Induction of chirality in achiral monolayers has garnered considerable attention in the recent past not only due to its importance in chiral resolutions and enantioselective heterogeneous catalysis but also because of its relevance to the origin of homochirality in life. In this contribution, we demonstrate the emergence of macroscopic chirality in multicomponent supramolecular networks formed by achiral molecules at the interface of a chiral solvent and an achiral substrate. The solvent-mediated chiral induction provides a simple, efficient, and versatile approach for the fabrication of homochiral surfaces using achiral building blocks.
Self-assembly of an achiral porphyrin at the interface between a chiral solvent and an atomically flat substrate renders the monolayer chiral, and a non-racemic solvent can even overrule the intrinsic expression of chirality in the self-assembly of chiral molecules.
Esta es la versión de autor del artículo publicado en: This is an author produced version of a paper published in: Copyright: © 2016 WILEY-VCH VerlagEl acceso a la versión del editor puede requerir la suscripción del recurso Access to the published version may require subscription Self-assembly provides the guidelines to engineer twodimensional (2D) molecular networks on flat surfaces. Two-Dimensional Nanoporous Networks Formed by Liquid-to-[1] Those presenting void spaces, the so-called "2D porous networks", [2] are especially interesting since they offer the possibility of immobilizing, in a repetitive and ordered way, different functional guest units that are complementary in size and shape. Such networks can be produced from the deposition of persistent covalent macrocycles.[3] Pore size and shape is in this way predefined during synthesis, but this approach can be tedious and time-consuming if tunable systems that allow for small pore modifications are to be produced. A more appealing alternative is the generation of lattices with regular cavities from small monomers that, once on the surface, interact via weaker noncovalent bonds.[4] Upon physisorption, several degrees of translational, rotational and vibrational freedom are lost and, as a result, molecules that display very weak and ill-defined binding in solution can form well-ordered, yet dynamic assemblies held by multiple supramolecular interactions when confined in two dimensions. However, although much has been learned during the last years, this second approach has the limitation that the kind of network attained, which depends on a subtle interplay between molecule-molecule, molecule-solvent and moleculesubstrate interactions, cannot be always reliably predicted.An intermediate and ideal situation would be reached in the case of macrocycles that are assembled in solution from reversible noncovalent interactions, [5] but robust enough to survive as well-defined, monodisperse species after the transfer process from solution to a substrate. These are indeed highly challenging requirements for self-assembled macrocycles, since the self-assembling rules change drastically when molecules are concentrated on a surface. On one hand, intra-and intermolecular binding events are compensated and chelate cooperativity, the key factor promoting cycle formation in diluted solutions, is downgraded. On the other, the general tendency of physisorbed molecules is to maximize molecule-substrate interactions, so that networks with empty spaces are usually avoided if an alternative, more densely packed lattice can be accessed. All these issues ultimately result in a low-fidelity liquid-to-substrate transfer of supramolecular information. In other words, self-assembly in solution is typically not reproduced at the surface and vice versa.Herein, we present a bioinspired approach that makes use of DNA-base [1g] pairing to produce tunable macrocycles (Figure 1) in solution whose supramolecular identity is reliably transferred to highly oriented pyrolytic graphite (HOPG)...
Two-dimensional supramolecular chirality is often achieved by confining molecules against a solid surface. The sergeants–soldiers principle is a popular strategy to fabricate chiral surfaces using predominantly achiral molecules. In this method, achiral molecules (the soldiers) are forced to assemble in a chiral fashion by mixing them with a small percentage of structurally similar chiral molecules (the sergeants). The full complexity of the amplification processes in chiral induction studies is rarely revealed due to the specific experimental conditions used. Here we report the evolution of chirality in mixed supramolecular networks of chiral and achiral dehydrobenzo[12]annulene (DBA) derivatives using scanning tunneling microscopy (STM) at the solution/solid interface. The experiments were carried out in the high sergeants–soldiers mole ratio regime in relatively concentrated solutions. Variation in the sergeants/soldiers composition at a constant solution concentration revealed different mole ratio regimes where either amplification of supramolecular handedness as defined by the sergeant chirality or its reversal was observed. The chiral induction/reversal processes were found to be a convolution of different phenomena occurring at the solution-solid interface namely, structural polymorphism, competitive adsorption and adaptive host–guest recognition. Grasping the full complexity of chiral amplification processes as described here is a stepping-stone toward developing a predictive understanding of chiral amplification processes.
Chiral induction in self-assembled monolayers has garnered considerable attention in the recent past, not only due to its importance in chiral resolution and enantioselective heterogeneous catalysis but also because of its relevance to the origin of homochirality in life. Here, we demonstrate the emergence of homochirality in a supramolecular low-density network formed by achiral molecules at the interface of a chiral solvent and an atomically-flat achiral substrate. We focus on the impact of structure and functionality of the adsorbate and the chiral solvent on the chiral induction efficiency in self-assembled physisorbed monolayers, as revealed by scanning tunneling microscopy. Different induction mechanisms are proposed and evaluated, with the assistance of advanced molecular modeling simulations.
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