Abstract
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.
Highlights
The conversion of solar energy into a storable fuel, such as hydrogen (H2 ) through sunlight-driven water splitting, is currently the subject of intensive research efforts [1,2]
We investigate the ultrafast excited state dynamics of two novel dye-catalyst assemblies designed for improved photoelectrocatalytic of two novel dye-catalyst assemblies designed for improved photoelectrocatalytic hydrogen production in dye-sensitized photocathodes [18]
As intersystem crossing (ISC) is absent in T2R despite the identical dye structure as in the dyads, the bithiophene structure cannot be the sole source of the ISC and the explanations offered in the literature likely do not fully account for the fast ISC in our systems
Summary
The conversion of solar energy into a storable fuel, such as hydrogen (H2 ) through sunlight-driven water splitting, is currently the subject of intensive research efforts [1,2]. The first functional H2 -evolving photocathodes integrating such molecular dyads were reported in the literature [2,5,9,11,15], paving the way for solar fuels production in dye-sensitized photoelectrochemical cells. Our group contributed to the field with the design of covalent dye-catalyst assemblies based on H2 -evolving cobalt catalysts [12,13,16].
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