Modulation of phase behaviors and charge carrier mobilities by linkage length in discotic liquid crystal dimers

Abstract

A clear structure–property relationship was revealed in a series of triphenylene-based dimers, which contained two triphenylene nuclei each bearing five β-OC₄H₉ substituents and are linked through a flexible O(CH₂)_nO polymethylene chain (n = 6–12). Dimers with the linkage close to twice the length of the free side chains (n = 8, 9) exhibited a single Col_hp phase, while others with the linkage shorter (n = 6, 7) or longer (n = 10, 11, 12) showed multiphase behaviors with a transition from the Col_hp phase to Col_h phase; hole mobilities of Col_hp phases reached 1.4 × 10⁻² cm² V⁻¹ s⁻¹ in the dimer for which the linkage is exactly twice the length of the free side chains (n = 8), and decreased regularly both with linkage length becoming shorter or longer. This modulation of phase behaviors and charge carrier mobilities was demonstrated to be generated by various steric perturbations introduced by linkages with different lengths, which result in different degrees of lateral fluctuations of discotic moieties in the columns.