Biscoumarin-containing acenes as stable organic semiconductors for photocatalytic oxygen reduction to hydrogen peroxide

Austrian-Polish bilateral WTZ program, the Austrian Science Fund FWF via the project TRP 294-N19; Wittgenstein Prize for N. S. Sariciftci (Solare Energie Umwandlung Z222-N19); National Centre for Research and Development (Polish-Taiwanese project PL-TWIII/17/2016); Polish Ministry of Science and Higher Education from the funds for the studies in the years 2012–2016; “Diamond Grant” program (statutory research project no DI2012000742); Knut and Alice Wallenberg Foundation within the framework of the Wallenberg Centre for Molecular Medicine.

Conversion of solar energy into chemical energy in the form of hydrogen peroxide and other reactive oxygen species has been predicted to be an efficient strategy, yet few organic materials systems support these types of photochemical conversion reactions. Herein we report a simple synthetic route to yield biscoumarin-containing acenes, semiconducting small molecules with exceptional stability and tunable electrochemical and electrical properties. We find that these semiconductors are photo(electro)catalysts capable of reducing oxygen to hydrogen peroxide. Visible light irradiation of thin films on insulating substrates in pure water results in H2O2 photogeneration with water as the sacrificial electron donor. Thin films on conducting substrates are robust catalytic photocathodes for producing H2O2. These semiconductor photoelectrodes retain their catalytic properties in a pH range from 2–13. Photocatalytic or photoelectrocatalytic deployment of biscoumarin-containing acenes does not lead to measurable degradation. This work demonstrates a strategy to synthesize stable organic semiconductors not only suitable for thin-film electronic devices but also next-generation photocatalytic concepts.