Solvo-Mechanical Flexing in Cryogenically 2D Flexible Single-Crystal-to-Single-Crystal Polymorphic Switch.

Area of Science:

• Materials Science
• Crystallography
• Mechanics

Background:

• Stimuli-responsive molecular crystals coupling mechanical flexibility and phase transformations are rare.
• Such materials are promising for smart material applications.

Purpose of the Study:

• To report a solvo-mechanical bending-induced single-crystal-to-single-crystal (SCSC) transformation in an indomethacin (IND) polymorph.
• To integrate two-dimensional (2D) elastic flexibility with polymorphic switching.

Main Methods:

• In situ time-resolved atomic force microscopy (AFM) to capture transformations.
• Mechanical strain analysis and energy framework calculations.
• Comparative studies with different indomethacin polymorphs.

Main Results:

• A 2D elastically bendable methanol solvate crystal of indomethacin (INDM) transforms into the IND-δ polymorph upon heating, retaining crystallinity and elasticity.
• IND-δ exhibits mechanical flexibility across various temperatures.
• A flexible-to-flexible-to-brittle polymorphic pathway (INDM → IND-δ → IND-γ) was established.
• Interactions like hydrogen bonding, π-π stacking, and halogen bonds enable directional elasticity.
• Indomethacin-delta and indomethacin-alpha demonstrate elasticity, contrary to previous reports.

Conclusions:

• This work demonstrates novel dynamic mechanical characteristics of indomethacin polymorphs.
• It offers new directions for designing adaptive crystalline materials with tunable mechanical properties.