  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.
