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/cm2, 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.