A novel photochemical sensor based on quinoline-functionalized phenazine derivatives for multiple substrate detection

Article abstract of DOI:10.1039/d0nj06175a

A novel photochemical sensor (FQ-5) based on quinoline-functionalized phenazine derivatives was designed and synthesized. TheFQ-5showed a good response to certain pH values in a wide pH range (from 2.0 to 13.0). Particularly, at pH = 12 and 13, the fluorescence emission showed obvious enhancement, the fluorescence quantum yields could reach 80.9% and 77.0%, respectively, and the color of solution changed from yellow to purple. Meanwhile, the sensor not only showed a rapid response toward CO₂, but also showed high selectivity and sensitivity for the detection ofl-Arg in buffer solution (pH = 7), and the limit of detection (LOD) was 8.1 × 10^?8. Furthermore, theFQ-5-based fluorescent writing material and CO₂gas reaction device were developed for the rapid detection ofl-Arg and CO₂. Therefore, this work will provide a new approach for photochemical sensing in the detection of multiple substrates.

Full text of DOI:10.1039/d0nj06175a

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A novel photochemical sensor based on
quinoline-functionalized phenazine derivatives
for multiple substrate detection†
Cite this: New J. Chem., 2021,
45, 5040
Tai-Bao Wei, *a Hong-Qiang Dong,a Xiao-Qiang Ma,a Qing-Yu Yang,a
ab
Zhong-Hui Wang,a Wen-Li Guan,a Yun-Fei Zhang,a You-Ming Zhang,
a
a
Hong Yao
and Qi Lin
*
A novel photochemical sensor (FQ-5) based on quinoline-functionalized phenazine derivatives was
designed and synthesized. The FQ-5 showed a good response to certain pH values in a wide pH range
(from 2.0 to 13.0). Particularly, at pH = 12 and 13, the fluorescence emission showed obvious
enhancement, the fluorescence quantum yields could reach 80.9% and 77.0%, respectively, and the
color of solution changed from yellow to purple. Meanwhile, the sensor not only showed a rapid
response toward CO2, but also showed high selectivity and sensitivity for the detection of L-Arg in buffer
solution (pH = 7), and the limit of detection (LOD) was 8.1 Â 10À8. Furthermore, the FQ-5-based
fluorescent writing material and CO2 gas reaction device were developed for the rapid detection of
L-Arg and CO2. Therefore, this work will provide a new approach for photochemical sensing in the
detection of multiple substrates.
Received 21st December 2020,
Accepted 7th February 2021
DOI: 10.1039/d0nj06175a
rsc.li/njc
Carbon dioxide (CO2), as a common gas, plays an important
role in plant photosynthesis,17 fire extinguishers18 and food
Introduction
As we all know, amino acids play a significant role in biological additives.19 However, with the rapid development of industry in
areas such as sustaining normal physiological processes, affect- recent years, a large amount of greenhouse gas including CO2
ing organ and tissue functions, and so on.1–3 L-Arginine (L-Arg) emission has led to natural hazards such as sea-level rise and
is a necessary amino acid for newborns, which is particularly ocean acidification.20,21 Although there have been many
important for participating in metabolism, protein synthesis significant advances in low-carbon renewable resources, fossil
and human immune function.4–8 However, excess L-Arg could fuels remain the main source of energy for human activities.22
cause symptoms such as elevated gastric acid levels, high blood Therefore, greenhouse gas including CO2 emission has attracted
pressure, and kidney failure.9–11 Due to the importance of L-Arg much attention from researchers. At present, the methods for
in human metabolism, many methods have been reported detecting CO2 gas mainly include electrochemistry,23 infrared
for detecting L-Arg, including gas chromatography, liquid imaging,24 and decarbonization25 techniques, but these detection
chromatography, and capillary electrophoresis methods.12–14 methods still face difficulties as they are relatively expensive and
However, these methods could suffer from high cost, low complicated.26 Consequently, many chemosensors have been
sensitivity and specificity, and complicated sample pretreatment. reported as effective tools for detection of CO2 due to their
In recent years, fluorescent sensors have been widely used in the simplicity, sensitivity, low cost and real-time responsiveness.27–30
detection field owing to their high sensitivity and high However, these chemosensors could only recognize CO2 by
selectivity.15 Therefore, it is still an important and challenging either a fluorescence method or colorimetric strategy. Therefore,
task to develop a novel chemosensor for conveniently and developing simple and feasible materials for dual-channel
efficiently detecting amino acids.16
detection of CO2 with high sensitivity and rapid response is still
a challenging task.31
a Key laboratory of Polymer Materials of Gansu Province, College of Chemistry and
Chemical Engineering, Northwest Normal University, Lanzhou, Gansu, 730070,
P. R. China. E-mail: weitaibao@126.com, linqi2004@126.com
b Deputy Director-General of Gansu Natural Energy Research Institute,
Renmin Road 23, Lanzhou, Gansu, 730070, P. R. China
In recent years, visual pH sensors have attracted much
attention in the fields of food safety, environmental monitoring,
analytical chemistry, and biomedicine,32–34 especially in biological
detection and chemical sensing.35 For example, the abnormal pH
values will cause many diseases36–38 such as cancer,39 Alzheimer’s
disease,40 and so on. On the other hand, many chemical reactions
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
d0nj06175a
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are often closely related to pH, such as Reimer-Tiemann and FQ-5 sensor could detect CO2 by dual-channel detection under
Cannizzaro reactions,41 and as a result, pH becomes one of the alkaline conditions. Moreover, FQ-5-based kits were prepared
important factors in determining the reaction yields. However, by immersing the kits into the FQ-5 solution, and as a result,
most pH sensors are biased toward acid or neutral detection,42–44 they could conveniently and efficiently detect L-Arg in water
and to date, very few literature studies have been reported on solution. A carbon dioxide gas reaction device was designed to
alkaline pH sensing, especially the strong alkaline pH region detect CO2 gas more directly and conveniently. Furthermore,
(pH 4 10). Therefore, development of pH sensors for alkaline the response mechanisms were also discussed based on the NMR
pH sensing is still rather necessary.45–48
titration experiment and density functional theory calculation.
Phenazine, as a class of dyes, is the most researchable
fluorophore due to its large conjugation system, large Stokes
displacement, high fluorescence quantum yields, and sample
background interference,49,50 etc. On this basis, the application
of phenazine derivatives is widely concerned in electroactive
materials,51,52 biological detection53,54 and ion detection
methods.55 However, there are only a few reports on utilizing
phenazines for amino acid detection.56 In addition, most of the
tests based on phenazine derivatives are single tests, and there
are only a few studies on multiple substrate detection.57 The
8-hydroxyquinoline moiety has valuable structural characteristics
of the most widely employed molecular platforms for constructing
many unique systems and effective light-emitting devices.58
Therefore, the design and development of photochemical sensors
based on phenazine derivatives is still a challenging task for the
detection of multiple substrates.
Materials and methods
General procedure for UV-vis experiments
All the UV-vis experiments were carried out using a Shimadzu
UV-2550 spectrometer. Any changes in the UV-vis spectra of the
synthesized sensors were recorded by the addition of HEPES
buffer solution with various pH values ranging from 2.0 to 13.
The host concentration was kept constant in all experiments.
General procedure for fluorescence experiments
All the fluorescence experiments were carried out using a
Shimadzu RF-5301PC spectrofluorophotometer. Any changes
in the fluorescence spectra of the synthesized sensors were
recorded by the addition of HEPES buffer solution with various
pH values ranging from 2.0 to 13. The host concentration was
kept constant in all experiments.
Based on previous works and as a part of our research
interest,59,60 we designed and developed a novel photochemical
sensor (FQ-5) based on a quinoline-functionalized phenazine
derivative (Fig. 1). The FQ-5 showed a rapid fluorescence
General procedure for pH adjustment
response for high pH, especially for pH = 12 and 13, which The pH measurements were carried out in air at room
indicated that it displayed good dual-channel detection with temperature using a Sartorius PB-10 acidometer. The pH was
quantum yields of 80.9% and 77.0%, respectively. It also adjusted by the addition of HClO4 and TBAOH, respectively, in
exhibits great recognition performance for L-Arg in the pH 7.0 the HEPES buffer system. The absorption and emission spectra
buffer solution and its LOD was 8.1 Â 10À8 M. Meanwhile, the were recorded using 10 mm quartz cuvettes after equilibration.
Fig. 1 Photochemical sensor FQ-5 for multiple substrate detection under different conditions.
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General procedure for fluorescence spectra experiments
Results and discussion
All the fluorescence spectroscopy experiments were carried pH response and response mechanism
out in a DMF/H2O (9 : 1, v/v) FQ-5 solution using a Shimadzu
First, the structure of the FQ-5 sensor is shown in Scheme 1.
We found that the FQ-5 sensor showed weak fluorescence
emission in pure DMF solution, and when water was added
to the solution, the strongest fluorescence emission was
reached at fw = 10% (Fig. 2a and Fig. S7, ESI†), which could
be attributed to the accumulation of FQ-5. At the same time, the
Tyndall effect was also observed in a 10% DMF/H2O (9 : 1, v/v,)
binary solution (Fig. 2b). However, when the water volume
fraction was higher than 10%, because water is a poor solvent
for FQ-5, the FQ-5 precipitated out from the solution, which
resulted in the decrease of the fluorescence emission.
Therefore, the pH response experiment was conducted in the
DMF/H2O (9 : 1, v/v) binary solution.
Next, the pH response properties of the FQ-5 sensor were
primarily investigated in the DMF/H2O (9 : 1, v/v) HEPES buffer
solution with various pH values (pH ranging from 2.0 to 13.0;
the step-size was 1.0 pH unit). When the pH value was changed
from 7 to 2, the fluorescence change was not obvious, but
compared to FQ-5, the fluorescence is quenched; however,
RF-5301 spectrometer. Any changes in the fluorescence
spectra of the synthesized compounds were recorded by the
addition of amino acids while keeping the ligand concentration
constant (1.0
Â
10À4 M) in all experiments. Different
amino acids (L-Phe, L-Gln, L-Ile, L-Thr, L-Glu, L-Ala, L-Ser,
L-Met, L-Val, L-Tyr, L-Arg, L-Asp, L-Pro, L-His, L-Leu, L-Gly, L-Trp,
L-Asn, L-Cys and L-Lys 0.1 M) were used for the fluorescence
experiments.
Computational details
The ground state geometries were derived by density functional
theory (DFT).61 All the computations were performed using
the Gaussian 09 program62 on a personal computer using
B3LYP in conjunction with 6-311G(d,p). All analyses as well as
drawing of various kinds of maps were finished using
the Multiwfn 3.7 code.63 In addition to an energy-optimized
structure, the electron densities of the targeted compounds
were investigated using HOMO–LUMO frontier orbital theory,
electrostatic potential (ESP) and noncovalent interactions
(NCIs).
Synthesis and characterization of chemosensor FQ-5
Synthesis of compounds 1 and 2. Compound 1 (2,3-
diaminophenazine) was prepared according to a previously
published procedure.59 Compound 2 was prepared by the
following procedure: 14.5 g of 1.00 mmol 8-hydroxyquinoline
was added to a solution of 75 mL of CH3CH2OH and 40%
NaOH. Subsequently, 32 mL of CHCl3 was slowly added to the
above solution. Then, the solution was reacted at 100 1C for
12 h and the pH was slowly adjusted to 4 with diluted HCl.
The solid was filtered off and the solvent was removed. The
crude product was isolated by column chromatography using
petroleum ether/ethyl acetate (40 : 1) to obtain a pink powder,
which is Compound 2. Yield: 10%.
Synthesis of compound FQ-5
Scheme 1 Synthesis of compounds 1 and 2, and FQ-5.
0.42 g of 2 mmol 2,3-diamino-phenazine (1), 0.38 g of 2.2 mmol
8-hydroxy-5-formylquinoline (2) and a catalytic amount of
acetic acid (AcOH) were combined in 20 mL of hot absolute
DMF. The reaction mixture was stirred at 85 1C for 8 h.
After cooling to room temperature, the brown precipitate
was filtered, washed with hot absolute ethanol three times,
and then recrystallized with DMF–H2O to obtain a brown
powdery product FQ-5 (yield: 22%. m.p. 4 300 1C), as
shown in Scheme 1. 1H NMR: (600 MHz, DMSO-d6, room
temperature) d (ppm) 13.31 (s, 1H), 10.11 (s, 1H), 9.02 (s, 1H),
8.10 (m, 9H), 7.35 (s, 1H). 13C NMR: (150 MHz, DMSO-d6, room
temperature,) d (ppm) 153.2, 152.2, 149.7, 144.7, 142.9, 137.4,
132.0, 130.2, 129.4, 125.7, 124.7, 122.3, 112.2. ESI-MS m/z:
(M + H+) calcd for C22H13N5O 363.11; found 364.11 (Fig. S3–
S6, ESI†).
Fig. 2 (a) Fluorescence intensity of FQ-5 in DMF/H2O binary solution with
different water fractions, solution concentration: 1.0 Â 10À4 M; (b) the
Tyndall effect of FQ-5 (1.0 Â 10À4 M) with different volumetric fractions of
water (0% and 10%).
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Scheme 2 Chemical structure of the photochemical sensor FQ-5 and its
sensing mechanism with H+/OHÀ.
that multiple interactions occurred under acidic conditions.
From the SEM images (Fig. S16, ESI†), it is understood that
FQ-5 shows an irregular block structure, which becomes a
coral-like structure when an H+ is added, then it becomes
a sheet-like structure, and when OHÀ is added, it becomes a
broken strip. These results definitely indicate that the fluorescence
changes were caused by intramolecular charge transfer (ICT).
As shown in Scheme 2, imidazole is an electron donor and
8-hydroxyquinoline is an electron acceptor. When the OHÀ
medium is added, the hydrogen atoms on the imidazole N are
taken away to form NÀ, the emission spectrum is blue-shifted,
and the fluorescence intensity increases. When the H+ medium is
added, imidazole and quinoline N are protonated, N+ is formed,
Fig. 3 FQ-5 (1.0 Â 10À4 M) at various pH values (from 2.0 to 13.0) in DMF/
H2O (9 : 1, v/v) HEPES buffer solution. (a) Fluorescence spectra (lex
=
400 nm, lem = 490 nm, ex = 5 nm, and em = 10 nm); (b) UV-vis absorption.
when the pH was changed from 7 to 13, we found that the and the electron-pulling ability of N+ becomes very strong.
fluorescence change was enhanced (Fig. 3(a) and Fig. S8, ESI†). Besides, the –OH groups are used as electron-donating groups.
It can be seen from Fig. 3a that when the pH is 12 and 13, new Furthermore, we have carried out dynamic light scattering (DLS)
absorption peaks appear in the UV spectrum. Simultaneously, experiments to study the aggregation behaviour of the FQ-5
the measured fluorescence quantum yields64 of pH = 12 and sensor (pH = 2) in solution. As shown in Fig. S17 (ESI†), the
13 were 80.9% and 77.0%, respectively (Fig. S9 and S10, ESI†). particle size of the FQ-5 sensor is mainly distributed at 296 nm;
In addition, we could see that the color of the solution changes simultaneously, we also confirmed the presence of p–p stacking
from yellow to purple (Fig. S11, ESI†). From the CIE diagram, interactions with X-ray diffraction peaks at 2y = 25.67 corres-
we could also see that the color of the fluorescence changes ponding to the d-spacing of 3.52 Å (Fig. S18, ESI†). This indicates
from grass green to yellow and then to blue (Fig. S12, ESI†). entire protonated forms multiple weak interactions, resulting the
Moreover, it can be observed from Fig. S13 (ESI†) that the acid– fluorescence showed red-shift and intensity decreases.
base reaction is not reversible. Therefore, the FQ-5 showed a
Furthermore, in order to further understand the interactions
good pH response for a specific pH change in a narrow pH and mechanism between the FQ-5 sensor and the H+/OHÀ
range (from 12.0 to 13.0) through obvious dual-channel medium, the energy-optimized structures of the FQ-5, FQ-
detection.
5(acid) and FQ-5(base) were obtained through theoretical
The detection mechanism of FQ-5 to H+/OHÀ was carefully calculations, as shown in Fig. 4a and Fig. S19–S21 (ESI†). At the
1
investigated via H NMR spectroscopy, 2D NOESY NMR, SEM same time, a vigilant inspection of the graphical representation
DLS, XRD and density functional theory techniques. As shown of noncovalent interaction (NCI) isosurfaces for the dimers of
in the 1H NMR titration experiments of FQ-5 for H+/OHÀ FQ-5 under acidic van der Waals force conditions (p–p stacking)
(Fig. S14, ESI†), after adding 0.5 equiv. OHÀ to the DMSO-d6 portrayed in Fig. S22, ESI† suggests a plethora of interactions
solution of FQ-5, we found that H1 showed downfield shifts and indicated by green isosurfaces extending over in the attractive
the peak shape became wider, but when 1.0 equiv. was added, low-gradient region. In addition, the frontier orbital energy
the peak disappeared. With the addition of OHÀ, H2 and H4 maps of FQ-5 under acidic and alkaline conditions are shown
showed upfield shifts, which indicates that the addition of OHÀ in Fig. S23 (ESI†). The HOMO–LUMO energy differences for
takes the H1 away from the imidazole functional group. When FQ-5 (Fig. S23-b, ESI†) under acidic conditions (Fig. S23-c, ESI†)
H+ was added, we found that H2 first showed downfield shifts, and alkaline conditions (Fig. S23-a, ESI†) were found to be
and then upfield shifts; H3, H4 and H5 showed both upfield and 0.11338, 0.05307 and 0.02329 eV, respectively. It could be seen
downfield shifts. Meanwhile, the H1 has not been recovered. that there are many overlapping parts of the HOMO–LUMO
Moreover, we validated the interaction mechanism via 2D orbitals, which increases the probability of charge transfer. This
NOESY NMR. As shown in Fig. S15 (ESI†), there are correlations also indirectly proves the rationality of the above mechanism
between the signals of protons H2, H3, and H4, which implied (Scheme 2).
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Fig. 4 Energy-optimized structure of (a) FQ-5, (b) FQ-5 under alkaline conditions, and (c) FQ-5 under acidic conditions.
Response of different amino acids at pH = 7
fluorescence titration experiment. As shown in Fig. 5b, the
fluorescence titration experiment indicated that the fluorescence
emission of FQ-5 exhibits gradual enhancement and reached a
plateau with the addition of L-Arg (0–4.67 equiv.). Based on the
The interference of common amino acids in the detection of pH
is also investigated. A series of amino-acid-containing aqueous
solutions (L-Phe, L-Gln, L-Ile, L-Thr, L-Glu, L-Ala, L-Ser, L-Met, L-Val,
L-Tyr, L-Arg, L-Asp, L-Pro, L-His, L-Leu, L-Gly, L-Trp, L-Asn, L-Cys and
L-Lys 0.1 M) were separately added to the FQ-5 (1.0 Â 10À4 M) in
pH 7.0 buffer solution (Fig. 5a). With the addition of 3.0 equiv. of
various amino acids, only L-Arg induced an obvious increase in
the fluorescence intensity of the FQ-5 sensor. In order to further
obtain the limit of detection (LOD) of L-Arg, we performed a
calculations by the 3d/m method, the LOD is 8.1 Â 10À8
M
(Fig. S24, ESI†),65 which is lower than those from other various
reported methods66,67 (Table S1, ESI†). The lower detection limit
revealed the high sensitivity of FQ-5 towards L-Arg. Interestingly,
the fluorescence color also showed an obvious change from yellow
to blue (Fig. S25, ESI†). The above-mentioned results are also well
consistent with the CIE results (Fig. S26, ESI†). However, this
fluorescence color is obviously different from the color observed
under alkaline conditions, and we guess that the recognition
mechanism also has certain differences. Moreover, the anti-
interference experiment was conducted at room temperature,
and the result showed that the sensor possesses high selectivity
for the detection of L-Arg (Fig. S27, ESI†).
To investigate the host–guest interaction mechanism
between FQ-5 and L-Arg, the 1H NMR titration, 2D NOESY,
DFT and SEM experiments were performed. Initially, in the
1H NMR titration spectra (Fig. 6), after the addition of 0.2 equiv.
L-Arg to FQ-5 DMSO-d6 solution, the H1 (N-hydrogen proton) of
the imidazole group disappeared. With the increasing amount
of L-Arg, the proton signals of H2, H3 and H4 on FQ-5 showed
upfield shifts. The above-mentioned results proved that the
N-hydrogen proton of the imidazole group disappeared with
the addition of L-Arg and thus the fluorescence emission
enhanced; meanwhile, the 2D NOESY results indicated that
the L-Arg may have interacted with the FQ-5 groups through the
host–guest interactions (Fig. S28, ESI†), which indicated that
part of L-Arg interacted with the two adjacent FQ-5 sensors,
respectively, through the synergistic effect.3 In the SEM images
shown in Fig. 7, FQ-5 shows an irregular block structure and
the morphology became coral-like after adding L-Arg. These
results also supported the rationality of the above mechanism.
Moreover, the response mechanism of FQ-5 for L-Arg was
further carefully explored using DFT calculations and the
electrostatic potential (ESP) maps of FQ-5 and L-Arg (Fig. 8),
where the negative region represents the preferred position of
the nucleophilic attack and is shown as the red region, while
Fig. 5 (a) Fluorescence spectra of FQ-5 (1 Â 10À4 M) in the presence of
excess (3.0 equiv.) of various amino acids; (b) fluorescence emission
titration spectra of FQ-5 (1 Â 10À4 M) with incremental (0.1 M) additions
of L-Arg. (lex = 400 nm, lem = 490 nm, ex = 5 nm, and em = 10 nm).
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Fig. 8 (a) The frontier orbitals (HOMO and LUMO) of FQ-5 and L-Arg;
(b) electronic potential maps (ESP, in atomic units) of FQ-5 and L-Arg at the
B3LYP/6-311G(d,p) level.
Fig. 6 Partial 1H NMR spectra of FQ-5 (5 mg) in DMSO-d6 with different
equiv. of L-Arg: (a) FQ-5, (b) 0.2 equiv., (c) 0.4 equiv., and (d) 0.6 equiv.
used to detect L-Arg. As shown in Fig. 9, when L-Arg was dipped in
the film, a significant color change was observed at 365 nm under
the irradiation of an ultraviolet lamp. Therefore, the film could be
used as a convenient test tool for detecting L-Arg.
Carbon dioxide detection
Interestingly, when a solution with a pH of 12/13 was exposed
to air, it was found that the color of the solution changed from
purple to orange over time (Fig. S31, ESI†). In order to better
explain the above phenomenon, a series of experiments were
carried out. We passed a large proportion of gas (nitrogen,
hydrogen, oxygen, and carbon dioxide) contained in air into a
strong alkaline solution, and found that only carbon dioxide
can change the color of the solution. In order to further
determine the changes caused by CO2, a device for producing
high-purity carbon dioxide was designed. As shown in Fig. S32
(ESI†), when carbon dioxide was added to the solution at
pH = 12, there was an obvious phenomenon that the color of
the solution turned from purple to orange; similarly, the same
phenomenon was observed at pH = 13. To this end, the UV-vis
Fig. 7 SEM photographs of (a) FQ-5, (b) FQ-5 + water, (c) L-Arg, and
(d) FQ-5 + L-Arg.
the blue region is the position of the electrophilic attack. absorption and fluorescence experiments were also performed
Meanwhile, the electron distribution of FQ-5 is more uniform, (Fig. 10 and 11). As shown in Fig. 10(a), when CO2 is introduced
leading to
a decrease in both polarization and dipole under alkaline conditions, the UV-vis absorption peak at
moment.68,69 On the other hand, the N molecules in L-Arg 410 nm drops significantly and moves to 394 nm; at the same
showed stronger positive electrical properties compared with time, color changes can also be seen significantly (Fig. 10b). In
that in FQ-5. It was further shown that the combination of addition, in the fluorescence spectrum (Fig. 11a), the addition
arginine and FQ-5 was reasonable. In addition, for revealing the of CO2 can also lead to fluorescence decline, and the fluores-
supramolecular interactions, the NCI graph was obtained cence color changes from bright blue to lake blue under an
through the IGM approach, which is used to further visualize ultraviolet lamp (Fig. 11b).
the interactions between FQ-5 and L-Arg, in which green
Moreover, the performance of FQ-5 for the detection of OHÀ
represents the van der Waals force (Fig. S29 and S30, ESI†). and CO2 was also investigated by FT-IR and ESI-MS spectroscopy.
From the above results, we propose the self-assembly mechanism In the FT-IR spectra (Fig. S33 and S4, ESI†), FQ-5 shows an N–H
of FQ-5 + L-Arg (Scheme 3b).
peak at 1662 cmÀ1 and an –OH peak at 3429 cmÀ1, and
Finally, in order to study the practical applications of the sensor, when OHÀ is added, the peak shape changes significantly;
glass sheets were immersed in the FQ-5 sensor (1.0 Â 10À4 M) in subsequently, with the addition of CO2, new absorption peaks
pH 7.0 buffer solution and dried in air. The FQ-5-based film was appear at 2514 and 928 cmÀ1, while the 928 cmÀ1 is the
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Scheme 3 (a) Proposed response mechanism of FQ-5 for L-Arg recognition; (b) recognition of CO2 with FQ-5 under alkaline conditions. Inset: Change
of FQ-5 with L-Arg and CO2 under natural light or UV-lamp (365 nm).
out-of-plane deformation of OHÁ Á ÁOQ in the acid dimer.
This is caused by the addition reaction, which fully proves that
the addition of CO2 under alkaline conditions leads to the
formation of COOH (Scheme 3c). Furthermore, the ESI-MS
peak also supports the formation of the NCO2 moiety (Fig. S34,
Fig. 9 Photographs of the thin film utilized for the detection of L-Arg
under irradiation at 365 nm using a UV lamp.
ESI†).
Conclusion
In this study, we designed and synthesized a photochemical
sensor FQ-5 based on quinoline-functionalized phenazine deri-
vatives. The FQ-5 could highly sense the pH = 12/13 within a
very narrow pH range with sharp optical spectra and obvious
fluorescence color changes, and the measured fluorescence
quantum yields were 80.9% and 77.0%, respectively.
Meanwhile, in pH 7.0 buffer solution, the sensor could ‘‘turn-on’’
fluorescence to detect L-Arg, and the LOD was 8.1 Â 10À8 M.
Moreover, FQ-5-OH shows dual-channel detection for CO2 with
Fig. 10 (a) UV-vis spectra titration of FQ-5 (1.0 Â 10À4 M) in alkaline
high selectivity. In addition, the FQ-5-based fluorescent writing
aqueous solution after CO2 injection; (b) photograph of color changes in
material and carbon dioxide gas reaction device were developed
for rapid detection of L-Arg and CO2. In summary, this work not only
provides an effective way for the detection of L-Arg, pH and CO2, but
also provides a new way to construct a photochemical sensor for
multiple substrate detection.
FQ-5 solution after CO2 injection under natural light.
Conflicts of interest
There is no conflict to declare.
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (Grant No. 21662031, 21661028 and
21574104) and the Program for Chang Jiang Scholars and
Innovative Research Team in University of Ministry of Education
of China (Grant No. IRT15R56).
Fig. 11 (a) Fluorescence spectra titration of FQ-5 (1 Â 10 À4 M) in alkaline
aqueous solution after CO2 injection (lex = 400 nm, lem= 490 nm, ex =
5 nm, and em = 10 nm); (b) photograph of color changes in alkaline
solution after CO2 injection under a UV lamp (365 nm).
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