Synthesis, Structural Characterization, and Phosphorescence Properties of Trigonal Zn(II) Carbene Complexes.

The sterically demanding N-heterocyclic carbene ITr (N,N'-bis(triphenylmethyl)imidazolylidene) was employed for the preparation of novel trigonal zinc(II) complexes of the type [ZnX2(ITr)] [X = Cl (1), Br (2), and I (3)], for which the low coordination mode was confirmed in both solution and solid state. Because of the atypical coordination geometry, the reactivity of 1-3 was studied in detail using partial or exhaustive halide exchange and halide abstraction reactions to access [ZnLCl(ITr)] [L = carbazolate (4), 3,6-di-tert-butyl-carbazolate (5), phenoxazine (6), and phenothiazine (7)], [Zn(bdt)(ITr)] (bdt = benzene-1,2-dithiolate) (8), and cationic [Zn(µ2-X)(ITr)]2[B(C6F5)4]2 [X = Cl (9), Br (10), and I (11)], all of which were isolated and structurally characterized. Importantly, for all complexes 4-11, the trigonal coordination environment of the ZnII ion is maintained, demonstrating a highly stabilizing effect due to the steric demand of the ITr ligand, which protects the metal center from further ligand association. In addition, complexes 1-3 and 8-11 show long-lived luminescence from triplet excited states in the solid state at room temperature, according to our photophysical studies. Our quantum chemical density functional theory/multireference configuration interaction (DFT/MRCI) calculations reveal that the phosphorescence of 8 originates from a locally excited triplet state on the bdt ligand. They further suggest that the phenyl substituents of ITr are photochemically not innocent but can coordinate to the electron-deficient metal center of this trigonal complex in the excited state.

Towards Fast Circularly Polarized Luminescence in 2-Coordinate Chiral Mechanochromic Copper(I) Carbene Complexes.

A series of chiral mechanochromic copper(I) cAAC (cAAC=cyclic (alkyl)(amino)carbene) complexes with a variety of amide ligands have been studied with regard to their photophysical and chiroptical properties to elucidate structure-property relationships for the design of efficient triplet exciton emitters exhibiting circularly polarized luminescence. Depending on the environment, which determines the excited state energies, either thermally activated delayed fluorescence (TADF) from 1/3 LLCT states or phosphorescence from 3 LLCT/LC states occurs. However, neither chiral moieties at the carbene nor at the carbazolate ligands provide detectable luminescence dissymmetries glum . An exception is [Cu(phenoxazinyl)(cAAC)], showing orange to deep red TADF with λmax =601-715 nm in solution, powders and in PMMA. In this case, the amide ligand can undergo distortions in the excited state. This design motif leads to the first linear, non-aggregated CPL-active copper(I) complex with glum of -3.4 ⋅ 10-3 combined with a high radiative rate constant of 6.7 ⋅ 105  s-1 .

Synthesis and Photophysical Studies of Copper(I) CAAC Half-Sandwich Complexes as a Highly Modifiable Class of Emitters.

Cyclopentadienyls are well-known strong donor ligands and have been successfully employed in catalysis as they tolerate a variety of substituents to adjust their steric and electronic properties. Although such highly modifiable ligands are of great interest for luminescence and photocatalytic applications, studies of CpR-containing photoactive transition-metal complexes are quite rare. In this work, we present a structural, electrochemical, and first elaborated photophysical investigation of a series of copper(I) half-sandwich complexes bearing cyclic alkyl(amino)carbenes (CAACs) as chromophore ligands and compare them with [Cu(Cp)(IDipp)] and [Cu(Cp*)(IDipp)] bearing a traditional N-heterocyclic carbene. Furthermore, we present the first molecular structure derived from single-crystal X-ray diffraction of a copper(I) indenyl complex, which can be described as an η2 (σ, π)-coordination. The CuI half-sandwich complexes show blue-green to orange phosphorescence with a photoluminescence quantum yield of up to 59% and radiative rate constants kr of up to 4 × 104 s-1 in the solid state, depending on the substitution pattern of the CpR ligand. Our TD/DFT calculations suggest that the emitting excited states are of 3MLCT/LLCT character. We determined the excited-state lifetime of the CuI half-sandwich complexes in solution to be as long as 600 ns, which in combination with the large π-surface of the CpR ligands allows for Dexter energy transfer for photocatalytic applications. In addition, the chiroptical properties of chiral [Cu(Cp/Cp*)(CAACMenthone)] were studied and compared to [CuCl(CAACMenthone)], of which we demonstrate that its circular polarized luminescence is the result of excimer formation and not, as previously reported, attributed to the monomeric C1-symmetric structure.

Food deserts in Winnipeg, Canada: a novel method for measuring a complex and contested construct. / Déserts alimentaires à Winnipeg (Canada) : une nouvelle méthodologie de mesure d'un concept complexe et controversé.

INTRODUCTION: "Food deserts" have emerged over the past 20 years as spaces of concern for communities, public health authorities and researchers because of their potential negative impact on dietary quality and subsequent health outcomes. Food deserts are residential geographic spaces, typically in urban settings, where low-income residents have limited or no access to retail food establishments with sufficient variety at affordable cost. Research on food deserts presents methodological challenges including retail food store identification and classification, identification of low-income populations, and transportation and proximity metrics. Furthermore, the complex methods often used in food desert research can be difficult to reproduce and communicate to key stakeholders. To address these challenges, this study sought to demonstrate the feasibility of implementing a simple and reproducible method of identifying food deserts using data easily available in the Canadian context. METHODS: This study was conducted in Winnipeg, Canada in 2014. Food retail establishments were identified from Yellow Pages and verified by public health dietitians. We calculated two scenarios of food deserts based on location of the lowest-income quintile population: (a) living ≥ 500 m from a national chain grocery store, or (b) living ≥ 500 m from a national chain grocery store or a full-service grocery store. RESULTS: The number of low-income residents living in a food desert ranged from 64 574 to 104 335, depending on the scenario used. CONCLUSION: This study shows that food deserts affect a significant proportion of the Winnipeg population, and while concentrated in the urban core, exist in suburban neighbourhoods also. The methods utilized represent an accessible and transparent, reproducible process for identifying food deserts. These methods can be used for costeffective, periodic surveillance and meaningful engagement with communities, retailers and policy makers.

INTRODUCTION: Les « déserts alimentaires ¼ ont vu le jour dans les 20 dernières années et forment des secteurs préoccupants pour les collectivités, les autorités en santé publique et les chercheurs en raison de leur effet négatif possible sur la qualité de l'alimentation et en raison de leurs conséquences sur la santé. Ce sont des espaces résidentiels, habituellement en milieu urbain, où les résidents à faible revenu n'ont que peu ou pas accès à des établissements de vente au détail d'aliments qui offrent suffisamment de variété à un prix abordable. La recherche sur les déserts alimentaires présente des défis méthodologiques, notamment la façon de repérer et de classer les magasins d'alimentation au détail, la définition de la population à faible revenu ainsi que les paramètres concernant le transport et la proximité. De plus, les méthodes complexes qui sont souvent employées dans la recherche sur les déserts alimentaires peuvent être difficiles à reproduire et à communiquer aux principaux intervenants. Pour surmonter ces difficultés, nous avons voulu montrer qu'on pouvait concevoir une méthode simple et reproductible pour repérer les déserts alimentaires, à l'aide de données facilement accessibles en contexte canadien. MÉTHODOLOGIE: Cette étude a été menée à Winnipeg (Canada) en 2014. Les établissements de vente au détail des aliments ont été trouvés à l'aide des Pages Jaunes et vérifiés par des diététistes en santé publique. Nous avons créé deux scénarios sur les déserts alimentaires en fonction de l'emplacement de la population à quintile de revenu le plus faible : a) celle qui habitait à 500 m ou plus d'une épicerie appartenant à une chaîne nationale et b) celle qui habitait à 500 m ou plus d'une épicerie appartenant à une chaîne nationale ou d'une épicerie à service complet. RÉSULTATS: En fonction du scénario utilisé, 64 574 ou 104 335 résidents à faible revenu vivaient dans un désert alimentaire. CONCLUSION: Les déserts alimentaires touchent une proportion importante de la population de Winnipeg et, même s'ils sont concentrés en centre-ville, ils sont présents également en banlieue. La méthodologie employée pour repérer les déserts alimentaires est accessible, claire et reproductible. Elle est utilisable pour exercer une surveillance périodique à faible coût, ainsi que pour favoriser un engagement significatif de la part des collectivités, des magasins de détail et des responsables des politiques.