Thermochromic compounds are materials that change color in response to temperature variations. These compounds can be found in various forms, including dyes and pigments, and are often used in products like mood rings, temperature-sensitive labels, and thermometers. The color change occurs due to structural changes in the molecules when heated or cooled. These compounds work through a process called thermochromism, where the molecular structure alters at specific temperatures, leading to a visible color shift. Thermochromic materials can be reversible, returning to their original color when the temperature changes back, or irreversible, permanently changing color after a certain temperature is reached.