Near-Infrared Electrophosphorescence from 1-(Benzo[b]thiophen-2-yl)isoquinoline-Based Platinum(II) Complexes with Aromatic Thiol Bridging Ligands through Intramolecular Pt–Pt Interactions

Cyclometalated platinum(II) complexes represent one of the important categories of phosphorescent transition-metal complexes. Their structural features and photophysical properties are highly related to the ligand denticity, ranging from bidentate to quadridentate, and the presence of Pt–Pt interactions. In this contribution, a pair of near-infrared (NIR) emissive cyclometalated platinum(II) complexes (PtI and PtII) are rationally designed and prepared by using 1-(benzo[b]thiophen-2-yl)isoquinoline as the cyclometalating ligand and aromatic thiol (i.e., benzo[d]oxazole-2-thiol and benzo[d]thiazole-2-thiol) as the bridging ligand. The aromatic thiol bridging ligand facilitates the formation of binuclear complexes through the intramolecular Pt–Pt interactions. Attributed to the presence of the metal-metal-to-ligand charge transfer state, these binuclear platinum(II) complexes show intense NIR room-temperature phosphorescence ranging from 721 to 737 nm with high photoluminescence quantum yields of up to 0.24 and photoluminescence lifetimes around 10 μs. Furthermore, both binuclear platinum(II) complexes are employed as the triplet emitters for the fabrication of efficient, partially solution-processed NIR organic light-emitting devices exhibiting electroluminescence centered at around 730 nm with shoulder emission extending to 800 nm and a high external quantum efficiency of 4.9%. These results highlight the promising potential of such binuclear platinum(II) complexes for optoelectronic applications.