Localised to intraligand charge-transfer states in cyclometalated platinum complexes:an experimental and theoretical study into the influence of electron-rich pendants and modulation of excited states by ion binding

The neopentyl ester of 1,3-di(2-pyridyl)benzene-5-boronic acid (dpy-B) is a useful intermediate in the divergent synthesis of N;C;N-coordinating, 1,3-di(2-pyridyl)benzene ligands, HL(n), that carry aryl substituents at the 5-position of the central ring. The platinum(ii) complexes, PtL(n)Cl, of several such ligands have been prepared, incorporating pendant anisoles, arylamines, an oxacrown, and an azacrown, all of which are strongly luminescent in solution at 298 K. The emission of the complexes is partially quenched by oxygen, and all of the compounds are very efficient sensitisers of singlet oxygen. The quantum yields of (1)O(2) formation have been measured on the basis of the intensity of the O(2)(1)Delta(g) emission at 1270 nm, and are in the range 0.25-0.65. Density functional theory (DFT) calculations have been carried out that include the effect of the solvent, on the unsubstituted complex PtL(1)Cl and on the derivatives incorporating p-dimethylaminophenyl and phenyl-15-mono-N-azacrown-5 pendants (PtL(9)Cl and PtL(12)Cl respectively). Absorption spectra have been simulated on the basis of the calculated singlet excitations: they closely resemble the experimental spectra. In particular, the DFT successfully accounts for the appearance of low-energy absorption bands that accompany the introduction of the aryl pendants, indicating the participation of the aryl group in the HOMO but not significantly in the LUMO. The calculated lowest energy triplet excitation of PtL(1)Cl is close to the observed 0-0 emission maximum of this complex in solution. Taking together data for this series of complexes and related compounds previously studied, the energies of the lowest-energy spin-allowed absorption bands are shown to correlate approximately linearly with the oxidation peak potential. The emission energies show a similar correlation in toluene, but in CH2Cl2 the value for PtL(9)Cl is anomalously low. The differing emission properties of this complex in the two solvents suggest a switch to a TICT-like state in CH2Cl2 (TICT = twisted intramolecular charge transfer), stabilised in the more polar environment. Transient DC photoconductivity measurements confirm that the dipole moment of the triplet excited state is larger in CH2Cl2 than in toluene. The azacrown PtL(12)Cl displays similar behaviour. Binding of metal ions such as Ca2+ to the azacrown unit of this complex leads to a pronounced blue shift in the emission, which can be readily understood in terms of the large increase in the TICT energy that will accompany the binding of the metal ion to the lone pair of the azacrown nitrogen atom

Optimising the luminescence of platinum(II) complexes and their application in organic light emitting devices (OLEDs)

In this contribution, we provide an overview of some of the strategies for maximising the luminescence efficiencies of simple square-planar platinum(II) complexes in solution, including the introduction of strong-field co-ligands into di- and tri-imine complexes, involvement of intraligand charge-transfer excited states, and cyclometallation. We then explore in more detail several classes of platinum(II) complexes containing cyclometallating bidentate and terdentate ligands, many of which are significantly luminescent in solution at room temperature. The background to the use of brightly emissive platinum(II) complexes as phosphors in organic light emitting devices (OLEDs) is discussed. Key recent studies on the use of Pt(II) complexes in OLEDs are reviewed

Host–guest interaction between cyclen based macrotricyclic ligands and phosphate anions. A potentiometric investigation

International audienceThe host-guest interaction between orthophosphate, pyrophosphate and triphosphate anions and three cyclen based macrotricyclic ligands possessing ortho- (TOC), meta- (TMC) and para-xylenyl (TPC) linkers was investigated by potentiometric measurements. The ternary species present in solution and their stability constants have been determined. The different behaviours are explained in terms of hydrogen bond formation and coulombic attraction between the organic host and the inorganic guest. The selectivity, illustrated with species distribution diagrams, is discussed. The results unambiguously showed the importance of the distance between the two cyclen cores and emphasized the increasing of the triphosphate species selectivity together with the cavity size of the ligand. A comparison of the present results with those obtained with their mono-bridged homologues is also discussed

Complexation of the triphosphate anion: tuning the structure of cyclen based macrotricycles with 1,3-dimethylbenzene and 2,6-dimethylpyridine linkers. A potentiometric and NMR study

International audienceThe host–guest interaction between orthophosphate, pyrophosphate and triphosphate anions and three cyclen-based macrotricyclic ligands was investigated by potentiometric measurements and NMR spectroscopy. The ligands differ from one another by the nature of their spacers, which are 1,3-dimethylbenzene (TMC), 2,6-dimethylpyridine (TPyC) or a combination of the two (TMPyC). In aqueous solution, each ligand gave protonated species that further formed ternary complexes after binding with anions; these complexes were analyzed as a result of hydrogen bond formation and coulombic attraction between the organic host and the inorganic guest. The equilibrium constants found for all the detected species are reported and the selectivity, illustrated with species distribution diagrams, is discussed. The results unambiguously showed that the ligand possessing a single supplementary anchoring site (the pyridinyl spacer) exhibited the greatest affinity for the phosphate species in a large p[H] range

New side-bridged bismacrocycles and cross-bridged macrotricycles. Syntheses and Cu(ii) complexation study

International audienceEight new cyclen based constrained macropolycycles (4a–4d, 5a–5d) have been obtained by reductive ring cleavage of polyaminal derivatives of bis-macrocycles or macrotricyclic polyammonium salts by sodium borohydride. The mononuclear and dinuclear Cu(II) complexes of these macropolycyclic ligands were isolated as solids and investigated by UV-Vis and EPR spectroscopies. The possibility to obtain the specific formation of mononuclear complexes constitutes an original feature of these new macropolycycles

Les salles de consommation de drogue à moindre risque

Une loi du 26 janvier 2016 a autorisé l’expérimentation de salles de consommation de drogues à moindre risque (SCMR). Le but est de réduire les risques liés aux pratiques des usagers de drogues, au niveau de l'usager comme de la collectivité, en termes de santé publique comme d’ordre public. Inédit en France et très controversé, le dispositif, prévu pour une durée maximale de six ans, donnera lieu à une double évaluation scientifique afin notamment d’en déterminer la pérennisation. C’est dans ce cadre nouveau que deux espaces de ce type ont d’ores et déjà été ouverts à Paris et Strasbourg à l’automne 2016. La France rejoint ainsi un mouvement international qui s’affirme progressivement, notamment dans plusieurs de nos voisins européens et au Canada. Cependant, cet approfondissement de la politique de réduction des risques en matière de drogues s’articule difficilement avec le modèle premier et dominant : le modèle prohibitionniste. Reposant notamment sur la liaison de la répression et de la médicalisation de la consommation de stupéfiants, celui-ci poursuit un objectif autrement radical : l’éradication des drogues. La controverse ne se réduit pas à la confrontation des SCMR au modèle prohibitionniste. Les débats procèdent également de l’ambivalence intrinsèque du dispositif considéré. Présenté comme pragmatique et humaniste, le dispositif est autrement complexe : il peut être lu comme l’avatar d’une approche gestionnaire des problèmes sociaux. Les SCMR posent donc des problèmes épineux que seule une approche pluridisciplinaire permet de poser. Parallèlement, elles sont au cœur de problématiques transversales qui les dépassent en même temps qu’elles les cristallisent. Les SCMR sont ainsi non seulement un objetde recherche mais encore un anglede recherche. Leur genèse retracée, ces deux logiques doivent être envisagées à plusieurs voix : suret parles SCMR. Faisant suite à un colloque pluridisciplinaire et international organisé dans cette perspective, à Rennes, les 7 et 8 novembre 2017, par l’UMR CNRS IODE, le présent dossier n’en est que l’écho partiel. Le choix a été fait de le concentrer sur les questions tenant aux principaux acteurs de la vie quotidienne d’une SCMR : intervenants en réduction des risques, usagers, riverains. Cette évocation est précédée de deux articles envisageant le dispositif de manière globale et suivie de trois contributions qui dépassent la seule question des SCMR pour, à partir d’elles, réfléchir à ce que peut vouloir dire (et faire), aujourd’hui, la notion d’autonomie