||The primary research work of this study is an attempt to correlate the structure-property relationship of the formation of blue phases in chiral liquid crystals in terms of variation of the achiral alkyl chain length (m), chiral alkyl chain length (n), structure of the rigid core, and achiral alkyl chain length (m) without ether linkage in the chiral liquid crystal materials.
Thus, the optically active alcohols, 1-ethyloxy-2-propanol, 1-propyloxy-2-propanol, 1-butyloxy-2-propanol, 1-pentyloxy-2-propanol, 1-hexyloxy-2-propanol, were designed and synthesized by reacting (S)-propylene oxide with alkyl alcohols under basic condition. In consequence, three novel homologous series of chiral materials, (R)-6-(1-alkyloxy-2-propyl)naphth-2-yl 4-alkyloxybenzoate, I(m=6-9, n=1-2), (R)-4-(1-alkyloxy-2-propyl)biphenyl 4-alkyloxybenzoate, II(m=6-9, n=1, 4, 5), (R)-4-(1-alkyloxy-2-propyl)biphenyl 4-heptylbenzoate, III(n=1-4), derived from these alcohols were synthesized for the investigation of the effect of the achiral alkyl chain length (m), ether linking group, chiral tail alkyl chain length (n) and rigid core structures on the mesomorphic.
The mesomorphic phases and their corresponding transition temperatures were primarily characterized by the microscopic textures and DSC thermograms.
The results of compounds I(m, n) composed of the rigid core structure of PhCOONa and chiral group of optical activity 1-ethyloxy-2-propanol and 1-propyloxy-2-propanol, showed that compound I(m=6-9, n=1) and I(m=6, 8, 9, n=2) exhibits the mesophases sequence of N*-Cr., and the compound I(m=7, n=2) exhibits the mesophases sequence of BPII-N*-Cr.. With the exception of I(m=7, n=2) that exists the widest temperature range of enantiotropic BPII phase.
The results of compounds II(m=6-9, n=1, 4, 5) composed of the same chiral group but differed in the rigid core structure (PhCOOPhPh) as compounds I(m, n). The compound II(m=8, n=2) exhibits the mesophases sequence of SmA*-Cr., the compound II(m=7, n=5) exhibits the mesophases sequence of BPI-N*-SmA*-Cr., the compound II(m=6-9, n=4) and I(m=8, n=5) exhibits the mesophases sequence of BPII-BPI-N*-SmA*-Cr., The widest temperature range of BP phases for these compounds appeared at II(m=9, n=4).
The results of compound III(n=1-4), the composed of the same rigid core structure as compound II(m, n) but differed in the achiral group where a reducible ether linkage is introduced, the compounds III(n=1) exhibit the mesophases sequence of SmA*-Cr., the compounds III(n=2) exhibit the mesophases sequence of BPI-N*-Cr., the compounds III(n=3-4) exhibit the mesophases sequence of BPII-BPI-N*-Cr..
In general, the results of mesomorphic phases show that compounds with the short alkyl lengths (n=1-2) at chiral groups generally suppress the formation of BP phase, however, compounds with longer length (n=3-5) enhance the thermal stability of BP phase. The results also show that, when the rigid core structures of the molecules change from PhCOONa to PhCOOPhPh, the clear point is increased and the stability of blue phase is also increased. Moreover, when extending the alkyl length (m) of achiral tail, the clear point is increased but the thermal stability of blue phase display no significant difference. Compounds having achiral group without ether linkage between the core display lower clear point, and lower the thermal stability of blue phase as compared to the compounds having ether linkage between the core and achiral alkyl chain. Among these three series of chiral compounds, compound II(m=9, n=4) has the widest BP phase temperature range (cal. 3.9℃), where BPI and BPII formed.