Sign-alternating optical reorientation in nematic liquid crystals with low-molar-mass and polymeric absorbing bis-azobenzene dopants

Abstract A comparative study of optical orientation in nematic liquid crystals (NLCs) doped with a low-molar-mass bis-azobenzene dye (monomer) and a high-molar-mass (comb-shaped polymer) with side fragments similar in structure to the monomer has been carried out. Both types of bis-azobenzene dopants induced a sign-alternating nonlinearity in the NLC: the positive when the angle Ψ between the light field and the director is less than a certain critical value Ψc and the negative in the opposite case of Ψc The magnitudes of the optical-torque enhancement factors due to trans- and cis-isomers (ηT and ηC), and the ratios ηT/ηC for the low- and high-molar-mass dopants are compared. The results obtained show the possibilities of increasing the orientational optical nonlinearity when passing from low-molar bis-azobenzene dye dopants to the corresponding polymers and are important for elucidating the optimal architecture of absorbing additives.