A multi-element encrypted and decrypted photoresponsive liquid crystal polymer network through the cooperation of cyanostilbene and spiropyran

Abstract

Photoresponsive polymer materials, in particular, light-driven liquid crystal polymer networks (LCNs) have attracted much attention due to their rapid and significant capacity for photodeformation. However, a single shape change could not meet the growing needs of the information encryption field. Therefore, we aimed to find a photoluminescent and photochromic LCN to enrich the application of photodeformable materials. Here, a light-driven LCN consisting of two distinct kinds of photosensitive moieties, cyanostilbene (CS) and spiropyran (SP), named CS∙SP∙LCN, has been designed and synthesized. The resultant LCN film displayed multiple photo/thermal responsive properties. On the one hand, the trans–cis photoisomerization of CS gave the film capacity for photodeformation. On the other hand, the reversible conversion between ring-closed SP and ring-opened merocyanine (MC) under alternating stimulation of UV irradiation and heating gave the film capacity for tunable photoluminescence and photochromism. The CS∙SP∙LCN film can bend and change color/luminescence under UV irradiation, leading to multi-element writing simultaneously. Then, the written information could be hidden by heating and stretching. Notably, the film resumed bending after the second heating due to the good stability of the cis isomer of CS, realizing the first decryption. Finally, the color/luminescence of the film resumed after the second UV irradiation, completing the second decryption of the information. The CS∙SP∙LCN films synthesized in this study could realize multi-element encryption and step-by-step decryption through the cooperation of CS and SP, achieving more advanced information storage and encryption possibilities.