Abstract: In this work,a series of fluorescein dye idonium salts were synthesized and their spectral and photochemical properties were studied.Results show that their spectral propertiescan be changed through the variation of their own structures. I_Ⅰ/I_Ⅱ was proposed to compare the relative degree of dissociation of these compounds in solvents. With increasing thesolvent polarity,the steric hindrance around the C- 6 position and the number of eletronwithdrawing groups, the I_Ⅰ/I_Ⅱvalue increases,so does the relative degree of dissociation.Followingly, the spectral properties change significantly and the rate of photoreaction decreases. The concentration of dye iodonium salts has different effects on their spectral andphotochemical properties in polar and nonpolar solvents respectively. It is shown that thesecompounds may not only be used as photoinitiators for photopolymerization and photocrosslinking,but also as probes for studing the enviromental properties.

Key words: iodonium salts, dye sensitization, ion pairs, spectral properties