2D Networks of Rhombic-Shaped Fused Dehydrobenzo[12]annulenes: Structural Variations under Concentration Control

Abstract

A series of alkyl- and alkoxy-substituted rhombic-shaped bisDBA derivatives 1a-d, 2a, and 2b were synthesized for the purpose of the formation of porous networks at the 1,2,4-trichlorobenzene (TCB)/graphite interface. Depending on the alkyl-chain length and the solute concentration, bisDBAs exhibit five network structures, three porous structures (porous A, B, and C), and two nonporous structures (nonporous D and E), which are attributed to their rhombic core shape and the position of the substituents. BisDBAs 1a and 1b with the shorter alkyl chains favorably form a porous structure, whereas bisDBAs 1c and 1d with the longer alkyl chains are prone to form nonporous structures. However, upon dilution, nonporous structures are typically transformed into porous ones, a trend that can be understood by the effect of surface coverage, molecular density, and intermolecular interactions on the system's enthalpy. Furthermore, porous structures are stabilized by the coadsorption of solvent molecules. The most intriguing porous structure, the Kagome pattern, was formed for all compounds at least to some extent, and the size of its triangular and hexagonal pores could be tuned by the alkyl-chain length. The present study proves that the concentration control is a powerful and general tool for the construction of porous networks at the liquid-solid interface.

Principles of molecular assemblies leading to molecular nanostructures

“…The concentration-in-control principle has since been confirmed by various other studies [31][32][33][34][35]. The concentration effects, however, are not limited to high-symmetry molecules.…”

“…Careful control over concentration can aid in selecting a specific structure, especially when two or more polymorphs are possible that differ in packing density or adsorption energy [30][31][32][33][34][35]. One of the first examples of concentration-dependent self-assembly was discovered in the case of alkoxylated DBA derivatives [30].…”

Two-dimensional molecular sieves: structure design by computer simulations

“…For example, it has been observed that chemically different tripod organic molecules are able to form isomorphic chiral porous networks with hexagonal cavities (Mu et al 2008;Liu et al 2010;Tahara et al 2009). A similar situation refers to cross-shaped molecules such as derivatized phthalocyanines, for which square pores were observed (Miyake et al 2008).…”

“…There have been reported numerous experimental results on the spontaneous formation of nanoporous molecular overlayers comprising different organic molecules able to form directional hydrogen bonds and metal-organic coordination bonds (Kudernac et al 2009;Stepanow et al 2008). Moreover, it has been shown that those superstructures can be sustained via van der Waals interactions, for example by interdigitation of long alkyl chains of star shaped building blocks such as alkyl-substituted phthalocyanines (Miyake et al 2008), dehydrobenzoannulenes (DBAs) (Tahara et al 2009) and stilbenoid compounds (Schull et al 2006). For those systems, a suitable choice of the building block results in the formation of networks with regular pores of different size and shape (Kudernac et al 2009), e.g.…”

“…For those systems, a suitable choice of the building block results in the formation of networks with regular pores of different size and shape (Kudernac et al 2009), e.g. square (Kühne et al 2009), rhombic (Ahn et al 2009), hexagonal (Tahara et al 2009) and so on (Gutzler et al 2009), as ob-served in scanning tunneling microscopy (STM) imaging. The distinct advantage of the porous networks is the regular spatial arrangement of nanometer-sized cavities with uniform well-defined shape.…”