Enabling Control over Mechanical Conformity and Luminescence in Molecular Crystals: Interaction Engineering in Action

Area of Science:

• Materials Science
• Organic Electronics
• Crystallography

Background:

• Molecular crystals offer superior charge transport but are often brittle, hindering device integration.
• Developing mechanically compliant organic electronic materials is crucial for flexible devices.

Purpose of the Study:

• To engineer mechanical conformity in π-conjugated molecular crystals.
• To control molecular packing and understand its effect on crystal bending properties.

Main Methods:

• Synthesized pyridine-appended thiazolothiazole derivatives.
• Controlled crystallization to obtain different polymorphs.
• Formed co-crystals using hydrogen and halogen bond donors.
• Investigated mechanical bending and luminescence properties.
• Performed DFT calculations (QM/MM) to understand fluorescence.

Main Results:

• Achieved control over mechanical conformity in single crystals by modulating molecular packing.
• Identified polymorphs with distinct bending behaviors (elastic vs. brittle).
• Co-crystals with specific hydrogen-bonding motifs exhibited enhanced elastic bending.
• Halogen-bonded co-crystals showed mechanical flexibility and luminescence, suitable for waveguiding.
• Hydrogen-bonded co-crystals were non-emissive due to excited state proton transfer.

Conclusions:

• Molecular packing and intermolecular interactions (hydrogen/halogen bonding) are key to controlling mechanical properties in organic crystals.
• Co-crystallization is an effective strategy to enhance the mechanical flexibility of π-conjugated molecular crystals.
• Tailored co-crystals offer potential for flexible optoelectronic and waveguiding applications.