Design, Synthesis And Mesomorphism Of Discotic Hexa-peri-hexabenzocoronene Derivatives

Organic opto-electrical functional materials represent one of the most important classes of advanced materials in recent years. The extensive amounts of research in the field are driven by the promise of low-cost processing applications that are typical of organic materials over their inorganic counterparts. The greatest advantage of organic materials is the diversity of structures and tunability of properties offered through molecular design.Discotic molecules, as molecular electronic materials, have strong tendency to form columnar stacking with strong overlap of adjacent molecular cores, providing for high charge mobility along the direction of central axis of assemblies. It is necessary that such molecules possess planar hard aromatic core which is nearly uniformly surrounded by long and soft chains in order that flexible aliphatic chains provides opportunities to control the solubility and thermal behavior. This kind of molecular design and synthesis have been continuing to play an important role in studying discotic liquid crystals.Hexabenzocoronene (HBC), as the smaller graphene fragment consisting of 13 fused benzene rings, possesses a strong tendency to stack together viaÏ€-electronic interactions. It has been becoming a challenge that how to modify HBCs chemically and extended analogues, such as the introduction of alkyl substituents with heteroatom-containing and functional groups as well as the variation of topologies and molecular symmetries.In this thesis, three synthons, 4, 4′- dibromodiphenylacetylene (a) 4,4′-dibromomethyldiphenylacetylene (b) and hexakis-(4– bromomethy l-1-yl) benzene(c)(Fig. 1), were synthezised efficiently for the fabrication of long-range oriented discotic molecules. By these synthons, two HBC derivatives HBC-C₁₂, HBC-C₁₅ (Fig. 2, X=CH₂, n = 9 and 12 respectively), bearing odd/even-carbon substituents as discotic liquid crystals were synthesized. These molecular structures were characterized by 1HNMR and UV-vis spectrum. The experimental results indicated that these compounds were obtained in good yields. The thermal and liquid crystalline properties of HBC-C15 were completely characterized by differential scanning calorimetry, polarized optical microscopy.In addition, a novel Hexabenzocoronene precursor, HPB-C-S-C₁₂, one of hexaphenylbenzene derivatives bearing hexa-substituents with heteroatom - containing, was synthezised successfully. Unfortunately, although taking a lot of efforts, this hexa- functionalized hexaphenyl- benzene could not be transferred to the corresponding HBC derivative (Fig.3), due to incompatibility between benzyl oxide and Lewis acid under nomal conditions.Further researches in this field by regulating the relevant factors, such as reaction temperature, different catalysts, the amount of catalysts and different solvents, were discussed.