sites was investigated by spectroscopic techniques which is supported
by DFT (Density Functional Theory).
2. Experimental
2.1 Materials and methods
All the analytical grade chemicals and reagents were procured from SD Fine Chemical
Ltd. (Mumbai, India) and were used without further purification. The reactions were
2

ACCEPTED MANUSCRIPT
monitored by thin layered chromatography (TLC) using 0.25 mm E-Merck silica gel 60
F254 pre coated plates, which were visualized with UV light. 1H NMR and 13C NMR spectra
were recorded on a 500 MHz and 125 MHz instrument of Agilent Technology, respectively.
Chemical shifts are expressed in 1 (ppm) using TMS as an internal standard. IR spectra
were recorded on JASCO FTIR 4100 spectrometer within the region of 4000–450 cm-1. HRMS
spectral data were recorded by time of flight (TOF) method. UV–visible and Fluorescence
spectra were recorded on Perkin Elmer Lambda 25 UV–VIS spectrophotometer and Varian
Cary Eclipse fluorescence spectrophotometer, respectively using a quartz cell of 1-cm path
length. DFT computations were performed using the Gaussian 09 (G09) program [34].
Optimized geometry of L and its complex with Sn2+ were carried out using B3LYP as hybrid
functional and 3-21G basis set.
2.2 Synthetic scheme and characterization of L and [L+ Sn2+] complex
<<Please insert Scheme1: Synthesis of (2-(2-hydroxyphenyl)-1H-benzo[d]imidazol-5-yl)(phenyl)
methanone (L)>>
The compounds 1 and 2 were prepared by the reported procedure [35,36].
Synthesis of (2-(2-hydroxyphenyl)-1H-benzo[d]midazole-5-yl)(phenyl) methanone (L)
2 (3-amino, 4-hydroxybenzophenone) (1mmol) and commercially available 3 (4-(N,N-
diethylamino)-2-hydroxybenzaldehyde) (1mmol) was dissolved in ethanol. The resulting
reaction mass was refluxed at 78-80°C for 2 hours (Scheme 1). After completion of reaction,
product was precipitated by adding 25 mL of water. Precipitate formed was filtered and dried in
oven at 50°C. Product was purified by recrystallization from ethanol. Yield= 72%. The
1
13
synthesized compound was characterized by H-NMR, C NMR and HRMS analysis. M.P. =
120-122°C.
a) L ((2-(2-hydroxyphenyl)-1H-benzo[d]midazole-5-yl)(phenyl) methanone) (Fig. S1-S4)
1H NMR (500 MHz, DMSO): δ 13.82 (s, 1H), 10.64 (s, 1H), 8.69 (s, 1H), 7.71 (d, J = 7.5 Hz,
2H), 7.68 (s, 1H), 7.64 (t, J = 7.5 Hz, 1H), 7.54 (t, J = 7.5 Hz, 2H), 7.43 (d, J = 8.3 Hz, 1H), 7.31
(d, J = 8.8 Hz, 1H), 7.02 (d, J = 8.3 Hz, 1H), 6.27 (d, J = 8.8 Hz, 1H), 6.01 (s, 1H), 3.38 (q, J =
7.0 Hz, 4H), 1.11 (t, J = 7 Hz, 6H) ppm.
3

ACCEPTED MANUSCRIPT
13C NMR (125 MHz, DMSO): δ 195.20, 172.99, 160.03, 151.26, 147.99, 141.42, 137.75,
137.18, 134.56, 132.26, 130.19, 129.82, 129.33, 128.33, 124.37, 119.32, 112.21, 104.06, 34.37,
14.82 ppm.
FT-IR: 3516 (phenolic O-H stretching), 3065 (Hydrogen bonded O-H stretching)
1650 (C=O stretch), 1615 (Imine C=N stretch), 1270 (C-N stretch) cm-1.
HRMS (EI): Calcd. for [(C24H25N2O3) = L+ H+], m/z 389.1865, found m/z 389.1867.
b) [L+ Sn2+] complex (Fig. S5-S8)
1H NMR (500 MHz, DMSO): δ 13.20 (s, 1H), 11.03 (s, 1H), 8.81 (s, 1H), 7.70 (d, J = 7.5 Hz,
2H), 7.68 (s, 1H), 7.65 (t, J = 7.5 Hz, 1H), 7.54 (t, J = 7.5 Hz, 2H), 7.43 (d, J = 8.3 Hz, 1H), 7.31
(d, J = 8.8 Hz, 1H), 7.03 (d, J = 8.3 Hz, 1H), 6.27 (d, J = 8.8 Hz, 1H), 6.01 (s, 1H), 3.41 (q, J =
7.0 Hz, 4H), 1.12 (t, J = 7 Hz, 6H) ppm.
13C NMR (125 MHz, DMSO): δ 195.21, 180.25, 163.87, 150.02, 147.99, 141.43, 137.74,
137.19, 134.55, 132.27, 130.18, 129.83, 129.33, 128.32, 124.38, 119.31, 112.22, 104.04, 34.38,
14.81 ppm.
FT-IR: 3323 (phenolic O-H stretching), 2974 (Hydrogen bonded O-H stretching)
1665 (C=O stretch), 1613 (Imine C=N stretch), 1270 (C-N stretch) cm-1.
HRMS (EI): Calcd for [(C26H33N2O5Sn2+) = L+ Sn2++ 2MeOH + H+], m/z 573.1411, found m/z
573.2513.
2.3 Screening and analysis
All the cations (Ba2+, Cu2+, Pb2+, Hg2+, Mn2+, Ni2+, Fe3+, Na+, Al3+, Ca2+, Mg2+and Sn2+) were
used in the form of their freshly prepared chloride salts. BaCl2, CuCl2, PbCl2, HgCl2,
MnCl2.4H2O, NiCl2.6H2O, FeCl3.6H2O, NaCl, AlCl3.6H2O, CaCl2, MgCl2 and SnCl2.2H2O salts
were dissolved in water to prepare the stock solution with the concentration of 5.0 x 10-3 M.
Similarly, L was dissolved in THF to prepare the stock solution with the concentration of 5.0 x
10-3 M. All the stock solutions were further diluted with THF (Tetrahydrofuran) - HEPES (2-[4-
(2-hydroxyethyl)piperazin-1-yl]ethanesulfonic acid) buffer (90:10, v/v, pH 7.4) to make
solutions which were used directly [37]. For the sensitivity measurement, different
concentrations of Sn2+ ions were added to the ligand (L) solution, and the fluorescence spectra
were recorded. Selectivity was checked by addition of Ba2+, Cu2+, Pb2+, Hg2+, Mn2+, Ni2+, Fe3+,
4

ACCEPTED MANUSCRIPT
Na+, Al3+, Ca2+ and Mg2+ into the ligand (L) solution. The emission spectra were recorded
between 445 and 650 nm by exciting the receptor at 445 nm. Excitation and emission slit
width was kept at 5 nm and 10 nm, respectively. All experimental parameters were kept
constant throughout in order to have precision and accuracy.
3. Results and discussion
3.1 UV–visible and fluorescence experiments
<<Please insert Fig. 1: a) Absorption spectra of L (5μM) in presence of various cations (10μM) b)
Emission spectra of L (5μM) in presence of various cations (10μM) in THF– HEPES buffer (90:10,
v/v, pH 7.4)>>
The optical behavior of L was initially studied using UV–Vis absorption and emission
spectra in THF– HEPES buffer (90:10, v/v, pH 7.4). Absorption spectra of L (5μM) exhibited
λmax at 380 nm. Upon addition of Sn2+ ions (10μM) new strong absorption band was observed
around 445 nm. On the other hand, the addition of other metal ions leads to only a weak
absorption band around 445 nm clearly indicated the efficient binding of Sn2+ as compared to
other metal ions (Fig. 1a). On excitation at 445 nm, a very strong 18 fold increase (compare to L
alone) in emission intensity was observed at around 488 nm for L+ Sn2+ while very weak
(around 20-50 a.u.) emission intensity was exhibited by other metal ions complexes (L+M+1/2/3
)
and L (excited at 380 nm) (Fig. 1b). The fluorescence enhancement may be caused by chelation-
enhanced fluorescence (CHEF) effect [38]. Alternatively, this could also be explained by
inhibition of PET (Photoinduced electron transfer), ESIPT (Excited state intramolecular proton
transfer) and C=N isomerization process caused enhancement in the emission [8,27,38,39].
3.2 Competitive experiments
<<Please insert Fig. 2: Competition experiment of selectivity of L towards Sn2+ in the presence of
other cations. [L] = 5μM, [Sn2+] = 10 μM, and [Xn+] = 10 μM in THF– HEPES buffer (90:10, v/v, pH
7.4) at λexc = 445 nm.>>
5

ACCEPTED MANUSCRIPT
To investigate the selectivity of probe L towards Sn2+ in presence of other metal ions, we
conducted competitive experiments. Emission intensity of ligand L (5μM) in presence of Ba2+,
Cu2+, Pb2+, Hg2+, Mn2+, Ni2+, Fe3+, Na+, Al3+, Ca2+ and Mg2+ metal ions solution (10μM) was
found to be around 20-50 a.u. and identical to L alone. Upon addition of Sn2+ (10μM) to these
solutions sufficiently strong fluorescence (12-15 fold enhancement) was observed (Fig. 2). The
emission intensities of the resulting solution was more or less same. Hence, receptor L was
shown to be a selective fluorescent sensor for Sn2+ in the presence of competing metal ions.
3.3 Quantitative analysis
In order to quantify the amount of Sn2+ ions required to bind completely to the ligand
L saturation point need to be determined. Upon addition of Sn2+ ions from 5μM to 30μM in L
(2.5 μM) solution we observed isosbestic point at around 410 nm clearly suggested the
conversion of L to [L-Sn2+] (Fig. 3a). Absorption spectra clearly suggested the formation of [L-
Sn2+] complex. On excitation at 445 nm [L-Sn2+] complex showed increasing emission intensity at
around 488 nm (Fig. 3b). There is no any significant increase in the emission intensity after addition of
25μM Sn2+ solution as saturation point has achieved. Relative fluorescence quantum yield (Фf) of
L was estimated to be 0.62% in THF– HEPES buffer (90:10, v/v, pH 7.4) while that of [L-Sn2+]
complex is found to be 79%. Relative fluorescence quantum yields were measured using quinine
sulfate in 0.1N H2SO4 as standard (Фf =0.546).
<<Please insert Fig. 3. a) Absorption spectra of L (2.5μM) with varying Sn2+ concentration in
THF– HEPES buffer (90:10, v/v, pH 7.4) b) Fluorescence spectra of L (2.5μM) with varying
Sn2+ concentration in THF– HEPES buffer (90:10, v/v, pH 7.4)>>
<<Please insert Fig. 4. Job plot (stoichiometric ratio) of L with Sn2+>>
Stoichiometry of the probe (L)–analyte (Sn2+) was determined by using Job’s plot as
continuous variation method. During this experiment the total concentration of the L and Sn2+
6

ACCEPTED MANUSCRIPT
was kept constant (10μM) and the mole ratios was varied for 10 different fractions. The Job’s
plot was obtained by plotting the fluorescence intensity (I) as a function of the mole fraction of
Sn2+. Complexation of L and Sn2+ showed 1:1 stoichiometry in Fig. 4.
From the fluorescence titration study, the association constant (Ka) for L-Sn2+ in THF–
HEPES buffer (90:10, v/v, pH 7.4) was determined as 1.5 x 104 M-1 by using Benesi-Hildebrand
plot (Fig. 5).
<<Please insert Fig. 5. Benesi-Hildebrand plot>>
<<Please insert Fig. 6. Plot for detection limit calculation>>
Limit of Detection (LOD) was calculated from the equation LOD= (3 X SD)/slope.
Fluorescence titration of the L (1μM) with Sn2+ was carried out by adding aliquots of Sn2+ from
10μM-100 μM. The standard deviation (SD) was obtained from 10 blank readings of the L (1μM).
From the plot of the fluorescence intensity (I-Io) as a function of the added Sn2+, the slope was
obtained. The detection limit was found to be 0.3898 ppb (Fig. 6).
Some known structural analogs of Ligand showing comparative sensitivity, binding
constant and detection limit is given in Table 1. Our ligand showed specific selectivity towards
Sn2+ ion as compare to naphtelene based ligand (Sn2+ and Al3+). Binding constant of our ligand L
(1.50 x 104 M-1) is quite high as compare to reported benzophenone based ligand (5.7 x 103 M-1).
<<Please insert Table 1 Comparative selectivity, binding constant, detection limits with
reported ligands>>
3.4 Binding sites determination
1
To better understand the complexation sites of receptor L with Sn2+, H NMR experiments
were carried out in DMSO. The spectral differences are depicted in Fig. 7. After addition of 1.0
equivalent of Sn2+ salt to L in DMSO, the protons of imine and hydroxyl proton of
benzophenone moiety were shifted down-field by 0.12 and 0.41 ppm, respectively while
hydroxyl proton of N, N diethyl aniline moiety was shifted up-field by 0.60 ppm as compared to
isolated L in DMSO. Up-field shift of hydroxyl proton indicated that acidic proton initially
7

ACCEPTED MANUSCRIPT
available for transfer to the imine nitrogen (ESIPT) was restricted during binding of Sn2+ ion
with expected atoms of L (Figure 7). Further addition of 2 equivalents of Sn2+ did not show any
significant changes in the spectrum which correlated the stoichiometry ratio 1:1.
<<Please insert Fig. 7. Comparative changes in 1H NMR of L when binds with Sn2+>>
3.5 Theoretical confirmation by DFT
To get insight details of the binding sites and geometry of L during binding of Sn2+ to L
computational calculations were performed. As expected, there is good correlation of DFT study
with the experimental results as far as binding sites are concerned. Sn2+ binds -N atom of imine
strongly having weak interactions with two Oxygen atoms of hydroxyl groups. Optimized
geometry of L and L- Sn2+ complex has shown in Fig. 8a-b
<<Please insert Fig. 8. a) Optimized geometry of L at B3LYP/3-21g level. b) Optimized geometry of
L- Sn2+ complex at B3LYP/3-21g level at gas phase >>
<<Please insert Table 2 Bond lengths of selected bonds>>
Calculated bond lengths of the selected bonds are tabulated in Table 2. Imine (–C=N-)
bond length has increased from 1.29379 Å to 1.3727 Å, both C-O bond lengths increased from
1.37598 Å to 1.44143 Å and from 1.374 Å to 1.3876 Å. Similarly, O-H bond length of
benzophenone moiety has increased from 0.99423 Å to 0.99606 Å while O-H bond length of N,
N diethyl aniline moiety has decreased from 0.99343 Å to 0.99134 Å which in correlation with
1H NMR shift shown in Fig. 7.
4. Conclusion:
A simple Schiff base receptor L was synthesized for selective detection of Sn2+. On
complexation with Sn2+, analyte L exhibited significantly distinct absorption peak at around 445
nm and pronounce increased emission intensity (18 folds) at 488 nm. The formation of complex
structure by interaction of nitrogen (imine) and oxygens (phenolic group) with Sn2+ has been
confirmed by spectroscopic techniques which was further supported by DFT study. The
stoichiometric binding ratio, binding constant (Ka) and limit of detection for complex is found to
8

ACCEPTED MANUSCRIPT
be 1:1, 1.50 x 104 and 0.3898 ppb, respectively. Specific selectivity to Sn2+, comparable binding
constant and a good limit of detection as compare to other reported chemosensor is observed.
Acknowledgements
The authors are greatly thankful to SAIF-I.I.T., Mumbai for recording HRMS of the dye. One of
the author Amol G. Jadhav is grateful to UGC for financial support.
References:
[1] R. Martínez-Máñez, F. Sancenón, Fluorogenic and Chromogenic Chemosensors and
Reagents for Anions, Chem. Rev. 103 (2003) 4419–4476. doi:10.1021/cr010421e.
[2] J. Yao, M. Yang, Y. Duan, Chemistry , Biology , and Medicine of Fluorescent
Nanomaterials and Related Systemsꢀ: New Insights into Biosensing , Bioimaging ,
Genomics , Diagnostics , and Therapy, Chem. Rev. 114 (2014) 6130–6178.
doi:10.1021/cr200359p.
[3] E.M. Nolan, S.J. Lippard, Tools and tactics for the optical detection of mercuric ion,
Chem. Rev. 108 (2008) 3443–3480. doi:10.1021/cr068000q.
[4] A.P. de Silva, H.Q.N. Gunaratne, T. Gunnlaugsson, A.J.M. Huxley, C.P. McCoy, J.T.
Rademacher, et al., Signaling Recognition Events with Fluorescent Sensors and Switches,
Chem. Rev. 97 (1997) 1515–1566. doi:10.1021/cr960386p.
[5] J.S. Kim, D.T. Quang, Calixarene-derived fluorescent probes, Chem. Rev. 107 (2007)
3780–3799. doi:10.1021/cr068046j.
[6] H.N. Kim, W.X. Ren, J.S. Kim, J. Yoon, Fluorescent and colorimetric sensors for
detection of lead, cadmium, and mercury ions, Chem. Soc. Rev. 41 (2012) 3210.
doi:10.1039/c1cs15245a.
[7] H.N. Kim, Z. Guo, W. Zhu, J. Yoon, H. Tian, Recent progress on polymer-based
fluorescent and colorimetric chemosensors., Chem. Soc. Rev. 40 (2011) 79–93.
doi:10.1039/c0cs00058b.
[8] V. Luxami, S. Kumar, ESIPT based dual fluorescent sensor and concentration dependent
reconfigurable boolean operators, RSC Adv. 2 (2012) 8734–8740.
doi:10.1039/c2ra21170j.
9

ACCEPTED MANUSCRIPT
[9] C. Kar, M. Deb Adhikari, A. Ramesh, G. Das, Selective sensing and efficient separation
of Hg2+ from aqueous medium with a pyrene based amphiphilic ligand, RSC Adv. 2
(2012) 9201–9206. doi:10.1039/c2ra21064a.
[10] Y. Wang, Y. Huang, B. Li, L. Zhang, H. Song, H. Jiang, et al., A cell compatible
fluorescent chemosensor for Hg2+ based on a novel rhodamine derivative that works as a
molecular keypad lock, RSC Adv. 1 (2011) 1294–1300. doi:10.1039/c1ra00488c.
[11] D.T. Quang, J.S. Kim, Fluoro- and Chromogenic Chemodosimeters for Heavy Metal Ion
Detection in Solution and Biospecimens, Chem. Rev. (2010) 6280–6301.
doi:10.1021/cr100154p.
[12] M. De la Guardia, A.R. Mauri, C. Mongay, Atomic absorption spectrometric
determination of gasoline additives by vapor phase sample introduction, J. Anal. At.
Spectrom. 3 (1988) 1035–1038.
[13] W.J. McShane, R.S. Pappas, V. Wilson-McElprang, D. Paschal, A rugged and transferable
method for determining blood cadmium, mercury, and lead with inductively coupled
plasma-mass spectrometry, Spectrochim. Acta Part B At. Spectrosc. 63 (2008) 638–644.
doi:10.1016/j.sab.2008.03.016.
[14] M. Hamberg, B. Samuelsson, Detection and isolation of an endoperoxide intermediate in
prostaglandin biosynthesis., Proc. Natl. Acad. Sci. U. S. A. 70 (1973) 899–903.
doi:10.1073/pnas.70.3.899.
[15] K.K. Upadhyay, R.K. Mishra, A. Kumar, A Convenient Synthesis of Some Coumarin
Derivatives Using SnCl2 · 2H2O as Catalyst, Catal. Letters. 121 (2008) 118–120.
doi:10.1007/s10562-007-9307-2.
[16] C.S. Cho, H.K. Lim, S.C. Shim, T.J. Kim, H.J. Choi, Ruthenium-catalysed synthesis of
indoles from anilines and trialkanolamines in the presence of tin(II) chloride dihydrate,
Chem. Commun. 3 (1998) 995–996.
[17] F. Li, J. Song, H. Yang, S. Gan, Q. Zhang, D. Han, et al., One-step synthesis of
graphene/SnO2 nanocomposites and its application in electrochemical supercapacitors.,
Nanotechnology. 20 (2009) 1–5. doi:10.1088/0957-4484/20/45/455602.
[18] M. Nath, Toxicity and the cardiovascular activity of organotin compounds: a review,
Appl. Organomet. Chem. 22 (2008) 598–612. doi:10.1002/aoc.1436.
[19] L.R. Sherman, J. Masters, R. Peterson, S. Levine, Tin Concentration in the Thymus
10

ACCEPTED MANUSCRIPT
Glands of Rats and Mice and Its Relation to the Involution of the Gland, J. Anal. Toxicol.
10 (1986) 6–9. doi:10.1093/jat/10.1.6.
[20] Q. Wang, C. Li, Y. Zou, H. Wang, T. Yi, C. Huang, A highly selective fluorescence
sensor for Tin (Sn4+) and its application in imaging live cells., Org. Biomol. Chem. 10
(2012) 6740–6. doi:10.1039/c2ob25895a.
[21] S. Sinha, R.R. Koner, S. Kumar, J. Mathew, M. P. V., I. Kazi, et al., Imine containing
benzophenone scaffold as an efficient chemical device to detect selectively Al3+, RSC
Adv. 3 (2013) 345. doi:10.1039/c2ra21967k.
[22] C. Hadad, S. Achelle, I. López-Solera, J.C. García-Martínez, J. Rodríguez-López, Metal
cation complexation studies of 4-arylvinyl-2,6-di(pyridin-2-yl)pyrimidines: Effect on the
optical properties, Dye. Pigment. 97 (2013) 230–237. doi:10.1016/j.dyepig.2012.12.023.
[23] S. Adhikari, S. Mandal, A. Ghosh, S. Guria, D. Das, Sn(ii) induced concentration
dependent dynamic to static excimer conversion of a conjugated naphthalene derivative,
Dalt. Trans. 44 (2015) 14388–14393. doi:10.1039/C5DT02146D.
[24] P.G. Cozzi, Metal-Salen Schiff base complexes in catalysis: practical aspects., Chem. Soc.
Rev. 33 (2004) 410–421. doi:10.1039/b307853c.
[25] D. Pucci, I. Aiello, A. Bellusci, A. Crispini, M. Ghedini, M. La Deda, Coordination
Induction of Nonlinear Molecular Shape in Mesomorphic and Luminescent Zn II
Complexes Based on Salen-Like Frameworks, Eur. J. Inorg. Chem. 2009 (2009) 4274–
4281. doi:10.1002/ejic.200900536.
[26] L. Wang, W. Qin, W. Liu, A sensitive Schiff-base fl uorescent indicator for the detection
of Zn 2+, INOCHE. 13 (2010) 1122–1125. doi:10.1016/j.inoche.2010.06.021.
[27] D. Udhayakumari, S. Saravanamoorthy, M. Ashok, S. Velmathi, Simple imine linked
colorimetric and fluorescent receptor for sensing Zn 2+ ions in aqueous medium based on
inhibition of ESIPT mechanism, Tetrahedron Lett. 52 (2011) 4631–4635.
doi:10.1016/j.tetlet.2011.06.097.
[28] Y. Dong, J. Li, X. Jiang, F. Song, Y. Cheng, C. Zhu, Na+ triggered fluorescence sensors
for Mg2+ detection based on a coumarin salen moiety, Org. Lett. 13 (2011) 2252–2255.
doi:10.1021/ol200530g.
[29] M. Naddaka, E. Mondal, J. Lellouche, Preparation of novel photoreactive polycarbazole-
based microparticles: Reactivity features, J. Polym. Sci. Part A Polym. Chem. 49 (2011)
11

ACCEPTED MANUSCRIPT
4687–4693. doi:10.1002/pola.24916.
[30] A. Peled, M. Naddaka, J.-P. Lellouche, Smartly designed photoreactive silica
nanoparticles and their reactivity, J. Mater. Chem. 21 (2011) 11511.
doi:10.1039/c1jm00055a.
[31] A. Peled, M. Naddaka, J. Lellouche, Controllable photodeposition of metal nanoparticles
on a photoreactive silica support, J. Mater. Chem. 22 (2012) 7580–7583.
doi:10.1039/c2jm16785a.
[32] G. Nishimura, Y. Shiraishi, T. Hirai, A fluorescent chemosensor for wide-range pH
detection., Chem. Commun. (Camb). 1 (2005) 5313–5. doi:10.1039/b508136j.
[33] M. Shyamal, P. Mazumdar, S. Maity, S. Samanta, G.P. Sahoo, A. Misra, Highly Selective
Turn-On Fluorogenic Chemosensor for Robust Quantification of Zn(II) Based on
Aggregation Induced Emission Enhancement Feature, ACS Sensors. 1 (2016) 739–747.
doi:10.1021/acssensors.6b00289.
[34] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, et
al., Gaussian 09, Revision C.01, Gaussian 09, Revis. B.01, Gaussian, Inc., Wallingford
CT. (2009).
[35] R. Andreozzi, M. Canterino, V. Caprio, I. Di Somma, R. Sanchirico, Salicylic Acid
Nitration by Means of Nitric Acid / Acetic Acid Systemꢀ: Chemical and Kinetic
Characterization Abstractꢀ:, Org. Process Res. Dev. 10 (2006) 1199–1204.
doi:10.1021/op060148o.
[36] B. Gong, F. Hong, C. Kohm, L. Bonham, P. Klein, Synthesis and SAR of 2-
arylbenzoxazoles, benzothiazoles and benzimidazoles as inhibitors of lysophosphatidic
acid acyltransferase-β, Bioorganic Med. Chem. Lett. 14 (2004) 1455–1459.
doi:10.1016/j.bmcl.2004.01.023.
[37] R. Pandey, L. Reddy, S. Ishihara, A. Dhir, V. Krishnan, Conformation induced
discrimination between picric acid and nitro derivatives/anions with a Cu-pyrene array:
the first decision making photonic device, RSC Adv. 3 (2013) 21365.
doi:10.1039/c3ra44036b.
[38] M. Yuan, W. Zhou, X. Liu, M. Zhu, J. Li, X. Yin, et al., A multianalyte chemosensor on a
single molecule: Promising structure for an integrated logic gate, J. Org. Chem. 73 (2008)
5008–5014. doi:10.1021/jo8005683.
12

ACCEPTED MANUSCRIPT
[39] M. Yuan, Y. Li, J. Li, C. Li, X. Liu, J. Lv, et al., A colorimetric and fluorometric dual-
modal assay for mercury ion by a molecule, Org. Lett. 9 (2007) 2313–2316.
doi:10.1021/ol0706399.
13

ACCEPTED MANUSCRIPT
Figures and Scheme
Fig. 1: a) Absorption spectra of L (5μM) in presence of various cations (10μM) b) Emission spectra
of L (5μM) in presence of various cations (10μM) in THF– HEPES buffer (90:10, v/v, pH 7.4)
Fig. 2: Competition experiment of selectivity of L towards Sn2+ in the presence of other cations. [L] =
5μM, [Sn2+] = 10 μM, and [Xn+] = 10 μM in THF– HEPES buffer (90:10, v/v, pH 7.4) at λexc = 445
nm.
Fig. 3. a) Absorption spectra of L (2.5μM) with varying Sn2+ concentration in THF– HEPES
buffer (90:10, v/v, pH 7.4)
b) Fluorescence spectra of L (2.5μM) with varying Sn2+
concentration in THF– HEPES buffer (90:10, v/v, pH 7.4)
Fig. 4. Job plot (stoichiometric ratio) of L with Sn2+
Fig. 5. Benesi-Hildebrand plot
Fig. 6. Plot for detection limit calculation
Fig. 7. Comparative changes in 1H NMR of L when binds with Sn2+
Fig. 8. a) Optimized geometry of L at B3LYP/3-21g level. b) Optimized geometry of L- Sn2+ complex at
B3LYP/3-21g level at gas phase.
Scheme1: Synthesis of (2-(2-hydroxyphenyl)-1H-benzo[d]imidazol-5-yl)(phenyl) methanone (L)
14

ACCEPTED MANUSCRIPT
Fig. 1: a) Absorption spectra of L (5μM) in presence of various cations (10μM) b) Emission spectra of L
(5μM) in presence of various cations (10μM) in THF– HEPES buffer (90:10, v/v, pH 7.4)
15

ACCEPTED MANUSCRIPT
Fig. 2: Competition experiment of selectivity of L towards Sn2+ in the presence of other cations. [L] =
5μM, [Sn2+] = 10 μM, and [Xn+] = 10 μM in THF– HEPES buffer (90:10, v/v, pH 7.4) at λexc = 445
nm.
16

ACCEPTED MANUSCRIPT
Fig. 3. a) Absorption spectra of L (2.5μM) with varying Sn2+ concentration in THF– HEPES
buffer (90:10, v/v, pH 7.4)
concentration in THF– HEPES buffer (90:10, v/v, pH 7.4)
b) Fluorescence spectra of L (2.5μM) with varying Sn2+
17

ACCEPTED MANUSCRIPT
Fig. 4. Job plot (stoichiometric ratio) of L with Sn2+
18

ACCEPTED MANUSCRIPT
Fig. 5. Benesi-Hildebrand plot
19

ACCEPTED MANUSCRIPT
Fig. 6. Plot for detection limit calculation
20

ACCEPTED MANUSCRIPT
Fig. 7. Comparative changes in 1H NMR of L when binds with Sn2+
21

ACCEPTED MANUSCRIPT
Fig. 8. a) Optimized geometry of L at B3LYP/3-21g level. b) Optimized geometry of L- Sn2+ complex at
B3LYP/3-21g level at gas phase.
22

ACCEPTED MANUSCRIPT
Scheme1: Synthesis of (2-(2-hydroxyphenyl)-1H-benzo[d]imidazol-5-yl)(phenyl) methanone (L)
O
O
O
2
NO2
OH
NH2
OH
HNO3,
Fe, HCl
MeOH
Acetic acid
OH
1
HO
O
Ethanol, 2-5 h,
78 0C
N
3
N
O
N
OH
OH
L
23

ACCEPTED MANUSCRIPT
Tables
Table 1 Comparative selectivity, binding constant, detection limits with reported ligands
Table 2 Bond lengths of selected bonds
24

ACCEPTED MANUSCRIPT
Table 1 Comparative selectivity, binding constant, detection limits with reported ligands
Sr.
Analyte (Ligand)
Sensivity/ Binding constant Detection Limit
Selectivity
Reference
No.
Sn2+
1.50 x 104 M-1
0.3898 ppb
This
1
N
work
O
N
OH
OH
Al3+
5.7 x 103 M-1
0.0081 ppb
21
23
2
3
O
N
OH
NH2
Sn2+ and 3.4 x 105 M-1
Al3+
2.72 ppb
N
OH
N
25

ACCEPTED MANUSCRIPT
Table 2 Bond lengths of selected bonds
C9=N10
C14-O21
C3-O23
(Å)
O21-H22
(Å)
O23-H24
(Å)
Compound
(Å)
(Å)
1.29379
1.3727
1.37598
1.44143
1.374
0.99423
0.99606
0.99343
0.99134
L
1.3876
L+Sn(II)
26

ACCEPTED MANUSCRIPT
Graphical abstract
27

ACCEPTED MANUSCRIPT
Highlights
 Simple novel benzophenone-based chemosensor has been synthesized for selective
sensing of Sn2+ ion.
 Specific selectivity and superiority of our fluorophore over another recently and only
reported fluorophore for Sn2+ ion sensing (along interference of Al3+ion) is explained.
 The specific Sn2+ recognition was investigated by spectroscopic techniques and DFT
study.
 Stoichiometric ratio, binding constant and LOD for complex is found to be 1:1 and 1.50 x
104 and 0.3898 ppb respectively.
28