The photosensitive initiating system composed of 7-diethylamino-3-(2’-N-methylbenzimidazolyl)coumarin dye (DBC) as sensitizer and diphenyliodonium hexafluorophosphate (DIH) as initiator

can be used to initiate the polymerization of methyl methacrylate (MMA) in visible light.When exposed to visible light

coumarin dye/iodonium salt undergoes quick electron transfer from DBC to DIH and free radicals are produced.The visible light photoinduced reaction between DBC and DIH is mainly through the excited singlet state of DBC and thus it is little sensitive to O2.The fluorescence of DBC can be quenched efficiently by DIH and the change is in accord with Stern-Volmer equation and the quench constant Kq can reach 1012M-1S-1.The influence of concentration of DBC on the polymerization rate of MMA shows that counarin free radical act mainly as chain terminator in polymerization and has a stronger tendency to terminate the chain reaction.