The simplest molecular chemosensor for detecting higher pHs, Cu2+ and S2- in aqueous environment and executing various logic gates

Article abstract of DOI:10.1016/j.jphotochem.2018.11.029

The sensory properties of the simplest Probe-1 are reported. Probe-1 exhibits colorimetric and fluorimetric responses towards higher pHs. Also, a borate aqueous solution of Probe-1 (pH = 10) could to detect the presence of Cu²⁺ in aqueous solut

Full text of DOI:10.1016/j.jphotochem.2018.11.029

Accepted Manuscript
Title: The simplest molecular chemosensor for detecting
higher pHs, Cu2+ and S2− in aqueous environment and
executing various logic gates
Authors: Awad I. Said, Nikolai I. Georgiev, Vladimir B.
Bojinov
PII:
S1010-6030(18)31404-7
DOI:
Reference:
https://doi.org/10.1016/j.jphotochem.2018.11.029
JPC 11601
To appear in:
Journal of Photochemistry and Photobiology A: Chemistry
Received date:
Revised date:
Accepted date:
27 September 2018
7 November 2018
19 November 2018
Please cite this article as: Said AI, Georgiev NI, Bojinov VB, The simplest molecular
chemosensor for detecting higher pHs, Cu2+ and S2- in aqueous environment and
executing various logic gates, Journal of Photochemistry and amp; Photobiology, A:
Chemistry (2018), https://doi.org/10.1016/j.jphotochem.2018.11.029
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The simplest molecular chemosensor for
detecting higher pHs, Cu2+ and S2- in aqueous
environment and executing various logic gates
Awad I. Said a,b, Nikolai I. Georgiev a, Vladimir B. Bojinov a *
a Department of Organic Synthesis, University of Chemical Technology and Metallurgy, 8
Kliment Ohridsky Str., 1756 Sofia, Bulgaria
b Department of Chemistry, Faculty of Science. Assiut University, Assiut, Egypt
* Corresponding author. Tel.: (+ 359 2) 8163206
E-mail address: vlbojin@uctm.edu (V. B. Bojinov)

Graphical abstarct
Highlights
 A highly water-soluble in alkaline window hydrazone derivative is synthesized.
 Hydrazone derivative acts as a molecular fluorescent pH probe.
 Probe manifests selective fluorescence response to Cu2+ in alkaline aqueous medium.
 Probe/Cu2+ complex serves as a highly sensitive molecular sensor for S2- anions.
 A series of logic gates of the probe are achieved.
A B S T R A C T
The sensory properties of the simplest Probe-1 are reported. Probe-1 exhibits colorimetric and
fluorimetric responses towards higher pHs. Also, a borate aqueous solution of Probe-1 (pH =
10) could to detect the presence of Cu2+ in aqueous solution with high selectivity and sensitivity
-
(3 μM). The Probe-1/Cu2+ complex responses selectively towards the presence of S2-, H2PO4
and P2O74- through a de-metallization mechanism, resulting in a fluorescence enhancement of
143%, 97% and 134%, respectively. On the other hand, the Probe-1 absorbance increases
significantly only by S2- (131%). Furthermore, Probe-1 executes many logic gates such as XOR,
AND, INHIBIT, IMPLICATION, TRANSFER and NOT TRANSFER.
Keywords: (E)-4-(1-hydrazonoethyl)benzene-1,3-diol; Fluorescence probe; Detection of Cu2+,
-
S2- and H2PO4 ; De-metallization; AND, XOR, INHIBIT, IMPLICATION, TRANSFER and NOT
TRANSFER logic gates.

1.
Introduction
pH plays an important role in most biological and industrial processes [1-8]. Although
electrochemical pH sensors are well known as a reliable tool for solving different tasks, some
disadvantages of pH electrodes, including the need for continuous calibration, a frequent
electrical interference and possibility of corrosion in alkaline media, greatly limit their
effectiveness [9]. Therefore, the considerable efforts of the researchers in recent years have
been directed towards the creation of optical sensors for detecting pH changes in the
environment [10-12], operating via different sensing mechanisms [13-18]. Among these,
molecular fluorescent pH sensors have gained a significant attention because of their high
sensitivity [19-22].
Cu2+, the third by quantity transition metal ion in the human body, has an important role
in numerous of physiological processes [23-25]. Overloading of copper in neuronal cytoplasm
is associated with Wilson and Alzheimer diseases [26,27]. That is why a number of researchers
have made serious efforts to develop molecular probes for detecting Cu(II) [28-43]. Although
a Cu2+ bound fluorophore usually causes a fluorescence quenching due to the paramagnetic
nature of Cu2+, the non-fluorescent Cu2+-fluorophore complex can provide an indirect route for
anion (as sulfide) recognition through Cu2+ demetallization approach [44]. Sulfides are
widespread in the environment and find significant use in the production of sulfur, sulfuric acid,
dyes and cosmetics [45]. Nevertheless, higher doses of sulfide lead to unpleasant physiological
problems such as mucosal irritation, loss of consciousness and respiratory paralysis [46].
A series of methods for the recognition of Cu(II) have been developed [47-49]. All of
them, however, unlike fluorescence probes, use time-consuming procedures and expensive
toolkit [50,51]. In the recent years many excellent chemosensors and chemodosimeters for
Cu(II) have been described. However, some of them have various shortcomings including
complicated synthetic procedures, high detection limit, use of organic solvents and interference
from other transition metals ions, which often coexist and have similar reactivity toward
molecular sensors [52-54]. Chemosensors containing 2-hydroxyl hydrazone are well known for
their ability to chelate and detect transition metal cations, especially Cu2+ [55,56].
Incorporation of the molecule scale into information technology in performing the
required logic gates and operations is a challenge since the last decades. Many scientists have

focused on the design of smart functional molecular systems capable of working as Boolean
logic gates as well as could to execute several high order functions like comparator [57-62],
half-adder/subtractor [63-65], memory device [66,67], key-pad lock [68,69], etc. These can
mimic modern semiconductor based devices to a dimension as small as in the nanoscale order.
In a previous work, we examined some photophysical characteristics of hydrazone of
2,4-dihydroxyacetophenone depending on the pH of the medium [57]. In this work, we
synthesized 2,4-dihydroxyl acetophenone hydrazone (Probe-1) by improved synthetic
procedure and investigated its unexpectedly interesting properties and the benefit to operate as
a simple fluorescent probe for pH and Cu2+. Probe-1 simultaneously performs both receptor and
reporter functions and is capable of selectively recognizing Cu2+ in the presence of other
representative transition metal ions. Also, we investigated the aptitude of the Cu2+/Probe-1
complex for the detection of sulfide and the selectivity of this detection as well as the ability of
the compound to execute different logical operations.
2.
Experimental
2.1. Materials
Commercially available 2,4-dihydroxyacetophenone (Aldrich) and hydrazine
monohydrate (Aldrich) were used as delivered. All solvents (Fisher Chemical, Aldrich) were
pure or of spectroscopy grade. All used salts as sources for metal ions Zn(NO3)2, Cu(NO3)2,
Ni(NO3)2, Co(NO3)2, Pb(NO3)2, Fe(NO3)3, Hg(NO3)2, Cd(NO3)2, Cr(NO3)3 and AgNO3 or
anions NaF, Na2SO4, NaHSO4, NaNO2, Na2S2O5, CH3COONa, Na2CO3, NaCN, Na2S, KBr,
NaH2PO4 and Na4P2O7 were of pure for analysis grade.
2.2. Methods
1
FT-IR spectrum was taken on a Varian Scimitar 1000 spectrometer. The H NMR
spectrum was registered on a Bruker DRX-250 spectrometer. Kofler microscope was used for
the determination of melting point. Absorption and fluorescence spectra were recorded on a
Hewlett Packard 8452A and Scinco FS-2 spectrophotometers, respectively. The excitation
source for the fluorescence measurements was a 150 W Xenon lamp and the excitation/
emission slits width was 5 nm.

2.3. Synthesis of (E)-4-(1-hydrazonoethyl)benzene-1,3-diol (Probe-1)
A mixture of 2,4-dihydroxyacetophenone (12.5 g, 100 mmol) and 46 mL of hydrazine
monohydrate was stirred for 4 h at room temperature in 50 mL of DMF. Then the reaction
mixture was diluted with 100 mL of water. The precipitate was filtered off and washed with
fresh water to give 16.1 g (97%) of desired compound (Probe-1). M.p 196-198oC; Rf = 0.32 in
ethyl acetate/petroleum ether = (2:1).
FT-IR (KBr) cm-1: 3292 (OH, NH); 2924 (CH); 1599 (-C=N). 1H NMR (CHCl3-d,
250.13 MHz)  ppm: 12.96 (s, 1H, Ph-OH); 11.08 (s, 1H, Ph-OH); 7.58 (d, 1H, J = 8.8 Hz, Ph-
H5); 6.39 (dd, 1H, J = 8.8 Hz, J = 2.4 Hz, Ph-H6); 6.22 (d, 1H, J = 2.4 Hz, Ph-H2); 3.29 (s, 2H,
NH2); 2.54 (s, 3H, CH3). Elemental analysis: Calculated for C8H10N2O2 (MW 166.18) C 57.82,
H 6.07, N 16.86 %; Found C 57.48, H 6.15, N 16.58 %.
3.
Results and discussion
3.1 Designing and synthesis of Probe-1
Probe-1 was prepared simply according to an improved previously described synthetic
procedure [57] by stirring 2,4-dihydroxyl acetophenone with access of hydrazine hydrate in
DMF solution at room temperature instead of under reflux for the same duration of 4 hours
(Scheme 1).
Insert here Scheme 1
As we demonstrated before, (E)-4-(1-hydrazonoethyl)benzene-1,3-diol (Probe-1) is in
equilibrium between the non-fluorescent benzenoid structure and non-fluorescent quinoid one
[57]. Fluorescence quenching of Probe-1 was ascribed to the excited state intramolecular proton
transfer (ESIPT) that can be blocked by deprotonation at higher pHs (Scheme 2). Hence, Probe-
1 can be used for detecting higher pHs. Also, the structure of Probe-1 due to the different
heteroatoms is an appropriate for chelating with metal ions that can be translated to optical
responses.

Insert here Scheme 2
3.2. Influence of pH on the absorption and fluorescence spectra of Probe-1
As is shown in Figure 1A, the maximal absorbance of Probe-1 between 300 and 430 nm
is centered at 374 nm, which is due to the typical for compounds of similar nature π→π*
transition [70]. In acid medium the absorption character of the compound retains approximately
the same. Conversely, in alkaline medium the absorption maximum is red shifted to 420 nm
with a pronounced increase in the molar extinction coefficient, indicating the transition of the
aromatic C-4 hydroxyl group to a phenolic anion and its conversion into dianion in a quinoidal
form (Scheme 2). It should be noted that Probe-1 and its acidic solution did not exhibits a
fluorescent emission (Figure 1B) which can be related to the existing ESIPT process. In basic
environment Probe-1 exists in a quinoid form. Therefore the ESIPT process is not possible, so
the fluorescence emission of the probe becomes feasible (Figure 1B).
Insert here Figure 1A and Figure 1B
These observations disclosed capability of the examined compound to work as a
molecular probe for high pH values. That is why we performed a complete pH titration of Probe-
1. The titration was started from high pH to assert the presence of the probe in the fluorescent
dianion quinoid form.
Figure 2 illustrates the effect of the pH titration on the absorption of the probe. At pH
13.4, the probe exhibits absorption peaks centered at 310 nm (ԑ = 6.1 × 104 L·mol-1·cm-1) and
420 nm (ԑ = 1.4 × 104 L·mol-1·cm-1). In decreasing the pH till pH ≈ 11 no significant change
was observed in the absorption spectrum. After pH ≈ 11 and till near pH ≈ 10; the absorbance
at 420 nm sharply decreases and is hypsochromically shifted to 380 nm, the absorbance at 310
nm sharply decreases as well and a new absorption band centered at 270 nm appears. After pH
≈ 10 and till near pH ≈ 2 the absorbance at 420 nm does not change significantly, and then
begins to increase again with a decrease in pH. The absorbance at 310 nm and 270 nm are
caused by n→π* transitions in the anion and neutral forms of Probe-1, respectively. The high
absorption and bathochromic shifts after pH near 2 are attributed to formation of a quinoid
structure induced by protonation of the imine nitrogen (Scheme 3).

Insert here Figure 2
Insert here Scheme 3
Using the absorption changes of Probe-1 at 420 nm in pH range 9.3-10.7 (Inset of Figure
2) the pKa value of 10.37 for the transformation from monophenolate to keto-hydrazine dianion
form was calculated according to Eq. (1), where Amax and Amin are the maximum and minimum
absorbance at 420 nm, respectively, A is the absorbance at the given pH value [71].
Insert here Equation (1)
On the other side, the fluorescence emission is high at higher pH values till near pH 12.5
and decreases significantly after pH ≈ 12.5. After pH ≈ 9.5, the fluorescence intensity becomes
constant unaffected by decreasing the pH (Figure 3). The low fluorescence after pH ≈ 2,
although the probe is in its quinoid form (Scheme 3), is attributed to quenching caused by ESIPT
process.
Insert here Figure 3
Using the fluorescence changes of Probe-1 at 500 nm in pH range 9.6-12.5 (Inset of
Figure 3) the pKa value of 10.40 for the transformation from monophenolate to keto-hydrazine
dianion form was calculated according to Eq. (2), where Fmax and Fmin are the maximum and
minimum fluorescence intensity at 500 nm, respectively, F is the fluorescence intensity at the
given pH value [72]. The pKa value of 10.40 is near to that obtained by the absorption.
Insert here Equation (2)
3.3. Influence of metal cations on the absorption and fluorescence of Probe-1
The signaling behavior of Probe-1 towards a wide range of representative transition
metal ions (Co2+, Cu2+, Fe3+, Cr3+, Ni2+, Pb2+, Cd2+, Zn2+, Hg2+ and Ag+ (as nitrate) was studied
in an aqueous solution (ethanol:water = 1:1, v/v) at pH = 10 (borate buffer) to assert the presence

of the probe in its fluorescent form. The influence of the cations was studied at low amount
(one equivalent) and at high amount (ten equivalents) of the cations.
The photophysical behavior of Probe-1 as a function of metal ion concentration up to 3
× 10-4 mol L-1 (10 equivalents) to 3 × 10-5 mol L-1 solution of the probe was also examined at
pH= 7.2 (HEPES buffer), however, no changes were observed. This indicates that Probe-1 is
inappropriate detector for metal ions in a neutral environment.
3.3.1. Influence on the absorption spectrum
In borate buffer (pH = 10), the probe exhibits two absorption peaks centered at 310 nm
(ԑ = 1.1 × 104 L·mol-1·cm-1) and 420 nm (ԑ = 4.2 × 103 L·mol-1·cm-1). As shown in Figure 4A,
after addition of one equivalent of the cations, the absorption at 420 nm was not affected
significantly by any of the cations under study, except Pb2+ that causes a little increase of 32%.
In the same time, Cu2+ causes a little decrease in the absorbance at 420 nm by 12 %. However,
after the addition of ten equivalents of cations, the effect of Pb2+ and Cu2+ becomes more
pronounced 112% and -38%, respectively (Figure 4B).
Insert here Figure 4AR1 and Figure 4BR1
The increase in absorption at 420 nm by Pb2+ ion is attributed to its binding to the
quinoid form of the probe, thus shifting the equilibrium to the quinoid form that absorbs at 420
nm. In the other side, the decrease in absorption by Cu2+ ion can be interpreted by its affinity to
coordinate with the benzenoid form. So, the equilibrium is shifted to benzenoid form.
3.3.2. Influence on the emission spectrum
No pronounced effect on the fluorescence emission of Probe-1 at 500 nm after the
excitation at 420 nm was observed by adding one equivalent of cations (Figure 5A). Using ten
equivalents of the cations, only Cu2+ caused a significant quenching (92%) (Figure 5B).
Insert here Figure 5A and Figure 5B
The quenching efficiency (QE) is calculated by Eq. (3), where Fo and F are the
fluorescence intensity in the absence and presence of the quencher (Cu2+), respectively.

Insert here Equation (3)
The quenching of the fluorescence of Probe-1 in the presence of Cu2+ is ascribed to two
factors: (i) The shifting of the equilibrium towards the non-fluorescent benzenoid form; (ii) The
paramagnetism of Cu2+ that causes an energy transfer from probe to the cation [73]. The
remarkable quenching only by excess of Cu2+ infers to the slow coordination between the probe
and the Cu2+ ion.
Because of the slow coordination between the probe and Cu2+, we studied the effect of
the time on the probe response towards the presence of Cu2+.
3.3.3. Effect of time on the Probe-1 response in the presence of Cu(II)
The response of Probe-1 towards Cu2+ as a function of the time was studied at different
equivalents of Cu2+.
When using one equivalent of Cu2+, the decrease in absorption at 420 nm by time is
slow (0.0031 per minute) and the equilibrium is reached after 30 minutes (Figure 6A). The
decrease of emission at 500 nm was slow as well (223 A.U. per minute) and the saturation is
achieved after 50 minutes (Figure 6B).
Insert here Figure 6A and Figure 6B
Using of 5 (Figure 7A) or 10 (Figure 7B) equivalents of Cu2+, the saturation was
achieved only after 3 minutes and faster quenching rates of florescence are observed.
Insert here Figure 7A and Figure 7B
The rate of decrease of both absorbance at 420 nm and emission at 500 nm of Probe-1
as well as the time of saturation at different equivalents of Cu2+ are summarized in Table 1.
Insert here Table 1

The increasing of the change rate in the absorption and emission spectra by excess of
Cu2+ confirms the slow reaction between Probe-1 and Cu2+, thus the equilibrium can be
achieved either by long time or adding excess of Cu2+.
3.3.4. The sensitivity of Probe-1 to Cu2+
Both the absorbance at 420 nm and the fluorescence intensity at 500 nm were decreased
by increasing the concentration of Cu2+ (Figure 8, A and B).
Insert here Figure 8A and Figure 8B
From the titration plots of the absorption at 420 nm and the fluorescence intensity at 500
nm of Probe-1 against the concentration of Cu2+ (Insets of Figure 8A and Figure 8B), the linear
range of sensitivity, correction coefficient R2 and slope b were determined. The standard
deviation σ was calculated after measuring the absorption or fluorescence emission of the probe
several times. The limit of detection was calculated from the formula LOD = 3σ/b [74] (Table
2).
Insert here Table 2
3.3.5. Stoichiometric ratio of Probe-1/Cu2+ complex
The Job’s plot analysis whether from the absorption spectra or from the fluorescence
emission spectra (Figure 9), revealed a 2:1 stoichiometry for the complexation between the
Probe-1 and Cu2+, respectively.
Insert here Figure 9A and Figure 9B
The supposed binding mechanism in accordance to the similar chemical structures [75]
is illustrated on Scheme 4.
Insert here Scheme 4

The binding constant of the Probe-1/Cu2+ complex was evaluated from the titration plot
of the fluorescence at 500 nm (λex = 420 nm) against the concentration of Cu2+ (Insets of Figure
8B) using Benesi-Hildebrand Eq. (4), where Io and I∞ are emission intensities of the free and
fully bound (saturation point) forms of Probe-1, respectively, I is emission intensity of the probe
in the presence of Cu2+ in known concentration, n represents the stoichiometry of binding of
the probe to Cu2+, K is the binding constant of the probe to the Cu2+ and [C]is the concentration
of Cu2+ [76].
Insert here Equation (4)
In substituting into Eq. (4) using n = Probe-1/Cu2+ = 2:1, the binding constant was found
to be 3 × 109 M-2.
3.3.6. Selectivity of Probe-1 to Cu2+
The effect of the interfering cations on the Probe-1 response towards Cu2+ was examined
by measuring the absorption and fluorescence intensity of the probe in medium of Cu2+ and the
corresponding interfering cation. It is found that when Cu+2 presents in concentrations higher
than one equivalent, the interfering cation do not affect significantly on the fluorescence
emission at 500 nm. At the same time, there is a significant influence on the absorption mode
at 420 nm by Fe3+ and Pb2+, which is expressed in an increase in the absorbance at 420 nm with
174% and 225% caused by Fe3+ and Pb2+, respectively (Figure 10). The effect by Fe3+ and Pb2+
was ascribed to the affinity of the probe to coordinate also with Fe3+ or Pb2+ in addition to Cu2+.
Insert here Figure 10A and Figure 10B
However, in the presence of lower amount (one equivalent) of Cu+2, when the binding
with the probe is slow, a strong interfering effect by Hg2+ and Ag+ on the probe’s fluorescent
response is observed. Hg2+ accelerates the decreasing rate of the absorption of Probe-1 and its
emission output (Figure 11). The higher decrease in the absorption and emission responses
towards Cu2+ in the presence of Hg2+ was ascribed to the similar behavior of Hg2+ and Cu2+ in
coordination with the benzenoid form.

Insert here Figure 11A and Figure 11B
Studying the effect of Ag+ (1 equivalent) on the absorption and emission response of
Probe-1 towards the presence of Cu+2 (1 equivalent), it is observed that in the presence of Ag+,
the absorption at 420 nm is increased sharply after one minute, then begins to decrease in rate
0.018 per minute and does not decease under the value of the probe itself even after 17 minutes
(Figure 12). In the contrary, in the absence of Ag+, the absorption at 420 nm decreases to 45%
after 17 minutes. On the other hand, in the presence of Ag+, the emission at 500 nm decreases
in rate 582 A.U. per minute by 75% after 15 minute, but in the absence of Ag+, the rate of
quenching is 223 A.U. per minute and the quenching efficiency is 31% after 15 minutes.
Insert here Figure 12A and Figure 12B
The low decrease rate of the absorption at 420 nm in the presence of Ag+ is attributed
to the coordination of Ag+ with the quinoid form of Probe-1 that competes with Cu2+
coordinating with the benzenoid form of the probe. On the other hand, the higher rate of
fluorescence quenching is probably due to the energy transfer from Probe-1 to Ag+.
3.4. Influence of anions on the absorption and fluorescence of Probe-1
No significant effect on the absorption and emission spectra of Probe-1 is observed by
2-
-
-
2-
2-
any of the anions under the study (including F-, SO4 , HSO4 , NO2 , S2O5 , CH3COO-, CO3 ,
-
4-
CN-, S2-, Br-, H2PO4 and P2O7 ), whether at one equivalent or at ten equivalents of anions.
3.4.1. Influence of anions on Probe-1/Cu2+ complex
The addition of any of the anions under study to Probe-1/Cu2+ complex did not affect
-
both absorption and fluorescence spectra of the complex, with the exception of S2-, H2PO4 and
P2O74- that caused fluorescence enhancements by 143%, 97% and 134%, respectively (Figure
13A). On the other hand, the absorbance at 420 nm was increased significantly (131%) only by
S2- (Figure 13B).
Insert here Figure 13AR1 and Figure 13BR1

The increase in the absorption at 420 nm and the fluorescence at 500 nm caused by S2-
can be attributed to the de-metallization of the Probe-1/Cu2+ complex liberating the Probe-1 as
a free and forming the covellite copper sulfide (CuS) nanoparticles that are responsible for the
strong absorbance at 420 nm [77] (Scheme 5).
Insert here Scheme 5
The increase in the fluorescence emission without change in the absorption by
phosphate and pyrophosphate anions can be attributed to the coordination of phosphate or
pyrophosphate anions around Cu2+ in the Probe-1/Cu2+ complex thus decreasing the efficiency
of fluorescence quenching by energy transfer from ligand to the Cu2+ ion.
The above indicates that Probe-1/Cu2+ complex could serve as a highly sensitive sensor
for S2- anions in absorption mode. From the plotting of the absorption at 420 nm against the
concentration of S2- (Figure 14), the linear range of sensitivity was found to be 0-30 μM,
correction coefficient R2 = 0.914, a slope b was 0.0011 × 106 M-1. The standard deviation σ was
calculated to be 0.00361 and the limit of detection was calculated to be 10 μM.
Insert here Figure 14
3.5. Logic gates by Probe-1
Thanks to the substantial changes in the absorption and fluorescence of Probe-1 in the
presence of protons, hydroxide, Cu2+, S2- and Pb2+, it would be able to act as a multifunctional
logic device. Using H+ and HO- as inputs, the XOR and INHIBIT logic gates based on the
absorption and emission output of Probe-1 were executed. Considering at the start point pH =
7 (coded as 00 for the inputs H+ and HO-), the absorbance of the probe at 420 nm and the
fluorescence emission at 500 nm (λex = 420 nm) were lower than the threshold barrier (coded
as 0 for output). Input H+ or HO- (10-1 mol L-1) alone increased the absorbance at 420 nm and
brought it to be higher than the threshold barrier (coded as 1 for output), however the
fluorescence emission was increased only by input HO- to be higher than the threshold barrier.
The simultaneous inputs of H+ and HO- annihilated each other and generated the initial low
states (Figure 15). The behaviors of the absorbance at 420 nm (Figure 15A) and the fluorescence

emission at 500 nm (Figure 15B) mimic the XOR and INHIBIT logic gates using H+ and -OH
as inputs (Table 3).
Insert here Figure 15A and Figure 15B
Insert here Table 3
Furthermore, in alkaline solutions (pH 10) using Cu2+ and Pb2+ as chemical inputs,
IMPLICATION, TRANSFER and NOT TRANSFER gates were achieved. As is shown in
Figure 16 and Table 4, the presence of input Cu2+ decreases the absorbance at 420 nm but the
presence of input Pb2+ increases this absorbance whatever it is alone or mixed with Cu2+.
Considering the barrier level of the absorbance at 420 is higher than that by input Cu2+ alone
but in the same time is lower than that by the Probe-1 alone, the behavior of the absorbance at
420 nm mimics IMPLICATION logic gate (Figure 16A, threshold A). However, considering
the barrier level is higher than the absorbance of Probe-1 alone, the absorbance changes at 420
nm mimic TRANSFER logic gate (Figure 16A, threshold B). On the other hand, the
fluorescence emission of the system is lower than the barrier level only in the presence of Cu2+
whether it is alone or mixed with Pb2+ and this fluorescence behavior mimics NOT TRANSFER
logic gate (Figure 16B).
Insert here Figure 16A and Figure 16B
Insert here Table 4
Also, using Cu2+ and S2- as chemical inputs and the absorption of Probe-1 as output,
AND logic gate at molecular scale could be constructed. Monitoring the absorbance at 420 nm
and considering the absorbance of the probe alone is in a low state (coded 0 for output), the
presence of any of the inputs alone remains the absorbance lower than the threshold. However,
the presence of the two inputs together increases the absorbance at 420 nm and brought it to be
higher than the threshold (coded as 1 for output) (Figure 17). Such behavior is very well
correlated with AND logic gate (Table 5).
Insert here Figure 17

Insert here Table 5
4.
Conclusions
In the present work we report the preparation of (E)-4-(1-hydrazonoethyl)benzene-1,3-
diol (Probe-1) in an improved synthetic procedure as well as the results of the detailed
examination of its photophysical characteristics as a function of pH of the medium and the
presence of a wide range of representative transition metal ions and anions. As a result of the
ESIPT process and equilibrium between the non-fluorescent benzenoid structure and the non-
fluorescent quinoid one Probe-1 has a high potential for use as a molecular sensor in an alkaline
environment. Furthermore, Probe-1 is capable of selectively recognizing Cu2+ ions in the
environment in concentrations higher than one equivalent (LOD = 3 μM), forming a complex
in a 2:1 ratio. At the same time, the Probe-1/Cu2+ complex itself serves as a highly sensitive
molecular sensor for S2- anions in absorption mode (LOD = 10 μM) due to its de-metallization
to covellite copper sulfide (CuS) nanoparticles. Finally, it has been shown that Probe-1 is
capable of executing many different logic gates such as XOR, AND, INHIBIT, IMPLICATION,
TRANSFER and NOT TRANSFER.
Acknowledgements
This work was supported by the Science Foundation at the University of Chemical
Technology and Metallurgy (Sofia, Bulgaria) – project No 11811/2018 and project No
11818/2018. Authors also acknowledge the Science foundation of Assiut University (Assiut,
Egypt).

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Tables
Table 1
Rate of decrease of emission and absorption of Probe-1 and time of saturation at different
equivalents of Cu2+.
Absorption at 420 nm
Emission at 500 nm
Equivalents
of Cu2+
Rate of decrease
Saturation
time (minute)
Rate of decrease
A.U. Per minute
Saturation time
(minute)
Per minute
One
Five
Ten
0.0029
0.022
0.034
50
3
223
3262
3427
50
3
3
3
Table 2
The linear range of sensitivity, correction coefficient, slope and the limit of detection (LOD)
using absorbance at 420 nm and emission at 500 nm for Probe-1 toward [Cu2+].
Linear
Correction
Standard
deviation (σ)
range of
detection
(μM)
Slope (b)
LOD
coefficient (R2)
(106 M-1)
-0.00689
-443.49
(μM)
27
Absorption (A420)
Emission (F500)
20-30
0-30
0.95685
0.0161
557.48
0.275.0
3
Table 3
The truth table for logic behavior of Probe-1 using H+ and HO- as chemical inputs
Chemical Inputs Outputs
Input 1
Input 2
Output 1
Output 2
H+
OH-
Absorbance (A420)
Fluorescence (F500)
0
0
1
1
0
.
0
1
0
1
0
1
1
0
0
0
INHIBIT (HO-)
Logic gate:
XOR

Table 4
The truth table for logic behavior of Probe-1 using Cu2+ and Pb2+ as chemical inputs.
Chemical Inputs
Outputs
Output 2
Input 1 Input 2
Output 1
Output 3
Absorbance (A420)
Absorbance (A420)
Cu2+
Pb2+
Fluorescence (F500)
Level A
Level B
0
0
1
1
0
.
0
1
1
0
1
0
1
1
1
0
0
1
0
1
TRANSFER (Pb2+) NOT TRANSFER (Cu2+)
Logic gate:
IMPLICATION
Table 5
The truth table for logic behavior of Probe-1 using Cu2+ and S2- as chemical inputs.
Input 1
Input 2
Output
Cu2+
S2-
Absorbance (A420)
0
0
1
1
0
0
.
0
0
0
1
1
Logic gate:
AND

Scheme Captions
Scheme 1. Synthesis of Probe-1.
Scheme 2. Structural changes of Probe-1 in alkaline media.
Scheme 3. Structural transformation of Probe-1 in strong acid medium.
Scheme 4. Binding between Probe-1 and Cu2+ at pH=10 (borate buffer).
Scheme 5. De-metallization of Probe-1/Cu2+ complex with S2- anion.

Figure Legends
Fig. 1. Effect of acid and base on (A) absorption and (B) fluorescence (λex = 420 nm) spectra
of Probe-1 in aqueous solution.
Fig.2. Effect of pH on the absorption spectrum of Probe-1 in ethanol/water (1:2, v/v) solution
(C = 1 × 10-5 mol L-1). Inset: Absorbance of Probe-1 at 420 nm as a function of pH.

Fig.3. Effect of pH on the fluorescence spectrum of Probe-1 (λex = 420 nm) in ethanol/water
(1:2, v/v) solution (C = 1 × 10-5 mol L-1). Inset: Fluorescence of Probe-1 at 500 nm as a function
of pH.
Fig. 4. Effect of (A) one equivalent (C = 3 × 10-5 mol L-1) and (B) ten equivalents (C = 3 × 10-
4 mol L-1) of the cations on the absorption spectrum of Probe-1 in aqueous solution (C = 3 × 10-
5 mol L-1) and borate buffer (C = 0.2 mol L-1, pH = 10).

Fig. 5. Effect of (A) one equivalent (C = 3 × 10-5 mol L-1) and (B) ten equivalents (C = 3 × 10-
4
mol L-1) of the cations on the fluorescence spectrum of Probe-1 (λex = 420 nm) in aqueous
solution (C = 3 × 10-5 mol L-1) and borate buffer (C = 0.2 mol L-1, pH = 10).