Design of high coordination number metallomesogens by decoupling of the complex-forming and mesogenic groups: Nematic and lamello-columnar mesophases

Liquid-crystalline complexes of rhenium(I), yttrium(III), lanthanum(III), neodymium(III), samarium(III), europium(III), erbium(III), and ytterbium(III) were obtained by coupling mesogenic 4-cyanobiphenyl groups via a long alkyl spacer to a substituted imidazo[4,5-f]-1,10-phenanthroline, which acts as the coordinating group. In the case of the rare-earth complexes, 2-thenoyltrifluoroacetonate was used as the coligand. The rhenium(I) complexes contain the bromotricarbonylrhenium(I) moiety. All the rare-earth complexes exhibit a nematic phase, whereas the rhenium(l) complexes and the imidazole-bearing phenanthroline derivatives show a nematic or a lamellar columnar phase, depending on the number of attached mesogenic groups. The phase structures of the lamellar columnar phases are discussed and described on the basis of both X-ray diffraction data and dynamic molecular modeling. The lanthanide complexes are highly luminescent in the solid phase and as a Solution in a nematic liquid-crystal host (5CB). The approach discussed in this paper can be generalized to obtain other high coordination number metallomesogens.