A systematic study on the influences of linkage length on phase behaviours and charge carrier mobilities of discotic dimers

ABSTRACT

Two series of discotic dimers T3Dn and T5Dn based on hexapropoxytriphenylene (HAT3) and hexapentyloxytriphenylene(HAT5), respectively, with polymethylene linkage O(CH₂)_nO (n = 3–12) have been synthesised. Their mesomorphism was investigated by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction. The results showed that side chains induced a phase transition from col_hp phase to col_h phase, namely dimers T3Dn (n = 6–12) based on HAT3 exhibiting a single col_hp phase, dimers T4Dn (n = 6, 7, 11, 12) based on HAT4 showing a highly ordered col_hp phase in low-temperature region and a col_h phase in high-temperature region, dimers T4Dn (n = 8–10) based on HAT4 displaying a single col_hp phase and dimers T5Dn (n = 6–11) based on HAT5 indicating a single col_h phase. Dimers T4Dn showed a phase competition between col_h phase and col_hp phase induced by linkages. Surprisingly, a unique phenomenon was found by us, that is, those compounds in which linkage lengths were twice those of side chains showed the largest enthalpies, the smallest intracolumnar spacings and the highest charge-carrier mobilities among their homologues, respectively, which implied that they formed the most highly ordered phase among their homologues.

Graphical Abstract

KEYWORDS:

• Discotic liquid crystal (LC)
• discotic dimer
• triphenylene
• perfect twin
• columnar phase

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

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Additional information

Funding

This work was supported by the Beijing Municipal Education Commission Project: [Grant Numbers 23190115024, 25000115006 and Byyc201316-007], the Importation and Development of High Caliber Talents Project of Beijing Municipal Institutions: [CIT&TCD201304123] and the National Natural Science Foundation of China:[21174016].