A useful scaffold based on acenaphthene exhibiting Cu2+ induced excimer fluorescence and sensing cyanide via Cu2+ displacement approach

Article abstract of DOI:10.1016/j.tet.2012.08.052

A new simple organic scaffold based on acenaphthene 4 was designed and synthesized. The chromogenic and fluorogenic properties of 4 toward different metal ions and anions were investigated in H₂O/MeCN (8:2, v/v) solution. The probe 4 in the pre

Full text of DOI:10.1016/j.tet.2012.08.052

Tetrahedron 68 (2012) 9076e9084
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
A useful scaffold based on acenaphthene exhibiting Cu2þ induced excimer
fluorescence and sensing cyanide via Cu2þ displacement approach
*
Mohammad Shahid, Syed S. Razi, Priyanka Srivastava, Rashid Ali, Biswajit Maiti, Arvind Misra
Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi 221 005, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 31 May 2012
Received in revised form 1 August 2012
Accepted 17 August 2012
Available online 24 August 2012
A new simple organic scaffold based on acenaphthene 4 was designed and synthesized. The chromogenic
and fluorogenic properties of 4 toward different metal ions and anions were investigated in H2O/MeCN
(8:2, v/v) solution. The probe 4 in the presence of Cu2þ exhibited strong static excimer emission at
507 nm along with a decrease in monomer emission at w400 nm ratiometrically, attributed to a com-
plexation through aldimine and amide groups of 4. Additionally, 4 upon interaction with different anions
illustrated significant fluorescence enhancement with cyanide. However, interaction of complex, 4-Cu2þ
with CNꢀ revealed fluorescence quenching attributed to formation of stable [Cu(CN)x]1ꢀx species in the
medium. A naked-eye sensitive fluorescent green color of solution was changed to blue. The mechanism
of interaction between 4 and Cu2þ and sensing of cyanide through Cu2þ displacement approach was
confirmed by the change in optical behaviors and 1H NMR and ESI-MS spectral data analysis.
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Chemosensor
Cu2þ
CNꢀ
Excimer
1. Introduction
element, which is widely distributed in a variety of cells and tissues
in different concentration level. The variation of copper ion con-
The development of selective and sensitive methods to detect
cations and anions have received considerable attention because of
important roles of these ions in biological, environmental, and in-
dustrial processes.1 Recently, major emphasis is on design and de-
velopment of novel organic scaffolds that can be potentially utilized
as a colorimetric and fluorescent sensors for cations and anions and
allow the sensing event, sensitive to naked-eye detection by a color
change, and without resorting expensive and sophisticated in-
struments.2 Among the several approaches fluorescent based
methods have advantages due to their high sensitivity, specificity,
real time monitoring, and fast response time.3 Moreover, the ratio-
metric fluorescent sensors, which are sensitive to variation in rela-
tive emission intensity, upon binding with ions are preferred
because the ratio of dual emission intensities can be utilized to an-
alyze the analyte concentration and to provide a built-in correction
for effects, such as, photobleaching, sensor molecule concentration,
the environment around the sensor molecules (pH, polarity, tem-
perature, and so forth) and stability on photoirradiation.4
centration in neuronal cytoplasm is responsible for diseases like
Alzheimer’s and Parkinson’s.6 The U.S. Environmental Protection
Agency (EPA) has set the limit of copper in drinking water around
1.3 ppm (w20
blood is around 15.7e23.6
m
M). The normal average concentration of copper in
m
M.6c In this context, significant progress
has been made to develop good sensors for selective detection of
Cu2þ however, practically most of these systems have limitations in
the sense of cross sensitivity toward other metal ions, low water
solubility, slow response, pH dependence, and a low fluorescence
quantum yield in the aqueous medium.7 Moreover, it is known that
copper induces fluorescence quenching due to its paramagnetic
nature.8
Likewise, cyanide can also cause biological and environmental
poisoning.9 The small amount of cyanide is lethal to human body10
11
due to its strong interaction with the active site of cytochrome a3
that inhibits cellular respiration in mammalian cells. The sources of
cyanide in water are discharge from chemical industries, metal
mining processes, and waste water treatment facilities.9 Cyanide has
also been used as a chemical warfare agent and even as a terror
material.12 The World Health Organization (WHO) has recom-
Among the soft transition metal ions and anions copper play
important role in various biological processes, such as, a catalytic
cofactor of a variety of metalloenzymes for instance superoxide
dismutase, cytochrome-c oxidase, and tyrosinase.5 It is a vital trace
mendedconcentrationofcyanideindrinkingwatertobew1.9 mMfor
a healthy life.13b Thus, detection of cyanide through coordination,14
covalent bonding12d or displacement method13,15 has also received
considerable interest among the scientific communities. Among the
various sensing mechanisms, based on different phenomena of
photophysics and chemical approaches Cu2þ displacement method
recently become one of the important approaches due to its high
* Corresponding author. Tel.: þ91 542 6702503; fax: þ91 0542 2368127, þ91
0542 2368175; e-mail addresses: amisra@bhu.ac.in, arvindmisra2003@yahoo.com
(A. Misra).
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2012.08.052

M. Shahid et al. / Tetrahedron 68 (2012) 9076e9084
9077
affinity for cyanide to form stable [Cu(CN)x]1ꢀx species in the me-
2.1. Optical behavior of 4 with different cations
The UVevis absorption spectrum of 4 (5 M) displayed a broad
dium.15 Thus, the ensemble based demetallization of copper by cy-
anide can be utilized as a good strategy to detect the cyanide in the
medium. It is also because the d9 electronic configuration of para-
magnetic Cu2þ have strong binding affinity toward cyanide and the
complexes with Cu2þ can recognize CNꢀ by ensuring high stabiliza-
tion effects on the ligand field.16 Therefore, the design and synthesis
of new systems that can display enhanced fluorescence upon in-
teraction with metal ions/anions are in great demand and of the
various optoelectronic techniques fluorescence spectroscopy has
advantages as it offers high detection sensitivity and simplicity.1,17
The chelating groups like eC]N and eC]O exhibit high bind-
ing affinity to transition and post transition metal ions in compar-
ison to alkali and alkaline earth metal ions.18 In addition to this
there are few systems, which utilize strong affinity of cyanide for
transition metals. In such systems, complexation of cyanide with
transition metal, like Cu2þ results a change in the photophysical
property of receptor and provide a method for detection. We herein
present first report on the design and synthesis of an acenaphthene
based scaffold for a sensitive and selective detection of Cu2þ
through enhanced excimer fluorescence and detection of cyanide
through copper displacement method in aqueous organic medium.
The probe 4 consists of acenaphthene units of almost negligible
fluorescence with amide and aldimine functions that has been
utilized as a potential binding site for the ions. Upon interaction
with Cu2þ the acenaphthyl units come close to each other and
generate high excimer fluorescence,8 in which the acenaphthene
units attained a stacked conformation, that ultimately leads to
m
absorption band between w280 and 340 nm (at w340 nm,
3
¼27,000 Mꢀ1 cmꢀ1) in H2O/MeCN (8:2, v/v) solution. The binding
behavior of 4 was investigated toward different metal ions by
UVevisible and fluorescence spectroscopy. Upon interaction with
different metal ions (10 equiv), such as, Naþ, Kþ, Agþ, Ca2þ, Co2þ
,
Ni2þ, Cu2þ, Zn2þ, Hg2þ, Agþ, Fe3þ, Pb2þ (as their nitrate salts) the
broad absorption band of 4 upon interaction with Cu2þ ion dis-
appeared and concomitantly a new transition band was appeared at
407 nm (Fig.1). The red shift observed in the absorption spectra may
be attributed to an increase in intramolecular
pep interaction be-
tween two acenaphthyl units as a result of coordination of Cu2þ
through the amide and aldimine functional groups of 4 in ground
state.8a The other tested metal ions failed to exhibit any significant
change in the absorption spectrum of 4 (Fig. 1).
0.4
0.3
Probe 4 + M
0.2
Cu
0.1
enhance intramolecular
pep interaction.
2. Results and discussion
0.0
300
375
450
Wavelength (n m)
Scheme 1 describes the synthetic route of probe 4. Aniline and
a
-bromoethylacetate in presence of KI and Na2HPO4 in acetonitrile
Fig. 1. Change in absorption spectra of 4 (5
(10 equiv) in H2O/MeCN (8:2, v/v).
mM) upon addition of different metal ions
(MeCN) were refluxed overnight under anhydrous condition to
obtain compound 2 as a viscous liquid in w75% yield. Compound 2
was constituted in ethanol and refluxed with ethylenediamine for
6 h to obtain compound 3 and 3a (confirmed by 1H NMR spectra),
which were separated by column chromatography in w37 and 51%
yield, respectively. Acenaphthene was reacted with phosphor-
ousoxychloride in N,N0-dimethylformamide (DMF) at 70 ꢁC to ob-
tain 5-formylacenaphthene by a reported procedure,19 and was
subsequently refluxed with 3 in ethanol at 80 ꢁC for 3 h to get
a brown colored semisolid compound 4 in w76% yield. The prod-
ucts were characterized by analytical and spectral data analysis
(Fig. S1e9, Supplementary data).
Theabsorption titration experimentwasperformed to understand
the binding affinity of 4 (5
M) with Cu2þ ion. Upon sequential ad-
m
ditionofCu2þ (0e3equiv)toasolutionof4thebroadbandcenteredat
340 nm reduced gradually with the formation of a new transition
band at 407 nm. An isosbestic point appeared at 348 nm clearly
suggested about the existence of more than one species in medium.
Job’s plot analysis revealed a 1:1 stoichiometry for a complexation
between 4 and Cu2þ. An association constant estimated by Bene-
sieHildebrand method20 utilizing nonlinear fitting of absorption ti-
tration data and was found to be Kassoc¼3.22ꢂ105 Mꢀ1 (Fig. 2).
The fluorescence spectrum of 4 (5 mM) in H2O/MeCN (8:2, v/v)
showed a very weak and broad monomer emission band in range of
380e420 nm, when excited at 340 nm. There was no band corre-
sponding to excimer emission that means two acenaphthene units
are not in stacked conformation. Among all the tested cations, 4
showed high selectivity toward copper metal ion whereas, in-
significant change was observed upon interaction with other cat-
ions. Upon interaction with Cu2þ emission spectrum of 4 illustrated
significant fluorescence enhancement, in which the weak emission
band of monomer red shifted to appear at 507 nm (Fig. 3) and color
of solution changed from a non-fluorescent to fluorescent green
under UV light (Inset, Fig. 3). The appearance of new emission band
of relatively high emission intensity signifies the formation of
a dimeric species in medium, in which two acenaphthene rings
occupied the stacked conformation probably due to coordination of
Cu2þ ion through the coordination sites available in form of amide
and aldimine functional groups. Thus, it is worth to mention that
copper induced a kind of driving force to bring two acenaphthyl
rings in stacked conformation.
O
O
O
N
N
NH
NH
HN
HN
N
N
2
(ii)
(i)
O
O
O
O
HN
NH
O
O
NH2
1
O
H2N
NH2
(iii)
3a
3
O
O
N
4
NH
HN
N
N
Scheme 1. (i) BrCH2COOEt/KI/Na2HPO4/CH3CN/
5-acenaphthenealdehyde/EtOH/
D, (ii) ethylenediamine/EtOH/D, (iii)
D.

9078
M. Shahid et al. / Tetrahedron 68 (2012) 9076e9084
0.12
0.09
0.06
0.03
0.00
60
(a)
(b)
0.3
0.2
0.1
0.0
Δ
A
40
y = 4.512x + 7.2
R² = 0.998
1 /
Δ
A
20
0
2
4
6
8
10
0.0
0.2
0.4
0.6
0.8
1.0
1 / [ Cu ] 5
μ M
[ 4 / 4 + Cu
]
250
300
350
400
450
Wavelength (n m)
Fig. 2. Absorption titration spectra of 4 (5
m
M) upon addition of Cu2þ ions (0e3 equiv) in H2O/MeCN (8:2, v/v). Inset (a) Job’s plot and (b) BenesieHildebrand plot of 4 for Cu2þ
.
300
The fluorogenic affinity of 4 (V4¼0.0022) with Cu2þ ions was
evaluated by fluorescence titration experiment (Fig. 5). Upon in-
creasing concentration of Cu2þ ions (0e3 equiv) to a solution of 4
relative fluorescence intensity increased significantly at 507 nm
along with fluorescence enhancement factor (FEF) 147 whereas, the
intensity of emission band at w400 nm decreased ratiometrically
Probe 4 + Cu
2+
4+Cu
4
225
150
75
with the formation of an isoemissive point at 439 nm. The quantum
yield of a probable complex, 4þCu2þ was increased (V
¼0.224)
2þ
4-Cu
Probe 4 + M
and the color of solution appeared as fluorescent green under UV
light. The high emission intensity observed at 507 nm is attributed
0
to formation of intramolecular excimer21 led enhanced
pep in-
400
480
560
640
Wavelength (n m)
teraction between the two acenaphthene rings in consequence to
complexation of Cu2þ ion through amide and aldimine functional
groups. Job’s plot analysis revealed consistently a 1:1 stoichiometry
for a complexation between 4 and Cu2þ ions. The binding constant
estimated from the fluorescence titration data was found to be
Fig. 3. Change in emission spectra of 4 (5 mM) upon addition of different metal ions
(10 equiv) in H2O/MeCN (8:2, v/v). Inset shows the change in color under UV light.
The practical applicability of compound 4 as a selective fluo-
rescent chemosensor for copper has been demonstrated by per-
forming the competitive metal ion interference experiments. For
that tested cations (10 equiv) were added to a solution of probable
complex, 4þCu2þ and reversibly by the addition of Cu2þ ion to
a solution of 4 containing excess of other metal ions (Fig. 4). No
significant variation in excimer emission was observed in com-
parison to emission spectra of 4 in either condition. The absorption
spectra upon addition of other tested cations illustrated in-
significant change in absorption band of a complex 4þCu2þ cen-
tered at 407 nm (Fig. S10, Supplementary data). Thus, the
experimental observation has suggested that compound 4 may be
utilized as a potential fluorescent chemosensor for Cu2þ ion.
1.18ꢂ105
M
ꢀ1. Moreover, a fluorescence intensity ratio plot4 ob-
tained between the relative fluorescence intensity ratio, I400/I507
and Cu2þ ion concentration suggested about the change in fluo-
rescence intensity ratiometrically after the addition of 0.5 equiv of
Cu2þ ion with
a mM (Fig. S11,
detection limit4 of w2.0
Supplementary data). The ESI-MS spectrum analysis of 4 and 3a
showed the molecular ions [MH]þ peaks at m/z 622 and 467, re-
spectively, (Fig. S5 and 9). Upon interaction between 4 and Cu2þ
a new peak observed at m/z 684 [4þCu]þ support the formation of
a complex, 4þCu2þ in the medium and also about a 1:1 stoichi-
ometry between probe 4 and Cu2þ (Fig. S12, Supplementary data).
Further, to examine the reversibility in complexation a strong
chelating reagent, ethylene diaminetetraacetate (EDTA) was added
(50 equiv) to a solution of probable complex, 4-Cu2þ. The observed
red-shifted low energy absorption and emission bands of complex
4þCu2þ were disappeared consistently, with the generation of
original bands at respective wavelengths. This may be attributed to
formation of a strong EDTAþCu2þ complex in medium (Fig. S13,
Supplementary data). Thus, the experimental observations have
suggested about the reversible mode of complexation and potential
application of probe 4 in the detection of copper in a repeated cy-
cle.7d Additionally, the fluorescence excitation spectra (Fig. S14,
Supplementary data) were acquired to understand that the ob-
served emission in case of complex, 4þCu2þ is due to excimer
formation and also to ensure whether it is static or dynamic.7f It is
also because if a probe and its probable complex upon excitation
corresponding to its emission bands do not show complete overlap
in their excitation spectra then the respective observed emission is
attributed to static excimer.7f For that probe 4 and its complex, 4-
Cu2þ were excited at emission wavelengths 402 and 507 nm, re-
spectively. The excitation spectra of 4-Cu2þ showed formation of
300
200
Δ
I
100
0
4 + M
4+ Cu2+ +M
Fig. 4. Bar diagram illustrate the change in relative emission intensity of 4 (5 mM) and
4-Cu2þ complex upon addition of competitive metal ions (10 equiv) at 507 nm in H2O/
MeCN (8:2, v/v).

M. Shahid et al. / Tetrahedron 68 (2012) 9076e9084
9079
0.10
60
(a)
(b)
300
200
100
0
0.08
0.06
0.04
0.02
0.00
y = 0.005x + 0.007
R² = 0.994
40
Δ
I
20
0
0.0
0.2
0.4
0.6
0.8
1.0
0
2
4
6
8
10
[ 4 / 4 + Cu
]
1 / [ Cu ] 5
μ M
400
480
560
640
Wavelength (n m)
Fig. 5. Emission titration spectra of 4 (5 m
M) upon addition of Cu2þ ions (0e3 equiv) Inset: (a) Job’s plot and (b) BenesieHildebrand graph for 4 with Cu2þ ions in H2O/MeCN (8:2, v/v).
a new intense band centered w400 nm whereas, no such band was
observed when probe 4 was excited at 402/507 nm. Thus, clearly
supporting that in the present sensing event the observed high
emission intensity is attributed to Cu2þ induced static excimer
fluorescence.
for probe 4 and its complex, 4þCu2þ using density functional the-
ory (DFT) method as implemented in Gaussian 03 suits of pro-
gram.22 All the calculations were performed using B3LYP density
functional theory method, a hybrid version of DFT and Har-
treeeFock (HF) methods, in which the exchange energy from
Becke’s exchange functional is combined with the exact energy
from HartreeeFock theory along with the component exchange
and correlation functionals, Becke’s three parameters define the
hybrid functional, specifying the extent of the exact exchange
mixed in. We have used a 6-31G(d,p) basis set for all the atoms
except metal atom (Cu2þ), for which an effective core LanL2DZ basis
set was chosen. A frequency calculation for the metal complex was
performed to make sure that the optimized structure is a real
minimum. The optimized structure of 4-Cu2þ complex (II and IV of
Fig. 7) indicates that Cu2þ ion coordinated with nitrogen-donor
atom of aldimine and amide functions of 4 in square planer con-
formation. Due to complexation of 4 with Cu2þ ion the acenaph-
thene moiety come closer while in probe 4 acenaphthene units
remained apart from each other (I and III of Fig. 7). The DFT opti-
mized structure showed two bond length between the Cu2þ and N-
2.2. Mechanism of complexation between 4 and Cu2D
The probable mechanism of complexation, as shown in Scheme
2 was confirmed by 1H NMR spectra of 4 in the presence of Cu2þ
ions (0.5, 1 and 2 equiv). The 1H NMR spectrum of 4 showed res-
onances for H10 and H30 proton at 6.46 ppm and a triplet for H20 at
d
d
6.97 ppm. The H4 proton of acenaphthene unit merged with
aldimine (eC]NH) proton to appear at 8.71 ppm whereas,
a broad signal appeared at 7.95 ppm may be attributed to amide
(eCONH) function proton. The other aromatic protons were
appeared between 7.25e7.76 ppm. Upon addition of
d
d
d
0.5e2.0 equiv of Cu2þ ions to a solution of 4 a significant downfield
shift in the resonances of amide and aldimine protons, Dd¼0.18 and
1.56 ppm, respectively, were observed and resonances of ace-
naphthyl ring protons become broadened (Fig. 6). Therefore, sug-
gested about the coordination of Cu2þ with both amide and
aldimine functions of 4 and that enforce acenaphthene rings to
occupy stacked conformation. Consequently, enhanced intra-
atom of amide are 2.45, 2.65 A and between the Cu2þ and N-atom of
ꢀ
ꢀ
aldimine are both of 1.92 A.
2.4. Optical behavior of complex 4-Cu2D with different anions
and CNL anion
molecular
pep interaction led to observe intense excimer fluo-
rescence7 and a nakedeeye sensitive green color was appeared in
the medium.
Among the various sensing approaches a metal chelate based
sensing method of copper complexes can be utilized to device
a good fluorescent sensor for CNꢀ because of high affinity of cya-
nide and copper to produce stable [Cu(CN)x]1ꢀx species in a me-
dium.15 To address this possibility we investigated optical behavior
3'
2'
1'
O
O
NH
N
N
NH
HN
O
O
of 4-Cu2þ complex (5
m
M) in the presence of different anions in
H2O/MeCN solution (8:2, v/v). Upon addition of different anions
(10 equiv), such as, Fꢀ, Clꢀ, Brꢀ, Iꢀ, SCNꢀ, H2PO4ꢀ, CNꢀ, AcOꢀ, PO34ꢀ
S2ꢀ (as their sodium salts) to a solution of 4-Cu2þ (5
M) significant
CN-
NH
HN
Cu2+
Cu2+
CH=N
N
N
4
6
5
N
N
7
8
,
[Cu(CN)x]1-x
4
m
3
change in the optical properties was observed only upon in-
teraction with CNꢀ ion, in which, both the absorption and emission
spectra of 4 rejuvenated almost completely. Some sort of in-
teraction was also observed with S2ꢀ ion, which interacts with 4-
Cu2þ complex and causes w40% fluorescence quenching (Fig. 8,
S15).
4
2
1
4-Cu2+
Scheme 2. Proposed mechanism for interaction of 4 with the Cu2þ and CNꢀ ions.
The binding affinity of a complex, 4-Cu2þ with CNꢀ ion was
estimated by performing absorption and emission titration exper-
iments (Fig. 9). Upon a sequential addition of CNꢀ (0e4 equiv) to
a solution of 4-Cu2þ absorption band centered at w400 nm de-
creased gradually and a new broad band around w340 nm was
generated with the formation of an isosbestic point at 350 nm
2.3. Quantum chemical calculations
Further to support our assumptions, experimental observations
and possible structural changes we have performed quantum
chemical calculations. The geometry optimization were performed

9080
M. Shahid et al. / Tetrahedron 68 (2012) 9076e9084
Fig. 6. Change in 1H NMR spectra of 4 (c¼1.02ꢂ10ꢀ2 M) upon addition with Cu2þ (0.5, 1and 2 equiv) in DMSO-d6.
Fig. 7. DFT optimized structure of 4 and 4-Cu2þ complex.
(a)
(b)
4-Cu , 4-Cu + Anions
300
200
100
0
0.4
0.3
0.2
0.1
0.0
4-Cu + CN
-
4-Cu +S
4-Cu , + Anions
4-Cu + S
4-Cu + CN
375
450
525
600
250
300
350
400
450
Wavelength (n m)
Wavelength (n m)
Fig. 8. Change in (a) absorption and (b) emission spectra of 4-Cu2þ (5
mM) upon addition of different anions (10 equiv) in H2O/MeCN (8:2, v/v).

M. Shahid et al. / Tetrahedron 68 (2012) 9076e9084
9081
(a)
(b)
300
0.4
0.3
0.2
0.1
0.0
200
100
0
375
450
Wavelength (n m)
m
M) upon addition of CNꢀ ions (0e4 equiv) in H2O/MeCN (8:2, v/v).
525
600
250
300
350
400
450
Wavelength (n m)
Fig. 9. (a) UVevis absorption and (b) fluorescence titration spectra of 4-Cu2þ complex (5
(Fig. 9a). Similarly, fluorescence intensity of emission band cen-
tered at 507 nm decreased ratiometrically while the relative in-
tensity of an emission band, centered at w400 nm increased along
with formation of an isoemissive point at 437 nm (Fig. 9b). The
color of solution readily visible to the naked-eye was changed from
a fluorescent green to non-fluorescent. The absorption and fluo-
rescence titration experiment data were utilized to estimate
binding constant of CNꢀ ion with a complex, 4-Cu2þ and were
found to be 1.32ꢂ106 and 2.05ꢂ106 Mꢀ1, respectively. The detection
limit of 4-Cu2þ complex for CNꢀ ion was estimated and was found
of different anions to a solution of 4þCNꢀ the relative emission
intensity of 4þCNꢀ remained unaltered (Fig. 11).
100
4 + CN
4+CN-
4
75
50
to be 1
mM (i.e., 25 ppb). The high sensitivity to the maximum
4 + Cl , Br , I ,H PO ,PO
AcO , F , SCN , NO ,S
permissive level in drinking water, 1.9 ppm recommended by WHO
authenticate the novelty of present mode of CNꢀ sensing mecha-
nism obviously attributed to demetallization of a probable com-
plex, 4þCu2þ by cyanide and formation of [Cu(CN)x]1ꢀx species in
the medium as shown in Scheme 2.
25
0
400
480
560
640
Wavelength (n m)
The stability constants (K) for the formation of probable differ-
ent complex, [Cu(CN)x]1ꢀx species15b in the medium are
[Cu(CN)2]ꢀ¼1.00ꢂ1024; and [Cu(CN)4]3ꢀ¼2.0ꢂ1030. Since, the es-
timated association constant of a complex between 4 and Cu2þ was
comparatively low, Kassoc¼1.18ꢂ105 Mꢀ1 than the stability constant
of copper and cyanide ions it is reasonable to understand that upon
addition of CNꢀ to a solution of complex, 4þCu2þ led to a formation
of [Cu(CN)x]1ꢀx species in the medium, due to which modulation in
both absorption and emission spectra were observed.
Fig. 10. Change in emission spectra of 4 (5
(50 equiv) in H2O/MeCN (8:2, v/v).
mM) upon addition of different anions
4+Anions
-
4+CN +Anions
80
60
2.5. Interaction of 4 with CNL anion
Δ
I
40
20
0
Compound 4 contains amide group and it is rationally concluded
that the amide unit reasonably form complexes with different an-
ions probably through hydrogen bonding between anions and
amide eNH fragment.23 Therefore, we intended to investigate
binding affinity of 4 toward different anions, such as, Fꢀ, Clꢀ, Brꢀ, Iꢀ,
SCNꢀ, H2PO4ꢀ, CNꢀ, NO3ꢀ, AcOꢀ, S2ꢀ, PO34ꢀ (as their sodium salts) in
H2O/MeCN (8:2, v/v) solution. The absorption spectrum of 4
showed insignificant change with different anions (Fig. S16). Con-
versely, the emission spectra upon addition of different anions
-
-
-
-
-
-
-
-
2-
-
4
Cl Br
I
AcO
F
CN NO H PO S SCN
3 2 4
(50 equiv) to a solution of 4 (5 mM) exhibited significant fluores-
Fig. 11. Bar diagram illustrate the change in relative emission intensity of 4 (5
m
M) (red
cence enhancement only upon interaction with CNꢀ. A new emis-
sion band was appeared at 452 nm and the color of solution
appeared blue. This may be probably attributed to formation of
excimer up to lesser extent relatively, in comparison to Cu2þ, upon
an interaction of CNꢀ with amide function of 4 through H-bonding
interaction whereas, insignificant spectral changes were observed
upon interaction with other tested anions (Fig. 10). A competitive
anion interaction studies were also performed to understand the
selectivity of 4 with cyanide anion. Upon addition of cyanide to
a solution of 4 containing different anions and reversibly addition
in color) and 4-CNꢀ complex (blue in color) upon addition of competitive anions
(50 equiv) at 452 nm in H2O/MeCN (8:2, v/v).
Contrary, one can also speculate about an opportunity of nu-
cleophilic addition reaction between 4 and cyanide, in which, cy-
anide can approach eC]O group of amide functionality to form
a new charged cyanohydrin species15 in the medium. A probability
for such type of chemical reaction is depicted in Scheme 3. Our this
speculation was based on speculation of much lower intrinsic hy-
dration energy of CNꢀ
(D
Hhyd¼ꢀ67 kJ molꢀ1) in comparison to very

9082
M. Shahid et al. / Tetrahedron 68 (2012) 9076e9084
O
OH
CN
O
O
N
N
N
NH
N
CN-
N
NH
N
HN
N
Proton
Transfer
CN-
CN-
O
N
O
CN
NH HN
N
4
X
N
4-CN-
4-CN-
Scheme 3. Probable mechanism of interaction between probe, 4 and CNꢀ anion.
high salvation energy for other anions, for instance, Fꢀ
constant estimated from nonlinear fitting of fluorescence titration
data was found to be Kassoc¼2.06ꢂ104 Mꢀ1 (Fig. 13). Comparatively,
the observed association constants for complex, 4þCNꢀ was rela-
tivelylow than of 4þCu2þ and4þCu2þþCNꢀ. Thus, clearlysuggesting
about the interaction between 4 and cyanide through H-bonding
rather than a possibility of nucleophilic addition reaction of cyanide
on to the imine, eC]NH as well as on carbonyl, eC]O group of
amide functional units. Further, to rule out the expected probability
for a nucleophilic addition reaction, Cu2þ was added to a solution of
probable complex, 4-CNꢀ. Fluorescence quenching occurred, in
which the intensity of the emission band, centered at 452 nm di-
minished completely and the emission spectra almost same to probe
4 was rejuvenated (Fig. S20). This may be attributed to the formation
of stable species, [Cu(CN)x]1ꢀx and free probe 4 in the medium.
Moreover, upon interaction with CNꢀ if the speculated chemical re-
action, leading to formation of cyanohydrin derivative was accurate,
(
(
(
D
D
D
Hhyd¼ꢀ505 kJ molꢀ1), Clꢀ
(
D
Hhyd¼ꢀ363 kJ molꢀ1), Brꢀ
Hhyd¼ꢀ336 kJ molꢀ1), Iꢀ
(D
Hhyd¼ꢀ295 kJ molꢀ1), CH3COOꢀ
Hhyd¼ꢀ375 kJ molꢀ1), and H2PO4ꢀ
(
D
Hhyd¼ꢀ260 kJ mol-1) in H2O/
MeCN (7:1, v/v) solution.24
To establish the actual mechanism, 1H NMR spectral data of 4 in
the presence of cyanide was acquired in DMSO-d6. Upon addition of
2e5 equiv of CNꢀ to a solution 4 a broad resonance attributed to
amide (eCO NH) function, at
d 7.95 ppm shifted downfield to ap-
pear at
d
8.19 ppm (Dd¼1.16 ppm). The H10 and H30 protons were
separated to appear at
d 6.45 and 6.53 ppm, respectively, whereas,
a marginal change in the resonances of aromatic ring protons as
well as in aldimine (eC]NH) proton, at 8.71 ppm were observed
(Fig. 12). Additionally, the 1H NMR spectrum of 4 showed doublet at
3.68 ppm attributable to methylene
d
d
3.6 (J¼5.7 Hz) and singlet at
d
protons (eCH2CH2e) and proton neighboring to carbonyl function
Fig. 12. 1H NMR titration spectra of 4 (c¼1.02ꢂ10ꢀ2 M) upon addition of CNꢀ (2, 5 equiv) in DMSO-d6.
of amide group, respectively, (Fig. S17). Upon interaction with CNꢀ
almost insignificant downfield chemical shift, rather than any up-
field shift was observed at the corresponding resonances (Fig. S18
and 19). Thus, suggesting that interaction of cyanide is primarily
through hydrogen bonding with the amide fragment of probe 4
rather than speculated chemical reaction, as shown in Scheme 3.
Further, to elucidate binding affinity of 4 for CNꢀ fluorescence
titration experiment was carried out. Upon addition of CNꢀ anions
(0e50 equiv) to a solution of 4 relative fluorescence intensity was
enhanced gradually (FEF¼8.2) and the quantum yield was increased
w34 times (V4-CNꢀ¼0.0754), which was relatively less in compari-
son to 4þCu2þ. Job’s plot analysis revealed a 1:1 stoichiometry for
a probable complexation between 4 and CNꢀ. The association
then upon addition of Cu2þ to a solution of 4-CNꢀ complex there
might be possibility for generation of a new band in the absorption
spectra and accordingly change in the fluorescence behavior. How-
ever, beyond our speculation no such significant spectral changes
were observed. Thus, fluorescence, UVevis absorption and 1H NMR
spectra exclusively validated the interaction of 4 with CNꢀ through
H-bonding25 and ruled out our assumption for a possible nucleo-
philic addition reaction leading to formation of possible cyanohydrin
derivative in the medium. This was further confirmed by ESI-MS data
analysis, in which no new signal corresponding to generation of cy-
anohydrin derivative was observed (Fig. S21).
Further, to strengthen our hypothesis for a probable mode of
interaction with Cu2þ and CNꢀ ions and involvement of excimer

M. Shahid et al. / Tetrahedron 68 (2012) 9076e9084
9083
(a)
(b)
0.16
36
100
80
60
40
20
0
y = 0.3005x + 0.0125
2
0.12
R = 0.9909
24
Δ
I
0.08
0.04
0.00
12
0
0.0 0.2 0.4 0.6 0.8 1.0
0.0 0.1 0.2 0.3 0.4 0.5
-
[ 4 / 4 + CN -
]
1 / [ CN
]
375
450
525
600
Wavelength (n m)
Fig. 13. Emission titration spectra of probe 4 (5
m
M) upon addition of different equiv of CNꢀ ions (0e50 equiv) in H2O/MeCN (8:2, v/v). Inset: (a) Job’s plot and (b) Bene-
sieHildebrand graph of probe 4 upon addition of CNꢀ ions in H2O/MeCN (8:2, v/v).
fluorescence upon interaction of 4 with Cu2þ and CNꢀ derivative, 3a
(5 mM) was utilized as a model compound. The affinity of 3a toward
band width of 5 nm/5 nm for both excitation and emission spectra,
respectively. FTIR spectra (KBr pellets) were recorded on a Perkin
Elmer Spectrum spectrometer. The 1H and 13C NMR spectra
different cations (50 equiv) and anions (100 equiv) was tested
under the same experimental condition. Compound 3a displayed
a weak monomer emission at 425 nm, when excited at 340 nm. In
contrast to 4 compound 3a upon interaction with different cations
exhibited fluorescence quenching with Cu2þ while oppositely, il-
lustrated fluorescent enhancement with CNꢀ, in which, the emis-
sion spectra displayed a bathochromic shift of w60 nm to appear at
485 nm (Figs. S22 and 23, Supplementary data). The association
constants estimated for a possible complexation between 3a and
Cu2þ/CNꢀ ions in a 1:1 stoichiometry, respectively, were found to
be 7.26ꢂ103 Mꢀ1 and 4.32ꢂ104 Mꢀ1 (Fig. S24, Supplementary data).
Moreover, upon addition of CNꢀ (40 equiv) to a probable complex of
3a-Cu2þ and conversely, Cu2þ (40 equiv) to a solution of probable
complex, 3a-CNꢀ the relative emission intensity revived, which
was almost close to the intensity signal of 3a (Fig. S25,
Supplementary data). Thus, the observed optical behavior clearly
suggested about the detection of cyanide via Cu2þ displacement
approach and also about the interaction of cyanide with derivative
3a through the H-bonding interaction.
(chemical shifts in d ppm) were recorded on a JEOL AL 300 FT-NMR
(300 MHz) spectrometer, using tetramethylsilane (TMS) as an in-
ternal standard. Mass spectra were recorded on a Micromass
Quattro II spectrometer. Elemental analysis was carried out on CE-
440 CHN Analyzer (Exeter Analytical Inc.).
4.2. Association constant/binding constant (Kassoc
)
The association constants have been calculated by non-linear
fitting of the spectroscopic titration curve by using Bene-
sieHildebrand method employing following equations 1 for 1:1
stoichiometry.
À
Á
À
Á
1=ðI ꢀ I0Þ ¼ 1= I ꢀ If þ 1=K I ꢀ If ½Mꢃ
(1)
Where, K is the association constant, I is fluorescence intensity or
absorbance of free fluorescent probe, I0 is the observed fluores-
cence intensity or absorbance of the complex (ProbeDions) and If
is the fluorescence intensity or absorbance at saturation.
3. Conclusion
4.3. Quantum yields (F)
Conclusively, a new simple probe 4 was designed and de-
veloped, which was capable to detect Cu2þ ion through the en-
hanced fluorescence intensity ratiometrically. The interaction of
copper with the amide and aldimine functional groups encouraged
excimer formation by reducing the distance between the two
The quantum yields were estimated in acetonitrile solution by
secondary method1 using Eq. 2 with respect to the quinine sulfate
(F
¼0.55 in 0.1 M H2SO4) as standard.
ꢀ
ꢁ
Q ¼ QR$ðI=IRÞ$ ðODR=ODÞ$ n2=nR2
(2)
acenaphthyl rings and increasing the
pep interaction, conse-
quently. The change in color of solution from non-fluorescent to
a fluorescent green was readily distinguishable to naked eye. On the
other hand, interaction of 4-Cu2þ with cyanide ion revealed fluo-
rescence quenching due to a strong copper-cyanide affinity leading
to the formation of stable [Cu(CN)x]1ꢀx species. The probe 4 also
exhibited sensing of CNꢀ in aqueous-MeCN solution, in which
fluorescence enhancement was observed at w452 nm.
Where, Q is the quantum yield, I is integrated area corresponding to
the fluorescence intensity, OD is optical density, and n is the re-
fractive index. The subscript R refers to the reference fluorophore of
known quantum yield.
4.4. Synthesis and characterization of probe 4
4.4.1. Synthesis of derivative 2. To the mixture of aniline (0.93 g,
4. Experimental
10 mmol), Na2HPO4 (2.84 g, 20 mmol), and KI (1.66 g, 10 mmol) in
anhydrous acetonitrile (MeCN),
a-bromoethylacetate (5.56 ml,
4.1. Instrumentation
50 mmol) was added. The reaction mixture was refluxed overnight
under nitrogen atmosphere. After completion of reaction (as
monitored on TLC) solvent was evaporated to dryness under re-
duced pressure, and cold water was added to it and then extracted
with chloroform. The organic layer was separated and dried over
anhydrous Na2SO4. Filtered and chloroform was evaporated under
The absorption and emission spectra were recorded at room
temperature on
a Shimadzu 1700 spectrophotometer using
a quartz cuvette (path length¼1 cm) and CARY Eclipse (VARIAN)
fluorescence spectrophotometer at 600 V PMT keeping a constant

9084
M. Shahid et al. / Tetrahedron 68 (2012) 9076e9084
reduced pressure to obtain a viscous liquid (1.98 g, 75%). Rf (CHCl3)
0.61; 1H NMR (300 MHz, CDCl3)
6.80 (m, 1H), 6.62 (d, 2H, J¼7.8 Hz), 4.27 (m, 4H), 3.89 (s, 4H), 1.32 (t,
6H, J¼6.9, 6.9 Hz).
Supplementary data
d
(ppm): 7.21 (t, 2H, J¼7.8, 7.5 Hz),
1H, 13C NMR, FTIR, ESI-MS, fluorescence, absorption spectral
data. Supplementary data related to this article can be found online
at http://dx.doi.org/10.1016/j.tet.2012.08.052.
4.4.2. Synthesis of derivative 3 and 3a. To a warm solution of 2
(1.33 g, 5 mmol) in ethanol (10 ml), ethylenediamine (5 ml) was
added and refluxed the reaction mixture for 5 h. After completion
of the reaction (as monitored on TLC), solvent was evaporated
under reduced pressure to obtain a yellow color viscous oil. The
cold water was added to the reaction mixture and product was
extracted with CHCl3 and separated by column chromatography to
get viscous oil. For 3 (0.52 g, 37%); Rf (CHCl3) 0.1; 1H NMR (300 MHz,
References and notes
1. (a) Yoon, J.; Kim, S. K.; Singh, N. J.; Kim, K. S. Chem. Soc. Rev. 2006, 35, 355; (b)
Czarnik, A. W. Ed.; American Chemical Society: Washington, DC, 1992. (c)
Gunnlaugsson, T.; Glynn, M.; Tocci, G. M.; Kruger, P. E.; Pfeffer, F. M. Coord. Chem.
Rev. 2006, 250, 3094.
2. (a) Zhang, J. F.; Zhou, Y.; Yoon, J.; Kim, J. S. Chem. Soc. Rev. 2011, 40, 3416; (b) Wu,
J.; Liu, W.; Ge, J.; Zhang, H.; Wang, P. Chem. Soc. Rev. 2011, 40, 3483; (c) Kim, H.
N.; Guo, Z.; Zhu, W.; Yoon, J.; Tian, H. Chem. Soc. Rev. 2011, 40, 79.
3. (a) Chen, X.; Pradhan, T.; Wang, F.; Kim, J. S.; Yoon, J. Chem. Rev. 2012, 112, 1910;
(b) Lodeiro, C.; Capelo, J. L.; Mejuto, J. C.; Oliveira, E.; Santos, H. M.; Pedras, B.;
Nunez, C. Chem. Soc. Rev. 2010, 39, 2948; (c) Qian, X.; Xiao, Y.; Xu, Y.; Guo, X.;
Qiana, J.; Zhu, W. Chem. Commun. 2010, 6418.
4. Grynkiewicz, G.; Poenie, M.; Tsien, R. Y. J. Biol. Chem. 1985, 260, 3440.
5. Kramer, R. Angew. Chem., Int. Ed. 1998, 37, 772.
6. (a) Multhaup, G.; Schlicksupp, A.; Hesse, L.; Beher, D.; Ruppert, T.; Masters, C. L.;
Beyreuther, K. Science 1996, 271, 1406; (b) Lovstad, R. A. Biometals 2004, 17, 111;
(c) Tak, W. T.; Yoon, S. C. KSN 2001, 20, 863.
CDCl3)
d
(ppm): 7.24 (t, 2H, J¼7.8, 7.8 Hz), 7.02 (br, 2H), 6.83 (t, 1H,
J¼7.2, 7.5 Hz), 6.63 (d, 2H, J¼8.1 Hz), 4.26 (br), 3.82 (d, 4H, J¼4.8 Hz),
3.35 (m, 4H), 2.81 (m, 4H).
For 3a (1.18 g, 51%); Rf (CHCl3) 0.5; 1H NMR (300 MHz, CDCl3)
d
(ppm): 7.21 (m, 2H), 7.04 (br, 2H), 6.80 (m, 1H), 6.63 (d, 2H,
J¼7.5 Hz), 3.81 (s, 4H), 3.42 (s, 4H); ESI-MS (3a): m/z 194 (100),
467.2 (70%, MHþ).
7. (a) Zhou, Y.; Wang, F.; Kim, Y.; Kim, S.-J.; Yoon, J. Org. Lett. 2009, 11, 4442; (b)
Mu, H.; Gong, R.; Ma, Q.; Sun, Y.; Fu, E. Tetrahedron Lett. 2007, 48, 5525; (c) Xu,
Z.; Yoon, J.; Spring, D. R. Chem. Commun. 2010, 46, 2563; (d) Martinez, R.;
Espinosa, A.; Tarraga, A.; Molina, P. Tetrahedron 2010, 66, 3662; (e) Misra, A.;
Shahid, M. J. Phys. Chem. C 2010, 114, 16726; (f) Manandhar, E. ,; Wallace, K. J.
Inorg. Chim. Acta 2012, 381, 15.
8. (a) Jung, H.; Park, M.; Han, D.; Kim, E.; Lee, C.; Ham, S.; Kim, J. S. Org. Lett. 2009, 11,
3378;(b)Kim,H.;Hong,J.;Hong, A.;Ham, S.;Lee, J.;Kim, J. S.Org. Lett. 2008,10,1963.
9. (a) Kulig, K. W. Cyanide Toxicity; U.S. Department of Health and Human Ser-
vices: Atlanta, GA, 1991.
4.4.3. Synthesis of probe 4. To a solution of 3 (0.29 g, 1 mmol) in
ethanol (10 ml), 5-formylacenaphthene (0.36 g, 2 mmol) was
added and reaction mixture was refluxed for 3 h and monitored
(on TLC). Solvent was reduced under vacuum and cold water was
added to the reaction mixture. The precipitate so obtained was
filtered and dried to give brown color semisolid compound
(0.47 g, 76%). Rf (CHCl3) 0.5; 1H NMR (300 MHz, CDCl3)
d (ppm):
8.60 (s, 2H), 8.54 (d, 2H, J¼8.1 Hz), 7.58 (m, 4H), 7.48 (m, 2H), 7.33
(m, 4H), 7.12 (t, 2H, J¼7.8, 7.5 Hz), 6.74 (t, 1H, J¼7.2, 6.9 Hz), 6.54
(d, 2H, J¼7.8 Hz), 3.76 (s, 4H), 3.72 (t, 4H, J¼4.8, 4.8 Hz), 3.39 (m,
10. Muir, G. D. Hazards in the Chemical Laboratory; The Royal Society of Chemistry:
London, UK, 1977.
11. Cyanide in Biology; Vennesland, B., Comm, E. F., Knownles, J., Westly, J., Wissing,
F., Eds.; Academic: London, 1981.
12H); 13C NMR (75 MHz, CDCl3)
d (ppm): 30.2, 39.9, 48.8, 61.2,
12. (a) Young, C.; Tidwell, L.; Anderson, C. Cyanide: Social, Industrial, and Economic
Aspects; Minerals, Metals, and Materials Society: Warrendale, 2001; (b)
Johnson, J. D.; Meisenheimer, T. L.; Isom, G. E. Toxicol. Appl. Pharmacol. 1986,
84, 464; (c) Koenig, R. Science 2000, 287, 1737; (d) Kim, H. J.; Lee, H.; Lee, J. H.;
Choi, D. H.; Jung, J. H.; Kim, J. S. Chem. Commun. 2011, 10918.
13. (a) Miller, G. C.; Pritsos, A. Cyanide: Social, Industrial and Economic Aspects; Pro-
ceeding of the TMS Annual Meeting: 2001; p 73; (b) Guidelines for Drinking-
Water Quality; World Health Organization: Geneva, Switzerland, 1996.
14. Zou, Q.; Li, X.; Zhang, J.; Zhou, J.; Sun, B.; Tian, H. Chem. Commun. 2012, 2095.
15. (a) Lou, X.; Qiang, L.; Qin, J.; Li, Z. Appl. Mater. Interfaces 2009, 1, 2529; (b) Song,
T.; Xu, J.; Cheng, G. Inorganic Chemistry; Higher Education: Beijing, 2004; (c) Xu,
Z.; Chen, X.; Kim, H. N.; Yoon, J. Chem. Soc. Rev. 2010, 39, 127; (d) Xu, Z.; Pan, J.;
Spring, D. R.; Cui, J.; Yoon, J. Tetrahedron 2010, 66, 1678.
16. (a) Huang, X. M.; Guo, Z. Q.; Zhu, W. H.; Xie, Y. S.; Tian, H. Chem. Commun. 2008,
5143; (b) Zhang, J. F.; Kim, S.; Han, J. H.; Lee, S.-J.; Pradhan, T.; Cao, Q. Y.; Lee, S.
J.; Kang, C.; Kim, J. S. Org. Lett. 2011, 13, 5294; (c) Fabbrizzi, L.; Marcotte, N.;
Stomeo, F.; Taglietti, A. Angew. Chem., Int. Ed. 2002, 41, 3811.
17. (a) Valeur, B.; Leray, I. Inorg. Chim. Acta 2007, 360, 765; (b) Kim, S. H.; Kim, H. J.;
Yoon, J.; Kim, J. S. In Calixarenes in the Nanoworld; Vicens, J., Harrowfield, J., Eds.;
Springer: Dordrecht, The Netherlands, 2007, Chapter 15; (c) Valeur, B.; Bourson,
J.; Pouget, J.; Czarnik, A. W. Fluorescent Chemosensors for Ion and Molecule
Recognition. ACS Symposium Series 538; American Chemical Society: Wash-
ington, DC, 1993; (d) Sharp, S. L.; Warmack, R. J.; Goudonnet, J. P.; Lee, I.; Ferrell,
T. L. Acc. Chem. Res. 1993, 26, 377.
113.1, 118.7, 118.9, 119.1, 119.8, 120.6, 122.1, 127.4, 127.7, 129.3, 131.5,
132.1, 139.5, 145.9, 146.1, 147.0, 149.9, 162.9, 192.9; FTIR (KBr) ymax
(cmꢀ1) 3400, 2923, 1663, 1623, 1601, 1503, 1442, 1313, 1260, 838,
749; Anal. Calcd For C40H39N5O2: C, 77.27; H, 6.32; N, 11.26%.
Found: C, 77.17; H, 6.70; N, 11.32%; ESI-MS (4): m/z 358 (70), 591
(22), 622.3 (100%, MHþ).
4.4.4. Synthesis of 5-formylacenaphthene. To a solution of ace-
naphthene (10 mmol, 1.54 g) in N,N0-dimethylformamide
(26 mmol, 2 ml) POCl3 (18 mmol, 1.6 ml) was added dropwise over
15 min with stirring at room temperature. After complete addition
of POCl3 the reaction was heated at 70 ꢁC for 3 h and then allowed
to cool in an ice bath. The reaction mixture was neutralised with
sodium acetate solution (10 g in 18 ml of water) and left for pre-
cipitation. The precipitate was filtered followed by washing with
water and dried in air to get the brown colored solid (5.7 mmol,
57%). Mp 103e105 ꢁC; Rf (20% EtOAc/hexane) 0.6; 1H NMR
(300 MHz, CDCl3)
d
(ppm): 10.29 (s, 1H, CHO), 8.82 (d, 1H, J¼8.4 Hz),
18. Yoon, S.; Albert, A. E.; Wong, A. P.; Chang, C. J. J. Am. Chem. Soc. 2005, 127, 16030.
19. (a) Shahid, M.; Srivastava, P.; Misra, A. New J. Chem. 2011, 35, 1690; (b) Misra, A.;
Shahid, M.; Srivastava, P. Sens. Actuators, B 2012, 169, 327.
20. Benesi, H. A.; Hildebrand, J. H. J. Am. Chem. Soc. 1949, 71, 2703.
21. Lakowicz, J. R. Principles of Fluorescence Spectroscopy, 2nd ed.; Kluwer Aca-
demic/Plenum: New York, NY, 1999.
7.96 (d, 1H, J¼7.2 Hz), 7.68 (t, 1H, J¼7.2, 8.4 Hz), 7.43 (d, 2H,
J¼6.6 Hz), 3.45 (s, 4H, CH2); FTIR (KBr) ymax (cmꢀ1) 3047, 2927, 2773,
1665, 1550, 1445, 1340, 1251, 1166, 1047, 838, 749.
22. Frisch, M. J.; Truncks, G. W.; Schlegel, H. B. GAUSSIAN 03, Revision E.01;
Gaussian: Wallingford, CT, 2007.
23. (a) de Silva, A. P.; Gunarantane, H. Q. N.; Gunnlaugsson, T.; Huxley, A. J. M.; McCoy,
C. P.; Rademacher, J. T.; Rice, T. E. Chem. Rev.1997, 97, 1515; (b) Martinez-Manez, R.;
Sancenon, F. Chem. Rev. 2003, 103, 4419.
Acknowledgements
The authors are thankful to the Council of Scientific and In-
dustrial Research (CSIR), New Delhi for financial support and fel-
lowships (to M.S., S.S.R., P.S.) and UGC (R.A.) to carry out research
work. Authors are also thankful to SAIF CDRI, Lucknow for pro-
viding ESI-MS spectral data.
24. Sluys, W. G. V. D. J. Chem. Educ. 2001, 78, 111.
25. (a) Sun, S.-S.; Lees, A. J. Chem. Commun. 2000, 1687; (b) Anzenbacher, P.; Tyson,
D. S., Jr.; Jursikova, K.; Castellano, F. N. J. Am. Chem. Soc. 2002, 124, 6232; (c)
Gimeno, N.; Li, X.; Durrant, J. R.; Vilar, R. Chem.dEur. J. 2008, 14, 3006; (d) Lee,
K.-S.; Lee, J. T.; Hong, J.-I.; Kim, H.-J. Chem. Lett. 2007, 36, 816.