Synthesis and Structural Analysis of Two Constitutional Isomeric Libraries of AB2-Based Monodendrons and Supramolecular Dendrimers

Abstract

The synthesis and structural analysis of two constitutional isomeric libraries of self-assembling AB2 monodendrons based on 3,4- and 3,5-disubstituted benzyl ether internal repeat units containing four different first generation monodendrons, i.e., 3,4,5-tris(n-dodecan-1-yloxy)benzyl ether, 3,4-bis(n-dodecan-1-yloxy)benzyl ether, 3,4,5-tris[p-(n-dodecan-1-yloxy)benzyloxy]benzyl ether, and 3,4-bis[p-(n-dodecan-1-yloxy)benzyloxy]benzyl ether, on their periphery are described. Regardless of the repeat unit on their periphery, the first three or four generations of the 3,4-disubstituted series of monodendrons self-assemble into spherical supramolecular dendrimers that self-organize into a Pm3̄n 3-D cubic lattice while the same generations of the 3,5-disubstituted series of monodendrons self-assemble into cylindrical supramolecular dendrimers that self-organize into a p6mm hexagonal columnar 2-D lattice. The internal repeat unit of the monodendrons determines the shape of the supramolecular dendrimers. However, for a particular internal repeat unit, the architecture from its periphery determines the size of the monodendron, the number of monodendrons that self-assemble into a supramolecular dendrimer, the solid angle of the monodendron, and the dependence of the size of the supramolecular dendrimer on generation number. Since ultimately all monodendrons must reach the shape of a single sphere, the diameter of cylindrical and spherical supramolecular dendrimers constructed from these building blocks is limited to less than 100 Å. The library of 3,5-disubstituted monodendrons also provided the first five examples of supramolecular dendrimers that undergo reversible shape changes induced by temperature and functionality at their focal point. In addition, a spherical supramolecular dendrimer based on a 3,5-disubstituted repeat unit that self-assembles in an Im3̄m 3-D cubic lattice was discovered in the same library. The structural information generated by these two AB2 and the previously reported AB3 libraries of quasi-equivalent monodendrons provides building blocks that enable the construction of externally regulated functional supramolecular, macromolecular, and single-molecule-based nanosystems self-organizable in predictable lattices.