Perhaps you're familiar with the strangeness of supercooled water: It stays liquid well below water's freezing point until you give it a whack, and bam, it suddenly turns into solid ice. You're probably less familiar diketopyrrolopyrrole (DPP) derivatives, which has similar but also odder properties.
In a new study, scientists introduce DPP8, one particular derivative that can be supercooled to 200F below its freezing point. When lightly touched, DPP8 suddenly crystallises, not unlike water turning into ice. The yellow crystals glow under ultraviolet light.
In other words, DPP8 is an extremely sensitive colour-changing touch sensor. The researchers suggest it could have applications in electronics or medicine. In the meantime, though, it's also pretty fun to drawn on.
Picture: Chung et al / ACS Central Science