Gelation ability of novel oxamide-based derivatives bearing a stilbene as a photo-responsive unit

Oxamide-based derivatives containing one or two oxamide moieties coupled to the 4- or 4,4'-positions of cis- and transstilbene have been synthesised. In order to modulate the solvent gelation tendencies, a series of derivatives with modified terminal functions were prepared from them. The transstilbene dioxamide-based derivatives were found to be sparingly soluble or insoluble in water and in organic solvents, whereas the trans-stilbene monooxamide-based derivatives are soluble in most organic solvents. Incorporation of a C-12 alkyl chain in the structure of the latter compounds results in a decreased solubility but in an increased gelation tendency of the substances. The ethyl ester oxamide-based derivative trans-3a and the amino acid oxamide-based derivative trans-3e act as efficient gelators of various organic solvents. In contrast, cis-3a shows a poor gelation ability or none at all, owing to its good solubility. Considering the difference in gelation abilities of the compounds trans-3a and cis-3a and the photo-responsive conformational changes of the stilbene part of the molecule, a controlled gelation by light was achieved. FT-IR and H-1 NMR spectroscopic measurements support the view that hydrogen bonding between the oxamide fragments plays an important role in gel formation. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)