Great efforts have been devoted to developing novel photocatalytic systems (e.g., CO2 reduction, water splitting, and photoredox catalysis system). However, many scientists and engineers have mainly focused on synthesizing superior systems, and the development of such systems still lacks element and molecular-level understanding. Most of the energy storage and production processes in photocatalytic systems are initiated by electron or energy transfer (EET, e.g., formation of photoelectron during photosynthesis); therefore, interpreting EET phenomena is crucial for material development. Element-specific responses from X-ray transient absorption spectroscopy (XTA) provide crucial information on mapping electron/energy transfer (EET) mechanisms, facilitating the synthesis of new class catalytic systems. This presentation aims to provide new insights into mechanisms studies by coupling XTA to conventional optical time-resolved studies (e.g., photoluminescence and optical transient absorption spectroscopy), which ultimately helps elucidate catalytic cycles' electronic and energy landscape. This presentation will highlight the recent discoveries on EET mechanisms of several catalytic systems using XTA technique. By taking examples of photoredox systems (e.g., Ir and Cu catalysts used for organic synthesis), we will highlight XTA enables to reveal the role of individual elements and actual ET dynamics different from widely accepted reaction mechanisms. Moreover, we will present the advantage of the XTA tool enabling reveal the role of singlet and triplet states of excited states of photosensitizers in catalytic efficiency by taking examples of iron porphyrin catalytic systems (e.g., Fe<sup>III</sup>-<i>p</i>-TMA and an organic photosensitizer, Phen2) for CO2 reduction.

Revealing the electronic and energy landscape of photocatalytic systems using X-ray transient absorption spectroscopy

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ACS Fall 2022

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