Polydiacetylenes

Polydiacetylenes are a class of conjugated polymers formed by the polymerization of diacetylene monomers. The resulting backbone features alternating single and triple bonds, giving a highly conjugated chain that extends along the polymer. PDAs are typically prepared in the solid state or in oriented thin films where diacetylene units are aligned in a head-to-tail arrangement, enabling topochemical polymerization to occur upon activation.

Synthesis and processing rely on arranging diacetylene monomers in close, ordered packing, often achieved through crystallization, Langmuir–Blodgett deposition, or self-assembly with complementary side chains. Polymerization is commonly triggered by ultraviolet light or moderate heat, creating the extended PDA backbone. The side chains attached to the diacetylene units influence packing, stability, solubility, and the efficiency of polymerization.

A hallmark of polydiacetylenes is their chromatic response. The extended conjugation gives intense visible absorption and a characteristic color, typically blue in the initial state. Stimuli such as mechanical pressure, heat, or chemical environment can induce a conformational change that shifts the color to red, a phenomenon known as thermochromism or mechanochromism. In many systems the color change is reversible, though some derivatives exhibit irreversible transitions or accompany changes in fluorescence and conductivity.

Functionalization with diverse side chains allows tuning of solubility, processability, and sensing performance. PDAs have been explored for colorimetric and optical sensors, mechanochromic indicators, electrochromic devices, and flexible optoelectronic components. Their stability and response characteristics depend on the specific monomer design and processing conditions, with ongoing work aimed at improving robustness and practical applications.