Rational design of benzoimidazoisoindolone-linked conjugated ladder polymer for enhanced visible-light-driven photocatalytic water oxidation

To elucidate how backbone topology dictates photocatalytic efficiency in solar water oxidation, we synthesized two π-conjugated analogues with a flexible single-strand linker (Lin-CP) and a rigid double-strand ladder linker (Lad-CP), respectively. Comprehensive optical-electrical analysis and density functional theory (DFT) converge on the conclusion that the ladder backbone suppresses torsional disorder by locking a planar conformation, thereby extending the effective π-conjugation length; band-structure calculations reveal a 0.36 eV narrowing of the optical gap (≈100 nm red-shift). Concomitantly, carrier mobility rises markedly. These synergistic effects accelerate bulk charge separation and inhibit recombination, resulting in a photocatalytic O₂ evolution rate for Lad-CP that is approximately twice that of Lin-CP. This study clearly establishes a structure-function relationship between double-chain connectivity and excellent charge transport.