Understanding loss pathways in a photochemical reaction network

Photochemical reactions, such as light-driven water splitting, have tremendous potential for both synthesis as well as energy conversion. However, they also present unique challenges in terms of understanding their inefficiencies and pathways via which photon energy is lost. To address this, we present a novel algorithm that allows for the quantification of loss pathways in a photochemical reaction network through the stochastic propagation of excitations through the reaction network. We use this approach to quantify losses in an unusual light-driven water splitting mechanism in which two photons are absorbed consecutively by two different intermediates. Through this analysis we find that the majority of excitation energy is lost due to unproductive excitations of the (inactive) monomeric starting complex (in contrast to the active dimeric state), as well as the rapid decay of the second-photon absorbing intermediate, which decays in most cases before it can absorb the second photon. The herein presented approach is generally applicable to the analysis of loss pathways in photochemical reactions and the required software is available open-source via a purpose-built Python package.