Redox Metal-Organic Framework for Photocatalytic Organic Transformation: The Role of Tetrazine Function in Radical-Anion Pathway.

Linker functionalization is a practical strategy to extend the applications of metal-organic frameworks (MOFs) in various fields. Here, this strategy is applied to synthesize a tetrazine-functionalized MOF [TMU-34(-2H), formulated [Zn(OBA) (DPT)]·DMF; HOBA and DPT are 4,4'-oxybis(benzoic acid) and 3,6-di(pyridin-4-yl)-1,2,4,5-tetrazine] for efficient photocatalytic synthesis of disulfides and benzimidazoles with maximum conversion after 90 and 120 min, respectively. The photocatalytic activity of TMU-34(-2H) originates from the electronic properties of tetrazine function, including absorption in the visible region and photogenerated redox activity. In the proposed mechanism, neutral tetrazine sites are excited upon visible-light irradiation. Then, photoexcited tetrazine sites accept one electron from the reactants leading to generation of tetrazine radical anions as electron mediator sites. Finally, the electrons transfer from the tetrazine radical anion sites to other substrates in the reaction. The results show that organic chromophores, such as tetrazine, are good candidates for extension of application of MOFs in visible-light photocatalysis.