Halogen bonding stabilizes a cis-azobenzene derivative in the solid state: a crystallographic study.

Area of Science:

• Crystallography
• Materials Science
• Organic Chemistry

Background:

• Azobenzene derivatives are photoresponsive molecules with distinct trans- and cis-isomers.
• The cis-isomer is often metastable, making its crystallization challenging.
• Understanding factors stabilizing the cis-isomer is crucial for developing photoresponsive materials.

Purpose of the Study:

• To synthesize and characterize fluorinated azobenzene isomers.
• To investigate the role of halogen bonding in stabilizing the cis-azobenzene isomer.
• To explore the influence of aliphatic chains on molecular packing and stability.

Main Methods:

• Single-crystal X-ray diffraction for structural characterization.
• Density Functional Theory (DFT) calculations to analyze bonding interactions.
• Synthesis of fluorinated azobenzene derivatives with aliphatic chains.

Main Results:

• Crystals of both trans- and cis-isomers of a fluorinated azobenzene were successfully grown and analyzed.
• Fluorine substitution increased the lifetime of the cis-isomer, enabling its crystallization.
• Halogen bonding (N...I synthon) was identified as a key interaction stabilizing the cis-isomer.
• Aliphatic chains induced phase segregation, stabilizing both isomers' molecular arrangements.

Conclusions:

• Halogen bonding plays a critical role in stabilizing the metastable cis-azobenzene isomer.
• The presence of fluorine atoms and aliphatic chains influences crystal packing and isomer stability.
• This study contributes to understanding non-covalent interactions in azobenzene isomers, informing the design of solid-state photoresponsive materials.