Chiral Solvent-Induced Homochiral Hierarchical Molecular Assemblies at the Liquid/Solid Interface.

We herein investigate the formation of homochiral hierarchical self-assembled molecular networks (SAMNs) via chirality induction by the coadsorption of a chiral solvent at the liquid/graphite interface by means of scanning tunneling microscopy (STM). In a mixture of achiral solvents, 1-hexanoic acid, and 1,2,4-trichlorobenzene, an achiral dehydrobenzo[12]annulene (DBA) derivative with three alkoxy and three hydroxy groups in an alternating manner forms chiral hierarchical triangular cluster structures through dynamic self-sorting. Enantiomorphous domains appear in equal probability. On the other hand, in chiral 2-methyl-1-hexanoic acid as a solvent, this molecule produces (i) homochiral small triangular clusters at a low solute concentration, (ii) a chirality-biased hierarchical structure consisting of triangular cluster structures with different cluster sizes at a medium concentration, and (iii) a dense structure with no chirality bias at a high concentration. We attribute the concentration-dependent degree of the chirality transmission to the number of coadsorbed solvent molecules in the SAMNs and to the difference in nucleus structure and size in the initial stage of the SAMN formation.

Homochiral hierarchical molecular assemblies through dynamic combination of conformational states of a single chiral building block at the liquid/solid interface.

We herein report the construction of homochiral, hierarchical self-assembled molecular networks (SAMNs) at the liquid/graphite interface using a single molecular building block, a chiral dehydrobenzo[12]annulene (cDBA) derivative with three chiral alkoxy and three hydroxy groups positioned in an alternating manner on the DBA core. The cDBA molecules form homochiral hierarchical SAMNs consisting of triangular clusters of several sizes, the size of which can be tuned by solvent polarity and solute concentration, reaching periodicities as large as 9.3 nm. We demonstrate the successful transmission of chirality information from the single molecular level to the hierarchical SAMN level, in a process that is mediated by dynamic self-sorting.

Influence of core size on self-assembled molecular networks composed of C3h-symmetric building blocks through hydrogen bonding interactions: structural features and chirality.

The effect of the core size on the structure and chirality of self-assembled molecular networks was investigated using two aromatic carboxylic acid derivatives with frameworks displaying C3h symmetry, triphenylene derivative H3TTCA and dehydrobenzo[12]annulene (DBA) derivative DBACOOH, each having three carboxy groups per molecule. Scanning tunneling microscopy observations at the 1-heptanoic acid/graphite interface revealed H3TTCA exclusively forming a chiral honeycomb structure, and DBACOOH forming three structures (type I, II, and III structures) depending on its concentration and whether the system is subjected to annealing treatment. Hydrogen bonding interaction patterns and chirality were carefully analyzed based on a modeling study using molecular mechanics simulations. Moreover, DBACOOH forms chiral honeycomb structures through the co-adsorption of guest molecules. Structural diversity observed for DBACOOH is attributed to its relatively large core size, with this feature modulating the balance between molecule-molecule and molecule-substrate interactions.

Solvent Mediated Nanoscale Quasi-Periodic Chirality Reversal in Self-Assembled Molecular Networks Featuring Mirror Twin Boundaries.

Grain boundaries in polycrystals have a prominent impact on the properties of a material, therefore stimulating the research on grain boundary engineering. Structure determination of grain boundaries of molecule-based polycrystals with submolecular resolution remains elusive. Reducing the complexity to monolayers has the potential to simplify grain boundary engineering and may offer real-space imaging with submolecular resolution using scanning tunneling microscopy (STM). Herein, the authors report the observation of quasi-periodic nanoscale chirality switching in self-assembled molecular networks, in combination with twinning, as revealed by STM at the liquid/solid interface. The width of the chiral domain structure peaks at 12-19 nm. Adjacent domains having opposite chirality are connected continuously through interdigitated alkoxy chains forming a 1D defect-free domain border, reflecting a mirror twin boundary. Solvent co-adsorption and the inherent conformational adaptability of the alkoxy chains turn out to be crucial factors in shaping grain boundaries. Moreover, the epitaxial interaction with the substrate plays a role in the nanoscale chirality reversal as well.

Hierarchical two-dimensional molecular assembly through dynamic combination of conformational states at the liquid/solid interface.

Self-sorting of multiple building blocks for correctly positioning molecules through orthogonal recognition is a promising strategy for construction of a hierarchical self-assembled molecular network (SAMN) on a surface. Herein we report that a trigonal molecule, dehydrobenzo[12]annulene (DBA) derivative having three tetradecyloxy chains and three hydroxy groups in an alternating manner, forms hierarchical triangular clusters of different sizes ranging from 2.4 to 16.4 nm, consisting of 3 to 78 molecules, respectively, at the liquid/graphite interface. The key is the dynamic combination of three different conformational states, which is solvent and concentration dependent. The present knowledge extends design strategies for production of sophisticated hierarchical SAMNs using a single component at the liquid/solid interface.