Issue 18, 2024

Unraveling the mechanisms of triplet state formation in a heavy-atom free photosensitizer

Abstract

Triplet excited state generation plays a pivotal role in photosensitizers, however the reliance on transition metals and heavy atoms can limit the utility of these systems. In this study, we demonstrate that an interplay of competing quantum effects controls the high triplet quantum yield in a prototypical boron dipyrromethene-anthracene (BD-An) donor–acceptor dyad photosensitizer, which is only captured by an accurate treatment of both inner and outer sphere reorganization energies. Our ab initio-derived model provides excellent agreement with experimentally measured spectra, triplet yields and excited state kinetic data, including the triplet lifetime. We find that rapid triplet state formation occurs primarily via high-energy triplet states through both spin–orbit coupled charge transfer and El-Sayed's rule breaking intersystem crossing, rather than direct spin–orbit coupled charge transfer to the lowest lying triplet state. Our calculations also reveal that competing effects of nuclear tunneling, electronic state recrossing, and electronic polarizability dictate the rate of non-productive ground state recombination. This study sheds light on the quantum effects driving efficient triplet formation in the BD-An system, and offers a promising simulation methodology for diverse photochemical systems.

Graphical abstract: Unraveling the mechanisms of triplet state formation in a heavy-atom free photosensitizer

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Article information

Article type
Edge Article
Submitted
27 Feb 2024
Accepted
29 Mar 2024
First published
02 Apr 2024
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2024,15, 6726-6737

Unraveling the mechanisms of triplet state formation in a heavy-atom free photosensitizer

T. P. Fay and D. T. Limmer, Chem. Sci., 2024, 15, 6726 DOI: 10.1039/D4SC01369G

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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