A Bifunctional Organic Photocatalyst for Efficient Single-Electron and Energy Transfer Activation

Area of Science:

• Organic Chemistry
• Photocatalysis
• Sustainable Chemistry

Background:

• Bifunctional photocatalysts mediating single-electron transfer (SET) and energy transfer (EnT) are rare, often relying on metal-based systems.
• Organic photocatalysts offer cost-effective and metal-free alternatives.

Purpose of the Study:

• To introduce a new family of organic photocatalysts, 3-thioaryl-4-hydroxycoumarins.
• To demonstrate their bifunctional capability for both SET and EnT processes.
• To enable the activation of redox-inert substrates for various bond-forming reactions.

Main Methods:

• Synthesis of 3-thioaryl-4-hydroxycoumarins.
• Photophysical characterization (e.g., redox potentials, triplet energy).
• Theoretical calculations and mechanistic studies.

Main Results:

• The developed organic photocatalysts exhibit a stabilized charge-transfer (CT) excited state.
• Achieved strong reducing power (E*_red = -3.08 V vs. SCE) for SET.
• Maintained high triplet energy (E_T = 67 kcal mol^-1) for EnT.
• Successfully mediated diverse C-S, C-P, C-B, and C-C bond formations via SET.
• Facilitated EnT-driven reactions like E/Z olefin isomerization and [2+2] photocycloadditions.

Conclusions:

• 3-thioaryl-4-hydroxycoumarins are effective bifunctional organic photocatalysts.
• Their dual SET and EnT reactivity broadens the scope of photocatalytic transformations.
• These catalysts offer a sustainable and metal-free approach to activating challenging substrates.