Binuclear Pt(II) Complexes with N̂ĈN Ligands: Synthesis, Photophysical Properties, and Vapochromic Responses

This article presents the synthesis of four dinuclear Pt(II) complexes, 1a, 1b, 2a, and 2b, utilizing PtLn-Cl as the starting materials, where Ln represents an N̂ĈN coordinating ligand. The ligand L1 features a 1,3-disubstituted phenyl ring and two nitrogen heterocycles, whereas L2 replaces the nitrogen heterocycles with isoquinoline. Auxiliary ligands A1 (N,N′-diphenylformamidine) and A2 (9H-pyrido[2,3-b]indole) contribute to the formation of these complexes, which exhibit red phosphorescence. Characterization of all four complexes was conducted by using nuclear magnetic resonance (NMR), high-resolution mass spectrometry (HRMS), and single-crystal X-ray diffraction (SCXRD). The crystallographic data reveal intricate bilayer structures with Pt–Pt distances of 3.055 Å, 3.054 Å, 2.988 Å, and 3.150 Å for complexes 1a′, 1b, 2a′, and 2b, respectively. Complexes 2a and 2b showcase near-infrared (near-IR) emission across solid, liquid, and PMMA film states. Notably, complex 1a exhibits the highest photoluminescence quantum yield (PLQY) of 73.2% and an emission lifetime of 3.1 μs when doped into a 1 wt % PMMA film. Due to its favorable photophysical properties, complex 1a was applied to quartz plates for the detection of organic solvent vapors, demonstrating distinct emission quenching in response to formic and acetic acid vapors.