Stable photoluminescence of lanthanide complexes in aqueous media through Metal-Organic Frameworks Nanoparticles with plugged surface

Abstract The photoluminescence stability of lanthanide complex in aqueous media is a prerequisite for diagnostics probes. The combination of building blocks working in concert to facilitate host–guest structures is now considered state of the art in surpassing this roadblock, yet there still remains a tremendous challenge. Here, a stable, highly-luminescent system was developed through trapping anionic complexes sensitized by tridentate pyridine-tetrazolate (pytz) ligands within the rigid framework of ZIF-8 (zeolitic imidazolate framework-8) particles (∼60 nm in size). The key to maintaining the stable luminescence of lanthanide complexes inside ZIF-8 frameworks is a stopcock design, i.e. stopper molecules (an imidazolium based ionic liquid) selectively plugged on the pore entrances located at the exterior surface of the ZIF-8 host, which protect both the host and the guests from deteriorations by surrounding ions/water molecules. Remarkably, the obtained Ln complex encapsulated ZIF-8 particles (Ln = terbium, europium) particles possessed high quantum yields (23.2% and 8.5%), large absorption cross-section (∼10 −12  cm 2 ), and long luminescence lifetimes (1.9 and 3.0 ms) in PBS buffer. In addition, the system can realize single/multi-color encoding by altering the loading amounts and the weight ratios of complexes emitting at different wavelengths.