Achiral Molecules Form Chiral Fluids

"Bent core" achiral organic molecules have the uncanny ability to organize themselves into liquid-crystalline fluids that are polar and chiral, according to Noel A. Clark of the University of Colorado, Boulder, and coworkers (Science 2009, 325, 452 and 456). In one paper, the researchers describe how the banana-shaped molecules (one type shown above) pack themselves into "dark conglomerate" layered phases that spontaneously organize into chiral domains. But the bent core of the molecules makes the layers susceptible to "saddle-splay deformation," a structural feature that is incompatible with long-range order. As a result, the fluid is optically active despite being isotropic on the macroscopic scale. In a second paper, the team shows that saddle-splay deformation makes related bent-core molecules form twisted layers that organize into helical nanofilaments. The twisting helps strike a balance between the polarity, chirality, and layering, the researchers note. "The implications of these supramolecular effects observed in fluid media could provide important insight into the transfer of chirality in soft materials," writes David B. Amabilino of the Barcelona Institute of Materials Science in an accompanying commentary.