Highly twisting enantiomeric radial multiyne dopants for discotic liquid-crystalline systems

Abstract

The synthesis and dopant properties of both the (R,R,R,R,R)- and (S,S,S,S,S)-hexadecyloxy{pentakis [4-(1-methylheptyloxy)-phenylethynyl]} benzene enantiomers are described. Although the materials were found not to be liquid-crystalline, it was found possible to induce left [for the (R,R,R,R,R)-enantiomer] and right handed [for the (S,S,S,S,S)-enantiomer] chiral discotic nematic phases (N_D*) as well as being only the second instance of the observation of discotic blue phases (BP_DIII and BP_DII) in binary mixtures with the hexayne host, hexakis(4-nonylphenylethynyl)benzene; a phase diagram is presented. The helical pitch and helical twisting power of the dopants was measured by use of the modified Cano method, and revealed far higher twisting powers than previously reported pentaynes. In addition the temperature dependent and angular dependent selective reflection spectra are reported, along with average refractive index approximations, which enable the pitch length of the chiral discotic nematic phase (N_D*) to be estimated to be of the order of 0.36 to 0.35 µm.