Design and development of novel Ru(II)-quinoline complex for copper(II) ion detection

The need for rapid, selective, and ultra-sensitive detection of metal-ion has driven extensive research into chemosensor design. Ruthenium(II) complexes, with their unique luminescence, redox activity, and photostability, have become attractive candidates for ion sensing. Quinoline-based ligands, when incorporated into ruthenium(II) frameworks, can provide a rigid coordination environment with extended π-conjugation which enhances the sensing performance. The current investigation concentrates on the design and synthesis of a novel [Ru(pqyCOOH)3]2+ ((pqyCOOH) = 2-(pyridine-2-yl)-quinoline-4-carboxylic acid) complex for a selective luminescent sensor for Cu2+ ions. The [Ru(pqyCOOH)3]2+ complex is characterized using UV-Visible, emission, FTIR, 1H NMR, 13C NMR and MALDI-TOF mass spectral techniques. The UV-Visible titration of the complex with Cu2+ ions displays a notable colour change forming a stable 1:1 Ru(II)-quinoline-Cu2+ adduct with a binding constant of 4.8× 105 M-1. Benesi-Hildebrand plot reveals a linear response, with the detection limit of 1.5×10-5 M. Selectivity tests demonstrate minimal interference from other metal ions such as Ba2+, Li+, Fe3+, Mg2+, Cd2+, Zn2+, Co2+, Ni2+ and Zr2+, confirming the probes specificity for Cu2+. This work expands the scope of Ru(II) based luminescent chemosensors and highlights the synergistic advantage of integrating quinoline ligands with Ru(II) centers for copper detection.