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
Pt···Pt, π−π, and C−H···O(crown ether) and intermolecular π−π 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 3MMLCT [dσ*→π*(C∧N∧N)] in nature. The close similarities between the emission energies in
acetonitrile solution and in the solid state at 298 K indicate that comparable Pt···Pt and π−π 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.