Naphthalene and pyrrole substituted guanidine in selective sensing of Cu2+, Hg2+, Pb2+ and CN? ions under different conditions

Article abstract of DOI:10.1080/10610278.2017.1287366

Naphthalene and pyrrole substituted guanidine 1 has been designed and synthesised. Compound 1 efficiently distinguishes Cu²⁺, Hg²⁺ and Pb²⁺ ions by exhibiting different responses in fluorescence. While compound 1 exhibited turn-on emission selectively in the presence of Hg²⁺ and Pb²⁺ ions in CH₃CN and CH₃CN–H₂O (1:1, v/v), respectively, it showed decrease in emission upon interaction with Cu²⁺ ion in CH₃CN. Furthermore, the Cu-1 ensemble has been established as a potential probe for selective detection of CN^? ion over a series of other anions involving colour change (in ordinary light: colourless to light yellow and under UV light: colourless to sky blue). Theoretical insight has been invoked to understand the mode of metal–ligand interaction.

Full text of DOI:10.1080/10610278.2017.1287366

Supramolecular Chemistry
ISSN: 1061-0278 (Print) 1029-0478 (Online) Journal homepage: http://www.tandfonline.com/loi/gsch20
Naphthalene and pyrrole substituted guanidine in
selective sensing of Cu2+, Hg2+, Pb2+ and CN− ions
under different conditions
Santanu Panja, Asoke P. Chattopadhyay & Kumaresh Ghosh
To cite this article: Santanu Panja, Asoke P. Chattopadhyay & Kumaresh Ghosh (2017):
Naphthalene and pyrrole substituted guanidine in selective sensing of Cu2+, Hg2+, Pb2+ and CN−
ions under different conditions, Supramolecular Chemistry, DOI: 10.1080/10610278.2017.1287366
To link to this article: http://dx.doi.org/10.1080/10610278.2017.1287366
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Date: 14 February 2017, At: 20:34

Supramolecular chemiStry, 2017
http://dx.doi.org/10.1080/10610278.2017.1287366
Naphthalene and pyrrole substituted guanidine in selective sensing of Cu2+,
Hg2+, Pb2+ and CN− ions under different conditions
Santanu Panja, Asoke P. Chattopadhyay and Kumaresh Ghosh
Department of chemistry, university of Kalyani, Kalyani, india
ABSTRACT
ARTICLE HISTORY
received 4 November 2016
accepted 20 January 2017
Naphthalene and pyrrole substituted guanidine 1 has been designed and synthesised. Compound
1 efficiently distinguishes Cu2+, Hg2+ and Pb2+ ions by exhibiting different responses in fluorescence.
While compound 1 exhibited turn-on emission selectively in the presence of Hg2+ and Pb2+ ions
in CH3CN and CH3CN–H2O (1:1, v/v), respectively, it showed decrease in emission upon interaction
with Cu2+ ion in CH3CN. Furthermore, the Cu-1 ensemble has been established as a potential probe
for selective detection of CN− ion over a series of other anions involving colour change (in ordinary
light: colourless to light yellow and under UV light: colourless to sky blue). Theoretical insight has
been invoked to understand the mode of metal–ligand interaction.
KEYWORDS
Fluorometric detection;
cu2+ and hg2+ sensing; pb2+
sensing; guanidine-based
ligand; cyanide detection
CO2CH3
H3CO2
C
NH
HN
H
H
N
N
N
In CH3CN
In CH3CN/H2O
Naphthalene and pyrrole substituted guanidine 1 has been designed and synthesised. It efficiently
distinguishes Cu2+, Hg2+ and Pb2+ ions by exhibiting different responses in fluorescence. The Cu-1
ensemble has been established as a potential probe for selective detection of CN- ion over a series
of other anions involving colour change.
Introduction
cofactor, such as superoxide dismutase, tyrosinase and
cytochrome oxidase (4).
Design and synthesis of new architectures capable of
sensing multiple metal ions of biological significance draw
attention in supramolecular chemistry research. Of the dif-
ferent transition metal ions, copper, mercury and lead ions
are considered to be important due to their pivotal roles in
biological system. Copper being essential element in our
life is linked with a variety of fundamental physiological
processes in organisms. It causes environmental pollution
and also serves as catalytic cofactor for a variety of metal-
loenzymes (1). Exposure to high levels of copper can cause
gastrointestinal disturbance and liver or kidney damage
(2). Excess accumulation of copper may cause Wilson’s dis-
ease (3). Various metalloenzymes involve Cu2+ as catalytic
Similarly lead is associated with digestive, neurologic,
cardiac diseases and mental retardation (5,6). Lead is a
highly toxic heavy metal ion. The accumulation of lead
in the environment causes lead pollution. It is associated
with a number of developmental disorders in children
including slowed motor responses, decreased IQs and
hypertension (6).
On the other hand, mercury is also a toxic metal ion.
Its accumulation in low concentration in the human
body causes a wide variety of diseases, such as prenatal
brain damage, serious cognitive disorders and Minamata
disease (7). The toxicity of mercury in living systems is
CONTACT Kumaresh Ghosh
ghosh_k2003@yahoo.co.in
Supplemental data for this article can be accessed 10.1080/10610278.2017.1287366.
© 2017 informa uK limited, trading as taylor & Francis Group

2
S. PANJA ET AL.
CO2CH3
H3CO2C
on reduction with HCOONH4 and Pd/C in ethyl acetate
yielded amine 4. Reaction of the amine 4 with 1-naphthyl
isothiocyanate introduced the compound 1 in appreciable
yield. The formation of 1 as unequivocally characterised by
usual spectroscopic techniques is explained according to
our suggested mechanism (Scheme 2).
NH
HN
H
H
N
N
N
1
Metal and Anion binding studies
Figure 1. Structure of compound 1.
Metal ion binding interaction of 1 (c = 2.50×10−5 M) was
examined by observing the change in its absorption and
emission spectra in organic as well as aqueous-organic
media. In CH3CN, on excitation at 280 nm, compound 1
displayed emission at 373 nm which was perturbed to
the different extents upon titration with different metal
ions (c = 1.0×10−3 M, taken as perchlorate salts). In this
regard, Figure 2 represents the change in fluorescence
ratio of 1 upon addition of 3 equiv. amounts of a particu-
lar metal ion. In the experiment, while the addition of Cu2+
ions to the solution of 1 in CH3CN quenched the emission
(Figure 3(a)), Hg2+ ions, under similar conditions, increased
the emission significantly (Figure 3(b)). Other metal ions
merely perturbed the emission of 1 (Figure 1S).
attributed to measurable affinities of the thiol group con-
taining proteins and enzymes that results in the malfunc-
tioning of the living cells (8).
Therefore, the detection and sensing of these toxic
metal ions by a simple synthetic system is highly desira-
ble. Multi-ion recognition with a single molecular probe is
recently becoming popular due to some advantages such
as cost reduction and more efficient analysis. The literature
survey reveals a series of examples on selective sensing of
Cu2+, Hg2+ and Pb2+ ions by artificial fluororeceptors (9).
Fluororeceptors are attractive due to the simplicity, high
sensitivity and real-time detection. In this manuscript,
we wish to report the synthesis of a guanidine-centred
pyrrole receptor 1 (Figure 1) that behaves as an efficient
fluorimetric sensor for Hg2+, Cu2+ and Pb2+ ions. While the
architecture 1 exhibits turn-on emission selectively in the
presence of Hg2+ and Pb2+ ions in CH3CN and CH3CN–H2O
(1:1, v/v), respectively, it shows decrease in emission upon
interaction with Cu2+ ion in CH3CN. Furthermore, the Cu-1
ensemble has been found to be a potential probe for selec-
tive detection of CN− ion over a series of other anions.
The selectivity in the binding of Cu2+ and Hg2+ ions was
understood by recording fluorescence of 1 in the presence
and absence of other metal ions (Figure 2S). The interfer-
ence study reveals that both Cu2+ and Hg2+ ions mutually
interfere whereas other metal ions are non interfering. In
Benesi–Hildebrand plots (11a), the linear fit of the change
in emission intensity of 1 against the reciprocal of metal
ion concentration suggested the formation of 1:1 com-
plex and the association constants were determined to
be 7.59×103 M−1 and 2.48×105 M−1 for Cu2+ and Hg2+
ions, respectively (Figure 3S). The detection limits (11b)
for Cu2+ and Hg2+ ions were calculated to be 5.75×10−5
and 9.74×10−6 M, respectively (Figure 4S).
M
Results and discussion
Synthesis
In UV–vis study, addition of both Cu2+ and Hg2+ ions
resulted in sharp decrease in absorption intensity at 270 nm
along with the appearance of a very weak band at 290 nm
(Figure 4). In case of titration with Cu2+ ions, the intensity of
this weak band was increased to the small extent for which
an isosbestic point at 285 nm was observed (Figure 4(a)).
Compound 1 was synthesised according to the Scheme 1.
In synthesising 1, compound 2 which was obtained by
reported procedure (10) was used as the starting mate-
rial. Reaction of pyrrole carbaldehyde 2 with NH2OH.HCl
in aqueous K2CO3 gave the corresponding oxime 3 which
OCH3
OCH3
(ii)
OCH3
H
(i)
HO
N
N
N
H
H
O
H
O
O
O
N
NH2
2
4
3
(iii)
1
Scheme 1. (i) Nh2oh.hcl, K2co3, h2o, 65 °c, 30 min, (ii) hcooNh4, pd-c, etoac, rt, 12 h, (iii) dry ch2cl2, 1-naphthylisothiocyanate,
diisopropyl ethylamine, rt, 20 min.

SUPRAMOLECULAR CHEMISTRY
3
S
C
N
NH2
O
H
HS
N
- H2S
N
N
O
C
H
N
H3CO
H3CO
C
NH
N
O
H
N
H3CO
H
N
1
HN
C
N
N
N
N
O
H
NH2
O
H
NH
HN
N
OCH3
H3CO2C
CO2CH3
H3CO
Scheme 2. probable mechanism for the synthesis of 1.
The Benesi–Hildebrand plot (11a) of emission inten-
sity of 1 against the reciprocal of Pb2+ ion concentration
exhibited linear relationship, indicating 1:1 stoichiometric
interaction. The association constant and the detection
limit have been determined (12) to be 2.33×103 M−1 and
9.80×10−6 M, respectively (Figure 7S). Selectivity in sens-
ing of Pb2+ ions as determined by performing competition
experiments as shown in Figure 8S reveals the interference
of both Cu2+ and Hg2+ ions.
Due to the presence of guanidine motif in the back-
bone, the pH effect of 1 in CH3CN–H2O (1:1, v/v) was inves-
tigated. As can be seen from Figures 9S and 10S, while
the change in intensity of emission and absorption of 1 is
merely affected up to pH 7.0, changes are considerable at
higher pH. This presumably occurs due to the ester group
in the structure. However, careful measurement of pH of
CH3CN–H2O (1:1, v/v), which was used in the present study
(Figure 5) without using buffer indicated a value of ~pH
6.5. To be further confirmed with the selective interaction
of 1 towards Pb2+ ions in CH3CN–H2O (1:1, v/v), we used
tris HCl buffer and the titration output for Pb2+ ions was
observed to be alike (Figure 11S).
In UV–vis study, steady decrease in absorption at
273 nm was observed during titration with Pb2+ ions
(Figure 12S). With Cu2+ and Hg2+ ions, weak ratiometric
response was observed (Figure 12S). Beside this, almost
similar changes in absorption spectra of 1 with rest of
the metal ions were observed. The absorption intensity
at 273 nm was decreased gradually almost to the equal
extent (Figure 12S).
Figure 2. change in fluorescence ratio of 1 (c = 2.50 × 10−5 m) at
373 nm upon addition of 3 equiv. amounts of different metal ions
(c = 1.0 × 10−3 m) in ch3cN (λex = 280 nm).
In case of Hg2+, such change in absorption is small. Other
metal ions did not show much interaction with 1 under
similar conditions (Figure 5S). These observations indicate
that the compound 1 is only capable of sensing the metal
ions in the excited state rather than in the ground state.
To verify the recognition behavior of 1 towards the
same metal ions in aqueous system, we performed sim-
ilar study in CH3CN–H2O (1:1, v/v). As the compound 1
was completely insoluble in water, on compromisation
we solubilised it in CH3CN–H2O (1:1, v/v). In this solvent
combination, compound 1 exhibited an emission at
380 nm on excitation at 280 nm in the absence of metal
ions. This emission was markedly enhanced with a blue
shift of 18 nm upon interaction with Pb2+ ions over the
other metal ions examined (Figure 5(a)). Figure 5(b) which
describes the fluorescence ratio of 1 at 398 nm in presence
of 25 equiv. amounts of different metal ions studied rep-
resents that the compound 1 is highly sensitive to Pb2+
ions (Figure 6S).
In order to realise the mode of interaction of 1 with
the metal ions, 1H-NMR of 1 in CDCl3 was recorded in the
presence of equiv. amount of Pb2+, Hg2+ (Figure 6) and
Cu2+ ions (Figure 13S). In the presence of Pb2+ and Hg2+
ions, small downfield chemical shift of the protons Ha, Hb

4
S. PANJA ET AL.
(a)
(b)
3x105
2x105
2x106
1x106
1x105
0
300
0
300
350
400
450
500
350
400
450
500
Wavelength (nm)
Wavelength (nm)
Figure 3. change in emission of 1 (c = 2.50 × 10−5 m) upon addition of 3 equiv. of (a) cu2+ (c = 1.0 x 10−3 m) and (b) hg2+ (c = 1.0 × 10−3 m)
in ch3cN (λex = 280 nm).
(a)
(b)
1.0
0.8
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
0.0
250
300
350
400
450
250
300
350
400
450
Wavelength (nm)
Wavelength (nm)
Figure 4. change in absorbance of 1 (c = 2.50 × 10−5 m) upon addition of 3 equiv. of (a) cu2+ and (b) hg2+ (c = 1.0 × 10−3 m) in ch3cN.
(b)
(a)
3x105
2x105
1x105
0
300
350
400
450
500
Wavelength (nm)
Figure 5. (a) change in emission of 1 (c = 2.50 × 10−5 m) upon addition of 25 equiv. amounts of pb2+ (c = 1.0 × 10−3 m) ions and (b)
change in fluorescence ratio of 1 (c = 2.50 × 10−5 m, λex = 280 nm) at 398 nm upon addition of 25 equiv. amounts of different metal ions
(c = 1.0 × 10−3 m) in ch3cN–h2o (1: 1, v/v).
and Hc by 0.02–0.04 ppm was noted. This occurs likely due
to electrostatic influence of the metal ion on the pyrrole
motif instead of the direct involvement of pyrroles in
metal coordination. Due to metal–ligand interaction, all
the naphthalene protons including Hd protons of guani-
dine motif also underwent small downfield chemical shift
(0.02–0.06 ppm). In case of Cu2+ ion, while the pyrrole NHas
showed small downfield shift, the guanidine NHds were
not observed possibly due to deprotonation (Figure 13S).
Further, to understand the metal–ligand interaction, a
DFT level (13) study of the complexes was conducted. The
optimised geometries for Cu2+, Hg2+-complexes in CH3CN

SUPRAMOLECULAR CHEMISTRY
5
(14) (Figure 15S) shows that while in Cu2+-complex the
H3CO2C
Hb
CO2CH3
Ha
NH
N
Hd
N
intense transition is HOMO to LUMO + 3, the same for
H
N
Hg2+ complex is HOMO to LUMO + 4 in CH3CN. In Cu2+
-
Hc
N
1
complex, the continuous presence of electron density
on the naphthalene and guanidine nitrogens shifts from
naphthalene to the pyrroles. In comparison, in Hg2+
-
complex the electron density at the guanidine motif is
pulled away towards the metal and naphthalene in the
associated transition.
In CH3CN/H2O system, the Pb2+-complex showed
intense transition at 287 nm indicating HOMO-5 to LUMO
transition. The occupancy of the depicted orbitals indi-
cates that electron density is pulled away from the guani-
dine centre to the metal centre and nearby atoms (Figure
15S). From such ground state findings, we believe that
in fluorescence (i.e. in the excited state), Hg2+ and Pb2+
ions-induced enhancement and Cu2+-induced quenching
in emission of 1 are attributed to the manifestation of elec-
tron transfer in between the excited state of naphthalene
and the metal occupied binding site in different ways for
which the photo-induced electron transfer (PET) process
is regulated differently.
To examine the anion sensing behaviour of the Cu- and
Hg-ensembles of 1 in CH3CN, a series of anions (counter
cation: tetrabutylammonim ion) were undertaken in the
study. Of the different anions, only CN−, on progressive
addition to the ensembles induced marked change in
emission. While the Cu-ensemble of 1 exhibited significant
increase in emission with a red shift of 52 nm on interac-
tion with CN− ion (Figure 8(a)), under similar conditions
the Hg-ensemble showed partial decrease in emission at
373 nm (Figure 16S) and thus validated Cu-ensemble more
potential in selective sensing of CN− ions over the other
anions examined (Figure 17S). In UV–vis study, in the pres-
ence of CN−, the absorption band of the Cu-ensemble at
270 nm was intensified with a red shift of 20 nm followed
by the appearance of a new band at 357 nm (Figure 8(b)).
Figure6.partial1hNmr(400mhz,cDcl3)of(a)1(c=7.78 × 10−3 m),
(b) 1 with pb2+ (1:1) and (c) 1 with hg2+ (1:1) ions.
and Pb2+-complex in CH3CN/H2O mixture are shown in
Figure 7 with relevant details. Careful scrutiny reveals that
while in Cu2+-complex the copper ion is chelated involving
the ester oxygens and guanidinium nitrogens, the metal
ions in both Hg2+- and Pb2+-complexes are coordinated
to ester oxygens leaving the guanidium motif untouched.
To understand the photophysical properties of the
metal complexes of 1, TDDFT calculations were carried
out in CH3CN for Cu2+ and Hg2+-complexes and in CH3CN–
H2O for Pb2+-complex. Compound 1 exhibited absorp-
tion at 267 nm indicating a transition from HOMO−1
(spread over pyrrole motif) to LUMO + 2 (spread over
pyrrole and naphthalene motifs) in CH3CN (14S). In
Cu2+ and Hg2+- complexes, the absorptions appeared
nearer to this wavelength showing marginal red shifts
(Figure 14S) and validated the proposed binding struc-
tures as shown in Figure 7. Analysis of frontier orbitals
Figure 7. (colour online) DFt optimised geometries of (a) cu-complex in ch3cN: cu-o1: 2.07, cu-o3: 2.17, cu-N1: 2.02, cu-N2: 3.63, cu-
N3: 3.84, cu-N4: 2.93, cu-N5 2.81; (b) hg-complex in ch3cN: hg-o1: 2.82, hg-o3: 2.34, hg-N1: 5.17, hg-N2: 6.79, hg-N3: 6.84, hg-N4: 3.94,
hg-N5: 3.40; (c) pb-complex in ch3cN–h2o: pb-o1: 2.29, pb-o3: 2.29, pb-N1: 3.44, pb-N2: 5.22, pb-N3: 5.51, pb-N4: 4.47, pb-N5: 4.73 (all
distances are in Å).

6
S. PANJA ET AL.
(a)
(b)
1.5x106
0.8
0.6
0.4
0.2
0.0
1.0x106
5.0x105
0.0
300
350
400
450
500
550
300
350
400
450
Wavelength (nm)
Wavelength (nm)
Figure 8. (colour online) change in (a) emission and (b) absorption spectra of the ensemble of 1 (c = 2.5 × 10−5 m) with 3 equiv. amounts
of cu2+ ions in ch3cN upon successive addition of 1 equiv. amount of cN− ion (c = 1.0 × 10−3 m); insets represent corresponding colour
change of the 1-cu ensemble with cN− ion under (a) uV light and (b) ordinary light.
The colour of the solution was changed from colourless
to light yellow.
living cells and thereby can directly lead to the death of
human beings in several minutes.
The Benesi–Hildebrand plot gave the association con-
stant of 3.95×104 M−1 (Figure 18S) for interaction of CN− to
the Cu-ensemble and the detection limit (12) was deter-
mined to be 4.00×10−7 M (Figure 19S).
Conclusion
In conclusion, guanidine-centred naphthalene-pyrrole
conjugate 1 has been designed and synthesised. The
compound has been obtained in moderate yield and its
formation has been explained by a suggested mecha-
nism. In CH3CN and CH3CN–H2O (1:1, v/v), compound 1
exhibited turn-on emission selectively in the presence of
Hg2+ and Pb2+ ions, respectively. Addition of Cu2+ ions in
CH3CN resulted in steady decrease in emission of 1 and
behaved differently from Hg2+ ions. Thus, the simple
compound 1 has successfully differentiated three metal
ions Cu2+, Hg2+ and Pb2+ through different responses in
fluorescence under different conditions. Furthermore, the
Cu.1 ensemble in CH3CN has been established as good
secondary probe for selective recognition of CN− ion over
a series of other anions. Multi-ion recognition with such
a single molecular probe is worthy and a new addendum
to the existing reports in the literature (17).
The CN−- induced enhancement in emission of
Cu-ensemble is attributed to the deprotonation of gua-
nidine and pyrrole NHs as confirmed by 1H NMR in Figure
13S due to which the metal–ligand interaction becomes
stronger instead of demetallation and modifies the PET
process presumably through the coordination of CN− to
the organic ligand-anchored copper ion. To understand
this, analysis of UV–vis spectra of 1 in the presence of
nBu4NOH and nBu4NCN individually revealed weak absorp-
tion at 327 nm which is assumed to be due to deproto-
nation [although CN− acts as weak base (15)] of weakly
acidic guanidine protons to the small extent (Figure 20S).
Interestingly, addition of Cu(ClO4)2 to CN−- treated solution
of 1 in CH3CN moved the absorption from 327 to 357 nm
with moderate intensity. This is in accordance with the
observation in Figure 8(b).
It is to note that compound 1 itself exhibited moderate
quenching of emission in CH3CN in the presence of CN−
ions (Figure 21S) and gave ~10 times lower association
constant than its Cu-ensemble (Figure 22S). However, 1
did not show any noticeable interaction with other anion
studied (Figure 21S). These findings indicate that 1-Cu2+
complex can be useful as a secondary probe for detec-
tion of CN− ion. Of various anions, CN− is considered to be
an important due to its rapid action and extreme toxicity
(16) that comes from its strong affinity for the heme unit
in the active site of cytochrome-c oxidase enzyme. This
interrupts the mitochondrial electron-transport, decreases
the oxidative metabolism as well as oxygen utilisation in
Experimental
Syntheses
(E)-methyl 5-((hydroxyimino)methyl)-1H-pyrrole-2-
carboxylate (3)
The carbaldehyde 210 (0.53 g, 3.49 mmol) was dissolved in
H2O (15 mL) at 65 °C and a solution of NH2OH.HCl (0.35 g,
5.24 mmol) and K2CO3 (0.72 g, 5.24 mmol) in 2 mL of H2O
was added dropwise. The reaction mixture was then
allowed to heat at 65 °C for 30 min. Then the reaction
mixture was cooled to obtain white precipitate which was
extracted with ethyl acetate. The organic layer was dried

SUPRAMOLECULAR CHEMISTRY
7
over anhydrous Na2SO4 and evaporated under reduced
pressure to get 3 as crude product. Recrystallisation of the
crude using diethyl ether afforded pure compound 3 in
appreciable yield (0.42 g, yield 80%, mp 98 °C). Compound
3 was directly used in the next step without any charac-
terisation. FTIR (KBr, cm−1): 3300, 1693, 1556, 1451, 1228.
basis set (18) and B3LYP functional (19) were employed.
MaSK software (13) was used to generate the molecular
orbitals. Onsager’s SCRF approximation (20) with polar-
isable continuum method (21) was used for calculation
involving solvent phase.
Acknowledgements
Methyl 5-(aminomethyl)-1H-pyrrole-2-carboxylate (4)
Compound 3 (1.0 g, 6.57 mmol) and HCOONH4 (4.13 g,
65.7 mmol) were taken in 50 mL of ethyl acetate. Then 10%
Pd-C (0.25 g) was added to the reaction mixture and the
mixture was allowed to stir at room temperature for 12 h
under nitrogen atmosphere. After completion of the reac-
tion, the reaction mixture was filtered using Celite bed and
washed well with ethyl acetate. Water was added to this
filtrate and the solution was stirred well for 15 min. Then
the organic layer was extracted, dried over anhydrous
Na2SO4 which on evaporation gave the compound 4 as
crude mass. Recrystallisation of the crude using diethyl
ether afforded compound 4 in pure form in 74% yield
(0.66 g, mp 140 °C). Compound 4 was directly used in the
next step without any characterisation. FTIR (KBr, cm−1):
3301, 1675, 1567, 1489, 1224.
We thank DST, West Bengal, for financial support under the
project (sanc. No. 755(Sanc.)/ST/P/S&T/4G-3/2014 dated
27.11.2014). SP thanks CSIR, New Delhi, India for a fellowship.
Funding
This work was supported by DST, West Bengal [project sanc. No.
755(Sanc.)/ST/P/S&T/4G-3/2014 dated 27.11.2014].
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Compound 1
To a stirred solution of compound 4 (0.13 g, 0.84 mmol) in
10 mL dry CH2Cl2 was added 1-naphthalene isothiocyanate
(0.15 g, 0.80 mmol) and diisopropyl ethylamine (0.19 mL,
1.26 mmol) at room temperature. The mixture was stirred
for 20 min. Then the solvent was evaporated off and the
crude mass was extracted with ethyl acetate. Evaporation
of the solvent under reduced pressure gave the crude
product which was purified by column chromatography
using 40% ethyl acetate in petroleum ether to afford the
1
compound 1 in 62% yield (0.24 g, mp. 104 °C). H NMR
(CDCl3, 400 MHz): δ 9.56 (brs, 2H), 7.83 (d, 1H, J = 8 Hz), 7.78
(d, 1H, J = 8 Hz), 7.63 (s, 2H), 7.48−7.43 (m, 2H), 7.39−7.34
(m, 2H), 7.25 (merged with CDCl3, 1H), 6.90 (d, 2H, J = 4 Hz),
6.23 (d, 2H, J = 4 Hz), 5.06 (s, 4H), 3.83 (s, 6H); 13C NMR
(CDCl3, 100 MHz): 184.2, 161.0, 135.1, 134.1, 131.4, 129.6,
128.4, 127.8, 126.6, 126.3, 125.4, 125.3, 123.8, 121.9, 115.6,
110.3, 51.6, 41.9; FTIR (KBr, ν in cm−1): 3288, 2920, 2078,
1699, 1491, 1228; HRMS (TOF MS ES+): calcd. 499.1544
(M+K+1)+, found 499.1402 (M+K+1)+.
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Structures of compound 1 and its complexes with Cu2+ and
Hg2+ were optimised in acetonitrile. Structure of 1 with
Pb2+ was optimised in acetonitrile:water mixture. TDDFT
calculations were carried out on all optimised structures in
the same solvents. Gaussian program suite (12) was used
in all calculations. For DFT and TDDFT calculations, SDD

8
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