Tetradentate platinum(II) complexes: Synthesis, photophysical properties, liquid crystalline characteristics and charge transport behaviour

摘要

Three new tetradentate phosphorescent Pt(II) complexes (Pt-6, Pt-12 and P-66) with half-disc molecule structure were designed and synthesized, which are based on tetradentate ligands with six alkoxyl chains on the periphery, (6,6'-bis((3',4',5'-alkoxy-{1,1'-biphenyl)-4-yl]oxy)-2,2'-bipyridine). All complexes show red phosphorescence in dichloromethane solution (lambda(em) approximate to 640 nm) with quantum yields in range of 4.3%-6.7% and phosphorescent lifetimes in range of 0.46-0.55 mu s in degassed dichloromethane solution. Among these complexes, the complex, Pt-12, with 12 carbons chain lengths shows columnar mesophase with liquid crystal temperature range of 22.0 degrees C to 77.8 degrees C, which was confirmed via polarized optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The complex, Pt-12, exhibits ambipolar carrier transport behaviors, which has been confirmed by the space charge limited current (SCLC) measurement. Moreover, the carrier mobility in mesogenic state is two orders of magnitudes greater than that in the amorphous state, showing ordering packing in liquid crystalline phase can facilitate the charge transport.