Photophysical and optoelectronic studies of 1.06 and 13.3 μm emissive neodymium complexes

Abstract

In this paper, four original ternary neodymium complexes, [Nd(hth)₃(L)_x] (where x = 1 or 2; hth = 4,4,5,5,6,6,6-heptafluoro-1-(2-thienyl)-1,3-hexanedione and L = 1,10-phenanthroline (phen, 1), 5-bromo-1,10-phenanthroline (Brphen, 2), 5-chloro-1,10-phenanthroline (Clphen, 3), and triphenylphosphine oxide (tppo, 4), are reported. The complexes are synthesised by a two-step method and characterized thoroughly. The single crystal X-ray diffraction (SC-XRD) analysis is performed only for complex 4 due to the good quality of its crystals. The SC-XRD analysis indicates that complex 4 possesses an eight-coordinate structure in the solid state, having three hth and two tppo ligands. The ¹H NMR analysis indicates that complexes 1–4 exhibit nine-coordinate structures in solution, having one coordinated water molecule besides hth and ancillary ligands. The Sparkle/PM7 optimized structures of the complexes are also presented, and complex 4 is compared with its crystal structure. Shape analyses reveal that complexes 1, 2, and 3 adopt biaugmented trigonal prism geometry, while complex 4 exhibits biaugmented trigonal prism J50 geometry. The photophysical investigations of the complexes were conducted in both solution and PMMA films in the near infrared (NIR) region. The results show that the hth ligand serves as an effective sensitizer and phen is the best antenna ligand. The TGA/DTA analysis indicates that the complexes are stable up to ∼200 °C, indicating their possible use in optoelectronic devices. Therefore, complex 4 is used as an emitting layer in a NIR-organic light-emitting device (OLED) with the following structure: ITO/MoO₃ (2 nm)/β-NPB (30 nm)/TcTa:[complex 4] (20 nm, 10 wt%)/TPBi:[complex 4] (10 nm, 10 wt%)/TPBi (25 nm)/LiF (0.1 nm)/Al (100 nm).