Linker Torsional Angle Engineering in Metal–Organic Frameworks Enables Boosted O 2 Photoactivation for Organic Synthesis

Steering the O2 photoactivation for boosting the generation of reactive oxygen species (ROSs) with moderate oxidant strength is crucial for fine organic synthesis, while it remains a huge challenge. Herein, by constructing a pair of metal–organic frameworks (MOFs) with isomeric linkers, i.e., Ni-TTPz-α and Ni-TTPz-β, we demonstrate the first achievement in modulating the chromophore linker torsional angle in MOFs for the precise regulation of ROSs generation. Ni-TTPz-α is equipped with a coplanar conjugated α-thiophene linker, while Ni-TTPz-β features misalignment between the bithiophene and pyrazole moieties due to the zigzag configuration of the β-linker. As a result, Ni-TTPz-α significantly boosts the production of superoxide radicals (O2•–) under visible light in air, whereas Ni-TTPz-β exclusively generates singlet oxygen (1O2) with much lower performance. The boosted generation of O2•– empowers Ni-TTPz-α to efficiently drive the oxidative coupling of benzylamine to imine, achieving a 99% yield within 12 h, which is significantly boosted than that of Ni-TTPz-β (48%). Experiments and theoretical calculations jointly confirm that planar α-thiophene features an angle-induced restricted twist effect that facilitates efficient electron transfer from the thiophene sulfur to the pyrazole unit and, ultimately, to the metal center, thereby driving single-electron oxygen reduction to produce O2•–.