Kinetic Insights into Bridge Cleavage Pathways in Periodic Mesoporous Organosilicas

Abstract

Bridging functionalities in periodic mesoporous organosilicas (PMOs) enable new functionalities for a wide range of applications. Bridge cleavage is frequently observed during anneals required to form porous structures, yet the mechanism of these bridge cleavages has not been completely resolved. Here, we reveal these chemical transformations and their kinetic pathways on sub-millisecond timescales induced by laser heating. By varying anneal times and temperatures, the transformation dynamics of bridge cleavage and structural transformations, and their activation energies, are determined. The structural relaxation time for individual reactions and their effective local heating time are determined and compared, and results directly demonstrate the manipulation of different molecules through kinetic control of the sequence of reactions. By isolating and understanding the earliest stage of structural transformations, this study identifies the kinetic principles for new synthesis and post-processing routes to control individual molecules and reactions in PMOs and other material systems with multi-functionalities.