Synthesis, structure, and solid-state phosphorescence of heteroleptic platinum(II) complexes bearing iminophenyl and iminophenoxy ligands

A series of heteroleptic platinum(II) complexes 1 bearing iminophenyl and iminophenoxy ligands have been synthesized and characterized using NMR, IR, and emission spectroscopies, mass spectrometry, and single crystal X-ray diffraction. The complexes exhibit intense phosphorescent emission with an absolute quantum efficiency (Φ298K) up to 0.29 in the crystalline state. Chromogenic control of solid-state emission over a range of 99 nm can be performed simply by introducing methoxy (MeO) groups at different positions on the aromatic rings. Hypsochromic and bathochromic shifts from the orange 1a crystal are observed with 4-/11-MeO (para-position of the imine moieties on the phenyl and phenoxy ligands; yellow emission) and 5-/12-MeO (para-position of the phenyl and phenoxy moieties; reddish orange and red emission) substitution, respectively. Time-dependent density functional theory (TD-DFT) calculations (B3LYP/6-31G*, LanL2DZ) indicated that the chromatic variation can be ascribed to the position-specific influence of the substituents on the HOMO and LUMO levels. The solid-state emission and heat-resistance are discussed based on the molecular packing of the crystals.