Influence of meta-extended rigid-core, complementary hydrogen bonding and flexible chain on polymorphism in Schiff-base liquid crystals: (4)MeOBD(3)AmBA:nOBAs

Schiff-base complementary hydrogen-bonded liquid crystals (HBLC), viz., (4)MeOBD(3)AmBA:nOBAs with flexible chain length for n = 3,4,5,6,7,8,9,10,11 and 12 are reported. 1H; 13C-NMR and Infra-Red spectroscopy used to confirm the formation of HBLCs. LC phases and transition temperatures (Tc) determined by polarised optical microscopy (POM) and differential scanning calorimetry (DSC). Tc and enthalpy (∆H) determined by DSC also. Odd-Even effect observed at clearing and melting transitions. Influence of Schiff base and Oxygen as bridging atom promote smectic phase abundance. HBLCs exhibit tetra- or penta-phase variance. Maximum (penta) phase variance is exhibited by n = 8 and 12 with long flexible chain. Prevalent abundance of quasi-two-dimensional (2D) LC phases of SmF and SmI is observed. Nematic phase is quenched. Lower (n = 4) and intermediate (n = 6) members exhibited SmBcryst phase. Predominant occurrence of enantiotropic LC phases is noticed. All members exhibited 3D tilted SmG phase. A-C transition exhibited by intermediate homologues (for n = 7, 8, 9 and 10) is found to be either second order or with very small enthalpy. Phase diagram reveals the abundance of multi-critical points with LC phasesinvolving exotic symmetries. Influence of meta-extended rigid core, complementary HB and flexibility is studied for the LC phase abundance with characteristic structural order. POM and DSC results are discussed in the wake of reports in other achiral calamitic LCs.

报道了具有可变链长度的Schiff碱基互补氢键液晶（HBLC），即（4）MeOBD(3)AmBA:nOBAs，其中n取值为3、4、5、6、7、8、9、10、11和12。利用1H；13C-NMR和红外光谱技术确认了HBLC的形成。通过偏光显微镜（POM）和差示扫描量热法（DSC）确定了液晶相和相变温度（Tc）。相变温度和焓变（∆H）亦由DSC测定。在消融和熔化转变过程中观察到奇偶效应。Schiff碱和氧作为桥连原子的存在促进了液晶向列相的丰富。HBLCs表现出四相或五相变异性。在n=8和12时，由于长柔性链的存在，表现出最大的（五相）变异性。观察到SmF和SmI的准二维（2D）液晶相的普遍丰富。向列相被淬灭。下（n=4）和中间（n=6）成员表现出SmBcryst相。观察到对映性液晶相的主导发生。所有成员均表现出三维倾斜的SmG相。中间同系物（n=7、8、9和10）的A-C转变被发现为二级或具有非常小的焓变。相图揭示了具有异质对称性的液晶相的多重临界点的丰富。研究了超扩展刚性核心、互补HB键和柔性的影响，以探究具有特征结构秩序的液晶相的丰富度。在非手性针状液晶的报道背景下，讨论了POM和DSC的结果。