Photochromic composites with fast light response, high contrast, and waterproof properties

Preparation of reusable photochromic materials is an effective strategy to alleviate resource waste, energy crisis and environmental problems. However, some weak links (such as slow light response rate, poor cycling stability, hydrophilicity, etc.) may limit their application in specific fields. Here, an intelligent material combines the advantages of inorganic compounds and organic substances, of which rapid charge transfer enables reversible color change assembly among semiconductors, polyoxometalates (POMs) and polymers. Specifically, Keggin-structure POMs are spontaneously attached to nitrogen-containing polymer by hydrogen bonds between terminal oxygen atoms of POMs and protons of amide nitrogen. Additionally, nano-TiO2 which acts as an extra electro donor is doped in this system. When exposed to UV light, the accelerated photoelectron transmission within the system achieves rapid color switching for a few seconds and achieves a reflection value difference of 64.12% within 60 s, displaying fast light response rate and high contrast. In addition, it also has stable cycling characteristics, with only a slight decrease in contrast after 20 times optical printing. On the premise of ensuring readability, a simple spraying treatment forms an anchorage of polydimethylsiloxane/TiO2 layer to photochromic layer, providing this material with waterproof properties. Encouragingly, this system can be applied by air-jet electrospinning, leading to a forward leap of self-fading time for compressing to 1 h. Overall, a waterproof photochromic composite has been developed based on the pain points of this material required overcoming, exhibiting potential in the fields of rewritable materials, anti-counterfeiting materials, indicator materials, etc.