Arylated versus Cyclometalated Platinum(II) Polypyridines: Photoluminescence from Pt(4′-R-trpy)Ph+ Systems (R = NMe2, N‑Pyrrolidinyl, or 1‑Pyrenyl)

Many platinum­(II) polypyridine complexes are good luminophores, an enigmatic exception being Pt­(trpy)­Ph+, where trpy denotes 2,2′:6′,2″-terpyridine. A new analysis suggests the complex is nonemissive due to 3SBLCT (sigma-bond-to-ligand charge transfer) character in the lowest energy excited state. Bases for two distinct strategies for inducing emission from aryl derivatives become clear. The standard approach of incorporating a phenyl group into a (N/\N/\C) cyclometalating ligand relies in part on the rigidity of the ligand framework. An alternative strategy, which involves expanding the chromophore and altering the orbital parentage of the emitting state, is capable of suppressing radiationless decay even further. Indeed, the Pt­(4′-pyren-1-yl-trpy)­Ph+ system emits from a low-lying 3π–π*­(pyrene) excited state that has a lifetime of 45 μs in fluid solution.