Diphosphine Bridge Control of Intramolecular Pt···Pt Association in Dinuclear Pt(II) Complexes with a Dimetalated N(∧)C(∧)C Ligand.

Dinuclear platinum(II) complexes capable of establishing reversible metal-metal interactions constitute attractive platforms for stimuli-responsive luminescent systems. Here, we report a family of diphosphine-bridged complexes of general formula [{Pt(dmtppy)}(μ-PP)] incorporating a dimetalated NCC ligand derived from 2-(4,4″-dimethyl-[1,1':3',1″-terphenyl]-5'-yl)pyridine, which enables systematic investigation of intramolecular Pt···Pt association. Structural studies reveal that the dppm-bridged derivative dppm = bis(diphenylphosphinomethane) adopts a stacked conformation featuring a Pt···Pt interaction in solution and in the solid state. In contrast, complexes containing longer diphosphine bridges do not exhibit metallophilic contacts. NMR and electronic spectroscopic studies demonstrate that the dppm complex establishes in solution a solvent- and temperature-dependent equilibrium between open and closed conformations. These conformers give rise to distinct emissive excited states, namely, a structured ILCT/MLCT emission associated with the open form and a lower-energy MMLCT emission arising from the Pt···Pt-associated species. The interconversion between both structures leads to dual emissions whose relative contributions can be tuned by solvent and temperature. In contrast, complexes containing longer diphosphine bridges display emissions localized on the individual {Pt(dmtppy)} fragments, with solution quantum yields influenced by linker length and flexibility. These results provide clear spectroscopic evidence for reversible intramolecular metallophilic association and highlight diphosphine-bridged architectures as promising platforms for responsive Pt(II) emitters.