Twists and turns in the hierarchical self-assembly pathways of a non-amphiphilic chiral supramolecular material

The formation of helical self-assembled fibres by a C-3 symmetric molecule incorporating three tetrathiafulvalene units is shown to be influenced dramatically by the processing conditions, leading to a variety of different chiral forms, including unprecedented croissants

Selective monosulfoxidation of tetrathiafulvalenes into chiral TTF-sulfoxides

Four inner tetrathiafulvalene-sulfoxides have been synthesized upon reaction of tetrathiafulvalene (TTF), tetramethyl-tetrathiafulvalene (TMTTF), tetrakis (thiomethyl)-tetrathiafulvalene (TMT-TTF), and bis(ethylenedithio)-tetrathiafulvalene (BEDT-TTF) with enantiopure (+) or (−)-(8,8-dichlorocamphorylsulfonyl)-oxaziridine as oxidizing agent. Chiral HPLC studies indicate very weak enantioselectivities for TTF-SO 3 and TMTTF-SO 4, formation of racemic mixture in the case of TMT-TTF-SO 5, and a rather good selectivity, up to 44% ee, in the case of BEDT-TTF-SO 1. The solid state structures of TMTTF-SO 4 and TMT-TTF-SO 5 have been determined by single crystal X-ray diffraction. Both compounds crystallize as racemates in the centrosymmetric triclinic space group P-1. Theoretical calculations at DFT/B3LYP/6-31+G* level afford optimized geometries in good accordance with the experimental structures and emphasize the participation of the chiral sulfoxide group in HOMO and LUMO. Time-dependent DFT calculations corroborated with electronic circular dichroism spectra allow the assignment of the absolute configuration (R) for the major enantiomer of 1 when the (+)-sulfonyl-oxaziridine is used as oxygen transfer reagent. Preliminary semipreparative HPLC separation provided enantioenriched fractions up to 63% ee

Hierarchical chiral expression from the nano- to meso-scale in synthetic supramolecular helical fibers of a non-amphiphilic C3-symmetrical ð-functional molecule

International audienceThe controlled preparation of chiral structures is a contemporary challenge for supramolecular science because of the interesting properties that can arise from the resulting materials, and here we show that a synthetic nonamphiphilic C3 compound containing π-functional tetrathiafulvalene units can form this kind of object. We describe the synthesis, characterization, and self-assembly properties in solution and in the solid state of the enantiopure materials. Circular dichroism (CD) measurements show optical activity resulting from the presence of twisted stacks of preferential helicity and also reveal the critical importance of fiber nucleation in their formation. Molecular mechanics (MM) and molecular dynamics (MD) simulations combined with CD theoretical calculations demonstrate that the (S) enantiomer provides the (M) helix, which is more stable than the (P) helix for this enantiomer. This relationship is for the first time established in this family of C3 symmetric compounds. In addition, we show that introduction of the “wrong” enantiomer in a stack decreases the helical reversal barrier in a nonlinear manner, which very probably accounts for the absence of a “majority rules” effect. Mesoscopic chiral fibers, which show inverted helicity, i.e. (P) for the (S) enantiomer and (M) for the (R) one, have been obtained upon reprecipitation from dioxane and analyzed by optical and electronic microscopy. The fibers obtained with the racemic mixture present, as a remarkable feature, opposite homochiral domains within the same fiber, separated by points of helical reversal. Their formation can be explained through an “oscillating” crystallization mechanism. Although C3 symmetric disk-shaped molecules containing a central benzene core substituted in the 1,3,5 positions with 3,3′-diamido-2,2′-bipyridine based wedges have shown peculiar self-assembly properties for amphiphilic derivatives, the present result shows the benefits of reducing the nonfunctional part of the molecule, in our case with short chiral isopentyl chains. The research reported herein represents an important step toward the preparation of functional mesostructures with controlled helical architectures

Isotopically enriched polymorphs of dysprosium single molecule magnets

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Lanthanide complexes involving multichelating TTF-based ligands

International audienceThe reaction between the 2-_TTF-fused-1H-benzimidazol-2-yl_ pyridine alkylated with either the di-( pyrazol-1-yl)-4-pyridyl (L-1) or dimethyl-2,2'-bipyridine (L-2) moiety and 1 equiv. of L-n(hfac)(3).2H(2)O (Ln(III) = Dy-III and Yb-III) leads to three dinuclear complexes of formula [Yb-2(hfac)(6)(L-1)].2(CH2Cl2).C6H14 (1) and [Ln(2)(hfac)(6)(L-2)].CH2Cl2 (Ln(III) = Yb-III (2) and Dy-III (3)). The X-ray structures highlight square antiprism (D-4d symmetry) and spherical tricapped trigonal prism (D-3h) for the eight-and nine-coordinated lanthanide ions, respectively. Irradiation of the lowest-energy HOMO -> LUMO ILCT absorption band induced a F-2(5/ 2) -> F-2(7/ 2) Yb-centered emission for 1 and 2. Both Yb-III ions displayed similar emissions in 2 while two distinct emissions, attributed to the two YbIII ions because of their different coordination environments, were observed in 1. Slow magnetic relaxation is detected by dynamic magnetic measurements for 3 with a measured relaxation time tau(0) = 3.7(1.3) x 10(-7) s and an energy barrier Delta = 39.6(2) cm(-1). Taking into account the environment of both DyIII ions in 3, it was expected that both metallic centers displayed similar dynamic magnetic behavior. The latter was rationalized by ab initio CASSCF/SI-SO calculations

Circularly polarized activity from two photon excitable europium and samarium chiral bioprobes

In this contribution, two couples of cationic enantiomeric complexes [(R,R)-[LnL]Cl and (S,S)-[LnL]Cl, with Ln = Sm and Eu and L = N,N′-bis(2-pyridylmethyl)-1,2-(R,R or S,S)-cyclohexanediamine functionalized at sp3 N with the picolinate antennae2] have been synthesized and spectroscopically characterized in polar protic solvents, such as water and methanol. The good sensitization of Sm(iii) and Eu(iii) luminescence by the picolinate antenna is documented, upon both a one photon absorption process (at about 330 nm) and a two photon absorption process (at 720 nm). The complexes exhibit good CPL activity, in particular for the magnetic dipole (MD) allowed transitions, which are the 4G5/2 → 6H5/2 (564 nm) of Sm(iii) and the 5D0 → 7F1 (593 nm) of Eu(iii). Both complexes are highly stable in aqueous solution (log K = 20.13 for the EuL species chosen as the representative) and only one main species is present at physiological pH (7.4). Among the three possible isomeric complexes, DFT calculations on the Y(iii) counterpart reveal the highest stability of the C1-symmetric cis-O, O-N, N isomer, in agreement with the presence of only one Eu(iii) emitting species in solution. Furthermore, one solvent molecule is bound to the metal ions, giving rise to 9-fold coordinated complexes. Preliminary biphotonic imaging experiments on the (S,S)-[EuL]Cl complex reveal that it can be easily internalized in two different cell lines (namely 293T cancer cells and THP-1 macrophages) with perinuclear diffuse localisation in the cytosol. Both Sm(iii) and Eu(iii) complexes can be considered promising candidates as NIR-to-RED in cellulo chiroptical bioprobes and a possible extension to the in vivo experiment will be further investigated

Chirality driven metallic versus semiconducting behavior in a complete series of radical cation salts based on dimethyl-ethylenedithio-tetrathiafulvalene (DM-EDT-TTF)

Enantiopure (S,S) and (R,R) dimethyl-ethylenedithio-tetrathiafulvalene (DM-EDT-TTF) 1donors are synthesized by cross coupling followed by decarboxylation reactions. In the solid state the methyl groups are arranged in axial positions within sofa-type conformation for the six-membered rings. Crystalline radical cation salts formulated as [(S,S)-1]2PF6, [(R,R)-1]2PF6, and [(rac)-1]2PF6 are obtained by electrocrystallization. When the experiment is conducted with enantioenriched mixtures both enantiopure and racemic phases are obtained. The monoclinic enantiopure salts, containing four independent donors in the unit cell, show semiconducting behavior supported by band structure calculations of extended Hückel type. The racemic salt contains only one independent donor in the mixed valence oxidation state +0.5. Under ambient pressure the racemic material is metallic down to 120 K, while an applied pressure of 11.5 kbar completely suppresses the metal–insulator transition. Band structure calculations yield an open Fermi surface, typical for a pseudo-one-dimensional metal, with unperfected nesting, thus ruling out the possibility of charge or spin density modulations to be at the origin of the transition. Raman spectroscopy measurements, in agreement with structural analysis at 100 K, show no indication of low-temperature charge ordering in the racemic material at ambient pressure, thus suggesting Mott-type charge localization for the observed metal–insulator transition