Dense or Porous Packing? Two‐Dimensional Self‐Assembly of Star‐Shaped Mono‐, Bi‐, and Terpyridine Derivatives

Abstract

The self-assembly behavior of five star-shaped pyridyl-functionalized 1,3,5-triethynylbenzenes was studied at the interface between an organic solvent and the basal plane of graphite by scanning tunneling microscopy. The mono- and bipyridine derivatives self-assemble in closely packed 2D crystals, whereas the derivative with the more bulky terpyridines crystallizes with porous packing. DFT calculations of a monopyridine derivative on graphene, support the proposed molecular model. The calculations also reveal the formation of hydrogen bonds between the nitrogen atoms and a hydrogen atom of the neighboring central unit, as a small nonzero tunneling current was calculated within this region. The title compounds provide a versatile model system to investigate the role of multivalent steric interactions and hydrogen bonding in molecular monolayers.

On-Surface Synthesis of Self-Assembled Monolayers of Benzothiazole Derivatives Studied by STM and XPS

“…The result is different from the dimer feature reported in the previous study, which might result from the solvent effect on the assembly structures . Actually, this close-packed arrangement is a typical assembly structure of star-shaped molecules, and no specific intermolecular interactions are required for this. − The average size of the triangles is measured to be 1.1 ± 0.1 nm, which is in agreement with the theoretical size of the TFB molecule. The parameters of the unit cell overlaid on the STM image of the TFB assembly were measured as follows: a = 1.5 ± 0.1 nm, b = 1.5 ± 0.1 nm, and α = 60 ± 1°.…”

“…Because of the steric effect, there is no specific strong interaction between assembled molecules. 51 Therefore, the instability induced by the lack of intermolecular interaction makes it easier to be disturbed by the STM tip when scanning, which may be the reason that the shapes of some molecules appear to be irregular in the STM image. It should be pointed out that despite the absence of intermolecular interaction the structure hardly changed with time, which could be attributed to the bonding between TFB-BT and the substrate that could keep the molecules from diffusing around to some extent.…”

“…To reduce steric hindrance, the assembled molecules are rearranged with a larger unit cell after the reaction, as illustrated by the molecular model overlaid on the STM image. Because of the steric effect, there is no specific strong interaction between assembled molecules . Therefore, the instability induced by the lack of intermolecular interaction makes it easier to be disturbed by the STM tip when scanning, which may be the reason that the shapes of some molecules appear to be irregular in the STM image.…”

Modeling of the 2D self-assembly of tripod-shaped functional molecules with patchy interaction centers

“…To answer this question, test experiments are usually required in which different probe molecular units are synthesized, and their self-assembly is monitored with such imaging techniques as the scanning tunneling microscopy (STM) (De Feyter and De Schryver 2005). To date, numerous examples of ordered adsorbed structures ranging from simple densely packed motifs (Trawny et al 2015), nanoporous networks (Kudernac et al 2009;Tahara et al 2011;Bischoff et al 2016) to openwork fractal aggregates (Shang et al 2015;Zhang et al 2015) have been realized using functional organic building blocks. In these instances, often linear (Kühne et al 2009a, b), bent-rod (Fan et al 2014(Fan et al , 2016Shang et al 2015;Zhang et al 2015) and star shaped (Kudernac et al 2009;Dienstmaier et al 2010;Shi et al 2011;Tahara et al 2011;Ciesielski et al 2013;Bischoff et al 2016) polyphenyl molecules with suitably attached functional groups, including nitrile (Kühne et al 2009a, b;Shang et al 2015), pyridyl (Shi et al 2011;Ciesielski et al 2013), carboxylic (Dienstmaier et al 2010), aldehyde (Zhang et al 2015) and others (Shang et al 2015) have been used.…”

Engineering porous and compact two-dimensional nanoarchitectures on surfaces taking advantage of bisterpyridine-derivatives self-assembly

“…[24][25][26][27][28][29][30][31][32][33] Pyridine units are a specially interesting substituent to drive molecular selfassembly. 34,35 This group allows the formation of double hydrogen-bonds (C-H/N) between neighboring molecules. Numerous pyridine-based molecular building blocks have been synthesized 36,37 and various nanoarchitectures have been engineered using these compounds.…”