Room-Temperature Luminescence from a Biscyclometalated Platinum(II) Complex Bearing Radical as Ancillary Ligand

Doublet emission from transition metal complexes presents a promising approach to enhance the long-term stability of organic light-emitting diodes (OLEDs) by mitigating triplet–triplet annihilation, a key factor that degrades OLED performance. In this study, a stable persistent radical (Pybtm)^• is incorporated as an ancillary ligand into a platinum(II) biscyclometalated complex to modulate its emission properties. Photophysical analysis of the newly synthesized and characterized complexes reveals distinct behaviors: doublet emission from the radical complex and phosphorescent emission for the neutral complex, observed both at room temperature in solution and in thin films (doped in poly(methyl methacrylate) (PMMA)) as well as in 2-Me-THF at 77 K. Detailed investigations, supported by density functional theory and time-dependent density functional theory calculations, corroborate that the emission properties are strongly dictated by the neutral and the radical ancillary ligand. Additionally, electron paramagnetic resonance spectroscopic studies verify the radical nature of these complexes, highlighting their potential for OLED applications.