Design, synthesis, and luminescence properties of bridged dimetallic lanthanide coordination compounds

I synthesized and characterized new homo- and heterodimetallic Eu 3+- and Tb3+-containing complexes. Solution-phase luminescence measurements and density functional theory (DFT)-optimized structures indicated that all complexes were nearly isostructural and contained a dimetallic lanthanide core bridged by three oxygen atoms that are covalently bound to the ligand backbone. The homodimetallic Eu3+ complex behaved as a concentration-independent pH sensor that correlates the luminescence-decay rate of the complex to pH. The probable mechanism of pH sensing was attributed to the modulation of a hydroxyl oscillator in the Eu3+ coordination sphere, which was a previously unreported method to sense pH. The heterodimetallic Tb 3+/Eu3+ complex displayed energy transfer from Tb 3+ to Eu3+ that is unprecedentedly efficient. The observed energy transfer confirmed that the Tb3+-Eu3+ distance in the heterodimetallic complex is within 10 Å and demonstrated a unique interaction between lanthanide ions.