Experimental and theoretical studies of novel hydroxynaphthalene based chemosensor, and construction of molecular logic gates

Article abstract of DOI:10.1016/j.jfluchem.2016.10.005

2-Hydroxynaphthalenyl-N(4)-cyclohexyl thiosemicarbazone (CHNT) was synthesized and characterized for selective sensing of fluoride, cyanide and copper ions. The interaction between CHNT with fluoride, cyanide and copper ions have been investigated through

Full text of DOI:10.1016/j.jfluchem.2016.10.005

Journal of Fluorine Chemistry 191 (2016) 129–142
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Experimental and theoretical studies of novel hydroxynaphthalene
based chemosensor, and construction of molecular logic gates$
Sabeel M. Basheera, Nattamai S.P. Bhuvaneshb, Anandaram Sreekantha,
*
a
Department of Chemistry, National Institute of Technology, Tiruchirappalli, Trichy-620015, India
b
Department of Chemistry, Texas A&M University, USA
A R T I C L E I N F O
A B S T R A C T
Article history:
2-Hydroxynaphthalenyl-N(4)-cyclohexyl thiosemicarbazone (CHNT) was synthesized and characterized
for selective sensing of fluoride, cyanide and copper ions. The interaction between CHNT with fluoride,
cyanide and copper ions have been investigated through their absorption, fluorescence and
electrochemical behavior, and binding constants of corresponding ions have been calculated, which
is in order of Cu2+ < CNꢀ < Fꢀ. The 1H NMR titration study strongly support the deprotonation was takes
place from the N2–H8 proton which is near to the naphthalene group. The fluoride and copper sensing
mechanism of CHNT has been investigated by DFT and TDDFT methods The theoretical results indicate
that the proton of the N2ꢀH in thiosemicarbazone group is captured by the added fluoride ion and then
deprotonated in excited state. The excited state proton transition mechanism was further confirmed with
NBO and PES analysis. The CHNT found good reversibility character with the alternative addition of Ca2+
and Fꢀ. The multi ion detection of CHNT was used to construct the NOR, XNOR and NAND molecular logic
gates.
Received 24 June 2016
Received in revised form 4 October 2016
Accepted 5 October 2016
Available online 5 October 2016
Keywords:
Chemosensing
Single crystal XRD
TDDFT
Molecular logic gate
ã 2016 Elsevier B.V. All rights reserved.
1. Introduction
interacts strongly with the heme group and causes cellular
respiration problem. There by affect the vascular, cardiac, visual
Cations and anions play a vital role in chemical and biological
processes [1–3]. The effective and selective detection of these
metal ions and anions are done by the chemosensors which has
grabbed the attention over a period [4,5]. The fluoride, cyanide ions
have major activity in human health, where one such example of
fluorine is used in the treatment of Osteoporosis5 and toxic when
its content (<1.5 mg/l) more in human body [6]. Due to small size
and highly electronegativity of the fluorine, it can form H-bonding
easily [7,8]. The fluoride chemosensors are mainly based on via
hydrogen bonding interaction, Lewis acid-base or selective
chemical reactions [9,10]. Based on these modes the fluorescent
probes were designed to sense the fluoride anion. Cyanide has a
wide spread importance in the industrial level, such as raw
material in many organic chemical production and in polymer
synthesis such as nitrils, nylon, and acrylic plastics [11–13]. As it
and metabolic activities [14,15]. The cyanide chemosensor are
constructed based on reversible binding and on the bases of
reaction [16]. Due to high solvation energy of cyanide in aqueous
medium it affects the hydrogen bonding between the receptor and
cyanide ion. The fluorescent sensing probes are of great use due to
its high sensitivity, image analysis and simple operating method
[17]. Copper has its wide spread application among other
transition metals and it acts as a catalytic cofactor of metal-
loenzymes in biological processes [18]. Copper is a required
nutrient for human health only trace quantity when the limit
exceeds or decreases it causes disorders like Alzheimer’s, Menkes
and Wilson diseases [19]. The bioavailability of copper concentra-
tion inside the cell are strictly regulated by copper homeostasis
system [20]. Even though there are only very few reports for the
detection of multi ions with a single receptor [21].
Understanding of the theoretical aspect and the detailed study
of chemosensing mechanism is critical for fluorescent chemo-
sensor to develop and design better chemosensor for the
applications in environmental protection and human health
[22,23]. Scientists proposed different mode of chemosensing
mechanisms such as photo-induced electron transfer (PET),
excimer and exciplex formation, intramolecular charge transfer
$
CCDC: 1477652 contains the supplementary crystallographic data for CHNT.
These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union
Road, Cambridge CB2 1EZ, UK.
* Corresponding author.
E-mail addresses: sreekanth@nitt.edu, sreekanth_a@yahoo.com (A. Sreekanth).
http://dx.doi.org/10.1016/j.jfluchem.2016.10.005
0022-1139/ã 2016 Elsevier B.V. All rights reserved.

130
S.M. Basheer et al. / Journal of Fluorine Chemistry 191 (2016) 129–142
(ICT), metal ligand charge transfer (MLCT), fluorescence resonance
energy transfer (FRET) and excited state proton transfer (ESPT)
[24–29]. The hydroxyl (OꢀꢀH) and amine (NꢀꢀH) group are well-
known proton donor site for strong hydrogen bonding of the anion
sites [30]. Now a days, the developments in supramolecular
chemistry have attracted great attention in the construction of
photonic devices that function as molecular level logic gate based
on optical signals [31]. The receptor with multiple detection of ions
are using to construct the logic gate, which results in the
development of molecular logic gates such as AND, OR, NOR,
INHIBIT, XOR, NAND [32–34]. Recently, the new area of fluorescent
probes for redox change was proposed [51–53].
In this connection we have designed and synthesized a novel
ratiometric colorimetric sensor toward fluoride, cyanide and
copper ions using photo-induced electron transfer (PES) and
internalcharge charge transfer (ICT) as a signaling mechanism for
the naked eye detection, and explained the logic gate behavior of
the receptor by analyzing the optical signal as input. The
chemosensing mechanism was revealed using computational
methods. Previously, we have reported the experimental studies
on selective anion sensing using the thiocarbohydrazone and
thiosemicarbazones based chemosensors [35–37].
2.2. Single crystal X-ray diffraction studies
A BRUKER Venture X-ray (kappa geometry) diffractometer was
employed for crystal screening, unit cell determination, and data
collection. The goniometer was controlled using the APEX3
software suite. The sample was optically centered with the aid
of a video camera such that no translations were observed as the
crystal was rotated through all positions. The X-ray radiation
employed was generated from a Cu-Ims X-ray tube (K = 1.5418 Å
a
with a potential of 50 kV and a current of 1.0 mA). The crystal
mounted on a nylon loop was then placed in a cold nitrogen stream
(Oxford) maintained at 100 K. The unit cell was verified by
examination of the hkl overlays on several frames of data. No
super-cell or erroneous reflections were observed. Integrated
intensity information for each reflection was obtained by reduction
of the data frames with the program APEX3. The integration
method employed a three dimensional profiling algorithm and all
data were corrected for Lorentz and polarization factors, as well as
for crystal decay effects. Finally the data was merged and scaled to
produce a suitable data set. The absorption correction program
SADABS was employed to correct the data for absorption effects. A
solution was obtained readily using XT/XS in APEX3, which was
confirmed using PLATON (ADDSYM). The structure was refined
(weighted least squares refinement on F2) to convergence [38].
Olex2 was employed for the final data presentation and structure
plots. The crystallographic data along with details of structure
solution refinements are given in Table 1.
2. Experimental section
2.1. Synthesis of CHNT
Ethanolic solution of cyclohexyl isothiocyanate (0.706 g,
5 mmol) and hydrazine hydrate (0.25 g, 5 mmol) were mixed
and kept in constant stirring for 1 h. The white precipitate N(4)-
cyclohexyl thiosemicarbazide was formed, which was then
filtered, washed, dried and recrystallized from ethanol. The
product (N-(4)-cyclohexylthiosemicarbazide, 0.346 g, 2 mmol)
was dissolved in methanol (30 ml) and was added to 2-hydrox-
yl-1-naphthaldehyde (0.344 g, 2 mmol), which was dissolved in
methanol (5 ml). The mixture then refluxed for 4 h after adding a
few drops of acetic acid. The reaction mixture was kept aside for
slow evaporation at room temperature. After evaporation, the
product has been formed was isolated. Further, the product was
recrystallized from chloroform and methanol mixture (1:1) and
was dried in vacuum (Scheme 1).
Table 1
Crystal data and structure refinement for CHNT.
Compound
CHNT
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
C18H21N3OS
327.44
100.0 K
1.54178 Å
Monoclinic
P 1 21/c 1
a = 14.5894(3), b = 5.79900(10),
c = 19.1169(4)
1617.36(6) Å3
4
1.345 Mg/m3
1.836 mm-1
696
Unit cell dimensions (Å)
Volume
Z
Density (calculated)
Absorption coefficient
F(000)
CHNT (pale green), Yield: 88%, M.P: 202–204 ꢁC, Chemical
Formula: C18H21N3OS, Anal Calcd: C 66.02, H 4.96, N 19.52, S 11.06;
Found: C 66.05, H 4.92, N 19.49, S 11.09; IR Data (cmꢀ1): 1537 (s,
y
Crystal size
0.216 ꢂ 0.047 ꢂ 0.045 mm3
Theta range for data collection 3.029 to 70.137ꢁ.
(C
¼N)), 1224 (s,
y
(C = S)), 3381 (br,
y(OꢀH)), 3130 (s,
y
(NꢀH)), 1H
Index ranges
ꢀ17 < =h < =17, ꢀ6 < =k < =6, ꢀ23 < =l < =23
NMR (500 MHz, CDCl3,
d
ppm): 10.76 (s, 1H), 10.19 (s, 1H), 9.06 (s,
Reflections collected
Independent reflections
Completeness to theta = 67.679ꢁ 99.9%
Absorption correction
Max. and min. transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I>2sigma(I)]
R indices (all data)
28474
1H), 8.00 (d, J = 8.5 Hz, 1H), 7.82 (dd, J = 16.0, 8.5 Hz, 2H), 7.57 (t,
J = 7.7 Hz, 1H), 7.41 (t, J = 7.4 Hz, 1H), 7.20 (d, J = 8.9 Hz, 1H), 6.62 (d,
J = 7.3 Hz, 1H), 4.40–4.32 (m, 1H), 2.13 (d, J = 10.0 Hz, 2H), 1.75 (d,
J = 13.4 Hz, 2H), 1.66 (d, J = 12.9 Hz, 1H), 1.46 (dd, J = 24.5, 11.9 Hz,
3058 [R(int) = 0.0699]
Semi-empirical from equivalents
0.7533 and 0.5640
Full-matrix least-squares on F2
3058/0/209
2H), 1.38–1.20 (m, 3H). 13C NMR (125 MHz, CDCl3,
d ppm) 175.2
(C12 = S), 157.7 (C1 ꢀ O), 143.9 (C11 = N), 133.6, 132.1, 129.2, 128.5,
128.0, 124.0, 120.3, 118.5, 108.1 (aromatic carbons, C2-C10), 53.4
(Cyclohexyl carbon (C13)), 32.7, 25.4, 24.7 (cyclohexyl carbons,
C14-C18); ESI MASS: 350.15 (Na + m).
1.087
R1 = 0.0411, wR2 = 0.0907
R1 = 0.0511, wR2 = 0.0967
n/a
0.335 and ꢀ0.292 e.Å-3
Extinction coefficient
Largest diff. peak and hole
Scheme 1. Synthesis of thiosemicarbazone compound (CHNT).

S.M. Basheer et al. / Journal of Fluorine Chemistry 191 (2016) 129–142
131
2.3. Computational method
CyꢀCꢀH and cyclohexyl protons. The 13C NMR spectrum has well
defined peaks at 175.35, 157.98 and 144.30 ppm assign to thionyl
carbon (C = S), hydroxyl group attached aromatic carbon
All calculations were performed using Gaussian 09 program.
The hybrid density functional theory (DFT) and time dependent
DFT (TDDFT) calculations were run to deal with the electronic
spectra and electronic excited state. The geometry optimizations
for the ground state were run using hybrid exchange-correlation
function B3LYP and 6–31G(d,p) basis set, which is moderate and
suitable for such large organic compounds. Considering that the
experiments were conducted in DMSO solvent, all computational
calculations were included polarizable continuum model (PCM)
(C
aromatic carbons in naphthalene group were found at
120 ppm. The cyclohexyl carbon attached to nitrogen was found at
53.05 ppm. The peaks at 32.7, 25.4 and 24.7 ppm corresponds to
¼
CꢀꢀOH) and azomethine (C
¼
N) groups respectively. The
d
110–
d
the cyclohexyl carbons.
3.2. Single crystal X-ray crystallography
with dielectric constant of DMSO (
e
= 46.826). The TDDFT analysis
The molecular structure of CHNT with the atom numbering and
molecular packing are shown in Fig.1 and Fig. 2, and the important
bond parameters were listed in Tables 2 and 2a. The suitable
colorless needle with very well defined faces with dimensions
(max, intermediate, and min) 0.216 ꢂ 0.047 ꢂ 0.045 mm3 from a
representative sample of crystals of the same habit. CHNT
crystallizes monoclinic P121/c1 in the space group with Z = 4.
The crystal structures of the compound showed the existence of an
intramolecular hydrogen bonding interaction between hydroxide
proton and imine nitrogen. The sulfur atom S(1) and the hydrazone
nitrogen N(3) are in the E position with respect to the C(12)–N(2)
bond. The N(1)–N(2) (1.373(2) Å) and N(2)–C(12) (1.354(2) Å) bond
distances in CHNT are intermediate between ideal values of
corresponding single [NꢀꢀN,1.45 Å; CꢀꢀN,1.47 Å] and double bonds
was carried out using CAM- B3LYP/6-31G(d,p) level, which is [50].
The B3LYP/LanL2DZ level used for CHNTꢀCu complex. The
transition state (TS) and intrinsic reaction coordinate (IRC)
calculations were carried out to figure out the mechanism of
the sensing [39]. The local minima in the ground state, transition
state, intermediate and excited state were confirmed with the
vibrational frequency analysis [40]. The charge distribution,
occupancy and the energy of the bonding orbitals were calculated
using natural bond orbital (NBO) analysis at the same theoretical
level as ground state and excited state geometry optimized
structure of CHNTꢀF and CHNTꢀCu complexes. The second order
perturbation energy of the CHNTꢀF and CHNTꢀCu were calculated
to evaluate the donor-acceptor interaction [41]. The potential
surface curve (PES) calculations were carried to confirm the
sensing mechanism (Table 2).
[N¼
N, 1.25 Å; C N, 1.28 Å], giving evidence for an extended
¼
p
-delocalization along the thiosemicarbazone chain [42].
3. Result and discussion
3.3. Colourimetric analysis and UV–vis spectroscopy
3.1. Characterization of CHNT
The interaction of the CHNT with various anions (such as Fꢀ,
CNꢀ, Clꢀ, Brꢀ, Iꢀ, ClO4ꢀ, H3PO4ꢀ, NO3ꢀ, HSO4ꢀ, OHꢀ and AcOꢀ) and
The CHNT was synthesized by schiff’s base condensation of 2-
cations (such as (Cr3+, Mn2+, Fe2+, Fe3+, Co2+, Ni2+, Cu2+ and Zn2+
)
hydroxylnapthaldehyde and cyclohexyl thiosemicarbazide, which
were investigated in DMSO solution through colourimetric
analysis. Noticeable and appreciable colour change was observed
with the addition of fluoride, cyanide and copper ions, imparting a
red, light red and deep yellow colour respectively. Addition of other
anions and cations didn’t show any visible colour changes. The UV–
vis spectra were recorded in DMSO solvent at room temperature.
The CHNT shows a broad peak at 258 nm which is the result of
is given in the scheme. It was well characterized by FT-IR, 1H, 13
C
NMR and MASS spectra before using in application. The elemental
analysis data where good agreement with calculated values. In the
FT-IR spectroscopy we get the information about the presence of
functional group in the compound such as CH
¼N, NꢀꢀNH, OꢀꢀH,
etc. by the absorption peak which arise due to the stretching
vibrations of the bond in the group. Sharp peaks observed at 1537
p
!p
* transition. While a second absorption peak with two
shoulder peak at 321 and 332 nm attributes the CHNT is a
* transition which is
and 1224 cmꢀ1 which attributes the presence of
y
(C
(C = S) groups respectively in the CHNT. The OꢀꢀH and NꢀꢀH
groups have its vibration frequency at a range of 3381 and
3130 cmꢀ1
The NMR spectroscopy is one of the principle
techniques which gives the structural information about mole-
cules. The 1H NMR of CHNT gives a singlet around
12.7 and
¼N) and
y
conjugated compound. There is also n !
p
confirmed by the peak at 370 nm. As Fig. 3 shows, the addition of
anions and cations to the CHNT didn’t show any spectral change,
except fluoride, cyanide and copper ions.
.
d
Upon the addition of fluoride ion to the CHNT results
bathochromic shift at a difference nearly 66 nm, new broad peaks
were found at 416 and 483 nm, simultaneously the peak at 370 nm
which is the result of intramolecular charge transfer of the
compound shows gradual hypsochromic shift. The formation of
new broad peaks attributes the presence of CHNTꢀF complex and
11.67 ppm corresponding to the N2ꢀH and N3ꢀH protons
respectively. The protons of the aromatic ring has its doublets
and triplets at around
9.06 ppm confirms the presence of N
multiplet peaks at
d
6.9–7.3 ppm. The sharp singlet found at
CꢀH proton. The lower field
d 2.13 and 1.5 ppm correspond to the presence of
d
¼
Table 2
Selected bond lengths (Å), bond angles (ꢁ) and torsion angles (ꢁ) of the CHNT.
Bond lengths (Å)
Bond angles (ꢁ)
Torsion angles (ꢁ)
S(1) ꢀꢀC(12)
O(1) ꢀꢀH(1)
O(1) ꢀꢀC(1)
N(1) ꢀꢀN(2)
N(1) ꢀꢀC(11)
N(2) ꢀꢀH(2)
N(2) ꢀꢀC(12)
N(3) ꢀꢀH(3)
N(3) ꢀꢀC(12)
N(3) ꢀꢀC(13)
1.693(2)
0.8400
1.352(2)
1.373(2)
1.294(2)
0.8800
1.354(2)
0.8800
1.335(2)
1.467
C(1)-O(1)-H(1)
C(11)-N(1)-N(2)
N(1)-N(2)-H(2)
C(12)-N(2)-N(1)
C(12)-N(2)-H(2)
C(12)-N(3)-H(3)
C(12)-N(3)-C(13)
C(13)-N(3)-H(3)
O(1)-C(1)-C(6)
N(1)-C(11)-C(2)
109.5
114.86(16)
119.1
121.83(16)
119.1
118.1
123.88(16)
118.1
115.91(17)
123.02(17)
O(1)-C(1)-C(2)-C(3)
O(1)-C(1)-C(2)-C(11)
O(1)-C(1)-C(6)-C(5)
N(1)-N(2)-C(12)-S(1)
N(1)-N(2)-C(12)-N(3)
N(2)-N(1)-C(11)-C(2)
N(3)-C(13)-C(14)-C(15)
N(3)-C(13)-C(18)-C(17)
C(1)-C(2)-C(11)-N(1)
C(11)-N(1)-N(2)-C(12)
178.66(16)
ꢀ3.2(3)
178.28(17)
173.85(13)
ꢀ6.8(3)
178.90(16)
ꢀ178.35(15)
179.83(16)
0.9(3)
ꢀ179.27(17)

132
S.M. Basheer et al. / Journal of Fluorine Chemistry 191 (2016) 129–142
Fig.1. Structure of AntCy with labelling of selected atoms. Anisotropic displacement ellipsoids Exhibit 30% probability levels. Hydrogen atoms are drawn as circles with small
radii.
450 nm, which is gradually increasing with increasing the
concentration of cyanide ion. Up on the addition of the Cu2+ to
the CHNT, new absorption band at 417 nm with a shoulder peak at
435 nm were observed which is due to the charge transfer from
ligand to metal. There are two isobistic points at 394 and 348 nm,
which implies the presence of multi complexes in the solution. The
change in the absorption band and the colour when CNꢀ and Fꢀ are
added to the CHNT is may be due to the formation of hydrogen
bond, and the deprotonation of CHNT. The bathochromic shift at
n !
p* is also the result of hydrogen bonding interaction between
the ion and CHNT. The spectral profile for fluoride, cyanide and
copper along with CHNT is shown in Fig. 4.
Job’s plot method was carried out to find the stoichiometric
ratio with CHNT and ions. As in Fig. 5, the fluoride and cyanide
bonded with 2:1 ratio, and copper is for 1:1 ratio with sensor CHNT.
The association constant Ka is calculated in accordance to the
Benesi-Hildebrand equation [43], which is as bellow,
1
1
1
1
¼
þ
A
A ꢀ A0
A
1 ꢀ A0K½Cꢃ
1 ꢀ A0
where ‘A, A0 and A1 are the absorbance with a specific ion
concentration, absorbance of free compound and absorbance at
excess amount of ion respectively. “K” and [C] is the association
constant (Mꢀ1) and the concentration of ion respectively. The
binding constant (K) values were calculated from the plot 1/(A-A0)
vs 1/[C], which shows a linear relationship. The calculated
association constant (Ka) for CHNT with fluoride, cyanide and
copper ions are found to be 3.51 ꢂ105, 2.07 ꢂ105 and
1.09 ꢂ105 Mꢀ1 respectively. Thus the sensor CHNT shows binding
affinity with ions in order of Cu2+ < CNꢀ < Fꢀ.
Fig. 2. Molecular packing viewed down c axis showing intermolecular interactions
in CHNT.
Table 2a
Hydrogen bonds for CHNT [Å and ꢁ]_.
D–H . . . A
d(D–H)
d(H . . . A)
d(D . . . A)
<(D–H–A)
O(1) ꢀꢀH(1)ꢄ ꢄ ꢄN(1)
0.84
0.88
1.91
2.52
2.65
3.37
145.8
164.1
N(2) ꢀꢀH(2) . . . S(1)
3.4. Fluorescence spectral studies
Symmetry transformation used to generate equivalent atoms:.
#1-X + 1, y + 2, ꢀz + 1.
In order to learn more about the sensing ability of the receptor,
fluorescence measurements were carried out similar to that of UV
titration. Moreover, compared to absorption spectroscopy, fluo-
rescent emission spectroscopy is a more effective approach for
anion sensing. The fluorescent property of CHNT with 369 nm
excitation wavelength in the presence of various anions and
cations was examined. For CHNT, the emission peak was found at
436 nm. While adding the fluoride and cyanide ion to the CHNT, the
fluorescence quenching was happened with appearance of new
hydrogen bond in between host-guest molecules. The newly
formed band in visible region shows the hyperchromic shift along
with the addition of fluoride ion. Very clear isobistic points where
observed at 397, 338 and 322 nm, which attributes the presence of
multi-compounds such as CHNTꢀF, deprotonated CHNT, etc in the
solution. While the presence of cyanide ion, a new broad peak at

S.M. Basheer et al. / Journal of Fluorine Chemistry 191 (2016) 129–142
133
Fig. 3. UV-vis spectra of CHNT with (a) different anions and (b) cations.
peak at 435 nm, and simultaneously a new fluorescence enhanced
peak was formed at 495 nm. The presence of fluoride and cyanide
ions with CHNT leads to fluoresce enhancement, which attributes
the PET process in the relaxation of excited state. The fluorescence
enhancement can also due to the presence of strong intramolecu-
lar hydrogen bond of O . . . H . . . ion and N . . . H . . . ion. Among the
cations, the selective sensing towards Cu2+ was shown by CHNT. As
in Fig. 2, the addition of copper ion to the CHNT, fluoresce
quenching happened at 435 nm, which is due the strong
interaction of copper ion with CHNT. The addition of other anions
(such as Clꢀ, Brꢀ, Iꢀ, ClO4ꢀ, H2PO4ꢀ, NO3ꢀ, HSO4ꢀ, OHꢀ and AcOꢀ)
and cations (such as (Cr3+, Mn2+, Fe2+, Fe3+, Co2+, Ni2+ and Zn2+) in
CHNT didn’t give any change in fluorescence spectra (see Fig. 6).
The binding constant was determined using modified Benesi-
Hildebrand equation [44] which is as follows,
The higher current value at the 0.0.137 V shows the formation of
strong Cu-CHNT bond. As in Fig. 7, there is no change observed
when other cations (such as Cr3+, Mn2+, Co2+, Fe3+, Fe2+, Ni2+ and
ꢀ
Zn2+) and the anions (such as Fꢀ, Clꢀ, Iꢀ, Brꢀ, OHꢀ, AcOꢀ, CNꢀ, NO3
,
ClO4ꢀ, HSO4 and H2PO4ꢀ) added to the CHNT. But, adding equal
mixture of different cations in the presence of copper ion gives an
extra cathodic peak at ꢀ0.46 V, which show the selective
electrochemical sensing of chemosensor towards copper ion.
The binding constants of the receptors with copper ion were
calculated using modified Bensesi-Hildebrand equation, which is
as below
ꢀ
1
Kb½Cꢃ
I2
¼
ðIp20 ꢀ Ip2Þ þ Ip21 ꢀ ½Cꢃ
where I2p, I2p0 and I21 are the reduction current of receptor, after
the addition of copper ion and excess addition of copper ion
respectively. The ‘Kb’ values of CHNT towards Cu2+ ion was
calculated from the reciprocal of slope, which is found to be
6.25 ꢂ105 Mꢀ1 (see Fig. 8). The binding constant value matches
with the previously calculated binding constants from UV–vis and
fluorescence spectral studies.
1
1
1
¼
þ
ðFx ꢀ F0Þ ðF1 ꢀ F0Þ K½CꢃðF1 ꢀ F0Þ
where F0 and Fx are corresponding emission intensity of CHNT
alone and CHNT with addition of ions respectively. ‘K’ is the
association constant and ‘C’ is the concentration of added ions. The
association constants were calculated from the plot of 1/(Fx-F0) vs
1/[C]. The binding constant of CHNT towards Fꢀ, CNꢀ and Cu2+ were
determined from the ratio of intercept/slope, and which found to
be 5.05 ꢂ105, 0.74 ꢂ105 and 1.38 ꢂ 105 Mꢀ1 respectively. From the
binding constant values, it is clear that the Fꢀ has higher
fluorescence binding affinity towards CHNT, which is confirming
the UV–vis calculation results.
3.6. 1H NMR Titration
For the better understanding of sensing mechanism, 1H NMR
titration were carried out for CHNT in the presence and absence of
TBAF in CDCl3. In the case of neat CHNT, single peak at 10.75, 10.18
and 9.06 ppm which are correspond to the protons of ‘N2ꢀH’,
‘N3ꢀH’, and N¼CꢀH respectively. As in Fig. 9, the addition of 1
3.5. Electrochemical studies
equivalent of fluoride ion, the singlet peak of the N2ꢀH proton
disappears completely and the peak corresponding to the N3ꢀH
proton is shifted downfield with a broadening of the signal.
Whereas, there is no noticeable change for the peak at 9.06 ppm,
CHNT shows the reversible reduction potential (Epc) at ꢀ0.46 V,
which is due to greater
p-conjugation caused by the electron
negative nitrogen atom. Up on the addition of Cu2+ ion in CHNT, a
new reduction peak was observed at ꢀ0.87 V, and the ‘Ip’ value at
that point keep on increasing with increasing the concentration of
copper ion. The newly formed cathodic peak indicate the
formation of CHNTꢀCu complex. But the equimolar addition of
copper ion to CHNT effect the disappearance of receptor’s
reduction peak, and further addition of copper ion results the
formation of two cathodic peaks at ꢀ0.47 and 0.13 V, which
attributes the formation of Cu2+/Cu+ and Cu+/Cu respectively [45].
which infer that the N
¼CꢀH proton has no involvement in the
sensing process. The peak broadening at 10.18 ppm attributes the
hydrogen bonding formation between fluoride anion and N3ꢀH
proton (N3ꢀH . . . F) [46]. The consequence addition of Fꢀ to the
CHNT results the complete peak disappearance at 10.18 ppm,
which attributes the deprotonation takes place from the N3ꢀH.
Simultaneously, the peak intensity at the 8.01 ppm decreased
along with the broadening of the peak. The changes in the 1H NMR

134
S.M. Basheer et al. / Journal of Fluorine Chemistry 191 (2016) 129–142
Fig. 4. UV–vis spectra of CHNT with different concentration of (a) fluoride, (b) cyanide and (c) copper ions. Fluoresence spectra of CHNT with different concentration of (d)
fluoride, (e) cyanide and (f) copper ions.

S.M. Basheer et al. / Journal of Fluorine Chemistry 191 (2016) 129–142
135
Fig. 5. Benezi-Hilderbrand diagram for CHNT with (a) fluoride, (b) cyanide and (c) copper ions. The Jobs plot diagram was given in incert.
Fig. 6. Fluorescence spectra of CHNT with different (a) anions and (b) cations.
Fig. 7. CV responds of CHNT with (a) different cations, and (b) various equivalents of copper ion.

136
S.M. Basheer et al. / Journal of Fluorine Chemistry 191 (2016) 129–142
and it increased to 148.080 at the excited state of CHNT. After the
bonding with fluoride ion, the dihedral angle twisted to 51.190. The
ground state optimized energy of the CHNTꢀF complex is less than
that of CHNT. After the formation of fluoride complex, the dihedral
angles between cyclohexyl group-thiosemicarbazone and naph-
thalene moiety-thiosemicarbazone found same. In the ground
state of CHNT, the OꢀH, N1ꢀH1 and C¼N bond distances were
found to be 0.96, 1.02 and 1.29 Å respectively, which were
increased in the CHNTꢀF complex. The bond length elongation
attributes the formation of single bond between CꢀN. While the
N2ꢀH2 and C = S bond distances found same in CHNT, the ground
state and the excited state CHNTꢀF complex. In the excited state of
CHNTꢀF complex (CHNTꢀF*), the calculated dihedral angle
between naphthalene moiety and thiosemicarbazone group is
158.390, which much higher than in the ground state structure of
CHNT and CHNTꢀF complex. The calculated bond length of CꢀO
show 1.30 Å for CHNTꢀF*, which is closer to double bond C
¼O. It
demonstrated that the CHNTꢀF and CHNTꢀF* are better conju-
gated than CHNT. In the CHNTꢀF*, the bond distance between
FꢀH21, FꢀH8 and FꢀH7 found as 1.49, 1.53 and 1.93 Å respectively.
The FꢀH21 and FꢀH7 are higher with comparing with the ground
state structure of CHNTꢀF complex, which indicate the excited
state proton transfer (ESPT) process. With considering two fluoride
ion attach to CHNT, the CHNTꢀF2 complex structure also
optimized. In CHNTꢀF2, the OꢀH and NꢀH bond distance found
higher that of CHNT and CHNTꢀF, which features the deprotona-
Fig. 8. Modified Benesi-Hildebrand plot of CHNT towards copper ion using CV data.
spectrum indicates that the formation of hydrogen bonding
between ‘N3ꢀH . . . F’ in the excess amount of fluoride.
3.7. COMPUTATIONAL METHODS
0
0
tion occurs from ‘O1 and ‘N2 . With comparing CHNT, the CꢀS and
N bonds have no noticeable change in CHNTꢀF2. The calculated
C¼
3.7.1. Geometric study
bond distance of FꢀH21 and FꢀH8 were found 1.02 and 1.40 Å
respectively, which are close to the single bond formation between
the atoms. The dihedral angle between naphthalene moiety and
thiosemicarbazone group are twisted to 20.880, which gives higher
planarity and conjugation than CHNT and CHNTꢀF complex. In the
fluoride complex, the negative charge on the fluoride ion might be
delocalized over other conjugated system. Therefore the photo-
physical properties of CHNTꢀF and CHNTꢀF2 are different from the
CHNT.
To reveal the sensing mechanism of the CHNT, the ground state,
excited state and deprotonated geometries were optimized with
and without the presence of ions, which are shown in Fig. 10. The
energy of CHNT in cis and trans form in the ground state is
ꢀ35.08 ꢂ 105 and ꢀ35.09 ꢂ105 Kcal/mol respectively. In the
ground state, the dihedral angle between naphthalene moiety
and thiosemicarbazone group is 137.170, which shows the
structure is not a coplanar. And the dihedral angle between boat
shaped cyclohexyl group and thiosemicarbazone group is 135.560,
Fig. 9. 1H NMR titration of CHNT with different equivalents of fluoride ion.

S.M. Basheer et al. / Journal of Fluorine Chemistry 191 (2016) 129–142
137
Fig. 10. Optimized structure of CHNT (A), trans CHNT(A-trans), ground state CHNTꢀF (AF), ground state trans CHNTꢀF complex (AF-trans), excited state CHNT (AF*), exccited
state trans CHNT (AF-trans*) and deprotonated CHNT (A-de1 and A-de2).
In the CHNTꢀCu complex, the CꢀS bond distance found to be
1.83 Å, which is higher than CHNT, and closer to single bond
distance. The CꢀN bond distance found elongated to 1.32 Å, which
attributes the single bond between CꢀN. The calculated dihedral
angle between NꢀNꢀCꢀS found 0.560, which is 13.430 in CHNT.
The CuꢀO, CuꢀN1 and CuꢀS bond distances were found as 1.84,
1.95 and 2.28 Å respectively, which attributes the CHNT act ass
tridentate ligand to form CHNTꢀCu complex. The dihedral angle
between naphthalene moiety and thiosemicarbazone group are
0.740, which attributes the naphthalene moiety and thiosemicar-
bazone group are in planar. In the CHNTꢀCu complex, the dihedral
angle between cyclohexyl group and thiosemicarbazone group is
twisted to 89.700. The dominant structural parameters in the
optimized structures of CHNT, CHNTꢀF, CHNTꢀF* and CHNTꢀCu
complexes are given in Table 3.
CAM-B3LYP/6-31G(d,p) level [47]. The molecular orbitals involved
in the main transition with the largest oscillator strength have
been shown in Fig.11. And the major absorption transition of CHNT,
CHNTꢀF and CHNTꢀCu complexes are given in Table 4. CHNT
shows an intense absorption band at 303 nm with 0.4325
oscillating strength as dominant
p-p* transition, which is from
highest molecular orbital (HOMO) to the lowest unoccupied
molecular orbital (LUMO). In the HOMO, the electron delocalized
through thione moiety and carbazonyl group. But in LUMO, the
electron delocalized mainly in naphthalene moiety. The second
dominant transition is at 254 nm with 4.51 eV energy gap, which is
corresponds to the experimental absorption band at 259 nm. This
transition is between HOMO-2 to LUMO, where in HOMO-2 orbital,
the electrons are delocalized through thionyl group and naphtha-
lene moiety. Whereas the CHNTꢀF2 complex, the bathochromic
shift was occurred and the peak shifted to 362 nm with 0.5827
oscillating strength. The major transition occurs between HOMO
3.7.2. UV–vis spectra and molecular orbital analysis
In order to investigate the absorption behavior of the CHNT in
the sensing process according to their optimized ground state
geometry, molecular excitation study were carried out at TDDFT/
and LUMO, which is assign as
LUMO, the electron delocalized though naphthalene moiety and
thiosemicarbazone group. The second major transition is between
p p* type transition. In HOMO and
!
Table 3
The dominant structure parameters in the optimized geometries.
OꢀH21
N2ꢀH8
N3ꢀH7
CꢀS
N1N2C10
S
FꢀH21
FꢀH8
FꢀH7
C8C7C1C9
C13C11N3C10
O1ꢀꢀH21-F
CHNT
CHNT*
CHNT-F
CHNT-F*
CHNT-F2
d-CHNT
0.96
0.96
1.06
1.05
1.37
–
1.02
1.02
1.03
1.07
1.10
–
1.01
1.01
1.03
1.03
1.04
–
1.70
1.68
1.71
1.71
1.73
1.82
13.43
0.052
15.01
30.31
0.712
2.24
–
–
–
47.71
21.25
51.19
158.3
20.88
10.69
135.5
88.41
138.2
90.09
138.8
85.54
1.34
1.49
1.02
–
1.7
1.66
1.93
1.63
–
164.9
176.9
177
1.53
1.40
–
–
OCuN
95.9
COCu
128.0
CuO
1.84
CuS
2.28
CuN
1.95
CSCu
91.4
CHNT-Cu
1.01
1.83
0.565
0.741
89.70

138
S.M. Basheer et al. / Journal of Fluorine Chemistry 191 (2016) 129–142
Fig. 11. The energy gap between HOMO and LUMO orbitals of CHNT, CHNT-trans, CHNTꢀF, CHNTꢀF trans and excited state CHNTꢀF complexes.
Table 4
Dominant absorption energies and the fluorescence emissions for the chemosensor for CHNT, CHNTꢀF, CHNTꢀF2 and CHNTꢀCu.
DE eV
l
f
%
Transition
DE eV
l
f
%
Transition
Absorption Energies
CHNT
ꢀ1335.61532105 AU.
CHNTꢀF
4.0810
4.5305
4.9077
CHNTꢀF2
3.4174
ꢀ1435.59152269 AU.
4.0837
4.5186
4.8684
CHNTꢀCu
1.3655
1.9193
303.61
274.39
254.67
0.4325
0.1821
0.1176
75.30
H ! L
303.80
273.67
252.63
0.4113
0.1950
0.2207
100
H ! L
42.16
24.95
H–3 ! L
H–2 ! L
35.53
27.00
H–3 ! L
H ! L + 1
ꢀ1142.38262722 AU.
ꢀ1535.54594158 AU.
907.96
646.00
560.74
0.0001
0.0006
0.0236
22.53
23.07
17.43
H–3 ! L
H–1 ! L
H–4 ! L
362.80
286.47
242.13
0.5827
0.4533
0.4796
100
53.15
30.30
H ! L
4.3280
5.1205
H ! L + 1
H–2 ! L
2.2111
Fluorescence Emissions Energies
CHNT
3.0063
3.8861
ꢀ1335.63437792 AU.
CHNTꢀF2
4.0810
4.3737
ꢀ1535.9561526 AU.
395.42
319.04
0.8812
0.0027
100
L! H
482.80
383.48
0.4113
0.0015
100
42.40
L ! H
52.51
L ! H-1
L + 1 ! H-1
HOMO to LUMO + 2 orbital, where the electron transition occurs
between hydroxyl group to thione group. In the CHNTꢀCu
complex, the major absorption transition with higher oscillator
strength is at 560 nm, which is between HOMO to LUMO. In the
HOMO, the electron delocalized through naphthalene moiety,
cyclohexyl group and thiosemicarbazone group. But in LUMO, the
electron delocalization absent in the cyclohexyl group. An excited-
state proton transfer (ESPT) process, induced by both intermolec-
ular and intramolecular hydrogen-bonding interactions, is pro-
posed to account for the fluorescence sensing mechanism of a
fluoride chemosensor [5]. The comparison of experimental and
computational spectral wavelength are given in Table 5.
complex, the Gibbs energy profile of CHNT with fluoride ion is as in
Fig. 12. In the ground state of CHNTꢀF, the bond distance between
fluorine atom and the H21, H8 and H7 hydrogen are found to be 1.34,
1.76 and 1.66 Å respectively, which attribute a weak hydrogen
binding interaction of CHNT with fluoride ion. Whereas, in the
0
excited state of CHNTꢀF complex, ‘H21 proton removed from the
CHNT, and form FH21 bond with 1.00 Å bond length. The total
3.7.3. Transition state and gibbs free energy calculations
In order to study the dynamic features of the deprotonation
process, we calculated the Gibb’s free energy of CHNT, CHNTꢀF
complexes in DMSO medium. The ground state and excited state
Gibb’s free energy of the CHNT was found to be ꢀ8.38 ꢂ 105 and
ꢀ8.46 ꢂ105 Kcal/mol respectively. The transition state calculations
were run between ground sate and excited state of CHNTꢀF
Table 5
Comparison of experimental and computational UV–vis and Fluorescence spectral
data of CHNT and CHNT-F complex.
Compound
UV–vis spectra (nm)
Fluorescence Spectra (nm)
Experimental
Theoretical
Experimental
Theoretical
Fig. 12. Gibbs free energy profile of the fluoride sensing mechanism.
A: CHNT:; A-Tra: CHNT-trans:; de-A: CHNT-de:; AF: CHNTꢀF:; AF*: CHNTꢀF excited
state
CHNT
CHNT-F
258
321
254.67
303.61
436
495
425.42
482.80

S.M. Basheer et al. / Journal of Fluorine Chemistry 191 (2016) 129–142
139
change in Gibbs free energy (
DG) in the reaction is 197.01 Kcal/mol.
The less G value shows the sensing process is reversible, and
D
strongly supporting for the explanation of the sensing mechanism.
Hꢀ
G) in the formation
4
4
The calculated entropy change ( s ¼
4
T
process of the hydrogen bridge involving fluoride ion is ꢀ0.0467
KJ/mol, where the negative sign indicate the sensing process is
thermodynamically allowed. The binding constant (Ka) of the
CHNT to fluoride ion was calculated from the following equation,
ꢀ
DG
lnKa
¼
RT
where, R, T and Ka are the universal gas constant, temperature and
the binding constant respectively. The Ka value was found
1.08 ꢂ 105 Mꢀ1, which was closer to the result get from the
experimental value. To know the binding energy of the sensing
process, the energy change (
D
E) and free energy (DG) calculated
using following equations,
ꢀ
D
D
E ¼ ðEdꢀCHNT þ EHF Þ ꢀ ðECHNT þ EF
Þ
Fig. 14. The calculated potential energy curve of CuꢀO, CuꢀS and CuꢀꢀN bond
length in ground state of CHNTꢀF complex.
ꢀ
G ¼ ðGdꢀCHNT þ GHFÞ ꢀ ðGCHNT þ GF
Þ
ꢀ1436.19 AU, where the FꢀH21 and FꢀH8 bond length are 1.31 and
1.74 respectively. Where as in the case of OꢀH bong length
calculation, the lowest energy at ꢀ1436.19 AU with the bond length
1.06 Å. In the case of CHNTꢀCu complex, the CuꢀO, CuꢀS and
CuꢀN bond length changes from 1.90 to 2.50 Å with the increment
of 0.035 Å. The optimized geometric energy is ꢀ2975.47 AU., where
the bond distance of CuꢀO, CuꢀS and CuꢀN at stable structure of
CHNTꢀCu complex was found to be 1.90, 2.24 and 1.90 Å
respectively. The detailed PES curves of CHNTꢀF and CHNTꢀCu
are as in Figs. 13 and 14.
where, ECHNT, Ed-CHNT, GCHNT and Gd-CHNT are energy of CHNT,
deprotonated CHNT and Gibb’s energy of CHNT and deprotonated
CHNT respectively. The calculated
DE and DG are found to be
ꢀ237.94 and ꢀ197.01 Kcal/mol respectively. The negative value of
the free energy indicate feasibility of the sensing process in
thermodynamic aspect.
3.7.4. Potential energy curve (PES)
To reveal more features of ESPT process in the chemosensing
process, the potential energy surface analysis study was carried out
both in ground sate and excited state of CHNTꢀF complex. From
the geometrical optimization structure, excited study and transi-
tion state calculation indicate the proton transfer was first takes
from the hydroxyl group of CHNT. To take this result, PES
calculations were carried out with only the variable parameter
of OH and FꢀH bond length separately at the ground state and
excited state of CHNTꢀF complex, where the variable parameter of
the bond length from 0.90 to 2.40 Å in the step of 0.05 Å. It is
obviously reveal from Fig. 13 that the energy of ground state
CHNTꢀF complex decreases with increasing the bond length
between FꢀH21 and FꢀH8, and it reaches at the lowest energy
3.7.5. NBO calculation
To understand the information about interactions in both filled
and virtual orbital spaces that could enhance the analysis of intra-
and inter-molecular interactions, Natural bond orbital (NBO)
studies carried out. The change in bond length between N2–H8,
OꢀH21 and H8ꢀF of optimized geometries in the ground state (S0),
excited state (S1) and the emission studies predicts proton from
nitrogen and oxygen. In order to support the proton transfer
process takes place from OꢀH16 rather than N3ꢀH17 proton in the
fluoride sensing process, NBO calculation was carried out at ground
Fig. 13. The calculated potential energy curve of FꢀH7, FꢀH8 and OꢀꢀH bond length in ground state of CHNTꢀF complex.

140
S.M. Basheer et al. / Journal of Fluorine Chemistry 191 (2016) 129–142
Table 6
calculated from the electron donor orbital, acceptor orbital and the
interacting stabilization energy in the ground state and excited
state and using this we can explain the weak interaction [48]. The
second order perturbation equation as below,
The second-perturbation energy E(2) (kcal/mol) of donor–acceptor interaction with
respect to CHNTꢀF in ground state and excited state states respectively.
Donor (i)
Acceptor (j)
Interaction E(2)
Kcal/mol
e
(j)-
e
(i) F(i,j)
qiF2
Ground state
ej ꢀiej i
Eð2Þ ¼
D
E ¼
LP (3) F 45 BD*(1) N 15 ꢀ H 22 n-
s
s
*
*
11.43
24.66
0.93
0.93
0.63
0.092
0.136
0.258
LP (3) F 45 BD*(1) N 17 ꢀ H 21 n-
LP (4) F 45 LP*(1) H 44
Excited State
n-n*
112.07
where E(2) is the second perturbation energy, Fij is the off-diagonal
element in the NBO Fock matrix, qi is the donor orbital occupancy,
and ei and ej are orbital energies. It can be seen from Table 6, that
the energies between two segments separated by FꢀH21, FꢀH8 and
FꢀH7 at the ground state are found to be 112.07, 24.66 and 11.43
Kcal/mol respectively. The higher energy value of FꢀH21 shows the
bonding between F and H21. All weak interactions have generated
LP (3) F 45 BD*(1) N 15 ꢀ H 22 n-
LP (3) F 45 BD*(1) N 17 ꢀ H 21 n-
LP (4) F 45 BD*(1) O 43 ꢀ H 44 n-
s*
s*
s*
12.94
29.02
94.57
1.06
1.06
1.01
0.105
0.157
0.276
state and excited state of CHNTꢀF. By comparing the binding
energies of FꢀH16 and FꢀH17 reveals the affinity of fluoride ion to
from lone-pair electron (n) of F to excited
s
* of NꢀH bond, in which
the N2ꢀH8 pair has larger interaction with fluoride atom than
N3ꢀH7. But, the FꢀH bond interaction is n-n*, which attributes the
bonding between fluoride atom and hydrogen atom. In the excited
state (CHNTꢀF*), the calculated bonding energies found as 94.57,
29.02 and 12.94 Kcal/mol for F-H21, F-H8 and FꢀH7 respectively.
And the FꢀH21 and FꢀH7 bond energy values are closer to the
hydrogen bonding, hence in excited state of CHNTꢀF complex
show hydrogen bonding via F . . . H8ꢀN1 and F . . . H7ꢀN2. The large
overlap of the electron density for the interaction confirms the
attach the hydrogen atom. The binding energy (DE) was calculated
from the equation
DE=EAB-(EA + EB) + BSSE, where A and B are two
fragments. The binding energy of FꢀH7, FꢀH and FꢀH8 are ꢀ150.65,
ꢀ159.64 and ꢀ162.59 Kcal/mol respectively. The smallest value of
the binding energy for F-H16 indicate the priority of the binding
affinity of fluoride ion towards H21 than H8 and H7. The strong
donor–acceptor interaction between fluoride and the CHNT can be
treated by the second-perturbation energy E(2) which has been
Fig. 15. (a) The UV–vis and (b) fluorescence spectral changes of CHNT with the addition of individual Fꢀ, CNꢀ and Cu2+ and its mixture.

S.M. Basheer et al. / Journal of Fluorine Chemistry 191 (2016) 129–142
141
strong donor–acceptor interaction, indicating the hydroxyl proton
prefer to interact with F atom rather than NꢀH proton. The proton
transfer was undergoes from S1 state, and which gives excited state
proton transfer (ESPT) process. In the case of CHNTꢀCu complex,
the bonding energy value between CuꢀO, CuꢀN and CuꢀS are
found to be 20.36, 15.25 and 9.86 Kcal/mol respectively, where
n ! n* interactions were shown between the atoms. The energy
values and interactions show the bond between copper towards
oxygen, nitrogen and sulfur atoms. In conclusion, the NBO analysis
with E(2) further confirms the presence of ESPT process by the
excitation of the light for fluoride ion sensing, and the priority of
hydroxyl proton and then N2ꢀH8 in attaching to fluoride atom
rather than N3ꢀH7 in ESPT process.
3.8. Logic gate behavior
The differential behavior of CHNT toward Fꢀ, CNꢀ and Cu2+ ions
enabled the receptor to elaborate molecular logic gates. Recently,
the molecular computing is the subarea of unconventional
computing based on chemical reactions that has stimulated
interest in the development of molecular logic gates and devices
at the molecular level. Molecular logic gates convert input
stimulations into output signals with basic protocols [49]. For
the analysis of their logic behaviors, the optical values from
absorption and emission spectral values are assigned and then
logic convention is used for their inputs and outputs signals. It
follows that the principles of binary logic can be applied to the
signal transduction operated by molecular switches. The absorp-
tion maximum at 370 nm of CHNT was reduced with the presence
of individual ions (Fꢀ, CNꢀ and Cu2+) and the mixture of ions, which
attributes the NOR logic gate.
Fig. 17. proposed sensing mechanism of CHNT with fluoride ion.
The addition of fluoride cyanide ions results the formation of
new peak at 482 nm. And the presence of copper ion didn’t show
any change at this wavelength. There is no new peak at 482 nm,
when Fꢀ and/or CNꢀ are mix with copper ion. This phenomenon is
help to develop the NAND gate. While the presence of copper ion in
the CHNT gave new peak at 417 nm, which is retained when the
copper ion mix with Fꢀ and CNꢀ ions, which can explained by
TRANSFER logic gate. The CHNT show high intense fluorescence
spectra at 433 nm. The presence of fluoride and cyanide ions
quench the fluorescence intensity of the CHNT, whereas copper ion
enhanced the fluorescence intensity. But in the presence of
mixture of ions (Fꢀ, CNꢀ and Cu2+), the CHNT show fluorescent
quenching. This property corresponds to the XNOR logic behavior.
However, the presence of fluoride and cyanide ions results red shift
along with the formation of new peak at 492 nm. But, which didn’t
show when the copper ion mix with Fꢀ and/or CNꢀ ion. This
behavior can be explained by NAND logic gate. The circuit and the
truth table are shown in Figs. 15 and 16.
4. Conclusion
The isobistic points indicates existence of multi compounds in
the solution, which indicates the formation of CHNT-ion complex.
From the Jobs plot, the stoichiometry between CHNT and anions
(Fꢀ and CNꢀ) are 1:2, which means, the one molecule CHNT binds
two molecules of F- or CNꢀ. The stoichiometric ratio of HCNT and
Cu2+ is 1:1, which show one CHNT molecule bind one copper atom.
It also indicate the tridentate behavior of the CHNTcompound. The
presence of Fꢀ and CNꢀ ions gives red colour to the CHNT, and Cu2+
ion gives bright yellow colour. The 1H NMR titration study strongly
support the deprotonation was taken from the hydroxyl proton,
then followed by the NꢀH proton which is near to the naphthalene
group. Proposed binding mode of CHNT towards Fꢀ/CNꢀ and Cu2+
ions, and their colour changes along with the complex formation is
as in Fig. 17 and Fig. 18.
The experimental findings have also been supported by the
theoretical (DFT and TD-DFT) calculations. The structural change
was calculated by the geometries o CHNT, CHNTꢀF, de-CHNT and
CHNTꢀCu complexes. The UV–vis and emission spectra were well
reproduced by various transition energies computed from ground
state and excited state geometries. The optimized energy values of
CHNT and CHNT-trans compounds indicate that the sensing
process was takes place in the trans form of hydroxyl proton
and NH protons in the CHNT. This results can be the explanation of
the experimental 1H titration results. The transition and interme-
diate state calculations were revealed the mechanism of the Fꢀ ion
sensing by CHNT. The excited state proton transition mechanism
was further confirmed with NBO and PES analysis. The second
order perturbation energy value confirms the hydrogen bonding
and deprotonation was happed in the excited state of CHNTꢀF
Fig. 16. (a) Changes of absorbance at 370, 483 nm and change in fluorescence
intensity at 433 and 492 nm for CHNT with Fꢀ/CNꢀ/Cu2+, and their truth table. (‘00
and ‘10 represent the absence and presence of the ion respectively). (b)
Combinatorial circuit diagram of CHNT with three input (Fꢀ, CNꢀ and Cu2+ ions).

142
S.M. Basheer et al. / Journal of Fluorine Chemistry 191 (2016) 129–142
Fig. 18. Proposed binding mode of CHNT towards Fꢀ/CNꢀ and Cu2+ ions, and their colour changes along with the complex formation.
complex. The theoretical results also confirms the deprotonation
was first happed from the hydroxyl proton then from the N2ꢀH8
proton which is near to the naphthalene moiety.
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