Supramolecular Eu(III)₄L₄ Tetrahedra-BasedFilms for Luminescence Sensing of Volatile Amines with Sub-ppt-LevelDetection Limit

Metal–organic cages are a class of discrete supramolecular architectures endowed with a well-defined cavity and diverse functionalities, offering a broad range of applications that, however, are predominantly confined to liquid phases. In this study, we present the self-assembly of supramolecular Eu(III)₄L₄ tetrahedra, constructed from triarylborane-cored tritopic tridentate ligands, which were fabricated into spin-coated films with bright emission, smooth surfaces, and uniform thickness. These films demonstrated ultralow detection limits for a series of volatile amines, reaching the sub-ppt level. This work serves as a compelling example of the preparation and application of metal–organic-cage-based films, paving the way for broader application scenarios.