A Soluble, Low-Temperature Thermochromic and Chemically Reactive Polydiacetylene

The majority of polydiacetylenes (PDAs) described to date display thermochromic transitions above room temperature. By following a strategy that employs headgroups that do not participate in strong interactions, we have designed and prepared a liquid diacetylene (DA) that solidifies at a temperature near 0 degrees C. The isocyanate-containing DA monomer, DA-NCO, having this property does not Undergo polymerization in its liquid state at room temperature. However, UV irradiation of frozen DA-NCO at 0 degrees C causes the instantaneous formation of a blue PDA (PDA-NCO). Interestingly, PDA-NCO was found to display a sharp blue-to-red color transition at a temperature near 11 degrees C. By taking advantage of its room temperature liquid-phase property, we were able to readily transfer the DA monomer to solid substrates by using common stamping and writing methods used for creating patterned PDA images. In addition, PDA-NCO dissolves in chloroform, giving a yellow solution that becomes red and simultaneously generates polymer aggregates when hexane is added. Finally, the isocyanate moieties present in PDA-NCO have been utilized to differentiate 1 degrees from 2 degrees and 3 degrees amines owing to the fact that a chloroform solution of PDA-NCO undergoes a rapid yellow-to-red color change associated with an insoluble urea-forming reaction with primary amines.