Cyclometalated Platinum(II) Complexes of Pyrazole-Based, N∧C∧N-Coordinating, Terdentate Ligands: the Contrasting Influence of Pyrazolyl and Pyridyl Rings on Luminescence

摘要: 1,3-Bis(1-pyrazolyl)-5-methyl-benzene, HL2, undergoes cyclometalation at the C2 position upon reaction with K2PtCl4, to generate an N∧C∧N-coordinated complex, PtL2Cl. This compound is luminescent in degassed solution 298 K, emitting blue region of spectrum on microsecond time scale (λmax = 453 nm, τ 4.0 μs, Φlum 0.02, CH2Cl2). Compared analogous complex Pt(dpyb)Cl that incorporates pyridyl rather than pyrazole rings {dpybH 1,3-di(2-pyridyl)-benzene}, excited state displaced higher energy by 1700 cm−1. effect rationalized terms poorer π-acceptor nature pyrazolyl compared rings, leading destabilization lowest unoccupied molecular orbital, which largely localized heteroaromatic both cases. Cyclic voltammetry and density functional theory calculations reinforce this interpretation, suggest lowest-energy probably best described as heavily mixed πL/dPt/pCl → π*L (IL/MLCT/LLCT) i...