Heteroleptic Ir(iii) and Pt(ii) complexes based on 2-(2,4-difluorophenyl)-pyridine and bisthienylethene BrLH: the influence of the metal center on structures, luminescence and photochromism

Abstract

Heteroleptic complexes [Ir(dfppy)₂(BrL)]·3CH₃OH (1) and [Pt(dfppy)(BrL)]·CH₃OH (2) have been prepared based on the same ligands including bisthienylethene BrLH and dfppyH = (2-(2,4-difluorophenyl)-pyridine). Complexes 1 and 2 reveal distinct crystal structures. The BrL⁻ anion uses its phenol-imidazole moiety to coordinate with an {Ir(dfppy)₂}⁺ unit in the former, while with a {Pt(dfppy)}⁺ unit in the latter. Neighboring [Ir(dfppy)₂(BrL)]/[Pt(dfppy)(BrL)] molecules are connected through extensive hydrogen bonds and aromatic stacking interactions, thus forming a supramolecular chain structure in 1, and a layer structure in 2. Upon irradiation with 380 nm light, compound 2 shows photochromic behavior in CH₂Cl₂, with a color change from nearly colorless to light green. However, no photochromism was observed in compound 1. At room temperature, compound 1 reveals phosphorescence with a predominant ³MLCT character both in CH₂Cl₂ solution (emissions at 495 and 513 nm) and in the solid state (emission at 524 nm). Compound 2 exhibits phosphorescence with a predominant ³LC character in CH₂Cl₂ solution (emission at 508 nm), but it is almost non-luminescent in the solid state. Our experimental results demonstrate that the metal centers in 1 and 2 could significantly influence their structures, photochromism, and luminescence behaviors.