Z. Liu et al. / Spectrochimica Acta Part A 71 (2008) 1212–1215
1213
Bruker ESQUIRE-3000plus LC–MS/MS spectrometer. Corrected flu-
orescence spectra were taken on a Hitachi F-4500 fluorescence
spectrophotometer with excitation and emission slits of 5.0/5.0 nm,
and absorption spectra were scanned on a Shimadzu UV224012PC
absorption spectrophotometer. Fluorescence quantum yields were
measured using quinine sulfate as a standard (0.546 in 0.5 mol L−1
H2SO4) [26]. Spectral titrations were carried out by injection of
aliquot of metal ion solution into fluoroionophore solution in a
1-cm quartz cell. Acetonitrile and deionized water for titrations
were redistilled, analytical grade metal salts were used as received
from commercial. Tris(hydroxymethyl)aminomethane hydrochlo-
ride (Tris–HCl) solution was prepared to pH 7.0 (5 mM).
2.2. Synthesis [24]
(1) Synthesis of phenylthiosemicarbazide: phenyl isothiocyanate
(0.540 g, 4 mmol) was dissolved in 30 mL of ethanol, and the
resulting solution was then slowly added to 50% hydrazine
hydrate (1.00 g, 10 mmol) in ethanol (10 mL). The mixed solu-
tion was stirred at room temperature for 8 h, and the white solid
was collected by filtration and recrystallized by ethanol.
Fig. 1. Absorption (a) and fluorescence (b) spectra of 1 (10 M) in CH3CN in the
presence of increasing concentration of Cu2+. The excitation wavelength was 320 nm.
(2) Synthesis of 1: phenylthiosemicarbazide (0.334 g, 2 mmol) was
dissolved in 20 mL of ethanol and added to a refluxing ethanol
solution of 0.728 g (2 mmol) 2-methoxybenzaldehyde. The
mixed solution was further refluxed for about 6 h, forming
white precipitate which was then filtered off under low pres-
sure and washed several times with ethanol. The product
was recrystallized from ethanol, and dried under vacuum for
4 h. mp: 153–155 ◦C, ESI-MS: M+ 284, Anal. Cacld. (%) for
C15H15N3OS: C, 63.13; H, 5.30; N, 14.73; O, 5.61; S, 11.24. Found
(%): C, 62.79; H, 5.43; N, 14.99; O, 5.82. 1H NMR (CDCl3, ı
ppm): 9.32 (s, 1H, NH), 9.22 (s, 1H, NH) 8.27 (s, 1H, CH),
7.88–7.86 (d, 1H, ArH), 7.69–7.67 (d, 2H, ArH), 7.42–7.38 (m, 3H,
ArH), 7.24–7.22 (d, 2H, ArH), 7.02–6.92 (m, 2H, ArH). 13C NMR
(100 MHz, CDCl3, ı ppm): ı 55.62, 111.25, 120.85, 121.46, 124.27,
126.05, 126.18, 128.75, 132.09, 137.92, 139.05, 158.46, 175.77.
(3) Synthesis of 2: the acetonitrile solution containing 2-
3
˚
˛ = 91.24(1), ˇ = 100.93(1), ꢂ = 92.466(8), V = 705.6(1) A , Z = 2,
Dc = 1.33 g/cm3, R1 = 0.0631, wR2 = 0.1701, GOF = 1.069, CCDC No.
657355.
The absorption spectrum of 1 in CH3CN exhibits a band peaked
at 337 nm with a shoulder at 311 nm and its molar extinction
coefficients of 2.92 × 104 and 2.47 × 104 L mol−1 cm−1, respectively
(Fig. 1a). In the presence of Cu2+, the band at 337 nm was attenuated
while a new peak appeared at 239 nm and a weak band at 450 nm
can be observed. Two clear isosbestic points at 278 and 357 nm were
observed during the spectral titration, indicating the formation of a
well-defined Cu2+–1 complex. A 1:2 stoichiometry of Cu2+ binding
to 1 was made evident from Job plots. The first binding constant of
Cu2+ with 1 in CH3CN evaluated by non-linearly fitting is at 105 M−1
orders of magnitude [25]. Similar spectral variations were observed
methoxybenzylidene-4-phenylthiosemicarbazide
(0.142 g,
0.5 mmol) and Cu(AcO)2 (1 mmol) stirred for 2 h at room
temperature, color of the solution turned to bright yellow. The
solution was dried over MgSO4, concentrated and the product
was separated by chromatographically on silica (elution with
EtOAc/petroleum ether = 1:2.5 (Rf = 0.3) to give yellow crystal
product. mp: 259–260 ◦C, ESI-MS: M+ 282, Anal cacld. (%) for
with the other tested transition metal ions such as Ag+, Zn2+, Hg2+
,
Co2+, and Ni2+ of which non-linear fitting data afforded first bind-
ing constants of comparable value at 105 M−1 orders of magnitude.
These observations indicate that Cu2+, Ag+, Zn2+, Hg2+, Co2+, and
Ni2+ bind to a similar extent to 1. Other metal ions like Li+, Ca+2
,
C
15H13N3OS: C, 63.58; H, 4.62; N, 14.83; O, 5.65; S, 11.32. Found
Pb+2, Fe+3, and Cd+2 had little effect on the absorption spectrum of
1.
(%): C, 63.73; H, 5.13; N, 14.14; O, 5.61. 1H NMR (CDCl3, ı ppm):
11.28 (s, 1H, NH), 7.38–7.43 (m, 5H, ArH), 7.34–7.37 (m, 2H,
ArH), 6.98–7.02 (m, 1H, ArH), 6.70–6.72 (d, 2H, ArH), 3.37 (s,
3H, CH3). 13C NMR (100 MHz, CDCl3, ı ppm): ı 55.14, 111.25,
121.12, 127.45, 128.94, 129.29, 131.83, 131.92, 133.06, 134.77,
157.33.
The fluorescence spectrum of 1 in CH3CN was obtained and
found to emit extremely weak fluorescence, but the fluorescence
was dramatically enhanced upon adding Cu2+ as can be seen in
sity changed with excess amount of Cu2+ added. Some metal ions
including Hg2+, Pb2+, Zn2+, Fe3+, Mn2+, and Li+ trigger little vari-
ations, while Cd2+, Ni2+, Ag+, Co2+, and Ca2+ do not affect on it
as can be seen in Fig. 2. The same experiment was carried out in
90:10 (v/v) CH3CN–H2O mixed solution and a prominent fluores-
cence enhancement was only observed for Cu2+ while the other
metal ions had very little effect on the fluorescence. These mean
that the fluorescent response of 1 show a high selectivity for Cu2+
against other tested metal ions even in CH3CN solution containing
10% water.
2.3. Crystal structure of 2
A
single
prism
crystal
with
dimensions
of
0.30 mm × 0.20 mm × 0.10 mm was selected for the X-ray diffrac-
tion and the reflection data were collected on Bruker SMART APEX
2000 CCD diffractometer operating with graphite-monochromated
˚
Mo K␣ radiation (ꢀ = 0.71073 A) in the range of 1.41 < ꢁ < 25. The
structure was solved by direct method and refined by full-matrix
least-squares technique against F2 using SHELX-97 package [27]. All
non-hydrogen atomswererefined anisotropicallyandthe hydrogen
atoms were placed in calculated positions and refined with a com-
mon isotropic thermal parameter. The crystal belongs to triclinic,
Fluorescence emission can be affected not only by metal ion
binding, but also by a metal ion promoted reaction. Cu(AcO)2 in
CH3CN can act as an effective oxidant for a variety of compounds,
therefore, it was presumed that Cu2+ could promote the oxidation
reaction of 1 into 2 in CH3CN. This was proved by the absorption
˚
space group P-1 with a = 6.9469(7), b = 9.6824(1), c = 10.699(1) A,