Densely Packed and Well-Aligned Liquid-Crystalline Scaffolds Drive Controllable Axial Crystal Strain

Area of Science:

• Materials Science
• Crystallography
• Organic Electronics

Background:

• Molecular crystals offer potential as actuators due to phase transition-induced shape changes.
• Achieving rational control over crystal-length strain in these materials is a significant challenge.

Purpose of the Study:

• To develop a strategy for rational control over crystal-length strain in molecular actuators.
• To establish a design rule for creating programmable uniaxial deformation in crystalline materials.

Main Methods:

• Densely packing liquid-crystalline (LC) scaffolds (nIB) within rigid crystalline lattices (Au-nIB).
• Utilizing thermally driven polymorphic transitions to reconfigure mesogen layer periodicity.
• Employing single-crystal X-ray diffraction to analyze structural changes and correlations.

Main Results:

• Established smectic-like layer arrangements within the crystalline lattice, with mesogen layers separated by alkyl chains.
• Achieved programmable uniaxial deformation with a crystal-length ratio (ρL) up to 1.52.
• Discovered a quantitative, inverse correlation (ρL ≈ 1/ρm) between macroscopic length and mesogen-layer thickness ratios, defining a design rule for axial strain.
• Demonstrated reconfigurable, multistep elongation-contraction in single crystals of Au-4IB through domain engineering.

Conclusions:

• Coupling LC softness with crystalline order provides a tunable platform for rationally designed crystal actuators.
• The developed strategy enables precise control over axial strain, applicable to compliant organic devices.
• This approach offers a general, chemically and functionally tunable method for creating advanced actuators.