Fluorescence of europium from absence to emergence in cadmium-induced heterobimetallic organic frameworks for ratiometric sensing

Abstract

Lanthanide–organic frameworks (Ln-MOFs) have garnered increasing research interest as photoluminescent materials. However, the characteristic fluorescence of Ln³⁺ ions is constrained by the energy level matching between Ln³⁺ ions and organic ligands, and the impact of the spatial structure of Ln-MOFs on the energy transfer process remains insufficiently explored, thereby limiting their broader optical applications. In this work, we propose a Cd²⁺-induced heterobimetallic Ln-MOF (HNU-72) as a fluorescence modulation strategy, marking a significant breakthrough in activating the characteristic fluorescence of Ln³⁺ ions, transitioning from absence to emergence. Both experimental measurements and theoretical calculations reveal that the incorporation of Cd²⁺ ions reconfigures the energy transfer pathway, thereby enhancing the energy transfer modulation between H₄TCPE (1,1,2,2-tetra(4-carboxyphenyl)ethylene) and Eu³⁺ ions. Furthermore, leveraging the dual fluorescence emission peaks observed in HNU-72, we achieved an ultra-low detection limit of 14 ppb for the proportional fluorescence detection of dimethyl sulfide in marine environments. This study not only deepens our understanding of the energy transfer mechanisms in Ln-MOF materials, but also paves the way for the development of multifunctional fluorescence sensing platforms.