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Comparative analysis of lanthanide excited state quenching by electronic energy and electron transfer processes

Parker, David; Fradgley, Jack D.; Delbianco, Martina; Starck, Matthieu; Walton, James W.; Zwier, Jurriaan M.

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Authors

Jack D. Fradgley

Martina Delbianco

Matthieu Starck

Jurriaan M. Zwier



Abstract

The relative sensitivities of structurally related Eu(III) complexes to quenching by electron and energy transfer processes have been compared. In two sets of 9-coordinate complexes based on 1,4,7-triazacyclononane, the Eu emission lifetime decreased as the number of conjugated sensitising groups and the number of unbound ligand N atoms increased, consistent with photoinduced electron transfer to the excited Eu(III) ion that is suppressed by N-protonation. Quenching of the Eu 5D0 excited state may also occur by electronic energy transfer, and the quenching of a variety of 9-coordinate complexes by a cyanine dye with optimal spectral overlap occurs by an efficient FRET process, defined by a Förster radius (R0) value of 68 Å and characterised by second rate constants in the order of 109 M−1 s−1; these values were insensitive to changes in the ligand structure and to the overall complex hydrophilicity. Quenching of the Eu and Tb excited states by energy transfer to Mn(II) and Cu(II) aqua ions occurred over much shorter distances, with rate constants of around 106 M−1 s−1, owing to the much lower spectral overlap integral. The calculated R0 values were estimated to be between 2.5 to 4 Å in the former case, suggesting the presence of a Dexter energy transfer mechanism that requires much closer contact, consistent with the enhanced sensitivity of the rate of quenching to the degree of steric shielding of the lanthanide ion provided by the ligand.

Citation

Parker, D., Fradgley, J. D., Delbianco, M., Starck, M., Walton, J., & Zwier, J. M. (2022). Comparative analysis of lanthanide excited state quenching by electronic energy and electron transfer processes. Faraday Discussions, 234, 159 - 174. https://doi.org/10.1039/d1fd00059d

Journal Article Type Article
Acceptance Date Nov 5, 2021
Online Publication Date Nov 5, 2021
Publication Date 2022
Deposit Date Sep 15, 2022
Publicly Available Date Sep 15, 2022
Journal Faraday Discussions
Print ISSN 1359-6640
Electronic ISSN 1364-5498
Publisher Royal Society of Chemistry
Peer Reviewed Peer Reviewed
Volume 234
Pages 159 - 174
DOI https://doi.org/10.1039/d1fd00059d

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