Changing N^C^O to C^N^O Coordination in Cyclometalated Pt(II) and Pd(II) Complexes Modulates Stability and Emission...

In this work, we present a new class of cyclometalated Pt(II) complexes bearing tridentate luminophoric chelators. Inspired by picolinato units usually acting as ancillary ligands for phosphorescent Pt(II) and Ir(III) complexes with high-lying triplet states, we herein incorporate this coordination pattern into chelating luminophores toward tridentate pincer ligands (C^N^O) and compared them with a benzoate-derived motif (N^C^O). Both frameworks exhibit excellent photoluminescence efficiencies with quantum yields (Φ_L) reaching up to 76% (N^C^O) and 75% (C^N^O). The versatile variation of the substitution patterns at the C^N^O motif was found to significantly affect the photophysical properties, yielding tunable emission maxima ranging from 475 to 693 nm. With the introduction of electron-donating substituents, it was demonstrated that an electron-rich cyclometalating ring at the luminophoric backbone enables the realization of Pd(II) complexes that are emissive in solution at room temperature, if combined with strong σ-donors (like N-heterocyclic carbenes) as co-ligands. This comparative study demonstrates that both coordination patterns yield highly efficient emitters with excellent solubilities in common organic solvents. Notably, the C^N^O-based motif offers distinct advantages for future applications, owing to its greater synthetic versatility and enhanced chemical accessibility.