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

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), 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 (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 mu s for Sm-III and 2.6 +/- 0.4% and 12.1 +/- 0.1 mu s 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.