An inkjet-printable microemulsion system for colorimetric polydiacetylene supramolecules on paper substrates

Owing to their flexible, light-weight and disposable properties, paper-based electronic and sensor systems have gained much attention. Efficient immobilization and patterning of functional materials on paper substrates are critical to device performance. Herein, we report an inkjet printable and photopolymerizable diacetylene (DA) containing microemulsion system that can be readily transferred to paper substrates using a common office inkjet printer. UV-induced polymerization afforded clean formation of polydiacetylene (PDA) supramolecules on paper and the polymer displayed a typical thermochromism. The resolution of the printed PDA images was found to be equivalent to that of conventional black ink. The randomly oriented DA in the oil phase was found to be transformed to self-assembled layered structures upon printing. The printed PDA supramolecules derived from 5,7-dodecadiyne-1,12-diol bis[((butoxycarbonyl)methyl)urethane] (4BCMU) displayed a blue-to-red-to-yellow color transition upon heating. Thus, the blue colored 4BCMU-derived polymer was converted to a red colored PDA at 100 degree C and further heating to 180 degree C resulted in the generation of a yellow colored PDA. Upon cooling to room temperature, the yellow colored PDA became red and a complete colorimetric reversibility was observed between red (30 degree C) and yellow (180 degree C). The thermally promoted reversible PDA phase transition was successfully applied to a banknote to demonstrate an application to a potential counterfeit prevention method.