Selective detection of cyanide ion in 100 % water by indolium based dual reactive binding site optical sensor

Article abstract of DOI:10.1016/j.jphotochem.2020.112571

The indolium based sensor (R) system was designed, synthesized, characterized and its cyanide recognizing abilities are examined in 100 % water. The sensor attach with cyanide ion through nucleophilic addition to C atom of the indolium C[dbnd]N group. Also the sensor displayed colorimetric and fluorimetric behavior and it can be simply observed by naked eye. The addition of other chosen anions does not affect the sensor response towards cyanide ion. Test strip constructed on R was act as a convenient test kit to distinguish cyanide ion. Besides, the recognizing ability of sensor has been effectively applied in real water samples and this was validated with HPLC technique. Thus the receptor can be used as an effective sensor to sense cyanide ion water.

Full text of DOI:10.1016/j.jphotochem.2020.112571

Journal of Photochemistry & Photobiology A: Chemistry 397 (2020) 112571
Contents lists available at ScienceDirect
Journal of Photochemistry & Photobiology A: Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Selective detection of cyanide ion in 100 % water by indolium based dual
reactive binding site optical sensor
1
1
Jong Ho Park , Ramalingam Manivannan , Palanisamy Jayasudha, Young-A Son*
Department of Advanced Organic Materials Engineering, Chungnam National University, 220 Gung-dong, Yuseong-gu, Daejeon 305-764, South Korea
A R T I C L E I N F O
A B S T R A C T
Keywords:
The indolium based sensor (R) system was designed, synthesized, characterized and its cyanide recognizing
abilities are examined in 100 % water. The sensor attach with cyanide ion through nucleophilic addition to C
atom of the indolium C]N group. Also the sensor displayed colorimetric and fluorimetric behavior and it can be
simply observed by naked eye. The addition of other chosen anions does not affect the sensor response towards
cyanide ion. Test strip constructed on R was act as a convenient test kit to distinguish cyanide ion. Besides, the
recognizing ability of sensor has been effectively applied in real water samples and this was validated with HPLC
technique. Thus the receptor can be used as an effective sensor to sense cyanide ion water.
Chemodosimeter
Colorimetric
Fluorimetric
Cyanide
Water
Real sample analysis
1. Introduction
useful even for a common man can visualize the presence of cyanide
[
26–29]. To get the better visual detection, the original color of the
Cyanide is one of most poisonous and chemical warfare species and
sensor molecule has to be intense. So that the color change while cy-
anide detection is easily noticeable for the ordinary human being. Thus
the developed sensor molecule must have intense color for the easy
detection of cyanide. Another important factor is the detection of cya-
nide in 100 % water. The initial molecule dissolves in 100 % water
means the detection of cyanide in water is possible and highly useful for
the real time application.
affects the living organisms and also to the environment [1–3]. Cya-
nides are formed naturally by certain fungi, algae and bacteria and are
originate in considerable volumes in certain fruit stones and seeds such
as those of sprouting potatoes, apricots, lima beans, peaches, apples and
bitter almonds [4–8]. Cyanide is also released artificially from some
industries like electroplating, gold mining and plastic industries.
Though it is used for manufacturing papers, plastics, resin etc, it is
highly harmful when releasing from the manufacture of above [9–12].
Even a small amount of intake of cyanide leads to death. The released
cyanide drags with the iron atom in cytochrome C oxidase in the mi-
tochondria of cells and preventing electron transports with the arrest of
aerobic cellular respiration which leads to death [13–18]. However, the
World Health Organization (WHO) inculcates that the determined safe
concentration level of cyanide allowed in drinking water is 1.9 μM [19].
So the detection of cyanide is highly necessary to the biological and
environmental living organisms. Thus, the progress of effective sensor
synthesis for the efficient finding of cyanide is essential.
By keeping all these points in mind, we have developed indolium
based sensor molecule (R) for the discerning recognition of cyanide ion
in 100 % water. The sensor molecule is designed with intramolecular
charge transfer (ICT) transition by taking diethyl amine as an electron
donating group and carboxylated indole as an electron withdrawing
group. The small change in the ICT transition leads to prominent color
and fluorescence change which is very effective for cyanide ion detec-
tion. Since cyanide acts as a strong nucleophile, it attacks the binding
site of indole which interrupts the π-conjugation throughout the mo-
lecule and thus exhibits a prominent colorimetric and fluorescence
variation. The adding of cyanide ion to the sensor molecule leads to
color variation from purple to colorless with simultaneous fluorescence
quenching. The developed sensor molecule R for cyanide ion exhibited
a high response, anti-interference ability with low detection limit.
Besides, the developed test kit is extremely selective and sensitive to
There are many procedures existing for the recognition of cyanide
such as spectrometry, chromatography, electrochemical, titrimetric,
and colorimetric and fluorimetric [20–25]. Among this colorimetric and
fluorimetric methods are quite useful for the detection of cyanide due to
its simplicity, low cost, easy detection and easy sample preparation. The
colorimetric method gives naked eye detection of cyanide which is
−
CN ion in water.
⁎
Corresponding author.
E-mail address: yason@cnu.ac.kr (Y.-A. Son).
These authors contributed equally to this work.
1
https://doi.org/10.1016/j.jphotochem.2020.112571
Received 29 December 2019; Received in revised form 25 March 2020; Accepted 11 April 2020
Available online 01 May 2020
1010-6030/ © 2020 Elsevier B.V. All rights reserved.

J.H. Park, et al.
Journal of Photochemistry & Photobiology A: Chemistry 397 (2020) 112571
C7H9N2O2 [M+H] : 153.0664, found 153.0654 (Fig. S3).
+
2. Experimental section
2.1. Chemicals
2.3.2. Synthesis of 2,3,3-trimethyl-3H-indole-5-carboxylic acid (2)
4
-hydrazinylbenzoic acid (1) (7.0 g, 46 mmol) and 3-methyl-2-bu-
To synthesis sensor R basic chemicals, anion in the form of tetra-
tanone (4.755 g, 55.21 mmol) were added to glacial acetic acid (30 mL)
in nitrogen atmosphere. The reaction mixture was stirred and refluxed
overnight. After removal of the solvent in vacuum, the rest was lique-
fied in chloroform, neutralized with saturated NaHCO
layer was dried over MgSO , cleaned, and concentrated underneath
condensed pressure. The rest was cleaned by recrystallization (CHCl /
3
hexane) to get the product as a solid (7.05 g, 75.4 % yield). H NMR
(600 MHz DMSO-d ): 1.291 (s, 6 H), 2.270 (s, 3 H), 7.520 (d, 1H,
J=7.8 Hz), 7.932 (dd, 1H, J = 7.8, 1.2 Hz),), 8.013 (d, 1H, J=1.2 Hz),
12.838 (s, 1 H) (Fig. S4). 13C NMR (150 MHz DMSO-d
): 15.798,
22.714, 53.921, 119.561, 123.169, 127.742, 130.075, 146.565,
butylammonium salts and solvents for experiments were obtained from
sigma aldrich and used as received. Complete experiments were done
using distilled water.
3
. The organic
4
2
.2. Instruments
1
Carbon and proton NMR spectra confirmed through Bruker spec-
6
trometer functioning under 150 and 600 MHz respectively, using in-
ternal standard as TMS. The chemical shifts in ppm units and J value in
Hz were expressed in the manuscript. HRMS analysis for the prepared
molecules was recorded using a 1290 infinity II/Triple TOF 5600 plus
mass spectrometer. UV–vis and fluorescence spectra were noted in an
Agilent (8453) spectrophotometer and Varian Cary Eclipse spectro-
photometer respectively at 25 °C. The slit width set as 3 nm for ex-
citation and emission. Silica gel plates TLC used for reaction mon-
itoring.
6
157.866, 167.956, 192.133 (Fig. S5). HRMS (m/z) calcd. for C12
[M+H] : 204.1025, found 204.1019 (Fig. S6).
H14NO
2
+
2
.3.3. Synthesis of 5-carboxy-1,2,3,3'-tetramethyl-3H-indol-1-ium iodide
(3)
2
,3,3-trimethyl-3H-indole-5-carboxylic acid (7 g, 33.4 mmol) and
methyl iodide (9.77 g, 68.88 mmol) were added to 120 mL of a mixture
of toluene and acetonitrile (2:1 v/v). This was stirred at 120 °C for 12 h
in nitrogen atmosphere, and then allowable to cool. The precipitate was
isolated by purification and washed with n-hexane. The product was
2
.3. Synthesis of sensor R
The sensor molecule R has been synthesized (Scheme 1) from the
1
following procedure.
dried overnight in vacuum at 50 °C to get a solid (6.7 g, 56 % yield). H
NMR (600 MHz DMSO-d
6
): 1.586 (s, 6 H), 2.840 (s, 3 H), 4.018 (s, 3 H),
8
.034 (d, 1H, J=8.4 Hz), 8.186 (d, 1H, J=8.4 Hz), 8.382 (s, 1 H) (Fig.
2
.3.1. Synthesis of 4-hydrazinylbenzoic acid (1)
-aminobenzoic acid (4.54 g, 33.1 mmol) was added to 1 N NaOH
43 mL). The mixture was added to 60 mL of 35 % HCl at 0 °C. NaNO
2.3 g. 33.3 mmol) in 20 mL H O was added drop wise for 10 min.
.2H O (35.8 g, 158.8 mmol)
in 35 % HCl 72 mL was added about 30 min. This was stirred at 0 °C for
h followed by overnight stirring. The precipitate was composed by
13
S7). C NMR (150 MHz DMSO-d
6
): 15.183, 21.973, 35.578, 54.724,
4
1
1
2
15.857, 124.658, 130.818, 132.049, 142.417, 145.718, 166.935,
99.475 (Fig. S8). HRMS (m/z) calcd. for C13
18.1176, found 218.1181 (Fig. S9).
(
(
2
+
2
H16NO [M+H] :
2
Afterward stirring for 40 min at 0 °C, SnCl
2
2
2
2.3.4. Synthesis of 2,2'-(butane-1,4-diylbis(oxy))bis(4-(diethylamino)
benzaldehyde) (4)
vacuum purification and wash away with 100 mL diethyl ether, dried
overnight at 50 °C to get the preferred product, which was used without
further purification (3.87 g, 85.2 % yield). H NMR (600 MHz DMSO-
4-(Diethylamino)salicylaldehyde (7.50 g, 38.81 mmol) was dis-
solved in THF (60 mL) under nitrogen. Tetrabutylammonium bromide
(0.51 g, 1.59 mmol), potassium hydroxide (5.36 g, 95.53 mmol), 1,4-
dibromobutane (4.19 g, 19.41 mmol) were added and the above mix-
ture was stirred and reflux for 48 h. This was cooled and poured into
1
d
1
1
6
): 7.009 (d, 2H, J=9.0 Hz), 7.831 (d, 2H, J=9.0 Hz), 8.944 (s, 1 H),
1
3
0.629 (s, 2 H) (Fig. S1). C NMR (150 MHz DMSO-d
6
): 113.595,
23.272, 131.057, 149.964, 167.440 (Fig. S2). HRMS (m/z) calcd. for
Scheme 1. Synthesis of R.
2

J.H. Park, et al.
Journal of Photochemistry & Photobiology A: Chemistry 397 (2020) 112571
−
4
Fig. 1. Color changes observed for R [1.25 × 10
M] upon the addition of various anions.
−
5
Fig. 2. UV–vis spectra of R [1 × 10 M] with incremental addition of TBACN
0-20 μM] in water (HEPES buffer pH 7.2).
[
−6
Fig. 3. Fluorescence spectra of R [1.5 × 10 M] upon addition of TBACN [0-
3
-
6
× 10 M] in water (HEPES buffer pH 7.2) (Inset: Linear plot of intensity with
water (700 mL) and stirred, after which the solid precipitate was col-
lected together by vacuum filtration and wash away with water. The
resulting crude product was recrystallized from ethyl acetate to give
desired product as a solid (6.8 g, 80 % yield). 1H NMR (600 MHz
concentration of cyanide ion).
2.4. Sample preparation for cyanide sensing
−3
CDCl
3
): 1.133 (t, 12H, J=7.2 Hz), 2.012 (s, 4 H), 3.332 (q, 8 H), 4.062
A stock solution of sensor R (1 × 10
M) was prepared in water
−
3
(
7
CDCl
1
s, 4 H), 5.959 (d, 2H, J=2.4 Hz), 6.202 (dd, 2H, J = 9.0, 1.8 Hz),
(
HEPES buffer, pH 7.2). Stock solutions of cyanide ion (1.0 × 10 M)
1
3
.627 (d, 2H, J=9.0 Hz), 10.102 (s, 2 H) (Fig. S10). C NMR (150 MHz
): 12.809, 26.231, 44.990, 67.614, 93.342, 104.576, 114.449,
30.634, 154.076, 163.788, 187.052 (Fig. S11). HRMS (m/z) calcd. for
were prepared in water (HEPES buffer, pH 7.2). UV–vis titration study
has been carried out as follows: To a fixed volume of R stock solution
3
-
5
-5
(
1 × 10 M), an incremental amount of cyanide ion (0−2 × 10 M)
+
26 37 2 4
C H N O [M+H] : 441.2753, found 441.2766 (Fig. S12).
solution was added. Fluorescence measurements has been carried out as
follows: To a fixed volume of R stock solution (1.5 × 10 M), an in-
cremental amount of cyanide ion (0−3 × 10 M) solution was added.
-
6
-
6
2
(
.3.5. Synthesis
diethylamino)-2,1-phenylene))bis (ethene-2,1-diyl))bis(5-carboxy-1,3,3-
trimethyl-3H-indol-1-ium) iodide (R)
,2′-(butane-1,4-diylbis(oxy))bis(4-(diethylamino)benzaldehyde)
of
2,2′-((1E,1′E)-((butane-1,4-diylbis(oxy))bis(4-
2.5. Protocol for practical application
2
(
(
3 g, 6.81 mmol), 5-carboxy-1,2,3,3-tetramethyl-3H-indol-1-ium iodide
4.7 g, 13.61 mmol) were added to ethanol 100 mL in nitrogen atmo-
Tap water and drinking water used for the analysis are obtained
from laboratory and stored as such. For quantitative estimation, dif-
ferent amounts of cyanide ions were added to these real water samples
because the existing water samples are free from cyanide ions. Then the
UV–vis spectra measured for the water samples in the absence and
presence of different concentration of cyanide ions. The same samples
are validated using HPLC.
sphere and stirred at reflux for 24 h. The reaction mixture was allow-
able to cool down to room temperature. The precipitate was isolated by
filtration and washed ethanol. The resulting crude product was re-
crystallized from acetonitrile and ethanol to give the desired product as
a solid (5.37 g, 72 % yield). H NMR (600 MHz DMSO-d
1
6
2
1
1
6
): 1.198 (t,
2H, J=7.2 Hz), 1.671 (s, 12 H) 2.163 (s, 4 H), 3.621 (q, 8 H), 3.830 (s,
H), 4.394 (s, 4 H), 6.326 (d, 2H, J=1.2 Hz), 6.664 (m, 2 H), 7.167 (d,
H, J=13.8 Hz), 7.648 (d, 2H, J=7.8 Hz), 8.061 (dd, 2H, J = 7.8,
.8 Hz), 8.136 (s, 4 H), 8.476 (d, 2H, J=13.8 Hz) (Fig. S13). 13C NMR
3
. Result and discussion
(
6
150 MHz DMSO-d ): 13.224, 25.786, 27.563, 32.983, 45.455, 50.102,
8.363, 94.385, 108.297, 112.948, 113.559, 123.724, 129.068,
The sensor R was synthesized from 2,2′-(butane-1,4-diylbis(oxy))bis
6
1
1
8
(
4-(diethylamino)benzaldehyde) with 5-carboxy-1,2,3,3-tetramethyl-
1
30.976, 142.117, 146.259, 156.312, 163.306, 163.408, 167.243,
3
H-indol-1-ium. The structure of the sensor was confirmed by H NMR,
+
1
3
79.433 (Fig. S14). HRMS (m/z) calcd. for C52
H
64
N
4
O
6
[M] :
C NMR and HRMS spectral analysis. The anion sensing property of the
1
40.4815, found 840.4825 (Fig. S15).
sensor was examined by UV–vis, fluorescence, H NMR, mass spectral
procedures and theoretical evaluations.
3

J.H. Park, et al.
Journal of Photochemistry & Photobiology A: Chemistry 397 (2020) 112571
−
Fig. 4. Competitive experiment showing detection of CN by sensor R in the
presence of other anions using fluorescence spectral technique.
3.1. Colorimetric response
−
4
The colorimetric sensing property of R (1.25 × 10
M) with dif-
-, and CN- TBA
3
- ions in water (HEPES buffer, pH 7.2) was carried
ferent anions including F-, AcO-, Br-, H
2
PO
4
- Cl-, I-, NO
3
−
Fig. 6. Mass spectrum of the product formed upon reaction of R with CN
.
2
-
salts and S , HSO
out by visual detection experiment. As implied in the introduction, the
intense color of initial molecule leads to striking color change with
cyanide ion and thus showed clear naked eye detection. Here in this
molecule, among the anions, CN- ion shows color change from purple to
colorless in water (HEPES buffer, pH 7.2) where all other anions did not
show any color change which may possibly be noticed by naked eye.
The results observed are shown in Fig. 1. This shows that the sensor is
very much selective to cyanide ion. For the effect of pH of sensor with
cyanide ion, the color of the receptor R at different pH values before
and after the addition of two equivalent of cyanide ion was also in-
spected. As evidenced from figure S16, the sensor exhibited the same
color change (purple to colorless) in neutral and basic media. However,
in acidic medium no noticeable color change was observed.
3.2. UV–vis spectral studies
The colorimetric ability of sensor R (1 × 10−5 M) is monitored by
electronic spectral readings. The UV–vis spectra was taken for R in
water (HEPES buffer, pH 7.2) in the presence of several anions of
−5
3 2 4
concentration (2 × 10 M) including F-, NO -, Br-, H PO -, AcO-, Cl-,
I- and CN-. Among these anions cyanide shows a blue shifted peak and
the added ions did not show any spectral variation of the sensor in
electronic spectrum (Fig. S17). This shows that the sensor R is
Fig. 5. (A) 1H NMR spectrum of R; (B) with addition of TBACN in DMSO-d6.
4

J.H. Park, et al.
Journal of Photochemistry & Photobiology A: Chemistry 397 (2020) 112571
Fig. 7. Frontier molecular orbitals and HOMO-LUMO energy level diagram of sensor R and its addition product.
accompanied by a variation in color of the solution from purple to
colorless. These clear changes indicated that nucleophilic addition of
cyanide ion to the sensor molecule inhibits the ICT transition which
results in the blue shift in the electronic spectra. The binding constant
was calculated by UV–vis data by following the described procedure
4
-1
[
30] (Fig. S18) and the obtained binding constant was 6.25 × 10 M .
The detection limit of cyanide was calculated (Fig. S19) using 3σ/k as
-
6
described in literature [31,32] and was found to be 0.978 × 10
M
which is lower than the WHO limit (1.9 μM).
−
The stoichiometry of R-CN complex was confirmed by Job’s con-
tinuous variation method [33]. In Job’s Plot, a curve with maximum at
0
)
.3 shows that the sensor molecule binds with cyanide ion in 1:2 (R:CN-
ratio (Fig. S20). It strongly suggests that sensor forms complex with
CN- in 1:2 ratio.
Fig. 8. Color change of test strip upon dipping in solution of cyanide ion in
water.
3.3. Fluorescent spectral studies
The fluorescent spectrum of R (1.5 × 10
−6
M) in water (HEPES
Table 1
−
Determination of CN in water samples.
buffer, pH 7.2) was taken towards after addition of various con-
-
6
centration of cyanide ion (0−3 × 10 M). It exhibited an emission
peak at 584 nm while excited at 303 nm. The increasing concentration
of cyanide ion quenches the fluorescence spectra of R and thus was
showing it forms a complex with CN- ion (Fig. 3). This changes in the
emission spectrum of sensor molecule additionally exposed that the
nucleophilic addition took place between the sensor molecule and cy-
anide ion, which efficiently blocks the conjugation and thus obstructs
the ICT transition. As shown in the inset of Fig. 3, the observed fluor-
escence intensity was proportional to the CN- concentration (0−2
eqv.). The binding constant was calculated by fluorescence quenching
data by following the described procedure [34] (Fig. S21) and the ob-
tained binding constant was 1.73 × 105 M . The detection limit of
cyanide was calculated (Fig. S22) using 3σ/k as described in literature
Present Method HPLC Method
Water
Added
Found
Recovery (%) Found
Recovery (%)
samples
(μM)
(μM)
(μM)
Tap water
5
4.98
10.02
15.04
5
9.98
14.98
99.6
100.2
1
1
5
10
1
0
5
100.3
100
99.8
99.9
15.01
14.96
100.1
99.7
Drinking
water
5
-1
exceedingly selective to cyanide ion. As shown in Fig. 2, on addition of
cyanide ions (0−20 μM) in water (HEPES buffer, pH 7.2) to the solu-
tion of R, the band at 534 nm reduced gradually and a fresh absorption
band appeared at 303 nm. The observed spectral change is
-
8
[
31,32] and was found to be 1.53 × 10 M which was lower than the
permissible level recommended by World Health Organization (WHO).
On comparing the values of binding constant and detection limit
5

J.H. Park, et al.
Journal of Photochemistry & Photobiology A: Chemistry 397 (2020) 112571
obtained from both UV–vis and fluorescence technique, it is found that
the values obtained from fluorescence data is higher due to its high
sensitivity. This analytical value showed that the synthesized sensor
molecule was sensitive enough to detect cyanide ion in drinking water.
we attempted to define the concentration of cyanide ion in real samples
like drinking water and tap water via the method of standard addition
(n = 3). The recovery outcomes were tabulated and confirmed with
HPLC technique (Table 1). The calibration plot (Fig. S19) showed that
there is a good linear correlation between the absorbance and cyanide
ion concentration (correlation coefficient = 0.988).
−
To further study the sensor selectivity for CN ion, the competitive
experiment was carried out using fluorescence spectral method in
company of additional chosen anions (Fig. 4). The sensor showed
negligible interference towards the detection of cyanide ion by the
added interfering anions. The emission intensity of sensor with cyanide
ion does not affect by the above chosen anions. Thus, the sensor is se-
lectively and sensitively effective for cyanide ion and which could be
used in real sample analysis.
4. Conclusion
To conclude, we have synthesized a simple indolium based sensor
which detects cyanide ion selectively in 100 % water. The sensor
showed an obvious color transformation from purple to colorless with
cyanide ion. The added cyanide shifted the intramolecular charge
transfer band of sensor towards shorter wavelength in absorption
spectra. Electronic and fluorescence studies showed that the sensor
3
.4. 1H NMR spectral studies
−
−
The above studies indicate the formations of R-CN adduct which is
forms complex with CN ion and the binding constant was found to be
−
1.73 × 105 M . Job’s plot showed that the stoichiometry ratio of R
-1
scientifically confirmed and its sensing mechanism of R with CN was
1
1
explained using H NMR spectra. The H NMR spectra was taken for
free sensor R and after addition of 1 eqv. of cyanide ion using DMSO-d
+CN- was found to be 1:2 ratio. The detection limit was calculated
-
8
6
using 3σ/k and was found to be 1.53 × 10 M which is lower than the
1
and was given in Fig. 5. From the figure, the singlet at 13.15 ppm
corresponding to the carboxyl OH group in the free sensor molecule
disappeared with cyanide addition owing to high acidity and all other
signals in the free sensor shifted to upfield. In the free sensor R, the
WHO permissible limit (1.9 μM). The H NMR spectra confirmed that
the sensing mechanism of sensor is nucleophilic addition cyanide at C]
N of indolium moiety. Theoretical studies were executed to support the
projected mechanism. Test strips were also prepared for the recognition
of cyanide ion which showed an immediate color change.
signals at 8.47 and 7.16 ppm equivalent to the Ha and Hb respectively
−
(
vinylic protons) is shifted to 7.08 and 6.12 ppm with the CN ion
addition. As well as, the signal of methyl group attached to indolium
CRediT authorship contribution statement
nitrogen (marked as Hc) was similarly shifted upfield from 3.83 to
2.73 ppm. The obtained results evidently signifying that the cyanide ion
Jong Ho Park: Conceptualization, Writing - original draft,
added to indolium C]N group [35]. From the above clear discussion of
Methodology. Ramalingam Manivannan: Writing - original draft,
Investigation, Data curation. Palanisamy Jayasudha: Formal analysis,
Visualization. Young-A Son: Writing - review & editing, Supervision.
1
H NMR spectra reveals that the sensing mechanism of sensor R in-
−
volves the nucleophilic addition of the CN ion on the C]N of in-
dolium moiety in the sensor molecule. The proposed mechanism is
further confirmed by HRMS spectral analysis by taking mass spectrum
Declaration of Competing Interest
65 6 6
of sensor with cyanide ion (Fig. 6). HRMS (m/z) calcd. for C54H N O
+
−
[
M+H] : 893.4966, found 893.4972 matching to R-CN species
−
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
seems signifying the formation of R-CN compound.
3
.5. Theoretical study
Appendix A. Supplementary data
The structural and electronic property of sensor was investigated by
Density Functional Theory by the basis set of B3LYP/6−31 G with
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.jphotochem.2020.
Gaussian 03 set [36]. The optimized geometry of the sensor and R
−
+
CN and also frontier molecular orbitals (MOs) are shown in the
112571.
Figs. 7 and S23. In the free sensor molecule, HOMO is localized on the
whole indole molecule which indicating the strong delocalization of
electron cloud density and energetic ICT process and benzene rings
References
−
while after the addition of cyanide ion (R-CN moiety), the conjugation
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−
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strips. The test strips were equipped by dipping Whatman filter paper
−4
into R (1.25 × 10
M) (water, HEPES buffer, pH 7.2) followed by
drying in air. After drying, the filter papers were dipped in different
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[
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6

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7