| 1. |
- Arkhypchuk, Anna I., et al.
(författare)
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[2+2] Cycloaddition of phosphaalkenes as a key step for the reductive coupling of diaryl ketones to tetraaryl olefins
- 2022
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Ingår i: Chemical Science. - : Royal Society of Chemistry. - 2041-6520 .- 2041-6539. ; 13:41, s. 12239-12244
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Tidskriftsartikel (refereegranskat)abstract
- Procedures for the reductive coupling of carbonyl compounds to alkenes in the literature rely either on a radical coupling strategy, as in the McMurry coupling, or ionic pathways, sometimes catalysed by transition metals, as in more contemporary contributions. Herein, we present the first example of a third strategy that is based on the [2 + 2] cycloaddition of ketone-derived phosphaalkenes. Removal of P-trimethylsilyl groups at the intermediary 1,2-diphosphetane dimer results in its collapse and concomitant release of the tetraaryl-substituted alkene. In fact, the presented strategy is the only alternative to the McMurry coupling in the literature that allows tetraaryl alkene formation from diaryl ketones, with yields as high as 85%. The power of the methodology is illustrated in the reaction of tethered bis-benzophenones which engage in intramolecular reductive carbonyl couplings to form unusual macrocycles without the need for high dilution conditions or templating.
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| 2. |
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Cover Feature : Analysis of Anion Binding Effects on the Sensitized Luminescence of Macrocyclic Europium(III) Complexes (Anal. Sens. 6/2022)
- 2022
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Ingår i: Analysis & Sensing. - : John Wiley & Sons. - 2629-2742 .- 2629-2742.
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Konstnärligt arbete (refereegranskat)abstract
- The cover feature image represents the differences in the luminescence response upon fluoride vs cyanide binding to a 1,4,7-triazacyclonane-based Eu(III) complex equipped with a carbostyril light-harvesting antenna. The addition of excess of fluoride boosts the Eu(III) emission quantum yield by up to 6-fold for such compounds. Cyanide addition extinguishes Eu(III) luminescence despite partial anion binding to a lanthanide 3+ ion. These compounds showed opposite responses upon fluoride and cyanide binding, and the results could facilitate the design of responsive probes for multiple anion types. More information can be found in the Research Article (https://doi.org/10.1002/anse.202200015) by K. E. Borbas and co-workers.
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| 3. |
- Kiraev, Salauat R., et al.
(författare)
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Analysis of Anion Binding Effects on the Sensitized Luminescence of Macrocyclic Europium(III) Complexes
- 2022
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Ingår i: Analysis & Sensing. - : Wiley-VCH Verlagsgesellschaft. - 2629-2742. ; 2:6
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Tidskriftsartikel (refereegranskat)abstract
- Four triazamacrocyclic and two tetraazamacrocyclic ligands carrying two and three coordinating donor groups, respectively, and a carbostyril light-harvesting antenna were synthesized. The antenna was linked to a macrocycle either via secondary or tertiary amide. Complexation with europium (Eu), gadolinium (Gd), terbium (Tb), and ytterbium (Yb) yielded overall +1 or +2 charged species. Paramagnetic 1H NMR, and steady-state and time-resolved luminescence spectroscopies showed that the complexes had 1–3 inner-sphere water molecules and displayed a variety of coordination geometries in solution. The antennae sensitized Eu(III) and Tb(III) emission with quantum yields of 0.3–4.3 % and 9.9–24.5 %, respectively. The addition of excess fluoride or cyanide to buffered Eu(III) complex solutions resulted in anion-dependent changes. Fluoride addition increased the Eu(III) luminescence intensity by displacing all inner-sphere water molecules and stabilizing the +3 oxidation state of Eu. Eu(III) luminescence increased up to 25-fold for one emitter. Cyanide quenched Eu(III) luminescence in all cases despite partial water ligand displacement.
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| 4. |
- Kiraev, Salauat R., et al.
(författare)
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Improved emission of Yb(iii) ions in triazacyclononane-based macrocyclic ligands compared to cyclen-based ones
- 2022
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry. - 1477-9226 .- 1477-9234. ; 51:43, s. 16596-16604
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Tidskriftsartikel (refereegranskat)abstract
- Yb(III) complexes based on ligands with a 1,4,7-triazacyclononane (tacn) macrocyclic core were synthesised. The complexes carry a 4-methoxymethyl-substituted carbostyril chromophore that serves as a light-harvesting antenna. The ligands supply 5 nitrogen and 3 oxygen donors via 1 methylenecarboxamide and 2 picolinate donors, creating +1 charged complexes with an octadentate binding environment. The electronic properties of the picolinates are modulated by varying the substitution at the 4 position with OMe, H, Cl, or CF3. Cyclic voltammetry indicated that the tacn-based Yb(III) complexes were easier to reduce than the analogous cyclen complexes. The first reductive event is likely picolinate-centred, followed by the formation of further reduced species. Antenna excitation yielded Yb(III) luminescence in the near-infrared (NIR) region in all cases. The antenna photophysical properties were consistent with intraligand photoinduced electron transfer from the excited carbostyril to the picolinate groups. The relative quantum yields of Yb(III) luminescence were determined. The lowest value was obtained for the complex with the most efficient antenna-to-picolinate photoinduced electron transfer. Despite intraligand electron transfer quenching of the antenna, the tacn-based Yb complexes were more emissive than their cyclen analogues, highlighting the influence of the ligand structure on the luminescence properties of NIR emissive lanthanide(III) ions.
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| 5. |
- Mathieu, Emilie, et al.
(författare)
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Sensitization Pathways in NIR-Emitting Yb(III) Complexes Bearing 0, +1, +2, or +3 Charges
- 2022
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 144:46, s. 21056-21067
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Tidskriftsartikel (refereegranskat)abstract
- Yb(III) complexes of macrocyclic ligands based on1,4,7,10-tetraazacyclododecane were synthesized. The ligands carried a carbostyril chromophore for Yb(III) sensitization, and carboxylate or carbamide donors for metal binding, forming complexes of 0, +1, +2, or +3 overall charge. The coordination geometry was little affected by the replacement of carboxylates with amides, as shown by paramagnetic 1H NMR spectroscopy. The Yb(III)/Yb(II) reduction potentials were dependent on the nature of the metal binding site, and the more positively charged complexes were easier to reduce. Carbostyril excitation resulted in Yb(III) luminescence in every complex. The residual carbostyril fluorescence quantum yields were smaller in complexes containing more reducible Yb(III) centers decreasing from 5.9% for uncharged complexes to 3.1−4.4% in +3 charged species, suggesting photoinduced electron transfer (PeT) from the antenna to the Yb(III). The relative Yb(III) luminescence quantum yields were identical within the experimental error, except for the +3 charged complex with fully methylated coordinating amides, which was the most intense Yb(III) emitter of the series in water. Quenching of the Yb(III) excited state by NH vibrations proved to limit Yb(III) emission. No clear improvement of the Yb(III) sensitization efficiency was shown upon faster PeT. This result can be explained by the concomitant sensitization of Yb(III) by phonon-assisted energy transfer (PAEnT) from the antenna triplet excited state, which was completely quenched in all of the Yb complexes. Depopulation of the triplet by PeT quenching of the donor singlet excited state would be compensated by the sensitizing nature of the PeT pathway, thus resulting in a constant overall sensitization efficiency across the series.
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