New phosphorescent platinum(ii) complexes with tetradentate C*N^N*C ligands: liquid crystallinity and polarized emission

New phosphorescent, liquid crystalline cyclometalated tetradentate platinum complexes (Pt-L16, Pt-L12 and Pt-L6) based on the tetradentate C*N^N*C ligands (C*N^N*C = 6,6'-bis(4-(alkoxy)-phenoxy)-2,2'-bipyridine) are designed and synthesized. Their crystal structure, and photophysical, electrochemical and liquid crystal characteristics were investigated. The X-ray structure of Pt-L12 shows a severe distortion of this complex towards a tetrahedral geometry. All complexes are emissive both in degassed solution and in the solid state at room temperature with emission maxima in the red region of the spectrum. Pt-L16 and Pt-L12 show monotropic smectic liquid crystal characteristics. Moreover, these liquid crystal complexes can be aligned on a rubbed nylon-6 glass substrate and produce polarized emission with a dichroic ratio of 5.1.