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/Eux), were synthesized by solvothermal reactions. Single-crystal X-ray diffraction revealed that MCF-53­(Tb/Eux) 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/Eux) 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.