Bridged bis-BODIPYs: their synthesis, structures and properties

Area of Science:

• Organic Chemistry
• Materials Science
• Photophysics

Background:

• Boron dipyrromethene (BODIPY) dyes are known for their strong fluorescence and photostability.
• Bis-BODIPY compounds offer potential for enhanced optical and electronic properties due to their extended conjugation.
• Understanding the structure-property relationships in bis-BODIPYs is crucial for designing new functional materials.

Purpose of the Study:

• To synthesize and characterize a series of bis-BODIPY compounds with diverse bridging units.
• To investigate the impact of different spacer groups on the spectroscopic and electronic properties of bis-BODIPYs.
• To explore the solid-state packing and intermolecular interactions in selected bis-BODIPY structures.

Main Methods:

• Synthesis of bis-BODIPY derivatives (compounds 1-6) using various organic linkers.
• Characterization using UV-Vis absorption, fluorescence spectroscopy, and NMR.
• X-ray crystallography for three selected bis-BODIPY compounds.
• Density Functional Theory (DFT) calculations to analyze electronic structure and interactions.

Main Results:

• Bis-BODIPYs bridged by thiophene, furan, N-alkylcarbazole, triphenylamine, and phenylene groups were successfully synthesized.
• Spectroscopic properties, including absorption and emission maxima, were modulated by the nature and size of the spacer units.
• X-ray structures revealed intermolecular C(H)π and ππ stacking interactions, with reduced dihedral angles between BODIPY units.
• DFT studies confirmed electronic communication between spacers and BODIPY units, with HOMO-LUMO gaps varying based on spacer bulkiness.
• Red-shifted absorption and emission were observed for furan and thiophene spacers compared to phenylene or carbazole.

Conclusions:

• Spacer selection is a critical factor in tuning the photophysical properties of bis-BODIPY systems.
• Increased electronic interaction between BODIPY units, facilitated by smaller dihedral angles, leads to altered redox potentials.
• The study provides valuable insights into the design of bis-BODIPY materials with tailored optical and electronic characteristics for applications in organic electronics and photonics.