Synthesis and photoactivity of novel cationic photoinitiators: (η6-Diphenylmethane) (η5-cyclopentadienyl) iron hexafluorophosphate and (η6-benzophenone) (η5-cyclopentadienyl) iron hexafluorophosphate

Two novel cationic photoinitiators (η6-diphenylmethane) (η5-cyclopentadienyl) iron hexafluorophosphate (PhCH2PhFe+CpPF6−) and (η6-benzophenone) (η5-cyclopentadienyl) iron hexafluorophosphate (PhCOPhFe+CpPF6−), were synthesized, characterized, and studied. PhCH2PhFe+CpPF6− was prepared by straightforward synthetic techniques with ferrocene and diphenylmethane and PhCOPhFe+CpPF6− was synthesized from oxidation of diphenylmethane–cyclopentadienyliron salt. Their activity as cationic photoinitiators was studied using real-time infrared spectroscopy. The results obtained showed that PhCH2PhFe+CpPF6− and PhCOPhFe+CpPF6− are capable of photoinitiating the cationic polymerization of epoxy monomer directly on irradiation with long-wavelength UV light. Comparative studies also demonstrated that PhCH2PhFe+CpPF6− exhibited better efficiency than I-261 and PhCOPhFe+CpPF6−. DSC studies showed that PhCOPhFe+CpPF6− and PhCH2PhFe+CpPF6− photoinitiators in epoxides possess good thermal stability in the absence of light.