Catalyst Hide-and-Seek Beneath Porous Support Surfaces: Pinpointing Active Site Distribution Through Resonance Energy Transfer.

Merging the high selectivity and efficiency of homogeneous catalysts with the recyclability of heterogeneous systems represents an attractive, industry-driven concept that can be realized through the "heterogenization" of existing molecular catalysts by incorporating them into porous solid-state matrices. The concept proposed herein uses Förster resonance energy transfer analysis to establish the first direct correlations among matrix topology, catalyst integration strategy, and active site positioning in porous materials without employing fluorescent model systems. This catalyst mapping method can be applied to several classes of porous materials, including metal-organic frameworks and mesoporous silica. It addresses the existing challenges in relating the factors that control the spatial surface (re)distribution of molecular catalysts within such matrices before and after catalytic transformations. On the example of a series of six different catalyst-integrated materials, Å-level mapping of active site distribution was correlated with the nature of the porous host and the catalyst integration mechanism, which dictates the loading and accessibility of integrated catalysts. Thus, these studies provide a foundation for developing a framework to guide the design of recyclable heterogeneous catalysts with well-defined active site distributions, both before and after catalytic transformations, which are key fundamental parameters for heterogeneous catalysis.