Structure–activity relationships in well-defined conjugated oligomer photocatalysts for hydrogen production from water

Aitchison, Catherine M. and Sachs, Michael and Little, Marc A. and Wilbraham, Liam and Brownbill, Nick J. and Kane, Christopher M. and Blanc, Frédéric and Zwijnenburg, Martijn A. and Durrant, James R. and Sprick, Reiner Sebastian and Cooper, Andrew I. (2020) Structure–activity relationships in well-defined conjugated oligomer photocatalysts for hydrogen production from water. Chemical Science, 11 (33). pp. 8744-8756. ISSN 2041-6520

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    Abstract

    Most organic semiconductor photocatalysts for solar fuels production are linear polymers or polymeric networks with a broad distribution of molecular weights. Here, we study a series of molecular dibenzo[b,d]thiophene sulfone and fluorene oligomers as well-defined model systems to probe the relationship between photocatalytic activity and structural features such as chain length and planarity. The hydrogen evolution rate was found to vary significantly with bridge head atom, chain length, and backbone twisting. A trimer (S3) of only three repeat units has excellent activity for proton reduction with an EQE of 8.8% at 420 nm, approaching the activity of its polymer analogue and demonstrating that high molar masses are not a prerequisite for good activity. The dynamics of long-lived electrons generated under illumination in the S3 oligomer are very similar to the corresponding polymer, both under transient and quasi-continuous irradiation conditions.