Exploiting the unique specialty of hydrazone functionality: Synthesis of a highly sensitive UV–Vis active solvatochromic probe

Article abstract of DOI:10.1016/j.saa.2020.119154

The unique physico-chemical attributes of the hydrazone functionality have been extensively studied for a diverse range of chemical, biological and analytical applications. The synthesis of a highly sensitive hydrazone based UV–Vis active solvatochromic p

Full text of DOI:10.1016/j.saa.2020.119154

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 247 (2021) 119154
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular
Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Exploiting the unique specialty of hydrazone functionality: Synthesis
of a highly sensitive UV–Vis active solvatochromic probe
Mudeha Shafat Khan a, Romana Khanam a, Sajad Ahmad Bhat a, Naheed Sidiq b, Tabasum Ismail c,
Pravin P. Ingole d, Rahul V. Pinjari e, Mohsin Ahmad Bhat a,
⇑
a Department of Chemistry, University of Kashmir, Hazratbal Srinagar 190006, India
b Department of Chemistry and Earth Sciences, Qatar University, Doha 2713, Qatar
c Department of Chemistry, SP College, Srinagar 190001, J & K, India
d Department of Chemistry, Indian Institute of Technology Delhi, New Delhi 110016, India
e School of Chemical Sciences, Swami Ramanand Teerth Marathwada University, Nanded 431606, India
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
(2,4-dinitrophenyl)-2-(2-nitrobenzyli
dene)hydrazone (DNPNBH), was
synthesized.
ꢀ
ꢀ
DNPNBH can act as a highly sensitive
UV–Vis active solvatochromic probe.
DNPNBH exhibits excellent
microenvironment polarity sensing
potential in solvents.
ꢀ
As a UV–Vis probe DNPNBH ensures
precise estimation of CMC of
surfactants.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 1 July 2020
Received in revised form 18 October 2020
Accepted 26 October 2020
Available online 4 November 2020
The unique physico-chemical attributes of the hydrazone functionality have been extensively studied for
a diverse range of chemical, biological and analytical applications. The synthesis of a highly sensitive
hydrazone based UV–Vis active solvatochromic probe that exhibits excellent sensitivity toward sensing
of solvent polarity, microstructural changes and onset of micellization in aqueous systems was carried
out. Specifically, synthesis of 2,4-dinitrophenyl-2-(2-nitrobenzylidene)hydrazone (DNPNBH), through
an easy to carry, atom economical, one-pot single step approach via use of low-cost precursors viz.
ortho-nitrobenzaldehyde and 2,4-dinitrophenyl hydrazine is presented. The UV–Vis absorption features
of the synthesized hydrazone exhibit excellent sensitivity toward the polarity of its immediate microen-
vironment. The microenvironment polarity sensing potential of DNPNBH is demonstrated for some single
solvent systems and DMF-Water mixture as a model binary solvent system and the results are supported
by quantum mechanical calculations. Use of the DNPNBH as a probe (at concentrations many orders
lower than required for conventional probes) to precisely reflect the onset of micellization and estimation
of critical micelle concentration (CMC) of amphiphilic molecules (5.25 mM for SDS, 1.53 mM for CTAB
and 0.055 mM for Brij56) in aqueous solutions is also demonstrated. The results clearly qualify the syn-
thesized hydrazone as a highly sensitive UV–Vis probe that can be employed for reliable sensing of sol-
vent polarity, composition dependence of physicochemical attributes in mixed solvent systems and the
estimation of CMC of surfactant systems via spectrophotometry.
Keywords:
2, 4-Dinitrophenyl-2-(2-nitrobenzylidene)
hydrazone
UV–Vis spectrophotometry
Solvatochromism
Microenvironment polarity
Critical micelle concentration (CMC)
Ó 2020 Elsevier B.V. All rights reserved.
⇑
Corresponding author at: Department of Chemistry, University of Kashmir,
Srinagar-190006, Jammu and Kashmir, India.
E-mail address: mohsin@kashmiruniversity.ac.in (M. Ahmad Bhat).
https://doi.org/10.1016/j.saa.2020.119154
1386-1425/Ó 2020 Elsevier B.V. All rights reserved.

M. Shafat Khan, R. Khanam, S. Ahmad Bhat et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 247 (2021) 119154
and hexane were procured from Spectrochem India. Cetyltrimethy-
lammonium bromide (CTAB, 99%), sodium dodecyl sulfate (SDS,
98%) and Brij 56, 98%) with ACS reagent grade purity were
procured from Sigma-Aldrich and were used as such without any
further purification. Deionized water was used throughout the
study.
1. Introduction
The diverse potentialities, sensitivity and selectivity of UV–Vis
spectrophotometry have established it as a versatile analytical tool
for research and analytical applications [1–3]. Simple experimental
protocols, inherent speed of analysis, high accuracy, selectivity,
sensitivity and reproducibility of measurements are some of the
highly appreciated features of UV–Vis spectrophotometry [1–3].
Though the comparison/estimation of direct interaction of light
with analyte samples continues to be the main working principle
of modern-day spectrophotometers, the recent technological,
material, mathematical and software-based advancements have
significantly widened the analytical utility of UV–Vis spectropho-
tometry. Solvatochromism based UV–Vis spectrophotometry
marks an important development in this regard [4–6]. Analysis of
published literature about solvatochromism based UV–Vis spec-
trophotometry returns hundreds of innovative demonstrations
about its analytical utility for diverse kind of applications [4–12].
In the solvatochromism based UV–Vis spectrophotometric investi-
gations, the impact of medium/process over the UV–Vis response
of an intelligently selected probe is translated into qualitative/
quantitative information about a system/process. Such investiga-
tions have been extensively employed for the estimation of bulk
and local microenvironment polarity of solvents/solvent mixtures,
solubilization capacity, identification of site of solubilization, onset
of aggregation of amphiphilic molecules, folding and unfolding of
proteins [10,13–17]. Design/selection of a suitable molecular probe
with specific characteristics that make its UV–Vis response extre-
mely sensitive to the process or parameter of interest constitutes
the most critical step in the successful design of solvatochromism
based UV–Vis spectrophotometric investigations [18]. Design and
search of such probes has been attracting a considerable attention
of synthetic chemists.
Owing to its unique physico-chemical attributes, the hydrazone
functionality has been extensively researched for a diverse range of
chemical, biological and analytical applications [19–21]. Among
different hydrazones, the ortho substituted ones with a nitro or a
like functionality close to the azomethine functionality, depending
upon the solvent/micropolarity of the local environment can exhi-
bit intra or inter molecular hydrogen bonding. The inter and intra
molecular hydrogen bonding shall result in significantly different
absorption characteristics for azomethine functionality based
hydrazones. Worth to mention, the hydrogen bonding ability of
the acidic NH proton present in >C=N-NH-C< skeleton has been
successfully exploited for sensing applications [19,22–26]. More-
over, these compounds are easy to synthesize and are reported
to be quite stable towards hydrolysis [27]. Motivated by these lit-
erature reports, design of an azomethine functionality based ortho-
nitrohydrazone viz. (2,4-dinitrophenyl)-2-(2-nitrobenzylidene)
hydrazone (DNPNBH), as a sensitive solvatochromic probe was
attempted. Potential of DNPNBH to sensitively sense the microen-
vironment polarity changes in single solvent and DMF-water
mixed solvent system is presented. Further, the use of DNPNBH
as a spectrophotometric probe is demonstrated to reflect the onset
of micellization and hence estimation of critical micelle concentra-
tion (CMC) of some model amphiphilic molecules in their aqueous
solutions.
2.2. Instrumentation
Melting points were determined on Buchii 570 melting point
apparatus. 1H NMR spectra was obtained on a Joel spectrometer
at 600 MHz in CD3CN. FTIR spectra was collected on FTIR-400 from
Perkin Elmer using ATR. UV–visible spectra were recorded on Shi-
madzu UV–vis spectrophotometer (UV-1650 PC) equipped with a
thermostat for temperature control with accuracy of 0.1 °C. To
ensure the reproducibility and to assess the degree of variance in
the measurements, all spectroscopic measurements for solva-
tochromic studies were repeated at least five times for the present
study.
2.3. Synthetic procedure
The desired product viz. (2,4-dinitrophenyl)-2-(2-nitrobenzyli
dene)hydrazone
(DNPNBH)
was
synthesized
from
2-
nitrobenzaldehyde and 2, 4-dinitrophenyl hydrazine through a
one-pot, single step easy to carry out reaction. Briefly an acidic
solution of 2, 4-dinitrophenyl hydrazine was prepared by carefully
adding conc. sulphuric acid (1.6 mL) to a suspension of 2, 4-
dinitrophenyl hydrazine (0.14 g, 0.7 mmoL) in CH3OH (8.5 mL).
This acidic solution of 2, 4-dinitrophenyl hydrazine was added
dropwise to a continuously stirred solution of 2-nitro benzalde-
hyde (0.3 g, 2 mmoL) in ethanol (3 mL). The mixture was stirred
at room temperature for 15 min. A yellow precipitate of DNPNBH
was obtained, filtered and dried. The crude product was recrystal-
lized from acetone and water to yield the pure (2,4-dinitrophenyl)-
2-(2-nitrobenzylidene)hydrazone as a yellow solid (93%). Melting
point of the recrystallized compound was found to be 250 1 °C.
The possible synthetic reaction scheme is shown as scheme 1.
Spectral data:
Yellow solid;
mp:
250 1 °C.
1H NMR
(600 MHz,
CDCN):
d 7.665–7.693 (m, 1H), 7.793–7.818 (m,
1H), 8.052 (d, 1H, J = 8.40 Hz), 8.137 (d, 1H,
J = 9.60 Hz), 8.248 (d, 1H, J = 9.60 Hz),
8.411 (d, 1H, J = 3 Hz), 8.794 (s, 1H, CH),
9.019 (s, 1H) 11.392 (s, 1H, NH).
3287 (m, NH),1615 (s, N = C), 1515 (s, NO
2), 1330 (s, NO 2), 883 (s), 786 (w), 742
(s),724 (w), 684 (s)
FTIR (cmꢁ1):
3. Results and discussion
3.1. Sensing solvent polarity
2. Experimental section
Fig. 1(A) depicts a sample concentration normalized UV–Vis
spectrum recorded for the DNPNBH in methanol. The spectrum
depicts a single absorption peak centered ca. 382 nm, which can
2.1. Chemicals
be attributed to the
p-p* transition of its imine unit [28]. Fig. 1
2-Nitro benzaldehyde, 2,4-dinitro phenyl hydrazine, sulphuric
acid were procured from Merck India. Spectroscopic grade solvents
viz. methanol, ethanol, butanol, carbon tetrachloride, ethyl acetate
(B) depicts a sample set of concentration normalized UV–Vis spec-
tra recorded for the DNPNBH in solvents of changing polarity. As
apparent from these depicted spectra, the position of the DNPNBH
2

M. Shafat Khan, R. Khanam, S. Ahmad Bhat et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 247 (2021) 119154
Scheme 1. Possible reaction pathway between 2-nitrobenzaldehyde and 2, 4-dinitrophenyl hydrazine to form (2,4-dinitrophenyl)-2-(2-nitrobenzylidene)hydrazone.
Fig. 1. (A) Model UV–Vis spectra of (2,4-dinitrophenyl)-2-(2-nitrobenzylidene)hydrazine (DNPNBH) in methanol with kmax of 382 nm. (B) UV–Vis spectra observed for
DNPNBH in different solvent systems. (C) Linear fit of kmax of DNPNBH obtained in different solvent systems as function of reported ET(30) values for such solvent systems.
characteristic absorption maxima (kmax) is sensitive to the solvent
polarity. To reveal the same, we analysed the changes in the posi-
tion of the kmax in the absorption band as a function of ET(30)
values reported for these solvents in the literature [29]. It is perti-
nent to mention here that the ET(30) parameter is considered as a
measure of the empirical solvent polarity and an index of the
hydrogen bonding and electrostatic interaction abilities of solvents
[29–33].
Fig. 1(C) depicts the variation observed for the kmax as a func-
tion of the literature reported ET(30) values for these solvents.
The depicted data points suggest a linear dependence of kmax over
ET(30) with a good statistics [R2 > 0.99] and the straight fit equa-
tion was found to be kmax = 344.402 + 0.695 ET(30). This observa-
tion clearly establishes the micropolarity sensing potential of the
synthesized hydrazone.
equilibrium electrochemistry and spectroscopic measurements
etc. have proved very useful for this kind of understanding about
solvent mixtures [34–38]. DMF-water mixtures have been
observed to exhibit interesting composition dependent physico-
chemical characteristics. Recently, our group has employed
conductance measurements, rheometry, density measurements,
and dynamic/equilibrium electrochemistry to probe the composi-
tion dependent physico-chemical properties like ion-pair associa-
tion, viscosity, di-electric, diffusion and heterogenous electron
transfer properties of DMF-water binary solvent system [38]. The
composition dependent nonlinear transitions reported for various
physicochemical and electrochemical characteristics in DMF-
water mixtures can be attributed to the competing water-water,
water-DMF and DMF-DMF hydrogen bonding patterns [38]. In light
of these findings the use of the DNPNBH was explored to sense the
microenvironment/solvatochramic changes associated with
change in composition of DMF-water mixtures. In spectrophoto-
metric measurements, the effect of change in composition of
DMF-water mixture on absorbance behaviour of DNPNBH in UV–
Visible range (330–500 nm) was monitored. Fig. 2(A) depicts sets
of UV–Vis spectra recorded for DNPNBH at changing percentage
composition of DMF in water at 298 K. A broad band corresponding
to absorption by DNPNBH was observed at 369 nm in water. Inter-
estingly, with increase in percentage of DMF in water, a red shift of
absorption maxima in the initial DMF-water compositions (10–40%
DMF in H2O) followed by blue shift in rest of the DMF-water com-
positions was observed. Such type of bathochromic shifts in the
absorption band of the DNPNBH are a characteristic of such types
of compounds in hydrogen bond accepting solvents like DMF and
DMSO [39,40]. These red shifts in such solvents are attributed to
stabilization of energy states due to hydrogen bonding between
the NH group of DNPNBH and the solvent resulting in the reduc-
tion of HOMO-LUMO gap. The non-linearity of the solvatochromic
shift (transition energy vs. the mole fraction of the more polar sol-
vent) observed for the DNPNBH implies that the local composition
sensed by this probe is different from the bulk environment [41].
This alteration in local mixture composition can be an outcome
3.2. Sensing composition dependent physicochemical changes in
solvent mixtures
The selective/preferential solvation and hence stabilization
potential of solvent molecules has been successfully employed to
control the reactivity and selectivity in a variety of reactions. Selec-
tion of an appropriate solvent system with desired physicochemi-
cal characteristics to ensure its desired impact on a chemical
process is always the most critical and challenging step in the
design of suitable reaction setups. In this context the use of solvent
mixtures offers simple means to arrive at desired standards of sol-
vent characteristics required for a particular chemical transforma-
tion [34–37]. Interestingly, the selective and unsymmetrical
solvation abilities of the components of the solvent mixtures for
reactants/products can be employed to tune the kinetic, thermody-
namic and mechanistic aspects of the reactions [34–37]. Therefore
a clear-cut understanding of composition dependency of physico-
chemical aspects of solvents is a must for the selection/design of
suitable solvent mixtures for their use in chemical transformations.
Techniques like density measurements, rheometry, conductance
measurements, tensiometery, dielectric measurements, dynamic/
3

M. Shafat Khan, R. Khanam, S. Ahmad Bhat et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 247 (2021) 119154
Fig. 2. (A) UV–Vis spectra of (2,4-dinitrophenyl)-2-(2-nitrobenzylidene)hydrazone (DNPNBH) recorded in changing compositions of DMF-water mixture. (B) Variation of
transition energy as a function of mole fraction of Water (XH O) in DMF-water mixture.
2
of non-specific interactions or preferential solvation (dielectric
enrichment) of the DNPNBH probe by the components of the
DMF-water mixture [42]. Therefore, the solvatochromic beha-
viour/spectral shifts associated with the probe as a function of sol-
vent composition can be attributed to its hydrogen bonding at the
higher mole fractions of polar component preceded by the dielec-
tric enrichment of the probe in lower mole fractions of polar com-
ponent [40–42].
solute leading to the formation of its clusters [40,43]. The solute
can be solvated in such solvent aggregates without any involve-
ment of the former in the construction of such molecular clusters.
In DMF-water mixture, formation of solvent aggregates and solva-
tion of the probe is expected to be more than in DMF and water
only. Therefore, the energy minima observed in the mole fraction
range of 0.85–0.975 with respect to H2O can be attributed to strong
stabilization of the DNPNBH by such solvent aggregates. However,
further extensive spectroscopic investigations are needed to sup-
port the said claim. The results presented herein and previously
published reports [38,40–43], make us to conclude that DNPNBH
possess excellent attributes to sense the solvent microenvironment
and thereby can be employed as a reliable solvatochromic probe
for solvent/solvent mixtures.
As previously reported [38], in its mixtures with solvent like
DMF, the water molecules exhibit a strong tendency to form closed
network structures among themselves rather than coordinating
with organic moiety. As an outcome of such a tendency of water
molecules, addition of DMF as co-solvent is expected to result in
the expulsion of DNPNBH, which shall force it to undergo intra-
molecular hydrogen bonding. As reported in our earlier study,
DMF is a structure breaking co-solvent and its addition to water
leads to structure breaking in water with formation of caged struc-
tures wherein water molecules are sheathed by DMF molecules
[38]. This transition in solvent structure might engage the DNPNBH
to undergo intermolecular hydrogen bonding. The transition in
absorption maxima/solvatochromic/spectral shift of DNPNBH
observed as a function of composition resembles with transition
reported for properties like viscosity, limiting molar conductivity,
diffusion coefficients and electron transfer rate constants reported
for DMF-Water plus electrolyte and redox probe solutions [38]. The
wavelengths corresponding to absorption maxima of DNPNBH
were used for the estimation of the energy required for the spec-
troscopic transitions using the equation [29]:
3.3. Sensing onset of micellization-estimation of CMC
Surface active agents (surfactants) are a promising class of
amphiphilic molecules used in a variety of consumer products,
technological, chemical and biological applications [44]. The for-
mation of organized structures called as micelles in aqueous solu-
tions of surfactants takes place only when their concentration
exceeds a specific value, regarded as the critical micelle concentra-
tion (CMC) of the surfactant. CMC value of surfactants not only
reflects the stability of their micelles, but it also serves as one of
the important parameters to assess the efficiency of surfactants
for their desired applications [45]. In this context the reliable and
accurate estimation of CMC values for surfactants becomes very
important. The methods presently employed for estimation of
CMC involve measurement of surface tension, turbidity, electrical
conductance, solubilization, self-diffusion and absorption phenom-
ena as a function of increasing concentration of surfactant [45,46].
It is worth to mention that among the above-mentioned tech-
niques employed for the estimation of CMC, the spectroscopic
measurements are easy to carry, safe, sensitive, reliable and most
readily available. However, spectroscopic measurements for CMC
estimations requires presence of suitable UV–Vis active probe.
The use of such a probe almost always alters the solvent structure
and the micellization ability of the surfactants and hence leads to
estimation of an apparent rather than the actual CMC [45,46].
Therefore, the design/fabrication of UV–Vis active molecule which
can be employed at very low concentrations to sense the microen-
vironment changes of surfactant solutions for CMC estimation is an
active area of research. A non-polar and ideally water insoluble
UV–Vis probe capable of penetrating deep into micellar core is
expected to negligibly influence the micellization process of sur-
factants and hence capable of reporting the near actual CMC of sur-
factants [47]. Our observations vis a vis sensitivity of UV–Vis
ET ðkJ=moleÞ ¼ 1:196 ꢂ 10ꢁ2 ꢂ ꢁ
m
ðcmꢁ1
Þ
The ET values obtained from the above equation plotted as a
function of mole-fraction of more polar solvent vizꢃH2O are
depicted in Fig. 2(B). Fig. 2(B) clearly suggests that the transition
energy of DNPNBH decreases as the DMF-water mixture becomes
rich in more polar solvent vizꢃH2O with an energy minimum in
the mole fraction range of 0.85–0.975 with respect to H2O. As indi-
cated from the plot as well as literature reports [41], ET values of
the probe in mixed solvent system show that the position of solva-
tochromic absorption band of the probe is dependent on medium
polarity. Therefore, as the mole fraction of more polar solvent
vizꢃH2O increases, the ET values corresponding to the
p-p* transi-
tion seem to decrease probably due to stronger solute–solvent
interaction which stabilizes the excited state of the former relative
to its ground state. Besides, solute–solvent interactions, the sol-
vent–solvent interactions play an important role in solvation of
solutes in mixed solvent systems [41]. Moreover, in such cases
one component of the binary mixture preferentially binds to the
4

M. Shafat Khan, R. Khanam, S. Ahmad Bhat et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 247 (2021) 119154
Table 1
absorption characteristics of DNPNBH motivated us to check its
utility for the estimation of CMC of surfactants. Hence, we followed
the variations in absorption characteristics of DNPNBH at its low-
est possible concentration following changing concentrations of
model surfactants viz. cetyl trimethyl ammonium bromide
(CTAB-a cationic surfactant), sodium dodecyl sulphate (SDS-an
anionic surfactant) and Brij56 (a nonionic surfactant). These sur-
factants were chosen in view of the vast literature available about
their micellization behavior and absence of any UV–Vis active
structural unit in their structure that necessities the use of an
external probe for spectrophotometric estimation of their CMC
[48]. Fig. 3(A) depicts a sample set of UV–Vis spectra recorded
Comparison of CMCs of SDS, CTAB and Brij56 obtained via use of (2,4-dinitrophenyl)-
2-(2-nitrobenzylidene)hydrazine (DNPNBH) as UV–Vis probe in present study with
reported values through different techniques:
Surfactant CMC
(mM)
Literature Values (mM)
References
SDS
5.25
1.53
0.055
4.84 [56], 3.46 [57], 6.02–8.1
[53,58–63]
0.65–1.51
[53,56,57,58–
63]
[53,57,61,63–
66]
CTAB
Brij56
0.051, 0.069
[67,68]
techniques. A comparison of CMCs reported in the literature for
these model surfactants viz. CTAB, SDS and Brij56 obtained
through different techniques with the values estimated in the pre-
sent work is provided in the form of Table 1. It can be seen from
the entries made in Table 1 that the CMC estimated in present
study for CTAB (cationic surfactant), SDS (anionic surfactant) and
Brij56 (nonionic surfactant) through use of DNPNBH as UV–Vis
active molecular probe are in good agreement with that reported
via use of other techniques. It is pertinent to mention here that
the estimation of CMC through probe assisted UV–Vis spectropho-
tometric estimations has been reported in the past as well [49–53].
However, unlike the other probes employed for the spectrophoto-
metric estimation of CMC in past, DNPNBH besides being cheap
and easy to synthesize is required in a very low concentration.
Additionally, estimation of the CMC from spectrophotometric data
with DNPNBH is very straight forward and requires no data pro-
cessing (that reduces the accuracy) [54,55] and complicated curve
fitting procedures [56] as is required for the case of probe assisted
spectrophotometric estimations of CMC with other probes.
for 5 lM aqueous solution of DNPNBH at changing concentration
of CTAB. As clearly noticed from the depicted spectra, increasing
concentration of the CTAB up to a specific concentration shifts
the absorption maximum (kmax) of DNPNBH toward lower wave
length. Any further increase in concentration of the CTAB was
observed to result in almost no change in the kmax of DNPNBH.
Similar observations were noticed for the addition of SDS and Bri-
j56 to 5 lM aqueous solution of DNPNBH. The wavelength corre-
sponding to kmax of DNPNBH plotted as a function of CTAB
concentration is depicted as Fig. 3(B). The data reflects an initial
linear decrease in the kmax up to a reproducibly specific CTAB con-
centration followed by an almost CTAB concentration independent
kmax of DNPNBH. Similar observations were noted for the kmax of
DNPNBH in presence of changing SDS (Fig. 3(C)) and Brij56
(Fig. 3(D)) concentration. The kmax vs. surfactant concentration
data for CTAB, SDS and Brij56 fits to two straight lines typical to
their tensiometric plots. The concentration corresponding to the
intersection point of these straight lines in Fig. 3(B) was found to
be 1.53 mM which exactly matches the literature reported CMC
value of CTAB (Table 1).
Similarly, the intersection point of the straight lines fitting the
two linear sets of data points in Fig. 3(C) and (D) were found to
be 5.25 mM and 0.055 mM respectively which are in good agree-
ment with the CMC of SDS and Brij56 determined through different
3.4. Quantum mechanical calculations
In order to further validate our experimental observations, we
performed quantum mechanical/theoretical calculations. All the
Fig. 3. (A) UV–Vis spectra of 5
lM (2,4-dinitrophenyl)-2-(2-nitrobenzylidene)hydrazine (DNPNBH) aqueous solution recorded as function of changing CTAB concentration.
Variation of absorption maxima (kmax) of 5
l
M DNPNBH aqueous solution as a function of (B) CTAB concentration. (C) SDS concentration. (D) Brij56 concentration.
5

M. Shafat Khan, R. Khanam, S. Ahmad Bhat et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 247 (2021) 119154
calculations for the present work were performed using Gaussian
16 programme [69]. The various conformers of the (2,4-dinitrophe
nyl)-2-(2-nitrobenzylidene)hydrazine (DNPNBH) were generated
using Gauss view 6 [70] and optimized in gas phase employing
B3YP functional [71,72] and 6-311++G(d, p) basis set [73]. The
optimized structures were confirmed to be minima from the real
value of the lowest vibrational frequency. Two lowest energy con-
formers are shown in Fig. 4.
In the conformer DNPNBH -C2, the 2-nitrophenyl ring is
flipped by ꢄ60° out of plane with respect to the exocyclic imine
bond coplanar with the 2,4-dinitrophenyl ring. Thus, the non-
planar conformer DNPNBH-C2 is 3.39 kcal/mol higher in energy
compared to DNPNBH-C1, other conformers are destabilized by
>8.0 kcal/mol and hence they are not considered further. The
UV–visible spectra of conformers DNPNBH-C1 and DNPNBH-C2
in various solvents viz. Hexane, chloroform, DMF and water are
computed employing time dependent density functional theory
(TDDFT) on 10 states using aforementioned density functional
and basis set. For the simulation of solvent effect, self-
consistence reaction field (SCFR) using conductive polarizable
continuum model (PCM) was employed [74,75]. These UV–visible
spectra are plotted using the Gabedit programme and shown in
Fig. 5 [76]. Fig. 5(A) clearly shows that the DNPNBH-C1 spectra
is sensitive to the polarity of the solvent and shows the red shift
with increasing polarity, which is consistent with the experimen-
tal observations.
Fig. 4. The B3LYP6-311++G (d, p) optimized geometries of two lowest energy conformers of (2, 4-dinitrophenyl)-2-(2-nitrobenzylidene)hydrazone (DNPNBH) and their
relative energies (kcal/mol) in gas phase.
Fig. 5. The UV visible spectra of the (2,4-dinitrophenyl)-2-(2-nitrobenzylidene)hydrazone (DNPNBH) simulated in various solvents employing B3LYP/6-311++G(d,p) level of
theory using gas phase optimized geometry: (A) spectra of conformer DNPNBH-C1 in hexane (green), chloroform (blue) and water (red). (B) Spectra of conformer DNPNBH -
C1 (red) and DNPNBH -C2 (dotted blue, intensity scaled by 2).
6

M. Shafat Khan, R. Khanam, S. Ahmad Bhat et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 247 (2021) 119154
[8] L. Ascherl, E. W. Evans, M. Hennemann, D. D. Nuzzo, A. G. Hufnagel, M. Beetz, R.
H. Friend, T. Clark, T. Bein, F. Auras, Solvatochromic covalent organic
frameworks, Nature Communications, https://doi.org/10.1038/s41467-018-
06161-w.
[9] K. Pal, A.L. Koner, Rationally designed solvatochromic fluorescent indoline
derivatives for probing mitochondrial environment, Chem. Eur. J. 23 (2017)
8610–8614.
[10] S. Concilio, I. Ferrentino, L. Sessa, A. Massa, P. Iannelli, R. Diana, B. Panunzi, A.
Rella, S. Piotto, A novel fluorescent solvatochromic probe for lipid bilayers,
Supramol. Chem. 29 (2017) 887–895.
The simulated UV–visible spectra of the DNPNBH -C1 and
DNPNBH -C2 in DMF (Fig. 5(B)) reveals that the conformational
change to higher energy DNPNBH -C2 lead to the blue shift of
the electronic transitions. This may be due to the reduced conjuga-
tion between the two phenyl rings, which leads to the increase in
the frontier orbital energy gap. Furthermore, the hypochromic shift
is observed for the transition ꢄ371 nm in the calculated spectra,
which is in consistence with the experimental observation when
DMF is used as solvent.
[11] Xin Yang, Wan-Hui, Liu Wei-Jun, Jin, Guo-Li Shen Ru-Qin Yu, DNA binding
studies of
a solvatochromic fluorescence probe 3-methoxybenzanthrone,
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 55
(1999) 2719–2727.
4. Conclusion
[12] G.S.Loving,M.Sainlos,B.Imperiali,Monitoringproteininteractionsanddynamics
withsolvatochromicfluorophores,TrendsBiotechnol.28(2010)73–83.
[13] L.P. Novaki, O.A.E. Seoud, Solvatochromism in aqueous micellar solutions:
effects of the molecular structures of solvatochromic probes and cationic
surfactants, Phys. Chem. Chem. Phys. 1 (1999) 1957–1964.
In conclusion, a cheap, easy to synthesize hydrazone viz. (2,4-
dinitrophenyl)-2-(2-nitrobenzylidene)
hydrazone
(DNPNBH)
through one-pot single step approach was designed. The as synthe-
sized DNPNBH was found to exhibit UV–Vis characteristics sensi-
tive to solvent polarity/structure/composition. The hydrazone
was explored as a UV–Vis active spectroscopic solvatochromic
probe to sense the polarity of different solvent systems and com-
position dependent physicochemical/structural properties of
mixed solvent systems. The experimental observations are well
supported by the quantum mechanical calculations. The DNPNBH
as a UV–Vis spectroscopic probe ensures estimation of CMC of con-
ventional surfactants with good accuracy and reproducibility.
[14] L.P. Novaki, O.A.E. Seoud, Microscopic polarities of interfacial regions of
aqueous cationic micelles: effects of structures of the solvatochromic probe
and the surfactant, Langmuir 16 (2000) 35–41.
[15] E. Fuguet, C. Ràfols, E. Bosch, M. Rosés, Characterization of the solvation
properties of sodium n-dodecyl sulfate micelles in buffered and unbuffered
aqueous phases by solvatochromic indicators, Langmuir 19 (2003) 55–62.
[16] M.M. Sartin, K. Kondo, M. Yoshizawa, S. Takeuchi, T. Tahara, Local environment
inside a novel aromatic micelle investigated by steady-state and femtosecond
fluorescence spectroscopy of an encapsulated solvatochromic probe, Phys.
Chem. Chem. Phys. 19 (2017) 757–765.
[17] S. Mallick, K.P. Apurba, L. Koner, Probing microenvironment of micelle and
albumin using diethyl 6-(dimethylamino) naphthalene-2,3-dicarboxylate: An
electroneutral solvatochromic fluorescent probe, J. Colloid Interface Sci. 467
(2016) 81–89.
[18] Luzia P. Novaki, Omar A. El Seoud, Solvatochromism in pure solvents: effects of
Credit authorship contribution statement
the
molecular
structure
of
the
probe,
Berichte
der
BunsengesellschaftfürphysikalischeChemie 100 (1996) 648–655.
[19] X. Su, Ivan Aprahamian, Hydrazone-based switches, metallo-assemblies and
sensors, Chem. Soc. Rev., 43 (2014) 1963–1981.
[20] F.J.U. Romo, C.J. Doonan, H. Furukawa, K. Oisaki, O.M. Yaghi, Crystalline
covalent organic frameworks with hydrazone linkages, J. Am. Chem. Soc. 133
(2011) 11478–11481.
Mudeha Shafat Khan: Visualization, Investigation, Data cura-
tion, Writing - original draft. Romana Khanam: Visualization,
Investigation, Data curation. Sajad Ahmad Bhat: . Naheed Sidiq:
Conceptualization, Supervision, Data curation, Writing - review &
editing. Tabasum Ismail: Data curation, Writing - review & editing.
Pravin P. Ingole: Conceptualization, Methodology, Supervision,
Writing - review & editing. Rahul V. Pinjari: Writing - original
draft. Mohsin Ahmad Bhat: Conceptualization, Methodology,
Supervision, Data curation, Writing - original draft, Writing -
review & editing, Funding acquisition.
[21] L. Stegbauer, K. Schwinghammer, B.V. Lotsch, A hydrazone-based covalent
organic framework for photocatalytic hydrogen production, Chem. Sci.
(2014) 2789–2793.
5
[22] L. Zhou, X. Zhang, S. Wu, Fluoride-selective colorimetric sensors based on
hydrazone functionality, Chem. Lett. 33 (2004) 850.
[23] S. Dalapati, S. Jana, N. Guchhait, Anion recognition by simple chromogenic and
chromo-fluorogenic salicylidene Schiff base or reduced-Schiff base receptors,
Spectrochim. Acta A 129 (2014) 499.
[24] W.A. Durai, A. Ramu, Hydrazone based dual-responsive colorimetric and
ratiometric chemosensor for the detection of Cu2+/Fꢁ ions: DNA tracking,
practical performance in environmental samples and tooth paste, J.
Fluorescence 30 (2020) 275–289.
Declaration of Competing Interest
[25] S.A. Khan, A.M. Asiri, Physicochemical properties of novel methyl 2-{(E)-[(2-
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared
to influence the work reported in this paper.
hydroxynaphthalen-1-yl)methylidene]
amino}-4,5,6,7-tetrahydro-1-
benzothiophene-3-carboxylate as turn-off fluorometric chemosensor for
detection Fe3 + ion, J. Mol. Liq. 243 (2017) 85–90.
[26] M.E.M. Zayed, A.M. Asiri, S.A. Khan, Microwave assisted synthesis,
spectrofluorometric characterization of azomethine as intermediate for
transition metal complexes with biological application, J. Fluorescence 26
(2016) 937–947.
Acknowledgements
[27] S. Swami, A. Agarwala, B. Malik, R. Shrivastavaa, A new class of efficient 4-
[(nitro substituted-phenyl)- hydrazonomethyl]-1-phenyl-1H-pyrazole-3-
carboxylate derived colorimetric chemosensor for selective sensing of
fluoride and other biologically important anions, J. Chem. Sci. 128 (2016) 1451.
Authors would like to thank Prof. G. M. Rather, Presently Head,
Department of Chemistry, IUST- Awantipora, J & K, and Dr. Aijaz
Ahmad Dar, Department of Chemistry, University of Kashmir, Sri-
nagar, for their valuable suggestions and support for the presented
work.
[28] A. Neeraj, S.K. Kumar, S.K.K. Asthana, Upadhyay,
salicylimine as
bright yellow emissive probe for Al3+
Photobiol. A 329 (2016) 69–76.
A
dichloro-substituted
a
,
J. Photochem.
[29] Prof. Dr. Christian Reichardt, Empirical Parameters of Solvent Polarity as
Linear Free-Energy Relationships. Angew Chem. lnt. Ed. Engl. 18 (1979) 98–
110.
References
[30] C. Reichardt, Pyridinium N-phenolate betaine dyes as empirical indicators of
solvent polarity: Some new findings, Pure Appl. Chem. 76 (2004) 1903–1919.
[31] C. Reichardt, Solvents and solvent effects: an introduction, Org. Process Res.
Dev. 11 (2007) 105–113.
[32] Y. Marcus, The properties of organic liquids that are relevant to their use as
solvating solvents, Chem. Soc. Rev. 22 (1993) 409–416.
[33] C. Reichardt, Pyridinium-N-phenolate betaine dyes as empirical indicators of
solvent polarity: Some new findings, Pure Appl. Chem. 80 (2008) 1415–
1432.
[34] R.L. Blackbourn, J.T. Hupp, Electron-transfer reactions in mixed solvents. An
electrochemical probe of unsymmetrical selective solvation, Inorg. Chem. 28
(1989) 3786–3790.
[1] D.A. Skoog, D.M. West, F.J. Holler, S.R. Crouch, Fundamentals of analytical
chemistry, 9th ed., international ed. Brooks/Cole, Cengage Learning, ISBN: 978-
1-285-05624-1, (2010).
[2] D. Harvey, Modern Analytical Chemistry, 1st ed., McGraw Hill: Boston, ISBN 0-
07-237547-7 (2000) 798 pp.
[3] D.C. Harris, Quantitative chemical analysis, W. H. Freeman; 9th edition. 9th ed.
ISBN-13: 978-1464135385, May 29 (2015).
[4] C. Reichardt, Solvatochromic dyes as solvent polarity indicators, Chem. Rev. 94
(1994) 2319–2358.
[5] C. Reichardt, Solvent and Solvent Effects in Organic Chemistry, 3rd ed., Wiley-
VCH, Weinheim, 2002.
[6] P. Suppan, N. Ghoneim, Solvatochromism, The Royal Society of Chemistry,
Cambridge, 1997.
[7] A.M. Aurora, M. Losa, A. Biancardi, B. Mennucci, What is solvatochromism?, J
Phys. Chem. B 114 (2010) 17128–17135.
[35] W. Miao, Z. Ding, A.J. Bard, Solution viscosity effects on the heterogeneous
electron transfer kinetics of ferrocene methanol in dimethyl sulfoxide-water
mixtures, J. Phys. Chem. B 106 (2002) 1392–1398.
7

M. Shafat Khan, R. Khanam, S. Ahmad Bhat et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 247 (2021) 119154
[36] S.G. Sivakolundu, P.A. Mabrouk, Cytochrome c structure and redox function in
mixed solvents are determined by the dielectric constant, J. Am. Chem. Soc.
122 (2000) 1513–1521.
[58] M.L. Corrin, W.D. Harkins, The effect of salts on the critical concentration for
the formation of micelles in colloidal electrolytes, J. Am. Chem. Soc. 69 (1947)
679.
[37] M.A. Prasad, M.V. Sangaranarayanan, Electrochemical reductive cleavage of
carbon tetrachloride in aqueous-nonaqueous binary solvents, J. Electroanal.
Chem. 569 (2004) 127–134.
[59] L. Cai, M. Gochin, K. Liu, A facile surfactant critical micelle concentration
determination, Chem. Commun. 47 (2011) 5527–5529.
[60] G.V. Jensen, R. Lund, J. Gummel, T. Narayanan, J.S. Pedersen, Monitoring the
Transition from spherical to polymer-like surfactant micelles using small-
angle X-Ray scattering, Angew. Chem. Int. Ed. 126 (2014) 11708–11712.
[61] J. Aguiar, P. Carpena, J.A.M. Bolívar, C.C. Ruiz, On the determination of the
critical micelle concentration by the pyrene 1:3 ratio method, J. Colloid
Interface Sci. 258 (2003) 116–122.
[38] S.A. Pandit, M.A. Rather, S.A. Bhat, R. Jan, G.M. Rather, M.A. Bhat, An insight into
a
fascinating DMF-water mixed solvent system: physicochemical and
electrochemical studies, ChemistrySelect 2 (2017) 5115–5127.
[39] M. Kumaravel, J.T. Mague, M.S. Balakrishna, Hydrazone derivatives appended to
diphenylphosphineoxideasanionsensors,J.Chem.Sci.129(2017)471–481.
[40] C. Lerf, P. Suppan, Hydrogen bonding and dielectric effects in solvatochromic
shifts, J. Chem. Soc. Faraday Trans. 88 (7) (1992) 963–969.
[62] L. Piñeiro, M. Novo, W. Al-Saufi, Fluorescence emission of pyrene in surfactant
solutions, Adv. Colloid Interface Sci. 215 (2015) 1–12.
[41] T. Bevilaqua, T.F. Goncalves, C.G. Venturini, V.G. Machado, Solute-solvent and
solvent-solvent interactions in the preferential solvation of 4-[4-
(dimethylamino)styryl]-1-methylpyridinium iodide in 24 binary solvent
mixtures, Spectrochim. Acta, Part A 65 (2006) 535–542.
[42] J. Midwinter, P. Suppan, Spectral shifts in solvent mixtures, Spectrochim. Acta
Part A 25 (1969) 953.
[43] P. Suppan, Hydrogen bonding effects in spectral solvent shifts, Spectrochim.
Acta 80 (1974) 1939–1952.
[44] D.F. Evans, The Colloidal Domain, Holmberg K, Jonsson B, Kronberg B, Lindman
[63] A. Mohr, P. Talbiersky, H.G. Korth, R. Sustmann, R. Boese, D. Blaser, H. Rehage, A
new pyrene-based fluorescent probe for the determination of critical micelle
concentrations, J. Phys. Chem. B 111 (2007) 12985–12992.
[64] S. Javadian, V. Ruhi, A. Heydari, A. Asadzadeh Shahir, A. Yousefi, J. Akbari, Self-
assembled CTAB nanostructures in aqueous/ionic liquid systems: effects of
hydrogen bonding, Ind. Eng. Chem. Res. 52 (2013) 4517–5452.
[65] Y.K. Shrestha, F. Yan, Determination of critical micelle concentration cationic
surfactants by surface-enhanced Raman scattering, RSC Adv. 4 (2014) 37274–
37277.
B
(2002) Surfactants and Polymers in aqueous solution, 2nd edn. Wiley,
[66] Critical Micelle concentrations of Aqueous Surfactant systems, NSRDS, U. S.
Department of Commerce, National Bureau of standards.
Chichester, West Sussex.
[45] M.J. Rosen, Surfactants and Interfacial Phenomenon, John Wiley, New York,
1978.
[46] T. Chakraborty, I. Chakraborty, S. Ghosh, The methods of determination of
critical micellar concentrations of the amphiphilic systems in aqueous
medium, Arabian J. Chem. 4 (2011) 265–270.
[47] B. Lindman, H. Wennerstrom, Micelles: Amphile Aggregation in Aqueous
Solution, Springer-Verlag, Berlin, 1980.
[48] M.A. Rather, G.M. Rather, S.A. Pandit, S.A. Bhat, M.A. Bhat, Determination of
cmc of imidazolium-based surface active ionic liquids through probe-less UV-
vis spectrophotometry, Talanta 131 (2015) 55–5856.
[67] P.A. Bhat, G.M. Rather, A.A. Dar, Effect of surfactant mixing on partitioning of
model hydrophobic drug, naproxen, between aqueous and micellar phases, J.
Phys. Chem. B 113 (2009) 997–1006.
[68] Y. Nakahara, T. Kida, Y. Nakatsuji, M. Akashi, New fluorescence method for the
determination of the critical micelle concentration by photosensitive
monoazacrypt and derivatives, Langmuir 15 (2005) 6688–6695.
[69] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R.
Cheeseman, G. Scalmani, V. Barone, G. A. Petersson, H. Nakatsuji, X. Li, M.
Caricato, A. V. Marenich, J. Bloino, B. G. Janesko, R. Gomperts, B. Mennucci,
H. P. Hratchian, J. V. Ortiz, A. F. Izmaylov, J. L. Sonnenberg, D. Williams-
Young, F. Ding, F. Lipparini, F. Egidi, J. Goings, B. Peng, A. Petrone, T.
Henderson, D. Ranasinghe, V. G. Zakrzewski, J. Gao, N. Rega, G. Zheng, W.
Liang, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T.
Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, K. Throssell, J. A.
Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. J. Bearpark, J. J. Heyd, E. N.
Brothers, K. N. Kudin, V. N. Staroverov, T. A. Keith, R. Kobayashi, J.
Normand, K. Raghavachari, A. P. Rendell, J. C. Burant, S. S. Iyengar, J.
Tomasi, M. Cossi, J. M. Millam, M. Klene, C. Adamo, R. Cammi, J. W.
Ochterski, R. L. Martin, K. Morokuma, O. Farkas, J. B. Foresman, D. J. Fox,
Gaussian 16, Revision B.01, Gaussian, Inc., Wallingford CT, (2016).
[70] R. Dennington, T. A. Keith, and J. M. Millam, Gauss View, Version 6, Semichem
Inc., Shawnee Mission, KS, 2016.
[49] D.T. Sawyer, W.R. Heineman, J. M. Beebe, Chemistry Experiments for
Instrumental Analysis; John Wiley: New York, Experiment 10-4 ‘‘Critical
Micelle Concentration of Surfactants”, (1984) p 283.
[50] S. Ghosh, S.P. Moulik, Interfacial and Micellization Behaviors of Binary and
Ternary Mixtures of Amphiphiles (Tween-20, Brij-35, and Sodium Dodecyl
Sulfate) in Aqueous Medium, J. Colloid Interface Sci. 208 (1998) 357–366.
[51] S. Ghosh, Surface chemical and micellar properties of binary and ternary
surfactant mixtures (cetyl pyridinium chloride, Tween-40, and Brij-56) in an
aqueous medium, J. Colloid Interface Sci. 244 (2001) 128–138.
[52] S. Ghosh, A.D. Burman, G.C. De, A.R. Das, Interfacial and self-aggregation of
binary mixtures of anionic and nonionic amphiphiles in aqueous medium, J.
Phys. Chem. B. 115 (2011) 11098–11112.
[53] S. Mondal, S. Ghosh, Role of curcumin on the determination of the critical
micellar concentration by absorbance, fluorescence and fluorescence
anisotropy techniques, J. Photochem. Photobiol., B 115 (2012) 9–15.
[54] M. Rujimethabhas, P. Wilairat, Determination of critical micelle concentration
using acridine orange dye probe. An undergraduate experiment, J. Chem. Educ.
55 (1978) 342.
[71] A.D. Becke, Density-functional exchange-energy approximation with correct
asymptotic behavior, Phys. Rev. A: At., Mol., Opt. Phys. 38 (1988) 3098–3100.
[72] A.D. Becke, Density-functional thermochemistry. III. The role of exact
exchange, J. Chem. Phys. 98 (1993) 5648–5652.
[73] W.J. Hehre, L. Radom, P.V.R. Schleyer, J.A. Pople, Ab Initio Molecular Orbital
Theory, John Wiley & Sons, New York, 1986.
[55] K.G. Furton, A. Norelus, Determining the critical micelle concentration of
aqueous surfactant solutions: using a novel colorimetric method, J. Chem.
Educ. 70 (1993) 254.
[56] W. Zhou, L. Zhu, Solubilization of pyrene by anionic nonionic mixed
surfactants, J. Hazard Mater 109 (2004) 213–220.
[57] B. Tanhaei, N. Saghatoleslami, M.P. Chenar, A. Ayati, M. Hesampour, M.
Mänttäri, Experimental study of CMC evaluation in single and mixed
surfactant systems, using the UV-Vis spectroscopic method, J Surfact. Deterg.
16 (2013) 357–362.
[74] S. Fantacci, F. De Angelis, A. Selloni, Absorption spectrum and
solvatochromism of the [Ru(4,4‘-COOH-2,2‘-bpy)2(NCS)2] molecular dye by
time dependent density functional theory, J. Am. Chem. Soc. 125 (2003) 4381–
4387.
[75] S. Fantacci, F. De Angelis, A. Sgamellotti, N. Re, A TDDFT study of the ruthenium
(II) polyazaaromatic complex [Ru(dppz)(phen)2]2+ in solution, Chem. Phys.
Lett. 396 (2004) 43–48.
[76] A.R. Allouche, Gabedit – a graphical user interface for computational chemistry
softwares, J. Comput. Chem. 32 (2011) 174–182.
8