A new family of coumarin derivatives containing amide group with different alkyl chain lengths was synthesized and their properties as organogelators were evaluated. It was found that the organogelation abilities were not obviously affected by the alkyl spacer length of amide group. Helical morphologies formed either in nonpolar or high polar solvents by most of the gelators. Occurrence of reversible and stereoselective photodimerization of the gel formed by 4-(7'-coumarinoxy)-N-octadecylbutanamide (3a) in cyclohexane was confirmed by H-1 NMR, UV absorption, and fluorescence spectra. The photoreaction of the gel proceeded without any dissolution, but the drastic microscopic changes of gel morphologies accompanied with the irradiation were identified using SEM and AFM investigations. (c) 2005 Elsevier Ltd. All rights reserved.
Photochemical reactions in constrained systems: changes in mode of solubilization due to long-chain hydrophobic groups