Guest-Dependent Dynamics in a 3D Covalent Organic Framework

Guest-dependent dynamics having both
crystal contraction and expansion
upon inclusion of various guests is uncovered in a 3D covalent organic
framework (COF) prepared with a facile and scalable method. A molecular-level
understanding of how the framework adjusts the node geometry
and molecular configuration to perform significant contraction and
large amplitude expansion are resolved through synchrotron in-house
powder X-ray diffraction (PXRD) and Rietveld refinements. We found
that the COF adopts a contracted phase at ambient conditions upon
capturing moisture and is also adaptive upon inclusion of organic
solvents, which is highlighted by a large crystal expansion (as large
as 50% crystallographic volume increment and a 3-fold channel size
enlargement). With this new knowledge of the structural adaptability,
the diverse responses and coherent switchability are thereby presented
to pave the way to rational design and deliberate control of dynamic
COFs.