Turning Imperfections into Assets: Defect-Engineered Conjugated Polymers for Benchmark Photocatalytic Hydrogen Evolution.

Structural defects in conjugated polymers are traditionally perceived as detrimental charge traps that impair optoelectronic performance. Here, we demonstrate a counterintuitive "defect-enabled" strategy for benchmark photocatalytic hydrogen evolution. Two donor (D)-acceptor (A) linear conjugated polymers (P-s and P-d) are synthesized via Suzuki-Miyaura polycondensation (P-s) and direct arylation polymerization (P-d), using dibenzothiophene-S, S-dioxide (DBTO) and 10-methylphenothiazine as A and D units, respectively. A comprehensive solid-state 13C NMR, XPS, Raman, and elemental analysis methodology is established to quantify structural defects, specifically A-A homo‑coupling (DBTO-DBTO) junctions that deviate from the ideal alternating D-A structure in these insoluble polymers. Remarkably, P-d exhibits approximately five-fold higher defect density (32.4% vs. 6.5%). This defect-induced DBTO enrichment simultaneously narrows the bandgap (1.81 vs. 2.10 eV), accelerates charge separation (evidenced by TRPL, TAS, and EIS), and provides abundant active sites (DFT-identified oxygen sites with ΔGH ≈ 1.38 eV). As a result, P-d achieves an outstanding hydrogen evolution rate of 476.38 mmol h- 1 g- 1 (with 2 wt.% Pt and 0.5% NP-40), surpassing most reported linear conjugated polymer photocatalysts. This work establishes a clear structure-property correlation for structural defects in polymeric photocatalysts and introduces a rational defect-engineering strategy for designing high-performance energy conversion materials.