Mechanism of primary photochemical reaction of eosin bis(diphenyliodonium) salt

摘要

Recently, visible light sensitive photoinitiation systems have been developing very quickly, owing to the rapid development of both laser and photocuring technologies. Of these systems intra-ion-pair electron transfer dye photosensitization systems specially attract great attention. One of the reasons for this is that a large variety of available dyes can almost cover the whole visible and near infrared spectrum range and thus can be chosen as the photosensitization component based on different requirements. On the other hand, the photosensitization and initiation components are placed together before irradiation by the coulombic attraction between the cations and anions, which overcomes the limitation of the diffusion process to ordinary bimolecular energy or electron transfer and thus increases the reaction probability and photoinitiation efficiency. This is especially true in highly viscous and rigid polymeric matrices. The authors previously reported a photoinitiation system of the above type,i.e. eosin anion-onium cation system. The results showed that it is very stable in the dark. When exposed to visible light, it undergoes rapid intra-ion-pair electron transfer, producing active initiating species which can initiate polymerization of vinyl monomers or crosslinking of unsaturated resins. In highly viscous reaction systems, ion-pair photoinitiators show great advantages over ordinary bimolecular photoinitiation systems. This type of photoinitiators might be used to form both color and monochromatic systems, which might have application in photoimaging technologies, such as real color holography, stereolithography and laser printing plate manufacturing. In the present work, using eosin bis(diphenyliodonium) salt as an example, the authorshave studied the mechanism of primary photochemical reaction of such systems.