Compression of a Flapping Mechanophore Accompanied by Thermal Void Collapse in a Crystalline Phase

Mechanical control of the molecular
energy landscape is an important
issue in modern materials science. Mechano­phores play a unique
role in that the mechanical responses are induced against the activation
barrier for intramolecular transformation with the aid of external
forces. Here we report an unprecedented activation process of a flexible
flapping mechano­phore. Namely, thermal void collapse in a crystalline
phase triggers mechano­phore compression in a definite proportion.
Unfavored conformational planarization of the flapping mechano­phore
is compulsorily induced by packing force, leading to a total energy
gain in crystal packing. Fluorescence chromism indicates extended
π conjugation resulting from the mechano­phore compression,
giving rise to an energy transfer from the unpressed to compressed
conformers.