5Potentially NLO-phore materials based on chitosan are described for the first time in this study. A series of fluorescent and quaternized pyridinium-chitosan derivatives have been synthesized by reaction of this polymer with easily available tunable pyrylium tetrafluoroborate salts. Among other spectroscopic techniques, 19 F NMR, 13 C CPMAS NMR and 2D diffusion experiments, were used to confirm the structures of the new pyridinium-chitosan complexes that show high fluorescence intensity. Degrees of N-10 substitution achieved, lower than 4.3 %, allowing the original physicochemical properties of the biopolymer to be preserved. DFT calculations have been performed to investigate molecular features related to NLO properties in these compounds. NLO behavior was found to be clearly dependent on the nature and location of substituent into pyridinium core. Theoretical data reveal large permanent dipolar moment, polarizabilities and hyperpolarizabilities making these molecules promising candidates as 15 supramolecular devices exhibiting NLO properties with potentially enhanced solvatochromic properties.