Self-Organization of Dipolar 4,4’-Disubstituted 2,2’-Bipyridine Metal Complexes into Luminescent Lamellar Liquid Crystals

Mononuclear cis-dichloro complexes, [(LMCl2)-M-n], with different metal centres (Pt-II, Ni-II, and Zn-II) and a series of palladium and platinum derivatives, [(LMX2)-M-2], in which chloride groups are replaced with iodide, bromide, and azide ligands, have been synthesized from 4,4'-disubstituted-2,2'-bipyridines. Upon complexation of these non-mesogenic ligands, the peculiar structural arrangement, characterized by intermolecular associations of the new derivatives, induces mesomorphism in most [(LMX2)-M-2] complexes, confirming the importance of coordination chemistry in metal-mediated formation of liquid crystals. Single crystal X-ray structures have been determined for dihexadecyl 2,2'-bipyridyl-4,4'-dicarboxylatopalladium and -zinc dichloride derivatives. Both the metal centres and the ancillary ligands have been varied to use dipole coupling as a tool to control molecular architecture: thermal, as well as spectroscopic properties, depend strongly upon molecular dipolar interactions. Tunable red and blue emitters based on Pd-II and Pt-II, both in solution and in the solid state, have been obtained.