Quantifying entatic states in photophysical processes: Applications to copper photosensitizers

Abstract

The concept of an entatic or rack-induced state describes how a protein fold can place a transition metal center in a strained geometric environment. This strain can finely tune the active site's electronic structure and thus its phys. and chem. properties. Beyond bioinorg. chem., the entatic state concept has relevance to a multitude of processes in chem. and materials science. However, entatic states and energetics have only been defined and quantified for a few systems. In this work, a combined exptl. and computational approach is developed and used to extend the entatic state description to dozens of Cu-based photosensitizers, a set of mols. widely studied for solar energy conversion, org. light emitting diodes, and photoredox catalysis. Entatic energies detd. here are the largest yet detd. (~20 kcal/mol) and approach typical chem. driving forces and barriers. Furthermore, the approach outlined here provides a method to decouple steric and electronic influences on the excited state potential energy surfaces and dynamics of transition metal complexes. These insights can guide the design of transition metal complexes with tailored excited state lifetimes and properties, as well as inspire the extension of entatic concepts to catalysis and magnetism.