Four triazamacrocyclic and two tetraazamacrocyclic ligands carrying two and three coordinating donor groups, respectively, and a carbostyril light-harvesting antenna were synthesized. The antenna was linked to a macrocycle either via secondary or tertiary amide. Complexation with europium (Eu), gadolinium (Gd), terbium (Tb), and ytterbium (Yb) yielded overall + 1 or + 2 charged species. Paramagnetic 1 H NMR, and steady-state and time-resolved luminescence spectroscopies showed that the complexes had 1-3 inner-sphere water molecules and displayed a variety of coordination geometries in solution. The antennae sensitized Eu(III) and Tb(III) emission with quantum yields of 0.3-4.3 % and 9.9-24.5 %, respectively. The addition of excess fluoride or cyanide to buffered Eu(III) complex solutions resulted in anion-dependent changes. Fluoride addition increased the Eu(III) luminescence intensity by displacing all inner-sphere water molecules and stabilizing the + 3 oxidation state of Eu. Eu(III) luminescence increased up to 25-fold for one emitter. Cyanide quenched Eu(III) luminescence in all cases despite partial water ligand displacement.
The cover feature image represents the differences in the luminescence response upon fluoride vs cyanide binding to a 1,4,7‐triazacyclonane‐based Eu(III) complex equipped with a carbostyril light‐harvesting antenna. The addition of excess of fluoride boosts the Eu(III) emission quantum yield by up to 6‐fold for such compounds. Cyanide addition extinguishes Eu(III) luminescence despite partial anion binding to a lanthanide 3+ ion. These compounds showed opposite responses upon fluoride and cyanide binding, and the results could facilitate the design of responsive probes for multiple anion types. More information can be found in the Research Article by K. E. Borbas and co‐workers.
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