"Cymothoe sangaris": an extremely stable and highly luminescent 1,2-hydroxypyridinonate chelate of Eu(III).

The synthesis, structure, and characterization of a new class of luminescent agents based on the 1,2-hydroxypyridinone chelator are reported. The prototype complex, [Eu(5LIO-1,2-HOPO)2]-, demonstrates superb aqueous stability [pEu = 18.64(10)] and is highly emissive [Phit = 0.21(3)], emitting almost pure "red" light (lambdaem = 612 nm). The crystal structure reveals a coordination geometry reminiscent of a "butterfly", hence the soubriquet of "Cymothoe sangaris" to identify with the unique species of red butterfly found only in Central Africa.