Aggregation-Induced Singlet Oxygen Generation: Functional Fluorophore and Anthrylphenylene Dyad Self-Assemblies

Area of Science:

• Supramolecular Chemistry
• Photochemistry
• Materials Science

Background:

• Monomeric building blocks can exhibit new properties upon self-assembly.
• Developing functional fluorophores with aggregation-dependent properties is an active research area.
• Reactive oxygen species (ROS) generation is crucial for applications like photodynamic therapy.

Purpose of the Study:

• To design a self-assembling fluorophore system that generates reactive oxygen species (ROS) exclusively in its aggregated state.
• To investigate the photophysical properties and mechanism of ROS generation in the designed molecular system.
• To explore the potential of aggregation-induced singlet oxygen generation (AISG) for photocytotoxicity.

Main Methods:

• Synthesis of a boron dipyrromethene (BODIPY) and anthrylphenylene (AP) dyad.
• Characterization of aggregate formation and photophysical properties in aqueous solution.
• Investigation of singlet oxygen generation using spectroscopic methods.
• X-ray crystallographic analysis to determine molecular packing in aggregates.
• Assessment of photocytotoxicity in vitro.

Main Results:

• Fluorescein-AP conjugates formed non-fluorescent H-aggregates.
• The BODIPY-AP dyad formed two-color-emissive aggregates via an intermolecular charge-transfer (CT) complex.
• BODIPY-AP aggregates exhibited significant singlet oxygen (¹ O₂) generation upon excitation.
• The CT state in the BODIPY-AP dyad was found to favor intersystem crossing.
• X-ray crystallography revealed lattice-like molecular packing responsible for aggregation-induced ¹ O₂ generation (AISG).

Conclusions:

• A novel BODIPY-AP dyad enables aggregation-induced singlet oxygen generation (AISG).
• The observed AISG is attributed to the formation of an intermolecular charge-transfer complex and favorable intersystem crossing within the aggregated state.
• The unique molecular packing in the aggregates is key to achieving efficient ¹ O₂ production.
• This study presents a promising platform for developing smart fluorescent materials with applications in sensing and photodynamic therapy.