Tetrahedral Zinc Complexes with Liquid Crystalline and Luminescent Properties: Interplay Between Nonconventional Molecular Shapes and Supramolecular Mesomorphic Order

Novel metallomesogens with luminescent properties and liquid crystalline behavior at room
temperature have been achieved by the preparation of zinc complexes with polycatenar pyrazole and bis(pyrazolyl)methane ligands. Their molecular structures do not have a conventional shape in that they are
far from the typical rod-like and flat disc-like geometries of common liquid crystals. They consist of a
nonplanar nucleus due to the methylene spacer and/or the coordination to the tetrahedral center, as
confirmed by single crystal analysis of the cores. The different numbers and positions of side chains in the
pyrazole ligand enabled us to access lamellar and columnar mesophases and, of particular interest, to
obtain columnar arrangements at room temperature. Supramolecular models for the organization of the
molecules in the mesophases are proposed on the basis of the small-angle XRD diffractograms. The zinc
complexes display luminescence in the near UV-blue region with large Stokes shifts. An interplay between
non-conventional molecular shapes (due to the tetrahedral core) and the supramolecular mesomorphic
order (due to the ligand design) led to materials that interestingly embody two rather opposite properties,
a columnar self-organizational ability and luminescence with weak intermolecular interactions.