Investigating Light-Induced Processes in Covalent Dye-Catalyst Assemblies for Hydrogen Production

• Main Authors: Sebastian Bold, Tatiana Straistari, Ana B. Muñoz-García, Michele Pavone, Vincent Artero, Murielle Chavarot-Kerlidou, Benjamin Dietzek
• Format: Article
• Language: English
• Published: MDPI AG 2020-11-01
• Series: Catalysts
• Subjects: solar energy conversion; push-pull dye; intersystem crossing
• Online Access: https://www.mdpi.com/2073-4344/10/11/1340

The light-induced processes occurring in two dye-catalyst assemblies for light-driven hydrogen production were investigated by ultrafast transient absorption spectroscopy. These dyads consist of a push-pull organic dye based on a cyclopenta[1,2-b:5,4-b’]dithiophene (CPDT) bridge, covalently linked to two different H₂-evolving cobalt catalysts. Whatever the nature of the latter, photoinduced intramolecular electron transfer from the excited state of the dye to the catalytic center was never observed. Instead, and in sharp contrast to the reference dye, a fast intersystem crossing (ISC) populates a long-lived triplet excited state, which in turn non-radiatively decays to the ground state. This study thus shows how the interplay of different structures in a dye-catalyst assembly can lead to unexpected excited state behavior and might open up new possibilities in the area of organic triplet sensitizers. More importantly, a reductive quenching mechanism with an external electron donor must be considered to drive hydrogen production with these dye-catalyst assemblies.