Untangling the Mechanochromic Properties of Benzothiadiazole-Based Luminescent Polymorphs through Supramolecular Organic Framework Topology

Two new luminophore
polymorphs of 4-bromo-7-(4-nonylphenyl)­benzo­[c]­[1,2,5]­thiadiazole
(1α and 1β) exhibiting different
color emissions, which switch into each other
in response to shear force and solvent vapors, are presented and their
X-ray structure is determined. Supramolecular organic framework topology
(SOFT) studies on the two polymorphic structures led us to conclude
that the mechanochromic phase transformation can be explained on the
basis of modifications in their respective topological nets: mab and pcu for 1α and 1β, respectively, as a result of the breaking and restoration
of a number of weak supramolecular interactions. The color changes
accompanying this transformation have been rationalized with the help
of time-dependent density functional theory. We firmly believe that
our findings will inspire future research on the design of novel stimuli-responsive
organic materials with switchable properties based on their supramolecular
interactions by establishing clear SOFT-property relationships.