title: Phototriggered self-assembly of hydrogen-bonded rosette.
abstract: Azobenzene-appended melamine M2 and barbiturate B2, both possessing bulky tridodecyloxyphenyl (TDP) wedge(s), were designed and synthesized to establish a photoresponsive hydrogen-bonded supramolecular assembly. The geometrical isomer EE-M2 bearing two E-azobenzene moieties easily complexed with B2, affording a remarkably stable cyclic hexamer EE-M2(3).B2(3) (rosette) in chloroform, toluene, and methylcyclohexane, as confirmed by size exclusion chromatography, dynamic light scattering, (1)H NMR, and UV-vis studies. The E --> Z photoisomerization of the azobenzene moieties upon irradiation with UV light was significantly suppressed in the rosette because of the steric crowding of the TDP wedges (total of nine TDP wedges in a rosette), whereas irradiation of the monomeric EE-M2 resulted in facile transformation into ZZ-M2 bearing two Z-azobenzene moieties. (1)H NMR studies of the complexation of the initially photogenerated ZZ-M2 with B2 revealed that it is hard for ZZ-M2 to form a rosette with B2 because of the intermolecular steric interaction between the TDP wedges. The photoregulatable complexation efficiency of M2 allowed us to accomplish the phototriggered formation of the rosette by irradiation of a monomeric mixture of ZZ-M2 and B2 using visible light.
authors.affiliation: Contribution from the Department of Materials Technology, Faculty of Engineering, and Department of Physics, Faculty of Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan.
authors.forename: Shiki
authors.initials: S
authors.lastname: Yagai
authors.forename: Toshiharu
authors.initials: T
authors.lastname: Nakajima
authors.forename: Takashi
authors.initials: T
authors.lastname: Karatsu
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Saitow
authors.forename: Akihide
authors.initials: A
authors.lastname: Kitamura