Gelation Ability of Novel Oxamide‐Based Derivatives Bearing a Stilbene as a Photo‐Responsive Unit

Abstract

Abstract Oxamide‐based derivatives containing one or two oxamide moieties coupled to the 4‐ or 4,4′‐positions of cis ‐ and trans ‐stilbene have been synthesised. In order to modulate the solvent gelation tendencies, a series of derivatives with modified terminal functions were prepared from them. The trans ‐stilbene 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 1 H NMR spectroscopic measurements support the view that hydrogen bonding between the oxamide fragments plays an important role in gel formation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)