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

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 cm), 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.