Alignment of palladium complexes into columnar liquid crystals driven by peripheral triphenylene substituents.

A new triphenylene-imine (ImH) and its ortho-palladated complexes (μ-X)2[Pd2Im2] (X = CH3COO(-), Cl(-), Br(-)), (μ-Cl)(μ-SCnH2n+1)[Pd2Im2] (n = 6, 12), [PdIm(acac)] [PdIm Cl(CNC6H4OC12H25)], [PdImCl(CNC6H3(OC12H25)2)], and [PdImCl(CNC6H2(OC12H25)3)] have been prepared. The free imine ligand is not a liquid crystal, but most ortho-metalated dinuclear palladium complexes and the mononuclear trialkoxyphenyl isocyanide derivative display columnar mesophases at temperatures close to ambient. For the dimeric complexes the mesophase obtained is always columnar rectangular (Colr), with an uncommon structure: the dimeric triphenylene-Pd complex-triphenylene molecules give rise to a triple-column stacking consisting of two columns of stacked triphenylene groups connected to a central column formed by stacking of two ortho-palladated dimeric moieties. For the trialkoxyphenyl isocyanide derivative a related polymer-like arrangement of columns alternating stacking of triphenylenes with stacking of two ortho-palladated dimeric moieties is found. The mesophase structure is columnar oblique (Colob). The free imine and all palladium complexes exhibit fluorescence at room temperature in dichloromethane solution, associated with the triphenylene core.