Eu3+ as a dual probe for the determination of IL anion donor power: A combined luminescence spectroscopic and electrochemical approach

This work is aimed at giving proof that Eu(Tf2N)3 (Tf2N=bis(trifluoromethanesulfonyl)amide) can act as both an optical and electrochemical probe for the determination of the Lewis acidity of an ionic liquid anion. For that reason the luminescence spectra and cyclic voltammograms of dilute solutions of Eu(Tf2N)3 in various ionic liquids were investigated. The Eu2+/3+ redox potential in the investigated ILs can be related to the Lewis basicity of the IL anion. The IL cation had little influence. The lower the determined halfwave potential, the higher the IL anion basicity. The obtained ranking can be confirmed by luminescence spectroscopy where a bathochromic shift of the 5D0→7F4 transition indicates a stronger Lewis basicity of the IL anion. [Display omitted] •Determination of IL anion Lewis basicity independent from the anion•Eu(Tf2N)3 serves as a dual probe.•Determination of Lewis basicity by photoluminescence possible•Determination of Lewis basicity by cyclic voltammetry possible•Same ranking of anion obtained for the two methods