Investigation of electron transfer between hexaarylbiimidazole and visible sensitizer

Hexaarylbiimidazole (HABI) is a widely used photopolymer photoinitiator (Structure I). 1,2 Triarylimidazolyl (lophyl = L) radicals recombine in the dark and form HABI reversibly. The L radical generated in the photodecomposition can interact with chain-transfer agents either by direct hydrogen abstraction or by electron transfer to produce an initiating species capable of being added to the monomer molecule 2,3 Because of the development of inexpensive visible and IR light sources, it is advantageous to develop materials sensitive in these spectral regions. Therefore, there has been considerable interest in producing L radicals with visible light excitation. It was observed that the polymerization processes may be initiated by a visible light excitation (λ > 480 nm) if certain visible absorption dyes such as JAW (Structure II) are added to the solution. 4–7

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