Two bisthienylethene–Ir(iii) complexes showing acid/base-induced structural transformation and on–off luminescence switching in solution

Abstract

Complexes [Ir(dfppy)₂(pbdtiH)](PF₆)·2CHCl₃ (1-H) and [Ir(dfppy)₂(pbdti)] (1) were synthesized by the reaction of bisthienylethene pbdtiH and an [Ir(dfppy)₂Cl]₂ dimer under neutral and basic conditions, respectively. Thus, the {Ir(dfppy)₂}⁺ unit is coordinated by pbdtiH in 1-H, and by pbdti⁻ in 1, which are confirmed by their crystal structures. The structures of 1-H and 1 could be interconverted in solution, upon alternately adding NEt₃ and TFA, thus resulting in reversible luminescence switching between the on-state of 1-H and the off-state of 1 at room temperature. In addition, both 1-H and 1 show solid-state luminescence, with a broad emission at 534 nm and 525 nm, respectively. The free pbdtiH ligand shows photochromic behavior in CH₂Cl₂ solution. However, no photochromism has been observed in 1-H and 1, indicating that the coordination of the pbdtiH/pbdti⁻ ligand to the {Ir(dfppy)₂}⁺ unit could suppress their photochromic behaviors.