Abstract: The fluorescence quenching processes of 9,10-dicyanoanthracene (DCA) by organic sulfides have been studied, and the fluorescent emissions from exciplexes have been observed for the DCA-sulfide systems. These seem to be the evidences supporting an electron-transfer mechanism. Diphenylsulfide, which is difficult to oxidize by singlet oxygen, dibutylsulfide and dihydroxyeSthylsulfide have been oxidized by using DCA as pho-tosensitizer. The reaction mechanism may be such a process: electron-transfer——formation of superoxide——oxidation of sulfide.