Organic photoredox catalysts can perform challenging, single electron reductions/oxidations in a variety of synthetic and sustainable applications. Organic photoredox catalysts offer greener alternatives to metallic catalysts in applications such as CO2 reduction. One such catalyst, p-terphenyl, reduces CO2 in its anionic state, which is formed by excitation with UV-light and subsequent reduction by a sacrificial electron donor, such as triethylamine (TEA). The reduction of p-terphenyl by TEA was proposed as a complete electron transfer. This study shows that for both excited p-terphenyl and p-quaterphenyl an exciplex forms with TEA that displays broad, red-shifted emission peaks characteristic of incomplete charge-transfer. The experimental observation of exciplexes motivates considering the exciplex state in any molecular studies, whether they focus on reduction or degradation pathways. Through time-dependent density functional theory (TDDFT) optimization, this study calculates the electronic and structural features of these exciplexes in various solvents. This study demonstrates the success of non-equilibrium solvation methods for describing emission out of excited state complexes, which was previously untested. The role of charge-transfer interactions in dictating emission energies for the exciplex state is explored through the newly developed excited state energy decomposition analysis (exEDA). This project thoroughly models the exciplex state of these catalysts due to its likely participation in catalyst degradation. Accurately modelling the charge-transfer interactions and electronic states of organic catalysts and their reductants is vital to understanding the productivity of organic photoredox catalysts.

Modelling exciplex formation during organic photoredox catalysis for CO2 reduction

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.