Iron aren salt photoinitiators

Iron arene photoinitiators have excellent light absorption properties in the ultraviolet and visible parts of the spectrum. As shown in Fig. 18, the absorption can be varied over a wide range by structural changes in the ligands. Iron arene salts can be sensitized, for example with anthracene derivatives... 

Besides the most important area of surface coatings, the use of photopolymers as photoresists in the manufacture of printed circuits is well established. Photoimaging with aryldiazonium salt photoinitiators and multifunctional cresol-novolac epoxides was first described by Schlesinger Crivello has mentioned several new photoresists based on the photopolymerization of epoxides with onium initiators Meier and Zweifel have shown that iron arene salts in combination with multifunctional cresol-novolac epoxides yield photoresists with high resolution and contrast. Dual functional epoxides (cf. Sect. 5) containing chalcone groups as light-sensitive units have been described as suitable photoresists especially... 

Iron-arene salts may also exhibit an appreciable absorption in the visible or near-UV part of the spectrum. The photochemistry of these compounds as well as their use as photoinitiators has recently been described by Lohse and Zweifel In certain applications the presence of strong acid m the photopolymer is desirable since the reaction continues after exposure. 

Photoinitiated cationic polymerization has been the subject of numerous reviews. Cationic polymerization initiated by photolysis of diaryliodonium and triarylsulfonium salts was reviewed by Crivello [25] in 1984. The same author also reviewed cationic photopolymerization, including mechanisms, in 1984 [115]. Lohse et al. [116], reviewed the use of aryldiazonium, diphenyliodonium, and triarylsufonium salts as well as iron arene complexes as photoinitiators for cationic ring opening polymerization of epoxides. Yagci and Schnabel [117] reviewed mechanistic studies of the photoinitiation of cationic polymerization by diaryliodonium and triarylsulfonium salts in 1988. Use of diaryliodonium and sulfonium salts as the photoinitiators of cationic polymerization and depolymerization was again reviewed by Crivello [118] in 1989 and by Timpe [10b] in 1990. 

In the (keto)coumarin/amine/ferrocenium salt system, the ferrocenium salt plays a crucial role that is rather complex. In a three-component photoinitiator system [238,239] consisting of a coumarin, an iron arene complex such as CpFe +Ar and a phenylglycine derivative as an amine, the first step of the photoreaction occurs between the dye and the complex according to an electron process. The amine reacts with the radical (created on the complex) through hydrogen abstraction. Therefore, no detrimental ketyl radicals are formed. 

Iron Arene Complexes-Based Photoinitiators Iron arene complexes or ferrocenium salts are attractive photoinitiators for cationic polymerization of... 

Organometallic compounds which can act as highly efficient photoinitiators for epoxide monomers have been described in the literature (25-27,69-71). The most commonly used organometallic compounds are the photoinitiators based on iron arene complex developed by the investigators at the Ciba-Geigy Corp. (37,69-71). These salts are generally prepared from ferrocene, as reviewed by Lohse and Zweifel (37). The molecular structure of a typical iron-arene complex is shown as (3). 

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