Mechanosynthesis of high molecular weight fluorescent derivatives of chitosan, linear and non-linear optical characterization

Three chitosan-derived compounds, Ch-I, Ch-Qn, and Ch-TPA, were synthesized through condensation reactions between high-molecular weight chitosan and three different aldehydes. Mechanosynthesis, a fast and solvent-free synthesis method, was used instead of a depolymerization. The chemical structure of the compounds was elucidated by Fourier-Transform Infrared (FT-IR) spectroscopy. The optical properties of the new compounds were evaluated by ultraviolet/visible (UV/Vis) and fluorescence spectroscopic techniques. The compounds Ch-I, Ch-Qn, and Ch-TPA presented absorptions in the range of 273 to 400 nm and emissions between 300 and 700 nm with Ch-TPA presenting the greatest redshift in absorption and emission. Ch-I, Ch-Qn, and Ch-TPA were characterized by the Z-scan technique, and the results indicate that Ch-I, Ch-Qn, and Ch-TPA exhibit non-linear optic behavior. Ch-TPA showed the most promising optical properties. These results indicate that it is possible to obtain promising materials derived from chitosan using mechanosynthesis and using high-molecular weight chitosan without the need to depolymerize it. Mechanosynthesis requires a short reaction time, is free of solvents, and has the potential for biomedical applications as optical and/or fluorescent biosensors.