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measurement of the piazselenol formed by the reaction of sele-
nium (IV) with 2,3-diaminonaphthalene (DAN) [11–15]. The disad-
vantages of these methods are the time consuming and the use of
toxic and unstable reagents.
was further purified by column chromatography (silica gel, petro-
leum ether/ethyl acetate at 5:1). A white crystal (2-Chloro-N-phe-
nyl-acetamide, 90%) was obtained. 1H NMR: (Fig. S1, CDCl3/TMS,
25 °C), d(ppm): 4.227 (s, 2H), 7.29 (s, H), 7.39 (t, J = 7.95, 2H),
7.56 (d, J = 7.8, 2H), 8.28 (s, H). M:(m/z) 169.
In recent years, the design and development of luminescent
probes for the detection of a variety of chemical species have at-
tracted great interest due to the highly sensitive, quick, simple
and real time monitoring of the fluorescence [16]. For sensitivity
reasons, chemosensors exhibiting fluorescence enhancement
(turn-on) are favored over those showing fluorescence quenching
(turn-off). But for Se determination, only a few luminescent probes
were developed and reported [17,18]. So the development of fluo-
rescent response especially fluorescence turn-on Se probes has
great prospect and importance.
In this paper, we reported the development of a new turn-on
fluorescent probe for Se determination base on 2-(2-Formyl-4-
methyl-phenoxy)-N-phenyl-acetamide (FMPPA). The chemosensor
exhibits dramatic fluorescence enhancement after coordinated
with Se (IV). The selectivity of this chemosensor was perfect; most
common cations had no interference on Se (IV) determination. The
high selectivity and sensitivity of FMPPA towards Se (IV) suggested
its potential for use in the detection of trace amounts of Se (IV)
ions.
Synthesis of 2-(2-Formyl-4-methyl-phenoxy)-N-phenyl-acetamide
(FMPPA, II)
0.150 g (1.1 mmol) of 2-Hydroxy-5-methyl-benzaldehyde,
0.186 g (1.1 mmol) of 2-Chloro-N-phenyl-acetamide (I), 0.304 g
(2.2 mmol) of K2CO3, and 20 mL of DMF were mixed in a round
flask and stirred overnight under temperature controlled between
30 and 40 °C. The mixture was washed 3 times with ethyl acetate
and water (40 mL Â 3). The organic phase was collected and then
dried with anhydrous Na2SO4 for 3 h. The solvent was removed un-
der reduced pressure. The crude product was further purified by
column chromatography (silica gel, petroleum ether/ethyl acetate
at 20:1). A yellow powder (2-(2-Formyl-4-methyl-phenoxy)-N-
phenyl-acetamide, 80%) was obtained. 1H NMR: (Fig. S2, CDCl3/
TMS, 25 °C), d(ppm): 2.467 (s, 3H), 4.732 (s, 2H), 6.947 (d, J = 8.4,
H), 7.144 (t, J = 6.9, H), 7.452 (q, 3H), 7.634 (s, H), 7.915 (d,
J = 8.7, 2H), 9.87 (s, H), 10.148 (s, H). 13C NMR: (Fig. S3, CDCl3/
TMS, 25 °C), d(ppm): 20.326, 67.925, 113.468, 119.740(2C),
124.430, 124.737, 129.032(2C), 131.833, 136.092, 136.747,
137.840, 155.291, 165.823, 191.251. M:(m/z) 269.
Experimental
Materials and measurements
All of the chemical materials were purchased from Beijing
Chemical Reagents Company (Beijing, China) and used as received
without further purification unless otherwise stated. 1H NMR spec-
tra was obtained using a Varian Mercury 300 NMR spectrometer
with CDCl3 as an internal standard. All fluorescence measurements
were carried out on a RF-5301PC spectrofluorometer (Shimadzu,
Japan). The photomultiplier tube (PMT) voltage was 600 V, the scan
speed was 600 nm minÀ1, the excitation and emission slit widths
were 5 nm and 2.5 nm, respectively, otherwise specified.
Results and discussion
Photophysical properties
Since the fluorescent emission intensity of the FMPPA moiety is
very weak. The excitation and emission slits were set as 10 nm
respectively, in order to observe the solvent effect clearly. The
fluorescence excitation and emission spectra of FMPPA (Fig. 1a
and b respectively) showed a gradual red shift with increasing sol-
vent polarity in the order ethyl acetate < acetonitrile < ethanol.
Such a distinct red-shift of the absorption and emission of FMPPA
in polar solvents indicated an ICT (intramolecular charge transfer)
character for the excited state [19–21]. The maximum emission
wavelength of FMPPA in ethanol solution was located at ca.
420 nm, in the range of visible spectrum. It is convenient for the
analytical application in practice. And considering the limited
water solubility, ethanol solution was selected as the solvent
throughout. A Job’s plot was used to determine the binding stoi-
chiometry of FMPPA with Se (IV). The total concentration of the
probe and Se (IV) was held constant (5.264 Â 10À6 mol/L) while
altering the mole fraction of Se (IV), and the fluorescence enhance-
ment value was plotted against the mole fraction (Fig. 1c). The
maximum fluorescence enhancement was acquired at a Se (IV)
mole fraction of 0.33, indicating that FMPPA chelated Se (IV) with
2:1 stoichiometry.
Molecular structure and synthesis of FMPPA
The molecular structure and preparation of FMPPA is described
in Scheme 1.
There are two steps for the synthesis of FMPPA.
Synthesis of 2-Chloro-N-phenyl-acetamide (I)
0.453 mL of aniline, 0.140 mL of triethylamide, and 30 mL of
dichloromethane were mixed in a round flask for 20 min. Then
0.397 mL of chloroacetyl chloride was added in dropwise at 0 °C,
the mixture was warmed to room temperature and allowed to re-
act overnight. The solvent was washed 3 times with 10% HCl and
saturated salt water mixed solution. The organic phase was
collected and then dried with anhydrous Na2SO4 for 3 h. The
solvent was removed under reduced pressure, The crude product
H
N
O
NH
2
DCM
TEA
Cl
Cl
+
Cl
O
(I)
H
OH
O
N
O
DMF
H
N
+
O
O
2K2CO3
Cl
O
(II)
Scheme 1. Structure and synthesis procedure of FMPPA.