INORGANIC ANION-INDUCED FLUORESCENCE QUENCHING OF A FEW BENZIMIDAZOLES AND THEIR MONOCATIONS

Fluorescence quenching of seven benzimidazoles and their monocations by inorganic anions in 1-2% methanol/H2O mixtures, has been studied. The quenching efficiency can be correlated linearly with the oxidation potentials of the anions. Results have indicated that quenching cannot be explained purely by the electron transfer mechanism. The non-fluorescent collision complex formed between the quencher and the excited state fluorophore may decay either to the triplet state or to the ground state depending on the values of the respective rate constants. Higher values Of k(q) for the fluorescence quenching of cations are due to the presence of coulombic interactions. The static quenching component can be explained with the help of a sphere of action model and the radius of the sphere of action varies from molecule to molecule.