Synthesis, characterization, and photophysical properties of novel orthometallated platinum phosphine complexes

Photophysical behaviors of novel orthometallated platinum(II) bisphosphine complexes have been investigated. This study reports sixteen novel square-planar Pt(II) complexes of the following types: (i) Pt(P^P) (NO₃)₂; (ii) Pt(P^P)(NO₃)(CI); and (iii) [Pt(P^P)(aromatic ligand)] (PF₆)_m, (P^P = bisphosphine). The aromatic ligands consisted of two types; the (N^C) type; e.g. 2-phenylpyridine, and the a- diimmine (N^N) type; e.g. 2,2'-bipyridine. The bisphosphine ligands used were bis(diphenylphosphino)methane, dppm; 1,2-bis(diphenylphosphino)ethane, dppe; and 1,3-bis(diphenylphosphino)propane, dppp, which respectively gave four-, five-, and six-membered Pt-bisphosphine-containing rings. These complexes were synthesized by a novel method which gave high yields. Trends among the set of ³¹P NMR spectral data for these compounds were discussed. Crystal structures of five compounds in this study have been obtained and their structural features discussed.

The photophysical properties of these compounds have been measured by three methods: (i) Ultraviolet-Visible Absorption spectroscopy; (ii) Emission spectroscopy; and (iii) Emission lifetime with respect to temperature. For compounds containing an aromatic ligand, the absorption and emission spectral properties, and the emission lifetimes, were dependent on the complexed aromatic ligand. Relative to the free ligand, the absorption spectra of the complexes exhibited a new low energy ¹MLCT band. The emission bands of these compounds resulted from one emitting state and have varying amounts of ¹MLCT and ³MLCT character. The emission energy was independent of the bisphosphine present.

The dependency of the emission lifetime at 77 K on both the bisphosphine and the aromatic ligand was attributed to variations in the bonding interactions between the Pt(P^P)²⁺ core and the aromatic ligand. The lifetime and temperature data was successfully modelled to yield activation energy and pre-exponential factors for the deactivation process of the excited state.

The ligand (Diphenylarsino)(diphenylphosphino)methane, dapm, was used to prepare nine new compounds. A reaction sequence was proposed for eight of these new compounds based on their ³¹P{¹H} NMR data and the crystal structure data of Pt(dapm-P)(2-(para-tolyl)pyridine-N,C)Cl.