Engineered crystal obeys inner bananas

Organic crystals composed of complex, carbon-based molecules offer scientists an abundance of features to manipulate when they’re devising novel materials.

Now, researchers at the University of Minnesota at Minneapolis St. Paul have programmed a property into an organic crystal by crafting the shape of a component molecule.

The researchers demonstrated that they could custom design a crystal to double the frequency of light passing through it. While many crystals have that optical ability, intentionally creating a particular crystal architecture that can lead to that trait is new, says Michael D. Ward, who led the research. He and his colleagues describe their work in the Nov. 30 Science.

To make the crystal, the researchers selected ionic, or charged, molecules to combine in a solution with selected organic compounds known to interact with light. The ionic components crystallized into a grid-like framework with a single light-interacting molecule in each of its pockets.

As predicted, because the framework’s pillars were curved like bananas, they distorted the crystal and caused an uneven distribution of electric charge, Ward explains. That caused all the light-manipulating molecules in the framework to line up in one direction, a requirement for the desired effect on light.

Ward says the capability to specify crystal architectures on paper and then synthesize compounds embodying them could be used to control other properties of crystals, such as electrical conductivity.

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