Mixed-Lanthanide Porous Coordination Polymers Showing Range-Tunable Ratiometric Luminescence for O₂ Sensing

Luminescent porous coordination polymers (PCPs) are emerging as attractive oxygen-sensing materials, but they are mostly based on single-wavelength luminometry. Here, we report a special mixed-lanthanide strategy for self-referenced ratiometric oxygen sensing. A series of isostructural, pure-lanthanide, or mixed-lanthanide PCPs, MCF-53(Tb/Eu_x), were synthesized by solvothermal reactions. Single-crystal X-ray diffraction revealed that MCF-53(Tb/Eu_x) is composed of complicated two-dimensional coordination networks, which interdigitate to form a three-dimensional supramolecular structure retaining one-dimensional ultra-micropores. MCF-53(Tb/Eu_x) can undergo multiple single-crystal to single-crystal structural transformations upon desorption/adsorption of coordinative and lattice guest molecules, and the lanthanide metal ions are partially exposed on the pore surface at the guest-free state. Tb(III) ions are not luminescent and only act as separators between Eu(III) ions, and the Tb(III)/Eu(III) mixing ratio can tune the relative emission intensities, luminescence lifetimes of the Eu(III) phosphorescence, and the ligand fluorescence, giving rise to not only ratiometric photoluminescence oxygen sensing but also tunable emission-color-changing ranges.