A novel colorimetric and fluorescent probe for trivalent cations based on rhodamine B derivative

Article abstract of DOI:10.1016/j.jphotochem.2017.10.005

A novel Schiff-base (HL) based on rhodamine B derivative was designed and synthesized as a highly selective and sensitive “turn-on” fluorescent probe for M³⁺ (Cr³⁺, Fe³⁺, and Al³⁺) in methanol. Upon addition of M³⁺, the spirolactam ring (colorless and nonfluorescent) of HL was opened to the ring-open forms (pink and orange-yellow fluorescence). These results indicated that HL could be used as a colorimetric and fluorescent probe for the detection of M³⁺ with low detection limit of 0.63 μM (Cr³⁺), 0.14 μM (Fe³⁺), and 0.22 μM (Al³⁺). The binding constant (Ka) of M³⁺ binding to HL were calculated to be 0.87 × 10⁴ M^?1 (Cr³⁺), 1.14 × 10⁴ M^?1 (Fe³⁺), and 4.48 × 10⁴ M^?1 (Al³⁺), respectively from a Benesi-Hildebrand plot. The binding stoichiometry between HL and M³⁺ was determined from the Job's plot (fluorescent spectrum) and ESI–MS spectrum data to be 1:1. Furthermore, the recognition process of the probe for M³⁺ was chemically reversible on the addition of fluorinion (F^?).

Full text of DOI:10.1016/j.jphotochem.2017.10.005

Journal of Photochemistry and Photobiology A: Chemistry 351 (2018) 1–7
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Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
A novel colorimetric and fluorescent probe for trivalent cations based
on rhodamine B derivative
*
Xiao-li Yue, Chao-rui Li, Zheng-yin Yang
College of Chemistry and Chemical Engineering, State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, PR China
A R T I C L E I N F O
A B S T R A C T
Article history:
A novel Schiff-base (HL) based on rhodamine B derivative was designed and synthesized as a highly
selective and sensitive “turn-on” fluorescent probe for M3+ (Cr3+, Fe3+, and Al3+) in methanol. Upon
addition of M3+, the spirolactam ring (colorless and nonfluorescent) of HL was opened to the ring-open
forms (pink and orange-yellow fluorescence). These results indicated that HL could be used as a
Received 7 August 2017
Received in revised form 2 October 2017
Accepted 3 October 2017
Available online 5 October 2017
colorimetric and fluorescent probe for the detection of M3+ with low detection limit of 0.63 M (Cr3+),
m
0.14 m m
M (Fe3+), and 0.22 M (Al3+). The binding constant (Ka) of M3+ binding to HL were calculated to be
Keywords:
0.87 ꢀ104 Mꢁ1 (Cr3+), 1.14 ꢀ104 Mꢁ1 (Fe3+), and 4.48 ꢀ 104 Mꢁ1 (Al3+), respectively from a Benesi-
Hildebrand plot. The binding stoichiometry between HL and M3+ was determined from the Job’s plot
(fluorescent spectrum) and ESI–MS spectrum data to be 1:1. Furthermore, the recognition process of the
probe for M3+ was chemically reversible on the addition of fluorinion (Fꢁ).
Fluorescent probe
Colorimetric
Rhodamine B
Ring-open
Trivalent cations
Reversibility
© 2017 Elsevier B.V. All rights reserved.
1. Introduction
hemochromatosis, liver damage, diabetes, and Parkinson’s disease
[19–22]. Therefore, it’s significant to design and synthesize optical
The design and synthesis of new chemosensors for trivalent
metal ions (M3+) is an important research subject because of their
biological significance and environmental importance. For in-
stance, as the third most abundant metal in the Earth’s crust,
aluminum is widely used in aluminum alloy, aircraft, automobiles,
trains, ships and other manufacturing industries [1–8]. However,
overdose of Al3+ not only disturbs Ca2+ metabolism, decreases liver
and kidney function, but also causes Alzheimer’s disease and
osteoporosis [9–12]. Cr3+, an essential trace element in human
nutrition, affects the metabolism of carbohydrates, fats, proteins
and nucleic acids through activating certain enzymes and
stabilizing proteins and nucleic acids. Excessive Cr3+ has a negative
impact on cellular structure, cellular function, glucose levels, and
lipid metabolism, while deficient Cr3+ may cause diabetes and
cardiovascular disease [13,14]. Moreover, industrial runoff of Cr3+
chemosensors for detecting the presence of trivalent cation ions
(Cr3+, Fe3+, and Al3+) in environmental and biological samples.
Over the past few years, a large number of chemosensors for
trivalent metal ions (Cr3+, Fe3+, and Al3+) have been reported [23–
28]. Barba-Bon et al. described a highly selective fluorescent probe
for trivalent cation ions (Cr3+, Fe3+, and Al3+) based on derivative of
fluorescein [11]. Recently, Samanta also reported a new fluorogenic
probe for sensing of trivalent cations in live cells [28]. However, the
two probes may face some challenges in bioimaging application
due to indigo fluorescence (475 nm) [11] and green fluorescence
(509 nm) [28]. In vivo fluorescence tracking studies, emission at
longer wavelengths is satisfactory because of the improved photon
tissue penetration and reduced background autofluorescence,
especially emission in the NIR region [29–32]. Tang et al. developed
a
fluorescent probe emitting red fluorescence for detecting
may cause adverse impact on industry and agriculture [15,16]. Fe3+
,
trivalent cations [12]. However, the probe had poor selectivity
for trivalent cations because it also responded towards Hg2+ in
similar condition.
The rhodamine B derivatives are excellent fluorophores due to
large molar extinction coefficient, high fluorescence quantum
yield, and long absorption, emission wavelengths. On the basis of
the equilibrium between spirocyclic (non-fluorescent) and ring-
open forms (highly fluorescent) [33–35], we designed and
synthesized a new turn-on fluorescent probe for the detection
of trivalent cations. The rhodamine B skeleton was used as the
an essential trace element in biological systems, plays an
important role in many chemical and biological processes such
as electron transfer reactions and oxygen transport due to its
adequate redox potentials and high affinity for oxygen [17,18].
Overdose of Fe3+ may cause some dysfunction of heart, pancreas,
and liver, while the deficiency of Fe3+ may also cause anemia,
* Corresponding author.
E-mail address: yangzy@lzu.edu.cn (Z.-y. Yang).
https://doi.org/10.1016/j.jphotochem.2017.10.005
1010-6030/© 2017 Elsevier B.V. All rights reserved.

2
X.- Yue et al. / Journal of Photochemistry and Photobiology A: Chemistry 351 (2018) 1–7
fluorophore and chromophore and the (4-Hydroxybenzoyl)hydra-
zine was used as the recognition group. The introduce of a hydroxyl
group in the terminal benzene ring could strengthen the electron
water and dried under reduced pressure to give the final product in
the field of 64%. Melting point: 192–195 ꢂC. 1H NMR (400 MHz,
CDCl3, TMS) (Fig. S1): dH ppm 1.16 (t,12H, NCH2CH3, J = 6.8 Hz), 3.33
(q, 8H, NCH2CH3, J = 6.8 Hz), 3.60 (s, 2H, NꢁꢁNH2), 6.28 (m, 2H),
cloud density of the para-position (C O) to enhance the oxygen
¼
coordination ability. The probe, 2-[[30,60-bis(diethylamino)-3-
oxospiro[1-isoindoline-1,90-xanthen]-2-yl]imino
6.41-6.46 (m, 4H), 7.09-7.11 (m, 1H), 7.44 (m, 2H), 7.92 (m, 1H). 13
C
NMR (400 MHz, CDCl3, TMS) (Fig. S2): dC ppm 12.63 (CH3), 44.88
]acetaldehyde-(4-hydroxybenzoyl)hydrazone (HL) exhibited
high selectivity towards trivalent cations over commonly mono-
valent and divalent metal ions in methanol. Significantly, the
binding of HL and trivalent cations was chemically reversible by
the addition of Fꢁ solution.
(CH2), 66.33, 98.08, 104.67, 108.12, 122.95, 124.24, 128.17, 130.35,
133.00, 149.12, 151.65, 154.33, 166.53 (C O).
¼
2.2.2. Synthesis of 2-[[30,60-bis(diethylamino)-3-oxospiro[1-isoindole-
1,90-xanthe-n]-2-yl]imino]acetaldehyde (2)
Rhodamine B hydrazine (0.46 g) was dissolved in absolute
ethanol (30 mL). An excess of glyoxal (2 mL) was added, and the
mixture was stirred overnight at room temperature. Then plenty of
saturated potassium chloride solution was added to precipitate the
crude product. The crude product was collected, washed with
ethanol and water, and dried under reduced pressure. 1H NMR
(400 MHz, CDCl3, TMS) (Fig. S3): dH ppm 1.16 (t, 12H, NCH2CH3,
J = 6.4 Hz), 3.33 (q, 8H, NCH2CH3, J = 6.4 Hz), 6.25 (d, 2H, Ar-H,
J = 8.4 Hz), 6.40-6.46 (m, 4H, Ar-H), 7.10 (d, 1H, Ar-H, J = 7.6 Hz), 7.38
2. Experimental section
2.1. Materials and instruments
Rhodamine B and cationic salts such as Al(NO3)3, Ba(OAc)2, Ca
(NO3)2, Cd(OAc)2, Co(OAc)2, Cr(NO3)3, Cu(NO3)2, Fe(NO3)2, Fe
(NO3)3, K(OAc), Mg(NO3)2, Mn(NO3)2, NaClO4, Ni(NO3)2, Pb
(OAc)2, Zn(NO3)2, Li(NO3), Ag(NO3), and HgCl2 were obtained from
commercial suppliers and used without further purification. 1H
NMR spectrum were measured on the JNM-ECS 400 MHz
spectrometer. Chemical shifts are reported in ppm using TMS as
an internal standard. ESI–MS were determined on a Bruker esquire
6000 spectrometer. UV–vis absorption spectrum were measured
with a Shimadzu UV-240 spectrophotometer. Fluorescence spec-
trum were determined on a Hitachi RF-4500 spectrophotometer
equipped with quartz cuvettes of 1 cm path length. The melting
point was determined on a Beijing XT4–100 x microscopic melting
point apparatus.
(d, 1H, CH
J = 7.2 Hz), 9.44 (d, 1H, CH
TMS) (Fig. S4): dC ppm 12.69 (CH3), 44.45 (CH2), 66.05, 98.17,
¼
N, J = 7.2 Hz), 7.46-7.56 (m, 2H, Ar-H), 8.04 (d, 1H, Ar-H,
¼
O, J = 7.6 Hz). 13C NMR (400 MHz, CDCl3,
103.79, 108.27, 123.95, 124.14, 126.72, 127.82, 128.82, 134.74, 141.21,
149.32, 152.66, 153.04, 166.04 (C O), 192.71 (CHO).
¼
2.2.3. Synthesis of 2-[[30,60-bis(diethylamino)-3-oxospiro[1-isoindole-
1,90-xanthe-n]-2-yl]imino]acetaldehyde-(4-hydroxybenzoyl)
hydrazone 3 (HL)
2-[[30,60-bis(diethylamino)-3-oxospiro[1-isoindole-1,90-
xanthen]-2-yl]imino]acetaldehyde (0.2483 g, 0.5 mmol) and (4-
hydroxybenzoyl)hydrazine (0.0761 g, 0.5 mmol) were mixed in
40 mL ethanol and refluxed overnight under N2. After cooling to
room temperature, the precipitate was collected, washed with cold
ethanol, and dried in vacuum. Yields: 40%. Melting point: 218 ꢂC. 1H
NMR (400 MHz, DMSO-d6, TMS) (Fig. S5): dH ppm 11.68 (s, 1H),
10.17 (s, 1H), 7.98 (s, 1H), 7.92 (d, 1H, J = 7.6 Hz), 7.85 (s, 1H), 7.79 (d,
1H, J = 8.8 Hz), 7.70 (d, 2H, J = 8.8 Hz), 7.60 (t, 1H, J = 7.6 Hz), 7.55 (t,
1H, J = 7.6 Hz), 7.06 (d, 1H, J = 7.6 Hz), 6.85 (dd, 2H, J = 8.8 Hz,
J = 16.8 Hz), 6.45 (d,1H, J = 2 Hz), 6.43 (s,1H), 6.41 (s,1H), 6.37 (d,1H,
J = 2.4 Hz), 6.35 (d, 1H, J = 2.4 Hz), 3.36-3.29 (q, 8H), 1.09 (t, 12H,
J = 6.8 Hz). 13C NMR (400 MHz, DMSO-d6, TMS) (Fig. S6): dC ppm
30.36 (CH3), 55.35 (CH2), 98.44, 106.99, 112.50, 119.03, 119.35,
2.2. Synthesis
(4-Hydroxybenzoyl)hydrazine was synthesized according to
the method reported [36]. The HL was synthesized according to the
route as shown in Scheme 1.
2.2.1. Synthesis of rhodamine B hydrazine (1)
To a 0.8 g of rhodamine B dissolved in 30 mL of methanol, an
excessive hydrazine hydrate (1 mL) was added and then the
reaction solution was refluxed till the pink color disappeared. After
cooling to room temperature, the solvent was removed under
reduced pressure. The precipitate was washed with deionized
Scheme 1. The synthetic route of 2-[[30,60-bis(diethylamino)-3-oxospiro[1-isoindole-1,90-xanthen]-2-yl]imino]acetaldehyde-(4-hydroxybenzoyl)hydrazone (HL). Reagents
and conditions: (a) methanol, hydrazine hydrate, 65 ꢂC, reflux, 12 h, compound 1 Yields: 64%; (b) absolute ethanol, glyoxal, saturated potassium chloride solution, room
temperature, 24 h, compound 2 Yields: 72%; (c) absolute ethanol, 80 ꢂC, reflux, 24 h, compound 3 Yields: 40%.

X.- Yue et al. / Journal of Photochemistry and Photobiology A: Chemistry 351 (2018) 1–7
3
122.28, 123.46, 124.28, 127.95 (3 ꢂC), 103.96, 119.07, 119.18, 122.13,
139.35, 142.11, 149.20, 151.81 (4 ꢂC). ESI–MS (Fig. S7) calculated for
[M + H]+ 631.7452, found 631.3431.
any significant color and spectral changes under the identical
conditions, except for Cu2+, which resulted in a slight change of
absorbance at 558 nm. Whereas, when the solution containing HL
and Cu2+ was subjected to fluorescence, the solution showed no
fluorescence (Fig. 3) due to the paramagnetic nature [39–41].
2.3. UV-vis and fluorescence spectra measurements
In addition, the absorption titrations of HL (50
in methanol were carried out (Fig. 2). Upon addition of M3+ (0–
100 M), the absorbance band at 558 nm gradually increased with
m
M) towards M3
Stock solutions of 5 ꢀ10ꢁ3 M various metal ions and HL were
prepared in ethanol and DMF, respectively. Additionally, the stock
solution of NaF was also prepared in distilled water. All absorption
and emission spectrum were performed in a quartz optical cell of
1 cm optical path length at room temperature. All fluorescence
measurements were carried out upon excitation at 480 nm, and the
emission was recorded from 500 to 700 nm. Both excitation and
emission slit widths were 3 nm.
+
m
the increase of M3+ concentration. Simultaneously, the absorbance
bands (262 and 293 nm for Cr3+, 266 and 290 nm for Fe3+, 265 and
292 nm for Al3+) increased, while the bands (278 and 323 nm for
Cr3+, 277 and 322 nm for Fe3+, 277 and 325 nm for Al3+) decreased.
These results clearly illustrated the process of M3+ metal ions-
induced the ring opening of the spirolactam.
3. Results and discussion
3.2. Fluorescence studies of HL towards M3+
The fluorescent emission of HL (50
m
M) towards trivalent
The emission of HL (50
Na+, K+, Ag+, Ca2+, Mg2+, Ba2+, Zn2+, Cu2+, Fe2+, Ni2+, Cd2+, Co2+, Pb2+
m
M) towards various metal ions (Li+,
cations showed an excitation-independent feature due to the
relative uniform surface state and size distribution [37,38]. As the
excitation wavelength varied from 360 to 480 nm (Fig. S8), their
maximum emission was all located at 583 nm, the strongest
emission intensity was obtained when the excitation wavelength
was fixed at 480 nm. Fig. S9 demonstrated fluorescent emission
data in different solvents. It could be seen in Fig. S9 that the
emission maximum was observed in methanol. To find out the
effect of water content in the fluorogenic response of HL towards
trivalent cations, we recorded the emission changes of HL towards
M3+ in different fractions of water-methanol mixture and the
strongest emission was obtained in absolute methanol (Fig. S10).
Therefore, further UV/vis and fluorescent studies were carried out
in absolute methanol.
,
Mn2+, Hg2+, Cr3+, Fe3+, and Al3+) was shown in Fig. 3. HL alone did
not exhibited any fluorescent emission in methanol, which
suggested that HL still existed in spirolactam form. Upon addition
of M3+, a new and strong emission band at 583 nm (orange-yellow
fluorescence) was observed, which indicated that M3+ induced the
ring-open formation of HL. However, other monovalent and
divalent cations did not cause any significant changes under the
same conditions. These results indicated that HL had high
selectivity towards M3+ over other monovalent and divalent
cations.
To obtain more insight into the fluorescent properties of HL as a
chemosensor for M3+, fluorescent titration experiments of HL
(50
carried out (Fig. 4). As shown in Fig. 4, HL hardly exhibited
m mM) were
M) towards increasing amounts of M3+ (0–100
3.1. UV/vis studies of HL towards M3+
fluorescent emission at 583 nm below 20 mM because the binding
between M3+ and the nitrogen atom in the spirolactam did not
induce successively the ring-open of rhodamine B. Upon addition
The UV/vis spectrum of HL (50
mM) towards various metal ions
(Li+, Na+, K+, Ag+, Ca2+, Mg2+, Ba2+, Zn2+, Cu2+, Fe2+, Ni2+, Cd2+, Co2+
,
of above 20 m mM), the spirolactam was
M M3+ to HL solution (50
Pb2+, Mn2+, Hg2+, Cr3+, Fe3+, and Al3+) was illustrated in Fig. 1. As
shown in Fig. 1, the solution of HL in methanol was colorless and
exhibited no absorption at 558 nm in the absence of M3+ due to the
spirolactam form of HL. Upon addition of M3+ (Cr3+, Fe3+, and Al3+),
a new and strong absorption peak at 558 nm appeared with the
solution color changing from colorless to pink, which was
attributed to the formation of the strongly fluorescent ring-
opened HL-M3+ complex. Such a dramatic color change suggested
that HL could serve as a “turn-on” and colorimetric fluorescent
probe for M3+. Other monovalent and divalent cations did not show
opened along with the appearance of fluorescent emission peak at
583 nm and the fluorescence intensity at 583 nm was gradually
increased with the progressive addition of M3+ and the intensity
remained constant after the addition of 2 equivalent of M3+ (Cr3+
,
Fe3+, and Al3+). These results suggested that HL could detect M3+
quantitatively with a large range.
3.3. Interference studies from other valent metal ions
As we all know, an ability to resist interference from other
analytes is an important characterization for a chemosensor. The
competitive experiments of HL (50
m
M) towards M3+ in the
presence of other valent cations (Li+, Na+, K+, Ag+, Ca2+, Mg2+, Ba2+
,
Zn2+, Cu2+, Fe2+, Ni2+, Cd2+, Co2+, Pb2+, Mn2+, Hg2+) were conducted
(Fig. 5). It was noticeable that the competitive metal ions did not
cause any significant changes in the fluorescence intensities of HL-
M3+ (except Hg2+ and Mn2+). This experimental results indicated
that monovalent and divalent cations did not influence the
fluorogenic response of HL towards M3+. Therefore, HL could be
used as a highly selective fluorescent probe for M3+
.
3.4. Reversible test of HL towards M3+ by NaF
Reversibility and regeneration are important indexes in
practical applications for
a chemosensor. To examine the
reversibility of the HL-M3+ complex, 2 equivalent NaF was added
to HL-M3+ solutions. As shown in Fig. 6, upon addition of 2
equivalent NaF to the solutions of HL-M3+ complex, the solution
color changed from pink to colorless and the fluorescence intensity
Fig. 1. UV-vis spectrum of HL (50 mM) before and after of 1 equiv. of various metal
cations in methanol. (inset) Visible color change of HL upon addition of M3+ in
ambient light.

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X.- Yue et al. / Journal of Photochemistry and Photobiology A: Chemistry 351 (2018) 1–7
Fig. 2. UV-vis spectrum of HL (50
m
M) in the presence of M3+ (0–100
m
M) in methanol. (a): Cr3+, (b): Fe3+, and (c): Al3+
.
analytes as a “1” state and the absence of analytes as a “0” state.
When input1 and input2 are “0” state, the output is “0” state (no
fluorescence). When upon addition of Fꢁ to HL solution (50
m
M),
i.e. input1 is “0” state and input2 is “1” state, the output is “0” state
(no fluorescence). When we add M3+ to HL solution (50
M), i.e.
m
input1 is “1” state and input2 is “0” state, the output is “1” state
(strong fluorescence). When upon addition of Fꢁ to HL-M3+
solution, i.e. input1 is “1” state and input2 is “1” state, the output is
“0” state (no fluorescence).
3.5. Binding constant, stoichiometry and detection limit
Association constant (Ka) and detection limit (LOD) of HL for M3
(Cr3+, Fe3+, and Al3+) were obtained from the fluorescence
+
titration experiments. The association constant (Ka) of HL-M3+
complex was determined by the Benesi-Hildebrand equation [42]:
Fig. 3. Fluorescence emission spectrum of HL (50
m
M) before and after of 1 equiv. of
1
1
1
¼
þ F
where F is the fluorescence inten-
KðFmaxꢁFminÞ½M3þꢃ
various metal ions in methanol. (inset) Fluorescence emission color change of HL
FꢁFmin
maxꢁFmin
upon addition of M3+ after illumination under UV light.
sity at 583 nm at any given M3+ concentration, Fmin is the
fluorescence intensity at 583 nm in the absence of M3+, and Fmax
is the maximal fluorescence intensity at 583 nm in the presence of
M3+. The Ka values of HL-M3+ complex were calculated to be
0.87 ꢀ104 Mꢁ1 (Cr3+), 1.14 ꢀ104 Mꢁ1 (Fe3+), and 4.48 ꢀ 104 Mꢁ1 (Al3
+), respectively by the plotting 1/(F-Fmin) against 1/[M3+] (Fig. S11)
according to the Benesi-Hildebrand equation. The detection limit
of the system was quenched obviously, demonstrating that M3+
was captured from HL-M3+ by NaF accompanied with the
regeneration of the free HL due to the binding constant of M3+
with Fꢁ is larger than that with HL. Then the M3+ was again added
to the system, the solution color changed from colorless to pink
and the fluorescence signals of the system were partly recovered.
(LOD) of HL for M3+ were calculated to be 0.63
(Fe3+), and 0.22 M (Al3+) according to the equation: DL = 3
where is the standard deviation of the blank solution and K is the
m mM
M (Cr3+), 0.14
These results suggested that HL is
a chemically reversible
m
s/K
fluorescent probe for M3+
.
s
This type of reversible behavior of HL mimics the INHIBIT logic
gate (integrated by combining a NOT, a YES, and an AND gate). The
INHIBIT logic gate, the truth table, and the output signals of
fluorescence are shown in Fig. 7. In this logic gate, M3+ and Fꢁ are
used as input1 and input2 respectively. We define the presence of
slope of the calibration curve (Fig. S12, Fig. S13, and Fig. S14) from
the fluorescence titration experiments [43]. The binding stoichi-
ometry of HL towards M3+ was obtained from the Job’s method on
the basis of fluorescence emission spectrum. As shown in Fig. 8, the
emission intensity showed a maximum when the molar fraction of
Fig. 4. Fluorescence emission spectrum of HL (50
intensity of HL at 583 nm upon the addition of progressive [M3+].
m m
M) in the presence of M3+ (0–100 M) in methanol. (a): Cr3+, (b): Fe3+, and (c): Al3+. Inset: Changes of fluorescence

X.- Yue et al. / Journal of Photochemistry and Photobiology A: Chemistry 351 (2018) 1–7
5
Fig. 5. Fluorescence response of HL (50
mM) upon addition of various metal cations (black bars: the fluorescence intensities of HL in the presence of other metal cations, red:
the fluorescence intensities of HL-Mn+ upon addition of 1 equiv. of M3+). (a): Cr3+, (b): Fe3+, and (c): Al3+
.
Fig. 6. Fluorescence spectral changes of HL (50
fluorescence reversibility.
m
M) after the sequential addition of M3+ and NaF (2 equiv.) in methanol. (a): Cr3+, (b): Fe3+, and (c): Al3+. Inset: Images of
Fig. 7. (a) The INHIBIT logic gate (integrated by combining a NOT, a YES, and an AND gate); (b) The corresponding truth table of this INHIBIT logic gate; (c) The output signals of
fluorescence of this logic gate in the presence of different inputs.
HL was 0.5, which indicated that
a
possible 1:1 binding
935.4058 corresponding to [HL＋Al3+＋NO3ꢁ + DMF + 8H2O ꢁ H+]+
stoichiometry between HL and M3+. To better confirm the binding
mode of HL towards M3+, the ESI mass spectrum of HL in the
presence of M3+ were carried out (Fig. S15: Cr3+, Fig. S16: Fe3+, and
Fig. S17: Al3+). The m/z peak for HL in the presence of Cr3+ at
716.0940 corresponding to [HL＋Cr3+＋Clꢁ－H+]+ and at 935.3586
corresponding to [HL＋Cr3+＋3DMF + Clꢁ－H+]+ (Fig. S15). The m/z
peak for HL in the presence of Fe3+ at 685.1025 corresponding to
(Fig. S17). Thus, the mass spectrum data corroborated the 1:1
binding stoichiometry between HL and M3+
.
3.6. Proposed sensing mechanism of HL towards M3+
To better understand the sensing mechanism of HL towards M3
+, the 1H NMR titration experiments of HL in the presence of M3+
(Fe3+) were carried out (Fig. S18). Upon addition of 1 equiv M3+ (Fe3
[HL＋Fe3+－H+]2+ and at 747.0802 corresponding to [HL＋Fe3+
＋
NO3ꢁ－H+]+ (Fig. S16). The m/z peak for HL in the presence of Al3+ at
820.1677 corresponding to [HL＋Al3+＋2DMF + H2O ꢁ H+]2+ and at
+) to the DMSO-d6 solution of HL, the proton signal of Hb (HNC
¼
O)
d
was broadened and shifted downfield from
d
10.17 ppm to

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X.- Yue et al. / Journal of Photochemistry and Photobiology A: Chemistry 351 (2018) 1–7
Fig. 8. Job’s plot for determining the stoichiometry of HL and M3+ in methanol, the total concentration of HL and M3+ was kept 100 M. (a): Cr3+, (b): Fe3+, and (c): Al3+
m .
Scheme 2. The proposed sensing mechanism of HL towards M3+
.
10.21 ppm. Furthermore, the proton signals of the (CH
moieties were broadened and shifted downfield from
¼
N) imines
7.85 ppm
formation of ring opening of the rhodamine spirolactam
(Scheme 2) [44–46].
d
and
proton signal of Hc (-CH3) was broadened and shifted up field from
1.09 ppm to 1.08 ppm and other proton signals on rhodamine B
d 7.98 ppm to d 7.94 ppm and d 8.03 ppm, respectively. The
4. Conclusion
d
d
were also broadened and shifted up field. Additionally, the proton
signal of Ha (-OH) was well retained with broadening and shifting
In summary, we have designed and synthesized
a new
colorimetric “turn-on” fluorescent probe for M3+ (Cr3+, Fe3+, and
Al3+) based on rhodamine B derivative. The methanol solutions of
HL in the presence of Cr3+, Fe3+, and Al3+ changed from colorless to
pink accompanied with emitting orange-yellow fluorescence via
the formation of ring-opened HL-M3+ complex. The Job’s plot and
downfield from
that the possible sensing mechanism is that M3+ binding with HL
via nitrogen on the two imine moieties (CH N), oxygen on the
spirolactam, and oxygen on the amide group (HNC O) induced the
d 11.68 ppm to d 11.70 ppm. These results indicated
¼
¼

X.- Yue et al. / Journal of Photochemistry and Photobiology A: Chemistry 351 (2018) 1–7
7
ESI-mass spectrometry analysis indicated that the 1:1 binding
stoichiometry of HL-M3+. Additionally, the binding of HL and M3+
was chemically reversible by the addition of fluorinion.
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Acknowledgments
This work is supported by the National Natural Science
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