Near-infrared electroluminescent lanthanide [Pr(iii), Nd(iii), Ho(iii), Er(iii), Tm(iii), and Yb(iii)] N,O-chelated complexes for organic light-emitting devices

Abstract

New near-IR electroluminescent complexes of Pr³⁺, Nd³⁺, Ho³⁺, Er³⁺, Tm³⁺, Yb³⁺ with N,O-chelated ligands, Ln₂(OON)₆ (OON = 2-(2-benzoxyazol-2-yl)phenolate) and Ln₂(SON)₆ (SON = 2-(2-benzothiazol-2-yl)phenolate), were synthesized by the reaction of Ln[N(SiMe₃)₂]₃ and the corresponding N,O-chelating ligand. X-Ray analysis for the Pr and Nd compounds reveals centrosymmetric dimeric structures of the complexes. The solid-state electronic absorption spectra and the electroluminescent spectra show long-wavelength 4f–4f transitions which provide potential use of the compounds as NIR emitting materials in organic light-emitting devices (OLEDs). When constructing OLEDs based on Ln₂(OON)₆ and Ln₂(SON)₆, the best results were achieved with the Nd³⁺ and Yb³⁺ complexes, where the NIR wall plug efficiency of the ITO/TPD/Ln-complex/BATH/Yb system is 0.82 and 1.22 mW W⁻¹, respectively.