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.