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

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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+ (τ3·Eu3+ = 1.42 ms compared to τ1·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.

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