Encapsulation of a Highly Acid-Stable Dicyano-Bodipy in Zr-Based Metal-Organic Frameworks with Increased Fluorescence Lifetime and Quantum Yield Within the Solid-Solution Concept

In this work, we have synthesized a more acid-stable variant of the classic chromophore difluoro-Bodipy by substituting the difluoro ligands at boron with cyano groups. This dicyano-Bodipy variant allowed the in situ incorporation during the MOF formation under acidic conditions and was investigated for the first time as dye@MOF composites using both post-synthetic and in situ incorporation into the zirconium-based metal-organic frameworks (MOFs) UiO-66, MOF-808, DUT-67 and MIP-206. The successful incorporation of dicyano-Bodipy was confirmed by PXRD, N2 sorption, digestion UV-Vis and fluorescence spectroscopy. Depending on the incorporation method used, significant lower BET surface areas could be determined. The luminescence properties of the resulting dicyano-Bodipy@MOF composites from the in situ incorporation had up to almost eight-fold extended photoluminescent lifetimes of 9.0 ns, compared to the neat dye in its solid state with 1.2 ns, which suggests the formation of a solid solution in which the incorporated Bodipy is protected from external influences within a well-defined MOF pore. The quantum yield could be enhanced to as high as 77% through post-synthetic incorporation into the MOF DUT-67 compared to the neat dye in its solid state with 9%.