Epoxy-based azo molecular glasses with four-arm architecture: Preparation,characterization and holographic recording

In this study, a series of epoxy-based azo molecular glasses with four-arm architecture was synthesized based on an intermediate (MDGA-AN), which was obtained from ring-opening reaction between 4,4'-methylene-bis(N,N'-diglycidylaniline) and N-methylaniline. The azo compounds were then synthesized through azo-coupling reaction between MDGA-AN and diazonium salts of 4-nitroaniline, 4-aminobenzonitrile, 4-aminobenzoic acid, 4-fluoroaniline and 4-methoxyaniline, respectively. The azo compounds were thoroughly characterized and the photoresponsive properties of their solid films were investigated at three different wavelengths (λ_ex=488, 532 and 589 nm). The results show that the electron-withdrawing groups on the azo chromophores can significantly affect the absorption band positions in visible light range, which shift to the longer wavelength with the enhanced push-pull effect. Both photoinduced birefringence and surface-relief-grating formation are closely related to the electronwithdrawing groups and excitation wavelengths of the actinic light, which show significant influences on the growth rates and saturated values of the photoinduced variations. In this series, the azo molecular glasses containing cyano and carboxyl groups as the electron-withdrawing groups show the significantly higher efficiency for both the photoinduced birefringence growth and the SRG formation compared with others under the same light irradiation conditions. The capability of the materials as a photo-storage medium is demonstrated by holographic recording.