Papers by AMRITA CHAKRABORTY
Physical Chemistry Chemical Physics, 2020
Halogen bonding interaction (X-Bond) is prevalent over hydrogen bonding (H-Bond) interaction in [... more Halogen bonding interaction (X-Bond) is prevalent over hydrogen bonding (H-Bond) interaction in [CH3OH–CCl4] mixtures/clusters: consequence in polar/non-polar mixtures and/or corresponding complexes in atmosphere needs to be investigated.
Chemical Physics, Sep 1, 2020
Abstract The anti-gauche conformational distribution of ethanol has been investigated using the O... more Abstract The anti-gauche conformational distribution of ethanol has been investigated using the O - H and symmetric C - C - O stretching infrared spectra in argon and nitrogen matrix. The dipole moment of the gauche conformer is higher compared to the anti conformer. The relative population of the anti and gauche conformer of ethanol depends on the rare gas mixture in the gas phase and also in the matrix after thermal cyclisation. In the gas phase, the anti conformer is more populated in nitrogen mixture whereas the gauche conformer is more populated in the argon mixture. After thermal cyclisation in the matrix, the anti conformer isomerise to the gauche conformer in nitrogen matrix and reverse happens in the argon matrix. Thermal cyclisation at 30 K in nitrogen matrix leads to the splitting of the gauche ± states that is probed by monitoring symmetric C - C - O stretching frequency mode.
Journal of Molecular Structure, Aug 1, 2022
Journal of Nanoscience and Nanotechnology, Jun 1, 2012
Bay-substituted tetrachloro-perylene diimide dianion salt was synthesized facilely by using K 2 C... more Bay-substituted tetrachloro-perylene diimide dianion salt was synthesized facilely by using K 2 CO 3 as reducing agent. The structure was confirmed by using a very thorough analysis based on the data from 1 H NMR, 13 C NMR, FT-IR and UVevis spectra. Perylene diimide dianion salt shows high stable characteristic in the air or in some specific solutions such as acidic solution or oxidizing metal ion dissolved in deionized water under solid condition. However, the dianion converts slowly into corresponding radical and neutral perylene diimide in alkali solutions. Furthermore, the perylene diimide dianion salt has high HOMO and LUMO energy levels in comparison with that of corresponding neutral perylene diimide derivatives.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2020
Ground state intramolecular proton transfer process has been comprehensively investigated in thre... more Ground state intramolecular proton transfer process has been comprehensively investigated in three salicylideneaniline Schiff base derivatives (SB1, SB2, and SB3) using experimental and theoretical methods. It has been confirmed that all the three Schiff base molecules in the ground electronic state exist in the enol form in non-polar and polar aprotic solvents. Keto form is being populated by the polar protic solvent through ground state intramolecular proton transfer (GSIPT) process. Ground state equilibrium between the enol and keto tautomers for SB1 and SB3 is mainly governed by the proton donating ability of the solvent. Ground state equilibria between the enol and keto tautomers of SB2 which is a positional isomer of SB3 is governed by the polarity and proton donating ability of the solvents. Excited state intramolecular proton transfer (ESIPT) process is also evidenced in all the three Schiff base molecules. Theoretical calculations at the B3LYP/cc-pVDZ level in the gas phase and in different solvents using polarisable continuum model (PCM) have failed to establish the GSIPT process. Microsolvation of individual enol and keto conformers has been investigated considering upto three solvent molecules. The energetics of the individual conformers together with the corresponding transition state have been calculated. It has been confirmed that the keto conformer is more stable compared to the enol conformer in microsolvated cluster of three methanol molecules. Lowering of activation energy for the enol to keto tautomerisation in the presence of methanol also supports the experimental observation for GSIPT process. TDDFT/B3LYP/cc-pVDZ single point calculations for microsolvated clusters of enol and keto form of the Schiff base molecules exhibit an excellent agreement with the experimentally obtained absorption spectra. Difference in spectral nature of the Schiff base molecules has been explained using natural bond orbital (NBO) analysis. Quantum theory of atoms in molecules (QTAIM) has also been utilised to understand the GSIPT process in detail.
Indian Journal of Physics, Jun 21, 2013
Photoswitchable characteristics of a novel dyad, 1-(4-chloro-phenyl)-3-(1-methoxy-3,4-dihydro-nap... more Photoswitchable characteristics of a novel dyad, 1-(4-chloro-phenyl)-3-(1-methoxy-3,4-dihydro-naphthalen-2-yl) propenone (MNCADH) have been investigated both experimentally and theoretically. In the ground state MNCADH is found exclusively as 'trans' isomer. From experimental findings, obtained by steady state and time resolved spectroscopic techniques, it is apparent that both 'cis' and 'trans' isomers are present in the excited state. 'Trans' isomer prefers to populate in polar medium, whereas 'cis' isomer mainly populates in nonpolar medium. Potential energy surface calculations at density functional theory level for trans-cis isomerism, in ground and excited states, unveil that the interconversion energy barrier is quite high in ground state as compared to that of excited state, so that switching form one conformer to another only becomes possible in excited state. Natural bond orbital analysis also supports the similar mechanism of interconversion processes.
Chemical Physics, Mar 1, 2022
Computational and Theoretical Chemistry, Feb 1, 2017
Complexes between para-substituted cationic phenol and SeH2 have been investigated in electronic ... more Complexes between para-substituted cationic phenol and SeH2 have been investigated in electronic ground state at the B3LYP, B3PW91, and ωB97xD levels of theory using 6-311++G(3df,3pd) basis set. Various electron-donating and withdrawing substituents (NH2, OH, CH3, H, F, Cl, CN, and NO2) are used to characterize electronic substituent effect on intermolecular +OH⋯Se hydrogen bond. Electron withdrawing substituent increases hydrogen bond stabilization energy and red shift in OH stretching frequency. Introduction of a positive charge transforms weak hydrogen bond of neutral OH⋯Se type into a strong hydrogen bond. Complexation induced changes on various hydrogen bond parameters, such as, stabilization energy, change in OH bond length, change in OH stretching frequency, extent of charge transfer from hydrogen bond acceptor to donor, hydrogen bond orders, electron density at the hydrogen bond critical point exhibit conventional electronic substitution effect. Stabilization energy of +OH⋯Y hydrogen bond are similar in the complexes between cationic phenol and SH2/SeH2, whereas it is almost twice with OH2 in case of +OH⋯Y hydrogen bond.
Journal of Physical Chemistry A, Feb 23, 2011
Intramolecular charge-transfer reaction in chiral (S) 1,2,3,4-tetrahydro-3-isoquinoline methanol ... more Intramolecular charge-transfer reaction in chiral (S) 1,2,3,4-tetrahydro-3-isoquinoline methanol (THIQM) has been investigated in the condensed phase and in jet-cooled conditions by means of laser-induced fluorescence, dispersed emission, resonance-enhanced two-photon ionization, and IR-UV double resonance experiments, as well as quantum chemical calculations. In the condensed phase, THIQM only shows local emission in nonpolar and protic solvents and dual emission in aprotic polar solvents, where the solvent-polarity dependent Stokes shifted emission is ascribed to a state involving charge transfer from the nitrogen lone pair to the benzene π-cloud. Ab initio calculations reveal two low-energy conformers, which are observed in jet-cooled conditions. In the most stable conformer, THIQM I , the CH 2 OH substituent acts as a hydrogen bond donor to the nitrogen lone pair in the equatorial position, while the second most stable conformer, THIQM II , corresponds to the opposite NH 3 3 3 O hydrogen bond, with the nitrogen lone pair in the axial position. The two low-energy jetcooled conformers of THIQM evidenced from the laser-induced fluorescence and dispersed emission spectra only show structured local emission. Complexes with usual solvents reproduce the condensed phase properties. The jet-cooled complex with aprotic polar solvent acetonitrile shows both local emission and charge transfer emission as observed in solution. The jet-cooled hydrate mainly shows local emission due to the unavailability of the nitrogen lone pair through intermolecular hydrogen bonding.
Physical Chemistry Chemical Physics, 2023
Se is a potential centre for hydrogen bond interactions.
Physical Chemistry Chemical Physics, 2009
Chemical Physics, 2006
The photophysical behaviour of trans-methyl p-(dimethylamino) cinnamate (t-MDMAC) donor–acceptor ... more The photophysical behaviour of trans-methyl p-(dimethylamino) cinnamate (t-MDMAC) donor–acceptor system has been investigated by steady-state absorption and emission spectroscopy and quantum chemical calculations. The molecule t-MDMAC shows an emission from the locally excited state in non-polar solvents. In addition to weak local emission, a strong solvent dependent red shifted fluorescence in polar aprotic solvents is attributed to highly polar intramolecular
Journal of Inclusion Phenomena and Macrocyclic Chemistry, May 6, 2008
Abstract The absorption and emission characteristics of donor− acceptor charge transfer system 4-... more Abstract The absorption and emission characteristics of donor− acceptor charge transfer system 4-amino-3-methyl benzoic acid methyl ester (AMBME), capable of dual emission, ie, local emission (LE) and charge transfer (CT) emission, have been investigated inside the ...
Journal of Photochemistry and Photobiology A-chemistry, Jun 1, 2010
Laser-induced fluorescence (LIF) excitation and dispersed fluorescence (DF) spectra of 4-amino 3-... more Laser-induced fluorescence (LIF) excitation and dispersed fluorescence (DF) spectra of 4-amino 3-methyl benzoic acid methyl ester (AMBME) and its solvated clusters with solvents such as methanol, water and acetonitrile have been investigated in a supersonic ...
Chemical Physics Letters, 2019
Complexes between para-substituted pyridine and SeH 2 have been investigated at the MP2/aug-cc-pV... more Complexes between para-substituted pyridine and SeH 2 have been investigated at the MP2/aug-cc-pVTZ level. Various electron donating and withdrawing substituents (-NH 2 ,-OH,-CH 3 ,-H,-F,-Cl,-CN, and-NO 2) are chosen in order to characterize their influence on Se-H⋯N intermolecular hydrogen-bonding interaction. The electron donating substituents lead to an increase of the stabilization energy along with elongation in the Se-H bond length and redshift in Se-H stretching frequency. Conventional electronic substitution effect has been observed on various hydrogen-bond parameters, such as, stabilization energy, change in Se-H bond length and stretching frequency, charge transfer, bond order, electron density at hydrogen-bond critical point.
Chemical Physics, 2006
The photophysical behaviour of trans-methyl p-(dimethylamino) cinnamate (t-MDMAC) donor–acceptor ... more The photophysical behaviour of trans-methyl p-(dimethylamino) cinnamate (t-MDMAC) donor–acceptor system has been investigated by steady-state absorption and emission spectroscopy and quantum chemical calculations. The molecule t-MDMAC shows an emission from the locally excited state in non-polar solvents. In addition to weak local emission, a strong solvent dependent red shifted fluorescence in polar aprotic solvents is attributed to highly polar intramolecular charge transfer state. However, the formation of hydrogen-bonded clusters with polar protic solvents has been suggested from a linear correlation between the observed red shifted fluorescence band maxima with hydrogen bonding parameters (α). Calculations by ab initio and density functional theory show that the lone pair electron at nitrogen center is out of plane of the benzene ring in the global minimum ground state structure. In the gas phase, a potential energy surface along the twist coordinate at the donor (–NMe2) and ac...
Physical Chemistry Chemical Physics, 2009
The structural modifications of (S)-1,2,3,4-tetrahydro-3-isoquinoline methanol (THIQM) upon ionis... more The structural modifications of (S)-1,2,3,4-tetrahydro-3-isoquinoline methanol (THIQM) upon ionisation have been investigated in jet-cooled conditions, by means of laser-induced fluorescence, REMPI, and IR-UV ion-dip spectroscopy of the neutral ground state and the ion. These results combined with ab initio calculations, support the presence in the jet of two low-energy conformers of THIQM. In the most stable Conformer I, the CH(2)OH substituent acts as a hydrogen bond donor to the nitrogen lone pair in the equatorial position. In this case, the nitrogen atom is in (S) configuration. Conformer II shows the opposite NHO hydrogen bond from the hydrogen atom in the equatorial position of nitrogen to the OH group. In this case, the nitrogen atom is in (R) configuration. This chirality dependence of the hydrogen bond direction is lost upon ionisation. While ionisation of Conformer II reinforces the NHO hydrogen bond, ionisation of Conformer I induces its isomerisation to the same ion as Conformer II, i.e. a change in hydrogen bond direction.
Journal of Molecular Structure, 2022
Chemical Physics, 2006
The photophysical behaviour of trans-methyl p-(dimethylamino) cinnamate (t-MDMAC) donor–acceptor ... more The photophysical behaviour of trans-methyl p-(dimethylamino) cinnamate (t-MDMAC) donor–acceptor system has been investigated by steady-state absorption and emission spectroscopy and quantum chemical calculations. The molecule t-MDMAC shows an emission from the locally excited state in non-polar solvents. In addition to weak local emission, a strong solvent dependent red shifted fluorescence in polar aprotic solvents is attributed to highly polar intramolecular
Chemical Physics
Abstract The anti-gauche conformational distribution of ethanol has been investigated using the O... more Abstract The anti-gauche conformational distribution of ethanol has been investigated using the O - H and symmetric C - C - O stretching infrared spectra in argon and nitrogen matrix. The dipole moment of the gauche conformer is higher compared to the anti conformer. The relative population of the anti and gauche conformer of ethanol depends on the rare gas mixture in the gas phase and also in the matrix after thermal cyclisation. In the gas phase, the anti conformer is more populated in nitrogen mixture whereas the gauche conformer is more populated in the argon mixture. After thermal cyclisation in the matrix, the anti conformer isomerise to the gauche conformer in nitrogen matrix and reverse happens in the argon matrix. Thermal cyclisation at 30 K in nitrogen matrix leads to the splitting of the gauche ± states that is probed by monitoring symmetric C - C - O stretching frequency mode.
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Papers by AMRITA CHAKRABORTY