title: 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 cross-sections (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-crystalline 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-bundle 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.
authors.affiliation: Department of Chemistry, Yonsei University Shinchon 134, Seoul 120-749, Korea. mslee@yonsei.ac.kr
authors.forename: Myongsoo
authors.initials: M
authors.lastname: Lee
authors.forename: Yang-Seung
authors.initials: YS
authors.lastname: Jeong
authors.forename: Byoung-Ki
authors.initials: BK
authors.lastname: Cho
authors.forename: Nam-Keun
authors.initials: NK
authors.lastname: Oh
authors.forename: Wang-Cheol
authors.initials: WC
authors.lastname: Zin