• • The optimized isomeric MC-COF achieves a photocatalytic H2O2 production rate of 3128 μmol g−1 h−1 under visible light, representing a significant performance metric for sustainable H2O2 generation.
• • Structural isomerism leads to opposing C=N bond orientations and distinct phenyl group alignments, resulting in different torsion angles that enhance planarity and π-π stacking, which are critical for charge separation and transport.
• • Enhanced planarity reduces exciton binding energy, facilitating efficient charge separation and improving photocatalytic activity, as evidenced by the superior H2O2 production rate.
• • The study demonstrates that subtle changes in linkage orientation can drastically alter the electronic band structure and photophysical properties of COFs, offering a design principle for optimizing photocatalytic systems.