A novel and efficient xanthenic dye–organometallic ion-pair complex for photoinitiating polymerization

The photochemistry of the complex formed between a Rose Bengal dianion (RB) and a ferrocenium salt [Fc(+)] is described in this article. Stoichiometric analysis of the crystal showed that the Fc(+):RB ratio is 2:1. The dissociation percentage of complex RB(Fc)₂ in several solvents was evaluated using fluorescence studies. In nonpolar media, in which most of the RB(Fc)₂ exists as contact ion pairs, the photodegradation rate of the complex was found to be unaffected by the presence of oxygen and led to photoproducts capable of initiating a radical polymerization reaction. Because of this, the initiation step showed low oxygen inhibition. In fact, in a visible-light photoinitiating system such as one composed of xanthene dye (Rose Bengal), ferrocenium salt, amine, and hydroperoxide, substituting the complex RB(Fc)₂ for the sensitizing dye RB led to an increase in efficiency of the polymerization (especially under aerated conditions) as compared to that obtained in the presence of benzoyl phosphine oxide derivatives. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2368–2376, 2001