title: Stimulus-responsive azobenzene supramolecules: fibers, gels, and hollow spheres.
abstract: Novel, stimulus-responsive supramolecular structures in the form of fibers, gels, and spheres, derived from an azobenzene-containing benzenetricarboxamide derivative, are described. Self-assembly of tris(4-((E)-phenyldiazenyl)phenyl)benzene-1,3,5-tricarboxamide (Azo-1) in aqueous organic solvent systems results in solvent dependent generation of microfibers (aq DMSO), gels (aq DMF), and hollow spheres (aq THF). The results of a single crystal X-ray diffraction analysis of Azo-1 (crystallized from a mixture of DMSO and H2O) reveal that it possesses supramolecular columnar packing along the b axis. Data obtained from FTIR analysis and density functional theory (DFT) calculation suggest that multiple hydrogen bonding modes exist in the Azo-1 fibers. UV irradiation of the microfibers, formed in aq DMSO, causes complete melting while regeneration of new fibers occurs upon visible light irradiation. In addition to this photoinduced and reversible phase transition, the Azo-1 supramolecules display a reversible, fiber-to-sphere morphological transition upon exposure to pure DMSO or aq THF. The role played by amide hydrogen bonds in the morphological changes occurring in Azo-1 is demonstrated by the behavior of the analogous, ester-containing tris(4-((E)-phenyldiazenyl)phenyl)benzene-1,3,5-tricarboxylate (Azo-2) and by the hydrogen abstraction in the presence of fluoride anions.
authors.affiliation: Department of Chemical Engineering, Hanyang University, Seoul 133-791, Korea.
authors.forename: Sumi
authors.initials: S
authors.lastname: Lee
authors.forename: Seungwhan
authors.initials: S
authors.lastname: Oh
authors.forename: Joosub
authors.initials: J
authors.lastname: Lee
authors.forename: Yashwardhan
authors.initials: Y
authors.lastname: Malpani
authors.forename: Young-Sik
authors.initials: YS
authors.lastname: Jung
authors.forename: Baotao
authors.initials: B
authors.lastname: Kang
authors.forename: Jin Yong
authors.initials: JY
authors.lastname: Lee
authors.forename: Kazunari
authors.initials: K
authors.lastname: Ozasa
authors.forename: Takashi
authors.initials: T
authors.lastname: Isoshima
authors.forename: Sang Yun
authors.initials: SY
authors.lastname: Lee
authors.forename: Masahiko
authors.initials: M
authors.lastname: Hara
authors.forename: Daisuke
authors.initials: D
authors.lastname: Hashizume
authors.forename: Jong-Man
authors.initials: JM
authors.lastname: Kim
mesh_terms: D001391:Azo Compounds / Q000737:chemistry*; D001549:Benzamides / Q000737:chemistry*; D018360:Crystallography, X-Ray; D005782:Gels / Q000737:chemistry; D046911:Macromolecular Substances / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D010316:Particle Size; D016062:Porosity; D013499:Surface Properties
chemical_list: D001391:Azo Compounds; D001549:Benzamides; D005782:Gels; D046911:Macromolecular Substances; C558700:benzene-1,3,5-tricarboxamide; C009850:azobenzene