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 LnIII complexes of general formula [LnL]NBu4 (where Ln = Sm (1), Gd (2), Er (3), Yb (4), Er0.5Yb0.5 (5), Er0.5Gd0.5 (6), Yb0.5Gd0.5 (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 (SmIII) and/or, NIR (SmIII, ErIII, YbIII) 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 SmIII, YbIII and ErIII luminescence. The emission quantum yields and the luminescence lifetimes at room-temperature are 3.4 ± 0.5% and 79.1 ± 1 μs for SmIII and 2.6 ± 0.4% and 12.1 ± 0.1 μs for YbIII in solid state. Furthermore the overall quantum yields and lifetime measurements for the mixed metallic complex show that YbIII → ErIII energy transfer occurs resulting in enhanced ErIII emission.