Dendritic Ligands for Magnetic Suspensions in Liquid Crystals

The synthesis of long-chain, aliphatic and space filling dendritic ligands containing (pro)mesogenic, aliphatic or nitrile biphenyl moieties for the stabilization of magnetic nanoparticles in liquid crystal hosts is described. A Negishi or Sonogashira cross-coupling is exploited as a key step in the synthetic sequence. These synthetic procedures enable the synthesis of various ligands which can be easily adapted to different types of liquid crystals [e.g. 4-pentyl-4′-cyanobiphenyl (5CB)]. For instance, a three-step sequence (i.e. etherfication, Sonogashira– Hagihara cross-coupling and Steglich-esterfication) yields a dendritic ligand in 77 % overall yield starting from literature known compounds. The length of the ligand is important to stabilize the magnetic nanoparticles, and, therefore, the length of the ligand may be easily modified by this approach. Indeed, the established synthesis can readily tackle this issue.