Optimization of a Safranine O three-component photoinitiating system for use in holographic recording

Abstract

The coupling between a holographic resin, combining multiple monomers and additives, with photoinitiating systems (PIS) is not straightforward. In this paper, a classic PIS based on Safranine O (SFH+) as dye, an amine (ethyl-4-(dimethylamino)benzoate) as electron donor, and a triazine derivative (2-(4-methoxyphenyl)-4,6-bis(trichloromethyl)-1,3,5-triazine) as electron acceptor for holographic recording was studied using time-resolved spectroscopic experiments. By taking into account the viscosity of the matrix, a method to evaluate the overall quantum yield of radicals released is proposed and the contribution of singlet and triplet excited states of SFH+ in the formation of radicals is evaluated. Then the corresponding photopolymerization efficiencies of the PIS, studied by real-time FTIR, are compared with holographic recording experiments: this system allows the formation of a hologram with high diffraction efficiency (0.9) in 3 s of irradiation time. It is shown that besides holographic resin formulation, the photochemistry of PIS also impacts the hologram formation.