Transient absorption spectroscopy shines light on photocatalysts

Photocatalysts are an important class of molecule, as they can harness energy from sunlight and use it to drive chemical reactions, such as splitting water to form hydrogen gas. Understanding exactly how a catalyst reacts when excited and the pathway it takes during relaxation are key to improving reaction efficiencies.

Li et al. discussed using transient absorption (TA) spectroscopy on organic photocatalysts to map the relaxation pathways of photocatalysts over multiple time scales. TA spectroscopy involves exciting a molecule with a short pump laser and probing the relaxation with a second laser pulse or continuous wave source. This makes it ideal for studying photocatalysts.

The key feature of a photocatalyst is the ability to move from an excited state to a relaxed state in a way that creates separated charges, which can be transferred to surrounding chemicals. However, any given catalyst often has multiple possible relaxation pathways, and elements of these pathways can occur over timescales from seconds to femtoseconds. TA spectroscopy can probe those various pathways across that entire time range.

“TA spectroscopy can provide insights into favorable and unfavorable pathways taken by the photocatalysts, which can provide rationales for why one photocatalyst has a higher efficiency than another,” said author Adrian Gardner. “This understanding is crucial for rational design of new, higher efficiency, organic photocatalysts.”

The authors aim to provide a guide for researchers curious about TA spectroscopy to incorporate it into their own studies.

“The aim of this review is to provide the foundations for researchers new to the field of TA spectroscopy to design, perform and interpret their own TA experiments to probe the photodynamics of organic photocatalysts,” said Gardner.

Source: “Transient absorption spectroscopic studies of linear polymeric photocatalysts for solar fuel generation,” by Chao Li, Alexander J. Cowan, and Adrian M. Gardner, Chemical Physics Reviews (2022). The article can be accessed at https://doi.org/10.1063/5.0098274 .