Browsing by Author "Pant, Debi D."

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Design and synthesis of amino acid appended azo dye hybrid: Characterization, solvatochromic and quantum-chemical calculations using experimental and theoretical approach
(Elsiever, 2016-09) Sakhuja, Rajeev; Pant, Debi D.
Amino acid appended azobenzene hybrid was synthesized and characterized using Spectroscopic techniques like 1H NMR, 13C NMR, FT-IR and Mass spectrometry analysis and its optical properties were investigated using UV–vis absorption and fluorescence spectroscopy in solvents of different polarity. Based on solvent refractive index and relative permittivity, by using the theory of solvatochromism, the excited-state (μe) and ground-state (μg) dipole moments was determined for (E)-4-((4-(heptyloxy)phenyl)diazenyl)benzyl((benzyloxy)carbonyl)glycinate (Gly-Azo-O7) based on the variation of Stokes shift as an effect of various solvent's. A bathochromic shift observed in absorption and emission spectra with increasing solvent polarity, which implied that the transition involved is π → π*. The ground state and excited state dipole moments were also calculated and compared using experimental and DFT calculations.
Detection of Hg2+ ions in aqueous medium using an indole-based fluorescent probe: Experimental and theoretical investigations
(Elsiever, 2017-12) Sakhuja, Rajeev; Pant, Debi D.
Mercury pollution is a widespread danger to human health and environment. Due to limitations associated with the existing Hg2+ chemosensors, development of new, efficient and selective chemosensors capable of sensing mercury ions in aqueous medium remains a demanding area of research. In this regard, an indole-based fluorescent probe has been synthesized and characterized by detailed spectroscopic analysis. The probe showed a high selectivity and sensitivity towards Hg2+ by giving significant fluorescence quenching over other tested cations in H2O/DMF (7:3, v/v) medium. The association constant (Ka) was 6.4 × 103 M− 1 between sensor and Hg2+. The detection limit of sensor to Hg2+ was found to be 0.143 μM (143 nM). The experimental results have been verified with Density Functional Theory.
Dynamic fluorescence quenching of quinine sulfate dication by chloride ion in ionic and neutral micellar environments
(AIP, 2014-04) Pant, Debi D.
Fluorescence quenching of Quinine sulfate dication (QSD) by chloride-ion (⁠⁠) in micellar environments of anionic, sodium dodecyl sulfate (SDS), cationic, cetyltrimethylammonium bromide (CTAB) and neutral, triton X-100 (TX-100) in aqueous phase has been investigated by time-resolved and steady- state fluorescence measurements. The quenching follows linear Stern-Volmer relation in micellar solutions and is dynamic in nature.
Dynamics of polar solvation at the surface of a ZrO2 nanoparticle
(Elsevier, 1998-07) Pant, Debi D.
Polar solvation dynamics of a 95:5% (v/v) water/acetone mixture have been measured at the ZrO2 nanoparticle surface by time-resolved fluorescence of a probe molecule adsorbed to the particle surface. The interfacial solvent response displays two sub-picosecond diffusive components with the same time constants as bulk solution. However, the relative amplitudes for the individual relaxation components are significantly different, leading to a faster average solvation response for molecules at the ZrO2 surface. Furthermore, the overall fluorescence Stokes shift is approximately three times smaller for dye molecules adsorbed to the nanoparticle surface. Implications for electron injection into semiconductor nanoparticles are discussed.
Edge excitation red shift and energy migration in quinine bisulphate dication
(Elsevier, 2006-01) Pant, Debi D.
Photoinduced excited state dynamical processes in quinine sulphate dication (QSD) have been studied over a wide range of solute concentrations using steady state and nanosecond time-resolved fluorescence spectroscopic techniques. The edge excitation red shift (EERS) of emission maximum, emission wavelength dependence of fluorescence lifetimes and the time dependence of emission maximum are known to occur due to the solvent relaxation process. With increase in solute concentration, the emission spectrum shifts towards the lower frequencies accompanied with decrease in fluorescence intensity, however, absorption spectrum remains unchanged. A decrease in EERS, fluorescence lifetimes, time dependent fluorescence Stokes shift (TDFSS), fluorescence polarization and the solvent relaxation time (τr) is observed with the increase in solute concentration. The process of energy migration among the QSD ions along with solvent relaxation has been found responsible for the above experimental findings.
Effect of nanosize micelles of ionic and neutral surfactants on the photophysics of protonated 6-methoxyquinoline: Time-resolved fluorescence study
(Elsevier, 2015-03) Pant, Debi D.
The excited state dynamic studies have been carried out to investigate the effects of micellar surface charge on the photophysics of protonated 6-methoxyquinoline (6MQ+) in anionic, sodium dodecylsulphate (SDS), cationic, cetyltrimethylammonium bromide (CTAB) and neutral, triton X-100 (TX100) surfactant at premicellar, micellar and postmicellar concentrations in aqueous phase at room temperature. At premicellar concentrations of SDS, there is a slight decrease in emission intensity and at micellar and postmicellar concentrations, increase in emission intensity and blue shift of spectrum has been observed. The blue shift in fluorescence spectrum and slight increase in quantum yield are attributed to incorporation of solute molecule to the micelles. Edge excitation red shift (EERS) in fluorescence maximum of 6MQ+ has been observed in all the surfactant solutions studied. The EERS has been ascribed in terms of solvent relaxation process. In SDS surfactant system, due to heterogeneous restricted motion of solvent molecules, the solvent viscosity increases which results in an increase in net magnitude of EERS. The fluorescence decay components of 6MQ+ fit with multi exponential functions in all the micellar systems studied. The location of the probe molecule in micellar systems is justified by a variety of spectral parameters such as refractive index, dielectric constant, ET (30), EERS, average fluorescence decay time, radiative and non radiative rate constants, and rotational relaxation time.
Estimation of ground and excited state dipole moments of 6-methoxyquinoline from solvatochromic effect on absorption and fluorescence spectra
(AIP, 2013-06) Pant, Debi D.
The electronic absorption and fluorescence spectra of 6-methoxyquinoline (6MQ) have been recorded at room temperature in solvents of different polarities. The spectral data have been used to evaluate the ground and first excited singlet state dipole moments using the solvatochromic shift method. Higher dipole moment is obtained for the excited state as compared to ground state. The results indicate a more polar excited state, which may be due to charge transfer character of 6MQ.
Estimation of ground and excited state dipole moments of quinidine and quinidine dication: Experimental and numerical methods
(Elsevier, 2013-03) Pant, Debi D.
Absorption and fluorescence spectra of quinidine (QD) and quinidine dication (QD2 +) have been measured at room temperature in solvents of different polarities. Ground and excited state electric dipole moments are determined experimentally using solvatochromic shift method based on bulk solvent properties. Numerical calculations are also performed using B3LYP/6-31G(D) level of theory for ground state and CIS/6-31G(D) level of theory for first excited singlet state. From both experimental and numerical studies it has been observed that dipole moment values of excited states (μe) are higher than corresponding ground state value (μg), of QD and QD2 +, which is attributed to the higher polarity of excited states of QD and QD2 + molecules.
Estimation of ground and excited state dipole moments of synthesized coumarin derivative [N-(2-oxo-2H-chromen-4-yl)imino]triphenyl-phosphorane
(Elsevier, 2014-12) Pant, Debi D.
Electronic absorption and fluorescence spectra of coumarin derivative [N-(2-oxo-2H-chromen-4-yl)imino] triphenyl phosphorane have been recorded at room temperature in wide range of solvents of different polarities. The absorption maximum remains almost unchanged with the increase in solvent polarity, whereas, a red shift in fluorescence emission maximum was observed. Synthesized compound [N-(2-oxo-2H-chromen-4-yl)imino] triphenyl phosphorane was characterized by 1H and 13C NMR, and FT-IR spectral studies. The ground and excited state dipole moments of molecule were obtained from Bakhshiev's and Bilot–Kawski's equations by means of the solvatochromic shift method. Very high value of dipole moment is observed for excited state as compared to ground state value and this is attributed to more polar excited state of the molecule. Numerical calculations are performed using B3LYP/6-31G+(d) and B3LYP/6-31G(d) level of theory for ground state in Gaussian 03. Studies in different solvents are also done using the CPCM method and UA0 radii with the same level of theory. A critical analysis between the values of dipole moment in gas phase and various solvents is also carried out for ground state.
Estimation of ground and excited-state dipole moments of synthesized coumarin derivative, (S)-(1-((7-hydroxy-2-oxo-2H-chromen-4-yl)methyl)-1H-1,2,3-triazol-4-yl)methyl 2-(((9H-fluoren-9-yl)methoxy)cabonylamino)-3-phenylpropanoate from a solvatochromic shift and theoretical methods
(Elsiever, 2015-09) Sakhuja, Rajeev; Pant, Debi D.
The electronic absorption and fluorescence spectra of coumarin derivative, (S)-(1-((7-hydroxy-2-oxo-2H-chromen-4-yl)methyl)-1H-1,2,3-triazol-4-yl)methyl2-(((9H-fluoren-9-yl)methoxy)cabonylamino)-3-phenylpropanoate have been studied in solvents of different polarities, and the data were used to study the solvatochromic properties. The absorption maximum remains almost unchanged with the increase in solvent polarity, whereas a red shift in fluorescence emission maximum was observed. Synthesized compound (S)-(1-((7-hydroxy-2-oxo-2H-chromen-4-yl)methyl)-1H-1,2,3-triazol-4-yl)methyl2-(((9H-fluoren-9-yl)methoxy)cabonylamino)-3-phenylpropanoate was characterized by 1H and 13C NMR, and FT-IR spectral studies. The ground and excited state dipole moments of molecule were obtained from Bakshiev's and Bilot–Kawski's equations by means of solvatochromic shift method. High value of dipole moment is observed for excited state as compared to ground state value and this is attributed to more polar excited state of molecule. Also, fluorescence emission peak undergoes a bathochromic shift with increase in the polarity of the solvent, confirming π → π* transition. Numerical calculations are performed using B3LYP/6-31G(d) level of theory for the ground state using Gaussian 03. Studies in different solvents are also done using IEF-PCM method and UA0 radii. A comparative analysis between the values of dipole moment in gas phase and various solvents is also done for the ground state.
Excited state solvation dynamics of 6-methoxyquinoline
(Elsevier, 1991-02) Pant, Debi D.
Steady state and transient studies of 6-methoxyquinoline (6MQ) were undertaken. 6MQ undergoes a large change of dipole moment on excitation. The low energy absorption band Lb does not change in position with solvent polarity whereas the emission maxima shift towards lower frequencies with broadening of the spectra. The edge excitation red shift, which is associated with the time-dependent red shift of emission, is observed in all polar solvents. The fluorescence decay is monoexponential and is dependent on emission wavelength. The data are explained with the help of the Bakhshiev model of solvent relaxation. The solvent relaxation time τr and the fluorescence lifetime τf increase with the polarity of the solvent. In aqueous solution, 6MQ undergoes a protolytic reaction in the excited state. The rate constant for the proton transfer is 1.2×108 s−1.
Experimental and Quantum Chemical Calculations of Imidazolium Appended Naphthalene Hybrid in Different Biomimicking Aqueous Interfaces
(ACS, 2016) Sakhuja, Rajeev; Pant, Debi D.
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 (Kb) 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.
Experimental and theoretical study: Determination of dipole moment of synthesized coumarin–triazole derivatives and application as turn off fluorescence sensor: High sensitivity for iron(III) ions
(Elsiever, 2015-12) Sakhuja, Rajeev; Pant, Debi D.
Electronic absorption and fluorescence spectra of two synthesized coumarin–triazole based probes (S)-(1-((7-hydroxy-2-oxo-2H-chromen-4-yl) methyl)-1H-1,2,3-triazol-4-yl)methyl 2-(tert-butoxycabonylamino)-3-phenylpropanoate and (S)-(1-((7-hydroxy-2-oxo-2H-chromen-4-yl)methyl)-1H-1,2,3-triazol-4-yl) methyl 2-(benzyloxycabonylamino)-3-phenylpropanoate have been recorded at room temperature in wide range of solvents of different polarities. Synthesized compounds were characterized by 1H and 13C NMR, and FT-IR spectral studies. The ground and excited state dipole moments of molecules were obtained from Bakshiev's and Bilot–Kawski's equations by means of solvatochromic shift method. A DFT based studies in different solvents are also performed using IEF-PCM method and UA0 radii. A comparative analysis between the values of dipole moment in gas phase and various solvents is also performed for the ground state. The potential sensor behaviors of these compounds to metal ions have also been examined by fluorescence spectroscopy and these compounds exhibited as fluorescence sensor for the determination of Fe3+ ions in solution. Effect of various metal ions on fluorescent behavior was also studied. Both the synthesized compounds act as selective and sensitive sensor for micromolar detection of Fe3+ ions. Binding stoichiometry of Fe3+ ion detection was also investigated. Conventional binding energy calculations are performed to determine the relative stability of Fe(III) complexes.
Fluorescence Quenching of a Benzimidazolium–based Probe for Selective Detection of Picric Acid in Aqueous Medium
(Wiley, 2016-06) Pant, Debi D.; Sakhuja, Rajeev
A novel fluorescent coumaryl linked benzimidazolium salt has found to be highly selective for nanomolar detection of explosive picric acid, over other aromatic explosives in aqueous medium. The quenching constant and detection limit of the sensor was found to be KSV=1.58 × 104 M−1 and 208 nM respectively for picric acid. UV-Visible studies, time resolved fluorescence results and Density Functional Theory (DFT) calculations inferred the ground-state charge-transfer complex formation as the predominant quenching mechanism for picric acid detection.
Ground and excited state dipole moments of quinine sulfate dication: Solvatochromic shift of absorption and fluorescence spectra
(Elsevier, 2012-08) Pant, Debi D.
Electronic absorption and fluorescence spectra of quinine sulfate dication (QSD) have been recorded at room temperature in a wide range of solvents of different polarities. The absorption maximum remains almost unchanged with the increase in solvent polarity, whereas a red shift in fluorescence emission maximum was observed. The ground-state dipole moment of QSD was obtained from quantum mechanical calculations and the first excited singlet state dipole moment of QSD was obtained from Bakhshiev's and Bilot–Kawski's equations by means of solvatochromic shift method. Very high value of dipole moment is observed for excited state as compared to the corresponding ground state value and this is attributed to the more polar excited state of QSD. Compared to the dipole moment of quinine sulfate, both the ground and excited state dipole moments of QSD are lower.
Highly Selective Sensing of Li+ in H2O/CH3CN via Fluorescence ‘Turn-on’ Response of a Coumarin-Indole Linked Dyad: an Experimental and Theoretical Study
(Springer, 2016-08-27) Sakhuja, Rajeev; Pant, Debi D.
A coumarin-indole dyad, N-((7-hydroxy-2-oxo-2H-chromen-4-yl)methyl)-1H-indole-2-carboxamide has been synthesized and characterized by 1H-NMR and 13C-NMR. Effect of various metal ions on fluorescent behavior was also studied. The synthesized compound showed remarkable specificity towards Li+ in organo-aqueous medium over other metal ions. Coordination of the compound with Li+ induces a turn-on fluorescence response. The sensor exhibited good binding constant and low detection limit towards Li+. Experimental results have been verified with Density Functional Theory and Time Dependent Density Functional Theory calculations.
Highly sensitive fluorescent imidazolium-based sensors for nanomolar detection of explosive picric acid in aqueous medium
(Elsevier, 2016-06) Pant, Debi D.; Sakhuja, Rajeev
Two novel fluorescent coumaryl linked imidazolium salts have been synthesized, characterized and found to be highly selective for nanomolar detection of commonly used explosive picric acid, over other aromatic explosives in aqueous medium. The compounds are highly photostable and are practically applicable for sensing picric acid in real environmental samples, in presence of interfering aromatic/non-aromatic explosives and metal ions. In solution, the high sensitivity of the sensors toward picric acid can be predominantly attributed to the ground-state charge-transfer complex formation based on UV–vis studies, time resolved fluorescence results and DFT calculations.
Highly sensitive fluorescent imidazolium-based sensors for nanomolar detection of explosive picric acid in aqueous medium
(Elsiever, 2016-06-28) Sakhuja, Rajeev; Pant, Debi D.
Two novel fluorescent coumaryl linked imidazolium salts have been synthesized, characterized and found to be highly selective for nanomolar detection of commonly used explosive picric acid, over other aromatic explosives in aqueous medium. The compounds are highly photostable and are practically applicable for sensing picric acid in real environmental samples, in presence of interfering aromatic/non-aromatic explosives and metal ions. In solution, the high sensitivity of the sensors toward picric acid can be predominantly attributed to the ground-state charge-transfer complex formation based on UV–vis studies, time resolved fluorescence results and DFT calculations.
Influence of restricted environment and ionic interactions on water solvation dynamics
(AIP, 1998) Pant, Debi D.
Polar solvation dynamics of water sequestered inside Aerosol OT (AOT) reverse micelles have been investigated as a function of the surfactant countercation, specifically replacing for and For Ca-AOT reverse micelles, the solvation dynamics for the smallest micelles probed occurs on a subnanosecond time scale. The K-AOT reverse micelles display an additional ultrafast component that is attributable to bulklike water motion. As previously reported for Na-AOT reverse micelles [Riter, Willard, and Levinger, J. Phys. Chem. B 102, 2705 (1998)], solvent mobility increases with increasing micellar size for both Ca-AOT and K-AOT reverse micelles. The solvation dynamics in strongly ionic aqueous solutions of and have also been investigated. The 10 M electrolyte solutions display water motion on significantly shorter time scales with substantial ultrafast components. These results show that the micellar interfacial structure plays a significant role in immobilizing intramicellar water and that solvent immobilization in the reverse micelles is not merely a result of solvent–ion interactions.
Interaction of 6-methoxyquinoline with anionic sodium dodecylsulfate micelles: Photophysics and rotational relaxation dynamics at different pH
(Elsevier, 2016-04) Pant, Debi D.
Interactions of different species of 6-methoxyquinoline (6MQ) with anionic micelles have been studied at different pre-micellar, micellar and post-micellar concentrations using steady state, time resolved fluorescence and fluorescence anisotropy techniques. The sensitivity of fluorescence of 6MQ to change in its local environment was used to probe sodium dodecylsulfate (SDS) micelles. At post-micellar concentrations of SDS, the observed blue shift in the fluorescence spectrum and increase in quantum yield are attributed to the incorporation of solute molecule to micelles. 6MQ has been found to bind to the surface of the anionic micelles instead of penetrating inside the core of micelles. The binding constant (Kb) calculated for 6MQ revealed that the electrostatic forces mediate charged probe–micelle association, whereas, hydrophobic interaction allowed neutral 6MQ to associate with SDS micelles. The charged 6MQ gets inserted deeper into the micelle surface than its neutral form. The fluorescence anisotropy decay of 6MQ in SDS micelles studied at different pH allowed determination of restriction of motion of the fluorophore. The location of the probe molecule in micellar systems is justified by a variety of spectral parameters such as refractive index, dielectric constant, ET(30), average fluorescence decay time, radiative and non-radiative rate constants, and rotational relaxation time. The micro-environment around the fluorophore reveals that the photophysics of 6MQ is very sensitive to the microenvironment of SDS and probe molecules reside at the water–micelle interface.