Structural and spectroscopic studies on Pt•••Pt and π-π interactions in luminescent multinuclear cyclometalated platinum(II) homologues tethered by oligophosphine auxiliaries

The synthesis and structural, spectroscopic, and electrochemical properties of a series of trinuclear tridentate cyclometalated platinum(II) complexes tethered by bis(diphenylphosphinomethyl)phenylphosphine (dpmp) have been studied and compared with their mono- and binuclear homologues and a propeller-like congener. The X-ray crystal structures of several derivatives show the presence of a variety of intramolecular (PtPt)-Pt-..., pi-pi, and C-(HO)-O-...(crown ether) and intermolecular pi-pi interactions. The trinuclear complexes display strong absorption in the 400-600 nm region and show intense red to near-infrared phosphorescence with microsecond lifetimes in fluid and glassy solutions and in the solid state. These emissions are generally assigned as (MMLCT)-M-3 [dsigma*-->pi*(Cboolean ANDNboolean ANDN)] in nature. The close similarities between the emission energies in acetonitrile solution and in the solid state at 298 K indicate that comparable (PtPt)-Pt-... and pi-pi configurations are maintained in both media, and hence a relationship between the photophysical behavior of these lumophores and their solid-state structural features is proposed. The tendencies of the absorption and emission energies to red-shift from mono- to linearly tethered bi- and trinuclear Pt(II) species are evident. A light-emitting electrochemical cell using a trinuclear Pt(II) derivative as emitter has been demonstrated.