Multistep Thermochromism due to Cold Crystallization and Solid–Solid Transition in Alkyl Derivative of Diketo-pyrrolo-pyrrole Pigment

The alkyl-derivatized diketo-pyrrolo-pyrrole pigment shows complicated thermal behavior. It shows polymorphism, cold crystallization (first report for pigments and dyes), and solid–solid transition, accompanied with a change in color. The role of alkyl chains in the thermal behavior is discussed based on the molecular structure, which has a rigid core and flexible chains.