<p>Conjugated porous organic framework photocatalysts for hydrogen peroxide production have attracted a lot of attention, yet achieving efficient exciton regulation remains a challenge. Here, we propose a one-dimensional donor length-engineering strategy to construct twin molecular junction catalysts for sacrificial-agent-free H₂O₂ production. Tuning aryl donor conjugation identifies an optimal structure that enhances π-delocalization and exciton dissociation, whereas overly short or long donors hinder charge separation. The covalent heptazine framework with p-terphenyl as the donor enables fast Frenkel-to-charge-transfer exciton conversion (0.36 ps) and highly efficient formation (89.16%) of long-lived ( &gt; 7 ns) charge-separated states. Spatially adjacent redox sites allow electrons and holes to drive oxygen reduction and water oxidation reactions simultaneously, improving the photocatalytic efficiency. In this work, the optimal material achieves 8595 μmol g⁻¹ h⁻¹ H₂O₂ production under visible light and 5042 μmol g⁻¹ h⁻¹ under natural solar/air conditions and remains stable over 400 h of continuous operation, demonstrating competitive performance.</p>