Complex architecture surpasses ligand lipophilicity for efficient Eu(III) sensing under acidic conditions

Efficient and selective sensing of lanthanides are crucial for identifying valuable lanthanide streams and designing effective extraction/masking agents for mining and nuclear waste management. Luminescence-based sensing often struggles with interference from water molecules. Common approaches to improve emissive lanthanide complexes in water involve increasing ligand lipophilicity and enclosing the emitting metal center. Herein, we have demonstrated that lipophilic ligands do not always lead to higher emissions. When strong coordinating groups are involved in the ligand, the complex may adapt special architecture to compensate the hydrophilic nature of the ligand by creating lipophilic microenvironment and lead to higher emissions. Our findings highlight the importance of the overall lipophilicity of both the ligand and the final complex, which could serve as important reference for future design of efficient lanthanide sensing and emissive complexes.