Influence of acidity on the fluorescence spectra of 2-pyridylbenzimidazoles in aqueous solution

摘要: The fluorescence spectra of 2-(3-pyridyl)benzimidazole (3PBI) and the quaternary salt 2-(1-methyl-4-pyridinio)-benzimidazole iodide (4PBIQS) in aqueous solutions covering a wide range acidities have been studied to investigate their photophysical behaviour acid–base processes occurring first excited singlet states these species. Depending on acidity, 3PBI exists state as dication, monocation protonated at benzimidazole N(3) atom (C*), neutral species anion. Of all possible interconversion among species, only protonation C* is fast enough compete with its deactivation. 4PBIQS too has same ground states: dication D*, positive charge pyridyl nitrogen (T*) zwitterion Z*. Deprotonation T* deprotonation by dihydrogen phosphate anion were detected. thus allow separate study properties two 2-pyridylbenzimidazole monocations, T*, no interference between two.