8‑Phenylquinoline-Based Tetradentate 6/6/6 Platinum(II) Complexes for Near-Infrared Emitters

A series of novel tetradentate 6/6/6 Pt­(II) complexes containing an 8-phenylquinoline-benzo­[d]­imidazole-carbazole ligand was designed; the Pt­(II) complexes could be synthesized by metalizing the corresponding ligand with K2PtCl4 in high isolated yields of 60–90%. Experimental and theoretical studies suggested that the ligand modification of the quinoline moieties of the Pt­(II) complexes could tune their electrochemical, photophysical, and excited-state properties. Notably, all the Pt­(II) complexes exhibited highly electrochemical stabilities with reversible redox processes except the quasi-reversible reduction of PtYL3. The large π-conjugation of the ligand together with increased metal-to-ligand charge-transfer (3MLCT) characters in T1 states enabled the Pt­(II) complexes to show broad Gaussian-type NIR emission spectra with high photoluminescence quantum efficiencies of 1.2–1.5% and short τ of 0.8–1.5 μs in dichloromethane at room temperature. This work should provide a valuable reference for the design and development of monomer NIR emitters.