Solar photocatalysis offers a mechanism to harness the sun’s energy and store it in chemical bonds, creating new fuels. While there are many known fuel-forming catalysts based on first-row transition metals, there are few examples of earth-abundant photosensitizers. Metal complexes of dipyrromethene (dipyrrin) ligands have potential as sensitizers for photocatalysis. These ligands possess the intense visible absorption properties of the related porphyrins, while being more synthetically accessible. First row transition metal complexes of dipyrrin ligands are known, but the photophysical properties of these complexes are generally unexplored. In zinc dipyrrin complexes the tetrahedral geometry allows for interligand charge transfer, forming a charge separated (CS) state. In polar environments the CS state is stabilized and quenches the S<sub>1</sub> fluorescence. It is theorized that the CS state also enhances the intersystem crossing (ISC) to the long lived T<sub>1</sub> state. This presentation will quantify the triplet extinction coefficient and quantum yield for a series of zinc dipyrrin complexes and their boron dipyrrin counterparts in both polar and non-polar solvents to determine if increased CS state formation (as determined by fluorescence quenching) does lead to increased triplet state formation.

Quantifying triplet state formation in zinc dipyrrin complexes

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ACS Fall 2022

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