Polynuclear aromatics, photoinitiators

Such compounds as polynuclear aromatics, heteroaromatics, ketones, quinones and dyes can serve as donors. Both excited singlet and triplet-states of these products can be involved in the PET. Diaryliodonium salts, triarylsulfonium salts, phosphonium salts, ammonium salts, pyrylium and thiapyrylium salts possess enough thermal stability and corresponding reduction potential to function as electron acceptors (R X+). In order to select suitable photoinitiator systems based on compounds discussed, the Weller-Eq. (5) can be employed. 

To increase the cure, photosensitizers have been used, which increase the response of photoinitiators to longer wavelengths. Electron rich polynuclear aromatic compounds, such as anthracene pyrene, perylene, coron-ene, 9,10-diphenylethynylanthracene, and carbazole compounds have been used. 

Subsequent research showed the SrnI mechanism to occur with many other aromatic compounds. The reaction was found to be initiated by solvated electrons, by electrochemical reduction, and by photoinitiated electron transferNot only I, but also Br, Cl, F, SCeHs, N(CH3)3, and 0P0(0CH2CH3)2 have been foimd to serve as electrofuges. In addition to amide ion, phosphanions, thiolate ions, benzeneselenolate ion (C HsSe"), ketone and ester enolate ions, as well as the conjugate bases of some other carbon acids, have been identified as nucleophiles. The SrnI reaction was observed with naphthalene, phenanthrene, and other polynuclear aromatic systems, and the presence of alkyl, alkoxy, phenyl, carboxylate, and benzoyl groups on the aromatic ring does not interfere with the reaction. ... 

Many other electron-rich polynuclear aromatic compounds also act as efficient electron-transfer photosensitizers for both diaryliodonium and triarylsulfonium salt cationic photoinitiators. Examples are pol5muclear aromatic compounds like pyrene, and perylene. The drawback, however, to using... 

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