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 2,21-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, eta, 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 Delta n and nonlinear index coefficient n(2) 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 (Delta epsilon) property of the LCs changes from the positive type to negative type and dielectric anisotropy values decrease with AD. (C) 2008 Elsevier Ltd. All rights reserved.