Abstract
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•The luminescence quenching of Ru(II)-diimine complexes by Cr(VI) ion in acidic aqueous media was investigated by applying steady-state and time-resolved measurements.•The experimental results show an upward curvature dependency to Stern–Volmer (S–V) equations.•Stern–Volmer quenching rate constants for the dynamic process (KD) and the bimolecular quenching rate constants (kq) are calculated by applying the Stern–Volmer equation to the luminescence decay data.•The analysis of the experimental data using ground-state complex formation and the sphere of action models emphasizes the presence of a static quenching insignificant in comparison with the dynamic one.
Luminescence quenching of [Ru(bpy)(CN)4]2−, [Ru(phen)(CN)4]2−, [Ru(bpy)3]2+ and [Ru(phen)3]2+ by hexavalent chromium ion in aqueous media were investigated by steady-state and time-resolved measurements. Effect of pH on the luminescence quenching process is also investigated. It has been found that luminescence changes due to the interaction of all Ru(II) complexes with Cr(VI) ions were high at pH values less than or equal to 5.0 and negligible at pH ≥ 8.0. The experimental data of the quenching process were analyzed using Stern–Volmer (S–V) equations. The steady state luminescence emission data shows an upward curvature, indicating that the quenching is preceded by both dynamic and static quenching. For all studied complexes, the lifetime of the excited 3MLCT state decreases with increasing Cr(VI) concentration implying that the diffusion is mainly responsible for the quenching process. The Stern–Volmer dynamic quenching constants (KD) and the bimolecular quenching rate constant for the quenching process (kq) were calculated by applying the Stern–Volmer equation to the luminescence decay data. The bimolecular quenching rate constants (Kq) were found to increase in the order [Ru(bpy)(CN)4]2− < [Ru(phen)(CN)4]2− < [Ru(phen)3]2+ < [Ru(bpy)3]2+ which correlates will with the oxidation potentials of Ru(II) complexes. The association constants for Ru(II)-Cr(VI) system were calculated using the Benesi-Hildebrand equation and found to be 3.0 × 103, 2.5 × 103, 1.2 × 103, 7.1 × 103 M−1 for [Ru(bpy)(CN)4]2−, [Ru(phen)(CN)4]2−, [Ru(bpy)3]2+ and [Ru(phen)3]2+ respectively, which is interpreted in terms of the dynamic (diffusion) and the sphere of action (static) quenching models.