Low-Energy Photons in Radical Chemistry: From Deep-Red to Near-Infrared Radical Generation for Organic Synthesis

Area of Science:

• Photochemistry
• Organic Synthesis
• Catalysis

Background:

• Radical intermediates are crucial for bond formations not achievable via ionic pathways.
• Visible-light photochemistry offers sustainable radical generation but often requires high-energy light.
• Deep-red (DR) to near-infrared (NIR) light offers advantages like tissue penetration and reduced side reactions.

Purpose of the Study:

• To review recent advancements in photochemical transformations using DR- to NIR-absorbing catalysts.
• To highlight strategies for efficient low-energy photon utilization in radical chemistry.
• To provide a mechanistic framework for understanding these reactions.

Main Methods:

• Review of literature on DR- to NIR-light driven photochemical reactions.
• Categorization of activation modes: single-photon absorption, triplet-triplet annihilation upconversion, two-photon absorption (TPA), and direct excitation.
• Analysis of molecular design principles for efficient photon harvesting.

Main Results:

• Development of chromophores and catalytic systems capable of absorbing low-energy photons.
• Demonstration of diverse radical transformations using DR- to NIR light.
• Identification of key molecular design strategies for enhanced efficiency.

Conclusions:

• NIR photochemistry presents unique advantages but faces challenges due to low photon energy.
• Significant progress has been made in harnessing low-energy photons for radical chemistry.
• Future opportunities lie in further developing molecular systems and expanding the scope of accessible transformations.