Dynamic Molecular Triplet Excitons in Lanthanide Complex Assemblies for Ultrasensitive Optical Oxygen Sensing

Abstract Optical oxygen sensors using the emission lifetimes of trivalent lanthanide complexes have attracted considerable attention in bioscience and aeronautical engineering owing to their spatially resolved mapping and real-time monitoring capabilities. Here, we report an ultrasensitive optical oxygen sensing method that utilizes an extended 4f−4f emission lifetime via dynamic molecular triplet excitons in lanthanide complex assemblies. To demonstrate our proof of concept, Yb3+-incorporated Lu3+ molecular crystals composed of dinuclear units with a phenanthrene bridging ligand (dcph: 2,7-bis(dicyclohexylphosphoryl)phenanthrene) and six anionic β-diketonate ligands (tmh: 2,2,6,6-tetramethyl-3,5-heptanedionate) were synthesized. These Yb3+−Lu3+ mixed crystals exhibited an extended Yb3+ emission lifetime due to slow triplet exciton migration between phenanthrene units. The oxygen sensitivity, evaluated by the emission lifetime ratio (τavg,0 kPa/τavg,20.3 kPa = 5200), is the highest among the reported optical oxygen sensors using lanthanide complexes. The present method provides a design strategy for ultrasensitive oxygen sensing using lanthanide complexes.