Photoinduced Reversible Phase Transition of Azobenzene-Containing Polydiacetylene Crystals

Abstract

Recently, incorporation of photoresponsive azobenzene moieties into supramolecular PDAs has been actively investigated. The photoinduced trans to cis isomerization of the azobenzene moieties in PDAs is interesting because it can potentially disrupt the ordered structures of the polymers and induce phase transitions of the PDAs. Herein, we explored the photoisomerization reaction of an azobenzene containing PDA. The results of this study show that this supramolecular system undergoes an interesting photoinduced reversible phase transition. UV irradiation of a single crystal of the azobenzene linked PDA was found to promote a blue-to-red color transition and that the blue-phase PDA is regenerated when the light source is removed. Interestingly, the photoinduced reversible color transition is accompanied by reversible tearing of the crystal. Photoinduced trans-cis isomerization of the azobenzene moieties in the polymer matrix is the cause of crystal tearing and the blue-to-red color transition. Reverse cis-trans isomerization of azobenzene moieties occurring in the dark is the process leading to restoration of the initial shape and blue-color of the PDA.