Photochromic transparent wood for photo-switchable smart window applications

Transparent wood with high optical transmittance, excellent thermal insulation and high toughness has attracted significant attention as an energy-saving building material. Many research efforts were dedicated to functional transparent wood, from luminescent to electrochromic transparent wood. However, photochromic transparent wood that is highly desirable and critical for smart window applications has been rarely studied. Herein, we experimentally demonstrate photochromic transparent wood with photo-switching of transmittance in the visible light region and color tuning properties. The photochromic transparent wood was obtained by infiltrating the lignin modified wood template with a mixture of photochromic material 3',3'-dimethyl-6-nitro-spiro[2H-1-benzopyran-2,2'-indoline]-1'-ethanol (DNSE) and pre-polymerized methyl methacrylate (MMA). This photochromic transparent wood exhibits a vibrant purple-to-colorless color change under the illumination of light. In addition, dichroic dye material doped photochromic woods were studied for providing more color change choices. The proposed photochromic transparent wood shows potential applications in mechanically robust, energy-efficient, photo-switchable, and colorful smart windows on a large scale.