Giant Birefringence Induced by Intermolecular Aromatic Interactions in Hydrogen-Bonded Organic Frameworks

Area of Science:

• Materials Science
• Optics
• Crystallography

Background:

• Birefringent crystals are essential for light polarization control.
• Developing organic crystals with giant birefringence remains a significant challenge.

Purpose of the Study:

• To propose a hydrogen-bonding self-assembly strategy for constructing organic framework birefringent crystals (HOFBCs).
• To achieve and analyze giant birefringence in novel HOFBC materials.

Main Methods:

• Utilized a hydrogen-bonding self-assembly strategy to create aromatic π-conjugated HOFBCs.
• Performed theoretical calculations and structural analyses to understand birefringence origins.
• Investigated thermal stability and birefringence of HOFBCs after heating.

Main Results:

• Synthesized an HOFBC with a record birefringence of 0.763@546 nm, exceeding all known organic and commercial birefringent crystals.
• Identified high polarizability anisotropy and intermolecular aromatic interactions as key factors for giant birefringence.
• Observed retained crystalline structure and layer-by-layer assembly in a thermally treated HOFBC (HOFBC-1-250), yielding an even higher birefringence of 0.800@546 nm.

Conclusions:

• The study presents a novel strategy for developing giant birefringent materials using hydrogen-bonded organic frameworks.
• The developed HOFBCs demonstrate exceptional birefringence, opening new avenues for optical applications.
• This research highlights the potential of HOF crystals in advanced birefringence technologies.