Near-infrared luminescence of Nd3+ and Yb3+ complexes using a polyfluorinated pyrene-based β-diketonate ligand

Abstract

A new polyfluorinated β-diketonate ligand containing a pyrene chromophore, namely, 4,4,5,5,6,6,6-heptafluoro-3-hydroxy-1-(pyren-1-yl)hex-2-en-1-one (Hhfpyr) has been designed and employed for the development of a series of near-infrared (NIR) emitting lanthanide complexes (Nd³⁺ and Yb³⁺) in the absence and presence of an ancillary ligand, 4,7-diphenyl-1,10-phenanthroline (bath). The isolated NIR-emitting lanthanide complexes [Nd(hfpyr)₃(H₂O) 1, Nd(hfpyr)₃(bath) 2, Yb(hfpyr)₃(H₂O) 3 and Yb(hfpyr)₃(bath) 4] have been characterized by various spectroscopic techniques and evaluated their photoluminescence properties. The photophysical properties disclosed that the developed pyrene-based β-diketonate ligand is well suited for the sensitization of Nd³⁺ as well as Yb³⁺ emissions, thanks to the favourable position of the triplet state (T¹) of the ligand (ΔE = T¹–⁴F_3/2 = 4700 cm⁻¹ for Nd³⁺ and ΔE = T¹–²F_5/2 = 6200 cm⁻¹ for Nd³⁺), as evidenced from the phosphorescence spectra of the corresponding Gd³⁺ complexes. Most importantly, the displacement of solvent molecules from the coordination sphere of the NIR emitting lanthanide binary complexes (1 and 3) with an ancillary ligand markedly enhances the quantum yields (Φ_overall = 0.45 for 1 to 1.07% for 2 and from 1.69 for 3 to 3.08% for 4) and excited state lifetime values (τ = 2.80 for 1 to 6.16 μs for 2 and from 6.88 for 3 to 13.45 μs for 4). Notably, Yb³⁺ ternary compound 4 with promising NIR luminescence properties was embedded into PMMA matrices, giving rise to a series of PMMA-supported hybrid materials (PMMA@4), where the thermal stability and the film-forming properties were significantly enhanced.