Synthesis and characterization of bent liquid crystal phases by microscopy, calorimetry, spontaneous polarization and low-frequency dielectric relaxation studies in Bent-7

Synthesis of the bent-shaped (or -shaped) achiral liquid crystal Bent 7, viz., 1,3-phenylene bis(4-heptyloxy benzoate) with resorcinol as central moiety is reported. Supra molecular formation is confirmed by KBr solid state IR spectra. Polarized Thermal Microscopy(TM), Differential Scanning Calorimetry (DSC) and Spontaneous Polarization(P_S) experiments infer a bivariant monotropic (cooling), phase sequence viz., Isotropic →B₂(FE) → B₅(AF) solid. Phase transition temperatures determined from temperature variation of Dielectric Constant (or relative permittivity _εr (T)) agree with TM and DSC. Dielectric dispersion reveals different re-orientation processes viz., a slow (LF ∼ 1 kHZ) and a fast (HF ∼ 1 MHz) one in both the B₂ and B₅ phases. Both the relaxations in B₅(AF) phase follow Arrhenius shift to infer 1.12 and 0.89 eV of activation energies, respectively. Off-centred dispersion studied through the Cole-Cole plots in B₅(AF) phase infer the increasing trend of dielectric increment δε and distribution parameter with decreasing temperature. Trends of δε and α-parameter suggest a greater fall of response width during slow reorientation and a relative freezing rate during fast reorientation.