Branched Alkyl Chain-Guided Modulation of BODIPY Packing Polymorphism for Engineering Thin-Film J-Aggregates

Area of Science:

• Materials Science
• Organic Chemistry
• Supramolecular Chemistry

Background:

• Boron dipyrrin (BODIPY) dyes are known for their photophysical properties.
• Controlling molecular arrangement in solid-state is crucial for advanced optical materials.
• J-aggregate formation in thin films can lead to enhanced optical properties.

Purpose of the Study:

• To develop a rational crystal-engineering strategy for thin-film J-aggregate formation.
• To investigate the role of branched alkyl chains in controlling BODIPY self-assembly.
• To achieve J-aggregate formation with sharp absorption and fluorescence bands.

Main Methods:

• Systematic modulation of volume fractions between BODIPY and alkoxy groups.
• Introduction of branched alkyl chains (isopentyloxy and dihydrocitronellyloxy) to the BODIPY skeleton.
• Fine-tuning the BODIPY core with iodine and nitrile substituents.
• Fabrication of spin-coated thin films.

Main Results:

• Branched alkyl chains were found to induce steric hindrance and conformational entropy, promoting J-aggregate formation.
• The introduced substituents influenced the cofacial arrangement and packing of BODIPY units.
• J-aggregates exhibiting exceptionally sharp absorption and fluorescence bands were successfully formed in spin-coated films.

Conclusions:

• A viable crystal-engineering strategy for fabricating BODIPY-based J-aggregates in thin films was established.
• The study highlights the importance of molecular design, particularly the role of branched chains, in controlling supramolecular assembly.
• The resulting J-aggregates show potential for applications requiring sharp optical responses.