Photophysical entatic states in transition metal complexes for solar energy conversion

The entatic state is a core concept in bioinorg. chem. and is present when a protein architecture places an active site in an energized geometry with enhanced electronic structural characteristics for function. Entatic states are not unique to bioinorg. chem., however, and can be leveraged to control and enhance functional characteristics throughout a variety of chemistries and materials science applications. That said, entatic contributions to reactivity and dynamics are difficult to define and quantify. Here we discuss the development of a combined exptl. and computational approach to quantify entatic contributions to the photophys. properties of transition metal complexes, including Cu-photosensitizers for solar energy conversion and solar fuels synthesis. Entatic contributions quantified here approach ~20 kcal/mol and are thus significant relative to typical chem. driving forces and barriers. Allowing the disentanglement of steric and electronic contributions to transition metal excited state lifetimes, the model can be used to guide the development of new mols. and materials with interesting functional and photophys. properties.