Ruthenium complex of bis(benzimidazole-yl ethyl)sulfide as chemo-sensor for the selective recognition of chloride ion, and its application in real bacterial samples

Abstract A ruthenium complex of bis(benzimidazole-ylethyl)sulfide (L1) was synthesized, and characterized completely by different analytical techniques. The recognition of chloride by the complex in CH3OH:H2O (3:1, v/v) was studied by the following studies like anion binding tests, interference and titration analyses; the fluorescence results reveal that the ruthenium complex detects selectively chloride ion without any interference from other anions (F-, Br-, I, NO3-, HSO4-, H2PO4-), performing as switch-ON mode, and the stoichiometry ratio of the Ru-complex with chloride was 1:1. This suggests that the interaction of Cl− with the receptor complex would be unfavored the Photo Electron Transfer (PET) in the excited state, and it facilitates the electron transfer from HOMO (donor) to low-lying HOMO of the acceptor (fluorophore) increasing the fluorescence intensity. This is consistent with the energy level of the system [ruthenium complex with chloride] which has been lowered to -9.776 eV from -4.060 eV, preventing the electron transfer effectively and it enhances the emission intensity. Interestingly, although bacterial cell growth was significantly inhibited in the presence of the complex, it further decreased by the sensing of chloride by the complex.