Synthesis and optical properties of fluorescent brighteners modified by chitosan

Replacing one of amino compounds of traditional fluorescent brighteners with chitosan,the fluorescent brighteners modified by chitosan(CS-FBs) were synthesized through three-step condensation reaction.The photophysical and photochemical characteristics and whitening properties in aqueous solutions and ethanol were studied by ultraviolet ray absorption spectra,fluorescence emission spectra,photoinduced isomerization phenomena and paper application test of CS-FBs.Fluorescence quantum yield are determined using quinine sulfate in 0.5mol/L H2SO4(ΦF=0.55)as fluorescence standard.The effect of concentration and polarity of solvents on fluorescence properties,as well as the ralationship of the structures and fluorescence properties were studied.The results show that,comparing with the traditional FBs,such as VBL,the light stability and fluorescence quantum yield of CS-FBs were greater,and photoinduced isomerization was lower,the whitening effect of coated paper and physical strength was enhanced.At the same time a red shift of fluorescence emmission wavelength and fluorescence quantum yield increaseing with the increase of solvent polarity.When the concenteation was over 9×10-4g/mL,the fluorescence was quenched.Meanwhile,the type of substituents in the triazine ring can affect directly the concentration of trans-and Cis-isomers,but not affect significantly absorption-fluorescence assignments.