Molecules in a solution behave like a crowd in a square: they can jostle randomly or line up in neat rows. An aqueous solution of disodium cromoglycate is a well-known model for chromonic liquid crystals, where such 'rows' form spontaneously. But if you shine ultraviolet light on the solution, order collapses: molecules start breaking apart.

These fragments, photodegradation products, wedge themselves between intact molecules and prevent them from assembling into tidy columns. As a result, the disordered region in the phase diagram expands, and the ordered phase retreats. Scientists confirmed this by combining X-ray scattering and polarized optical microscopy: the scattering pattern reveals how regular structures disappear.

This is not just a lab curiosity. It turns out that light can finely tune the properties of soft materials: irradiate, and the liquid becomes less ordered; wait, and it partially recovers. Such a 'light switch' could be useful in creating smart coatings, sensors, or even in biomedicine, where a reversible response to an external stimulus is important.