Rational Design of the First Spherical Supramolecular Dendrimers Self-Organized in a Novel Thermotropic Cubic Liquid-Crystalline Phase and the Determination of Their Shape by X-ray Analysis

Abstract

The rational design, the synthesis via a new convergent approach, and the characterization of four generations of monodendrons based on the AB3 building block methyl 3,4,5-trishydroxybenzoate are described. The first generation monodendrons are crystalline. The second generation methyl 3,4,5-tris-3‘,4‘,5‘-[tris(n-dodecyloxy)benzyloxy]benzoate (12Gn-AG-CH 3 , n = 2), the corresponding benzyl alcohol (12G2-AG-CH 2 OH) and benzoic acid (12G2-AG), and all higher generation monodendrons with n = 3 and 4 exhibit in addition to the crystal phase an isomorphous cubic liquid-crystalline (LC) phase of Pm3̄n space group. The cubic unit cell parameters of 12G2-AG, 12G3-AG, and 12G4-AG are 68.3, 79.2, and 84.0 Å, respectively. Computed electron density profiles demonstrated that in the cubic phase 12, 6, and 2 monodendrons of generation 2, 3 and 4 are self-assembled in supramolecular dendrimers resembling spherical micelles when they are centered at the corners and the body-center and respectively highly rounded tetrahedra when they are at 1/4 and 3/4 distance along one of the bisectors of each face of the cubic cell. This novel thermotropic LC phase is similar to that of the lyotropic Pm3̄n phase of biological lipids. These supramolecular dendrimers contain a poly(benzyl ether) core dispersed in an aliphatic matrix of nearly uniform density which is made up of the melted terminal long alkyl chains of the monodendrons. The size of the supramolecular dendrimer and of the entire unit cell increases with generation number as a result of a disproportionately large increase in the number of AB3 repeat units relative to the number of terminal alkyl chains in a monodendron which decreases its average cone angle. The present experiments provide the first examples of monodendrons which self-assemble into spherical supramolecular dendrimers forming a thermotropic cubic LC phase.

Maximizing Entropy by Minimizing Area: Towards a New Principle of Self-Organization

“…However, these effects are subdominant when the dendrimers are packed very closely. In fact, it is known that the density is nearly constant in the volume occupied by the chains, 14 and we thus expect that our model should provide a robust description of the system. The thickness d of the coronal matrix depends on the density since the dodecyl bilayer must fill the space between the hard cores.…”

Towards engineering of self-assembled nanostructures using non-ionic dendritic amphiphiles

“…These observations, including the higher CAC and coexistence of two morphologies, indicate that amphiphile 2 is the most dynamic of all the G2 derivatives due to the lipophilic part's dissymmetry, which imparted a more cone-like shape for this molecule. Reports in the literature that the shape of a dendritic block influences supramolecular self-assembly [35][36][37] in the bulk phase clearly show that cone-like amphiphiles lead to a spherical supramolecular arrangement and that tapered amphiphiles arrange themselves in columns. In the case of amphiphile 2, a simple packing argument could explain our observations.…”

Functional liquid-crystalline polymers and supramolecular liquid crystals

“…They have extended the design of LC dendrimers to cone-shaped and semicircular dendrons, which exhibit micellar cubic and columnar phases, respectively. 112 The LC phases can be systematically modulated by changing the volume of dendritic moieties. 113,114 Attachment of rigid-rod mesogenic moieties on the terminal position of the dendrimers can produce LC dendritic molecules.…”