Samiran Kar - Academia.edu (original) (raw)

Papers by Samiran Kar

Research paper thumbnail of Photoinduced intramolecular charge transfer (ICT) reaction in trans-methyl p-(dimethylamino) cinnamate: A combined fluorescence measurement and quantum chemical calculations

Research paper thumbnail of Novel copper(II)-mediated photocyclization of methoxynaphthyl analogues of chalcone: unusual electron transfer from excited vinyl arenes

Journal of the Chemical Society, Chemical Communications, 1995

Research paper thumbnail of Photoinduced Intramolecular Charge Transfer Reaction in ( E )-3-(4-Methylamino-phenyl)-acrylic Acid Methyl Ester: A Fluorescence Study in Combination with TDDFT Calculation

The Journal of Physical Chemistry a, Dec 1, 2006

Research paper thumbnail of Spectroscopic study of excited state intramolecular charge transfer in ethyl ester of N, N′-Dimethylaminonaphthyl-(acrylic)-acid

Chemical Physics, Dec 1, 2007

In this work, we have studied the twisted intramolecular charge transfer process in ethyl ester o... more In this work, we have studied the twisted intramolecular charge transfer process in ethyl ester of N,N 0-Dimethylaminonaphthyl-(acrylic)-acid (EDMANA) using absorption and emission spectroscopy. Single conformer of EDMANA present in the ground state gives rise to local and charge transfer emission in different solvents. Solvatochromic effect on the Stokes shifted emission band clearly indicates the charge transfer character of the emitting singlet excited state. Considering twisted intramolecular charge transfer model, the ground and excited state properties of EDMANA have been evaluated along the donor and acceptor twisting coordinates separately using density functional theory (DFT) and time dependent density functional theory (TDDFT), respectively, with B3LYP functional and 6-31G basis set. The effect of solvent on the spectral properties has been explored theoretically at the same level with time dependent density functional theory-polarized continuum model (TDDFT-PCM) and the theoretical results support the solvent polarity dependent Stokes shifted emission of EDMANA molecule.

Research paper thumbnail of Secondary amino group as charge donor for the excited state intramolecular charge transfer reaction in trans-3-(4-monomethylamino-phenyl)-acrylic acid: Spectroscopic measurement and theoretical calculations

Journal of Photochemistry and Photobiology a Chemistry, Jul 1, 2006

The emission properties of a synthesized donor–acceptor substituted aromatic system trans-3-(4-mo... more The emission properties of a synthesized donor–acceptor substituted aromatic system trans-3-(4-monomethylamino-phenyl)-acrylic acid (t-MMPAA) have been investigated both experimentally and theoretically. The molecule t-MMPAA shows dual fluorescence in ...

Research paper thumbnail of ChemInform Abstract: Photoinduced Electron Transfer Reaction: Photocyclization of Methoxynaphthyl Analogues of Chalcones

Cheminform, 2010

ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Research paper thumbnail of Photoinduced intramolecular charge transfer phenomena in 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2011

Description of synthetic procedures 6-Dimethylamino-3H-isobenzofuran-1-one (6-DMAPd, referred to ... more Description of synthetic procedures 6-Dimethylamino-3H-isobenzofuran-1-one (6-DMAPd, referred to in this work as 6dimethylaminophthalide) was prepared quantitatively from 6-nitro-3H-isobenzofuran-1-one by simultaneous hydrogenation and reductive methylation over 10% Pd/C catalyst in the presence of 35% aqueous formaldehyde while maintaining conditions similar to those reported by Stanetty et al. 1 , except the reaction was carried out under normal pressure of hydrogen. White crystals from n-hexane, m. p.: 122° C, (lit. 121-122° C) 1 .

Research paper thumbnail of Photoinduced intramolecular charge-transfer reactions in 4-amino-3-methyl benzoic acid methyl ester: A fluorescence study in condensed-phase and jet-cooled molecular beams

Journal of Chemical Sciences, 2007

Photoinduced intramolecular charge-transfer reactions in 4-amino-3-methyl benzoic acid methyl est... more Photoinduced intramolecular charge-transfer reactions in 4-amino-3-methyl benzoic acid methyl ester (AMBME) have been investigated spectroscopically. AMBME, with its weak charge donor primary amino group, shows dual emission in polar solvents. Absorption and emission measurements in the condensed phase support the premise that the short wavelength emission band corresponds to local emission and the long wavelength emission band to the charge

Research paper thumbnail of ChemInform Abstract: Photoinduced Electron Transfer Reaction: Photocyclization of Methoxynaphthyl Analogues of Chalcones

ChemInform, 2002

ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Research paper thumbnail of ChemInform Abstract: Photochemical Intramolecular Cyclization Routes to Heterocycles

Research paper thumbnail of Excited state intramolecular proton transfer in 3-hydroxy-2-naphthaldehyde: A combined study by absorption and emission spectroscopy and quantum chemical calculation

Chemical Physics, 2006

The photophysical behavior of 3-hydroxy-2-napthaldehyde (HN32) has been investigated on the basis... more The photophysical behavior of 3-hydroxy-2-napthaldehyde (HN32) has been investigated on the basis of steady state absorption and fluorescence spectroscopy, time-resolved emission spectroscopy and quantum chemical calculations. In the ground state, depending on the nature of solvents, HN32 exists as closed (intramolecular hydrogen bonded), open and intermolecular hydrogen bonded conformers. The closed conformer present in the hydrocarbon as well as other

Research paper thumbnail of Photoinduced intramolecular charge transfer in methyl ester of N, N′-Dimethylaminonaphthyl-(acrylic)-acid: Spectroscopic measurement and quantum chemical calculations

Journal of Photochemistry and Photobiology A-chemistry, 2008

The excited state intramolecular charge transfer process of a synthesized donor–acceptor naphthal... more The excited state intramolecular charge transfer process of a synthesized donor–acceptor naphthalene chromophoric system methyl ester of N,N′-Dimethylaminonaphthyl-(acrylic)-acid (MDMANA) has been investigated spectroscopically in combination with quantum chemical calculation. Apart from the local emission the molecule shows a solvent polarity dependent low energy emission from the charge transfer excited state. In polar protic solvents ground state hydrogen bonded clusters of

Research paper thumbnail of Selective fluorescence sensing of Cu(ii) and Zn(ii) using a new Schiff base-derived model compound: naked eye detection and spectral deciphering of the mechanism of sensory action

The Analyst, 2013

A new Schiff base compound 2-((benzylimino)-methyl)-naphthalen-1-ol (2BIMN1O) has been synthesize... more A new Schiff base compound 2-((benzylimino)-methyl)-naphthalen-1-ol (2BIMN1O) has been synthesized and characterized by 1 H NMR, 13 C NMR, DEPT, FT-IR and mass spectroscopic techniques. The significantly low fluorescence yield of the compound has been rationalized in connection with photo-induced electron transfer (PET) from the imine receptor moiety to the naphthalene fluorophore unit. Subsequently, an evaluation of the transition metal ion-induced modification of the fluorophorereceptor communication reveals a promising prospect for the title compound to function as a fluorosensor for Cu 2+ and Zn 2+ ions selectively, through remarkable fluorescence enhancement. While perturbation of the PET process in 2BIMN1O has been argued to be the responsible mechanism behind the fluorescence enhancement, the selectivity for these two metal ions has been interpreted on the grounds of an appreciably strong binding interaction. Particularly notable aspects regarding the chemosensory activity of the compound are its ability to detect the aforesaid transition metal ions down to the level of micromolar concentration (detection limit being 0.82 and 0.35 mM respectively), along with a simple and efficient synthetic procedure. Also the spectral modulation of 2BIMN1O in the presence of the transition metal ions paves the way for the construction of a calibration curve in the context of its fluorescence signaling potential.

Research paper thumbnail of COCHO-modified oxides nanoparticles by using phosphonic acid as grafting agent

Tetrahedron Letters, 2003

The synthesis of phosphonic acid 4 possessing a protected COCHO group, by using the Heck reaction... more The synthesis of phosphonic acid 4 possessing a protected COCHO group, by using the Heck reaction is described. After grafting of the phosphonic acid 4 on metal oxides Al 2 O 3 , TiO 2 or SnO 2 , the cleavage of the dithiane group was successful. The reactivity of the supported-COCHO group was examined by using model reactions with hydroxylamine and hydrazine derivatives.

Research paper thumbnail of Steric-controlled excimer formation in naphthalene analogues of chalcone

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2004

Naphthalene analogues of chalcone (typical vinylarenes) are well known for their intramolecular c... more Naphthalene analogues of chalcone (typical vinylarenes) are well known for their intramolecular charge transfer (CT) process. The all four possible isomers NC1, NC2, NC3 and NC4 were observed to give structure-less broad CT bands, whereas, excimer formation at higher concentration was reported only for NC4 [Res. Chem. Intermed. 25 (1999) 903]. However, conventional GMMX calculation data reveals that the naphthalene portion of all the isomers are planar, hence, excimer emission is expected from all of them, i.e., if NC4 can form an excimer, then the rests are also capable of doing it. In this paper we have actually succeeded in resolving the excimer peaks for all these four isomers by optimization of concentration, though the extent of excimer formation was observed to be the maximum for NC4. These differential tendencies of excimer formation can be explained by the change in extent of intermolecular stacking interaction of the naphthalene moieties. Variation occurs here due to steric perturbation arising from the specific orientation of the near resident non-planar aroyl component with respect to the naphthalene moiety.

Research paper thumbnail of Photoinduced properties of methyl ester of 2,6-dimethyl-1-amino-4-benzoic acid: Evidence of charge transfer emission from a weak primary amino donor

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2010

Photophysical properties of methyl ester of 2,6-dimethyl-1-amino-4-benzoic acid (M26DMB) have bee... more Photophysical properties of methyl ester of 2,6-dimethyl-1-amino-4-benzoic acid (M26DMB) have been investigated using steady state absorption and emission spectroscopy and time-resolved emission spectroscopy. Interestingly, not only in polar solvents, the molecule M26DMB having a weak primary amino donor group shows broad red-shifted emission band even in non-polar environment which in all probability arises from closely spaced local and charge transfer (CT) states. Clear dual fluorescence in polar protic solvents comprises of less intense local emission band and strong red-shifted CT band. The position of the red-shifted emission band is dependent on both the polarity and the hydrogen-bonding ability of the solvent.

Research paper thumbnail of Intramolecular Charge Transfer in Naphthalene Analogues of Chalcone#

Research on Chemical Intermediates, 1999

... where and asample and asta" A_j and Asta, and 11sample and rlsta are the quantum yie... more ... where and asample and asta" A_j and Asta, and 11sample and rlsta are the quantum yield, area under the emission spectra, absorbance and refractive index of the sample under study ... D. Huppert, SD Rand, PM Rentzepis, PF Barbara, WS Struve, and ZR Grabowski, J. Chem. ...

Research paper thumbnail of Photoinduced intramolecular charge-transfer reactions in 4-amino-3-methyl benzoic acid methyl ester: A fluorescence study in condensed-phase and jet-cooled molecular beams

Journal of Chemical Sciences, 2007

Photoinduced intramolecular charge-transfer reactions in 4-amino-3-methyl benzoic acid methyl est... more Photoinduced intramolecular charge-transfer reactions in 4-amino-3-methyl benzoic acid methyl ester (AMBME) have been investigated spectroscopically. AMBME, with its weak charge donor primary amino group, shows dual emission in polar solvents. Absorption and emission measurements in the condensed phase support the premise that the short wavelength emission band corresponds to local emission and the long wavelength emission band to the charge transfer emission. Laser-induced fluorescence excitation spectra show the presence of two low-energy conformers in jet-cooled molecular beams. Theoretical calculations using density functional theory help to determine structure, vibrational modes, potential energy surface, transition energy and oscillator strength for correlating experimental findings with theoretical results.

Research paper thumbnail of A Schiff base-derived new model compound for selective fluorescence sensing of Cu(II) and Zn(II) with ratiometric sensing potential: Synthesis, photophysics and mechanism of sensory action

Journal of Photochemistry and Photobiology A: Chemistry, 2011

A new Schiff base compound 2-[(naphthalen-1-ylmethylimino)-methyl]-naphthalen-1-ol (2N1YMN1O) has... more A new Schiff base compound 2-[(naphthalen-1-ylmethylimino)-methyl]-naphthalen-1-ol (2N1YMN1O) has been synthesized and characterized by 1 H NMR, 13 C NMR, DEPT, and FT-IR spectroscopy. A spectral deciphering of the photophysics of 2N1YMN1O has been undertaken by stationary absorption, emission and time-resolved emission techniques. A significantly low fluorescence yield of the compound has been realized in connection with photo-induced electron transfer (PET) to the naphthalene fluorophore unit from the imine receptor moiety. Subsequently, an assay for the transition metal ion-induced modulation of the fluorophore-receptor communication reveals the promising prospect of 2N1YMN1O to function as a fluorosensor for Cu 2+ and Zn 2+ ions selectively, through noticeable fluorescence enhancement. While perturbation of Cu 2+ /Zn 2+ ion-induced PET in 2N1YMN1O has been argued to be the operating mechanism behind the fluorescence enhancement, the selectivity for these two metal ions has been interpreted on the grounds of an appreciably strong binding interaction. Particularly noticeable aspects regarding the chemosensory activity of the compound are: (i) its selectivity for Cu 2+ and Zn 2+ ions, (ii) ratiometric sensing potential, (iii) the construction of a calibration curve for detection of Cu 2+ and Zn 2+ , (iv) ability to detect the transition metal ions down to the level of micromolar concentration, (v) a simple synthetic route, (vi) exploring the function of an imine nitrogen as a receptor unit in the proposed PET mechanism.

Research paper thumbnail of Lactim–lactam tautomerism is favoured over enol–keto tautomerism in 2-hydroxy-5-(4-fluorophenyl)nicotinic acid: Experimental and quantum chemical approach

Journal of Photochemistry and Photobiology A: Chemistry, 2010

A model compound, 2-hydroxy-5-(4-fluorophenyl)nicotinic acid (HFPNA) has been synthesized and its... more A model compound, 2-hydroxy-5-(4-fluorophenyl)nicotinic acid (HFPNA) has been synthesized and its ground and excited-state properties towards tautomerisation via possible two ways of proton transfer process have been elaborately examined by means of steady-state absorption, emission and timeresolved emission spectroscopy and quantum chemical calculations. The theme issue of the present contribution is to illustrate a direct competition between two potential excited-state intramolecular proton transfer (ESIPT) pathways within the same molecule. By a direct comparison of spectral characteristics of HFPNA with those of salicylic acid (SA) and 2-hydroxypyridine (2HP) under similar experimental conditions it has been demonstrated that lactim-lactam tautomerisation dominates over enol-keto tautomerisation in HFPNA. Experimental evidences and structural calculation at Density Functional Theory (DFT) (B3LYP/6-31G**) and Hartree-Fock (6-31G**) levels predict the existence of both lactim and lactamforms in the ground state. The ground and excited-state theoretical potential energy surfaces (PES) of HFPNA along both the ways of proton transfer coordinate at DFT level reveal that PES of HFPNA resemble well with that of 2HP while there are prominent differences from that of SA. We also report on the possibility of application of the studied molecule as a sensor of medium-pH following its sensitive response towards pH of the medium.

Research paper thumbnail of Photoinduced intramolecular charge transfer (ICT) reaction in trans-methyl p-(dimethylamino) cinnamate: A combined fluorescence measurement and quantum chemical calculations

Research paper thumbnail of Novel copper(II)-mediated photocyclization of methoxynaphthyl analogues of chalcone: unusual electron transfer from excited vinyl arenes

Journal of the Chemical Society, Chemical Communications, 1995

Research paper thumbnail of Photoinduced Intramolecular Charge Transfer Reaction in ( E )-3-(4-Methylamino-phenyl)-acrylic Acid Methyl Ester: A Fluorescence Study in Combination with TDDFT Calculation

The Journal of Physical Chemistry a, Dec 1, 2006

Research paper thumbnail of Spectroscopic study of excited state intramolecular charge transfer in ethyl ester of N, N′-Dimethylaminonaphthyl-(acrylic)-acid

Chemical Physics, Dec 1, 2007

In this work, we have studied the twisted intramolecular charge transfer process in ethyl ester o... more In this work, we have studied the twisted intramolecular charge transfer process in ethyl ester of N,N 0-Dimethylaminonaphthyl-(acrylic)-acid (EDMANA) using absorption and emission spectroscopy. Single conformer of EDMANA present in the ground state gives rise to local and charge transfer emission in different solvents. Solvatochromic effect on the Stokes shifted emission band clearly indicates the charge transfer character of the emitting singlet excited state. Considering twisted intramolecular charge transfer model, the ground and excited state properties of EDMANA have been evaluated along the donor and acceptor twisting coordinates separately using density functional theory (DFT) and time dependent density functional theory (TDDFT), respectively, with B3LYP functional and 6-31G basis set. The effect of solvent on the spectral properties has been explored theoretically at the same level with time dependent density functional theory-polarized continuum model (TDDFT-PCM) and the theoretical results support the solvent polarity dependent Stokes shifted emission of EDMANA molecule.

Research paper thumbnail of Secondary amino group as charge donor for the excited state intramolecular charge transfer reaction in trans-3-(4-monomethylamino-phenyl)-acrylic acid: Spectroscopic measurement and theoretical calculations

Journal of Photochemistry and Photobiology a Chemistry, Jul 1, 2006

The emission properties of a synthesized donor–acceptor substituted aromatic system trans-3-(4-mo... more The emission properties of a synthesized donor–acceptor substituted aromatic system trans-3-(4-monomethylamino-phenyl)-acrylic acid (t-MMPAA) have been investigated both experimentally and theoretically. The molecule t-MMPAA shows dual fluorescence in ...

Research paper thumbnail of ChemInform Abstract: Photoinduced Electron Transfer Reaction: Photocyclization of Methoxynaphthyl Analogues of Chalcones

Cheminform, 2010

ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Research paper thumbnail of Photoinduced intramolecular charge transfer phenomena in 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2011

Description of synthetic procedures 6-Dimethylamino-3H-isobenzofuran-1-one (6-DMAPd, referred to ... more Description of synthetic procedures 6-Dimethylamino-3H-isobenzofuran-1-one (6-DMAPd, referred to in this work as 6dimethylaminophthalide) was prepared quantitatively from 6-nitro-3H-isobenzofuran-1-one by simultaneous hydrogenation and reductive methylation over 10% Pd/C catalyst in the presence of 35% aqueous formaldehyde while maintaining conditions similar to those reported by Stanetty et al. 1 , except the reaction was carried out under normal pressure of hydrogen. White crystals from n-hexane, m. p.: 122° C, (lit. 121-122° C) 1 .

Research paper thumbnail of Photoinduced intramolecular charge-transfer reactions in 4-amino-3-methyl benzoic acid methyl ester: A fluorescence study in condensed-phase and jet-cooled molecular beams

Journal of Chemical Sciences, 2007

Photoinduced intramolecular charge-transfer reactions in 4-amino-3-methyl benzoic acid methyl est... more Photoinduced intramolecular charge-transfer reactions in 4-amino-3-methyl benzoic acid methyl ester (AMBME) have been investigated spectroscopically. AMBME, with its weak charge donor primary amino group, shows dual emission in polar solvents. Absorption and emission measurements in the condensed phase support the premise that the short wavelength emission band corresponds to local emission and the long wavelength emission band to the charge

Research paper thumbnail of ChemInform Abstract: Photoinduced Electron Transfer Reaction: Photocyclization of Methoxynaphthyl Analogues of Chalcones

ChemInform, 2002

ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Research paper thumbnail of ChemInform Abstract: Photochemical Intramolecular Cyclization Routes to Heterocycles

Research paper thumbnail of Excited state intramolecular proton transfer in 3-hydroxy-2-naphthaldehyde: A combined study by absorption and emission spectroscopy and quantum chemical calculation

Chemical Physics, 2006

The photophysical behavior of 3-hydroxy-2-napthaldehyde (HN32) has been investigated on the basis... more The photophysical behavior of 3-hydroxy-2-napthaldehyde (HN32) has been investigated on the basis of steady state absorption and fluorescence spectroscopy, time-resolved emission spectroscopy and quantum chemical calculations. In the ground state, depending on the nature of solvents, HN32 exists as closed (intramolecular hydrogen bonded), open and intermolecular hydrogen bonded conformers. The closed conformer present in the hydrocarbon as well as other

Research paper thumbnail of Photoinduced intramolecular charge transfer in methyl ester of N, N′-Dimethylaminonaphthyl-(acrylic)-acid: Spectroscopic measurement and quantum chemical calculations

Journal of Photochemistry and Photobiology A-chemistry, 2008

The excited state intramolecular charge transfer process of a synthesized donor–acceptor naphthal... more The excited state intramolecular charge transfer process of a synthesized donor–acceptor naphthalene chromophoric system methyl ester of N,N′-Dimethylaminonaphthyl-(acrylic)-acid (MDMANA) has been investigated spectroscopically in combination with quantum chemical calculation. Apart from the local emission the molecule shows a solvent polarity dependent low energy emission from the charge transfer excited state. In polar protic solvents ground state hydrogen bonded clusters of

Research paper thumbnail of Selective fluorescence sensing of Cu(ii) and Zn(ii) using a new Schiff base-derived model compound: naked eye detection and spectral deciphering of the mechanism of sensory action

The Analyst, 2013

A new Schiff base compound 2-((benzylimino)-methyl)-naphthalen-1-ol (2BIMN1O) has been synthesize... more A new Schiff base compound 2-((benzylimino)-methyl)-naphthalen-1-ol (2BIMN1O) has been synthesized and characterized by 1 H NMR, 13 C NMR, DEPT, FT-IR and mass spectroscopic techniques. The significantly low fluorescence yield of the compound has been rationalized in connection with photo-induced electron transfer (PET) from the imine receptor moiety to the naphthalene fluorophore unit. Subsequently, an evaluation of the transition metal ion-induced modification of the fluorophorereceptor communication reveals a promising prospect for the title compound to function as a fluorosensor for Cu 2+ and Zn 2+ ions selectively, through remarkable fluorescence enhancement. While perturbation of the PET process in 2BIMN1O has been argued to be the responsible mechanism behind the fluorescence enhancement, the selectivity for these two metal ions has been interpreted on the grounds of an appreciably strong binding interaction. Particularly notable aspects regarding the chemosensory activity of the compound are its ability to detect the aforesaid transition metal ions down to the level of micromolar concentration (detection limit being 0.82 and 0.35 mM respectively), along with a simple and efficient synthetic procedure. Also the spectral modulation of 2BIMN1O in the presence of the transition metal ions paves the way for the construction of a calibration curve in the context of its fluorescence signaling potential.

Research paper thumbnail of COCHO-modified oxides nanoparticles by using phosphonic acid as grafting agent

Tetrahedron Letters, 2003

The synthesis of phosphonic acid 4 possessing a protected COCHO group, by using the Heck reaction... more The synthesis of phosphonic acid 4 possessing a protected COCHO group, by using the Heck reaction is described. After grafting of the phosphonic acid 4 on metal oxides Al 2 O 3 , TiO 2 or SnO 2 , the cleavage of the dithiane group was successful. The reactivity of the supported-COCHO group was examined by using model reactions with hydroxylamine and hydrazine derivatives.

Research paper thumbnail of Steric-controlled excimer formation in naphthalene analogues of chalcone

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2004

Naphthalene analogues of chalcone (typical vinylarenes) are well known for their intramolecular c... more Naphthalene analogues of chalcone (typical vinylarenes) are well known for their intramolecular charge transfer (CT) process. The all four possible isomers NC1, NC2, NC3 and NC4 were observed to give structure-less broad CT bands, whereas, excimer formation at higher concentration was reported only for NC4 [Res. Chem. Intermed. 25 (1999) 903]. However, conventional GMMX calculation data reveals that the naphthalene portion of all the isomers are planar, hence, excimer emission is expected from all of them, i.e., if NC4 can form an excimer, then the rests are also capable of doing it. In this paper we have actually succeeded in resolving the excimer peaks for all these four isomers by optimization of concentration, though the extent of excimer formation was observed to be the maximum for NC4. These differential tendencies of excimer formation can be explained by the change in extent of intermolecular stacking interaction of the naphthalene moieties. Variation occurs here due to steric perturbation arising from the specific orientation of the near resident non-planar aroyl component with respect to the naphthalene moiety.

Research paper thumbnail of Photoinduced properties of methyl ester of 2,6-dimethyl-1-amino-4-benzoic acid: Evidence of charge transfer emission from a weak primary amino donor

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2010

Photophysical properties of methyl ester of 2,6-dimethyl-1-amino-4-benzoic acid (M26DMB) have bee... more Photophysical properties of methyl ester of 2,6-dimethyl-1-amino-4-benzoic acid (M26DMB) have been investigated using steady state absorption and emission spectroscopy and time-resolved emission spectroscopy. Interestingly, not only in polar solvents, the molecule M26DMB having a weak primary amino donor group shows broad red-shifted emission band even in non-polar environment which in all probability arises from closely spaced local and charge transfer (CT) states. Clear dual fluorescence in polar protic solvents comprises of less intense local emission band and strong red-shifted CT band. The position of the red-shifted emission band is dependent on both the polarity and the hydrogen-bonding ability of the solvent.

Research paper thumbnail of Intramolecular Charge Transfer in Naphthalene Analogues of Chalcone#

Research on Chemical Intermediates, 1999

... where and asample and asta" A_j and Asta, and 11sample and rlsta are the quantum yie... more ... where and asample and asta" A_j and Asta, and 11sample and rlsta are the quantum yield, area under the emission spectra, absorbance and refractive index of the sample under study ... D. Huppert, SD Rand, PM Rentzepis, PF Barbara, WS Struve, and ZR Grabowski, J. Chem. ...

Research paper thumbnail of Photoinduced intramolecular charge-transfer reactions in 4-amino-3-methyl benzoic acid methyl ester: A fluorescence study in condensed-phase and jet-cooled molecular beams

Journal of Chemical Sciences, 2007

Photoinduced intramolecular charge-transfer reactions in 4-amino-3-methyl benzoic acid methyl est... more Photoinduced intramolecular charge-transfer reactions in 4-amino-3-methyl benzoic acid methyl ester (AMBME) have been investigated spectroscopically. AMBME, with its weak charge donor primary amino group, shows dual emission in polar solvents. Absorption and emission measurements in the condensed phase support the premise that the short wavelength emission band corresponds to local emission and the long wavelength emission band to the charge transfer emission. Laser-induced fluorescence excitation spectra show the presence of two low-energy conformers in jet-cooled molecular beams. Theoretical calculations using density functional theory help to determine structure, vibrational modes, potential energy surface, transition energy and oscillator strength for correlating experimental findings with theoretical results.

Research paper thumbnail of A Schiff base-derived new model compound for selective fluorescence sensing of Cu(II) and Zn(II) with ratiometric sensing potential: Synthesis, photophysics and mechanism of sensory action

Journal of Photochemistry and Photobiology A: Chemistry, 2011

A new Schiff base compound 2-[(naphthalen-1-ylmethylimino)-methyl]-naphthalen-1-ol (2N1YMN1O) has... more A new Schiff base compound 2-[(naphthalen-1-ylmethylimino)-methyl]-naphthalen-1-ol (2N1YMN1O) has been synthesized and characterized by 1 H NMR, 13 C NMR, DEPT, and FT-IR spectroscopy. A spectral deciphering of the photophysics of 2N1YMN1O has been undertaken by stationary absorption, emission and time-resolved emission techniques. A significantly low fluorescence yield of the compound has been realized in connection with photo-induced electron transfer (PET) to the naphthalene fluorophore unit from the imine receptor moiety. Subsequently, an assay for the transition metal ion-induced modulation of the fluorophore-receptor communication reveals the promising prospect of 2N1YMN1O to function as a fluorosensor for Cu 2+ and Zn 2+ ions selectively, through noticeable fluorescence enhancement. While perturbation of Cu 2+ /Zn 2+ ion-induced PET in 2N1YMN1O has been argued to be the operating mechanism behind the fluorescence enhancement, the selectivity for these two metal ions has been interpreted on the grounds of an appreciably strong binding interaction. Particularly noticeable aspects regarding the chemosensory activity of the compound are: (i) its selectivity for Cu 2+ and Zn 2+ ions, (ii) ratiometric sensing potential, (iii) the construction of a calibration curve for detection of Cu 2+ and Zn 2+ , (iv) ability to detect the transition metal ions down to the level of micromolar concentration, (v) a simple synthetic route, (vi) exploring the function of an imine nitrogen as a receptor unit in the proposed PET mechanism.

Research paper thumbnail of Lactim–lactam tautomerism is favoured over enol–keto tautomerism in 2-hydroxy-5-(4-fluorophenyl)nicotinic acid: Experimental and quantum chemical approach

Journal of Photochemistry and Photobiology A: Chemistry, 2010

A model compound, 2-hydroxy-5-(4-fluorophenyl)nicotinic acid (HFPNA) has been synthesized and its... more A model compound, 2-hydroxy-5-(4-fluorophenyl)nicotinic acid (HFPNA) has been synthesized and its ground and excited-state properties towards tautomerisation via possible two ways of proton transfer process have been elaborately examined by means of steady-state absorption, emission and timeresolved emission spectroscopy and quantum chemical calculations. The theme issue of the present contribution is to illustrate a direct competition between two potential excited-state intramolecular proton transfer (ESIPT) pathways within the same molecule. By a direct comparison of spectral characteristics of HFPNA with those of salicylic acid (SA) and 2-hydroxypyridine (2HP) under similar experimental conditions it has been demonstrated that lactim-lactam tautomerisation dominates over enol-keto tautomerisation in HFPNA. Experimental evidences and structural calculation at Density Functional Theory (DFT) (B3LYP/6-31G**) and Hartree-Fock (6-31G**) levels predict the existence of both lactim and lactamforms in the ground state. The ground and excited-state theoretical potential energy surfaces (PES) of HFPNA along both the ways of proton transfer coordinate at DFT level reveal that PES of HFPNA resemble well with that of 2HP while there are prominent differences from that of SA. We also report on the possibility of application of the studied molecule as a sensor of medium-pH following its sensitive response towards pH of the medium.