A research group has developed a new method for selectively synthesizing three-dimensional macrocycles,⁽¹⁾ in which four panels are arranged in a square, by connecting planar π-conjugated molecules⁽²⁾ at right angles.

This method is applicable to a wide variety of π-conjugated molecules and allows the size of the internal cavity to be designed. Furthermore, the resulting square macrocycles exhibit acid responsiveness, reversibly changing color under the action of a mild acid, while acid-mediated hydrolysis enables the starting monomers to be recovered in high yield—realizing a sustainable molecular synthesis that reverts to and regenerates the starting materials. The originality of this work lies in having a single imine bond play three roles: creating the shape, responding to stimuli and reverting back.

These research results were published in the Journal of the American Chemical Society on Monday, June 1, 2026. The team includes Associate Professor Yasutomo Segawa and Assistant Professor Takashi Harimoto at the Institute for Molecular Science (National Institutes of Natural Sciences) and the Graduate University for Advanced Studies (SOKENDAI).