Liquid crystals so good, they’re a scream!

When Edvard Munch completed his famed painting “The Scream” in 1893, he probably didn’t expect it to have such a profound and lasting effect on the cultural zeitgeist. Just as likely, he probably never imagined that it would at one point hold the record for the most expensive work ever sold at auction; the painting fetched a cool $120 million back in 2012.

Thankfully, contemporary museum goers can see this expression of Munch’s personal anxieties, as access to the painting is still attainable for the rest of us plebians who can’t afford to casually drop millions of dollars on a canvas. The painting is on public display at the National Museum of Oslo, Norway.

For those who don’t have the means to plan a trip to the painting’s current home, a recent advancement in liquid crystals could provide a view of the work that you won’t even find in Oslo. Researchers from Dartmouth College and Southern Methodist University (SMU) have designed a molecular switch that can trigger shape changes in liquid crystals that allow them to reflect different colors. So far, the study has created reproductions of Munch’s “The Scream” as well as Vincent van Gogh’s “The Starry Night.”

Edvard Munch’s “The Scream” (left) compared to the Dartmouth and Southern Methodist University (SMU) reproduction made via a molecular switch. Courtesy of Dartmouth College.

The switch in question is made up of the organic molecule triptycene and a class of compounds, called hydrazones, that can flip on and off with a pulse of light, which functions as a stimulus. The researchers demonstrated that these hydrazones can be attached to triptycene in such a way that the molecule’s symmetry breaks, making it chiral. When chiral triptycene interacts with a liquid crystal molecule, it sets a chain of events into motion that causes other liquid crystal molecules to fall in line, rearranging themselves in twisted, DNA-like helices.

Once in helical form, the liquid crystals reflect ambient light at different wavelengths based on their pitch, or how far apart the coils in their helical structure are spaced — stretching and compressing the helix triggers vivid color changes. This is similar to what happens when, say, a chameleon changes color or a painter whitewashes a canvas after getting all of the colors wrong.

The reproductions were made using this technique, along with a microscope from an SMU lab rejiggered into a mini slide projector. In a process reminiscent of multicolor screen printing, the researchers used the projector to beam light through a series of stencils on a makeshift screen made of liquid crystals doped with chiral triptycene. New colors were added by shining the light for varying lengths of time on parts of the screen left exposed by the stencil.

Though the liquid crystal paintings aren’t permanent, the technique’s ability to enable colors to remain on the pattern for multiple days has researchers excited. Advancements such as liquid crystal lasers, display screens that could be easily printed and erased, and microscopic tags that could, for example, be added to bank notes to deter counterfeiters, could become a reality in the near future with this newfound molecular switch.

But while applications such as these are useful, a lingering question remains: Can they be deployed to elicit a case of existential dread in a museum viewing room? Perhaps we’ll just have to wait and see.

The research was published in Nature Chemistry (www.doi.org/10.1038/s41557-024-01648-0).