NIR luminescence of a series of benzoyltrifluoroacetone erbium complexes

Abstract

A series of five β-diketone erbium complexes with various azacyclo-auxiliary ligands, namely, Er(Hbta)₃(H₂O)₂ (1), Er(Hbta)₃(bpy) (2), Er(Hbta)₃(phen) (3), Er(Hbta)₃(dpq) (4) and Er(Hbta)₃(dppz) (5) (Hbta = benzoyltrifluoroacetone, bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline, dpq = pyrazino[2,3-f][1,10]phenanthroline, dppz = dipyrido[3,2-a:2′,3′-c]phenazine) have been isolated and characterized by X-ray crystallographic analysis. Near-infrared luminescence analysis reveals that all complexes 1–5 exhibit strong NIR luminescence of Er(III) ions around 1535 nm with the highest lifetime of 4.532 μs, quantum yield of 3.24 × 10⁻⁴ and broadband emission around 1.5 μm for complex 5, in which the azacyclo-auxiliary ligand absorbs and transfers the energy leading to complete quenching of the ligand-associated visible emission. The energy transfer processes among benzoyltrifluoroacetone, the Er(III) ion and the auxiliary ligands in complexes 1–5 have been investigated.