title: Photoresponsive dithienylethene-urea-based organogels with "reversed" behavior.
abstract: Dithienylperhydrocyclopentene-bisurea-based low molecular weight gelators are described that function as photoresponsive organogels that show a remarkable gel-to-liquid transition upon irradiation. The two series of derivatives, with and without alkyl spacers between the urea hydrogen bonding groups and the photochromic unit, show different gelation behavior. Upon UV irradiation of the gels, a gel liquified at only 1.4% conversion of the photochromic unit. Transmission electron microscopy (TEM) shows that the gel fibres consist of thin ribbons. Semi-empirical (PM3) calculations indicate that the hydrogen bonding between the open-ring isomer (o) molecules is weak, and that formation of the closed-ring isomer (c) destabilises the hydrogen bonding further. The results indicate that a small amount of the closed-ring isomer will disrupt the intermolecular hydrogen-bonding, leading to disintegration of the gel fibre ribbons and hence reversible liquification.
authors.affiliation: Department of Materials Chemistry, Faculty of Science and Technology, Ryukoku University, CREST-JST, Seta, Otsu, Shiga 520-2194, Japan.
authors.forename: Masako
authors.initials: M
authors.lastname: Akazawa
authors.forename: Kingo
authors.initials: K
authors.lastname: Uchida
authors.forename: Jaap J D
authors.initials: JJ
authors.lastname: de Jong
authors.forename: Jetsuda
authors.initials: J
authors.lastname: Areephong
authors.forename: Marc
authors.initials: M
authors.lastname: Stuart
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Caroli
authors.forename: Wesley R
authors.initials: WR
authors.lastname: Browne
authors.forename: Ben L
authors.initials: BL
authors.lastname: Feringa