In this work, we report the first synthesis of photochromic aerogels and films based on TEMPOoxidized cellulose and chitosan modified with tungsten trioxide nanoparticles. The blue coloring of aerogels based on WO 3 -modified biopolymers under UV light occurs due to the reduction of W +6 to W +5 . The coloration of films of the same composition occurs due to the reduction of W +6 to W +5 and W +4 . The photochromic properties of aerogels and films are reversible; oxidation by atmospheric oxygen leads to bleaching of materials. At that, films become colorless within a few days while aerogels with a high specific surface area (200 m 2 /g) become colorless within several minutes. The antioxidant properties of the WO 3 sol and the WO 3 /TEMPOoxidized cellulose/chitosan composite were studied by luminol-activated chemiluminescence method. The antioxidant capacity of WO 3 /TEMPO-oxidized cellulose/chitosan gel is 1.5 times higher than that of the commercially available antioxidant mexidol. KEYWORDS Aerogel, hybrid materials, nanocomposite, biopolymers, cellulose, chitosan, tungsten oxide, photochromic material, antioxidant. ACKNOWLEDGEMENTS S. V. Kameneva thanks the Council for Grants of the President of the Russian Federation for supporting the study (SP-4398.2021.4).

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