Photoresponsive dithienylethene-urea-based organogels with "reversed" behavior.
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.
Akazawa
Masako
M
Department of Materials Chemistry, Faculty of Science and Technology, Ryukoku University, CREST-JST, Seta, Otsu, Shiga 520-2194, Japan.
Uchida
Kingo
K
de Jong
Jaap J D
JJ
Areephong
Jetsuda
J
Stuart
Marc
M
Caroli
Giuseppe
G
Browne
Wesley R
WR
Feringa
Ben L
BL