Solubility in Fluorinated Medium and Thermal Properties of Europium(III) Complexes with Phosphine Oxides

Abstract

Relationships between molecular structures of three types of europium complexes and solubility in hexane and fluorinated media were investigated. The solubility of europium complexes with β-diketones (type-1) was correlated to the substituents of β-diketones. Introducing bulky substituents was effective for enhancing solubility. On the other hand, europium complexes with β-diketones and phenanthroline (type-2) were scarcely soluble in either solvent. Among europium complexes with β-diketones and phosphine oxides (type-3), complex 16 which has bulky substituents at β-diketones and two different phosphine oxides, was found to be highly soluble even in a fluorinated medium. Thermal properties of europium complexes were correlated to the molecular structures and solubility. ΔHf of 16 is characteristically small compared with similar type-3 complexes. The transparent fluorescent solid in which complex 16 was dissolved plays an important role as a fluorescent layer of light-emitting diodes (LEDs) for realizing large luminous flux (over 870 mlm when 20 mA of direct current was applied to the ultraviolet (maximum wavelength: 402 nm) LED chip).