Self-Assembly of Molecular Dumbbells into Organized Bundles with Tunable Size

Abstract

Dumbbell-shaped molecules consisting of three biphenyls connected through vinyl linkages as a conjugated rod segment and aliphatic polyether dendritic wedges with different crosssections (i.e., dibranch (1), tetrabranch (2) and hexabranch (3)) were synthesized and characterized. The molecular dumbbells self-assemble into discrete bundles that organize into three-dimensional superlattices. Molecule 1, based on a dibranched dendritic wedge, organizes into primitive monoclinic-crystal-line and body-centered, tetragonal liquid crystalline structures, while molecules 2 and 3, based on tetra-and hexabranched dendritic wedges, respectively, form only body-centered, tetragonal liquid crystalline structures. X-ray diffraction experiments and density measurements showed that the rod-bun-dle cross-sectional area decreases with increasing cross-section of the dendritic wedges. The influences of supramolecular structure on the bulk-state optical properties were investigated by measuring the UV/Vis absorption and steady state fluorescence spectroscopies. As the cross-section of the dendritic wedge of the molecule increases, the absorption and emission maxima shift to higher energy. This can be attributed to a quantum size effect of the three-dimensionally confined nanostructure.

Cubic and Other3DThermotropic Liquid Crystal Phases and Quasicrystals

“…We have seen how studies of 3D thermotropic phases led to the opening of an entirely new field of soft and nanoscale (14) [47], (c) [65], (d) (27) [18], (e) (16) [10], and (f) [13].…”

“…Lee et al [14] synthesized three dumbbell-shaped compounds having a rodlike conjugated core consisting of three biphenyls connected via vinylene groups. An aliphatic ether dendron group was attached at each end.…”

“…Starting in the 1970s, but mainly in the 1980s and 1990s, researchers such as Levelut, Impéror-Clerc [8], and Diele [9] contributed much to our understanding of thermotropic cubic phases. In the late 1990s, the so-called micellar cubics [10][11][12] were discovered and had their structures solved, and in the 2000s, the noncubic [13,14] 3D phases, which had no precedents in the lyotropics, were found.…”

Supramolecular honeycomb and columnar assemblies formed by self-assembly of coil-rod-coil molecules with a conjugated rod segment

“…[9][10][11][12][13][14] It has been reported that ordered nanostructures can be precisely controlled by rod-coil block systems which self-assemble into lamellar, cylindrical, and discrete nanostructures depending on the relative volume fraction of the rod or coil segment. [15][16][17][18][19] Molecules based on a conjugated rod building block, which have unique optical and electronic properties, are of great interest due to the physical properties of these molecules or polymers and are dramatically influenced by the creation of their wellordered diverse supramolecular nano-structures. 4,8,20 Lee and coworkers have reported synthesis and electro-optical studies of self-organizing coil-rod-coil triblock molecules consisting of three biphenyls connected through vinylene linkages as a conjugated rod segment and poly(propylene oxide) (PPO) as the coil segment (molecules 9 and 10 see Scheme I).…”

Self-assembling structures and thin-film microscopic morphologies of amphiphilic rod–coil block oligomers

“…When the π -conjugated rods are incorporated into the rod-coil block molecules, their photophysical properties are associated, to a large extent, with their self-assembling nanostructure and microscopic morphology on solid supports [8][9][10][11][12]. It has been confirmed that the self-assembling structure and microscopic morphology of rod-coil block molecules on solid supports are not only related to the molecular composition and the block ratio, which determine the nanostructure of rod-coil molecules in solution and bulk state [13][14][15], but also related to the preparation condition of thin films [16][17][18]. However, a comprehensive understanding of the self-assembling behaviors of rod-coil block molecules on solid supports, such as their morphologies, structures, and molecular alignments, is still lacking.…”