K.K. Rohatgi-Mukherjee

Solvent effect on photophysics of the molecular forms of rhodamine B. Solvation models and spectroscopic parameters

Abstract Photophysics and spectral characteristics of the zwitterionic and cationic forms of rhodamine B have been studied in a number of protic and aprotic solvents with different solvation properties. The results have been discussed on the basis of the molecular structures of the dye, role of carboxyphenyl group and specific solute-solvent interactions.

Solvent effects on the photophysics of the molecular forms of rhodamine B. Internal conversion mechanism

Abstract The fluorescence characteristics, φ f and τ f , for two molecular forms of rhodamine B, RB ± and RBH + , have been measured in a number of solvents selected for their hydrogen donor and/or acceptor properties, dielectric constant, viscosity, etc. The activation energies E a calculated from the temperature dependence of φ f are also solvent dependent. The results do not agree with the internal conversion mechanism suggested by Drexhage based on rotational motion of the diethylamino group. No single mechanism seems to be valid for both molecular forms. Two likely mechanisms are suggested.

Anthracene sulphonate sensitized photooxidation of iodide ion in aqueous solution via singlet oxygen

Abstract The participation of I O 2 in the photosensitized oxidation of 1 − by 1-, 2-, and 1,5-anthracene (A)sulphonates is established by the use of N − 3 as the quencher of the photoreaction. The reaction follows two pathways (i) formation of AO 2 which oxidizes 1 − and (ii) formation of an IO − 2 charge-transfer complex leading to oxidation.

Photogeneration of long-lived porphyrin cation by interaction between (meso-tetrakis (4-carboxyphenyl) porphyrin and poly (N-vinyl-2-pyrrolidone): a spectral and flash-kinetic study

Abstract Laboratory-synthesized meso-tetrakis (4-carboxyphenyl)porphyrin (TPPC) binds with the water-soluble polymer poly (N-vinyl-2-pyrrolidone) (PVP) at pH 10, with a binding constant K = 3.7 × 10 6 M −1 . The fluorescence lifetime of TPPC becomes biexponential in the polymer matrix. Generation of a radical-ion pair on photoexcitation has been established from flash-photolytic studies where the polymer acts as an electron acceptor. The growth rate of the radical-ion pair agrees with the decay rate of TPPC triplets.

Spectroscopy of Ni(II) and Zn(II) tetra(p-vinylphenyl) porphyrin: Aggregation characteristics and luminescence properties

Abstract Concentration effects on the absorption and emission properties of Ni(II) and Zn(II) tetra( p -vinylphenyl) porphyrins have been studied in benzene solutions. Whereas exciton splitting of the Soret band is observed for the Ni(II) complex, only a hypochromic effect is observed for the Zn(II) complex. The exciton parameters calculated for the Ni(II) complex are: U = 710 ± 40 cm −1 , θ = 78 ± 2° and R = 4.5 ± 0.3 A. Fluorescence is observed only for the Zn(II) complex. The 77 K spectrum is red shifted compared with the room temperature spectrum.

Study of exciton interaction and the nature of bonding in the aggregation of phenosafranine from concentration-dependent spectral changes

Abstract The formation constants and absorption spectra of the dimer and trimer of phenosafranine in aqueous solution are evaluated. The geometric structure of the monomers in the aggregates are studied by means of exciton theory. The nature of the association forces is also discussed.

Spectral and flash kinetic studies of water-soluble zinc porphyrins in poly-N-vinyl-2-pyrrolidone matrix

Abstract A series of water-soluble zinc porphyrins, ZnTPPS, ZnTPPC and ZnTPPOH, have been synthesized. Their absorption, emission, singlet and triplet state quenching by electron acceptors like MV2+ and 1,5-AQDS2− have been studied in homogeneous aqueous solutions and bound to a PVP matrix. Binding constants for the systems under study do not vary much and give a low value for ΔG0 = −13.37 kJ M−1. However, the number of monomer units required for binding any individual porphyrin species varies with the size of the molecule. It appears that these water-soluble porphyrins are embedded in hydrophobic pockets in the polymer matrix and are only partially available to outside quenchers like MV2+ and 1,5-AQDS2−. From flash photolysis studies, formation of porphyrin radical cations and quencher anions is observed. Porphyrin cations are long-lived and are also formed on self-quenching and by disproportionation reactions in the absence of quencher. ZnTPPOH behaves differently.

Detection of Hidden 1Lb - 1A1 Transition of Anthracene Disulphonates in Glycerol Glass at 77K by Photoselection Technique

Abstract Attempts are made to detect the weakly absorbing 1Lb bands in anthracene 1,5- and 1,8-disulphonates in glycerol glass by the method of photoselection. The fluorescence and absorption (excitation) spectra are separated into two component spectra based on short and long axis polarized transition dipoles and their vibrational analysis are made. The vibrational bands around 29762 cm−1 in 1,5-AS and 30303 cm−1 in 1,8-AS in absorption spectra are mainly due to 1Lb band.