M. Iniya et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 120 (2014) 40–46
41
[
[
10], napthalic anhydride [11], anthracene [12] and cyclen moiety
13]. Tang et al. reported that dipicolylamine appended quinoline
Synthesis of 4-amino-3-phenyl-1H-1,2,4-triazole-5(4H)-thione (3)
2
+
senses Zn over othercompeting cations, based on chelation en-
hanced fluorescence [14]. Ferrocenyl seleno unit has been utilized
for the fluorescent detection of Zn2 based on ICT mechanism by
Jing et al. [15]. Recently Zhao et al. reported 1,8 naphthalimide con-
A mixture of methyl benzoate (1.36 ml, 1 mM) and hydrazine
hydrate (0.5 ml, 1 mM) was allowed to reflux for 6 h. The total vol-
ume of the solution was reduced to half and it was cooled in ice
water. The crystals formed were filtered, washed thoroughly with
water to yield benzoic acid hydrazide (1). The benzoic acid hydra-
zide (1.36 g, 1 mM) was treated with alcoholic solution of KOH
(0.84 g, 1.5 mM) and carbondisulphide (1.45 ml, 1.5 mM) for 15 h
at room temperature with constant stirring. After dilution with
anhydrous ether, precipitated potassium 3-benzoyl dithiocarbazi-
nate (2) was washed with anhydrous ether and dried under vac-
+
2+
taining receptor for Zn and successfully applied it to detect
2
+
endogenous Zn ions in live cells [16]. Considerable efforts like
this have been made towards the design and synthesis of various
fluorescent chemo-sensors for the in vitro and in vivo detection
of Zn . However most of reported sensors lack either ratiometric
response, or bio-compatibility besides suffering from interference
2
+
2
+
of Cd ions. To the best of our knowledge, very few chemosensors
satisfying the above-mentioned requirements have been reported.
Therefore, the design of simple and easily accessible Zn(II) selective
ratiometric chemosensor is still a challenge. Amongst the different
photo physical processes, Excited State Intramolecular Proton
Transfer (ESIPT) has gained a special status due to unique emission
features such as the large stokes shift and the transient character of
ground state of emissive species of ESIPT chromophores (i.e. the
keto tautomer) [17]. ESIPT facilitates fluorescence probing of
chemicals, bio-molecules, and ions due to its unique spectral sen-
sitivity to environmental medium [18]. The fluorescence of ESIPT
chromophores can be perturbed by many intermolecular interac-
tions, such as removal of the hydrogen involved in the ESIPT pro-
cess, thus paving way for sensing metal ions [19]. Triazoloyl-
containing compounds especially 1,2,3-triazoles have been em-
ployed as fluorescent indicators for metal ions [20] and recently,
uum.
To
the
suspension
of
potassium
3-benzoyl
dithiocarbazinate (2.49 g, 1 mM) in water, hydrazine hydra-
te(1.5 ml, 3 mM) was added and refluxed for 3 h with occasional
shaking. It was diluted with water; acidified and resulting solid
was filtered, washed thoroughly with water and recrystallized
1
from ethanol to yield (3). H NMR (300 MHz, DMSO-d
6
): 7.7 (m,
5H, Ar-H), 7.9 (s, 2H, NH
(3 + H)
2
), 3.5 (s, 1 H, HN-C). MS (ESI) m/z: 193
+
Synthesis of 4-((2-hydroxynaphthalen-1-yl)methyleneamino)-3-
phenyl-1H-1,2,4-triazole-5(4H)-thione (TZNP)
A mixture of 4-amino-3-phenyl-1H-1,2,4-triazole-5(4H)-thione
(
1.92 g, 1 mM) (3) and 2-Hydroxy-1-napthaldehyde (1.72 g, 1 mM)
in hot ethanol was treated with concentrated HCl (0.5 ml) and al-
lowed to reflux for 3 h. The solid formed on cooling was filtered,
washed with cold ethanol, then dried and recrystallized from eth-
anol to yield TZNP. Yield, 70%; Anal. Found: C: 65.6, H: 4.1, N: 16.3,
1
,2,4-triazole moiety has been utilized for electrochemical sensing
of Gd(III) ion, and L-tyrosine [21,22]. The derivatives of 1,2,4-tria-
zoles are well known for its wide range of therapeutic properties
1
S: 9.4. Cal. for: C: 65.4, H: 3.9, N: 16.1, S: 9.2%. H NMR (300 MHz,
[
23], this work adds a new dimension to the class of 1,2,4-triazoles
DMSO-d
H, OH) and 13.5 (s, 1 H, HN-C); C NMR (75 MHz, DMSO-d ):
d = 166.4, 162.9, 160.6, 148.8, 136.4, 132.2, 131.1, 129.3, 129.1,
29.0, 128.7, 128.4, 125.9, 124.3, 123.8, 118.8, 108.7; MS (ESI) m/
6
): d = 6.41–7.91 (m, 11H, ArH), 9.42 (s, 1H, CH@N), 10.4 (s,
2
+
as an ESIPT based fluorescent sensor for the recognition of Zn
over other metal ions with significant increase in fluorescence.
In continuation of our ongoing research for the development of
fluorescent chemosensors [24–28], herein, we report the synthesis
and photonics of a triazole appended simple fluorescent chemo-
sensor namely 4-((2-hydroxynaphthalen-1-yl)methyleneamino)-
13
6
1
1
+
z: 347 (TZNP + H) ;
Cation recognition studies and quantum yield calculation
3
-phenyl-1H-1,2,4-triazole-5(4H)-thione (TZNP). This probe exhib-
its features such as large stoke shifted emission, ratiometric re-
sponse in addition to sensing Zn2 with high sensitivity and
excellent selectivity. Apart from this it has good cell-permeability
and bio-compatibility.
The recognition properties of TZNP towards cations were inves-
tigated in DMSO/H O (2:8 v/v) system through UV–Vis and Fluo-
2
+
rescence measurements. The solutions of metal ions
ꢂ3
(
1 ꢁ 10 mol/L) were prepared in distilled water. A solution of
ꢂ5
TZNP (1 ꢁ 10 mol/L) was made up with DMSO solvent. Different
ion solutions were added in portions to TZNP and absorption/fluo-
rescent intensity changes were recorded at room temperature after
Materials and methods
General
each addition. The fluorescence quantum yield
s
U was estimated
from the absorption and fluorescence spectra of probe according
to Eq. (1), where the subscript s and r stand for the sample and ref-
All the chemicals used were of analytical reagent grade and pur-
chased from Sigma–Aldrich Chemical Company. Solvents used
were of HPLC grade unless otherwise stated. Binding properties
of metal ion with TZNP were evaluated by chloride salts of metal
erence (rhodamine B,
f
U = 0.97 in ethanol), respectively. U is the
quantum yields, A represents the absorbance at the excitation
wavelength, S refers to the integrated emission band areas and
+
+
2+
2+
2+
3+
+
2+
2+
2+
ions such as K , Na , Ca , Fe , Mg , Fe , Ag , Mn , Cu , Co
,
n
D
is the solvent refractive index.
Ni , Cd , Cr , Pb and Hg2+ ions. Metal solutions were prepared
with Double distilled water. UV–Vis absorption spectra were re-
corded using JASCO V-550 spectrophotometer. Fluorescence spec-
2
+
2+
3+
2+
2
S A n
S
r
DS
uS
¼
ur
ð1Þ
2
S
R
A
S
n
Dr
tra measurements were performed on
a
F-4500 Hitachi
fluorescence spectrophotometer. The excitation and emission slit
1
13
width was kept constant at 5 nm. H and C NMR spectra were re-
corded on a Bruker 300 MHz NMR instrument. IR spectra in KBr
discs were recorded using JASCO FT-IR Spectrophotometer. Electro-
spray Ionisation mass spectral (ESI–MS) analysis was performed in
the positive ion mode on a liquid chromatography–ion trap mass
spectrometer (LCQ Fleet, Thermo Fisher Instruments Limited, US).
Computational details
Density functional theory (DFT) calculations were performed
*
with 6-31G and LANL2DZ basis set using Gaussian 03 program
to understand the turn on fluorescence behavior of TZNP on com-
2
+
plexation with Zn . The geometries of keto and enol form of TZNP
2
+
Fluorescence quantum yields (
U
f
) were determined with respect
= 0.97).
and TZNP-Zn were optimized by DFT-B3LYP using 6-31G and
LANL2DZ basissets respectively.
to Rhodamine B in ethanol solution (
U
f