Emission “Off–On” effect from europium complexes triggered by AcO anion: Synthesis, characterization and sensing performance

• The correlation between emissive performance and ligand structure was studied.
• Conjugation chain might trigger energy transfer roll-back and compromise emission.
• The presence of AcO anion could stop the energy transfer roll-back.
• A sensing system was developed with high sensitivity and selectivity.

In this paper, a series of Eu(III) complexes based on four diamine ligands and two diketone ligands were synthesized. Their single crystal structures were studied, where intermolecular π–π stacking was found. The photophysical parameters of these Eu(III) complexes were measured, along with their ligand triplet levels. The energy transfer mechanism between ligand and metal center was discussed in detail. Energy transfer roll-back was found in Eu(III) complexes owing large-conjugated diamine ligands, compromising emissive performance. This energy transfer roll-back, however, could be stopped by the presence of AcO anion, leading to Eu(III) complex emission enhancement. The sensing performance of such Eu(III) complexes was thus investigated in detail. High sensitivity and selectivity were observed.

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