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

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• 作者：Ion Danila ; Fran莽ois Riob茅 ; Flavia Piron ; Josep Puigmart铆-Luis ; John D. Wallis ; Mathieu Linares ; Hans 脜gren ; David Beljonne ; David B. Amabilino ; Narcis Avarvari
• 刊名：Journal of the American Chemical Society
• 出版年：2011
• 出版时间：June 1, 2011
• 年：2011
• 卷：133
• 期：21
• 页码：8344-8353
• 全文大小：1264K
• 年卷期：v.133,no.21(June 1, 2011)
• ISSN：1520-5126

文摘

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 C₃ compound containing 蟺-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 鈥渨rong鈥?enantiomer in a stack decreases the helical reversal barrier in a nonlinear manner, which very probably accounts for the absence of a 鈥渕ajority rules鈥?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 鈥渙scillating鈥?crystallization mechanism. Although C₃ symmetric disk-shaped molecules containing a central benzene core substituted in the 1,3,5 positions with 3,3鈥?diamido-2,2鈥?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.