H. Wang et al.
Journal of Photochemistry & Photobiology, A: Chemistry 405 (2021) 112958
Fig. 5. Anti-interference experiments between 1O at the methanol solution and
different metal ions (5 equiv.) Black Blank: 1O and different metal ions Red
Fig. 4. The emission intensity of 1O’ irritated by UV/Vis light.
Blank: 1O and different metal ions added with Al3+
.
from colorless to Aqua green. Meanwhile, after the other metal ions were
added in the 1O solution, the fluorescence intensity remained.
Furthermore, the free ligand 1O and the metal complex 1O’ were
determined its fluorescence quantum yield as 0.007 and 0.058, and
Except for aluminum metal ligands, the fluorescence quantum yield of
other metal ligands is basically unchanged as 1O. Therefore, 1O could
serve as a highly selective chemosensor for the detection of Al3+ even
competing with other metal ions in methanol.
Al3+. As shown in Fig. 5, the other ions had no influence on the detection
of Al3+, except there was a mild inhibition with Fe3+. This shows its
excellent anti-interference performance, which provides us with the
possibility of detecting actual water samples in the future.
3.4. The mechanism of 1O detecting Al3+
Job’s plot of the irradiation with UV/Vis light, as the alteration of
Al3+: Al3++1O, was used to study the relationship between the emission
intensity and the ratio of Al3+ over Al3++1O in methanol. As shown in
Fig. 6, when the molar ratio of Al3+ over Al3++1O reached to 0.5, the
emission intensity reaches the maximum, suggesting that the combina-
tion ratio of 1O and Al3+ probably was 1:1. Meanwhile, according to the
Benesi-Hildebrand equation, the associated constant (Ka) between 1O
and Al3+ in methanol was 4.15 × 104 Mꢀ 1 (R = 0.99387) (Fig. 6B). As
shown in (Fig. 6C), the limit of detection (LOD) of 1O to Al3+ could
reach to 3.26 × 10-8 mol L-1.
3.3. Fluorescence properties of 1O toward Al3+
The fluorescence titration experiments in methanol were done to
explore the relationship between the fluorescence emission intensity
and the concentration of Al3þ. As shown in (Fig. 3A), without Al3þ in the
methanol solution of 1O, no fluorescence emission was observed. With
the addition of Al3+, the fluorescence emission intensity was increased
quickly with a new peak appearing at 533 nm. When the quantity of Al3+
was more than 4 equiv., the fluorescence emission intensity reached the
maximum of 1758. In the fluorescence titration, a new complex 1O þ
Al3þ (1O’) was formed with the color from dark to aqua green.
Reversely, with the addition of EDTA solution, the fluorescence emission
intensity of 1O’ methanol solution descended steadily. When excessive
EDTA was added in the 1O solution, the emission recovered to the
original state, and the color changed from aqua green to dark. Because
the reaction between 1O and Al3+ was reversible, after the addition of
Al3+, 1O reacted Al3+ to form 1O’ with the chelation enhancement
fluorescence (CHEF) effect. Additionally, as shown in (Fig. 3B), within a
certain rang, the concentration of Al3+ had a linearship with the emis-
sion intensity of 1O methanol solution.
The stoichiometry between 1O and Al3+ was further confirmed as 1:1
according to the ESI mass spectrometry (ESI-MS). As shown in Fig. S3,
there was a peak at 738.1353 m/z which contributed to [1O-H]ꢀ . As
shown in (Fig. S4), a new peak at 888.0850 m/z was observed and the
peak could be considered as [1O+Al3++2NO3ꢀ -2 H]ꢀ . 1H NMR titration
experiments in acetonitrile were carried out to confirm the binding
mode between 1O and Al3+. Results showed that the peak at 11.74 was
from the hydrogen of hydroxyl of 1O. With the addition of Al3+ from 0 to
5 equivalents, this peak descended gradually and even disappeared,
indicating that the bind of hydroxyl of 1O was dissociated with the
3+
titration of Al3+ and OA
was formed. Meanwhile, the height of
–
l
–
proton ( NH) peak at 10.73 ppm showed a downward trend with a shift
of 0.01 ppm from 10.73 ppm to 10.74 ppm, which proved that the
As shown in Fig. 4, upon the irradiation of UV light (297 nm), 1O’
formed into 1C-Al3+ (1C’) with the fluorescence emission decreasing
and the solution color changing from aqua green to dark green. When
the PSS was reached, the fluorescence emission intensity was down close
to 0. Reversely, with the stimulation of visible light (λ>500 nm), the 1C’
solution could recover to the state of 1O’, and the fluorescence emission
intensity gradually ascended. The color of solution steadily changed
from aqua green to dark green. The above characteristics indicated that
1O can act as a reversible fluorescence switch and can be used to
construct molecular logic switches.
3+
3+
–
l
–
bond and another O Al bond. As shown in
formation of NA
–
Fig. 7, the benzyl N H did not change during the experiment, indicating
that the carbonyl oxygen atom in the amide structure was not involved
in the coordination. Therefore, a detecting mechanism of 1O to Al3+
could be proposed and shown in the Fig. 7.
4. The application of logic circuit
Due to the fluorescence of 1O in methanol can be adjusted with UV/
Vis, Al3+ and EDTA, ultraviolet, visible light, the concentration of Al3+
and EDTA can be considered as input signals and the fluorescence of 1O
as output signal. Here, as shown in Fig. 8, a logic circuit was created with
the signals of ultraviolet, visible light, aluminum ion and EDTA as input
signals of InA, InB, InC and InD, respectively, and with the fluorescence
To confirm the selectivity of 10 to Al3+ over other ions, the anti-
interference experiments were done through observing the change of
emission intensity at 533 nm. Al3+ was added in the 1O methanol so-
lution containing 5 equivalents of another metal ion, such as Zn2+, Fe3+
,
Cu2+, Mg2+, Pb2+, K+, Mn2+, Ba2+, Sr2+, Cd2+, Cr3+, Co2+, Hg2+ and
4