Volume 234, 2022

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

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.

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

Associated articles

Supplementary files

Article information

Article type
Paper
Submitted
27 اگست 2021
Accepted
05 نومبر 2021
First published
05 نومبر 2021
This article is Open Access
Creative Commons BY license

Faraday Discuss., 2022,234, 159-174

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

D. Parker, J. D. Fradgley, M. Delbianco, M. Starck, James W. Walton and J. M. Zwier, Faraday Discuss., 2022, 234, 159 DOI: 10.1039/D1FD00059D

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