The 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 C(3) 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 C(3) 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 C(3) 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.

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.

International audienceTwo C3 symmetric tris(TTF) derivatives, based on a central unit containing the rigid core 1,3,5-tricarbonyl-benzene substituted with three 3,3′-diamino-2,2′-bipyridines, have been synthesized by a convergent strategy. Single crystal X-ray analysis of the precursor 3′-[(ethylenedithio-tetrathiafulvalenyl)formylamino]-2,2′-bipyridine-3-amine shows a planar transoid conformation for the bipyridine unit, favored by intramolecular hydrogen bonding. The compound N,N′,N″-tris{3[3′-[bis(ethylthio)-tetrathiafulvalenyl]formylamino]-2,2′-bipyridyl}-benzene-1,3,5-tricarboxamide, having C3 symmetry, presents gelator properties in chlorinated solvents. The gel formed in ortho-dichlorobenzene provided—after evaporation of the solvent—a xerogel constituted by a complex network of thick and thinner fibers as demonstrated by TEM and AFM microscopies. The thick fibers were about 100 nm wide and between 1 and 5 µm long, and the thinner ones between 12 and 18 nm wide and 50 to 500 nm long. Iodine doping of the material induced the formation of a mixed valence system with charge transfer, as indicated by IR-NIR spectroscopic measurements. The doped material has a TTF:I3 ratio of 2.4:1 ten minutes after doping, but slowly loses iodine over days. The morphology of the gel did not change after the doping process, as revealed by SEM and AFM experiments. Current sensing AFM measurements showed that the thicker fibers are more conducting than the thinner ones, a likely consequence of the better ordering and/or more effective interfiber contacts in the former