Stereospecific Epitaxial Growth of Bilayered Porous Molecular Networks.

Stereocontrolled multilayer growth of supramolecular porous networks at the interface between graphite and a solution was investigated. For this study, we designed a chiral dehydrobenzo[12]annulene (DBA) building block bearing alkoxy chains substituted at the 2 position with hydroxy groups, which enable van der Waals stabilization in a layer and potential hydrogen-bonding interactions between the layers. Bias voltage-dependent scanning tunneling microscopy (STM) experiments revealed the diastereospecificity of the bilayer with respect to both the intrinsic chirality of the building blocks and the supramolecular chirality of the self-assembled networks. Top and bottom layers within the same crystalline domain were composed of the same enantiomers but displayed opposite supramolecular chiralities.

Transfer of chiral information from a chiral solvent to a two-dimensional network.

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.

Two-Dimensional Nanoporous Networks Formed by Liquid-to-Solid Transfer of Hydrogen-Bonded Macrocycles Built from DNA Bases.

We present an approach that makes use of DNA base pairing to produce hydrogen-bonded macrocycles whose supramolecular structure can be transferred from solution to a solid substrate. A hierarchical assembly process ultimately leads to two-dimensional nanostructured porous networks that are able to host size-complementary guests.

Complex Chiral Induction Processes at the Solution/Solid Interface.

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.

On the stability of surface-confined nanoporous molecular networks.

Self-assembly of molecular building blocks into two-dimensional nanoporous networks has been a topic of broad interest for many years. However, various factors govern the specific outcome of the self-assembly process, and understanding and controlling these are key to successful creation. In this work, the self-assembly of two alkylated dehydrobenzo[12]annulene building blocks was compared at the liquid-solid interface. It turned out that only a small chemical modification within the building blocks resulted in enhanced domain sizes and stability of the porous packing relative to the dense linear packing. Applying a thermodynamic model for phase transition revealed some key aspects for network formation.

'Sergeants-and-Corporals' principle in chiral induction at an interface.

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.

Solvent-induced homochirality in surface-confined low-density nanoporous molecular networks.

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.