Diffusion-Controlled Luminescence Quenching in Metal-Organic Frameworks

摘要

Diffusion-controlled luminescence quenching of a phosphorescent metal-organic framework built from the Ru(bpy)_3~(2+)-derived bridging ligand (MOF-1) was studied using a series of amines of different sizes as quenchers. The dynamics of amine diffusion into solvent-filled MOF-1 channels was probed by modeling time-dependent luminescence quenching data, which provide quantitative diffusion coefficients for the amine quenchers. Triethylamine, tripropylamine, and tributylamine were found to follow Fickian diffusion with a diffusivity of (1.1 ± 0.2) X 10~(-13), (4.8 ± 1.2) × 10~(-14), and (4.0 ± 0.4) × 10~(14)m~2/s, respectively. Diisopropylethylamine (DIPEA), on the other hand, was found to be too large to enter the MOF channels. Despite its size, 4-MeOPhNPh_2 can enter the MOF channels via a slow, complicated framework/guest intercalation process to result in extensive framework distortion as revealed by powder X-ray diffraction. This work represents the first quantitative study of the dynamics of molecular diffusion into solvent-filled MOF channels. Such quantitative information on molecular diffusion in MOFs is of fundamental importance to many of their potential applications (e.g., heterogeneous catalysis).