A new tetrakis β-diketone ligand for NIR emitting LnIII ions: luminescent doped PMMA films and flexible resins for advanced photonic applications

Abstract

A new antenna molecule containing four benzoyltrifluoroacetone (BTFA) moieties anchored to a single carbon atom and connected through four flexible methoxy groups, namely 1,1′-(4,4′-(2,2-bis((4-(4,4,4-trifluoro-3-oxobutanoyl)phenoxy)methyl) propane-1,3-diyl)bis(oxy)bis(4,1-phenylene))bis(4,4,4-trifluorobutane-1,3-dione) [H₄L], has been designed and synthesized. Using this ligand, a series of homo- and hetero-metallic Ln^III complexes of general formula [LnL]NBu₄ (where Ln = Sm (1), Gd (2), Er (3), Yb (4), Er_0.5Yb_0.5 (5), Er_0.5Gd_0.5 (6), Yb_0.5Gd_0.5 (7) and NBu₄ = tetrabutyl ammonium) have been isolated. All these complexes have high molar absorption coefficients (>40 000 M⁻¹ cm⁻¹ around 330 nm in DMF) and display strong visible (Sm^III) and/or, NIR (Sm^III, Er^III, Yb^III) luminescence in solid state and in DMF solution upon irradiation at the ligand-centred bands in the range 250–400 nm. Furthermore, these complexes have been doped into PMMA matrices yielding highly luminescent, photo-stable films and flexible resins made of fibres with average diameter 300–400 nm. Photoluminescence studies show that the newly designed ligand is an adequate sensitizer for Sm^III, Yb^III and Er^III luminescence. The emission quantum yields and the luminescence lifetimes at room-temperature are 3.4 ± 0.5% and 79.1 ± 1 μs for Sm^III and 2.6 ± 0.4% and 12.1 ± 0.1 μs for Yb^III in solid state. Furthermore the overall quantum yields and lifetime measurements for the mixed metallic complex show that Yb^III → Er^III energy transfer occurs resulting in enhanced Er^III emission.