Engineering Photocatalytic Porous Organic Materials for Directing Redox versus Energy Transfer Processes

Two organic materials containing phenanthroline and triazine fragments, but connected in different ways, are presented. The imine-based material Phen-Tz-covalent organic framework (COF) preferentially shows photocatalytic activity through an energy transfer pathway as observed for olefin photoisomerization. However, an analogous covalent triazine framework (Phen-CTF) behaves as a powerful photoredox catalyst able to activate C-X (X=Br, Cl) bonds. The analysis of this phenomenon by means of theoretical calculations enables the rationalization of the different photocatalytic behavior observed. Phen-CTF behaves as a donor-acceptor material resulting in efficient charge separation upon excitation, while the imine groups present in Phen-Tz-COF hamper charge separation contributing to the rapid recombination between electrons and holes. This justifies a better activation via electron transfer in Phen-CTF and via energy transfer in Phen-Tz-COF. Two organic materials, Phen-Tz-covalent organic framework (Phen-Tz-COF) and Phen-covalent triazine framework (Phen-CTF), feature phenanthroline and triazine fragments with distinct connectivity. Phen-Tz-COF exhibits preferential photocatalytic activity via energy transfer, while Phen-CTF serves as a potent photoredox catalyst. Theoretical calculations rationalize these differences due to different electron-hole separation in the two materials.image (c) 2023 WILEY-VCH GmbH