Triggering Emission with the Helical Turn in Thiadiazole-Helicenes.

Introduction of heterocycles into the helical skeleton of helicenes allows modulation of their redox, chiroptical, and photophysical properties. This paper describes the straightforward preparation and structural characterization by single-crystal X-ray diffraction of thiadiazole-[7]helicene, which was resolved into M and P enantiomers by chiral HPLC, together with its S-shaped double [4]helicene isomer, as well as the smaller congeners thiadiazole-[5]helicene and benzothiadiazole-anthracene. A copper(II) complex with two thiadiazole-[5]helicene ligands was structurally characterized, and it shows the presence of both M and P isomers coordinated to the metal center. The emission properties of the heterohelicenes are highly dependent on the helical turn, as the [7]- and [5]helicene are poorly emissive, whereas their isomers, that is, the S-shaped double [4]helicene and thiadiazole-benzanthracene, are luminescent, with quantum efficiencies of 5.4 and 6.5 %, respectively. DFT calculations suggest quenching of the luminescence of enantiopure [7]helicenes through an intersystem-crossing mechanism arising from the relaxed excited S1 state.

Tetrathiafulvalene mono- and bis-1,2,3-triazole precursors by click chemistry: structural diversity and reactivity.

The donor ortho-dimethyl-TTF-(N-n-Bu-1,2,3-triazole) 1,5-isomer has been synthesized by click chemistry following a ruthenium-catalyzed azide-alkyne cycloaddition procedure. The single crystal X-ray analysis showed a planar conformation between the TTF and triazole units and a set of intermolecular interactions at the supramolecular level in the solid state. The same procedure allowed the preparation of the corresponding ortho-dimethyl-TTF-bis(triazole) which was also structurally characterized. Because of the steric hindrance, the triazole units are no longer planar with the TTF backbone. The reactivity of the triazole ring has been investigated in protonation and alkylation reactions, monitored by UV-visible spectroscopy, which clearly showed the red shift of the intramolecular charge transfer band. A TTF-methyl-triazolium salt has been isolated and analyzed by single crystal X-ray analysis. All of the TTF-triazoles and triazolium salts are valuable precursors for radical cation salts due to their oxidation potentials and variety of possible intermolecular interactions.

Ethylenedithio-tetrathiafulvalene-helicenes: electroactive helical precursors with switchable chiroptical properties.

Electroactive fused ethylenedithio-tetrathiafulvalene-[4]helicene and -[6]helicenes have been synthesized through a strategy that involved the preparation of 2,3-dibromo-helicene derivatives as intermediates. The dihedral angles between the terminal helicenes, as determined by single-crystal X-ray analysis, are 22.7° and 50.7° for the [4]helicene and [6]helicene, respectively. Their solid-state architectures show interplay between S⋅⋅⋅S and π⋅⋅⋅π intermolecular interactions. The chiroptical properties of the enantiopure EDT-TTF-[6]helicene derivatives have been investigated and supported by TDDFT calculations. Remarkable redox switching of the circular dichroism (CD) signal between the neutral and radical-cation species has been achieved.

Electroactive tetrathiafulvalenyl-1,2,3-triazoles by click chemistry: Cu- versus Ru-catalyzed azide-alkyne cycloaddition isomers.

Two series of 4- and 5-tetrathiafulvalenyl-1,2,3-triazoles, as multifunctional ligands and precursors for molecular materials, have been synthesized by copper- or ruthenium-based "click" chemistry. The solid-state structures of three ligands and two Cu(II) complexes were determined. Large differences in the electron-donating properties between the 1,4- and 1,5-isomers were evidenced by cyclic voltammetry. Theoretical calculations support this observation and allow the assignment of the electronic transitions observed in UV/Vis spectra of the ligands.

Chiral and extended π-conjugated bis(2-pyridyl)phospholes as assembling N,P,N pincers for coordination-driven synthesis of supramolecular [2,2]paracyclophane analogues.

Chiral, π-conjugated 3,4-butano-1-phenyl-2,5-bis(2-pyridyl)phosphole derivatives 1a(2,2') and 1a(3) with chiral trans-1,2-diol moieties and fused pinene derivatives, respectively, were prepared from the corresponding chiral diynes by using the Fagan-Nugent method. Their UV/Vis absorption and chiroptical properties (optical rotation and circular dichroism) were studied. Their behavior as N,P,N chelates towards coordination of Cu(I) and formation of chiral supramolecular assemblies with π-conjugated ditopic dicyano ligands was investigated. Chiral C(2)-symmetric rectangles that are [2,2]paracyclophane analogues were obtained, as demonstrated by X-ray crystallography. During the course of this study, the first stable water-soluble phosphole derivative (1a(2)·2 HCl) was prepared. Furthermore, achiral 3,4-butano-1-phenyl-2,5-bis(aza[4]helicene)phosphole 1a(4) was synthesized and displays extended π conjugation. A supramolecular rectangle was obtained by coordination to Cu(I) and assembly with a dicyano stilbene. This coordination-driven supramolecular assembly contains a total of four aza[4]helicene moieties and displays two types of π-π stacking interactions in the solid state, that is, between two helicene moieties and between one helicene and a bridging dicyano ligand. All the supramolecular arrangements are discussed by comparing them with previous work on the parent 3,4-butano-1-phenyl-2,5-bis(2-pyridyl)phosphole.

[Percutaneous liver biopsy before organ removal-Impact on organ allocation and costs in liver transplantation]. / Perkutane Leberbiopsie vor Organentnahme ­ Einfluss auf Organallokation und Kosten in der Lebertransplantation.

BACKGROUND: The value and safety of percutaneous liver biopsy (PLB) in brain-dead donors before organ removal and its impact on organ allocation and costs of liver transplantation (LT) in the Eurotransplant (ET) region is still a matter of ongoing debate. MATERIAL AND METHODS: A PLB was performed in 36 brain-dead organ donors. The complication rate, ultrasonography findings, macroscopic evaluation and histological results of PLB and donor characteristics were analyzed. Additionally, a nationwide survey was conducted among 11 liver transplantation experts. The need for PLB and its impact on the liver allocation process were evaluated. Possible cost savings were calculated for different scenarios based on cost data provided by the German Organ Transplantation Foundation. RESULTS: No complications of PLB were observed. The survey revealed that the PLB has a substantial impact on the allocation of donor organs, especially in organs fulfilling extended donor criteria (EDC). The cost calculation revealed an enormous potential for cost savings due to an optimized organ allocation process and avoidance of futile organ procurement. CONCLUSION: The PLB is a safe procedure and has tremendous potential for the optimization of the organ allocation process before organ procurement by reducing the cold ischemia time, avoiding unnecessarily discarding donor organs and saving costs. These data emphasize the clinical relevance and impact of PLB on the organ allocation process.

Triplet state CPL active helicene-dithiolene platinum bipyridine complexes.

Chiral metal dithiolene complexes represent a family of chiral precursors, which can give rise to molecular materials with properties resulting from the interplay of chirality with conductivity, magnetism, and photophysics. We describe herein the first examples of chiral metal diimine dithiolene complexes, by the use of a platinum(ii) centre coordinated by 2,2'-bipyridine and helicene-dithiolene ligands. The straightforward synthesis of racemic and enantiopure complexes allows the preparation of luminescent Pt(bipy) [4] and [6]helicene compounds for which the solid-state structure was determined as well. TD-DFT calculations support the assignment of the low-energy bands observed in the UV-vis absorption spectra as mixed metal-ligand-to-ligand charge transfer transitions and confirm that the emission band results from the T1 excited state. Interestingly, the enantiopure [6]helicene complexes show CPL activity at room temperature in acetonitrile solutions with an anisotropy factor of 3 × 10-4.