FLUORESCENCE QUENCHING OF BENZIMIDAZOLES BY CHLORINATED METHANES

Fluorescence quenching of benzimidazole (BI), 2-methylbenzimidazole (MBI) 5, 6-dimethylbenzimidazole (DMBI), 1-ethyl-2-methyl-benzimidazole (EMBI), 2, 5, 6-trimethylbenzimidazole (TMBI), 2-phenylbenzimidazole (PBI) and 1-ethyl-2-phenylbenzimidazole (EPBI) by CH2Cl2, CHCl3 and CCl4 have been studied in cyclohexane, methanol and acetonitrile and the values of k(q) have been determined. Correlation of log k(q) versus electron affinity (EA) of the quencher clearly indicates that deactivation of the excited state of BI's by above quenchers proceeds through the formation of charge transfer type complex. The high value of k(q) in more polar acetonitrile as compared to that in non-polar cyclohexane could be due to the stability of charge transfer complex in acetonitrile as compared to that in cyclohexane. The static quenching component can be described by the sphere of action model with a radius of 1 nm for BI and TMBI. The quenchig efficiencies of CCl4 is nearly unity, 0.36 to 10(-2) for CHCl3 and 10(-3) to 10(-2) for CH2Cl2 respectively.