Wide blue phase range observed in simple binary mixture systems containing rodlike racemic biphenyl mesogens with 2-octyloxy tails

Abstract

Four series of simple and rodlike racemic biphenyl mesogens possessing a 2-octyloxy tail and different substituents at the inner-core position of the phenyl ring were easily prepared. The mesophases of these racemic biphenyl mesogens were confirmed by variable-temperature XRD and the characteristic texture of POM. In general, cubic BPs can be induced by adding an appropriate ratio of chiral additive S811 or ISO(6OBA)₂ into these racemic biphenyl mesogens during the heating and cooling processes. Interestingly, BPIII (5–6 K) easily dominates in highly chiral conditions for the blended mixture composed of mono-substituted biphenyl mesogens and chiral dopant S811. In addition, the formation temperature of BPIII is near room temperature (36 °C) when compound C₆OBiPhI-OH is blended with 35 wt% S811 during the cooling process. Stable BPs with more than 20 K present in the blended mixture system were composed of chiral dopant ISO(6OBA)₂ and no substituted biphenyl mesogens C_nOBiPhI-H or difluoro substituted C_nOBiPhI-FF. Notably, the widest temperature range of BP (∼34 K) can be induced by adding only 10 wt% chiral dopant ISO(6OBA)₂ with high HTP into the biphenyl compound C₆OBiPhI-H. The properties of the BPs were characterized by POM, DSC and reflection spectra. On the basis of our experimental results and molecular modeling, we demonstrated that the appearance and temperature range of BPs in this simple type of biphenyl mesogen with 2-octyloxy tail are affected by the molecular dipole moment and biaxiality.