Thermochromic materials change colour in response to changes in what?

• A. Temperature
• B. Light levels
• C. Humidity
• D. Pressure

Answer: (A)

Thermochromic materials change colour when temperature changes. Temperature affects their internal structure or phase, which alters how they interact with light and so shifts the color you see. For example, some use liquid-crystal structures where heating moves them between phases and changes light interference, while others use leuco dyes where the balance between a colored form and a colorless form shifts with temperature. The other factors listed would cause color change in different types of materials—light changes lead to photochromic effects, moisture affects hygroscopic systems, and pressure can trigger color changes in mechanochemical materials—so they don’t describe why thermochromic materials change color.