H Pal | Bhabha Atomic Research Centre (original) (raw)
Papers by H Pal
Physical Chemistry Chemical Physics, 2011
The influence of confinement in the supramolecular β-cyclodextrin nanocavity on the excited state... more The influence of confinement in the supramolecular β-cyclodextrin nanocavity on the excited state torsional dynamics of the amyloid fibril sensor, Thioflavin-T, is explored using subpicosecond fluorescence up-conversion spectroscopy. In the presence of β-cyclodextrin, the emission intensity and the fluorescence lifetime of Thioflavin-T significantly increases, indicating the confinement effect of the nanocage on the photophysical behaviour of the dye. Detailed time-resolved fluorescence studies show an appreciable dynamic Stokes' shift for the dye in the β-cyclodextrin nanocavity. Analysis of the time-resolved area normalized emission spectra (TRANES) indicates the formation of an emissive TICT state. The rate of formation of the TICT state, as calculated from the time dependent changes in the peak frequency and the width of the emission spectra, is found to be substantially slower in the β-cyclodextrin nanocavity compared to that in bulk water. Present results indicate that ultrafast torsional motion in Thioflavin-T is significantly retarded due to confinement by the β-cyclodextrin nanocavity.
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](Chemical Communications, 2008
Journal of Chemical Physics, May 8, 2002
ABSTRACT
Journal of the Indian Chemical Society, 1993
Photochemistry and Photobiology, 2007
Both steady-state (SS) and time-resolved (TR) studies show that the fluorescence of the dye Nile ... more Both steady-state (SS) and time-resolved (TR) studies show that the fluorescence of the dye Nile red (NR) is quenched by various aromatic amines (ArA). Bimolecular quenching constants (kq) from both SS and TR measurements are observed to match well, indicating that the interaction is dynamic in nature. The quenching interaction in the present systems has been attributed to electron transfer (ET) from ArA to excited NR, based on the variations in the kq values with the oxidation potentials of the amines. The kq values calculated within the framework of Marcus' outer-sphere ET theory at different free-energy changes (deltaG0) of the ET reactions match well with the experimental ones, supporting the ET mechanism in the systems studied. The reorganization energy (lambda) estimated from the correlation of the experimental and the calculated kq values is quite similar to the solvent reorganization energy (lambda(s)), calculated on the basis of the solvent dielectric continuum model along with the assumption that the reactants are the effective spheres. Although a modest error is involved in this lambda(s) calculation, the similarity in lambda and lambda(s) values suggests that the solvent reorganization plays a dominant role in governing the ET dynamics in the present systems.
Photochemistry and Photobiology, 2004
Studies on the electron transfer (ET) interaction of 1,4dihydroxy-9,lO-anthraquinone and 6,1l-dih... more Studies on the electron transfer (ET) interaction of 1,4dihydroxy-9,lO-anthraquinone and 6,1l-dihydroxy-S,lZ-naphthacenequinone with aliphatic and aromatic amine (AIA and ArA, respectively) donors have been investigated in acetonitrile solutions. Steady-state (SS) measurements show quenching of the quinone fluorescence by amines, without indicating any change in the shape of the fluorescence spectra. No significant change in the absorption spectra of the quinones is also observed in the presence of the amines. For all the quinoneamine pairs, the bimolecular quenching constants (k,) estimated from SS and time-resolved measurements are found to be similar. Variation in the k, values with the oxidation potentials of the amines indicates the involvement of the ET mechanism for the quenching process. A reasonably good correlation between the k, values and the free energy changes (AGO) for the ET reactions following Marcus' outer-sphere ET theory also supports this mechanism. It is seen that for both the quinone-ArA and quinone-AIA systems, the k, values initially increase and then get saturated at some diffusion-controlled limiting values (k r) as AGO values gradually become more negative. Interestingly, however, it is seen that the k r value for the quinone-AIA systems is substantially lower than that for quinone-ArA systems. Such a large difference in the k r values between quinone-AIA and quinone-ArA systems is quite unusual. Present results have been rationalized based on the assumption that an orientational restriction is imposed for the lbsted on the website on
Journal of Physical …, 2006
The photophysical properties of the phenazine-based dye neutral red were investigated in aqueous ... more The photophysical properties of the phenazine-based dye neutral red were investigated in aqueous solution in the presence of the macrocyclic host molecule cucurbit[7]uril (CB7) using ground-state absorption as well as steady-state and time-resolved fluorescence ...
Springer Series in Chemical Physics
Radiation Physics and Chemistry
ABSTRACT
Journal of the Chemical Society, Faraday Transactions, 1992
... Pulse radiolytic one-electron oxidation of some dihydroxy-substituted anthraquinones. Haridas... more ... Pulse radiolytic one-electron oxidation of some dihydroxy-substituted anthraquinones. Haridas Pal, Dipak K. Palit, Tulsi Mukherjee and Jai P. Mittal J. Chem. Soc., Faraday Trans., 1992, 88, 681-687. DOI: 10.1039/FT9928800681 ...
The Journal of Physical Chemistry A, 2001
ABSTRACT
The Journal of Physical Chemistry A, 2003
In a recent paper, 1 Jonsson et al. reported the redox and acidbase properties of 2,2′-and 4,4′-b... more In a recent paper, 1 Jonsson et al. reported the redox and acidbase properties of 2,2′-and 4,4′-biphenols in aqueous solutions. We disagree with the reported first and second acidity constants (pK a1 and pK a2 , respectively) of 4,4′-biphenol. 1 It may be noted that we have recently published a paper 2 on the photophysical properties of 2,2′-and 4,4′-biphenols, where we have discussed in detail the pK a1 and pK a2 values of the two biphenols. The pK a1 and pK a2 values were determined following the changes in the absorption spectra of these molecules with the pH/H-(basicity function) 3 of the solutions. The detailed spectral changes with pH/Hof the solutions are also discussed in
The Journal of Physical Chemistry A, 2002
Characteristics of the reduced radicals of a series of 7-aminocoumarin dyes (C) have been investi... more Characteristics of the reduced radicals of a series of 7-aminocoumarin dyes (C) have been investigated in different solvents using pulse radiolysis (PR) technique. Since these coumarin dyes are almost insoluble in water, a mixed solvent (MS) system containing 5.0 mol dm-3 of 2-propanol (2PNL) and 1.0 mol dm-3 of acetone (ACT) in water has been used in the present work to substitute the aqueous solvent. In MS, for a wide pH range of ∼1-9, the reduced coumarin radicals are formed in the neutral form, CH •. These radicals show two absorption bands, one in the 300-400 nm region and the other in the 500-600 nm region. As the coumarin dyes undergo hydrolysis in strongly alkaline solutions, PR studies in MS could not be extended beyond pH ∼9. In 2PNL, the reduced coumarin radicals are also formed in the CH‚ form, even in the presence of ∼1 mol dm-3 of a strong proton acceptor like triethylamine (TEA). Since the pK b value of TEA is 3.19, it is indicated that the acid dissociation constant of the CH‚ radicals (pK a R) must be >11. The PR results in MS and 2PNL clearly indicate that the anionic form of the reduced coumarin radicals (C •-) formed by initial one-electron reduction of the dyes undergo very fast protonation to give the CH • form in the solution. To avoid protonation of C •-, PR experiments were carried out in acetonitrile (ACN) solutions in the presence of ∼1 mol dm-3 of aniline (AN). With this high concentration, AN efficiently scavenges the cation radicals from the solvent ion pairs (ACN + ‚‚‚e-) formed following the electron pulse, and thus the equivalent amount of electrons become available to reduce C to C •-. It is seen that the C •radicals of all the coumarin dyes studied have unusually weak absorption bands in the 500-800 nm region. Since the coumarin dyes are good electron acceptors, present results on CH • and C •radicals will be useful in elucidating the ET mechanism using coumarin dyes as the electron acceptors.
Photochemistry and Photobiology, 1999
Photophysical properties of the cationic form of neutral red (NRH'), a phenazine-based dye of bio... more Photophysical properties of the cationic form of neutral red (NRH'), a phenazine-based dye of biological importance, have been investigated in several protic and aprotic solvents using optical absorption, steady-state and time-resolved fluorescence and picosecond laser flash photolysis techniques. Absorption and fluorescence characteristics of the dye in protic solvents indicate the existence of intermolecular hydrogen bonding between the NRH+ and solvent molecules in the ground state as well as in the excited state. Measurements of the fluorescence lifetime in normal and heavy water also support the formation of intermolecular hydrogen bonding. Time-resolved transient absorption spectra obtained in the picosecond laser flash photolysis experiments show only the absorption band due to the S, t S1 absorption. The picosecond transient absorption results do not indicate any spectral shifts attributable to the hydrogen bond formation dynamics between the excited NRH+ and the protic solvent molecules. It is inferred that the hydrogen bonding dynamics are much faster than the time resolution of our picosecond setup (-35 ps).
Photochemistry and Photobiology, 1998
The effect of solvent polarity on the electronic absorption and fluorescence properties of neutra... more The effect of solvent polarity on the electronic absorption and fluorescence properties of neutral red (NR), a phenazine-based dye of biological importance has been investigated in several neat and mixed solvents. An unusual dual solvatochromic behavior has been observed that reveals the existence of two closely spaced electronic excited states in NR. In low-polarity solvents the fluorescence of the NR is mainly emitted from the localized excited state, whereas in high-polarity solvents the emission from the charge transfer state dominates. The dipole moments of the localized and charge transfer states of NR have been estimated from the solvatochromic shifts. The dipole moment of the localized excited state (4.8 D) is only slightly higher than that of the ground state (2.0 D), while that of the charge transfer state is drastically higher (17.5 D). Fluorescence quantum yields and the lifetimes of NR have been determined in different solvents and correlated with the solvatochromic shifts.
Photochemistry and Photobiology, 2004
Experimental results on various photophysical properties of coumarin-30 (C30) dye, namely, Stokes... more Experimental results on various photophysical properties of coumarin-30 (C30) dye, namely, Stokes' shift (Av), fluorescence quantum yield (Qf), fluorescence lifetime (q), radiative rate constant (kf) and nonradiative rate constant (knr), as obtained using absorption and fluorescence measurements have been reported. Though in most of the solvents the properties of C30 show more or less linear correlation with the v o s t e d on the website on 28 May 2004 *To whom conespondence should be addressed Radiation Chemistry and
Photochemical & Photobiological Sciences, 2009
The interaction of 1,4-dihydroxy-9,10-anthraquinone, (quinizarin; QZ), with alpha-, beta- and gam... more The interaction of 1,4-dihydroxy-9,10-anthraquinone, (quinizarin; QZ), with alpha-, beta- and gamma-cyclodextrin (CD) hosts, has been investigated using absorption, and steady-state and time-resolved fluorescence measurements, in order to understand the effects of cavity size of CDs on the binding of QZ molecule and the changes in the photophysical properties of QZ in the microenvironment of the hosts. The results demonstrate that QZ forms inclusion complexes with all the CDs. The low binding constants as well as the thermodynamic parameters indicate that the mode of interaction between QZ and CDs is mainly hydrophobic in nature. The relative magnitudes of the binding constants and the differential enhancements in the fluorescence intensity of QZ upon complexation with the CDs can be explained by considering the relative dimensions of the host cavity and the guest molecule, as well as the orientation of the guest molecule inside the CD cavity. It is proposed that the unsubstituted benzene ring of QZ is encapsulated within alpha- and beta-CD cavities whereas the dihydroxy-substituted aromatic ring is encapsulated within the gamma-CD cavity. This is further supported by the complexation studies of the QZ.CD systems with Al(III) ions. It is observed that the complexation of QZ with the metal ion is enhanced in the QZ.alpha-CD and QZ.beta-CD systems whereas it is significantly reduced in the QZ.gamma-CD system, due to shielding of the chelating groups of the dye inside the CD cavity in the latter case.
Photochemical & Photobiological Sciences, 2005
The photophysical properties of 2-amino-9,10-anthraquinone (2AAQ) have been investigated in diffe... more The photophysical properties of 2-amino-9,10-anthraquinone (2AAQ) have been investigated in different solvents and solvent mixtures and correlated with the Lippert-Mataga solvent polarity parameter, Deltaf. In the low solvent polarity region with Deltaf < ca. 0.1, the dye shows unusually high fluorescence quantum yields (Phif) and lifetimes (tauf) in comparison to those in other solvents of medium to high polarities. Similarly, the radiative rate constants (kf) are relatively lower and the non-radiative rate constants (knr) are relatively higher in the low polarity solvents in comparison to those in the medium to high polarity solvents. The current results have been rationalized assuming that the dye adopts different structural forms below and above the Deltaf value of approximately 0.1. It is inferred that in the low solvent polarity region the dye exists in a non-planar structure, with its 2-NH2 plane away from that of the 9,10-anthraquinone moiety in the ground state. In solvents of medium to high polarities, the dye exists in a polar intramolecular charge transfer (ICT) structure, where the amino lone pair of the 2-NH2 group is in strong resonance with the anthraquinone pi-cloud in the ground state. In all the solvents, however the dye is inferred to exist in the ICT structure in its excited (S1) state. Supportive evidence for the above hypothesis has been obtained from the solvent polarity effect on the Stokes' shifts for the dye. Quantum chemical studies on the structures of 2AAQ dye in the gas phase also give qualitative support for the inferences drawn from the photophysical properties of the dye in different solvents.
Optical Materials, 2004
ABSTRACT
Journal of Photochemistry and Photobiology A: Chemistry, 2008
... Keywords: Micellar electron transfer; Triton-X-100; Brij-35; Cetyltrimethylammonium bromide; ... more ... Keywords: Micellar electron transfer; Triton-X-100; Brij-35; Cetyltrimethylammonium bromide; Marcus inversion; Quinone. Article Outline. 1. Introduction 2. Experimental 3. Results and discussion 4. Conclusions Acknowledgements References. 1. Introduction. ...
Physical Chemistry Chemical Physics, 2011
The influence of confinement in the supramolecular β-cyclodextrin nanocavity on the excited state... more The influence of confinement in the supramolecular β-cyclodextrin nanocavity on the excited state torsional dynamics of the amyloid fibril sensor, Thioflavin-T, is explored using subpicosecond fluorescence up-conversion spectroscopy. In the presence of β-cyclodextrin, the emission intensity and the fluorescence lifetime of Thioflavin-T significantly increases, indicating the confinement effect of the nanocage on the photophysical behaviour of the dye. Detailed time-resolved fluorescence studies show an appreciable dynamic Stokes' shift for the dye in the β-cyclodextrin nanocavity. Analysis of the time-resolved area normalized emission spectra (TRANES) indicates the formation of an emissive TICT state. The rate of formation of the TICT state, as calculated from the time dependent changes in the peak frequency and the width of the emission spectra, is found to be substantially slower in the β-cyclodextrin nanocavity compared to that in bulk water. Present results indicate that ultrafast torsional motion in Thioflavin-T is significantly retarded due to confinement by the β-cyclodextrin nanocavity.
Chemical Communications, 2008
Journal of Chemical Physics, May 8, 2002
ABSTRACT
Journal of the Indian Chemical Society, 1993
Photochemistry and Photobiology, 2007
Both steady-state (SS) and time-resolved (TR) studies show that the fluorescence of the dye Nile ... more Both steady-state (SS) and time-resolved (TR) studies show that the fluorescence of the dye Nile red (NR) is quenched by various aromatic amines (ArA). Bimolecular quenching constants (kq) from both SS and TR measurements are observed to match well, indicating that the interaction is dynamic in nature. The quenching interaction in the present systems has been attributed to electron transfer (ET) from ArA to excited NR, based on the variations in the kq values with the oxidation potentials of the amines. The kq values calculated within the framework of Marcus' outer-sphere ET theory at different free-energy changes (deltaG0) of the ET reactions match well with the experimental ones, supporting the ET mechanism in the systems studied. The reorganization energy (lambda) estimated from the correlation of the experimental and the calculated kq values is quite similar to the solvent reorganization energy (lambda(s)), calculated on the basis of the solvent dielectric continuum model along with the assumption that the reactants are the effective spheres. Although a modest error is involved in this lambda(s) calculation, the similarity in lambda and lambda(s) values suggests that the solvent reorganization plays a dominant role in governing the ET dynamics in the present systems.
Photochemistry and Photobiology, 2004
Studies on the electron transfer (ET) interaction of 1,4dihydroxy-9,lO-anthraquinone and 6,1l-dih... more Studies on the electron transfer (ET) interaction of 1,4dihydroxy-9,lO-anthraquinone and 6,1l-dihydroxy-S,lZ-naphthacenequinone with aliphatic and aromatic amine (AIA and ArA, respectively) donors have been investigated in acetonitrile solutions. Steady-state (SS) measurements show quenching of the quinone fluorescence by amines, without indicating any change in the shape of the fluorescence spectra. No significant change in the absorption spectra of the quinones is also observed in the presence of the amines. For all the quinoneamine pairs, the bimolecular quenching constants (k,) estimated from SS and time-resolved measurements are found to be similar. Variation in the k, values with the oxidation potentials of the amines indicates the involvement of the ET mechanism for the quenching process. A reasonably good correlation between the k, values and the free energy changes (AGO) for the ET reactions following Marcus' outer-sphere ET theory also supports this mechanism. It is seen that for both the quinone-ArA and quinone-AIA systems, the k, values initially increase and then get saturated at some diffusion-controlled limiting values (k r) as AGO values gradually become more negative. Interestingly, however, it is seen that the k r value for the quinone-AIA systems is substantially lower than that for quinone-ArA systems. Such a large difference in the k r values between quinone-AIA and quinone-ArA systems is quite unusual. Present results have been rationalized based on the assumption that an orientational restriction is imposed for the lbsted on the website on
Journal of Physical …, 2006
The photophysical properties of the phenazine-based dye neutral red were investigated in aqueous ... more The photophysical properties of the phenazine-based dye neutral red were investigated in aqueous solution in the presence of the macrocyclic host molecule cucurbit[7]uril (CB7) using ground-state absorption as well as steady-state and time-resolved fluorescence ...
Springer Series in Chemical Physics
Radiation Physics and Chemistry
ABSTRACT
Journal of the Chemical Society, Faraday Transactions, 1992
... Pulse radiolytic one-electron oxidation of some dihydroxy-substituted anthraquinones. Haridas... more ... Pulse radiolytic one-electron oxidation of some dihydroxy-substituted anthraquinones. Haridas Pal, Dipak K. Palit, Tulsi Mukherjee and Jai P. Mittal J. Chem. Soc., Faraday Trans., 1992, 88, 681-687. DOI: 10.1039/FT9928800681 ...
The Journal of Physical Chemistry A, 2001
ABSTRACT
The Journal of Physical Chemistry A, 2003
In a recent paper, 1 Jonsson et al. reported the redox and acidbase properties of 2,2′-and 4,4′-b... more In a recent paper, 1 Jonsson et al. reported the redox and acidbase properties of 2,2′-and 4,4′-biphenols in aqueous solutions. We disagree with the reported first and second acidity constants (pK a1 and pK a2 , respectively) of 4,4′-biphenol. 1 It may be noted that we have recently published a paper 2 on the photophysical properties of 2,2′-and 4,4′-biphenols, where we have discussed in detail the pK a1 and pK a2 values of the two biphenols. The pK a1 and pK a2 values were determined following the changes in the absorption spectra of these molecules with the pH/H-(basicity function) 3 of the solutions. The detailed spectral changes with pH/Hof the solutions are also discussed in
The Journal of Physical Chemistry A, 2002
Characteristics of the reduced radicals of a series of 7-aminocoumarin dyes (C) have been investi... more Characteristics of the reduced radicals of a series of 7-aminocoumarin dyes (C) have been investigated in different solvents using pulse radiolysis (PR) technique. Since these coumarin dyes are almost insoluble in water, a mixed solvent (MS) system containing 5.0 mol dm-3 of 2-propanol (2PNL) and 1.0 mol dm-3 of acetone (ACT) in water has been used in the present work to substitute the aqueous solvent. In MS, for a wide pH range of ∼1-9, the reduced coumarin radicals are formed in the neutral form, CH •. These radicals show two absorption bands, one in the 300-400 nm region and the other in the 500-600 nm region. As the coumarin dyes undergo hydrolysis in strongly alkaline solutions, PR studies in MS could not be extended beyond pH ∼9. In 2PNL, the reduced coumarin radicals are also formed in the CH‚ form, even in the presence of ∼1 mol dm-3 of a strong proton acceptor like triethylamine (TEA). Since the pK b value of TEA is 3.19, it is indicated that the acid dissociation constant of the CH‚ radicals (pK a R) must be >11. The PR results in MS and 2PNL clearly indicate that the anionic form of the reduced coumarin radicals (C •-) formed by initial one-electron reduction of the dyes undergo very fast protonation to give the CH • form in the solution. To avoid protonation of C •-, PR experiments were carried out in acetonitrile (ACN) solutions in the presence of ∼1 mol dm-3 of aniline (AN). With this high concentration, AN efficiently scavenges the cation radicals from the solvent ion pairs (ACN + ‚‚‚e-) formed following the electron pulse, and thus the equivalent amount of electrons become available to reduce C to C •-. It is seen that the C •radicals of all the coumarin dyes studied have unusually weak absorption bands in the 500-800 nm region. Since the coumarin dyes are good electron acceptors, present results on CH • and C •radicals will be useful in elucidating the ET mechanism using coumarin dyes as the electron acceptors.
Photochemistry and Photobiology, 1999
Photophysical properties of the cationic form of neutral red (NRH'), a phenazine-based dye of bio... more Photophysical properties of the cationic form of neutral red (NRH'), a phenazine-based dye of biological importance, have been investigated in several protic and aprotic solvents using optical absorption, steady-state and time-resolved fluorescence and picosecond laser flash photolysis techniques. Absorption and fluorescence characteristics of the dye in protic solvents indicate the existence of intermolecular hydrogen bonding between the NRH+ and solvent molecules in the ground state as well as in the excited state. Measurements of the fluorescence lifetime in normal and heavy water also support the formation of intermolecular hydrogen bonding. Time-resolved transient absorption spectra obtained in the picosecond laser flash photolysis experiments show only the absorption band due to the S, t S1 absorption. The picosecond transient absorption results do not indicate any spectral shifts attributable to the hydrogen bond formation dynamics between the excited NRH+ and the protic solvent molecules. It is inferred that the hydrogen bonding dynamics are much faster than the time resolution of our picosecond setup (-35 ps).
Photochemistry and Photobiology, 1998
The effect of solvent polarity on the electronic absorption and fluorescence properties of neutra... more The effect of solvent polarity on the electronic absorption and fluorescence properties of neutral red (NR), a phenazine-based dye of biological importance has been investigated in several neat and mixed solvents. An unusual dual solvatochromic behavior has been observed that reveals the existence of two closely spaced electronic excited states in NR. In low-polarity solvents the fluorescence of the NR is mainly emitted from the localized excited state, whereas in high-polarity solvents the emission from the charge transfer state dominates. The dipole moments of the localized and charge transfer states of NR have been estimated from the solvatochromic shifts. The dipole moment of the localized excited state (4.8 D) is only slightly higher than that of the ground state (2.0 D), while that of the charge transfer state is drastically higher (17.5 D). Fluorescence quantum yields and the lifetimes of NR have been determined in different solvents and correlated with the solvatochromic shifts.
Photochemistry and Photobiology, 2004
Experimental results on various photophysical properties of coumarin-30 (C30) dye, namely, Stokes... more Experimental results on various photophysical properties of coumarin-30 (C30) dye, namely, Stokes' shift (Av), fluorescence quantum yield (Qf), fluorescence lifetime (q), radiative rate constant (kf) and nonradiative rate constant (knr), as obtained using absorption and fluorescence measurements have been reported. Though in most of the solvents the properties of C30 show more or less linear correlation with the v o s t e d on the website on 28 May 2004 *To whom conespondence should be addressed Radiation Chemistry and
Photochemical & Photobiological Sciences, 2009
The interaction of 1,4-dihydroxy-9,10-anthraquinone, (quinizarin; QZ), with alpha-, beta- and gam... more The interaction of 1,4-dihydroxy-9,10-anthraquinone, (quinizarin; QZ), with alpha-, beta- and gamma-cyclodextrin (CD) hosts, has been investigated using absorption, and steady-state and time-resolved fluorescence measurements, in order to understand the effects of cavity size of CDs on the binding of QZ molecule and the changes in the photophysical properties of QZ in the microenvironment of the hosts. The results demonstrate that QZ forms inclusion complexes with all the CDs. The low binding constants as well as the thermodynamic parameters indicate that the mode of interaction between QZ and CDs is mainly hydrophobic in nature. The relative magnitudes of the binding constants and the differential enhancements in the fluorescence intensity of QZ upon complexation with the CDs can be explained by considering the relative dimensions of the host cavity and the guest molecule, as well as the orientation of the guest molecule inside the CD cavity. It is proposed that the unsubstituted benzene ring of QZ is encapsulated within alpha- and beta-CD cavities whereas the dihydroxy-substituted aromatic ring is encapsulated within the gamma-CD cavity. This is further supported by the complexation studies of the QZ.CD systems with Al(III) ions. It is observed that the complexation of QZ with the metal ion is enhanced in the QZ.alpha-CD and QZ.beta-CD systems whereas it is significantly reduced in the QZ.gamma-CD system, due to shielding of the chelating groups of the dye inside the CD cavity in the latter case.
Photochemical & Photobiological Sciences, 2005
The photophysical properties of 2-amino-9,10-anthraquinone (2AAQ) have been investigated in diffe... more The photophysical properties of 2-amino-9,10-anthraquinone (2AAQ) have been investigated in different solvents and solvent mixtures and correlated with the Lippert-Mataga solvent polarity parameter, Deltaf. In the low solvent polarity region with Deltaf < ca. 0.1, the dye shows unusually high fluorescence quantum yields (Phif) and lifetimes (tauf) in comparison to those in other solvents of medium to high polarities. Similarly, the radiative rate constants (kf) are relatively lower and the non-radiative rate constants (knr) are relatively higher in the low polarity solvents in comparison to those in the medium to high polarity solvents. The current results have been rationalized assuming that the dye adopts different structural forms below and above the Deltaf value of approximately 0.1. It is inferred that in the low solvent polarity region the dye exists in a non-planar structure, with its 2-NH2 plane away from that of the 9,10-anthraquinone moiety in the ground state. In solvents of medium to high polarities, the dye exists in a polar intramolecular charge transfer (ICT) structure, where the amino lone pair of the 2-NH2 group is in strong resonance with the anthraquinone pi-cloud in the ground state. In all the solvents, however the dye is inferred to exist in the ICT structure in its excited (S1) state. Supportive evidence for the above hypothesis has been obtained from the solvent polarity effect on the Stokes' shifts for the dye. Quantum chemical studies on the structures of 2AAQ dye in the gas phase also give qualitative support for the inferences drawn from the photophysical properties of the dye in different solvents.
Optical Materials, 2004
ABSTRACT
Journal of Photochemistry and Photobiology A: Chemistry, 2008
... Keywords: Micellar electron transfer; Triton-X-100; Brij-35; Cetyltrimethylammonium bromide; ... more ... Keywords: Micellar electron transfer; Triton-X-100; Brij-35; Cetyltrimethylammonium bromide; Marcus inversion; Quinone. Article Outline. 1. Introduction 2. Experimental 3. Results and discussion 4. Conclusions Acknowledgements References. 1. Introduction. ...