3
54
J.-C. Qin et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 152 (2016) 352–357
1
5
9
in DMSO-d
6
) (Fig. S4) d: 12.516 (s, 1H, H ), 11.589 (s, 1H, H ),
3.2. Fluorescence study
1
1,13
1,5
8
.822 (s, 2H, H
), 7.997 (d, J = 7.5 Hz, 2H, H ), 7.848 (d,
1
0,14
2,4
3
The effect of Al3+ on the fluorescence properties of the sensors
was investigated in ethanol. As shown in Fig. 2, the free sensors
A, B displayed weak fluorescence intensity upon excitation at
J = 6.0 Hz, 2H, H
.461 (s, 3H, CH
), 7.402 (m, 2H, H ), 7.111 (m, 1H, H ),
8
6
ꢁ1
2
(
3
, H ), and 2.377 (s, 3H, CH
Fig. S5): 3427, 1633, 1594. ESI–MS (Fig. S6): [M + 1] : 336.01.
3
, H ). IR (KBr, cm
)
+
+
+
3
69, 375 nm. Upon addition of several metal ions such as Na , K ,
+
2+
3+
2+
2+
3+
2+
3+
2+
2+
2+
2+
Ag , Ca , In , Cd , Co ,Ga , Ni , Fe , Mn , Mg , Pb , Cu
,
Cr , Ba , Zn and Al3+ , the fluorescence of A, B were only signif-
3
+
2+
2+
3
. Results and discussion
.1. UV–Vis analysis
The sensors properties were initially investigated as a function
icantly enhanced with fluorescence emission wavelength change
3
+
3
from 557 to 450 nm in the presence of Al , the changes of fluores-
cence intensity could be better exhibited through fluorescence
titrations. As shown in Fig. 3, with addition of increasing concen-
3+
3
+
of the concentration of Al by UV–Vis analysis in ethanol. In the
tration of Al , the sensor showed maximum fluorescence emission
3
+
3
+
presence of Al , the changes of the absorption spectra were similar
between the sensor A and the sensor B, the the extent of variation
were different as shown in Fig. 1. The maximum absorption wave-
at about 450 nm which are because the addition of Al resulted in
inhibiting photo-induced electron transfer (PET) process
(
Scheme 2). More specifically, the fluorescence bands of the sen-
3+
length was observed at about 380 nm in the absence of Al . Upon
3+
sors without Al at about 450 nm were with low intensity due
to the quenching mechanism by photo-induced electron transfer
3
+
titration of Al , the absorption band at about 380 nm gradually
disappeared and a new absorption bands appeared at 300 nm with
increasing intensity. Moreover, a clear isosbestic points at 350 nm
appeared which clearly indicated the presence of new complex in
equilibrium with the receptor. All of these might be attributed to
the interaction the sensors with Al3 which were further confirmed
by ESI–MS, IR.
(PET) which was induced by lone pair electrons from the nitrogen
3
+
atom of –C@N. After addition of Al , because of the chelation of
+
Fig. 2. (a) Fluorescence spectra of A (10 lM) upon the addition of metal salts (9.0
2+
+
+
+
2+
3+
2+
3+
2+
3+
2+
2+
2+
2+
equiv.) of Na , K , Ag , Ca , In , Cd , Co ,Ga , Ni , Fe , Mn , Mg , Pb , Cu
,
3+
2+
2+
3+
Fig. 1. (a) Changes in the absorption spectra of A (10
temperature as a function of added Al(NO (0,1, 2, 3, 4, 5, 6, 7, 8, 9, 10
Changes in the absorption spectra of B (10 M) in ethanol at room temperature as a
function of added Al(NO (0,1, 2, 3, 4, 5, 6, 7, 8, 9, 10 M).
lM) in ethanol at room
Cr , Ba , Zn , Al in ethanol (slit widths: 3 nm/3 nm). (b) Fluorescence spectra of
+
+
+
2+
3+
)
3 3
lM). (b)
B (10 lM) upon the addition of metal salts (6.0 equiv.) of Na , K , Ag , Ca , In ,
2+ 2+
3+
2+
3+
2+
2+
2+
2+
3+
2+
2+
3+
l
Cd , Co ,Ga , Ni , Fe , Mn , Mg , Pb , Cu , Cr , Ba , Zn , Al in ethanol (slit
widths: 3 nm/3 nm).
)
3 3
l