| 1. |
- Kócsi, Dániel, et al.
(författare)
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Reduced quenching effect of pyridine ligands in highly luminescent Ln(iii) complexes : the role of tertiary amide linkers
- 2021
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry. - 1477-9226 .- 1477-9234. ; 50:45, s. 16670-16677
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Tidskriftsartikel (refereegranskat)abstract
- Luminescent Eu(iii) and Tb(iii) complexes were synthesised from octadentate ligands carrying various carbostyril sensitizing antennae and two bidentate picolinate donors. Antennae were connected to the metal binding site via tertiary amide linkers. Antennae and donors were assembled on a 1,4,7-triazacyclononane (tacn) platform. Solution- and solid-state structures were comparable to those of previously reported complexes with tacn architectures, with nine-coordinate distorted tricapped trigonal prismatic Ln(iii) centres, and distinct from those based on 1,4,7,10-tetraazacyclododecane (cyclen) macrocycles. In contrast, the photophysical properties of these tertiary amide tacn-based complexes were more comparable to those of previously reported systems with cyclen ligands, showing efficient Eu(iii) and Tb(iii) luminescence. This represents an improvement over secondary amide-linked analogues, and is due to a greatly increased sensitization efficiency in the tertiary amide-linked complexes. Tertiary amide-linked Eu(iii) and Tb(iii) emitters were more photostable than their secondary amide-linked analogues due to the suppression of photoinduced electron transfer and back energy transfer.
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| 2. |
- Kovacs, Daniel, et al.
(författare)
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Electron transfer pathways in photoexcited lanthanide(iii) complexes of picolinate ligands
- 2021
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry. - 1477-9226 .- 1477-9234. ; 50:12, s. 4244-4254
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Tidskriftsartikel (refereegranskat)abstract
- A series of luminescent lanthanide(iii) complexes consisting of 1,4,7-triazacyclononane frameworks and three secondary amide-linked carbostyril antennae were synthesised. The metal binding sites were augmented with two pyridylcarboxylate donors yielding octadentate ligands. The antennae carried methyl, methoxymethyl or trifluoromethyl substituents in their 4-positions, allowing for a range of excited state energies and antenna electronic properties. The H-1 NMR spectra of the Eu(iii) complexes were found to be analogous to each other. Similar results were obtained in the solid-state by single-crystal X-ray crystallography, which showed the structures to have nine-coordinate metal ions with heavily distorted tricapped trigonal prismatic geometries. Steady-state and time-resolved luminescence spectroscopy showed that the antennae could sensitize both Tb(iii) and Eu(iii), however, quantum yields were lower than in other octadentate complexes lacking pyridylcarboxylate. Complexes with more electron-poor pyridines were less emissive even when equipped with the same antenna. The oxidation and reduction potentials of the antennae and the pyridinecarboxylates, respectively, were determined by cyclic voltammetry. The obtained values were consistent with electron transfer from the excited antenna to the pyridine providing a previously unexplored quenching pathway that could efficiently compete with energy transfer to the lanthanide. These results show the crucial impact that photophysically innocent ligand binding sites can have on lanthanide luminescence.
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| 3. |
- Kocsi, Daniel, 1989-
(författare)
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Energy Transfer Processes and Quenching Pathways in Lanthanide Complexes: The Role of Structural Changes
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Due to their unique magnetic and luminescent properties, trivalent lanthanides (Ln(III)) have been widely utilised in cellular imaging. Ln(III) luminescence is usually sensitized by a light-harvesting ‘antenna’, a chromophore that can transfer the excitation energy to the Ln(III). Our research focuses on the understanding and tuning of the luminescent properties of Ln(III) coordination compounds. In order to obtain bright emitters, the optimisation of energy transfer and minimisation of quenching processes are key challenges. In complexes of reducible Ln(III) ions photoinduced electron transfer (PeT) from the excited state antenna to the Ln(III) is possible, often quenching both antenna fluorescence and Ln(III) luminescence. Chapter 1 is a brief introduction to luminescent Ln(III) coordination compounds. In Chapter 2 intraligand PeT from the excited state antenna to the pyridines was studied in picolinate-containing TACN (1,4,7-triazacyclononane)-based Ln(III) complexes. Such PeT was found to be thermodynamically favoured and strongly dependent on the electron accepting ability of pyridines. Chapter 3 addresses the importance on how distant structural changes can lead to improved luminescent properties in Ln complexes. Two sets of complexes with identical coordination environments and antennae were compared. In the first set the antenna was connected to the metal-binding site via a secondary amide linker, while in the second the linker was replaced with a tertiary amide. All tertiary amide linked Ln(III) complexes showed increased quantum yields compared to their secondary amide analogues. Moreover, tertiary complexes showed improved photostability compared to the secondary-amide linked ones.In Chapter 4 and 5 we investigated the effects of fluorinated antennae in secondary and tertiary amide-linked DO3A (cyclen-1,4,7-triacetate)-based, and pyridyl-containing TACN-based Ln(III) complexes. Photophysical characterisation revealed that monofluorination yielded no significant improvement in the luminescent quantum yields compared to the non-fluorinated analogues. The fluorination of the carbostyril antenna in the 3 position drastically effected the excited state behaviour. The presence of several emissive species was observed possibly caused by changes in the coordination environment. 3-CF3 and the 4-fluoro carbostyrils were excellent sensitisers of Eu(III) and Tb(III) emission. Changes in the antenna T1 resulted in 5–12-fold increase in Tb(III) luminescent quantum yields in the 3-CF3 series compared to the 4-CF3 analogues. Eu(III) luminescent quantum yields and the sensitisation efficiencies were systematically lower in the 3-CF3 compounds vs the 4-CF3 emitters, which might be attributed to the differences in the PeT quenching in these complexes.
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| 4. |
- Kócsi, Dániel, et al.
(författare)
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Tuning the photophysical properties of luminescent lanthanide complexes through regioselective antenna fluorination
- 2022
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Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; 58:48, s. 6853-6856
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Tidskriftsartikel (refereegranskat)abstract
- Carbostyrils monofluorinated in the 3, 5, or 6 positions were synthesised from olefinic precursors via a photochemical isomerisation-cyclisation route, and incorporated into octadentate cyclen triacetate ligands that formed luminescent complexes with Tb(iii) and Eu(iii). The photophysical properties of the emitters were strongly dependent on the position of the fluorination.
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| 5. |
- Sollert, Carina, et al.
(författare)
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C-glycosylated pyrroles and their application in dipyrromethane and porphyrin synthesis
- 2021
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Ingår i: Journal of Porphyrins and Phthalocyanines. - : World Scientific. - 1088-4246 .- 1099-1409. ; 25:7-8, s. 741-755
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Tidskriftsartikel (refereegranskat)abstract
- Pyrrole C-glycosylated in either the 2- or the 3-position could be prepared by the acid-catalyzed reaction between trichloroacetimidate glycosyl donors and pyrrole, or N-phenyl-trifluoroacetimidate glucosyl donor and N-TIPS pyrrole, respectively. Pyrroles carrying glucose, mannose, galactose and lactose in the 2-position, and glucose in the 3-position were obtained. The configurations of the products could be assigned using a combination of 1D and 2D NMR spectroscopy. A number of undesired background reactions yielding a variety of stereo- and regioisomers were identified; in several cases these could be eliminated. Glycosylpyrroles could be incorporated into mono- and diglycosylated dipyrromethanes, a diglycosylated BODIPY dye, and a monoglycosylated Zn(II) porphyrin without damaging the sugar unit.
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| 6. |
- Tomar, Monika, et al.
(författare)
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Photocatalytic Generation of Divalent Lanthanide Reducing Agents
- 2023
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 145:41, s. 22555-22562
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Tidskriftsartikel (refereegranskat)abstract
- Divalent lanthanide (Ln) compounds are excellent reducing agents with unique reactivity profiles. These reagents are typically used in superstoichiometric amounts, often in combina-tion with harmful additives. Reactions catalytic in Ln(II) reagents that retain the reactivity and selectivity of the stoichiometric transformations are currently lacking due to the absence of effective and selective methods to form reactive Ln(II) species from stable precursors. Here, active Ln(II) is generated from a Ln(III) precursor through reduction by a photoexcited coumarin or carbostyril chromophore, which, in turn, is regenerated by a sacrificial reductant. The reductant can be metallic (Zn) or organic (amines) and can be used in strictly stoichiometric amounts. A broad range of reactions, including C-halogen, C=C, C=X (X = O, N), P=O, and N=N reductions, as well as C-C, C-X (X = N, S, P), and N-N couplings were readily carried out in yields and selectivities comparable to or better than those afforded by the analogous stoichiometric transformations. The reaction outcomes could be altered by changing the ligand or the lanthanide or through the addition of environmentally benign additives (e.g., water). EPR spectroscopy supported the formation of both Ln(II) and oxidized chromophore intermediates. Taken together, these results establish photochemical Ln(II) generation as a powerful strategy for rendering Ln(II)-mediated reactions catalytic.
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