Photochromic azobenzene cellulose ethers were prepared by homogeneous etherification of cellulose with 2,3-epoxypropoxy-azobenzene (EA) in N,N-dimethylacetamide/lithium chloride solution. The EA with epoxy group could highly efficiently react with cellulose to synthesize 3-azobenzyloxy-2-hydroxypropyl-cellulose (Azo-cellulose) ethers with controllable degree of substitution (DS(azo)). The DS(azo) was in a range of 0.2-2.0 adjusted by the molar ratio of EA to anhydroglucose unit of cellulose. The Azo-celluloses with DS(azo)≥0.53 were soluble in aprotic solvents like dimethylsulfoxide. Their chemical structures and properties were characterized by elemental analysis, FT-IR, NMR, and thermogravimetric analysis. They showed reversible trans-cis-trans transition when Azo-cellulose/DMAc solutions were irradiated by successive irradiation of UV and visible light. The transition between trans- and cis- isomers could be effectively controlled by simply adjusting the irradiation time. The photo-stimulated trans-cis-trans conformational change induced conformation transition between rod-like shape of trans-isomer and skewed shape of cis-isomer.
Keywords: Azo polymers; Cellulose; Photochemistry; Photochromic behavior.
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