Synthesis and characterisation of fluorescent chitosan derivatives containing substituted naphthalimides

Chitosan, derived from β-chitin, was reacted with 4-bromonaphthalic anhydride to produce a new chitosan derivative N-(4-bromonaphthalimide)-chitosan. The degree of substitution and molecular weight of the products were dependent upon the reaction conditions. The new chitosan polymer was reacted with the nucleophiles dimethylamine, piperidine and methoxide to produce substituted N-naphthalimide-chitosan derivatives. The materials were characterised by microanalyses, IR, GPC, 1H NMR, UV-vis and fluorescence spectroscopy. All four new polymers were fluorescent in acetic acid buffer solution and the nature of the fluorescence was dependent on the substituent.