Cyclometalated Ir(iii) complexes [Ir(tpy)(bbibH2)Cl][PF6] and [Ir(tpy)(bmbib)Cl][PF6]: intramolecular ππ 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 ππ stacking interactions between the non-coordinated N-methylbenzoimidazole/benzimidazole unit and the tpy ligand, but there are no such ππ 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 ππ interactions and Nimidazole-H/Nimidazole-CH3 units in 1·PF6 and 2·PF6 on their syntheses and luminescence.