Tris-Azo Triangular Paraphenylenes: Synthesis and Reversible Interconversion into Radial π-Conjugated Macrocycles

Area of Science:

• Organic Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Cycloparaphenylenes (CPPs) are macrocyclic aromatic hydrocarbons with unique structural and electronic properties.
• Azo groups (-N=N-) are known for their photochromic and electrochemical activity.
• Combining CPPs with azo functionalities offers a route to novel photoresponsive molecular architectures.

Purpose of the Study:

• To synthesize and characterize cycloparaphenylene derivatives incorporating tris-azo groups.
• To investigate the structural, thermal, and photochemical properties of these novel compounds.
• To explore the influence of molecular shape and electronic structure on their behavior.

Main Methods:

• Multi-step organic synthesis to construct the cycloparaphenylene scaffold with tris-azo linkages.
• Single-crystal X-ray diffraction to determine the solid-state structures.
• UV-Vis spectroscopy and photochemical experiments to study isomerization.
• Density Functional Theory (DFT) calculations to analyze electronic properties.

Main Results:

• Successful synthesis of [3]cycloazobenzene derivatives with tris-azo groups.
• The smaller derivative exhibits a stable, triangular all-cis conformation with Kagome-patterned crystal packing.
• The biphenylene-bridged derivative undergoes photoinduced isomerization and selective acid-catalyzed conversion to an all-trans form.
• DFT calculations show a correlation between shape change (triangular to circular) and electronic structure modification (HOMO increase, LUMO decrease).

Conclusions:

• Tris-azo functionalization of cycloparaphenylenes leads to unique structural and photophysical properties.
• Ring strain and crystal packing significantly influence the stability of the all-cis isomer.
• Photoisomerization and acid-induced transformations offer pathways for controlling molecular shape and electronic characteristics.
• These findings contribute to the development of novel π-conjugated systems with tunable properties for advanced applications.