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.