Abstract
A new synthetic approach to highly substituted triphenylboroxines 11 is described. Their mesomorphic properties were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X-ray diffraction (SAXS, WAXS). The tris(3,4,5-trialkyloxy)phenyl functionalized derivatives 11b–e showed broad mesophases for a minimum alkyl chain length of C9. The phase widths ranged from 110 K to 77 K near room temperature, thus decreasing with enhanced alkyl chain lengths. Textures observed under POM indicated a columnar hexagonal (Colh) mesophase symmetry that was confirmed by X-ray diffraction experiments.
Highlights
The discovery of stable liquid crystalline phases formed by disk-shaped molecules with long alkyl chains in their periphery is generally dated to the seminal work of Chandrasekar published in 1977 [1]
Due to the one dimensional charge and ion transport in the columnar mesophase, the ability of liquid crystals (LCs) to self-heal structural defects by thermal annealing and the ease of processing via spin coating, drop casting and other solution processing methods highly useful applications [5,6,7] could berealized such as organic solar cells [8], organic field effect transistors [3] and organic light emitting diodes [9]
Besides tri- and hexasubstituted benzenes, in particular triphenylenes [10], perylenes [11], hexa-peri-hexabenzocoronenes [12,13], porphyrins [14,15], phthalocyanines [15], quinoxalines and other aza analogues of polycyclic aromatic hydrocarbons were used as mesogenic subunits
Summary
The discovery of stable liquid crystalline phases formed by disk-shaped molecules with long alkyl chains in their periphery is generally dated to the seminal work of Chandrasekar published in 1977 [1].Since discotic liquid crystals have attracted the attention of many research groups worldwide [2,3,4].Due to the one dimensional charge and ion transport in the columnar mesophase, the ability of liquid crystals (LCs) to self-heal structural defects by thermal annealing and the ease of processing via spin coating, drop casting and other solution processing methods highly useful applications [5,6,7] could berealized such as organic solar cells [8], organic field effect transistors [3] and organic light emitting diodes [9].From a molecular perspective, several scaffolds have turned out to be successful candidates for the nanosegregation, which led into the formation of columnar mesophases. The discovery of stable liquid crystalline phases formed by disk-shaped molecules with long alkyl chains in their periphery is generally dated to the seminal work of Chandrasekar published in 1977 [1]. Due to the one dimensional charge and ion transport in the columnar mesophase, the ability of liquid crystals (LCs) to self-heal structural defects by thermal annealing and the ease of processing via spin coating, drop casting and other solution processing methods highly useful applications [5,6,7] could berealized such as organic solar cells [8], organic field effect transistors [3] and organic light emitting diodes [9]. Disk-shaped mesogens, and non-conventional [16] and supramolecular and hydrogen bonded liquid crystals [17] can self-assemble into columnar aggregates. While a variety of LC materials containing heterocyclic 6-membered rings have been synthesized [18], e.g., triazines such as
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