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

Area of Science:

• Materials Science
• Crystallography
• Supramolecular Chemistry

Background:

• Solid-state phase transitions are crucial for molecular-level control of macroscopic properties.
• Predictable design strategies for solid-state phase transitions are currently limited.
• Luminescent molecular crystals offer potential for functional responses through structural changes.

Purpose of the Study:

• To investigate polymorphic structure-property switching in luminescent molecular crystals.
• To explore the role of competing intermolecular interactions in controlling crystal structures and photoluminescence.
• To develop rational design strategies for predictable solid-state phase transitions.

Main Methods:

• Synthesis of cyano-β-substituted distyrylbenzene derivatives with bromo and methoxy side chains.
• Single-crystal X-ray diffraction analysis to determine crystal structures and molecular packing.
• Photophysical measurements (photoluminescence spectroscopy) to assess optical properties.
• Thermal and mechanical stimuli to induce phase transitions.
• Crystal framework calculations to elucidate kinetic and thermodynamic controls.

Main Results:

• Competing homotypic and heterotypic noncovalent interactions led to distinct polymorphic crystal structures.
• Subtle differences in interaction hierarchies influenced molecular orientation and photoluminescence.
• Irreversible thermal and pseudo-reversible mechanical stimuli induced distinct phase transitions with visible emission color changes.
• Demonstrated control over polymorph formation through kinetic and thermodynamic pathways.

Conclusions:

• Multifunctional molecular side chains enable diverse interaction landscapes for encoded structure-property switching.
• The study provides a framework for interpreting dynamic structural behaviors in molecular crystals.
• This work advances the rational design of materials exhibiting predictable solid-state phase transitions and functional responses.