OLIGOSACCHARIDE-BASED THERMOTROPIC LIQUID-CRYSTALS .4. SYNTHESIS OF CELLOBIOSE-BASED TWIN AND TRIPLET DERIVATIVES AND THEIR MESOPHASE PROPERTIES

Previous work from this laboratory has shown that cellobiose octaalkan oate (COA) functions as a thermotropic discotic mesogen, forming a hex agonal ordered columnar phase (D-ho). In this work, we prepared the CO A-based discotic twin and triplet derivatives and examined the mesomor phic properties of the derivatives by DSC, polarization microscopy and X-ray diffraction. In the former derivative, two cellobiose heptadeca noate (CHD) molecules (monomers) are combined through an alkyl spacer of varying length by ether and ester linkages at the C-1 position of t he reducing end units of the monomers. Three CHD molecules having an a lkyl spacer are connected with a coupling agent for the latter derivat ive. The results revealed that (i) all the twin derivatives form a dis tinct discotic columnar phase, (ii) the thermal stability of the mesop hases of the twins is enhanced, compared with that of the monomer, whe n the length of the flexible spacer is appropriate, (iii) the twins wi th a relatively short spacer form a discotic rectangular ordered (D-ro ) phase, while those with a longer spacer form a pseudo-D-ho phase, (i v) the triplets also form a discotic columnar mesophase, but not a hex agonal ordered columnar (D-ho) phase, (v) the thermal stability of the mesophases of the triplets strongly depends on the chemical nature of coupling cores, and (vi) the packing structures of the cellobiose cor es within the columns of both derivatives are markedly different from that of the monomer.