Dienone-ether macrocycles may be reversibly switched from the thermodynamically stable E,E,E,E-isomers, with an open central cavity, to globular, cavity-closed E,E,Z,Z-isomers by the action of sunlight. They are restored to their open forms by gentle heating, but more intense heating may result in an intramolecular reaction, closing the cavity in a less easily reversed fashion.