Platinum(ii) 1,10-phenanthroline complexes of acetylides containing redox-active groups

Abstract

The new diimine ligand 3,8-di-n-pentyl-4,7-di(phenylethynyl)-1,10-phenanthroline (1) was used for the synthesis of a range of Pt^II complexes, viz. [Pt(1)Cl₂], [Pt(1)(CC–Ph)₂], [Pt(1)(CC–Fc)₂] and [Pt(1)(CC–p-C₆H₄–CC–Fc)₂] (Fc = ferrocenyl). Crystal structure analyses were performed for [Pt(1)Cl₂] and [Pt(1)(CC–Ph)₂] and revealed that the di(acetylide) π-tweezer of the latter binds a molecule of chloroform through C–H⋯π hydrogen bonds. The redox and optical properties of 1 and its complexes were investigated by (spectro-)electrochemistry, UV–Vis and luminescence spectroscopy, and an energy level diagram was derived for [Pt(1)(CC–Fc)₂] and related compounds on the basis of the data collected. The ferrocenyl-substituted Pt^II complexes are donor–sensitiser assemblies. Intramolecular quenching of the photoexcited Pt^II diimine unit leads to very short luminescence lifetimes for [Pt(1)(CC–p-C₆H₄–CC–Fc)₂] (2 ns) and [Pt(1)(CC–Fc)₂] (0.3 ns), as opposed to [Pt(1)(CC–Ph)₂] (0.7 µs). Excimer formation has been observed for [Pt(1)(CC–Ph)₂] at room temperature in dichloromethane and at low temperatures in frozen glassy dichloromethane and 2-methyltetrahydrofuran solution, but not in the solid state.