Li, Y.; Zhang, W.-B.;* Hsieh, I-F.; Zhang, G.; Cao, Y.; Li, X.; Wesdemiotis, C.; Lotz, B.; Xiong, H.;* Cheng, S. Z. D.* Breaking Symmetry towards Non-Spherical Janus Particles Based on Polyhedral Oligomeric Silsesquioxanes: Molecular Design, “Click” Synthesis, and Hierarchical Structure. J. Am. Chem. Soc. 2011, 133, 10712-10715. [Link] [PDF]

Abstract
The design, synthesis, and self-assembly of a series of precisely defined, nonspherical, polyhedral oligomeric silsesquioxane (POSS)-based molecular Janus particles are reported. The synthesis aims to fulfill the “click” philosophy by using thiol–ene chemistry to efficiently install versatile functionalities on one of the POSS cages. In such a way, both the geometrical and chemical symmetries were broken to create the Janus feature. These particles self-organize into hierarchically ordered supramolecular structures in the bulk. For example, the Janus particle with isobutyl groups on one POSS and carboxylic groups on the other self-assembles into a bilayered structure with head-to-head, tail-to-tail arrangements of each particle, which further organize into a three-dimensional orthorhombic lattice. While the ordered structure in the layers was lost upon heating via a first-order transition, the bilayered structure persisted throughout. This study provides a model system of well-defined molecular Janus particles for the general understanding of their self-assembly and hierarchical structure formation in the condensed state.