Synthesis And Mesomorphism Of Ferrocenyl Organometallic Liquid Crystals And Calamitic Liquid Crystals Containing Fluorinated Alkyl Chains

Liquid crystalline compounds containing a metallic atom in their structure combine properties (color, electronic denstity, magnetism and polarizability) of the metal with those of the mesogens. A large and predominant class of metallomesogens is ferrocene containing metallomesogens.Little work has been reported on monosubstituted ferrocene compounds, this could be attributed to their unfavorable molecular (L-shaphed geometry) and also to the repulsive steric effects of ferrocene unit. A possible way of minimizing the unfavorable steric effect would be to lengthen the mesogenic unit. Even small changes of the shape and structure of the molecules could have great influence over the type mesophase and transition temperature ranges. It's well known that fluorination has dramatic effect on mesomorphic behaviour. Fluorinated liquid crystals have been focused most attentions for its excellent feature, such as higher clearing points, wider mesophase temperature ranges, higher thermal stability than corresponding hydrocarbon ones. In general, nematic phases are depressed while segregated phases, such as smectic phases are favoured and sometimes even new mesophase types are generated.The thesis consists of four chapters:1. Chapter one briefly introduced the elementary knowledge about organometallic liquid crystal materials, then mostly introduced the studies on mono-substituted ferrocene-containing metallomesogens.2. Di-esters bridged monosubstituted ferrocene-containing metallomesogens, Fc-C6H4-COO-C6H4-OOC-C6H4-C6H4-OCnH2n+1 (n = 3~12, 14) , Fc-C6H4-COO-C6H4-OOC-C6H4-C6H4-OOCC8H17,Fc-C6H4-CO2-C6H10-OOC-C6H4-C6H4-OC6H13, C6H5-COO-C6H4-OOC-C6H4-C6H4-OCnH2n+1 (n = 6, 7) have been synthesized in chapter two. Studies of DSC and POM texture observations revealed that all of the compounds showed thermotropic nematic phases, their melting points and clearing points gradually lowering as the alkoxy chains lengthening, and the mesophase ranges are not narrowed. The phase types and mesophase temperature ranges are highly impacted by the orientation of the di-esters groups. Quantum chemistry calculations have showed that the alternation of the ester linkage results in a remarkable change in the dipole moments of ferrocene metallomesogens.3. In chapter 3, two series of liquid crystals: C6H5COO-C6H4-C6H4-OOCR,C6H5COO-C6H4-OOCR (R = -C2H4-C6X13 , -C6H4-C6X13 , X = F,H) and C6H5COO-C6H4-OOCC6H4-OC6H13 were synthesized and their mesomorphic behaviour were investigated through POM and DSC, those liquid crystals containing fluorinated terminal chains have higher clearing points and much broader ranges than their counterparts with hydrocarbon chains. And liquid crystalline properties also depend on length of rigid cores. The molecules with biphenyl core have higher melting points and clearing points than those with phenyl core.4. Chapter four gave the summary and conclusion of the thesis.