Fluorescence quenching of benzimidazoles by chlorinated methanes

Abstract

Fluorescence quenching of benzimidazole (BI), 2-methylbenzimidazole (MBI), 5, 6- dimethyl-benzimidazole (DMBI), 1-ethyl-2-methyl-benzimidazole (EMBI), 2, 5, 6-trimethylbenzimidazole (TMBI),2-phenylbenzimidazole (PBI) and 1-ethyl-2-phenylbenzimidazole (EPBI) by CH₂CI₂, CHCI₃ and CCI₄ have been studied in cyclohexane, methanol and acetonitrile and the values of <em>k</em>_q have been determined. Correlation of log <em>k</em>_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 <em>k</em>_q in more polar acetonitrile as compared to that in non-polar cyclohexane. The static quenching can be described by the sphere of action model with a radius of 1nm for BI and TMBI. The quenching efficiency of CCl₄ is nearly unity, 0.36 to 10^-2 for CHCl₃ and 10^-3 to 10^-2 for CH₂Cl₂ respectively.