Molecular design of azo-carbazole monolithic dyes for updatable full-color holograms

For the use of updatable full-color holography in practical applications, azo-carbazole (ACzE) monolithic dyes dispersed in poly(methyl methacrylate) (PMMA) films with high diffraction efficiency, write/delete capabilities and transparency are of extreme importance. We synthesized seven types of novel ACzE monolithic dyes and examined the influence of substituents introduced in the para position of the phenyl ring and the distinct strength of the substituents (NO2: NACzE, CN: CACzE, CH3CO: AACzE, F: FACzE, CH3O: MACzE, OH: HACzE and NH2: AmACzE) on the phenyl ring of the ACzEs. Spectroscopic and holographic optical properties, including absorption coefficient α, wavelength dependence of diffraction efficiency η, response time τ, the thickness of the recorded gratings d, the Bragg angle Δϑ and the Q-factor, required for the optimization of updatable full-color holograms were investigated. On the basis of the spectroscopic and holographic optical results, the appropriate writing/reading beams were determined as follows: 561/>600 nm for NACzE, 532/>560 nm for CACzE (and AACzE), 491/>530 nm for MACzE (and HACzE). According to the spectroscopic and holographic optical results, we propose here an insight designed to allow updatable full-color holography using ACzEs, and demonstrate a multi-color hologram in MACzE/PMMA.