Achieving reversible thermochromism of bisdiynamide polydiacetylene via self-assembling in selected solvents

Abstract This contribution demonstrates a new approach for achieving reversible thermochromism of bisdiynamide polydiacetylene(bis-PDA). The use of specific solvent as a medium can promote molecular organization and crystal growth of bis-PDA assemblies, which in turn results in reversible thermochromism. In this study, bis-PDAs constituting symmetric alkyl tails were prepared by self-assembling in water or alkanes. The preparation by using water as a medium produces bis-PDA assemblies with relatively small particle size and irregular shape. In this system, the bis-PDA exhibits irreversible thermochromism. Interestingly, the use of nonpolar alkanes promotes crystal growth of the bis-PDA assemblies into micron-size sheet-like structure. We have found that the increase of particle size and molecular ordering results in reversible thermochromism. X-ray diffraction reveals lamellar structure with uncharacteristically high tilting angle of the alkyl side chain with respect to the lamellar plane. Infrared spectroscopy also detects the variation of segmental arrangement within the bis-PDA assemblies. Our study points to new and rather simple approach for achieving reversible thermochromism of bis-PDA-based materials that can extend their applications as colorimetric sensors, smart ink or responsive paint/pigment.