Shape-Persistent Linear, Kinked, and Cyclic Oligo(phenylene-ethynylene-butadiynylene)s: Self-Assembled Monolayers

Abstract

Shape-persistent rigid phenylene-ethynylene-butadiynylenes form lamellar self-assembled monolayers (SAMs) at the HOPG/TCB interface, which were studied by scanning tunneling microscopy (STM) with submolecular resolution. Substitution of the terminating acetylene functions with polar cyanopropyldimethylsilyl groups leads to 2D phase separation and defined rod-rod interactions, which determine the packing distances between the rigid rods. The results stimulated the connection of rigid rods via septiarylene clamp units. They covalently link two rigid rod units and define the intramolecular rod-rod distance that matches the alkoxy substituent chain lengths. The systems can be described as half-ring structures of two rigid rods connected via a rotatable joint unit. These acetylene-terminated half-ring structures were also oligomerized under Cu and Pd catalysis to yield defined acyclic and cyclic oligomers. Detailed STM studies decoded the molecular origin of the surface patterning of such systems. The dodecyloxy side chains are adsorbed along the HOPG main axes and, together with the alkoxy backbone angle, determine the adsorption direction of the adlayers.

Mono- and multilayers of molecular spoked carbazole wheels on graphite

“…The degrees of freedom of each MSW 2 are reduced (as compared to 1 ), and the lower flexibility of the MSWs together with their large size and the resulting molecule–surface interaction decrease the ability to form a regular pattern, probably (also) due to a lower compound solubility. We observed a similar behavior for phenylene–ethynylene–butadiynylene macrocycles which we compared to their acyclic analoga of identical oligomerization degree [ 7 ].…”

“…They are non-collapsible monodisperse cyclooligomers with a fixed and predictable conformation, and their side-chain substitution guarantees their solubility in organic media. Our previous works on freely rotating chains of rigid rod segments and on shape-persistent macrocycles [ 6 – 7 ] have recently led us to a set of molecular polygons (macrocycles) of discrete sizes and symmetries, e.g., triangles, squares, pentagons, and hexagons [ 8 ]. These represent basic building blocks for a supramolecular Archimedean surface tessellation system [ 9 ].…”

Nanopatterns of molecular spoked wheels as giant homologues of benzene tricarboxylic acids

“…7 c ,8 Moreover, o - and m -phenylene units add rotational degrees of freedom to the otherwise linear segments, sometimes leading to polydispersity regarding conformers. 9 Such limits can be overcome in strutted architectures, and molecular spoked wheels (MSWs) are prominent examples thereof. 7 b ,10 The lateral fixation of (smaller) molecular rigid backbones on HOPG can be mediated by a variety of functional groups, such as carboxylic acids as, e.g.…”

STM study of oligo(phenylene-ethynylene)s

“…Oligo(phenylene ethynylene)s (OPEs) have been discussed as candidates for molecular wires since the early nineties [1][2][3][4][5][6]. While there has been tremendous progress in the synthesis of these molecular wires over the last decade, enabling complex U-shaped, kinked and cyclic geometries [7][8][9], the physical properties of these wires are not yet well understood calling for a more detailed study. Although similar molecules have been extensively studied in break junctions [10,11], scanning-probe studies of OPE molecules have so far been limited to the self-assembled monolayers (SAMs) of OPEs or OPEs inserted into SAMs of other molecules [12][13][14][15][16][17][18] while the adsorption of single, isolated OPE molecules has not been studied at all.…”