Delocalized Triplet State for Efficient Generation of Superoxide Radical

Area of Science:

• Photochemistry
• Organic Chemistry
• Materials Science

Background:

• Type-I photodynamic action requires suppressing singlet oxygen formation.
• Multichromophoric systems are key but face challenges with nonradiative decay hindering intersystem crossing (ISC).

Purpose of the Study:

• To rationally design asymmetric boron dipyrromethene (BODIPY) dimers to overcome limitations in Type-I photodynamic action.
• To elucidate structure-dependent dynamics governing photophysical pathways.

Main Methods:

• Time-resolved spectroscopy
• Quantum chemical calculations
• Design of asymmetric BODIPY dimers

Main Results:

• Identified strong interchromophoric coupling and molecular asymmetry as crucial design principles.
• Demonstrated that asymmetry enables efficient mixing between delocalized exciton (DE) and intramolecular charge-transfer (ICT) states, enhancing spin-orbit coupling (SOC).
• Achieved SOC-enhanced ISC rates competitive with nonradiative decay, facilitating triplet formation below the singlet oxygen energy gap.

Conclusions:

• The developed BODIPY dimers preferentially utilize the Type-I pathway.
• Deciphered key relaxation pathways and provided a framework for high-performance Type-I photosensitizers.