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

Abstract

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. A holographic system that uses low-cost materials to capture and rewrite full-colour 3D images has been developed by Japanese researchers. Naoto Tsutsumi from the Kyoto Institute of Technology and co-workers recently developed a red-coloured hologram based on an azo-carbazole dye that can be aligned, similar to a liquid crystal, using polarized light. Now, to tune the colour output, the team has modified phenyl rings on the original dye with a series of small, electron-donating and -withdrawing chemical groups. Spectroscopic and optical trials revealed that the colours from the functionalized dyes depend on the laser wavelengths used to write and read the hologram. The researchers exploited this behaviour with a system that combines red, green and blue holograms together in an updateable, full-colour video display. We report novel azo-carbazoles that can be applied to updatable full-color holography. We introduced a molecular design concept of updatable full-color holographic systems based on spectroscopic and optical characteristics. Taking advantage of characteristics of the designed azo-carbazoles, updatable red, yellow and green holograms can be recorded, which enabled us monochromic hologram as well as full-color hologram in the future.