Light-regulated templated self-assembly of bilayered nanotoroids

Abstract

Controlled molecular self-assembly driven by noncovalent interactions provides access to ordered architectures beyond the molecular scale. Yet the precise construction of higher-order assemblies remains difficult because directionality of noncovalent interactions progressively decreases as structural hierarchy increases. Here we show that bilayered toroids can be generated by introducing trans-azobenzene units into a scissor-shaped diphenylnaphthalene dyad that otherwise forms toroidal assemblies. Rapid evaporation of a toluene solution of the azobenzene-appended dyad affords monolayered toroids, whereas slow evaporation yields bilayered toroids, indicating that the trans-azobenzene unit promotes formation of a second toroidal layer. Consistent with their distinct dimensions, both monolayered and bilayered toroids organize on a substrate into two-dimensional hexagonal arrays with distinct lattice parameters while the bilayered toroids further exhibit stacking along the z axis. In a less polar medium, this hierarchical stacking proceeds to give corrugated cylinders composed of approximately 10 bilayered toroids. The role of azobenzene units in forming the bilayered structure can be demonstrated by slow evaporation of a toluene solution of the photogenerated cis isomer, which affords only monolayered toroids, supporting the conclusion that the trans-azobenzene unit serves as a structural scaffold for bilayer formation.