Luminescence properties of m-terphenyl-based Eu3+ and Nd3+ complexes: visible and near-infrared emission

Abstract

Two novel m-terphenyl-based organic ligands (2 and 3) have been synthesized. Photophysical studies show that the ligands form stable complexes with Eu³⁺, since typical Eu³⁺ luminescence is observed upon excitation of the ligand. The acyclic complex 2·Eu³⁺ shows relatively long lifetimes in methanol (e.g.τ = 0.72 ms in CH₃OH). The acylic ligand 2 allows the additional coordination of two solvent molecules and their high-energy vibrational modes form the main quenching pathway for the Eu³⁺ luminescence. In comparison with 1·Eu³⁺, the more rigid dioxolane-containing complex 3·Eu³⁺ provides an additional donor atom, which reduces the solvent coordination of 3·Eu³⁺ (τ_3·Eu³⁺ = 1.42 ms compared to τ_1·Eu³⁺ = 0.75 ms in CH₃OH). The high-energy vibrational modes of the organic ligand 3 are the most important quenchers. Typical near-infrared Nd³⁺ emission at 1060 and 1350 nm resulting from 3·Nd³⁺ has been observed. Quenching by the solvent is still operative for 3·Nd³⁺, because of the larger ionic radius of the Nd³⁺ ion.