Triple Action Sensing Behaviour of a Single Receptor for the Detection of Multiple Analytes via Different Approaches

Article abstract of DOI:10.1007/s10895-021-02700-9

The thiosemicarbazide based receptor was synthesized with 4-(diethylamino)salicylaldehyde and N- phenyl-thiosemicarbazide by the simple condensation method and the properties were studied under the naked eye, UV-Vis and fluorescence studies etc. The synthesized receptor detects cyanide, cobalt, and mercury in acetonitrile medium. The observed color changes included colourless to yellow for cyanide, colourless to green for cobalt and colourless to yellow for mercury which were seen under naked eye without the aid of any instruments. Furthermore, the cyanide bound receptor detects Cr³⁺ by the relay recognition method. The detection limit of receptor with cyanide, cobalt & mercury was found to be 5.8 × 10^{? 7}?M, 3.6 × 10^{? 7}?M and 8.1 × 10^{? 7}?M respectively. Experimental results were verified by DFT calculations. Receptor was successfully employed in the construction of INHIBIT and IMPLICATION logic gates. Graphical Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10895-021-02700-9

Journal of Fluorescence (2021) 31:733–745
https://doi.org/10.1007/s10895-021-02700-9
ORIGINAL ARTICLE
Triple Action Sensing Behaviour of a Single Receptor
for the Detection of Multiple Analytes via Different Approaches
Ganesan Punithakumari1 & Sivan Velmathi1
Received: 21 December 2020 /Accepted: 11 February 2021
/ Published online: 23 February 2021
#
The Author(s), under exclusive licence to Springer Science+Business Media, LLC part of Springer Nature 2021
Abstract
The thiosemicarbazide based receptor was synthesized with 4-(diethylamino)salicylaldehyde and N- phenyl-thiosemicarbazide
by the simple condensation method and the properties were studied under the naked eye, UV-Vis and fluorescence studies etc.
The synthesized receptor detects cyanide, cobalt, and mercury in acetonitrile medium. The observed color changes included
colourless to yellow for cyanide, colourless to green for cobalt and colourless to yellow for mercury which were seen under naked
eye without the aid of any instruments. Furthermore, the cyanide bound receptor detects Cr3+ by the relay recognition method.
The detection limit of receptor with cyanide, cobalt & mercury was found to be 5.8 × 10− 7 M, 3.6 × 10− 7 M and 8.1 × 10− 7
M
respectively. Experimental results were verified by DFT calculations. Receptor was successfully employed in the construction of
INHIBIT and IMPLICATION logic gates.
.
.
.
Keywords Thiosemicarbazide Turn on‐fluorescence Logic gate DFT
Introduction
detection of cobalt ion [9]. Mercury is a notorious metal ion
that causes many diseases in humans. High levels of mercury
poisoning are often associated with pneumonia, respiratory
diseases, drug allergies and chronic mercury poisoning, as
well as neurological, Parkinson’s and chronic psychological
problems [10–13]. For these dangerous ions we need a simple
and easy method of detection. Many techniques available for
the detection of these ions are ascribed with difficult synthesis,
poor sensitivity & selectivity and also interference of other
ions like F−, AcO−. Chemical sensors have many amazing
unique advantages in overcoming these shortcomings, as well
as many other advantages such as high sensitivity and selec-
tivity, making it easy to see target ions visually and at a low
cost [14]. For cyanide ion detection, Chemchem and co-
workers reported the receptor for cyanide ion detection in
the DMSO / H2O medium, which detects cyanide ions
through a deprotonation and ICT mechanism [15]. Wang
and co-workers developed a receptor with coumarin deriva-
tive with benzothiazole Schiff base moiety which sense cya-
nide ion by nucleophilic addition mechanism [16]. In cobalt
ion detection, Vashisht and co-workers achieved the colori-
metric receptor with coumarin moiety for the selective detec-
tion of Co2+ ion in near aqueous medium by ICT (intramolec-
ular charge transfer) [17]. Jeong Na and co-workers developed
a novel receptor for the selective detection of cobalt ions in a
near perfect aqueous solution through LMCT (ligand-to-metal
Nowadays, anion & metal ions sensor plays an important role
in the field of chemical sensors. Compared to other ions, cy-
anide is one of the most toxic and dangerous ions to humans
and the environment. Food sources such as potatoes, apple
seeds, almonds and cassava contain trace amount of cyanide
[1]. Still the food samples containing CN− ion may lead to
rigorous health problems such as respiratory problems, cardi-
ac arrest, unconsciousness and eventually death [2, 3].
Cyanide ion plays an important role in electroplating, gold
mining and polymer processing. The other ion of interest,
cobalt, is one of the biologically important trace elements.
This ion was responsible for protein synthesis, myelin forma-
tion, and production of red blood cells and also used in the
high cholesterol treatment [4–7]. Moreover intake of high
concentration of cobalt ions leads to DNA damage, cardio
toxicity and low cardiac output to human beings [8]. A very
limited number of literature reports are available for the
* Sivan Velmathi
velmathis@nitt.edu
1
Organic and Polymer Synthesis Laboratory, Department of
Chemistry, National Institute of Technology, Tiruchirappalli, Tamil
Nadu 620015, India

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Scheme 1 Synthesis of receptor
charge-transfer) [18]. Marimuthu and co-workers were
achieving a new and simple fluorescent receptor bearing
mono-sulfur and tetra-sulfur tetrahydro dibenzo
phenanthridine derivatives for the selective sensing of Hg2+
ion by twisted intramolecular charge transfer (TICT) mecha-
nism [19]. Tripathy and co-workers reported a receptor based
on styrylpyridinium donor-π-acceptor (D-π-A) chromophore
containing NS2O2 binding site for the selective sensing of
mercury ion via ICT mechanism [20]. All the above cases, a
single receptor detect single metal ions only. Generally due to
its biological and analytical application thiosemicarbazide and
its derivatives are very important and also get immense inter-
est in anticancer, antiHIV, antibacterial, antiviral and antifun-
gal activities. They play an important role in the regulation of
plant growth. Some literature review based on
thiosemicarbazide moiety are, Harikrishnan et al. reported
the thiosemicarbazide based receptor which detects F−, CN−
and Cu2+ ion through deprotonation followed by hydrogen
bonding [21]. Islam et al. reported the thiosemicarbazide
based receptor which detects cyanide, fluoride and acetate
ion by deprotonation [22]. Udhayakumari et al. reported
thiosemicarbazone based sensors that detect the transition
metal ions in aqueous media due to photon induced electron
transfer mechanism [23]. Lei et al. reported the receptor with
thiosemicarbazide moiety for the selective detection of mer-
cury ion by aggregation induced emission.[24]. Amuthakala
et al. reported the thiosemicarbazide based chemosensor
which detects manganese, cobalt, nickel, copper and zinc cat-
ions, and fluoride anion through deprotanation [25]. Sahu
et al. reported the pyridine appended thio–semicarbazide
based receptor for the selective detection of Cu2+ and Ag+
ions via ICT process [26]. All the above cases, a single recep-
tor detect multiple ion with a single approach. Herein we
report the application of the thiosemicarbazide based receptor
synthesized from 4-(N,N-diethylamino) salicylaldehyde and
N- phenyl-thiosemicarbazide. Though this thiosemicarbazide
is known for quite a few years and have been well studied for
its biological activities no report is available on the application
of this molecule as chemosensor. This is the first time this
receptor was used to detect ions using chemosensor method.
Herein we report the receptor with thiosemicarbazide moiety
for multiple ion detection with different approaches. The pro-
posed receptor was also applicable in DFT and logic gate
application.
Materials and Instruments
R e q u i r e d c h e m i c a l s l i k e 4 - ( N , N - d i e t h y l
amino)salicylaldehyde, N-phenylthiosemicarbazide, tetra bu-
tyl ammonium salts of AcO−, F−, I−, Cl−, CN−, Br−,
−
−
H2PO4 ,HSO4 , NO3 −, OH− and metal ions such as Mn
(OAc)2, CoCl2, Cu (NO3)2, ZnCl2, Cd (CH3COO)2, HgCl2,
NiCl2, CrCl3, FeCl3 and AlCl3 were purchased from Sigma
Aldrich and used without any purification or modification.
1
13
Using Bruker 500 MHz NMR spectrometer, H and
C
NMR spectra were recorded with tetramethylsilane (TMS)
as an internal standard and CDCl3 as a solvent. IR-spectra
were recorded by the KBr pelletization method using a
Thermo Fisher Nicolet FT-IR spectrometer. Shimadzu UV-
2600 was used to measure the UV-Vis spectrum. Shimadzu-
RF-5301PC spectrofluorometer was used to run the fluores-
cence spectra. For all UV and PL titrations, 5 × 10− 5 M solu-
tion in ACN medium was taken as a standard. 0 equ. − 2.0
equ. of the analyte was used for the incremental addition.
Receptor Synthesis
As per the literature report [27] the receptor was synthesized
with 98 % yield (Scheme 1). The melting point was 145°C;
1
(The reported melting point was 147°C) [28]. H NMR
(CDCl3, 500 MHz, δ ppm) 10.3 (s, 1H, O-H proton) 9.6
(s,1H,NH-Proton) 8.0 (s,1H,imine proton) 8.3 (s,1H, NH-
proton) 7.6 (d, 2H J = 7.5 Hz) 7.4 (t, 2H, J = 8 Hz) 7.3
(s,1H,) 7.0 (d,1H, J = 9 Hz) 6.27 (d,1H, J = 8.5 Hz) 6.25
(d,1H, J = 8.5 Hz) 6.1 (d,1H, J = 8.5 Hz) 2.4 (m,4H, CH2−pro-
ton) 1.19 (t, 6H, CH -proton) 13 C NMR (CDCl3,125 MHz, δ
3
ppm) 12.6, 44.6, 97.7, 104.5, 105.3, 124.9, 126.4, 128.8,
133.4, 137.7, 148.8, 151.3,159.6,174.4.
Fig. 1 Colorimetric detection of
receptor (5.0 × 10− 5 M in ACN)
with all anions (1 × 10− 4 M in
ACN)

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735
Fig. 2 Colorimetric detection of
receptor (5.0 × 10− 5 M in ACN)
with all cations (1 × 10− 4 M) in
H2O
Fig. 3 (a) UV-Vis spectral studies of the receptor (5.0 × 10− 5 M in ACN) with all anions (1 × 10− 4 M in ACN) (b) UV-Vis Incremental addition of the
receptor with CN− ion (1 × 10− 4 M in ACN)
Results and Discussion
responsible for the strong hydrogen bonding and the
deprotonation of the NH protons by the CN- ions in
solution.
Naked Eye Detection of Anions and Cations
Visual detection in acetonitrile medium was performed to
examine the selective detection of receptor towards different
cations. As shown in Fig. 2, the receptor showed a significant
color change from colourless to light green for cobalt and
colourless to yellow upon the addition of Hg2+ ions. In the
presence of Co2+ ions, the absorption band at 375 nm appar-
ently decreased and a new absorption band appeared at 400
nm. At the same time adding Hg2+ ions to the receptor solu-
tion reduces the band at 375 nm to form a new band at 393 nm.
Other cations did not show any significant spectrum and color
changes.
The sensitivity of the receptor was tested with various
anions and cations by naked eye detection in acetonitrile
medium. By adding cyanide ion to the receptor it
changed from colorless to yellow. However there is no
visible color change for other ions (Fig. 1). The colour
change of the receptor was associated with the large red
shift of 443 nm in UV-Vis spectra upon the addition of
cyanide ion. However, by the addition of 2.0 equ.of
cyanide ion into the receptor its get saturated. Large
bathochromic shift and observed color change are
Fig. 4 a Spectral studies of receptor (5.0 × 10− 5 M in ACN) with all cations in 1 × 10− 4 M in H2O. b Incremental titration of receptor with Co2+ ions (1 ×
10− 4 M in H2O). c Incremental titration of receptor with Hg2+ ions (1 × 10− 4 M in H2O)

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Fig. 5 (a) PL-studies of receptor (5.0 × 10− 5 M in ACN) with various anions (1 × 10− 4 M in ACN) (b) Incremental addition of CN− ion (1 × 10− 4 M in
ACN) with receptor
Spectral Studies of Receptor with All Anions
studies, Mn(OAc)2, CoCl2, Cu(NO3)2, ZnCl2, Cd
(CH3COO)2, HgCl2, NiCl2, CrCl3, FeCl3 and AlCl3 were tak-
en in aqueous media. By the addition of all cations into the
receptor solution Co2+ and Hg2+ ion only got a colour change
and it changes its colour into light green for cobalt and yellow
for mercury. By the addition of cobalt ion, the receptor peak at
375 nm get decreases and formed a new peak with two clear
isosbestic points. The two isosbestic point at 330 nm and
400 nm indicates the stable complex formation between the
receptor and cobalt ion. At the same time by the addition of
mercury ion into the receptor the absorbance band of the re-
ceptor at 375 nm get decreases and the new band get increase
with a clear isosbestic point at 393 nm which was depicted in
(Fig. 4a). In incremental addition of receptor with these two
cations get saturated by the addition of 0 equ. to 2.0 equ.
which is shown in (Fig. 4b and c).
To examine the sensitivity of the receptor, UV-visible studies
of the receptor with all ions were carried out in acetonitrile
−
medium. Anions like CN−, Br−, F−, I−, Cl−, AcO−, HSO4 ,
H2PO4 , and NO3 and OH− are taken in the form of their
tetrabutyl ammonium salts. By the addition of all anions into
the receptor, only the cyanide ion got a colour change from
colourless to yellow with red shift. By adding cyanide ion into
the receptor, the peak at 375 nm get decreases and formed the
new peak at 445 nm. (Fig. 3a). The new peak is due to the ICT
band between the receptor (> NH/CN−) and signalling ben-
zene units. As the CN− ion in the receptor solution increases,
the CN− ion peak gradually increases, eventually becoming
saturated. Moreover there is an isosbestic point at 404 nm
which indicates the stable complex formation of the
receptor-cyanide complex.
−
−
Fluorescence Studies of All Anions with Receptor
Spectral Studies of Receptor with All Cations
To find out the emission properties of the receptor with all
anions the fluorescence titration was done with the help of
spectrofluorometer with slit width as 5 nm and the excitation
The sensitivity of the receptor was further examined by UV-
Vis spectroscopic titration in ACN medium. For cation
Fig. 6 a PL-studies of receptor (5.0 × 10− 5 M in ACN) with various cations (1 × 10− 4 M in H2O). b Incremental addition of Co2+ ion (1 × 10− 4 M in
H2O) with receptor. c Incremental addition of Hg2+ ion (1 × 10− 4 M in H2O) with receptor

J Fluoresc (2021) 31:733–745
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Fig. 7 Competitive titration
studies of receptor with all anions
with CN− ion
wavelength as 350 nm. By the addition of all anions into the
receptor, only cyanide ion got a fluorescence enhancement
with slight red shift from 439 nm to 471 nm (Fig. 5a). By
the ongoing addition of cyanide ion into the receptor upto
2.0 equ. its intensity got gradually enhanced which was
depicted in (Fig. 5b). This is due to the deprotonation take
place in the hydroxyl O-H and the NH group in the receptor.
Fluorescence Studies of All Cations with Receptor
To find out the emission properties of cations with receptor,
addition of all cations were added into the receptor solution.
Only Co2+ and Hg2+ gave a fluorescence enhancement where-
as all the other cations did not give any fluorescence change
(Fig. 6a). For the addition of Co2+ and Hg2+ ion into the
Fig. 8 Interference studies of
receptor with all cations with
Co2+ ion

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Fig. 9 Interference studies of the
receptor with all cations with
Hg2+ ion
receptor solution the emission maxima of Co2+ and Hg2+ ion
are 433 nm & 434 nm respectively. On adding either Hg2+ or,
Co2+ ion, remarkable fluorescence enhancement was ob-
served (Fig. 6b and c).This turn-on fluorescence is due to the
inhibition of PET (photo induced electron transfer).
simultaneously in the solution shown in Fig. 8. Thus the
chemosensor has a better selectivity towards Co2+.
Competitive Interaction Studies of Hg2+ with All
Cations
Achieving the best selection for specific analysis of competing
species remains a challenge in the development of sensors. To
evaluate the selectivity of the receptor in practice, competitive
tests were also performed in which the receptor was added to
the solution of Hg2+ in the presence of other individual cations
as shown in Fig. 9. This observation further confirms that
these ions do not exhibit obvious interference with Hg2+ de-
tection, and that selective detection of Hg2+ is not affected by
the presence of common metal ions. However, since the Hg2+
and Co2+ ions in the UV-Vis and PL spectra both induce the
same effect, it cannot completely rule out the interference of
the Co2+ ion.
Interference Studies of Cyanide with All Anions
The plausible interference study was done and it was observed
by UV–Vis spectra. Initially by the addition of all anions into
the receptor, and then followed by adding CN− ion. The re-
sults suggested that, the receptor is highly sensitive and selec-
tive towards cyanide ion over other ions. There was no inter-
ference of other anions (Fig. 7).
Competitive Titration Studies of Co2+ with All Cations
One of the important features of the chemical sensor is its high
selectivity towards the specific metal ion and its resistance to
other interfering ions. To evaluate the selectivity of the recep-
tor for the detection of Co2+ in the presence of other metals, it
should not be disturbed by the presence of other metal ions
Job’s Plot, Benesi–Hildebrand Plot and Limit of
Detection of CN−, Co2+ and Hg2+ ions
Job’s plot studies show the stoichiometry of receptor + cya-
nide ion interaction. The interaction follows 1: 1 binding stoi-
chiometry (Supplementary data-S1). By plotting the straight
line using 1/ΔA and 1/[CN−], the Benesi–Hildebrand plot
(Supplementary data-S2) Similarly the detection limit was
calculated using the formula 3* σ/m. The limit of detection
of receptor with cyanide ion is displayed in (Supplementary
data-S3). The significant bathochromic shift induced by CN−
is most probably due to the deprotonation of the hydroxy
Table 1 Binding ratio, association constant and limit of detection of
receptor with CN−, Co2+ and Hg2+
Sl.No Ions Binding ratio Binding constants Limit of detection
1
2
3
CN− 1:1
Co2+ 1:1
Hg2+ 1:1
1.6×105 M−1
1.9×105 M−1
1.0×105 M−1
5.8×10−7
3.6×10−7
8.1×10−7
M
M
M

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Fig. 10 1H NMR titration studies of receptor with CN− ion (0.equ − 2.0 equ.) in CDCl3 solvent
group and NH-group in the receptor. The resultant change in
the electronic environment of the receptor is readily transmit-
ted across the conjugated circuit, which leads to an extension
of π-conjugation, giving rise to the color change.
In Job’s plot studies, the binding ratio of the receptor with
cobalt ion shows 1:1 ratio which is shown in (Supplementary
data-S4). Binding constant and LOD was depicted in
(Supplementary data-S5 and S6). Further Job’s plot studies
shows the receptor with mercury ion describe the binding ratio
as 1: 1 (Supplementary data-S7).The association constant and
limit of detection was revealed in (Supplementary data-S8) &
(Supplementary data-S9). The stoichiometric ratio, Benesi–
Hildebrand plot and LOD value of receptor with CN−, Co2+
and Hg2+ ions are revealed in (Table 1).
Scheme 2 Possible binding
mechanism of receptor with CN−
ion
Scheme 3 Possible binding
mechanism of receptor with Co2+
and Hg2+ ion

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J Fluoresc (2021) 31:733–745
Fig. 11 Naked eye sensing of
receptor with CN− and all cations
1H NMR Titration Studies of Receptor with CN− ion
radical anion [30, 31]. The molecular structure of the receptor
consists of a D-group (thiourea) and an A-group
(salicylaldehyde) and completes the generally accepted mech-
anism of an endogenous PET fluorescent receptor (D-A) [32,
33]. The mechanism for the detection of cobalt ions by the
receptor is shown in Scheme 3. The formation of Co2+ com-
plex was observed while adding the CoCl2 to the receptor and
the formation was discussed in the mechanism. Complexation
has happened between the nitrogen donor atoms in the recep-
tor, in which imine nitrogen was coordinated to cobalt metal
via neutral fashion and the remaining N-H moiety of the re-
ceptor was coordinated through anionic mode. The ratio of
receptor and cobalt was 1:1 in the complex. Based on the
above results and literature [34] cobalt can be bound as shown
in Scheme 3. Similarly, receptor can coordinate to mercury
through anionic mode [35–38]. The proposed binding method
of the receptor with cobalt and mercury is shown in Scheme 3.
To prove this mechanism IR- spectrum for free receptor, re-
ceptor with Co2+ ion and receptor with Hg2+ ion were taken.
In the IR spectral data, the intense band in the region 1628–
1634 cm− 1 associated with C = N stretching vibration of free
receptor and it is shifted to lower frequencies (1588–
1598 cm− 1) in the spectra of corresponding to metal com-
plexes (Co2+, Hg2+). This indicated the coordination of
azomethine nitrogen to the metal ion [39]. phenolic O-H dis-
appeared in the IR spectra of the complexes in the region
3279–3360 cm− 1, suggesting deprotonation proceeding to co-
ordination to metal ion. In addition, a band appeared in the
region 1268–1300 cm− 1 due to phenolic C-O stretching in the
The interaction and binding behavior of CN− with receptor
1
was studied by H NMR titration using CDCl3 as a solvent
with TMS act as an internal standard. The free receptor shows
the OH-peak at 10.3 ppm and the NH- proton peak at
9.65 ppm and imine proton resonance at 8.3 ppm. Upon ad-
dition of 2.0 equ. of CN− ion into receptor, the peak at
10.3 ppm and 9.65 ppm get vanished and also the intensity
of the imine proton get decreases this is due to the deproton-
ation take place and also the CN− ion go to attack the N-H
moiety and followed by the electron density on phenyl protons
is increased, resulting in an upfield shifting in NMR signals.
This was shown in Fig. 10. and this mechanism was shown in
Scheme 2.
Possible Binding Mechanism of Receptor with Co2+
Hg2+ Ion
&
Cobalt’s binding pattern can further confirm the possibility of
ICT and PET occurring between the electron-releasing amino
group at thiourea and, as mentioned above, the carbonyl group
at salicylaldehyde, which causes the receptor to turn off con-
dition [29]. Changes in charge density at the N-binding sites of
the receptor after complexation with Co2+ inhibit the PET and
ICT processes, so that a fluorescence with a slight red-change
is activated as a result. Photo-induced electron transfer (PET)
from a donor (D) to acceptor (A) leads to the formation of a
charge-separated state with donor radical cation and acceptor
Fig. 12 a UV-Vis spectroscopic changes of receptor with CN− ion (1 × 10− 4 M in ACN) and cations in (1 × 10− 4 M in water); b Photoluminescence
studies of receptor with CN− in (1 × 10− 4 M in ACN) and cations in (1 × 10− 4 M in water)

J Fluoresc (2021) 31:733–745
741
(receptor + CN−). (Supplementary-data. S11). Upon addition
of Cr3+ion into the [receptor + CN−] solution spectrum of re-
ceptor was revitalized (Fig. 12a and b).
Table 2 Truth table of inhibition and implication logic gates of the
receptor, receptor + CN−, receptor + Cr3+ ions
Sl.No
Input-1
Input-2
Output-
1
Output-
2
CN−ion addition Cr3+ion addition
375 nm
445 nm
Logic Gate Application
1
2
3
4
0
1
0
1
0
0
1
1
1
0
1
1
0
1
0
0
Theoretically, implication and inhibition logic gates could be
developed from an integrated study that effectively detects
CN− and Cr3+ ions. Two absorptions are specified, indicating
that the absorbance at 375 nm, the implication logic gate is in
the “switch-on” position. Conversely, the inhibition gate is in
‘switch-off’ position, while the absorption at 445 nm is in the
“switch-on” position. Instead the implication gate is in the
“switch off” position. The input signals are CN− (input 1)
and Cr3+ (input 2). Absorption at 375 nm and 445 nm are
output 1 and output 2, respectively as shown in (Table 2).
Absorption at 375 nm, the receptor is in colorless, indicat-
ing that the implication gate is in the ‘on’ position. The addi-
tion of cyanide ion to the receptor solution changes its color
from colorless to yellow, indicating that the inhibition logic
gate is ‘switched on’ with absorption at 445 nm. The receptor
changes its color from yellow to colorless by adding Cr3+ ion
to the solution, while at 375 nm the implication gate is
‘switched on. Although the Cr3+ ions are added to the recep-
tor-CN− ion complex, the implication logic gate is ‘switched
on’ again, which is seen under the naked eye (Fig. 13a). This
change was further confirmed by the UV-Vis spectroscopic
studies (Fig. 13b). By the addition of 2.0 equ.of cyanide ion
and chromium ion in to the receptor solution colourless-
yellow-colourless cycle was repeated. The reason is Cr3+ ion
minimizes the synergy within the cyanide ion and the recep-
tor. Based on the repeating cycle we have developed another
logic gate namely memory machine. Here we use two input
signals ‘set’ (adding cyanide ion) & ‘reset’ (adding chromium
ion). IMP and INH are two output signals, taken as two logic
gates (Fig. 14a). The memory machine is executed depending
on the output signal. The logic circuit i.e. ‘write-read-delete-
read’ cycles is derived from the repetitive functions of the ‘on-
off’ process (Fig. 14b). The truth table of the memory machine
is illustrated in (Table 3).
free ligand has been shifted to 1310–1344 cm− 1 in the IR
spectra of the complexes indicating the coordination through
phenolic oxygen atom [40]. IR spectrum showed two NH-
bands at 3406 and 3470 cm− 1. These bands remained unal-
tered in the spectrum of the corresponding metal complexes
revealing non participation of NH2 in coordination [41]. A
band which appeared in the region 3127–3175 cm− 1 due to
N-H proton disappeared on complexation this was shown in
Supplementary data-S10.
Relay Recognition Studies
In cascade recognition studies, metal ion such as Cu2+,
Ni2+,Co2+, Hg2+, Mn2+, Cd2+, Zn2+, Cr3+, Al3+ and Fe3+ are
used. Conversely, receptor showed no color change and spec-
tral change with chromium. In the presence of cyanide ion, it
shows an admirable answer for Cr3+ ion, which changes its
yellow colour to colourless while notable change was not
observed for other ions. The reason is Cr3+ ion reacts more
rapidly with receptor than other ions and also the interaction
between hard acids and hard bases is mainly electrostatic,
increasing the stability of complexes containing hard acids
and hard bases as the positive charge of the metal ion increases
and its radius decreases [42, 43]. For this reason the receptor
interacts with Cr3+ion than other cations. This naked eye ob-
servation was exposed in Fig. 11. And this was confirmed by
UV-Vis and PL-studies. With the addition of the cyanide ion,
the fluorescence is enhanced, while the emission is quenching
by the addition of the Cr3+ ion to the reaction mixture
Fig. 13 (a) Colorimetric sensing
of receptor with CN−, CN− and
Cr3+(b) Corresponding UV-Vis
spectroscopic studies of receptor
with CN−, CN− and Cr3+

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Fig. 14 a Implication and Inhibition logic circuits for molecular gates; b Memory machine logic circuits for the corresponding ions
why our receptor got a color change from colourless
Table 3 Truth table for memory machine device
(375 nm) to yellow (445 nm).
Sl.No
Set
Reset
Output
(Absorbance in 445 nm)
CN- addition
Cr3+ addition
DFT Calculations of Receptor with Co2+ Ion
1
2
3
4
0
1
0
1
0
0
1
1
0
1
0
0
To find out the detail information about the interaction of
receptor with cobalt ion, structure of the receptor and its com-
plex were optimized using Gaussian 0.9 program with the
parameter of B3LYP/6-311G (d,p) in solvent medium.
Using DFT- calculation the binding of receptor with cobalt
ion may be calculated. Here the experimental energy gap of
receptor and receptor with cobalt ion as 3.27 eV and 0.27 eV
respectively which was shown in (Fig. 16). Thus the energy
gap of receptor with cobalt ion decreases due to the
bathochromic shift occurs in the UV-Vis spectrum. From this
evidence it is clear that if the wavelength increases automati-
cally the energy gap decrease that’s why our receptor got a
color change from colourless (375 nm) to light green (400 nm)
in UV-Vis spectrum.
DFT Calculations of Receptor with CN− Ion
To find out more details about the inclination of the re-
ceptor and CN−, the structure of the receptor and its com-
plex with CN− were discretely optimized in acetonitrile
solvent, using DFT-B3LYP/6-311G (d,p). Figure 15 shows
the optimized configuration of the receptor with CN- ion
in ground state. The structural parameters of the optimized
structures of the receptor and its CN− complex were per-
formed using Gaussian 09 program. The energy gap of
HOMO-LUMO of receptor was 3.27 eV and the
receptor-cyanide complex energy gap was 1.74 eV.The
energy gap of HOMO–LUMO of receptor with cyanide
ion is reduced. The reason was when the energy gap
decreases automatically the wavelength increases. That’s
DFT Calculations of Receptor with Hg2+ Ion
To find out the detail information about the interaction of
receptor with mercury ion, structure of the receptor and its
Fig. 15 DFT-calculation of the
optimized structure of receptor,
and its complex with CN− ion

J Fluoresc (2021) 31:733–745
743
Fig. 16 DFT-calculation of the
optimized structure of receptor,
and its complex with Co2+ ion
complex were optimized using Gaussian 0.9 program with the
parameter of B3LYP/6-311G (d,p) in solvent medium. Using
DFT- calculation the binding of receptor with mercury ion
may be calculated. Here the experimental energy gap of re-
ceptor and receptor with mercury ion as 3.27 eV and 1.72 eV
respectively which was shown in (Fig. 17). Thus the energy
gap of receptor with mercury ion decreases due to the
bathochromic shift occurs in the UV-Vis spectrum. From this
evidence it is clear that if the wavelength increases automati-
cally the energy gap decrease that’s why our receptor got a
color change from colourless (375 nm) to yellow (393 nm) in
UV-Vis spectrum.
Conclusions
In summary, we have developed the receptor for the selective
and sensitive detection of cyanide, cobalt and mercury in ace-
tonitrile medium. The synthesized receptor shows colorimet-
ric transitions from colourless to yellow for cyanide,
colourless to light green for cobalt ion and colourless to yel-
low for mercury. The strong hydrogen bonding between the
amino groups of the receptor and CN− ions and / or the depro-
tonation of the -NH proton by CN− ions caused large
bathochromic shift and observed color change. Furthermore,
the cyanide bound receptor detects Cr3+ by relay recognition
Fig. 17 DFT-calculation of the
optimized structure of receptor,
and its complex with Hg2+ ion

744
J Fluoresc (2021) 31:733–745
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which were lower than the permissible level given by World
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Supplementary Information The online version contains supplementary
material available at https://doi.org/10.1007/s10895-021-02700-9.
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Author Contributions G. punithakumari synthesised the molecule and
did all the experiments, data collection and first draft of the manuscript.
Dr. S. Velmathi has funded the project, conceptualised the idea, and
corrected the manuscript and overall coordinator of the work.
Funding One of the authors S.V. thanks Council of Scientific and indus-
trial Research (CSIR) India for a sponsored project 01(2949)/18/EMR-II
dated 01-05-2018 for financial assistance.
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interactions, theoretical study and DNA-binding properties.
Tetrahedron 74:6897–6906
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Schiff’s base structure as chemosensor for cyanide and copper ions.
Inorg Chem Comm 71:102–104
Data Availability Job Plot, Binding constant, Detection limit plots IR
spectra of complexes and other associated data are available as supporting
information.
17. Vashisht D, Kaur K (2019) Colorimetric chemosensor based on
coumarin skeleton for selective naked eye detection of cobalt (II)
ion in near aqueous medium. Sens Actuators B Chem 280:219–226
18. Na YJ, Choi YW (2016) A novel selective colorimetric
chemosensor for cobalt ions in a near perfect aqueous solution.
Sens and Actuators B Chem. 223:234–240
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chemosensor for the detection of mercury ions using mono- and
tetra-sulfur bearing phenanthridines. New J Chem 42:8530–8536
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mogenic and fluorogenic dual mode chemosensor for selective de-
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molecular logic gate. Dyes Pigments 174:108054
Code Availability Not applicable.
Declarations
Conflict of Interest Authors declare no conflict of Interest.
Ethics Approval Not Applicable.
Consent to Participate All authors have agreed for participation.
Consent for Publication All authors have agreed for publication.
21. Harikrishnan VK, Basheer SM (2017) Colorimetric and fluorimet-
ric response of salicylaldehydedithiosemicarbazone towards fluo-
ride, cyanide and copper ions: Spectroscopic and TD-DFT studies.
Acta A Mol Biomol Spectrosc1825:160–167
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