Synthesis and mesomorphism of mixed ether-ester tail triphenylene discotic liquid crystals with long alkyloxy peripheral chains

Abstract

Symmetrical and asymmetrical triphenylene discotic liquid crystals with two kinds of different peripheral chains, sym-TP(OC₁₁H₂₃)₃(O₂CR)₃ and asym-TP(OC₁₁H₂₃)₃(O₂CR)₃, (R= CH₂OC₂H₅, CH₂OC₃H₇, CH₂OC₄H₉, CH₂OC₅H₁₁, C₃H₇, C₄H₉, C₅H₁₁, C₆H₁₃, C₇H₁₅) were synthesized. Their thermotropic liquid crystalline properties were studied by polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). The results showed that the asymmetrical compounds had higher melting and clearing points than that of their corresponding symmetrical compounds. For the same series of compounds, TP(OC₁₁H₂₃)₃(O₂CR)₃, their melting points decrease and clearing points increase gradually with the lengthening of ester chains. Most of the b-oxygen containing esters of triphenylene derivatives, TP(OC₁₁H₂₃)₃(O₂CR)₃, (R=CH₂OC₂H₅, CH₂OC₃H₇, CH₂OC₄H₉, CH₂OC₅H₁₁), symmetrically or asymmetrically attached on triphenylene cores, have higher melting and clearing points than those of triphenylene derivatives, TP(OC₁₁H₂₃)₃(O₂CR)₃, (R=C₄H₉, C₅H₁₁, C₆H₁₃, C₇H₁₅), with the same length of peripheral chains. The triphenylene derivatives with longer peripheral chains have shown mesophase at room temperature.

Keywords

triphenylene / discotic liquid crystal / columnar mesophase / ether-ester mixed tail / beta-oxygen effect / molecular symmetry

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