Nanocomposites of Polydiacetylene and Rare Earth Ions with Reversible Thermochromism

We report a facile approach to water-dispersible polydiacetylene/rare earth ions nanocom-posites with reversible thermochromism. The nanocomposites were prepared by doping rare earth ions Dy³⁺ or Sm³⁺ into layer-structured 10,12-pentacosadiynoic acid (PCDA) nanopar-ticles to obtain PCDA/rare earth ions nanocomposites (PCDA-RE) and subsequently an-nealing PCDA-RE at the temperature slightly higher than the melting point of pure PCDA crystals, followed by topochemically polymerizing the annealed PCDA-RE. The polymerized PCDA-RE, i.e. poly(10,12-pentacosadiynoic acid)/rare earth ions nanocomposites (PDA-RE: PDA-Dy or PDA-Sm), are largely reversible (PDA-Sm) or even completely reversible (PDA-Dy) in the thermochromism, while, without the doping, pure PDA is completely irre-versible. It is con rmed that, PDA-RE are also layer-structured with a d-spacing of 5.4 nm, higher than the d-spacing of pure PDA (4.7 nm). In PDA-RE, the rare earth ions form a layer in-between and interact strongly with the PDA bilayers, being responsible for the high degree or even the complete reversibility. This is the rst example to make PDA completely reversible through the doping of rare earth ions; the annealing process is essential for the complete reversibility since it removes any defects in the structure.