Aqueous EuII-Containing Complex with Bright Yellow Luminescence

Eu-II-containing materials have unique luminescence, redox, and magnetic properties that have potential applications in optoelectronics, sensors, and imaging. Here, we report the synthesis and characterization of Eu-II-containing aza-222 cryptate that displays yellow luminescence and a quantum yield of 26% in aqueous media. The crystal structure reveals a staggered hula-hoop geometry. Both solid-state and solution-phase data are presented that indicate that the high quantum yield is a result of the absence of OH oscillators in the inner sphere of the complex. We expect that Eu-II-containing aza-222 cryptate is a step toward Eu-II-containing luminescent materials that can be used in a variety of applications including biological imaging.