Local Hydrogen Bonding Determines Branching Pathways in Intermolecular Heptazine Photochemistry

Area of Science:

• Photochemistry
• Materials Science
• Spectroscopy

Background:

• Heptazine is a core component of carbon nitride photocatalysts.
• Understanding excited-state reactions is crucial for photocatalyst design.

Purpose of the Study:

• To spectroscopically identify reactive radical species formed during excited-state proton-coupled electron-transfer (PCET) in heptazine derivatives.
• To characterize the spectral signatures of these radical intermediates and their dependence on the local environment.

Main Methods:

• Femtosecond transient absorption spectroscopy
• Global analysis of spectroscopic data
• Control experiments including radical quenchers and spectroelectrochemistry

Main Results:

• Distinct product absorption signatures at ~520, 1250, and 1600 nm were identified.
• These signatures were assigned to the hydrogenated heptazinyl radical (TAHzH•).
• The study revealed the sensitivity of heptazine photochemistry to solvent hydrogen-bonding characteristics.

Conclusions:

• The spectral assignment of the TAHzH• radical facilitates future studies of heptazine and carbon nitride photochemistry.
• Findings can guide the design of improved PCET-based photochemical systems for applications like catalysis and solar energy conversion.