| 1. |
- Arkhypchuk, Anna I., et al.
(author)
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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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In: Chemical Science. - : Royal Society of Chemistry. - 2041-6520 .- 2041-6539. ; 13:41, s. 12239-12244
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Journal article (peer-reviewed)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. |
- Bhimpuria, Rohan, et al.
(author)
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Synthesis of styrene, phenyl acrylate and allyloxyphenyl-functionalized porphyrins, and preliminary exploration of their utility for assembling multiple porphyrin units
- 2023
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In: Journal of Porphyrins and Phthalocyanines. - : World Scientific. - 1088-4246 .- 1099-1409. ; 27:07N10, s. 1398-1408
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Journal article (peer-reviewed)abstract
- Three free-base and two Zn(II) porphyrins carrying one alkene-substituted meso-aryl group and three solubilizing pentyl groups were prepared via mixed aldehyde-type syntheses. A meso p-allyloxyphenyl porphyrin was obtained via the corresponding 5-(p-allyloxyphenyl) dipyrromethane. The porphyrins were fully characterized using a combination of NMR spectroscopy, high-resolution mass spectrometry, and UV-Vis absorption and emission spectroscopies. Two of the free-base porphyrins were heated in the presence of AIBN or benzoyl peroxide as the initiator. The major isolated products of these reactions contained two porphyrin units based on the results of MALDI-MS and H-1 NMR analysis data, which was supported by the results of FTIR, UV-Vis absorption and emission spectroscopies, and gel permeation and liquid chromatographies. Additionally, the acrylamide-functionalized porphyrin could be attached to a polylysine scaffold under basic conditions. These results suggest that the olefinic handle can be used to assemble structures containing multiple porphyrinic macrocycles.
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| 3. |
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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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In: Analysis & Sensing. - : John Wiley & Sons. - 2629-2742 .- 2629-2742.
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Artistic work (peer-reviewed)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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| 4. |
- Green, Joshua P., et al.
(author)
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Heavier pnictogens - treasures for optical electronic and reactivity tuning
- 2019
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In: Dalton Transactions. - : Royal Society of Chemistry. - 1477-9226 .- 1477-9234. ; 48:14, s. 4460-4466
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Research review (peer-reviewed)abstract
- We highlight recent advances in organopnictogen chemistry contrasting the properties of lighter and heavier pnictogens. Exploring new bonding situations, discovering unprecedented reactivities and producing fascinating opto-electronic materials are some of the most prominent directions of current organopnicogen research. Expanding the chemical toolbox towards the heavier group 15 elements will continue to create new opportunities to tailor molecular properties for small molecule activation/reactivity and materials applications alike. This frontier article illustrates the elemental substitution approach in selected literature examples.
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| 5. |
- Kiraev, Salauat R., et al.
(author)
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Analysis of Anion Binding Effects on the Sensitized Luminescence of Macrocyclic Europium(III) Complexes
- 2022
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In: Analysis & Sensing. - : Wiley-VCH Verlagsgesellschaft. - 2629-2742. ; 2:6
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Journal article (peer-reviewed)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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| 6. |
- Kiraev, Salauat R., et al.
(author)
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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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In: Dalton Transactions. - : Royal Society of Chemistry. - 1477-9226 .- 1477-9234. ; 51:43, s. 16596-16604
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Journal article (peer-reviewed)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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| 7. |
- Kócsi, Dániel, et al.
(author)
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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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In: Dalton Transactions. - : Royal Society of Chemistry. - 1477-9226 .- 1477-9234. ; 50:45, s. 16670-16677
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Journal article (peer-reviewed)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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| 8. |
- Kovacs, Daniel, et al.
(author)
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Coordination Environment-Controlled Photoinduced Electron Transfer Quenching in Luminescent Europium Complexes
- 2020
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In: Journal of the American Chemical Society. - : AMER CHEMICAL SOC. - 0002-7863 .- 1520-5126. ; 142:30, s. 13190-13200
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Journal article (peer-reviewed)abstract
- The quenching of sensitized Eu(III) luminescence by photoinduced electron transfer from the excited light-harvesting antenna to Eu(III) was investigated. A series of complexes incorporating different metal binding sites and thus having varying Eu(III)/Eu(II) reduction potentials were prepared. The complexes were fully characterized using a combination of single-crystal X-ray crystallography and paramagnetic H-1 NMR spectroscopy, the results of which support the structural similarity of the complexes. The redox and photophysical behavior of the Eu(III) center and the light-harvesting antenna were studied using cyclic voltammetry and steady-state and time-resolved emission spectroscopy on the nanosecond and millisecond time scales. The contribution of photoinduced electron transfer to the overall reduction of the Eu(III) luminescence quantum yield was found to be comparable and, in many cases, larger than the quenching caused by well-established processes such as coupling to X-H oscillators. These results suggest that the elimination or mitigation of photoinduced electron transfer could substantially improve the emissive properties of the widely used Eu(III)-based emitters.
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| 9. |
- Kovacs, Daniel, et al.
(author)
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Electron transfer pathways in photoexcited lanthanide(iii) complexes of picolinate ligands
- 2021
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In: Dalton Transactions. - : Royal Society of Chemistry. - 1477-9226 .- 1477-9234. ; 50:12, s. 4244-4254
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Journal article (peer-reviewed)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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| 10. |
- Laurans, Maxime, et al.
(author)
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Immobilising molecular Ru complexes on a protective ultrathin oxide layer of p-Si electrodes towards photoelectrochemical CO2 reduction
- 2021
-
In: Dalton Transactions. - : Royal Society of Chemistry. - 1477-9226 .- 1477-9234. ; 50:30, s. 10482-10492
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Journal article (peer-reviewed)abstract
- Photoelectrochemical CO2 reduction is a promising approach for renewable fuel generation and to reduce greenhouse gas emissions. Owing to their synthetic tunability, molecular catalysts for the CO2 reduction reaction can give rise to high product selectivity. In this context, a Ru-II complex [Ru(HO-tpy)(6-mbpy)(NCCH3)](2+) (HO-tpy = 4 '-hydroxy-2,2 ':6 ',2 ''-terpyridine; 6-mbpy = 6-methyl-2,2 '-bipyridine) was immobilised on a thin SiOx layer of a p-Si electrode that was decorated with a bromide-terminated molecular layer. Following the characterisation of the assembled photocathodes by X-ray photoelectron spectroscopy and ellipsometry, PEC experiments demonstrate electron transfer from the p-Si to the Ru complex through the native oxide layer under illumination and a cathodic bias. A state-of-the-art photovoltage of 570 mV was determined by comparison with an analogous n-type Si assembly. While the photovoltage of the modified photocathode is promising for future photoelectrochemical CO2 reduction and the p-Si/SiOx junction seems to be unchanged during the PEC experiments, a fast desorption of the molecular Ru complex was observed. An in-depth investigation of the cathode degradation by comparison with reference materials highlights the role of the hydroxyl functionality of the Ru complex to ensure its grafting on the substrate. In contrast, no essential role for the bromide function on the Si substrate designed to engage with the hydroxyl group of the Ru complex in an S(N)2-type reaction could be established.
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| 11. |
- Mathieu, Emilie, et al.
(author)
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Sensitization Pathways in NIR-Emitting Yb(III) Complexes Bearing 0, +1, +2, or +3 Charges
- 2022
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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 144:46, s. 21056-21067
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Journal article (peer-reviewed)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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| 12. |
- Posada Urrutia, Mauricio, et al.
(author)
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Access to long-lived room temperature phosphorescence through auration of 2,1,3-benzothiadiazole
- 2024
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In: Dalton Transactions. - : Royal Society of Chemistry. - 1477-9226 .- 1477-9234. ; 53:12, s. 5658-5664
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Journal article (peer-reviewed)abstract
- A series of 2,1,3-benzothiadiazole–Au(I)–L complexes have been synthesised, structurally characterised and investigated for their photophysical properties. These are the first organometallic Au(I) complexes containing a C–Au bond on the highly electron-deficient benzothiadiazole unit. The complexes exhibit solution-phase phosphorescence at room temperature, assigned to the intrinsic triplet state of the benzothiadiazole unit that is efficently populated through its attachment to gold. Comparison with routinely reported Au(I) complexes, which include intervening alkenyl linkers, suggests that previous assignments of their phosphorescence as 1π → π*(CCR) might be incomplete. Our observations affirm that, in addition to the heavy atom effect, breaking symmetry in the involved aryl motif may be of importance in controlling the luminescence properties.
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| 13. |
- Shameem, Muhammad Anwar, et al.
(author)
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One, Two Three : Phosphaalkene Decoration Tailoring Solubility and Electronic Properties of Truxene-Based Electron Acceptors
- 2023
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In: Chemistry - A European Journal. - : John Wiley & Sons. - 0947-6539 .- 1521-3765. ; 29:32
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Journal article (peer-reviewed)abstract
- We report the functionalization and deplanarization of truxenes using pnictaalkene fragments. Selective introduction of one, two, or three Mes*-Pn fragments provides up to three fully reversible reductions based on the Pn=C fragments. The incorporation of the unsaturated heteroelement fragment as well as the contortion of the truxene core result in significantly red-shifted absorption spectra and interesting opto-electronic properties which are studied by electrochemistry and spectro-electrochemistry. Incorporation of arsaalkene (As=C) motifs gives significantly milder reduction potentials and red-shifted absorption, while phosphaalkene decorated truxene P3 can be functionalized using Au(I)Cl coordination. Furthermore, solubility is markedly increased upon incorporation of the Pn-Mes* fragments which renders these materials suitable for solution processing.
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| 14. |
- Wells, Jordann A. L., et al.
(author)
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Core and double bond functionalisation of cyclopentadithiophene-phosphaalkenes
- 2020
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In: Inorganic Chemistry Frontiers. - : Royal Society of Chemistry (RSC). - 2052-1545 .- 2052-1553. ; 7:21, s. 4052-4061
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Journal article (peer-reviewed)abstract
- The heterofulvenoid cyclopentadithiophene-phosphaalkene is a versatile building block for opto-electronic tuning with donor and acceptor moieties. Both the annulated thienyl rings and the phosphaalkene bond can be functionalised using a variety of chemical transformations, e.g. forming C-C, C-E (E=Si, Br) bonds, or oxidation and metal coordination, respectively. Solid-state structures, optical and electronic properties are probed theoretically and experimentally, illustrating the opto-electronic tailoring opportunities at this motif.
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