Aryl bridged 1-Hydroxypyridin-2-one: Effect of the bridge on the Eu(III) sensitization process

摘要

The efficiency of Eu3+ luminescence by energy transfer from an antenna ligand can be strongly dependent on the metal ion coordination geometry. The geometric component of the Eu(III) sensitization has been probed using series of tetradentate 1,2-HOPO derivatives that are connected by bridges of varying length and geometry. The ligands are N,N’-(1,2-phenylene)bis(1-hydroxy-6-oxo-1,6-dihydropyridine-2-carboxamide) for the ligand (L¹), 1-hydroxy-N-(2-(1-hydroxy-6-oxo-1,6-dihydropyridine-2-carboxamido)benzyl)-6-oxo-1,6-dihydropyridine-2-carboxamide (L²) and N,N’-(1,2-phenylenebis(methylene))bis(1-hydroxy-6-oxo-1,6-dihydropyridine-2-carboxamide) (L³). Spectroscopic characterization of both the Gd(III) and Eu(III) metal complexes, TD-DFT analysis of model compounds and evaluation of the kinetic parameters for the europium emission were completed. Some striking differences were observed in the luminescence quantum yield by altering the bridging unit. The [Eu(L²)2]⁻ derivative shows efficient sensitization coupled with good metal centered emission. For [Eu(L³)2]⁻, the large quenching of the luminescence quantum yield compared to [Eu(L²)2]⁻ is primarily a result of one inner sphere water molecule bound to the europium cation while for [Eu(L¹)2]⁻, the low luminescence quantum yield can be attributed to inefficient sensitization of the europium ion.