Electro-optical characteristics of photoinduced isomerization in 2,2′-azobis[5,6-bis(dodecyloxy)quinoxaline]-azo-dye-doped nematic liquid crystals

The formation of photoinduced gratings was realized and dielectric properties were investigated in a nematic liquid crystal (LC) doped by 2,2′-azobis[5,6-bis(dodecyloxy)quinoxaline] azo dye (AD). The enhancement of the optical and electrical properties of the system was studied by dielectric spectroscopy and diffraction grating measurements. We report the electro-optical properties of LC cells containing pure LC (E7) and its doped form with 1% (wt/wt) 2,2′-azobis[5,6-bis(dodecyloxy)quinoxaline] AD. Diffraction efficiencies, η, of 441 nm pump and 632 nm probe beams were measured in two-wave-mixing experiment. Diffraction efficiency has a noteworthy increase in AD-doped nematic liquid crytals. A maximum diffraction efficiency of 14% was found for cell doped with AD, while cells without AD had a maximum efficiency of 1%. Photoinduced refractive index change Δn and nonlinear index coefficient n2 were also determined by the two-wave-mixing method. The dielectric parameters of AD-doped E7 and pure E7 LC have been investigated in the frequency range 1 kHz–1 MHz by the dielectric-spectroscopy method. Dielectric anisotropy (Δε) property of the LCs changes from the positive type to negative type and dielectric anisotropy values decrease with AD.