Panoscopic Structures by Hierarchical Cascade Self-Assembly of Inorganic Surfactants with Magnetic Heads Containing Dysprosium Ions†

The control over structural organization on different length scales is an important prerequisite to interface nanosystems to the macroscale. Depending on the number of structural levels involved and their interconnection, one might describe such materials as hierarchical or even panoscopic (see Figure 1). The formation of mesoscopic, higher-ordered structures requires special tools for positioning and assembling nanosized building blocks. The dimensions of mesoscopic tools are obviously distinct from atomic dimensions or the macroscopic world. One very powerful approach involves the self-organization of materials. While magnetic interactions have already been exploited for the self-organization of nanoparticles, there are only few reports about magnetic forces that guide the formation of supramolecular nanostructures. Molecular self-organization is very well documented for surfactants, which are broadly used on a multiton scale as detergents, in cosmetics, as emulsification agents, and as phase-transfer catalysts. Furthermore, the development of nanoscience would not have been possible without surfactants because of their capability to stabilize phases with high surface-to-volume ratio. Their special molecular architecture with the two joined parts of very different solvent compatibility is responsible for their concentration-dependent self-organization behavior, including micellization or the formation of mesophases at low concentration, and the formation of lyotropic liquid crystal (LLC) at higher concentration. More than 99% of surfactants applied in a technological context are organic in nature, with head groups such as ammonium (cationic), oligo(ethylene glycol) (neutral), or carboxylic acid (anionic). Therefore, it is highly desirable to equip surfactants with an enhanced set of properties, which is characteristic for transition-metal ions (e.g., different redox states, magnetic momentum, catalytic activity, etc.). In particular, surfactants with magnetic heads appear to be interesting targets, because the additional, magnetic interaction could guide the formation of unique supramolecular structures. Such inorganic surfactants can be assigned to the larger class of so-called metallomesogens, which can be devided into two classes. Class 1 includes the coordination of a charged