Distinct layered structure with density modulation in solid phase formed from B2 phase of banana molecules

Area of Science:

• Liquid Crystal Physics
• Materials Science
• X-ray Crystallography

Background:

• Banana molecules exhibit complex phase behavior.
• Smectic liquid crystal phases are known for layered structures.
• Bromine substitution can influence molecular packing and phase transitions.

Purpose of the Study:

• To investigate the low-temperature phase (X1) of a bromine-substituted banana molecule.
• To elucidate the unique two-dimensional (2D) long-range structure observed in the X1 phase.
• To understand the relationship between molecular structure and observed phase behavior.

Main Methods:

• Synchrotron radiation (SR) X-ray scattering measurements were employed.
• Analysis of layer line reflections to determine structural parameters.
• Interpretation of diffraction data to model the 2D lattice structure.

Main Results:

• A unique 2D long-range structure was identified in the X1 phase.
• The X1 phase exhibits long-range layer modulation order.
• A 2D lattice with specific parameters (a=173 Å, c=53.4 Å, β=81.1°) was determined, indicating an undulated layer structure.
• Electron density modulation along the layers and staggered splay defects were observed.

Conclusions:

• The observed 2D structure is attributed to periodically occurring polarization splay defects.
• The angle between lattice axes suggests a staggered arrangement of these defects in adjacent layers.
• This finding provides insights into the complex structural organization in functional organic materials.