Luminescent Binuclear Pd (II) N^C^N-Pincer Complexes With N^N Bridging Ligand

Two novel binuclear cyclometalated Pd (II) complexes with two tridentate phenylpyridine ligands and a N^N ligand were readily synthesized. Both structures were unambiguously characterized via X-ray single crystal diffraction, nuclear magnetic resonance (NMR) spectra, and high-resolution mass spectrometry (HRMS). The crystal structure data reveals that the Pd–Pd distances of [Pd(1,3-di(2-pyridyl)benzene)]₂(Dpf) (DpfH = N,N′-diphenyl formamidine) Pd1 and [Pd(1,3-di(2-pyridyl)benzene]₂(α-Car) (α-CarH = α-carboline) Pd2 measure 3.0046(3) and 3.1518(8) Å, respectively. The absorption spectra of Pd1 and Pd2 display metal–metal-to-ligand charge transfer (MMLCT) transitions. In the solid state, they show triplet emissions at 635 and 607 nm, respectively. While in 1 wt% PMMA film, the emission peaks are located at 602 and 571 nm, respectively. In contrast, both complexes show very weak emission in the solution state, and their maximum emission wavelengths are significantly red-shifted. Based on their photophysical properties, the Pd1 in 1 wt% PMMA films on quartz squares was placed in different organic or acid solvents for 30 min and then was utilized to detect organic solvent vapor. The film showed unique emission quenching for the vapor of acetone.