Synthesis and mesomorphic properties of symmetric and non-symmetric multi-functionalized oligomers

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dc.contributor.authorHng, Tiang Chuan
dc.date.accessioned2014-11-03T02:21:14Z
dc.date.available2014-11-03T02:21:14Z
dc.date.issued2009
dc.descriptionPhDen_US
dc.description.abstractSix series of novel symmetric and non-symmetric oligomers with multi-functional groups have been synthesized and characterized. The oligomers comprise two series of non-symmetric dimers, three series of symmetric trimers and one series of non-symmetric trimers. The first series of non-symmetric dimers, α-(4-benzylidene-substituted-aniline-4’-oxy)-ω-[2-methylbutyl-4’-(4”-phenyl)benzoateoxy]alkanes consists of ten homologues varying in terms of terminal substituents, X = H, CH3, F, Cl and Br as well as C6H12 and C8H16 spacers. The dimers exhibit the enantiotropic nematic phase except compounds with X = H. Both Br-substituted dimers also exhibit the intercalated SmA phase. The intercalated arrangement is the result, at least in part, of the more favourable interaction between the two unlike cores. The non-symmetric dimers in the second series, α-(4-benzylidenechloroaniline-4’-oxy)-ω-[4-(thiophene-2-carboxyl)benzylideneaniline-4’-oxy]alkanes with spacers ranging from C5H10 to C12H24 are all enantiotropic mesogens. The nematogenic properties indicate the predominant terminal attraction between the 4-benzylidenechloroaniline and thiophene-2-carboxylate cores. Strong odd-even effect in terms of the nematic-isotropic transition temperatures of the dimers has also been recorded. In the third series of oligomers, the symmetric trimeric 4,4’-bis{ω-[2-methylbutyl-4’-(4”-phenyl)benzoateoxy]alkyloxy- benzylidene}-1,4-diaminobenzenes are chiral nematogens and smectogens. Apart from the chiral nematic phase, every homologue in this series also exhibits the SmA phase enantiotropically. The chiral SmC phase is also observed for the homologues with spacers from C5H10 to C9H18. Additionally, the odd members exhibit the blue phase and monotropic high-order smectic phase. Another two series of trimers with lateral substituents namely the 4,4’-bis{ω-[2-methylbutyl-4’-(4”-phenyl)benzoateoxy]-3-methoxy-4-alkyloxybenzylidene}- 1,4-diaminobenzenes and 4,4’-bis{ω-[2-methylbutyl-4’-(4”-phenyl)benzoateoxy]-3-bromo-4-alkyloxybenzylidene}-1,4-diaminobenzenes have been prepared. With the presence of lateral methoxy groups, the four even trimers exhibit the enantiotropic chiral nematic phase whilst the odd members are not mesogenic. On the other hand, every Br-substituted trimer in the series exhibits the enantiotropic chiral nematic phase except the trimers with C5H10 and C11H22 spacers. Whilst the C5H10 trimer is not mesogenic, the member with C11H22 spacers exhibits the monotropic chiral nematic phase. The trimers with C7H14 and C9H18 spacers also show the blue phase. The lower phase thermal stability and nematogenic behaviour of the trimers with lateral substituents is the result of lateral hindrance for intermolecular interaction. In the sixth series of oligomers, the non-symmetric trimeric 4-ethyl- and 4-fluoroanilinebenzylidene-2’,4’-oxybis(4”-halogenoanilinebenzylidene-4”’-oxy)alkanes incorporate either a terminal chlorine or bromine atom. The trimers also vary from each other in terms of C4H8 and C6H12 spacers. The trimers are nematogenic with low transition temperatures due to the branched molecular architecture. Three of the members with ethyl group are also glassy nematogens with glass transition temperatures less than 15°C.en_US
dc.identifier.urihttp://hdl.handle.net/123456789/283
dc.language.isoenen_US
dc.subjectChemical scienceen_US
dc.subjectMesomorphicen_US
dc.subjectOligomersen_US
dc.titleSynthesis and mesomorphic properties of symmetric and non-symmetric multi-functionalized oligomersen_US
dc.typeThesisen_US
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