2. Photoinitiator of
photopolymerization.
PI plays an extremely important role in photopolymerization reaction, it
undergoes a series of complex physical or chemical changes in initiating
process.[17-19] As is shown in Figure 2, PI
absorbs light, then is excited from ground state (S0) to
singlet state (S1) which could be returned to ground
state by fluorescence emission or nonradiative deactivation, also may
reach to triplet state (T1) by intersystem crossing
(ISC). Similarly, PI of triplet state can return to ground state by
phosphorescence or nonradiative deactivation as well. When active
species are generated by cleavage or hydrogen abstraction of PI in
triplet state, photopolymerization can be initiated.