Photocatalytically Active Ladder Polymers

Conjugated ladder polymers (cLaPs) are introduced as organic semiconductors for photocatalytic hydrogen evolution from water under sacrificial conditions. Starting from a linear conjugated polymer (cLiP1), two ladder polymers are synthesized via post-polymerization annulation and oxidation techniques to generate rigidified, planarized materials bearing dibenzo[ b , d ]thiophene ( cLaP1 ) and dibenzo[ b , d ]thiophene sulfone subunits ( cLaP2 ). The high photocatalytic activity of cLaP1 (1307 μmol h −1 g −1 ) in comparison to cLaP2 (18 μmol h −1 g −1 ) under broadband illumination (λ >295 nm) in presence of a hole-scavenger is attributed to a higher yield of long-lived charges (µs–ms timescale), as evidenced by transient absorption spectroscopy. Additionally, cLaP1 has a larger overpotential for proton reduction and thus an increased driving force for the evolution of hydrogen under sacrificial conditions.