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

This article presents the synthesis of four dinuclear Pt(II) complexes, <b>1a, 1b, 2a,</b> and <b>2b</b>, 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 (<i>N</i>,<i>N</i>′-diphenylformamidine) and A2 (9<i>H</i>-pyrido[2,3-<i>b</i>]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 <b>1a′</b>, <b>1b</b>, <b>2a′</b>, and <b>2b</b>, respectively. Complexes <b>2a</b> and <b>2b</b> showcase near-infrared (near-IR) emission across solid, liquid, and PMMA film states. Notably, complex <b>1a</b> 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 <b>1a</b> was applied to quartz plates for the detection of organic solvent vapors, demonstrating distinct emission quenching in response to formic and acetic acid vapors.