Flexible Photochromic Synaptic Devices for UV Perception and Spatiotemporal Encoding

Flexible synaptic devices with short‐term optical dynamics offer promising building blocks for low‐power and visualized neuromorphic perception, yet introducing time‐dependent weight update and visual readout remains highly challenging. Herein, we establish a universal strategy for constructing flexible optical synaptic devices based on the photochromic hydrogels containing viologen molecules. Taking transmittance as the optical synaptic weight, the photochromic synaptic devices demonstrate their short‐term synaptic plasticity dependent upon the intensity, the duration, and the history of the UV light stimulation. Typically, under UV irradiation at 20 mW/cm 2 , the transmittance of the photochromic synaptic device at 602 nm reaches 88.1% after 30 s and further decreases to 46.5% after multiple stimulations. Such synaptic device enables visualized perception of various degrees of UV irradiation, which is further utilized to craft a wearable wristband for direct and intuitive visual indication of UV exposure level. Moreover, by accelerating the coloration process of the hydrogel with a photo‐sensitizer, a robust platform for optical information encoding/decoding is developed by implementing a 3 × 3 photochromic device array. The present finding not only introduces the versatile flexible photochromic synaptic device, but also explores its potential applications in UV perception and spatiotemporally coupled information encoding.