Curvature-induced vitrification and polymorphism in corannulene.

Area of Science:

• Materials Science
• Physical Chemistry
• Crystallography

Background:

• Polymorphism in polyarenes is crucial for applications but underexplored in curved structures.
• Corannulene, the simplest geodesic polyarene, lacks detailed understanding of its solid-state behavior.

Purpose of the Study:

• To investigate the polymorphism and thermodynamic stability of corannulene.
• To explore the phase transitions and structural dynamics of solid corannulene.

Main Methods:

• Fast scanning calorimetry to determine thermal transitions.
• X-ray diffraction to analyze crystal structure and density changes.
• Analysis of atomic displacement parameters to understand molecular motion.

Main Results:

• Corannulene exhibits a glass transition (Tg) at 323 K when cooled rapidly from the melt (>500 K s⁻¹).
• Three new polymorphs were identified upon heating, associated with thermally activated molecular rotations.
• Diffraction data indicate distinct structural differences below and above Tg, suggesting two different material states.

Conclusions:

• Corannulene displays unanticipated complexity in its solid-state structure and thermodynamic response.
• The identified polymorphs and glass transition reveal unique behavior compared to flat polyarenes.
• Findings advance the understanding of structure-property relationships in curved polycyclic aromatic hydrocarbons.