Regulating the Position of N Atoms in One-Dimensional Covalent Organic Frameworks (1D COFs) for Efficient Photocatalytic Organic Transformation and Hydrogen Generation

N-doping has been taken as a pivotal method for modulating the photocatalytic activity of covalent organic frameworks (COFs). To elucidate the relationship between the nitrogen position and the photocatalytic performance in one-dimensional (1D) COFs, three 1D COFs (Pd-COF, PdA-COF, and Pz-COF) (Pd-pyrimidine, PdA-asymmetric pyrimidine, Pz-pyrazine) were synthesized by different N-heterocycle-functionalized nonlinear C₂ linkage (with different N positions) and planar C₄ knots. Pd-COF and PdA-COF incorporate N atoms in the form of pyrimidine, while Pz-COF contains pyrazine units. Pd-COF and PdA-COF demonstrated superior photocatalytic hydrogen generation activity compared to Pz-COF, with rates of 99.6 and 44.6 mmol g^-1 h^-1, respectively, versus 18.0 mmol g^-1 h^-1 for Pz-COF. However, for the oxidation of hydroxyl groups from arylboronic acids, the Pz-COF and PdA-COF with N atoms introduced into the pores are more suitable. The conversion rates of Pz-COF (up to 99%) and PdA-COF (up to 90%) are significantly higher than that of PA-COF (up to 85%). This may result from the position of the N atom affecting the electron cloud density of the aromatic ring, which facilitates the different intramolecular charge transfers. Furthermore, N atoms located within the pore could also increase the active sites, promote the contact between arylboronic acid and active sites, thus improving the catalytic efficiency. This study provides an effective strategy for designing COFs-based photocatalysts with efficient photocatalytic hydrogen generation ability and emphasizes the potential of N-doping 1D COFs in the field of photocatalysis.