A Spiropyran-Based Hydrogel Composite for Wearable Detectors to Monitor Visible Light Intensity to Prevent Myopia

A wearable detector to monitor visible light intensity is realized by the restrained photochromism of a hydrogel composite containing light-responsive spiropyran with hydroxyl groups (SPOH). When exposed to visible light, the SPOH experiences a ring-opening to a ring-closed transition accompanied by discoloration from red to yellow. Unlike in the solution, the photochromism/discoloration rate is strongly correlated to the cross-linking points. By reducing the amount of cross-linker from 40 to 5 mg, the photochromism rate of SPOH is 300% faster. Inspired by the Chinese Jade Loong from Hongshan, the hydrogel composite is shaped into a Loong to monitor the light intensity. By increasing the amount of cross-linker in the head, body, and tail, the photochromism/discoloration rate sequentially turns slower from one region to the other. Higher light intensity is required to realize the discoloration in the hydrogel composite containing a larger amount of the cross-linker. Because the initial colors are identical, the light intensity can be easily traced by checking the discoloration of these pieces containing different amounts of cross-linker. Based on this unique and reversible photochromic capability, the present hydrogel composite can be used for monitoring the visible light intensity to prevent myopia, especially for children and students.