• M Sarkar

      Articles written in Journal of Chemical Sciences

    • Resonance Raman studies of tetraphenylporphinato manganese(III) chloride

      M Sarkar A L Verma

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      Resonance Raman spectra of Mn(III)TPPCl in different solvents as well as in KBr pellets have been obtained with laser excitations in different regions of the atypical absorption spectrum of the system. The selective enhancement of vibrational modes arising from different parts of the molecule under excitation in different absorption regions has been used to assign the electronic transitions of Mn(III)TPPCl. The strong absorption band at ∼ 476 nm originates from a charge transfer transition porphyrin and metal orbitals, while a weaker band at ∼ 530 nm has been identified due to singlet-triplet (π, π*) transitions. The present data do not provide distinct evidence for activation of the phenyl group modes under resonance Raman conditions indicating thereby that the phenyl groups may not be conjugated with the porphyrin macrocycle. Depolarization ratios for some isolated bands show dispersion with excitation wavelengths due to reduction of the chromophore symmetry.

    • Synthesis, photophysical and metal ion signalling behaviour of mono- and di-azacrown derivatives of 4-aminophthalimide

      N B Sankaran M Sarkar A Samanta

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      Synthesis, photophysical behaviour and metal ion signalling ability of 3-component systems, I and II, comprising a 4-aminophthalimido moiety as fluorophore, a dimethylene spacer and two different azacrown receptors, are reported. The fluorescence quantum yields and lifetimes of both the systems have been found to be significantly lower than that of the parent fluorophore indicating the occurrence of photoinduced electron transfer (PET) between the terminal moieties. PET is found to be more efficient in II, presumably due to the presence of more than one electron-donating centre in the receptor moiety. Fluorescence decay behaviour of the systems suggests a through-space nature of PET. The systems exhibit off-on fluorescence signalling in the aprotic media in the presence of several metal ions, some of which are well known for their fluorescence quenching abilities. Diazacrown derivative, II, appears to be a somewhat better signalling system than the monoazacrown derivative, I.

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