Bifurcation of excited state trajectories toward energy transfer or electron transfer directed by wave function symmetry

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 118; no. 4; pp. 1 - 7
• Main Authors: Oviedo, Paola S., Baraldo, Luis M., Cadranel, Alejandro
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 26-01-2021
• Subjects: Physical Sciences; energy transfer; wave function symmetry; excited state electronic coupling; electron transfer; photoinduced mixed valence
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.2018521118

This work explores the concept that differential wave function overlap between excited states can be engineered within a molecular chromophore. The aim is to control excited state wave function symmetries, so that symmetry matches or mismatches result in differential orbital overlap and define low-energy trajectories or kinetic barriers within the excited state surface, that drive excited state population toward different reaction pathways. Two donor–acceptor assemblies were explored, where visible light absorption prepares excited states of different wave function symmetry. These states could be resolved using transient absorption spectroscopy, thanks to wave function symmetry-specific photoinduced optical transitions. One of these excited states undergoes energy transfer to the acceptor, while another undertakes a backelectron transfer to restate the ground state. This differential behavior is possible thanks to the presence of kinetic barriers that prevent excited state equilibration. This strategy can be exploited to avoid energy dissipation in energy conversion or photoredox catalytic schemes.