Photocatalytically Active Ladder Polymers

Abstract

<p>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[<i>b</i>,<i>d</i>]thiophene (<b>cLaP1</b>) and dibenzo[<i>b</i>,<i>d</i>]thiophene sulfone subunits (<b>cLaP2</b>). The high photocatalytic activity of <b>cLaP1</b> (1307 μmol h<sup>−1</sup> g<sup>−1</sup>) in comparison to <b>cLaP2</b> (18 μmol h<sup>−1</sup> g<sup>−1</sup>) 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, <b>cLaP1</b> has a larger overpotential for proton reduction and thus an increased driving force for the evolution of hydrogen under sacrificial conditions.</p>