Interaction Hierarchy and Polymorphic Structure–Property Dynamics in Luminescent Molecular Crystals

ABSTRACT Solid‐state phase transitions provide a powerful platform for translating subtle molecular‐level interactions into macroscopic functional responses; however, rational design strategies that enable predictable control over such transitions remain limited. Herein, we report polymorphic structure–property switching behaviors associated with competing intermolecular interactions in luminescent molecular crystals. Cyano‐ β ‐substituted distyrylbenzene derivatives bearing bromo and methoxy side chains were designed to incorporate competing homotypic and heterotypic noncovalent interactions with distinct interaction characteristics. Single‐crystal analyses reveal that subtle differences in the hierarchical ordering of dispersion‐, dipole–dipole‐, and electrostatically dominated interactions give rise to polymorphic crystal structures with distinct molecular orientations and photoluminescence properties. Thermal and mechanical stimuli induce distinct phase transitions: an irreversible thermally induced single‐crystal‐to‐single‐crystal transition and a pseudo‐reversible mechanochemical pathway via an amorphous intermediate, both directly visualized as pronounced emission color changes. Kinetic and thermodynamic controls over polymorph formation are elucidated through a combination of structural analysis, photophysical measurements, and crystal framework calculations. This study suggests that multifunctional molecular side chains enable access to diverse interaction landscapes, allowing multiple structure–property switching pathways to be encoded within a single molecular framework. The presented framework provides a qualitative perspective for interpreting dynamic structural behaviors in molecular crystals.