Synthesis and Luminescence Properties of a New Complex of Divalent Europium with Cinnamic Acid, Eu(L)2(THF)4 (L = Cinnamate Anion, С6H5СH=СHCOO–)

Abstract

A previously unknown luminescent complex of divalent europium, Eu(L)₂(THF)₄ (L = cinnamate anion, С₆H₅СH=СHCOO^–), was prepared by the reaction of europium(III) cinnamate crystal hydrate Eu(L)₃∙H₂O with diisobutylaluminum hydride (iso-C₄H₉)₂AlH in tetrahydrofuran at room temperature and atmospheric pressure. The complex Eu(L)₂(THF)₄ was isolated in the solid state and was characterized by complexometric titration (Eu²⁺) and elemental analysis (C, H, O). The yield of the complex Eu(L)₂(THF)₄ was 68%. The quantum yield of the photoluminescence (PL) of the complex (φ_PL = 0.05), the PL and PL excitation spectra, and the lifetime (τ = 377 ns) of the europium excited state, Eu²⁺*, in the complex were measured. The PL of the complex Eu(L)₂(THF)₄ is due to the interconfigurational transition 4f⁶5d¹ → 4f⁷ and is manifested as a broad diffuse band in the green part of the spectrum (λ_PL = 515 nm) with the nanosecond lifetime of the excited Eu²⁺* ions. The complex Eu(L)₂(THF)₄ exhibiting bright PL visible by naked eye can be used as a phosphor in the development of new materials with preset photophysical properties.