A new tetrakis β-diketone ligand for NIR emitting Ln~(III) ions: luminescent doped PMMA films and flexible resins for advanced photonic applications

摘要

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_(0.5)Yb_(0.5) (5), Er_(0.5)Gd_(0.5) (6), Yb_(0.5)Gd_(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.