Y. Xu, et al.
JournalofPhotochemistry&PhotobiologyA:Chemistry392(2020)112348
Scheme 1. Synthesis routes of X. Conditions: (a) THF/ethanol, r.t./refluxed, 20 h/4 h; (b) ethanol, r.t., overnight; (c) ethanol, r.t., TsOH, 48 h.
moiety, which is often used to synthesize schiff base because of their
water solubility, good planarity and structural rigidity [41,42]. Mean-
while, heterocyclic azoles, containing imidazole and thiazole ring, are
important active molecules that can provide N or S as donor atoms to
bind metal ions [43,44]. The study of schiff base with heterocyclic and
julolidine structures is of great value and should be paid more attention.
Obviously, most of the sensors that have been reported are single-ion
responsive, and a few are capable of detecting multiple targets in re-
spective systems [45–48]. Multi-objective detection of metal ions can
better reflect the diversity of the properties of a sensor, which should be
valued and favored.
room temperature until the orange precipitate appeared. After the re-
action, the orange precipitate was collected by filtration and washed
with cold ethanol to obtain the pure orange solid X. Yield: 141 mg, 41.9
%. Ms (ESI): m/z = 382.14 [M+H]+, 404.12 [M + Na]+. FTIR (KBr,
cm−1): 3312 (N-H), 1673 (C = O), 1673 (C = N). 1H NMR (400 MHz,
DMSO) δ 12.03 (s, 1 H), 8.63 (s, 1 H), 8.55 (s, 1 H), 8.20 (d, J =4.5 Hz,
1 H), 7.64 (d, J =4.5 Hz, 1 H), 6.86 (s, 1 H), 3.38 (dd, J = 10.7, 5.1 Hz,
4 H), 2.85 – 2.77 (m, 4 H), 2.07 (dt, J = 11.2, 5.6 Hz, 4 H). 13C NMR
(101 MHz, DMSO) δ 157.73, 155.08, 151.27, 145.60, 140.81, 128.57,
125.97, 120.72, 116.72, 115.89, 112.88, 106.81, 106.43, 49.80, 49.34,
26.95, 22.00, 21.18, 20.69.
In this work, a new schiff base, X, was designed and synthesized by
a simple condensation of 8-hydroxy-2,3,6,7-tetrahydro-1H,5H-pyrido
[3,2,1-ij]quinoline-9-carbaldehyde and imidazo[2,1-b]thiazole-6-car-
bohydrazide. As expected, X could be used as a multifunctional sensor
with high sensitivity and selectivity for sequential detection of Zn2+
and PPi in acetonitrile buffer solution and for cyclic detection of In3+ in
DMF buffer solution.
3. Results and discussion
As shown in scheme 1 , X was designed and synthesized in medium
yield according to the synthetic route. Compound 1 (ethyl imidazo[2,1-
b]thiazole-6-carboxylate) and compound 2 (imidazo[2,1-b]thiazole-6-
carbohydrazide) were synthesized according to a previous report. Then,
X was synthesized by the reaction of Compound 1 and 2 with 41.9 %
yield in ethanol and characterized by 1H NMR (Fig. S1), 13C NMR (Fig.
S2), FTIR (Fig. S3), ESI-MS (Fig. S4). All of the data in the spectra were
in whole accordance with the structure.
2. Experimental section
2.1. General methods
3.1. The spectroscopic studies of X toward Zn2+ and P2O74− in acetonitrile
buffer solution
All reagents and solvents in this project were of analytical grade and
were used without any treatment. The counter anions of all metal ions
are chloride, sulfate or nitrate ions. All anionic solutions are corre-
sponding sodium or potassium solutions. The Stock solutions of the ions
(0.03 M) were prepared by distilled water and tap water. The stock
solution of X (1 × 10−5 M) was prepared in acetonitrile/H2O and
DMF/H2O at 25 ℃. The fluorescence spectral and UV–vis spectra were
obtained by Edinburgh Instruments Ltd-FLS920 Fluorescence
The fluorescence sensing properties of X toward various metal ions
(Zn2+, Ag+, Cr3+, Mg2+, In3+, Al3+, Co2+, Cu2+, Ga3+, K+, Li2+
,
Cd2+, Mn2+, Hg2+, Ni2+ and Fe3+) were explored in acetonitrile/
buffer solution (v/v = 9/1, tris =10 mM, pH = 7.4). As shown in
Fig. 1(a) and (b), the fluorescence intensity of X was weak under ex-
citation wavelength of 365 nm, which was significantly enhanced
(about 12 times) at 491 nm when Zn2+ was added, while the fluores-
cence intensity did not change in the presence of other metal ions [50].
Furthermore, fluorescence pictures of a solution of X in the absence and
presence of various metal ions under UV light were shown in Fig. 1(c).
Consistent with the fluorescence spectrum change, the color of the so-
lution was weak when no metal ions were present, had significant
change from colorless (Ф = 0.02) to bright yellow-green (Ф = 0.26)
when Zn2+ were added, demonstrating that X could be used as a sensor
for Zn2+. The UV–vis spectral studies of X toward various metal ions
were also shown in Fig. S5. Zn2+, Co2+, Cu2+, Mn2+ and Ni2+ could
cause significant changed in the UV spectrum, which mean that they
could form complexes with X. However, after complexing with X, their
optical phenomena under ultraviolet lamp were different. Furthermore,
competition experiments were also shown in Fig. S6. The presence of
Co2+ and Cu2+ could interfere with the specific recognition of Zn2+ by
X [51,52]. These results indicated that X could be used as a sensor for
Zn2+ even in the presence of most metal ions.
Spectrophotometer and Shimadzu 3100 spectrometer. 1H NMR and 13
C
NMR measurement was performed on a Bruker AV III NMR spectro-
meter with tatramethysilane (TMS) as internal standard and DMSO as
solvent at 400 and 100 MHz, respectively. Infrared spectral data was
obtained on a Bruker Vertex 70 FT-IR spectrometer using samples as
KBr pellets. The sensing mechanism of X to metal ions (Zn2+ and In3+
)
were examined by Density functional theory (DFT) calculation which
carried out by Gaussian 09 program based on B3LYP/6-31 G(d) and
B3LYP/LanL2DZ basis set [48].
2.2. Synthesis of X
Compound 1 and 2 were synthesized according to the previous re-
ported reference [49]. Synthesis of (E)-N'-((8-hydroxy-2,3,6,7-tetra-
hydro-1H,5H-pyrido[3,2,1-ij]quinolin-9-yl)methylene)imidazo
[2,1-b]thiazole-6-carbohydrazide (X). imidazo[2,1-b]thiazole-6-car-
bohydrazide (compound 2, 161 mg, 0.884 mmol) and 8-hydroxy-
2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinoline-9-carbaldehyde
(210 mg, 0.967 mmol) were mixed in 10 ml of ethanol. Then, 2 mg of
TsOH (4-methylbenzenesulfonic acid) as a catalyst were added to the
above reaction mixture. After that, the mixture was stirred for 48 h at
To further explore the sensing properties of X toward Zn2+, the
fluorescence and absorption titration spectral were carried out in
acetonitrile/buffer solution (v/v = 9/1, tris =10 mM, pH = 7.4). As
2