Cyclometalated Ir(iii) complexes [Ir(tpy)(bbibH2)Cl][PF6] and [Ir(tpy)(bmbib)Cl][PF6]: intramolecular π⋯π interactions leading to facile synthesis and enhanced luminescence

Abstract

Cyclometalated Ir(III) complexes [Ir(tpy)(bbibH₂)Cl][PF₆] (1·PF₆) and [Ir(tpy)(bmbib)Cl][PF₆] (2·PF₆), and the control complex [Ir(tpy)(mbib)Cl][PF₆] (3·PF₆) were synthesized at 135 °C for 10 hours for the former two complexes, while at 190 °C for 24 hours for the latter complex, in which the cyclometalated ligands bbibH₂⁻, bmbib⁻ and mbib⁻ incorporate one or two N-methylbenzoimidazole/benzimidazole units in order to explore the influence of the molecular structures of these complexes on their synthesis conditions and luminescence behaviors. The ¹H NMR and crystal structure measurements indicate that both 1·PF₆ and 2·PF₆ contain intramolecular π⋯π stacking interactions between the non-coordinated N-methylbenzoimidazole/benzimidazole unit and the tpy ligand, but there are no such π⋯π interactions in 3·PF₆. At room temperature, these complexes in CH₃CN reveal an emission with a combination of ³MLCT and ³LC characteristics, occurring at 534 nm with a quantum yield Φ = 39.5% and a lifetime τ = 2.39 μs for 1·PF₆, 536 nm with Φ = 66.4% and τ = 2.94 μs for 2·PF₆, and 558 nm with Φ = 27.0% and τ = 1.75 μs for 3·PF₆. Moreover, both 1·PF₆ and 2·PF₆ exhibit a TFA-induced luminescence decrease. Based on the comparison among 1·PF₆, 2·PF₆ and 3·PF₆, we discuss the influence of intramolecular π⋯π interactions and N_imidazole–H/N_imidazole–CH₃ units in 1·PF₆ and 2·PF₆ on their syntheses and luminescence.