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Photoinduced Electron Transfer in Luminescent Lanthanide Complexes
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström. (Borbas)ORCID iD: 0000-0002-5615-3204
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Luminescence from the trivalent lanthanides is used for detection in biological systems. Lanthanide luminescence is usually sensitized by a light-harvesting organic chromophore (’antenna’). An ideal emitter has an antenna that efficiently transfers energy to the lanthanide, and a ligand that shields the metal from quenching solvent molecules.

Additional photophysical processes can impact the luminescence quantum yield. One such process is electron transfer from the excited state antenna to the lanthanide, yielding a lanthanide(II) and an antenna radical cation. Back electron transfer returns the antenna and a lanthanide(III), which, may or may not emit a photon.

This thesis summarizes my work on the investigation of the photoinduced electron transfer in lanthanide complexes. Chapter 1 is a brief introduction. Chapter 2 describes a structure-activity relationship in a focused library of lanthanide complexes. PeT was observed with most antennae and in a larger of lanthanides than previously assumed.

In Chapter 3, the role of the linker connecting the antenna and the metal binding site is investigated. Replacement of the secondary amide linker with a tertiary amide yielded unexpectedly high luminescence quantum yields. This was attributed to an improved sensitization efficiency due to a combination of factors (structural as well as electronic) in the Eu complexes, and a reduced back energy transfer in the Tb complexes.

In Chapter 4, the role of the ligand in PeT was investigated. Stabilization of the lanthanide(III) state by encapsulation of the ion in a highly negatively charged ligand resulted in a recovery of some of the excitation energy lost to PeT. The addition of external a strongly coordinating anionic ligand, fluoride, which could replace the charge-neutral water ligand, had a similar effect. The changes in the lanthanide redox potential was confirmed by cyclic voltammetry.

Finally, complexes equipped with azide and alkyne reactive handles are described. The introduction of bioconjugatable groups had only a small effect on the luminescent properties of the compounds. We attempted to improve the luminescence quantum yields by excluding the lanthanide-bound water molecule that has been occupying the ninth coordination. However, the nonadentate ligands did not yield appreciably better emitters due to a carbostyril-to-pyridine PeT.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. , p. 99
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1809
Keywords [en]
Lanthanide, Luminescence, Photoinduced electron transfer
National Category
Inorganic Chemistry
Research subject
Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-381905ISBN: 978-91-513-0657-5 (print)OAI: oai:DiVA.org:uu-381905DiVA, id: diva2:1305182
Public defence
2019-06-10, Häggsalen, 10132, Ångstömlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2019-05-20 Created: 2019-04-16 Last updated: 2019-06-17
List of papers
1. Photophysics of Coumarin and Carbostyril-Sensitized Luminescent Lanthanide Complexes: Implications for Complex Design in Multiplex Detection
Open this publication in new window or tab >>Photophysics of Coumarin and Carbostyril-Sensitized Luminescent Lanthanide Complexes: Implications for Complex Design in Multiplex Detection
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2017 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 139, no 16, p. 5756-5767Article in journal (Refereed) Published
Abstract [en]

Luminescent lanthanide (Ln(III)) complexes with coumarin or carbostyril antennae were synthesized and their photophysical properties evaluated using steady-state and time-resolved UV-vis spectroscopy. Ligands bearing distant hydroxycoumarin-derived antennae attached through triazole linkers were modest sensitizers for Eu(III) and Tb(III), whereas ligands with 7-amidocarbostyrils directly linked to the coordination site could reach good quantum yields for multiple Ln(III), including the visible emitters Sm(III) and Dy(III), and the near-infrared emitters Nd(III) and Yb(III). The highest lanthanide-centered luminescence quantum yields were 35% (Tb), 7.9% (Eu), 0.67% (Dy), and 0.18% (Sm). Antennae providing similar luminescence intensities with 2-4 Ln-emitters were identified. Photoredox quenching of the carbostyril antenna excited states was observed for all Eu(III)-complexes and should be sensitizing in the case of Yb(III); the scope of the process extends to Ln(III) for which it has not been seen previously, specifically Dy(III) and Sm(III). The proposed process is supported by photophysical and electrochemical data. A FRET-type mechanism was identified in architectures with both distant and close antennae for all of the Lns. This mechanism seems to be the only sensitizing one at long distance and probably contributes to the sensitization at shorter distances along with the triplet pathway. The complexes were nontoxic to either bacterial or mammalian cells. Complexes of an ester-functionalized ligand were taken up by bacteria in a concentration-dependent manner. Our results suggest that the effects of FRET and photoredox quenching should be taken into consideration when designing luminescent Ln complexes. These results also establish these Ln(III)-complexes for multiplex detection beyond the available two-color systems.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2017
National Category
Chemical Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-322722 (URN)10.1021/jacs.6b11274 (DOI)000400321500029 ()28388066 (PubMedID)
Funder
Swedish Research Council, 2013-4655Stiftelsen Olle Engkvist Byggmästare
Available from: 2017-05-29 Created: 2017-05-29 Last updated: 2019-04-16Bibliographically approved
2. Highly luminescent lanthanide complexes sensitised by tertiary amide-linked carbostyril antennae
Open this publication in new window or tab >>Highly luminescent lanthanide complexes sensitised by tertiary amide-linked carbostyril antennae
2018 (English)In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 47, no 31, p. 10702-10714Article in journal (Refereed) Published
Abstract [en]

Carbostyrils are among the most widely used sensitising antennae for luminescent lanthanides; they afford bright complexes with Eu and Tb, and can also sensitise the emissions of the less commonly used Sm, Dy, Yb and Nd. Systematic studies on the effect of structural variations on the photophysical properties and lanthanide sensitising abilities of carbostyrils can therefore have a large impact. We replaced the secondary amide linker that connects the metal binding site to the antenna with a carboxymethyl-substituted tertiary amide. Eight Tb and Eu complexes were prepared. All had higher lanthanide luminescence quantum yields (phi(Ln)) than their secondary amide analogues; three Tb emitters had phi(Tb) > 40%. Eu complexes had phi(Eu) up to 11.6%. The antenna singlet and triplet excited states are slightly shifted, while the metal coordination sphere is unchanged by the introduction of the carboxymethyl group.

National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-363106 (URN)10.1039/c8dt01270a (DOI)000441151700043 ()29923567 (PubMedID)
Funder
Swedish Research Council, 2013-4655Swedish Research Council, 2017-04077
Available from: 2018-10-15 Created: 2018-10-15 Last updated: 2019-04-16Bibliographically approved
3. Controlling photoinduced electron transfer in luminescent europium complexes
Open this publication in new window or tab >>Controlling photoinduced electron transfer in luminescent europium complexes
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(English)Manuscript (preprint) (Other academic)
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-381903 (URN)
Funder
Swedish Research Council, 2017-04077
Available from: 2019-04-15 Created: 2019-04-15 Last updated: 2019-04-17Bibliographically approved
4. Controlling the Yb sensitization pathway in luminescent complexes through the modulation of the Yb(II)/Yb(III) redox potential
Open this publication in new window or tab >>Controlling the Yb sensitization pathway in luminescent complexes through the modulation of the Yb(II)/Yb(III) redox potential
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(English)Manuscript (preprint) (Other academic)
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-381901 (URN)
Funder
Swedish Research Council, 2017-04077
Available from: 2019-04-15 Created: 2019-04-15 Last updated: 2019-04-17Bibliographically approved
5. Highly emissive Eu- and Tb-emitting bioconjugatable complexes of octa- and nonadentate macrocyclic ligands
Open this publication in new window or tab >>Highly emissive Eu- and Tb-emitting bioconjugatable complexes of octa- and nonadentate macrocyclic ligands
(English)Manuscript (preprint) (Other academic)
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-381902 (URN)
Funder
Swedish Research Council, 2017-04077
Available from: 2019-04-15 Created: 2019-04-15 Last updated: 2019-04-17Bibliographically approved

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