Proton-coupled electron transfer (PCET) is when an electron is transferred from one site to another and this process is accompanied by the relocation of one or more protons. PCET plays an essential role in natural and artificial photosynthesis, thus making this process the main focus of many studies in this field. High-resolution two-dimensional <sup>14</sup>N hyperfine sublevel correlation spectroscopy (HYSCORE) and computational chemistry can be used as tools in the characterization of systems that undergo PCET and the products that are formed. Understanding the mechanism of PCET and the geometric and energetic features of the products formed could facilitate the design of new and efficient artificial photosynthetic constructs. In this research, we use computational chemistry in combination with experimental 2D HYSCORE spectroscopy to characterize an artificial photosynthetic construct that is capable of light-driven one-electron–two-proton transfer (E2PT). The construct consists of a high oxidation potential porphyrin (PF15) which is covalently bonded to a benzimidazole-phenol moiety (BIP) and a second proton acceptor site. We have performed density functional theory (DFT) calculations on several conformations of this construct to calculate the electronic structure for comparison with the experimental 2D HYSCORE data. We have also explored the effect of hydrogen bonding of explicit water molecules on the electronic structure of the PCET intermediates. The results of this study indicate that hydrogen bonding interactions of the proximal water molecules have an important impact on spin delocalization of the E2PT construct.

2D HYSCORE and DFT studies of one-electron–two-proton transfer in a bioinspired artificial photosynthetic reaction center

ACS Spring 2022

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