Asymmetric bimetallic ruthenium(II) complexes selectively sense cyanide in water through significant modulation of their ground and excited state properties

Abstract

This paper deals with anion recognition and sensing aspects of a new family of asymmetric bimetallic Ru(II) complexes derived from a heteroditopic bridging ligand (tpy-Hbzim-dipy) consisting of both bipyridine and terpyridine chelating sites covalently connected via phenyl-imidazole spacer. The recognition event was visualized in both organic as well as aqueous medium through different optical channels and spectroscopic techniques by taking profit of metal ligand interaction in the complexes. Absorption, and both steady state and time-resolved emission spectroscopic measurements were carried out as a function of pH in order to determine the ground- and excited state pKa values of the complexes. The complexes act as sensors for F−, CN−, AcO−, S2−, H2PO4− and P2O74− in acetonitrile without much selectivity. By contrast, the selectivity increased to a great extent in aqueous medium and all the four complexes act as chromogenic and fluorogenic sensors CN−, S2−, and P2O74−. Equilibrium/binding constants of the interaction process and detection limits of the complexes towards selected anions were determined from UV–vis absorption and luminescence titration profiles and the values were found to lie in order of 106M−1 and 10−9M, respectively. In addition to the steady state luminescence spectral changes, the excited-state lifetimes of the complexes were also modulated to a great extent by the selected anions which can lead to the utility of the complexes as suitable lifetime-based sensors for selected anions. Finally, test strips were also fabricated based on the metalloreceptors for their probable use as efficient test kits to detect CN−, S2−, and P2O74− in pure water for field measurements that do not require any equipment.