STM Investigations of the Two-Dimensional Ordering of Perylenetetracarboxylic Acid N-Alkyl-diimides on HOPG and MoS₂ Surfaces

Abstract

The 2D structures of a variety of n-alkyl-substituted perylene diimides adsorbed onto HOPG and MoS2 surfaces from phenyloctane solutions were studied using scanning tunneling microscopy (STM). Both rectangular, or herringbone-like, structures and row structures were observed. Surprisingly, the lattice constants, and thus the area per molecule of the rectangular structures, did not increase as expected when the alkyl chain length was increased. Protrusion of the alkyl tails into the solvent above the 2D layer is proposed to account for this behavior. Row structures, where the alkyl tails lie flat on the substrate surface, were also observed wherein the area per molecule increases as expected for the increase in the length of the alkyl tail. The formation of domains with a particular orientation with respect to the underlying lattice was observed for many of the 2D structures. The alignment of the molecular layers with the substrate could be explained with a point-on-line coincidence model. Formation and filling of missing molecule defects within the oriented domains was observed during continuous scanning of the STM.

Self-assembly of tetraalkoxydinaphthophenazines in monolayers on HOPG by scanning tunneling microscopy

“…6c). Such behavior of alkyl substituents in ordered monolayers has been previously suggested for alkyl derivatives of different organic molecules, for example: viologen [40] and perylene diimides [41].…”

Monolayer structure of a liquid crystalline perylene derivative on bare and on thiol-terminated Au(111) surfaces

“…However, the proposed PTCDI-C13 monolayer phases presented here are consistent with earlier reports detailing the role of alkyl chains in determining the arrangement of solution-grown alkyl-substituted PTCDI monolayers. 11 In Fig. 1͑b͒, the underlying gold 23ϫ ͱ 3 herring bone reconstruction pattern, 12,13 comprising parallel zigzag lines, is clearly observed.…”

Columnar Mesophases Based on Zinc Chlorophyll Derivatives Functionalized with Peripheral Dendron Wedges

“…The slightly smaller value obtained in STM could be attributed to the protrusion of the dendron alkyl chains in the supernatant solution instead of extending in full length flat on the HOPG surface. [34] Based on these comparisons of dimensions and considering the size of the aromatic and aliphatic segments of ZnChl 1 molecule, it appears reasonable to propose a model for the molecular arrangement within the column stratum similar to the nano-phase segregated cyclic arrangement revealed by STM, where the chlorin cores are arranged towards the column center and dendron side chains radiate towards the column periphery (Figure 8 A). The differences in the unit cells and lattice parameters by these two methods (i.e., XRD and STM) find its origin in the different interactions involved in the bulk solid state and on surface.…”

“…[34] The unit cell parameters obtained for the cyclic structures were a = b = (7.37 AE 0.08) nm and a = (60 AE 5)8, and the tentative hexagonal packing model is represented in Figure 7 C. The cyclic structures were mediated by the steric hindrance imposed by the dendron wedges and the slightly darker areas in the center of the cyclic structures probably correspond to holes.…”