Fluorescent molecular systems based on carborane-perylenediimide conjugates

Area of Science:

• Materials Science
• Organic Chemistry
• Nanotechnology

Background:

• Perylene diimides (PDIs) are known for their excellent optical properties but often suffer from aggregation-caused quenching.
• Ortho-carboranes (o-carboranes) are boron-rich cage compounds with potential applications in medicine and materials science.

Purpose of the Study:

• To synthesize novel PDI-o-carborane derivatives (PDI-CB1 and PDI-CB2) with enhanced solubility and maintained optical properties.
• To investigate the impact of o-carborane incorporation on the photophysical behavior and aggregation of PDIs.
• To explore the potential of these new materials in theranostics, specifically for boron neutron capture therapy (BNCT).

Main Methods:

• Synthesis of alkyne-terminated PDIs (PDI1 and PDI2).
• Insertion of decaborane into PDI1 and PDI2 to form PDI-CB1 and PDI-CB2 using a methylene linker.
• Optical property measurements (absorption, fluorescence quantum yield) in solution.
• Aggregation studies in various solvents.
• Solid-state emission analysis and nanoparticle formation.

Main Results:

• Successful synthesis of PDI-CB1 and PDI-CB2 with retained high fluorescence quantum yields (~100%) in solution.
• Enhanced solubility of PDI-CB1 and PDI-CB2 in both nonpolar and aqueous solvents compared to parent PDIs.
• Aggregation-caused fluorescence quenching observed in the solid state for both derivatives.
• PDI-CB1 demonstrated bright red excimer-type emission in solid state and in water-dispersible nanoparticles.

Conclusions:

• The incorporation of o-carborane groups via a methylene linker effectively enhances PDI solubility without compromising solution optical properties.
• Solid-state emission is susceptible to aggregation, but PDI-CB1 exhibits unique red excimer emission.
• PDI-CB1's ability to form stable nanoparticles with preserved red emission indicates significant potential as a theranostic agent for fluorescence imaging and BNCT.