Molecular Structural Control of the Amorphous-Crystalline Balance in Solids: Structure-Phase Correlation in DADQs...

Area of Science:

• Materials Science
• Solid-State Chemistry
• Supramolecular Chemistry

Background:

• The amorphous/crystalline (A/C) assembly in molecular solids significantly influences their mechanical, pharmaceutical, electronic, and photophysical properties.
• Understanding the molecular features and interactions governing the preference for amorphous (A), crystalline (C), or bi-stable A-C states is crucial for materials design.

Purpose of the Study:

• To systematically analyze the molecular determinants of phase preference and stability in molecular solids.
• To establish a structure-phase correlation for alkoxyalkyl diaminodicyanoquinodimethanes (ROR'-DADQs) and explore their potential as phase-change materials.

Main Methods:

• Investigated a large family of ROR'-DADQs, monitoring fluorescence changes across solution, amorphous, and crystalline states.
• Utilized thermal analysis, single-crystal X-ray diffraction, and Hirshfeld surface analysis to probe intermolecular interactions and lattice structures.

Main Results:

• Fluorescence enhancement across solution, amorphous, to crystalline states served as a signature for phase preference and stability.
• Spectroscopic observations were confirmed by thermal and structural analyses, highlighting the impact of molecular structure, H-bonds, and lattice orientation on phase stability.
• A structure-phase correlation was established, enabling the identification of borderline systems as functional phase-change materials.

Conclusions:

• Molecular structural features and intermolecular interactions critically govern the amorphous or crystalline forms of molecular solids.
• The established structure-phase correlation allows for the design of novel materials with tunable supramolecular structures and controllable interconversions.
• Demonstrated reversible fluorescence switching between A/C states, verifying the potential of identified systems as functional phase-change materials.