Lanthanide-Containing Nematic Phases with Controlled Polarized Luminescence at Room Temperature

Abstract
Lanthanidomesogens combine the orientation behavior of liquid crystalline mesophases with the luminescent properties of lanthanide ions. The presence of a nematic phase in lanthanide complexes is very promising property but it is rare observed. Although a significant number of publications devoted to the synthesis of lanthanide-containing liquid crystals (LCs) is known, only a limited number of successful attempts to obtain nematics is reported about. Thereby, the creation of lanthanide-containing LC systems with nematic mesomorphism in a wide temperature range and study of their optical and luminescent properties become an actual and practically important task. This work describes a preparation of liquid crystalline adduct of europium (III) tris(β-diketonate) with 5,5'-diheptadecyl-2,2'-bipyridine, which demonstrates nematic mesomorphism and has high-efficient luminescence. An interesting characteristic of the obtained complex is the ability to vitrify on cooling with the same packing of molecules as in the mesophase. On the base of the mixture of oxycyanobiphenyls (5OCB, 7OCB) and europium complex, compositions showing nematic mesophase in a wide range of temperature including room temperature were obtained. Liquid crystalline, orientation and luminescent properties of the compositions were studied. The work shows possibility of obtaining the oriented lanthanide-containing LC media with controlled polarization of luminescence.

Keywords: liquid crystals, lanthanide (III) complexes, nematics, polarized luminescence