Channel Structures from Self-Assembled Hexameric Macrocycles in Laterally Grafted Bent Rod Molecules

Abstract

Internally grafted bent rod molecules consisting of a bent-shaped nona-p-phenylene and different lengths of oligoether chains at the bay position were synthesized and characterized. All of the bent-shaped molecules showed ordered bulk-state structures as characterized by differential scanning calorimetry, X-ray scatterings, and transmission electron microscopy. The bent rod based on a short oligo(propylene oxide) chain self-assembles into a 2-D channel-like columnar structure, whereas the molecules with an intermediate length of flexible chains self-assemble into discrete channels that self-organize into honeycomb layers. A further increase in the length of the flexible chain induces a layered structure. In contrast to the bent-shaped molecules based on a linear chain, the molecules based on a branched chain self-assemble into an inverted 2-D columnar structure with an aromatic core surrounded by branched chains. We proposed the model of the channel structure on the basis of experimental data obtained from X-ray results and density measurements. Within the channels, six bent rods self-assemble into hexameric macrocycles that stack on one another to form channel-like columns where the interiors are filled by the flexible oligoether chains. Remarkably, the elongated channels break up into discrete channels of a well-defined length with increasing length of the oligoether chain. The resulting discrete channels self-organize into a hexagonally ordered honeycomb layer. The defined length of a channel is believed to be responsible for the formation of unique honeycomb layers.