Experimental and quantum chemical calculations of imidazolium appended naphthalene hybrid in different biomimicking aqueous interfaces

Article abstract of DOI:10.1021/acs.jpca.6b05864

The effect of solvent polarity and micellar headgroup on a newly designed imidazolium based ionic liquid (IL) conjugated with naphthalene, 1,2-dimethyl-3-((6-(octyloxy)naphthalen-2-yl)methyl)-1H-imidazol-3-ium chloride (IN-O8-Cl), was studied using steady state and time-resolved fluorescence techniques. We observed that the dipole moment in the excited state is remarkably higher than the ground state. The effect of micellar surface charge on the photophysics of IN-O8-Cl in aqueous phase at room temperature was investigated. Formation of premicellar aggregates in sodium dodecylsulfate (SDS) was perceived; further the microenvironment of IN-O8-Cl was examined using steady-state fluorescence spectroscopy. Micropolarity of the micellar environment of SDS was found to be lower than that of cetyltrimethylammonium bromide (CTAB) and triton X-100 (TX100) following the order SDS < TX-100 < CTAB. The binding constant (K_b) and edge excitation red shift (EERS) from the emission maximum suggest that the probe binds strongly to the micelles. Multiexponential behavior was observed in time-resolved fluorescence lifetime studies in all micellar environments. We have observed an increase in rotational correlation time as we move from pure aqueous phase to solution containing surfactants of different head charge. Varieties of spectral parameters were used to justify the region in which the probe is present. The experimentally obtained dipole moment data were justified and explained by the DFT calculations of the electronic properties of IN-O8-Cl molecules in gas phase and in selected solvents.

Full text of DOI:10.1021/acs.jpca.6b05864

Article
pubs.acs.org/JPCA
Experimental and Quantum Chemical Calculations of Imidazolium
Appended Naphthalene Hybrid in Different Biomimicking Aqueous
Interfaces
,
†
‡
§
†
§
Tej Varma Yenupuri,* Lucia Mydlova, Devesh S. Agarwal, Ritika Sharma, Rajeev Sakhuja,
,‡
,†
Malgorzata Makowska-Janusik,* and Debi D. Pant*
†
Department of Physics, Birla Institute of Technology and Science (BITS) Pilani, Pilani 333031, Rajasthan, India
‡
Institute of Physics, Faculty of Mathematics and Natural Science, Jan Dlugosz University, Al. Armii Krajowej 13/15, 42-200
Czestochowa, Poland
§
Department of Chemistry, Birla Institute of Technology and Science (BITS) Pilani, Pilani 333031, Rajasthan, India
S Supporting Information
*
ABSTRACT: The effect of solvent polarity and micellar
headgroup on a newly designed imidazolium based ionic liquid
(
(
IL) conjugated with naphthalene, 1,2-dimethyl-3-((6-
octyloxy)naphthalen-2-yl)methyl)-1H-imidazol-3-ium chlor-
ide (IN-O8-Cl), was studied using steady state and time-
resolved fluorescence techniques. We observed that the dipole
moment in the excited state is remarkably higher than the
ground state. The effect of micellar surface charge on the
photophysics of IN-O8-Cl in aqueous phase at room
temperature was investigated. Formation of premicellar
aggregates in sodium dodecylsulfate (SDS) was perceived;
further the microenvironment of IN-O8-Cl was examined
using steady-state fluorescence spectroscopy. Micropolarity of the micellar environment of SDS was found to be lower than that
of cetyltrimethylammonium bromide (CTAB) and triton X-100 (TX100) following the order SDS < TX-100 < CTAB. The
binding constant (K ) and edge excitation red shift (EERS) from the emission maximum suggest that the probe binds strongly to
b
the micelles. Multiexponential behavior was observed in time-resolved fluorescence lifetime studies in all micellar environments.
We have observed an increase in rotational correlation time as we move from pure aqueous phase to solution containing
surfactants of different head charge. Varieties of spectral parameters were used to justify the region in which the probe is present.
The experimentally obtained dipole moment data were justified and explained by the DFT calculations of the electronic
properties of IN-O8-Cl molecules in gas phase and in selected solvents.
1
. INTRODUCTION
absorption and fluorescence bands and also minor Stokes shift
to change in solvent polarity, high molar-absorption coefficient,
Fluorescence techniques have been successfully employed for
the investigation of different fundamental processes in
biological systems due to their capability for rapid, precise,
conscientious, and reproducible detection of proteins and
biomolecules at the single-molecule level. Concrete efforts
have been devoted to fluorescence labeling, sensing, and
quantification of proteins and other biomolecules by
fluorescent organic dyes and their derivatives. It has been
attributed to the diversified spectral properties possessed by
mentioned fluorescent probes and the ease of their structural
modification. Although, a variation in fluorescence intensity or
a deviation in the fluorescence band is usually accompanied by
interaction of a fluorescent probe with a protein or
biomolecule, irreversible photobleaching during prolonged
illumination and lack of photostability reduces effective sensing
4
and modest quantum yield. In addition, with very few
5
exceptions, such as acridone dye, the fluorescence decay
lifetime is in the range of about 5 ns in the visible region and
around 1 ns in the infrared region for numerous organic dyes
and usually is short-lived for efficient temporal discrimination
from cellular autofluorescence and scattered excitation light by
isolation or temporarily blocking a portion of time, thereby
1
,2
3
,4
5
lowering the sensitivity. Also, the function of biomolecules
might get influenced due to structure, charge, and hydro-
philicity of organic dye. In addition, complex and tedious
preparation and workup methodologies, low yields, and poor
water-solubility limit the practical applicability of these
fluorescent probes for sensing proteins and biomolecules in
3
of these organic molecules. A large number of fluorescein and
Received: June 10, 2016
Revised: July 27, 2016
rhodamine dyes, most cyanine dyes, and 4,4′-difluoro-4-bora-
3a,4a-diaza-s-indacene dyes possess comparatively exiguous
©
XXXX American Chemical Society
A
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Scheme 1. Synthesis of 1, 2-Dimethyl-3-((6-(octyloxy)naphthalen-2-yl)methyl)-1H-imidazol-3-ium Chloride (IN-O8-Cl).
6
,7
real biological environments. Hence development of alternate
fluorescence probes for sensing in water or biological
environment is highly desirable.
2.1.1. Synthesis of Ethyl 6-Hydroxy-2-naphthoate (2). To a
stirred solution of 1 (10.6 mmol) in ethanol, conc H SO (0.02
mmol) was added at 0 °C, and the reaction mixture was heated
at 80 °C for 12 h. After consumption of starting material as
determined by TLC, the solvent was evaporated under reduced
2
4
Efforts toward improving the water solubility of these organic
molecules have led to design of ionic liquid-based fluorescent
More specifically, the use of room-temperature
ionic liquids (RTILs) is more favorable due to their large size,
excellent thermal stabilities, conformational flexibility of the
ions, and controllable physical and chemical properties that
favor the liquid state. In addition acting as environmentally
benign solvent systems, ionic liquids have been utilized recently
as designer substrates for preparing functionalized materi-
8
−10
probes.
pressure, and 2 N NaHCO (30 mL) solution was added at 0
3
°C. The precipitate was filtered under suction to yield product
(2) as an off white solid, which was used as such without any
further purification. Yield: 92% (2.11 g); mp 110−110.6 °C.
2.1.2. Synthesis of Ethyl 6-(Octyloxy)-2-naphthoate (3). To
a stirred solution of 2 (9.2 mmol) in acetone, K CO (20.2
11
12
2
3
mmol) was added at 0 °C. The reaction mixture was stirred for
1
3−15
als.
The physical chemistry of imidazolium-based ionic
1
5 min at 0 °C, after which 1-bromo octane (1.0 mmol) was
liquids have been investigated due to their particular dimen-
sional heterogeneity emerging from the internal polar/nonpolar
segregation. These molecules exhibit fluorescence when they
are excited in the ultravoilet or initial visible region, and the
excitation wavelength plays a crucial role in the fluorescence
behavior due to the existence of analytically different correlated
forms of the fundamental ions of the ionic liquids that prolong
added and the reaction was refluxed for 12 h. After completion
of the reaction as determined by TLC, the solvent was removed
under high pressure. The reaction was quenched by adding
water (50 mL). The water layer was extracted using ethyl
acetate (20 mL × 2). The ethyl acetate layer was dried over
anhydrous sodium sulfate, and ethyl acetate was removed at
high temperature and low pressure to give product 3 as
colorless oil. Yield: 90.8% (2.75 g).
16,17
the relaxation of the excited state in these solutions.
Chen
and co-workers reported the use of ILs as potential fluorescent
2.1.3. Synthesis of (6-(Octyloxy)naphthalen-2-yl)methanol
1
8,19
19
probes
for the sensing of biomacromolecules. Sub-
20
(
4). To dry THF (20 mL), LAH (22.8 mmol) was added and
sequently, Liu et al. studied a novel functional fluorescent
imidazolium-based IL probe for detecting superoxide anion
radicals. Recently, Galpothdeniya and co-workers reported a
fluorescein-based IL sensor for label-free detection of serum
albumins. IL-based materials have also been utilized for
detection of vapors and for estimation of the pH value.
stirred at 0 °C for 15 min; to this, a solution of 3 (7.6 mmol)
was added. After 4 h of stirring, complete consumption of
starting material was observed by TLC. The reaction was
quenched by adding 1 N NaOH solution (30 mL) after cooling
the reaction mixture to 0 °C. Ethyl acetate (20 mL × 2) was
added to the reaction solution, and the mixture was filtered
through Celite. Subsequently mother liquor was separated into
organic layer and water layer, and finally the organic layer was
dried over anhydrous sodium sulfate, and ethyl acetate was
evaporated at low temperature and high pressure to give
2
1
2
2,23
Despite the significant potential of imidazolium-based ILs for
sensing of biomolecules, their use as fluorescence probes is still
limited due to their low fluorescence efficiency. To the best of
our knowledge, the fluorescent efficacy of imidazolium-based
fluorescent probes has not been much explored in different
micellar environments. In the context of the above discussions,
we herein report the synthesis of a highly fluorescent
naphthalene-appended imidazolium-based IL, whose fluores-
cent intensity could be significantly increased or quenched
upon addition of surfactants. The high fluorescence efficiency
product 4 as off white solid. Yield: 82.6% (1.80 g); mp 98.2−
1
9
9.0 °C. H NMR (400 MHz, CDCl ) δ 7.76 (dd, J = 8.9, 4.7
3
Hz, 3H), 7.50 (dd, J = 8.5, 1.8 Hz, 1H), 7.25−7.20 (m, 2H),
4
1
.77 (s, 2H), 4.11 (t, J = 6.6 Hz, 2H), 1.94−1.85 (m, 2H),
.60−1.50 (m, 2H), 1.44−1.33 (m, 8H), 0.96 (t, J = 6.9 Hz,
13
24
3H). C NMR (101 MHz, CDCl ) δ 151.27, 135.86, 134.17,
3
imparted by the naphthalene moiety and the hydrophilic
nature of the IL makes it a favorable fluorescent probe
candidate for effective sensing of proteins and biomolecules in
different well-known biomimicking environments of micelles.
1
6
29.28, 128.68, 127.18, 125.81, 125.59, 119.34, 106.48, 68.06,
5.62, 31.85, 29.41, 29.28, 29.27, 26.14, 22.69, 14.14.
.1.4. Synthesis of 2-(Chloromethyl)-6-(octyloxy)-
2
naphthalene (5). At 0 °C to a solution of 4 (5.9 mmol) in
toluene, SOCl (89.0 mmol) was added. After 4 h, TLC
2
2
. EXPERIMENTAL SECTION
.1. Materials. Synthesis of 1,2-dimethyl-3-((6-(octyloxy)-
showed the complete disappearance of the starting material.
Toluene was removed under reduced pressure, and the reaction
was quenched by adding NaHCO3 solution (40 mL) to
maintain the pH at 10, while cooling the reaction to 0 °C. The
2
naphthalen-2-yl)methyl)-1H-imidazol-3-ium chloride (IN-O8-
Cl) is presented in Scheme 1.
B
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sodium bicarbonate layer was extracted using ethyl acetate (20
mL × 2). Finally the ethyl acetate layer was dried over
anhydrous sodium sulfate, and the organic layer was
excited and ground state. Thus, molecular changes in solvent
are accompanied by changes in their polarity and in
consequence by the evaluation of dielectric constant in the
surrounding medium. Hence F (ε,η) and F (ε,η) are being used
to determine the ground and excited state dipole moments
from different organic solvents.
concentrated at high pressure low temperature to give product
1
2
1
5
as colorless oil. Yield: 95.8% (1.73 g). H NMR (400 MHz,
CDCl ) δ 7.74 (d, J = 8.3 Hz, 3H), 7.47 (dd, J = 8.6, 1.2 Hz,
3
1
1
0
1
1
2
H), 7.20−7.13 (m, 2H), 4.84 (s, 2H), 4.09 (t, J = 6.6 Hz, 2H),
The molecular structure of the IN-O8-Cl molecule is shown
in Figure S1. The absorption and fluorescence spectra of IN-
O8-Cl (10 M) were measured at room temperature in various
solvents. The absorption spectrum recorded for IN-O8-Cl
dissolved in DMSO normalized to one is shown in Figure 1.
.92−1.83 (m, 2H), 1.57−1.48 (m, 2H), 1.42−1.29 (m, 8H),
1
3
−4
.92 (t, J = 6.9 Hz, 3H). C NMR (101 MHz, CDCl ) δ
3
57.73, 134.46, 132.38, 129.41, 129.08, 128.27, 127.51, 126.81,
19.63, 106.51, 68.11, 46.93, 31.89, 29.45, 29.33, 29.28, 26.17,
2.74, 14.19.
2
.1.5. Synthesis of 1, 2-Dimethyl-3-((6-(octyloxy)-
naphthalen-2-yl)methyl)-1H imidazol-3-ium Chloride (IN-
O8-Cl) (7). To a stirred solution of 1,2 dimethyl imidazole
(
6.6 mmol) in ethanol (10 mL), 5 (5.5 mmol) was added, and
the reaction mixture was heated at 80 °C for 12 h. The
completion of the reaction was monitored by TLC. After the
completion of the reaction, the solvent was evaporated under
reduced pressure, and ethyl acetate (10 mL) was added to the
crude product and stirred overnight. This process was repeated
3
times to remove excess of 6, and finally the ethyl acetate was
decanted, and the product was dried to give colorless oil, which
became semisolid on standing. Yield: 92% (2.05 g). H NMR
1
(
400 MHz, DMSO-d ) δ 7.87−7.78 (m, 4H), 7.72 (d, J = 2.0
6
Hz, 1H), 7.42 (dd, J = 8.5, 1.6 Hz, 1H), 7.34 (d, J = 2.2 Hz,
H), 7.19 (dd, J = 8.9, 2.4 Hz, 1H), 5.55 (s, 2H), 4.07 (t, J = 6.5
1
Hz, 2H), 3.78 (s, 3H), 2.65 (s, 3H), 1.80−1.73 (m, 2H), 1.47−
1
6
1
1
2
.41 (m, 2H), 1.35−1.20 (dd, J = 13.7, 6.8 Hz, 8H), 0.86 (t, J =
.6 Hz, 3H). 13C NMR (101 MHz, CDCl ) δ 157.27, 145.12,
3
Figure 1. Normalized UV−vis absorption spectra measured in DMSO
and normalized fluorescence spectra of IN-O8-Cl performed in
DMSO, acetonitrile, and isopropanol.
34.52, 130.06, 129.83, 128.52, 128.04, 127.20, 126.38, 123.21,
23.15, 121.75, 119.91, 107.02, 68.04, 51.21, 35.31, 31.72,
9.23, 29.16, 29.09, 26.04, 22.57, 14.14.
2
.2. Computational Details. The initial geometry of the
IN-O8-Cl molecule was built up using the ACD/ChemSketch
software. Before calculation of its electronic properties, the
geometry was optimized according to the energy minimization
procedure applying the density functional theory (DFT) with
The absorption band shows very low sensitivity (∼1 nm)
toward solvents with decreasing polarity. Hence one can
conclude that solvent effects are negligible in the ground state
of the molecule. The fluorescence emission spectra (see Figure
25,26
DFT/B3LYP functional
implemented in the Gaussian09
1
and Table S1) show one structured peak in all selected
2
7
program package. It was performed for molecule in vacuum
solvents. When the solvent polarity is increased from that of
cyclohexane to that of water, the fluorescence peak is shifted
toward longer wavelengths. This is caused by the strong
intermolecular interactions occurring for the IN-O8-Cl being in
the excited state in polar solvent environment. Moreover, the
weak change in absorption spectra compared with that of the
emission spectra indicates that the molecule is less polarized by
the polar solvents in the ground state than in the excited state.
These results firmly suggest that the nonbonding electrons are
not involved in n → π* transition but involved in π→ π*
28
using Berny algorithm in redundant internal coordinates. The
potential energy surface minimum was calculated by applying
the restricted Hartree−Fock (RHF) methodology with the 6-
31+G(d,p) basis set in C1 symmetry. The minimum of the
energy in molecular ground state was checked by the absence of
imaginary frequencies caring out the Hessian evaluation. It
ensures the thermodynamic equilibrium of the molecule.
29,30
Subsequently, taking the same level of theory
electronic
and optical properties of IN-O8-Cl molecule were calculated.
Namely, the HOMO and LUMO orbitals, as well as dipole
moment, of the molecule in gas phase and in different solvents
were evaluated. The solvent effect was taken into account using
35
transition due to charge transfer.
3
.2. Experimental Estimation of Ground and Excited
State Dipole Moment. To get further insight on the
solvatochromic behavior of the IN-O8-Cl, spectroscopic
properties are correlated with relevant solvent polarities scales.
31,32
the polarizable conductor calculation model (CPCM)
implemented under the self-consistent reaction field (SCRF)
3
3,34
approach.
For the studied molecule, also time dependent
Figure S2 shows ν − ν versus F (ε,η), while Figure S3 shows
̅
a
̅
f
1
DFT (TD-DFT) calculations were curried out to investigate its
excited state properties.
F (ε,η) versus ν + ν /2. The linear behavior of the solvent
polarity versus Stoke’s shift demonstrates solvent effects as a
2
a
f
function of refractive index and dielectric constant. The slopes
3
. RESULTS AND DISCUSSION
.1. Effect of Solvent on Absorption and Emission
of the fitted lines from Figure S2 and S3 were found to be S =
1
3
296 and S = −363, respectively. With the methodology and
2
36−38
Spectra. Knowledge of the solvent effect on absorption and
emission spectra is important, because the spectral behavior of
molecules is related strongly to their electronic structure in the
equations presented in our previous works,
solute cavity
radius (a ) for IN−O8-Cl was found to be 5.75 Å, and
o
calculated ground and excited state dipole moments of the
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molecule are μ = 2.53 D and μ = 24.95 D, respectively. All
data related to experimental dipole moment have been
summarized in Table 1.
that the naphthalene group is planar and simultaneously it is
perpendicular to the imidazole group. The chlorine atom is
located in the cage formed by naphthalene and imidazole
planes. In Figure 2 is also presented location of the dipole
moment of the IN-O8-Cl calculated at the B3LYP/6-31+G-
g
e
Table 1. Solute Cavity Radius, Slope of the Stoke’s Shift
Dependence vs Solvent Polarity, and Dipole Moment Data
Measured for IN-O8-Cl in Ground and Excited States
(
d,p) level in gas phase. One may see that the dipole moment
does not lie along the molecular structure but is positioned at
an angle to its plane, which is caused by twisting of the
imidazole group.
In Figure S4, the HOMO and LUMO orbitals of the ground
state of the IN-O8-Cl molecule calculated at the B3LYP/6-
a0
(Å)
S
1
S
2
μg
Δμ
molecule
(cm−1)
296
(cm−1)
(D) μe (D)
(D)
μe/μg
IN-O8-Cl 5.75
−363
2.53
24.95
22.42
9.86
3
1+G(d,p) level are presented. One may see that the HOMO
The large increase in dipole moment of the excited state to
that of the ground state is due to the redistribution of charge
leading to conformational changes during excitation. This
demonstrates that the molecule is much more polar in the
excited state compared with the ground state. Also change in
dipole moments on excitation indicates twisted intramolecular
charge transfer (TICT) in the excited state. Due to ICT, the
planarity of the molecular structure increases on excitation,
leading to a high change in dipole moment. Seeing the change
in ground and excited state dipole moments and the sensitivity
of the emission spectra by varying the environment around the
IN-O8-Cl, we decided to study this molecule in a more
restricted environment using surfactants as an effect of head
charge.
orbital of the molecule in the gas phase is located at the
chlorine atom and the electrons belonging to the naphthalene
group create the LUMO orbital. All selected solvents change
the nature of the HOMO orbitals leaving the LUMO orbitals
unchanged. The selected solvents decrease the energy of
HOMO and LUMO orbitals compared with the energies of
these orbitals in the gas phase (see Table 2). The HOMO−
LUMO energy difference forming the HOMO−LUMO energy
gap splitting (ΔE
) for the molecule in different
HOMO−LUMO
solvents is unchanged and is equal to 4.43 eV. In the gas phase,
the ΔE is equal to 3.70 eV. This means that all of
HOMO−LUMO
the selected solvents increase the ΔE
of IN-O8-Cl.
HOMO−LUMO
The selected solvents also increase the ground state dipole
moment of the molecule. The level of growth of the dipole
moment depends on the dielectric constant of the solvent. The
higher the dielectric constant of the solvent, the greater is the
change of the dipole moment of the molecule.
3
.3. Computational Analysis. The properties of excited
states of molecules play an important role in their chemical and
physical behavior. As an example, many reactions can be
initialized by electronic excitation or proceed via the excited
state of the reactants. Excited states are important in many
chemical processes, including photochemistry and electronic
spectroscopy. Excitation of the molecule changes its charge
distribution causing conformational changes. Both of these
phenomena lead to alteration of dipole moment of the active
molecule. Dipole moment of the excited sate can increase or
decrease compared with ground state.
The shapes of the molecular electrostatic potential (MEP) of
the IN-O8-Cl in ground state are reported in Figure S4. The
electron density (per unit volume) is the greatest at the
imidaloze group in all solvents. In the case of gas phase, the
electrons are more spread through the carbon chain. This
means that the solvents move the electrons to the imidaloze
group causing the increase of its donating character. One may
see that the more polar solvents more strongly move the
electrons to the imidaloze group. It is significantly seen in the
case of water and DMSO solvents.
The optimized structure of the IN-O8-Cl is presented in
Figure 2. The molecule has a rod-like structure. One may see
In Figure S5, the UV−vis absorption spectra calculated for
the IN-O8-Cl molecule at B3LYP/6-31+G(d,p) level are
presented. The first absorption peak obtained for the
investigated molecule calculated in gas phase comes from
HOMO to LUMO electron transfer. The second peak occurs
from HOMO − 1 to LUMO electron absorption, while the
HOMO − 1 orbital is located at the naphthalene group.
Analyzing the UV−vis absorption spectra calculated in the
solvent environment, one may see that they slightly depend on
the solvent polarity. The investigated molecule demonstrates
the hypsochromic shift for all selected solvents. This means that
the IN-O8-Cl is negatively solvatochromic. The solvent
Figure 2. Gas phase optimized structure of the IN-O8-Cl molecule at
B3LYP/6-31+G(d,p) level showing the overall dipole moment (red
arrow).
Table 2. Dipole Moment and HOMO and LUMO Energies Calculated for the IN-O8-Cl Molecule at the B3LYP/6-31+G(d,p)
Level of Theory in Gas Phase and Selected Solvents
ground state
first excited state
EHOMO [eV]
solvent
dielectric constant
μg [D]
EHOMO [eV]
ELUMO [eV]
μe1 [D]
ELUMO [eV]
gas phase
DCM
7.82
13.62
15.09
15.30
15.45
−4.58
−5.60
−5.65
−5.66
−5.66
−0.88
−1.16
−1.22
−1.23
−1.23
4.29
12.69
14.84
14.92
15.02
−2.93
−5.40
−5.43
−5.43
−5.44
−2.14
−1.54
−1.59
−1.59
−1.59
8.93
35.69
46.83
80.00
acetonitrile
DMSO
water
D
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changes the intensity of the first absorption peak, because in the
solvent environment the HOMO orbital is located at the
naphthalene group. The obtained data are in agreement with
the experimentally measured spectrum presented in Figure 1.
It should be noted that the theoretical spectra are shifted in
relation to the experimental ones to the red wavelength side
due to the regularity of the DFT methodology, although the
shape of the calculated spectra is in agreement with the
measured one (see Figure 1 and Figure S5). The spectral shift
and apparent inconsistencies may be caused by ICT occurring
between IN-O8-Cl and the solvent molecules, as well as by
electron−phonon interaction present in the investigated
system, which was not taken into account during quantum-
chemical calculations. The HOMO and LUMO orbitals of the
molecule in the excited state have exactly the same shape as that
calculated for the molecule in ground state and presented in
Figure S4. The ΔE
value calculated for IN-O8-Cl in
HOMO−LUMO
its excited state in the solvent environment decreases compared
of the
with the values in the ground state. The ΔE
IN-O8-Cl molecule in the gas phase excited state also
drastically decreases.
HOMO−LUMO
The theoretically found values of excited and ground state
dipole moments in the gas phase as well as in four different
solvents are presented in Table 2. The calculated ground state
dipole moment is found to be higher than the experimentally
obtained one. This is usually the case in molecules having long
carbon chain. This could be attributed to the fact that in the
modeled system the inhomogeneous electronic distribution
through the molecule is overestimated compared with that of
the real structure. Also, the differences between theoretical and
experimental values of dipole moment arise due to the
incompleteness of the used basis set and inappropriate nature
of the chosen DFT functional. An appreciable change in dipole
moment has been observed when we move from gas phase to
solvent phase. In polar solvent, the solute is significantly
polarized compared with that of nonpolar solvent. One may
observe an increase in dipole moment moving from nonpolar
to polar solvents, and it complies with the experimental data.
Analyzing the data obtained theoretically for the excited state
dipole moment of the IN-O8-Cl, one may see that the first
excited state dipole moment is lower than the ground state
dipole moment. This means that in excitation process of the
IN-O8-Cl molecule charge transfer appears to occur between
molecules. The CPCM methodology used in presented work
does not take into account the mentioned processes. It may be
investigated by applying a discrete local field model
Figure 3. Steady state UV−vis absorption spectra of IN-O8-Cl in
aqueous solution with varying concentrations of (a) SDS, (b) CTAB,
and (c) TX-100.
39
implemented in our previous work. The conformational
changes of the molecular structure during photoexcitation are
affected by the occurrence of the ICT which is not taken into
account using the CPCM model to investigate the solvent
effects. Even in the gas phase, the excited state dipole moment
is lower than the one in ground state. This confirms that the
IN-O8-Cl interacts with the other molecules exchanging
charges, which is not modeled in presented work.
the vicinity of the probe is slightly lower than that of the pure
40−43
aqueous form.
Addition of SDS causes a minor enhance-
ment in both bands with a small red shift in the 329 nm band. A
similar change was observed for triarylmethane (TPM) dyes
44
bound to polyelectrolytes. Similarly, a minor enhancement
was observed in CTAB and TX-100.
In aqueous solution, IN-O8-Cl shows a strong fluorescence
with emission maximum at 359 nm. With the addition of
surfactants, significant spectral changes are observed in all the
three environments as shown in Figure 4. The emission band
gets blue-shifted to 353 nm in SDS and 354 nm in TX-100
micelles. The enhancement is larger in the neutral TX-100
micelles compared with anionic SDS micelles. The increase in
fluorescence intensity along with the blue shift in the presence
of anionic and neutral micelles compared with that of bulk
water could be attributed to certain factors such as dipole
3
.4. Steady-State Results in Aqueous Micellar Envi-
ronment. The absorption spectra of IN-O8-Cl in aqueous
solution with varying concentrations of SDS, CTAB, and TX-
100 are shown in Figure 3. The IN-O8-Cl exhibits broad low
energy absorption bands at 318 and 329 nm in bulk water. It is
observed that on addition of surfactants (studied in this paper)
there is an increase in absorbance along with a minor
bathochromic shift in the first absorption band ∼2−3 nm in
the aqueous micellar environment indicating that the polarity in
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fluorescence quantum yield with increasing concentration of
SDS, and variations in quantum yield along with nonradiative
decay are shown in Figure S6.
In CTAB, no perceptible change in intensity of the
fluorescent spectrum of IN-O8-Cl below CMC was observed.
However, beyond CMC, there is gradual decrease in
fluorescence intensity (Figure 4b) accompanied by a shift in
fluorescence emission maximum. The decrease in the
fluorescence intensity in the presence of CTAB micelles
−
45
could be attributed to Br induced fluorescence quenching.
Hypsochromic shift of the fluorescence band along with an
enhancement or reduction (SDS or TX-100 vs CTAB) of
fluorescence intensity reflects that the microenvironment
around the probe in surfactant solution is quite different from
that in bulk aqueous phase. The hypsochromic shift indicates
that the polarity in micellar solutions is lower compared with
pure aqueous solution, and the variations in intensity suggest
incorporation of IN-O8-Cl to SDS, CTAB, and TX-100. This
change viewed in spectral properties can be attributed to overall
46
change in viscosity or polarity.
.5. Edge Excitation Red Shift (EERS). In the present
3
−1
study, the difference in the wavenumber (cm ) between the
emission maximum obtained with excitation at 300 and 350 nm
of the IN-O8-Cl in bulk and micellar solution is used to express
EERS. As seen from Table 3, the emission spectrum of IN-O8-
Table 3. Spectroscopic Data of IN-O8-Cl in Bulk Water and
Different Surfactant Systems
emission maximum (nm)
medium
bulk
λex = 300 nm
λex = 350 nm
EERS (cm−1)
359
353
356
354
366
365
367
365
533
916
842
931
7
1
5
5 mM SDS
0 mM CTAB
mM TX-100
Cl shows considerable dependence on excitation wavelength.
The EERS values obtained for IN-O8-Cl in bulk water and at
concentration higher than CMC for SDS, CTAB, and TX-100
surfactant systems are given in Table 3. The magnitude of
−
1
EERS of IN-O8-Cl in bulk water solution is 533 cm and in
Figure 4. Emission spectra of IN-O8-Cl in aqueous solution with
varying concentration of (a) SDS, (b) CTAB, and (c) TX-100.
−1
micellar environments is 916, 842, and 931 cm for SDS,
CTAB, and TX-100, respectively. The increase in magnitude of
EERS is due to decrease in the solvent reorganization rate in
response to the change in a concentration of ionic and neutral
surfactant in the solution, whereas the increase in magnitude of
EERS could be attributed to the fact that the viscosity around
the probe in micellar systems increases. The interfacial region
being the most viscous region is a suitable site for solubilization.
This suggests that IN-O8-Cl is restricted in an inhomogeneous
micellar environment, presumably at the water−micelle inter-
face or deeper, in all the three environments.
moment and hydrogen bonding with water. The excited state is
more polar than the ground state. So the excited state is less
stable than the ground state in the less polar environment of
the micelles than in water. This causes an increase in energy
gap between the excited state and ground state, which would
hinder the rate of nonradiative deactivation, resulting an
increase in intensity with a consequent blue shift in emission in
SDS and TX-100 micelles.
The other attributing factor is the formation of hydrogen
bonds with water, which could quench the emission (as
observed in SDS at premicellar concentrations, Figure 4a) due
to an increase in nonradiative decay. But as the probe IN-O8-Cl
moves from bulk water to micelles, the hydrogen bonding
reduces due to the less polar environment of the micelles,
thereby reducing the nonradiative transitions leading to the
enhancement in SDS micelles. As we have observed the initial
quenching followed by enhancement in intensity in SDS
micelles, we have calculated and determined the change in
3
.6. Microenvironment around and Probable Loca-
tion of the Probe Molecule. To further understand the
interactions between probe molecule and different micelles, we
have calculated the binding constant (K ) from the fluorescence
intensity plots. The method used for calculating the binding
constant in SDS and TX-100 has been discussed in our earlier
works. The binding for CTAB with IN-O8-Cl has been
calculated using the equation.
b
47
48,49
log(F − F)/F = log K + n log[Q]
(1)
0
b
F
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The Journal of Physical Chemistry A
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−1
where n is the number of binding sites and K is the binding
in kJ mol . The Gibbs’ free energies for SDS, CTAB, and TX-
100 are tabulated in Table 4. The negative value indicates
spontaneous binding in general but more favorable binding for
inclusion in TX-100 micelles comparatively among all micelles.
b
constant, which can be determined from the slope and the
intercepts of log(F − F)/F vs log[Q].
0
Table 4 gives the value of K in all the three micellar
b
environments using these two methods. The high K values in
Microenvironment such as polarity (E (30)), dielectric
b
T
constant (ε), and refractive index (η) of biomimicking
environments could be determined using fluorescent
Table 4. Different Solvent Parameters, Spectral Data,
Binding Constant, Change in Gibbs’ Free Energy of IN-O8-
Cl in Different Micellar Environments
52,53
probes.
By studying the spectral properties of IN-O8-Cl
in pure solvents of known polarities and comparing them with
spectral properties in micellar environments such parameters
ν − ν
K (L
ΔG (kJ
1,54,55
̅
a
̅
f
)
b
−1
−1
−1
could be estimated.
The micropolarity is a solvent
solvent
ε
η
ET(30)
(cm
mol
)
mol )
parameter conveyed in equivalent scale of E (30) correlating
T
bulk
water
80.00
1.33
63.10
2521
the fluorescence behavior of the probe in micellar systems to
53,56,57
5
3
5
SDS
10.9
44.91
17.6
1.41
1.33
1.39
37.67
51.40
40.29
1828
2121
1883
2.06 × 10
0.41 × 10
9.43 × 10
−30.52
−14.94
−34.31
that in homogeneous solvents of varying polarities.
The
CTAB
TX-100
procedure used to determine the microenvironment for various
47,58
micellar systems is given in our previous work.
The plots of Stoke’s shifts of IN-O8-Cl in different
homogeneous solvents against E (30), refractive index, and
SDS and TX-100 could be considerable due to increase in the
fluorescence intensity of IN-O8-Cl along with a hypsochromic
shift upon addition of SDS and TX-100 and above CMC
T
dielectric constant are shown in Figure 6. Using this plot and
the Stoke’s shift values of IN-O8-Cl presented in Table S1,
microenvironment around the probe has been estimated by
interpolating the values of Stoke’s shift of IN-O8-Cl in different
micellar systems on the calibration curve, and the values are
tabulated in Table 4. We have also observed an increase in
refractive index and decrease in dielectric constant compared
with bulk water suggesting that the molecule is in restricted
environment.
(
Figure 4a,c). In CTAB, we calculated the number of binding
sites (n = 1.09) between IN-O8-Cl and CTAB, which is
approximately equal to 1, indicating that there is only one
50,51
binding site. Arikan et al.
and many others obtained a
similar order of binding constant for CTAB micelles. The
higher binding constant in nonionic micelles (TX-100) and
anionic micelles (SDS) could be due to stronger hydrogen or
electrostatic bonding at the micellar head in the palisade layer
compared with the hydrophobic binding in CTAB as it can be
seen in Figure 5. Furthermore, the higher value of the binding
constant for the probe in the nonionic TX-100 micelles is
reflective of the fact that in contrast to the ionic micelles,
hydrophobic interactions contribute to stronger binding of the
dye to the neutral micelles due to TX-100 having a chain like
structure with an iso-octyl phenyl group at one end. The Gibbs’
free energy changes for the probe−micelle binding process in
different micelles were calculated by the following equation at
room temperature:
It is observed that the micropolarity is very similar for IN-
O8-Cl in the SDS and TX-100 micellar environments studied at
concentrations higher than CMC. The reported E (30) values
T
of water, ethanol, and n-heptane are 63.1, 51.9, and 31.3 kcal
−1
mol , respectively. Our estimated E (30) values for TX-100
T
and SDS are lower than that of ethanol and higher than that of
n-heptane; our values being much higher than n-heptane rules
out the possibility of the probe penetrating into the core of the
micelles. Finally, we could conclude that SDS/TX-100
penetrates deeper into micelle, maybe between the headgroup
and first few carbons. In CTAB, it is at the water−micelle
interface.
ΔG = −RT ln(K )
(2)
b
3
.7. Effect of Ionic and Neutral Micelles on IN-O8-Cl
where R = 8.314 J K− mol−1 is the universal constant, T is the
1
Fluorescence Lifetime. Besides steady state studies, it is
room temperature in kelvin, and ΔG is the Gibbs’ free energy
important to get an idea about excited state photophysical
Figure 5. Illustration of electrostatic and hydrophobic interaction of IN-O8-Cl in different micellar environments at concentrations higher than
CMC.
G
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Figure 6. Stoke’s shift vs solvent dielectric constant, E (30), and refractive index for IN-O8-Cl in (1) Water, (2) DMSO, (3) DMF, (4) Acetonitrile,
T
(
5) Methanol, (6) Ethanol, (7) Isopropanol, (8) DCM, (9) Ethyl Acetate, (10) Cyclohexane, (11) Benzene, (12) SDS, (13) CTAB, and (14) TX-
1
00.
processes that can be understood using time-resolved
fluorescence measurements. Fluorescence lifetime measure-
ments not only serve as an excellent indicator to explore the
54,59,60
environment around the probe
but also locate the probe
in the micellar environment. Further, in order to determine the
interactions between the probe and micelle, the excited state
lifetimes of a fluorophore in micellar solutions have been
5
4,61−63
studied.
In aqueous solution of IN-O8-Cl, the emission
decay (λex = 300 nm) monitored at different emission
wavelengths shows a biexponential behavior. Such biexponen-
tial behavior in micellar systems is due to the presence of
54
hydrogen bonds forming with surrounding solvent.
Multiexponential decay was observed with a longer lifetime
component depending upon the type of the surfactant on
addition of successive surfactants. Figure 7 depicts the
fluorescence decay profile of IN-O8-Cl in water and different
micellar environments at highest concentrations above CMC. It
is evident from Figure 7 that the fluorescent lifetime decay in
cationic CTAB is slower than that in anionic SDS and nonionic
TX-100. The lifetime in CTAB decreases to 4.73 ns compared
with 9.91 ns in aqueous solution; this is due to the presence of
heavy Br ion causing a decrease in the lifetime of IN-O8-Cl.
The lifetime of IN-O8-Cl with addition of SDS or TX-100 is
longer, due to the association of the fluorophore within SDS or
TX-100 micelles, also indicating that the probe molecule
resides inside the more viscous micelles. The decrease of
lifetime of IN-O8-Cl with CTAB occurs due to exit of the
probe molecule from inside the micelle to the surface at
Figure 7. Time resolved fluorescent decay of IN-O8-Cl in bulk water
and aqueous micellar environments (λ = 30 0 nm and λ = 375 nm).
ex
em
concentrations higher than CMC. The larger lifetime in anionic
micelles may be because the molecule resides deep inside SDS
micelles, which was also inferred from the steady state and
microenvironment measurements.
Decay of IN-O8-Cl fluorescence in micellar systems exhibits
multiexponential fitting. Multiexponential fluorescence decay
for a probe is usually due to the presence of the probe in
different polarity regions. Drawing meaningful conclusions in
micellar systems often becomes tough when the fluorescence
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decays are found to be multiexponential in nature. We choose
to use the average fluorescence lifetime given by eq 2 of SI
because it is an important parameter for understanding the
dynamic motion of the probe in micellar systems, instead of
placing too much stress on the individual magnitudes of the
decay constants. The average lifetime values of IN-O8-Cl in all
the micellar environments, thus estimated, are tabulated in
Table S2. Fluorescence lifetime decays of IN-O8-Cl in aqueous
solution with varying concentrations of different surfactants
The QY values of SDS and TX-100 are in agreement with the
decrease in nonradiative relaxation and increase in the
fluorescence intensity at concentrations higher than CMC,
whereas in CTAB the QY remains constant in bulk and at
premicellar concentrations, but at and above CMC, a
continuous decrease in QY was observed, which is in concert
with the decrease in fluorescence intensity and increase in the
nonradiative relaxation
3.8. Time-Resolved Anisotropy Study. In order to
(
SDS, CTAB, and TX-100) are shown in Figure S7.
Experimentally calculated values of lifetimes, taken at almost
understand the effect of micellar environment on rotational
1
,40
correlation time of the fluorophore in organized assemblies,
1
0 times the CMC of SDS and TX-100, are significantly longer
we have recorded fluorescence anisotropy time dependent
decay. In bulk water, the anisotropy decay is monoexponential,
and the time constant is 0.45 ns. In order to contrast the
constraint imposed on the probe in the micellar system relative
to bulk solution, rotational correlation times were calculated. In
SDS and CTAB, IN-O8-Cl shows single exponential anisotropy
decay. The observed single exponential anisotropy decay rules
out the probability of the probe rotating within or along with
the micelle in SDS and CTAB micellar media. In SDS and
CTAB micelles, monoexponential decays of IN-O8-Cl might
imply solubilization of the probe in a single region, either in the
head region or in the core region of the micelles. The decay in
TX-100 micelles follows a biexponential pattern. The
biexponential anisotropy decay r(t) in micelles can be
represented as follows
than those observed in water, indicating that the probe is not
soluble in bulk water surrounding the micelles, but the longer
and shorter lifetime component could be attributed to the
presence of the probe in stern layer and water−micellar
interface in SDS or TX-100 micellar environments. The longer
lifetime component assumes values close to 14 ns, indicating
the suppression of nonradiative pathways of de-excitation when
IN-O8-Cl interacts with both anionic and neutral micelles.
However, for SDS, the occurrence of the third (lowest) lifetime
component could indicate that the probe could be partially
exposed to the aqueous environment, whereas for CTAB from
the pre-exponential factors it could be concluded that the
majority of the probe molecules (80−95%) are solubilized at
the water−micellar interface and only 5−20% are at the stern
layer.
r(t) = r [a exp(−t/τ ) + a exp(−t/τ )]
(5)
The quantum yield QY (φ) is calculated from the total
fluorescence emission area over the whole spectral range, using
quinine sulfate dication in bulk water as standard. The radiative
0
1
1r
2
2r
where r is the limiting anisotropy, τ and τ2r are the two
0
1r
reorientation times of the probe in TX-100 micelles, and a and
1
(
κ ) and nonradiative (κ ) rate constants were calculated from
r nr
a2 are the corresponding relative amplitudes.
the fluorescence quantum yield (φ) and average lifetimes ⟨τ⟩
The restriction imposed on the fluorophore in the micellar
systems relative to bulk aqueous solution can be compared by
calculating the average rotational correlational times using the
eq 2 (SI). The anisotropy decay parameters in bulk and
micellar systems are summarized in Table S3, whereas Figure 8
shows the anisotropy decay of IN-O8-Cl in SDS, CTAB and
TX-100 micellar solutions.
using the relations
κr = φ/⟨τ⟩
(3)
(4)
κnr = (1 − φ)/⟨τ⟩
The parameters are tabulated in Table 5.
An increase in the sternness of the nearby environment of a
probe results in a slower rotational correlation time. The
average rotational times of IN-O8-Cl in all micellar environ-
ments, SDS (790 ps), CTAB (1280 ps), and TX-100 (2740 ps),
Table 5. Quantum Yields and Radiative and Nonradiative
Rate Constants of IN-O8-Cl in Aqueous and Micellar
Environments
surfactant
concentration (mM)
φ
κ (10 s−1)
8
κnr (10 s−1)
8
r
0
0.12
0.06
0.13
0.15
0.11
0.09
0.04
0.12
0.10
0.12
0.12
0.09
0.11
0.12
0.11
0.09
0.07
0.12
0.10
0.10
0.91
1.50
0.70
0.68
0.91
0.98
1.60
0.88
0.83
0.69
SDS
0.4
8.0
7
5.0
CTAB
0.1
1
5
.0
.0
TX-100
0.05
0
5
.2
.0
Initially at premicellar concentrations of SDS, formation of
nonfluorescent ion pairs causes a decrease in fluorescent
intensity, which is reflected in the decrease in QY compared
with that of bulk. The QY remains constant (∼0.06) at
premicellar concentration of SDS, but at CMC, there is
remarkable increase in QY (∼0.13), and it remains almost
constant as concentration of SDS increases. In TX-100 as the
concentration increases, the QY pretty much remains constant.
Figure 8. Time resolved fluorescence anisotropy decay profiles for IN-
O8-Cl in bulk, 75 mM SDS, 50 mM CTAB, and 5 mM TX-100
micellar solution, λex = 300 nm, λem = 360 nm.
I
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are slower compared with pure aqueous solution, suggesting
that the probe is restricted motionally in the micellar
environment compared with bulk water.
phenyl group at one end; this chain structure facilitates better
binding of the probe with TX-100 micelles.
In micelles, biexponential decays of IN-O8-Cl might imply
two different distributions of the fluorophore. Biexponential
anisotropy decay in the case of TX-100 implies that the
coefficients a and a amount to the possibility of finding the
4. CONCLUSIONS
In this paper the values of the ground and excited state dipole
moment of IN-O8-Cl molecule were determined. The excited
state dipole moment is much higher than that of ground state.
From the DFT quantum chemical calculation, the effect is
completely different, which implies that the conformational
changes of the IN-O8-Cl during photoexcitation are affected by
the ICT process, which is not taken into account using CPCM
model. This confirms that IN-O8-Cl, even in the gas phase,
interacts with neighboring molecules exchanging charges, which
is not modeled in presented work. The weak change in
absorption spectra in comparison to that of the emission
spectra indicates that the molecule is less polarized by the polar
solvents in the ground state than in the excited state. These
results firmly suggest that the nonbonding electrons are not
involved in n → π* transition but involved in π→ π* transition
due to charge transfer. From steady state spectral data of IN-
O8-Cl, the EERS, binding constant, micropolarity values, and
also probable location of the probe were calculated. Time-
resolved studies revealed that the fluorescence lifetime decay
shows multiexponential behavior in bulk and micellar solution,
whereas anisotropy decay of IN-O8-Cl in bulk, SDS, and CTAB
are monoexponential, but the decay in TX-100 is biexponential.
Finally, from the steady state and time-resolved fluorescence
techniques, various spectral parameters such as micropolarity,
refractive index, dielectric constant, EERS, binding constant,
fluorescence lifetime, and anisotropy have been determined.
One may be able to conclude that IN-O8-Cl binds strongly to
the micelles and resides at the water−micellar interface for
CTAB, whereas it resides between the head and first few
carbons for SDS and TX-100.
1
2
probe in the headgroup region and the core region. The
possibility of finding the probe is low in the core region because
it does not satisfy the condition a ≫ a , in agreement with our
2
1
investigation described in section 3.5. Hence, the biexponential
decay in TX-100 is not because of the probability of the probe
being solubilized either at the head or in the core but because it
6
4−67
experiences different kinds of motion.
The probe
molecule, depending on its position, undergoes fast wobbling
motion in an imaginary cone described by semiangle θ and also
slow lateral diffusion at or near the interface of the micelle.
These two motions are coupled to the rotation of the micelle.
The fast and slow reorientation times are related to the time
constants for wobbling motion, τ , lateral diffusion, τ , and
W
L
whole rotation of the micelle, τ , by the following relations,
M
assuming that the fast and slow motions are separable,
1
1
/τslow = 1/τ + 1/τM
(6)
(7)
L
/τfast = 1/τW + 1/τslow
where τslow and τfast are the observed slow and fast components.
The time constant for the overall rotation of the micelle has
been obtained using Stokes−Einstein−Debye (SED) hydro-
68
dynamic theory with the stick boundary condition,
τ = ηV /(KT)
(8)
M
h
where η is the viscosity of the medium and Vh is the
hydrodynamic volume of the micelle obtained from hydro-
dynamic radius (r ) of the micelle (calculated from eq 9). K
and T are the Boltzmann constant and absolute temperature,
respectively,
M
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.jpca.6b05864.
■
*
S
1
/3
r = (3N (27.4 + 26.9n)/(4π))
M
agg
(9)
and n is the number of carbons of the surfactant’s alkyl chain.
The hydrodynamic radius of TX-100 micelle in water is
Dipole moment analysis, the ground state HOMO and
LUMO orbitals and computed MEP surface in gas, and
1
calculated to be 2.73 nm. The calculated τ value is of much
fluorescence lifetime of IN-O8-Cl. Original copies of H
M
NMR and 13C NMR spectra of Compound 4, 5, 7 are
higher magnitude compared with that of τ and τ values,
1
2
thereby proving that the decay is not due to the overall rotation
but attributed the fluorescence depolarization becoming
negligible due to the long reorientation time for the overall
rotation of the micelles. In order to get a fair interpretation
about the possible location of the probe the order parameter
also included. (PDF)
AUTHOR INFORMATION
Corresponding Authors
Tel: +420 773207978. E-mail: ytejvarma@gmail.com.
Tel: +48 343614919, int. 271. E-mail: m.makowska@ajd.czest.
■
*
*
(
S) has been calculated. The value of S is obtained from the
relative amplitude of the slow component by using the equation
pl.
2
S = a1
(10)
*Tel: +91 1596515288. E-mail: ddpant@pilani.bits-pilani.ac.in.
Notes
The magnitude of the S is a measure of spatial restriction. The
value of S obtained is 0.68; this high value of order parameter
indicates restricted motion. Compared with that of bulk water,
the anisotropy decay of IN-O8-Cl bound to SDS, CTAB, and
TX-100 micelles is found to be slower. The motional restriction
of IN-O8-Cl molecules follows the order TX-100 > CTAB >
SDS. It can be thus concluded that IN-O8-Cl is bound to the
ionic and nonionic micelles. The fluorophore is restricted more
motionally in TX-100 environment of micelles, which could be
due to TX-100 having a chain like structure with an iso-octyl
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We acknowledge University grants commission (UGC) and
DST, New Delhi, for major research project to D.D.P., and
T.V.Y. thanks Birla Institute of Technology and Sciences, Pilani
Campus, for Research fellowship. D.A. is thankful to DST, New
Delhi, for JRF, R.S. is thankful to DST, New Delhi, for major
research project. Quantum chemical calculations have been
J
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carried out in Wroclaw Centre for Networking and Super-
computing (http://www.wcss.wroc.pl) (Grant no. 171).
(23) Yung, K. Y.; Schadock-Hewitt, A. J.; Hunter, N. P.; Bright, F. V.;
Baker, G. A. ‘Liquid Litmus’: Chemosensory pH-Responsive Photonic
Ionic Liquids. Chem. Commun. 2011, 47, 4775−4777.
(24) Zhao, F.; Ma, M. L.; Xu, B. Molecular Hydrogels of Therapeutic
REFERENCES
■
Agents. Chem. Soc. Rev. 2009, 38, 883−891.
(
1) Lakowicz, J. R. Principles of Fluorescence Spectroscopy; Kluwer
Academic: New York, 1999.
(25) Becke, A. D. Density-functional Thermochemistry. III. The Role
of Exact Exchange. J. Chem. Phys. 1993, 98, 5648−5652.
(26) Lee, C.; Yang, W.; Parr, R. G. Development of the Colle-Salvetti
(
2) Dobretsov, G. E. Fluorescent Probes for Studying Cells, Membranes
and Protein; Nauka, Moscow, 1989 (in Russian).
3) Iniewski, K. Smart Sensors for Industrial applications; CRC Press:
Boca Raton, FL, 2013.
4) Resch-Genger, U.; Grabolle, M.; Cavaliere-Jaricot, S.; Nitschke,
Correlation-Energy Formula into a Functional of the Electron Density.
Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 37, 785−789.
(
(27) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.
P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.;
Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin,
K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.;
Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega,
N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.;
Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.;
Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.;
Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.;
Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09,
revision D.01; Gaussian, Inc.: Wallingford, CT, 2009.
(
R.; Nann, T. Quantum Dots versus Organic Dyes as Fluorescent
Labels. Nat. Methods 2008, 5, 763−775.
(
5) Mihindukulasuriya, S. H.; Morcone, T. K.; McGown, L. B.
Characterization of Acridone Dyes for Use in Four-Decay Detection in
DNA Sequencing. Electrophoresis 2003, 24, 20−25.
(
6) Sun, Y.; Wei, S.; Zhao, Y.; Hu, X.; Fan, J. Interactions between 4-
(
2-dimethylaminoethyloxy)-N-octadecyl-1,8-naphthalimide and Serum
Albumins: Investigation by Spectroscopic Approach. J. Lumin. 2012,
32, 879−886.
7) Kar, C.; Ojha, B.; Das, G. A. Novel Amphiphilic Thiosemicarba-
1
(
zone Derivative for Binding and Selective Sensing of Human Serum
Albumin. J. Lumin. 2013, 28, 339−344.
(
8) Rogers, R. D.; Seddon, K. R. Ionic Liquids - Solvents of the
Future? Science 2003, 302, 792−793.
9) Anderson, J. L.; Armstrong, D. W.; Wei, G. T. Ionic Liquids in
Analytical Chemistry. Anal. Chem. 2006, 78, 2892−2902.
10) Crank, J. A.; Armstrong, D. W. Towards a Second Generation of
(
28) Schlegel, H. B. Optimization of Equilibrium Geometries and
Transition Structures. J. Comput. Chem. 1982, 3, 214−218.
29) Hohenberg, P.; Kohn, W. Inhomogeneous Electron Gas. Phys.
Rev. B 1964, 136, 864−871.
30) Parr, R. G.; Yang, W. Density-Functional Theory of Atoms and
Molecules; Oxford University Press: New York, 1989.
31) Barone, V.; Cossi, M. Quantum Calculation of Molecular
(
(
(
Ionic Liquid Matrices (ILMs) for MALDI-MS of Peptides, Proteins,
(
and Carbohydrates. J. Am. Soc. Mass Spectrom. 2009, 20, 1790−1800.
(
11) Plechkova, N. V.; Seddon, K. R. Applications of Ionic Liquids in
(
the Chemical Industry. Chem. Soc. Rev. 2008, 37, 123−150.
12) Welton, T. Room-Temperature Ionic Liquids. Solvents for
Synthesis and Catalysis. Chem. Rev. 1999, 99, 2071−2083.
13) Giernoth, R. Task-Specific Ionic Liquids. Angew. Chem., Int. Ed.
010, 49, 2834−2839.
14) Davis, J. H., Jr. Task-Specific Ionic Liquids. Chem. Lett. 2004, 33,
072−1077.
15) Lee, S. Functionalized Imidazolium Salts for Task-Specific Ionic
Liquids and Their Applications. Chem. Commun. 2006, 1049−1063.
16) Katayanagi, H.; Hayashi, S.; Hamaguchi, H.; Nishikawa, K.
Energies and Energy Gradients in Solution by a Conductor Solvent
(
Model. J. Phys. Chem. A 1998, 102, 1995−2001.
(32) Cossi, M.; Rega, N.; Scalmani, G.; Barone, V. Energies,
(
2
(
1
Structures, and Electronic Properties of Molecules in Solution with the
C-PCM Solvation Model. J. Comput. Chem. 2003, 24, 669−681.
(
33) Miertus, S.; Tomasi, J. Approximate Evaluations of the
Electrostatic Free Energy and Internal Energy Changes in Solution
(
Processes. Chem. Phys. 1982, 65, 239−245.
(34) Miertus, S.; Scrocco, E.; Tomasi, J. Electrostatic Interaction of a
(
Solute with a Continuum. A Direct Utilization of ab initio Molecular
Potentials for the Prevision of Solvent Effects. Chem. Phys. 1981, 55,
Structure of an Ionic Liquid, 1-n-butyl-3-methylimidazolium iodide,
Studied by Wide-angle X-ray Scattering and Raman Spectroscopy.
Chem. Phys. Lett. 2004, 392, 460−464.
1
(
17−129.
35) Tway, P. C.; Love, L. J. C. Photophysical Properties of
(
17) Mele, A.; Tran, C. D.; De Paoli Lacerda, S. H. The Structure of a
Benzimidazole and Thiabendazole and Their Homologs. Effect of
Substituents and Solvent on the Nature of the Transition. J. Phys.
Chem. 1982, 86, 5223−5226.
Room-Temperature Ionic Liquid with and without Trace Amounts of
Water: The Role of C_H···O and C_H···F Interactions in 1-n-butyl-3-
methylimidazolium tetrafluoroborate. Angew. Chem., Int. Ed. 2003, 42,
(36) Varma Y, T.; Joshi, S.; Pant, D. D. Solvatochromatic Shift of
4
(
364−4366.
Absorption and Fluorescence Spectra of 6-methoxyquinoline:
Estimation of Ground and Excited State Dipole Moments. J. Mol.
Liq. 2013, 179, 7−11.
18) Shu, Y.; Liu, M.; Chen, S.; Chen, X.; Wang, J. New Insight into
Molecular Interactions of Imidazolium Ionic Liquids with Bovine
Serum Albumin. J. Phys. Chem. B 2011, 115, 12306−12314.
(37) Joshi, S.; Bhattacharjee, R.; Varma Y, T.; Pant, D. D. Estimation
(
19) Chen, X. W.; Liu, J. W.; Wang, J. H. A Highly Fluorescent
of Ground and Excited State Dipole Moments of Quinidine and
Quinidine Dication: Experimental and Numerical Methods. J. Mol. Liq.
Hydrophilic Ionic Liquid as a Potential Probe for the Sensing of
Biomacromolecules. J. Phys. Chem. B 2011, 115, 1524−1530.
2
(
013, 179, 88−93.
(
20) Liu, H.; Zhang, L.; Chen, J.; Zhai, Y.; Zeng, Y.; Li, L. A Novel
38) Sharma, R.; Joshi, S.; Bhattacharjee, R.; Pant, D. D. Solvent
Functional Imidazole Fluorescent Ionic Liquid: Simple and Efficient
Fluorescent Probes for Superoxide Anion Radical. Anal. Bioanal. Chem.
Effect on Absorption and Fluorescence Spectra of Cinchonine and
Cinchonidine Dications: Estimation of Ground and Excited State
Dipole Moments by Experimental and Numerical Studies. J. Mol. Liq.
2015, 206, 159−164.
(39) Reis, H.; Makowska-Janusik, M.; Papadopoulos, M. G.
Nonlinear Optical Susceptibilities of Poled Guest-Host Systems: A
Computational Approach. J. Phys. Chem. B 2004, 108, 8931−8940.
(40) Das, P.; Mallick, A.; Haldar, B.; Chakrabarty, A.; Chattopadhyay,
N. Effect of Nanocavity Confinement on the Rotational Relaxation
Dynamics: 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine
in Micelles. J. Chem. Phys. 2006, 125, 044516.
2
(
013, 405, 9563−9570.
21) Galpothdeniya, W. I. S.; Das, S.; De Rooy, S. L.; Regmi, B. P.;
Hamdan, S.; Warner, I. M. Fluorescein- based Ionic Liquid Sensor for
Label-Free Detection of Serum Albumins. RSC Adv. 2014, 4, 17533−
1
7540.
(
22) Galpothdeniya, W. I. S.; McCarter, K. S.; De Rooy, S. L.; Regmi,
B. P.; Das, S.; Hasan, F.; Tagge, A.; Warner, I. M. Ionic Liquid-based
Optoelectronic Sensor Arrays for Chemical Detection. RSC Adv. 2014,
4, 7225−7234.
K
DOI: 10.1021/acs.jpca.6b05864
J. Phys. Chem. A XXXX, XXX, XXX−XXX

The Journal of Physical Chemistry A
Article
(
41) Das, P.; Sarkar, D.; Chattopadhyay, N. Photophysics of a β-
(60) Sarker, N.; Das, N.; Das, S.; Datta, A.; Nath, D.; Bhattacharyya,
K. Excited-State Intramolecular Proton Transfer of 2-(2′-hydrox-
yphenyl) benzimidazole in Micelles. J. Phys. Chem. 1995, 99, 17711−
17714.
carboline based non-Ionic Probe with Anionic and Zwitterionic
Liposome Membranes. Chem. Phys. Lipids 2008, 154, 38−45.
(
42) Mahata, A.; Sarkar, D.; Bose, D.; Ghosh, D.; Das, P.;
Chattopadhyay, N. Photophysics and Rotational Relaxation Dynamics
of a β-carboline based Fluorophore in Cationic Alkyl Trimethyl
Ammonium Bromide Micelles. J. Colloid Interface Sci. 2009, 335, 234−
(61) Maciejewski, A.; Kubicki, J.; Dobek, K. The Origin of Time-
Resolved Emission Spectra (TRES) Changes of 4-Aminophthalimide
(
4-AP) in SDS Micelles. The Role of the Hydrogen Bond between 4-
AP and Water Present in Micelles. J. Phys. Chem. B 2003, 107, 13986−
3999.
62) Chattopadhyay, A.; Mukherjee, S.; Raghuraman, H. Reverse
2
41.
43) Mahata, A.; Sarkar, D.; Bose, D.; Ghosh, D.; Girigoswami, A.;
1
(
(
Das, P.; Chattopadhyay, N. Photophysics and Rotational Dynamics of
a β-carboline Analogue in Nonionic Micelles: Effect of Variation of
Length of the Head Group and the Tail of the Surfactant. J. Phys.
Chem. B 2009, 113, 7517−7526.
Micellar Organization and Dynamics: A Wavelength -Selective
Fluorescence Approach. J. Phys. Chem. B 2002, 106, 13002−13009.
(63) Prendergast, F. G. Time-Resolved Fluorescence Techniques:
Methods and Applications in Biology. Curr. Opin. Struct. Biol. 1991, 1,
054−1059.
64) Quitevis, E. L.; Marcus, A. H.; Fayer, M. D. Dynamics of Ionic
(
44) Jones, G., II; Oh, G.; Goswami, K. The Photochemistry of
1
(
Triarylmethane Dyes Bound to Polyelectrolytes: Photoinduced
Electron Transfer Involving Bound Dye Monomers and Dimers. J.
Photochem. Photobiol., A 1991, 57, 65−80.
Lipophilic Probes in Micelles: Picosecond Fluorescence Depolariza-
tion Measurements. J. Phys. Chem. 1993, 97, 5762−5769.
(
45) Koner, A. L.; Mishra, P. P.; Jha, S.; Datta, A. The Effect of Ionic
(65) Wittouck, N.; Negri, R. M.; Ameloot, M.; De Schryver, F. C.
Strength and Surfactant on the Dynamic Quenching of 6-
methoxyquinoline by Halides. J. Photochem. Photobiol., A 2005, 170,
AOT Reversed Micelles Investigated by Fluorescence Anisotropy of
Cresyl Violet. J. Am. Chem. Soc. 1994, 116, 10601−10611.
2
1−26.
46) Hu, Z.; Margulis, C. J. Room-Temperature Ionic Liquids: Slow
Dynamics, Viscosity, and the Red Edge Effect. Acc. Chem. Res. 2007,
0, 1097−1105.
47) Varma, Y. T.; Pant, D. D. Interaction of 6-methoxyquinoline
(66) Maiti, N. C.; Mazumdar, S.; Periasamy, N. Dynamics of
(
Porphyrin Molecules in Micelles. Picosecond Time-Resolved Fluo-
rescence Anisotropy Studies. J. Phys. Chem. 1995, 99, 10708−10715.
4
(
(67) Krishna, M. M. G.; Das, R.; Periasamy, N.; Nityananda, R.
Translational Diffusion of Fluorescent Probes on a Sphere: Monte
Carlo Simulations, Theory, and Fluorescence Anisotropy Experiment.
J. Chem. Phys. 2000, 112, 8502−8514.
with Anionic Sodium Dodecylsulfate Micelles: Photophysics and
Rotational Relaxation Dynamics at different. Spectrochim. Acta, Part A
2
(
016, 158, 9−17.
(68) Debye, P. Polar Molecules; Dover: New York, 1929.
48) Tian, J. N.; Liu, J. Q.; Zhang, J. Y.; Hu, Z. D.; Chen, X. G.
Fluorescence Studies on the Interactions of Barbaloin with Bovine
Serum Albumin. Chem. Pharm. Bull. 2003, 51, 579−582.
(
49) Hu, Y. J.; Liu, Y.; Sun, T. Q.; Bai, A. M.; Lu, J. Q.; Pi, Z. B.
Binding of Anti-Inflammatory Drug Cromolyn Sodium to Bovine
Serum Albumin. Int. J. Biol. Macromol. 2006, 39, 280−285.
(
50) Arikan, B.; Tuncay, M. Miceller Effects and Reactant
Incorporation in Reduction of Toluibine Blue by Ascorbic Acid.
Dyes Pigm. 2005, 64, 1−8.
(
51) Gul, F.; Khan, A. M.; Shah, S. S.; Nazar, M. F. Spectroscopic
Study of Alizarin Reds Binding with Cetyltrimethylammonium
Bromide at Low Concentrations. Color. Technol. 2010, 126, 109−113.
(
52) Chakrabarty, A.; Mallick, A.; Haldar, B.; Das, P.; Chattopadhyay,
N. Binding Interaction of a Biological Photosensitizer with Serum
Albumins: A Biophysical Study. Biomacromolecules 2007, 8, 920−927.
(
53) Macgregor, R. B.; Weber, G. Estimation of the Polarity of the
Protein Interior by Optical Spectroscopy. Nature 1986, 319, 70−73.
(
54) Mallick, A.; Haldar, B.; Chattopadhyay, N. Spectroscopic
Investigation on the Interaction of ICT Probe 3-acetyl-4-oxo-6,7-
dihydro-12H indolo-[2,3-a]quinolozine with Serum Albumins. J. Phys.
Chem. B 2005, 109, 14683−14690.
(
55) Shannigrahi, M.; Bagchi, S. Dual Probe Solubilization in two
Distinct Regions of Pure and Mixed Micelles: A Pico-Second Time
Resolved Fluorescence Study. Chem. Phys. Lett. 2004, 396, 367−371.
(
56) Das, R.; Guha, D.; Mitra, S.; Kar, S.; Lahiri, S.; Mukherjee, S.
Intramolecular Charge Transfer as Probing Reaction: Fluorescence
Monitoring of Protein-Surfactant Interaction. J. Phys. Chem. A 1997,
1
(
01, 4042−4047.
57) Dennison, S. M.; Guharay, J.; Sengupta, P. K. Excited-State
Intramolecular Proton Transfer (ESIPT) and Charge Transfer (CT)
Fluorescence Probe for Model Membranes. Spectrochim. Acta, Part A
1
(
999, 55, 1127−1132.
58) Tej Varma, Y.; Joshi, S.; Pant, D. D. Effect of Nanosize Micelles
of Ionic and Neutral Surfactants on the Photophysics of Protonated 6-
methoxyquinoline: Time-Resolved Fluorescence Study. Spectrochim.
Acta, Part A 2015, 138, 818−826.
(
59) Paul, B. K.; Samanta, A.; Guchhait, N. Modulation of Excited
State Intramolecular Proton Transfer Reaction of 1-hydroxy-
2
2
napthadehyde in Different Supramolecular Assemblies. Langmuir
010, 26, 3214−3224.
L
DOI: 10.1021/acs.jpca.6b05864
J. Phys. Chem. A XXXX, XXX, XXX−XXX