Phosphorescent platinum(II) complexes bearing 2-vinylpyridine-type ligands: Synthesis, electrochemical and photophysical properties, and tuning of electrophosphorescent behavior by main-group moieties

A series of 2-vinylpyridine-type platinum(II) complexes bearing different main-group blocks (B(Mes)₂, SiPh₃, GePh₃, NPh₂, POPh₂, OPh, SPh, and SO₂Ph, where Mes = 2-morpholinoethanesulfonic acid) were successfully prepared. As indicated by the X-ray single-crystal diffraction, the concerned phosphorescent platinum(II) complexes exhibit distinct molecular packing patterns in the solid state to bring forth different interactions between individual molecules. The photophysical characterizations showed that the emission maxima together with phosphorescent quantum yield of these complexes can also be affected by introducing distinct main-group moieties with electron-donating or electron-withdrawing characters. Furthermore, these 2-vinylpyridine-type platinum(II) complexes exhibit markedly different photophysical and electrochemical properties compared with their 2-phenylpyridine-type analogues, such as higher-lying highest occupied molecular orbital levels and lower-energy phosphorescent emissions. Importantly, these complexes can show good potential as deep red phosphorescent emitters to bring attractive electroluminescent performances with Commission Internationale de L'Eclairage (CIE) coordinates very close to the standard red CIE coordinates of (0.67, 0.33) recommended by the National Television Standards Committee. Hence, these results successfully established structure-property relationship concerning photophysics, electrochemistry, and electroluminescence, which will not only provide important information about the optoelectronic features of these novel complexes but also give valuable clues for developing novel platinum(II) phosphorescent complexes.