New computational insights use Marcus theory to harness the potential of photocatalysis

Dr. Albert Solé-Daura and Prof. Feliu Maseras investigated the application of Marcus theory, traditionally used to model electron transfer, to estimate the free energy barriers underlying energy transfer (EnT) processes. These results confirm that Marcus theory can be effectively applied in combination with density functional theory (DFT) calculations to predict the height of EnT barriers and motivate computational research on EnT, which is a fundamental event in photocatalysis.

Computer exploration was presented in the journal Chemical sciences. The study also reveals that using the “asymmetric” variant of Marcus theory provides more accurate barriers for alkene sensitization via EnT. Conversely, the “symmetric” approach leads to larger, although still reasonable, deviations.

“This computational approach should open up new possibilities for large-scale screenings, making experimental work faster and more efficient, while helping us to better understand the structure-activity relationships that govern these processes. This in turn opens the door to the design of new, more efficient photocatalytic systems, leading to major advances in the growing field of EnT photocatalysis,” says Professor Maseras.

A special application of Marcus’ theory

Marcus theory was initially developed to provide a fundamental understanding of the kinetics of single electron transfer (SET). Although EnT can be viewed as two concomitant SET events between donor and acceptor molecules, modeling EnT processes using Marcus theory has been much less explored.

Current state-of-the-art approaches rely on computationally demanding wavefunction-based methods, which hinders their systematic application for large-scale computational screenings.

Prof. Maseras’ group investigated the potential of classical Marcus theory, which neglects electronic coupling between reactant and product states, as a cost-effective and easy-to-use computational alternative to more sophisticated methods for estimating EnT barriers, and evaluated its performance against experimental data.

They also explored for the first time the application of an “asymmetric” variant of Marcus theory, according to which the state surfaces of reactants and products are described by symmetric parabolas of different widths, demonstrating that the latter approach allows an excellent prediction of the free energy barriers EnT.

“EnT photocatalysis has great potential and is attracting increasing attention, but EnT events remain a largely unexplored area of ​​computational chemistry. This is likely because they are more difficult to model than traditional bond-forming and bond-breaking reactions,” said Dr. Albert Solé-Daura, first author of the study.