Thermochromism of polydiacetylene with a hysteresis loop in the solid state and in solution

Partly crystalline polydiacetylene 1, which is soluble in many organic solvents at room temperature, was prepared by the solid-state polymerization of 4-methoxybenzyl 10, 12-penta-cosadiynoate. We found a reversible change in the UV-vis absorption spectrum of 1 in a solid film, polymer matrix, and solution with a hysteresis loop as a function of temperature.