Ruthenium(II) complex-based chemosensors for highly sensitive and selective sequential recognition of copper ion and cyanide

Abstract Two new ruthenium(II) complexes of [Ru(bpy) 2 (L 1 )](ClO 4 ) 2 ( RuL 1 ) and [Ru 2 (bpy) 4 (L 2 )](ClO 4 ) 4 ( RuL 2 ) {bpy = 2,2′-bipyridine, L 1  = 4-hydroxy-3-(1 H -imidazo[4,5- f ][1,10]phenanthrolin-2-yl)benzaldehyde and L 2  = 2,4-bis(1 H -imidazo[4,5- f ][1,10]phenanthrolin-2-yl)phenol} were synthesized and characterized using IR, 1 H NMR, 13 C NMR, ESI–MS, and elementary analysis. The uncoordinated 2-hydroxyphenyl imidazo moiety in RuL 1 and RuL 2 could specifically bind with Cu 2+ , leading to luminescence quenching of the two sensor instantaneously in aqueous buffered solution (20 mM HEPES, pH = 7.2) containing 1% (v/v) CH 3 CN. The forming RuL 1 –Cu 2+ and RuL 2 –Cu 2+ ensembles could sensitively and selectively detect a low concentration of cyanide ions in 99% aqueous solutions by a “turn-on” fluorescent response. The detection limits for cyanide ions (0.36 μM for RuL 1 –Cu 2+ and 0.87 μM for RuL 2 –Cu 2+ ) were lower than World Health Organization guideline value for a maximum allowable concentration of 1.90 μM in drinking water. The 2-hydroxyphenyl imidazo appended ruthenium complex-based ensemble systems were expected to be a potential and efficient way for the detection of submicromolar concentrations of cyanide ions in nearly 100% aqueous solutions.