Co-reactant and Annihilation Electrogenerated Chemiluminescence of [Ir(df-ppy)2(ptb)]⁺ Derivatives

© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim The [Ir(df-ppy)2(ptb)]+ complex (where df-ppy=2-(2,4-difluorophenyl)pyridine anion; ptb=1-benzyl-1,2,3-triazol-4-ylpyridine) has previously been shown to be a promising blue luminophore for electrogenerated chemiluminescence (ECL). Herein, we examine the ECL of three [Ir(df-ppy)2(ptb)]+ derivatives (containing df(CF3)-ppy-Me, df(CN)-ppy, or df-ppy-CF3 ligands) in comparison with the parent complex. In the annihilation mode, all four complexes exhibited ECL, although the emission from [Ir(df(CN)-ppy)2(ptb)]+ was weak and red-shifted from its photoluminescence. The absence of this shift in the corresponding reductive-oxidation co-reactant ECL with benzoyl peroxide (BPO), and the very low ECL intensity in oxidative–reductive co-reactant ECL with tri-n-propylamine (TPrA) enables this effect to be ascribed to oxidative degradation. The [Ir(df-ppy-CF3)2(ptb)]+ complex gave the greatest ECL intensities of the four [Ir C^N2(ptb)]+ complexes in the annihilation mode and through both co-reactant pathways, and shows great potential as a blue electrochemiluminophore. In “mixed annihilation” ECL experiments involving the oxidation of Ir(ppy)3 and the reduction of the [Ir (C^N)2(ptb)]+ complexes, only [Ir(df-ppy)2(ptb)]+ and [Ir(df(CF3)-ppy-Me)2(ptb)]+ elicited the green ECL from Ir(ppy)3*, as the electron-withdrawing substituents on the other two complexes lower the SOMO energy of the reduced complexes below that required to attain the Ir(ppy)3* excited state upon reaction with [Ir(ppy)3]+.