Enhanced Photoluminescence Quantum Yields through Excimer Formation of Cyclometalated Platinum(II) N‑Heterocyclic Carbene Complexes

We report a new class of C∧C* platinum­(II) complexes in which excimer formation enhances the quantum yield while shortening the phosphorescence lifetime. Selective excitation of the monomer or dimer could be achieved at different wavelengths. These complexes exhibit strong phosphorescent emissions in the blue part of the visible spectrum around 450 nm with quantum yields of up to 93%. The emission behavior is controlled through the steric demand of the substituents at the 2,4-pentanedione ligand. We see dual emission with high photoluminescence quantum yields (PLQY) from monomeric and aggregated excited states.