Photophysical properties of a series of cycloplatinated(ii) complexes featuring allyldiphenylphosphane

Abstract

A series of cycloplatinated(II) complexes with a general formula of [Pt(C^N)(Me)(PPh₂allyl)], 1–4, where C^N = deprotonated form of 2-phenylpyridine (ppy, 1), 2,2′-bipyridine (bpy, 2), 2,2′-bipyridine N-oxide (O-bpy, 3) and 7,8-benzo[h]quinoline (bzq, 4) ligands, has been synthesized. The new complexes were characterized spectroscopically and the structures of complexes 1 and 4 were confirmed by single crystal X-ray crystallography. With the exception of complex 3 (containing O-bpy), all of the complexes exhibited strong luminescence at 298 K (solid) and 77 K (solution and solid). Upon photoexcitation, these complexes revealed structured emission profiles which had mixed ³ILCT/³MLCT (L = cyclometalated moieties) character in the emissive states. Besides, they represent long luminescence lifetimes in the microsecond domain, displaying the phosphorescent nature of the emission. Complex 1, containing the ppy ligand, exhibits the brightest color and highest quantum yield value compared to the other complexes (2 and 4). Also, this complex is brighter than its other analogues ([Pt(ppy)(Me)(PPh₂Me)], A, and [Pt(ppy)(Me)(PPh₃)], B) and this arises from some particular intermolecular C(sp²)–H⋯π short contacts imposed by the allyl group. The aforementioned short contacts are not available in the structures of complexes A and B. The interactions perhaps enforce extra structural rigidity and resulted in a high quantum efficiency for complex 1. Finally, all of the photophysical results were supported by density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations.