Publication
This work describes the synthesis as well as the photophysical and mesomorphic properties of new luminescent liquid crystals able to emit narrow bands in the visible range, and featuring lanthanide ions incorporated into pro-mesogenic coronands. In order to induce liquid crystalline phases, polar pendent arms with benzoate or benzamide groups have been attached onto the macrocyclic core of the ligands. These arms are further fitted with long aliphatic chains with the purpose of increasing the anisotropy of the system and of generating selective intermolecular interactions pertaining to the formation of the mesophases. Aromatic rings inserted into the receptor function as chromophoric groups for sensitizing the luminescence of lanthanide ions. The first part of this work deals with the study of dibenzo-18-crown-6 derivatives. However, the complexes formed with these ligands do not show any mesomorphic properties and their luminescence in the solid state is low, which led us to improve the design of the receptors. In the second part, ligands from the (2.2) coronand family have been synthesized. The latter are pro-mesogenic since they are able to self-organize into hexagonal columnar superstructures after complexation of a lanthanide ion. This change of state represents the macroscopic expression of the host-guest interaction. In other words, the complexation induces a change in the information coding of the receptor enabling it to self-associate with neighbours, leading to the formation of the mesophase. This is a kind of information transcription, from the microscopic to the macroscopic scale. Moreover, the mesomorphic properties of the complexes have been investigated in terms of the structure of the ligand, the nature of the metal ion and the counter-ion. Photophysical properties of the ligands and the complexes have also been studied. Time-resolved luminescence showed emission of the lanthanide ions in the solid state as well as in the liquid crystalline state. Finally, it was shown how the europium ion can be used as a probe to accurately determine a crystalline-to-liquid crystalline phase transition in Eu-containing liquid crystals. The luminescence changes around the phase transition do not simply arise from common factors, such as the increase in temperature-dependant deactivating processes, and the intensity decrease due to the lower value of the refractive index in the mesophase. There is an additive contribution intrinsic to the phase change and which is the manifestation of the macroscopic effect onto the non-radiative deactivating processes of the metal.