Hierarchical Chiral Expression from the Nano- to Mesoscale in Synthetic Supramolecular Helical Fibers of a Nonamphiphilic C₃-Symmetrical π-Functional Molecule

Abstract

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.

Helical Self-Assembly and Photopolymerization Properties of Achiral Amphiphilic Platinum(II) Diacetylene Complexes of Tridentate 2,6-Bis(1-alkylpyrazol-3-yl)pyridines

“…On the basis of the emission results at room temperature and at 77 K as well as the related studies on the emission of red PDA, 43 the new emission band of the complex after UV irradiation is believed to originate from red PDA with the typical vibronic-like split band pattern of the emission separated by about 1258 cm −1 , resulting from the 1B u and 2A g states. 48 On the contrary, an emission origin of an admixture of the [dπ(Pt) → π*(2,6-bis(1-alkylpyrazol-3-yl)pyridine)] 3 MLCT and [π(CC) → π*(2,6-bis(1-alkylpyrazol-3-yl)pyridine)] 3 LLCT excited states was assigned at 77 K before UV irradiation. After polymerization, emission bands typical of red PDA and the [dπ(Pt) → π*(2,6-bis(1-alkylpyrazol-3-yl)pyridine)] 3 MLCT/[π(CC) → π*(2,6-bis(1-alkylpyrazol-3-yl)pyridine)] 3 LLCT excited states become apparent.…”

“…Research Article that an energetically accessible or lower lying nonemissive 3 LLCT excited state, due to a relatively higher lying pπ(C CR) orbital brought about by the ester/amide substituent, would quench the 3 MLCT excited state.…”

Role of Achiral Nucleobases in Multicomponent Chiral Self‐Assembly: Purine‐Triggered Helix and Chirality Transfer

“…Left-handed helices appear in the co-hydrogel of Fmoc-l-Glu and A( Figure 1a). [7] Pyrimidine nucleobases Cor Tc annot trigger Fmoc-Glu to build any chiral structures.I n the case of T, short but wide ribbons with width of about 300 nm form ( Figure S3c,c'), which are significantly larger than that of Fmoc-Glu/A (G). By contrast, right-handed helices were found when Fmoc-d-Glu is used.…”

Enantiopure Radical Cation Salt Based on Tetramethyl-Bis(ethylenedithio)-Tetrathiafulvalene and Hexanuclear Rhenium Cluster

“…Nevertheless, differences in conducting properties between the enantiopure and racemic counterparts were also observed as a consequence of the structural disorder in TTF-oxazoline [11,12] based conductors [13,14], or the different packings in DM-EDT-TTF salts [15]. Other interests of chiral TTFs are related to the modulation of the chiroptical properties [16,17] or the preparation of electroactive helical fibers [18][19][20][21]. Regarding the enantiopure TM-BEDT-TTF donor 1 an important issue is the conformation adopted by the methyl substituents of the dithiin rings, as this strongly influences the packing and intermolecular contacts between the donors, and, consequently, the transport properties.…”