Chiral columns forming a lattice with a giant unit cell

Area of Science:

• Materials Science
• Crystallography
• Organic Chemistry

Background:

• Mesogenic materials, specifically quinoxaline derivatives, are investigated for their unique structural and photophysical properties.
• Previous studies have explored columnar phases in liquid crystals, but a novel 3D columnar phase with an Fddd lattice is now reported.

Purpose of the Study:

• To synthesize and characterize novel quinoxaline derivatives with semi-flexible cores.
• To investigate the formation of a new 3D columnar phase and its crystallographic properties.
• To explore the photophysical properties, including fluorescence and charge transport, of these materials.

Main Methods:

• Synthesis of quinoxaline derivatives with varying molecular structures.
• X-ray diffraction analysis to determine crystallographic structure and lattice type (Fddd).
• Spectroscopic techniques (e.g., fluorescence spectroscopy) to measure quantum yield and emission properties.
• Charge transport measurements to assess photogeneration and mobility of charge carriers.

Main Results:

• A new 3D columnar phase with a large unit cell and Fddd lattice was observed below the columnar hexagonal phase.
• The 3D columnar structure arises from the frustrated arrangement of helical columns of opposite chiralities into a triangular lattice.
• Fluorescence properties are tunable; extended π-conjugated systems lead to quenched fluorescence, while flexible structures achieve up to 25% quantum yield.
• Rigid mesogenic cores suppress fluorescence but enable effective photogeneration of charge carriers.
• Bipolar hole and electron transport were observed in some of the studied materials.

Conclusions:

• Quinoxaline derivatives can form a novel 3D columnar phase with unique crystallographic features.
• Molecular design allows for tuning of fluorescence properties, from quenched emission to high quantum yields.
• Materials with suppressed fluorescence exhibit promising characteristics for photogeneration of charge carriers and bipolar transport, suggesting potential applications in organic electronics.