10. Patented Literature 2616 10.1. Esterification 2616 10.2. Ether Formation 2619 10.2.1. Etherification without Cyclization 2619 10.2.2. Etherification with Cyclization 2624 10.3. N-Alkylation 2625 10.4. Other Reactions 2627 11. Summary and Outlook 2628 12. Note Added in Proof 2628 13. Abbreviations Used in This Review 2629 14. Acknowledgments 2629 15. Supporting Information Available 2630 16. References 2630

Mitsunobu and Related Reactions: Advances and Applications

This review focuses on structure-property relationships in liquid crystal oligomers, which consist of molecules containing two or more mesogenic units linked via flexible spacers essentially in a linear fashion and so does not consider, for example, liquid crystal dendrimers and tetrapodes. Previous reviews have tended to focus mainly on liquid crystal dimers in which just two mesogenic units are interconnected by a single spacer. By contrast, this review is largely devoted to higher oligomers such as liquid crystal trimers and tetramers containing three or four mesogenic units connected by two or three spacers, respectively.

Liquid crystal oligomers: going beyond dimers

Retention in reversed-phase liquid chromatography as a function of mobile-phase composition

A liquid crystal dimer is composed of molecules containing two conventional mesogenic groups linked via a flexible spacer. These materials show quite different behaviour to conventional low molar mass liquid crystals and in particular their transitional behaviour exhibits a dramatic dependence on the length and parity of the flexible spacer. In this review a comprehensive overview of the relationships between molecular structure and liquid crystallinity in dimers is provided. This includes a description of the novel modulated and intercalated smectic phases exhibited by dimers.

Liquid Crystal Dimers

The synthesis and characterisation of three sets of non-symmetric liquid crystal dimers consisting of a cholesteryl-based unit and either 4-methoxybiphenyl, 4-cyanobiphenyl or (S)-2-methylbutyl 4′oxybiphenyl-4-carboxylate are described. The transitional properties of these non-symmetric dimers are compared to those of the corresponding parent symmetric dimers. The symmetric dimers exhibit only chiral nematic or nematic phase behaviour. By contrast, members of the non-symmetric dimer series containing either 4-cyanobiphenyl or (S)-2-methylbutyl 4′-oxybiphenyl-4-carboxylate groups exhibit smectic behaviour. The former series show an interdigitated smectic A phase while for the latter the structure of the smectic A phase depends on the length of the flexible spacer. Specifically, for short spacer lengths a monolayer arrangement is seen while for long spacers an intercalated smectic A phase is formed. For an intermediate spacer length, the small-angle X-ray scattering pattern for the intercalated smectic A ph...

Symmetric and non-symmetric chiral liquid crystal dimers

A series of 4‐decyloxy‐4′‐hydroxybiphenyl esters of α,ω‐alkanedicarboxylic acids containing two mesogenic units connected by a methylene spacer was synthesized. The mesogenic properties of the compounds were investigated by polarising optical microscopy, differential scanning calorimetry and X‐ray diffraction methods. A strong influence of the spacer length and its parity on the mesomorphic properties was found. A dramatic odd–even effect was observed for the clearing temperatures and entropies. Compounds with an even number of carbon atoms in the methylene spacer formed tilted smectic phases, whereas compounds with an odd number of carbon atoms in the spacer exhibited the B4 phase, characteristic of bent‐shaped molecules.

Odd–even effect in biphenyl‐based symmetrical dimers with methylene spacer – evidence of the B4 phase

A series of novel side chain polymers−silylated polyethylenes were prepared containing 4‘-methoxyphenyl-4-(ω-alkenyloxy)benzoate mesogenic groups of the general formula {−CH2−CH[SiMe2(CH2)mOC6H4C(O)OC6H4OMe]}n−, where m = 4, 5, 8, 11. The ones having five and eight carbon atoms in the alkane moiety of a flexible spacer proved to be liquid crystalline, independent of molecular weight (DP = 75, 230). Alternative synthetic pathways have been described starting with anionic polymerization of Me3SiVi or Me2PhSiVi in the presence of BuLi, followed by functionalization of side silyl group to give reactive Si−H bonds and hydrosilylation of terminal, mesogenic alkenes. The properties of liquid crystal polyethylenes were compared with those of side chain polycarbosilanes of similar structure. The advantage of polyethylenes, while preserving all important features of polycarbosilanes, is shown by their broad temperature range of mesophase formation and the economically attractive synthesis.

Vinylsilanes as monomers for side chain polymer liquid crystals

Synthesis and liquid crystalline properties of cholesteryl bisesterimides with poly(ethylene oxide)s as central spacers

The series of liquid crystalline 4-[(4′-decyloxybiphenyl-4-yl)oxycarbonyl]phthalimide alkane acid methyl esters has been synthesized and studied by DSC, polarized optical microscopy and X-ray diffraction methods. All compounds form a monolayer smectic A phase. It was found that 2-{4-[(4′-decyloxybiphenyl-4-yl)oxycarbonyl]-phthalimido}propanoic acid methyl ester and 4-[(4′-decyloxybiphenyl-4-yl)oxycarbonyl]phthalimidoacetic acid methyl ester also form a ribbon S
 phase. It was shown clearly that in the former compound, transition from the S
 A1
 to S
 phase occurs via an intermediate S
 C1
 phase. The 6-{4-[(4′-decyloxybiphenyl-4-yl)oxycarbonyl]phthalimido}-hexanoic acid methyl ester exhibits smectic A
 1
 and C
 1
 phases only.

Evidence of the smectic antiphase in 4-decyloxybiphenyl ester imide derivatives

Synthesis and characterization of liquid crystal polycarbosilanes: poly(1-methyl-1-silaethylene), poly(1-methyl-1-silabutane) and poly(1-silabutane) with pendant mesogenic groups

Irma Śledzińska

Papers

Odd–even effect in biphenyl‐based symmetrical dimers with methylene spacer – evidence of the B4 phase

Vinylsilanes as monomers for side chain polymer liquid crystals

Synthesis and liquid crystalline properties of cholesteryl bisesterimides with poly(ethylene oxide)s as central spacers

Evidence of the smectic antiphase in 4-decyloxybiphenyl ester imide derivatives

Synthesis and characterization of liquid crystal polycarbosilanes: poly(1-methyl-1-silaethylene), poly(1-methyl-1-silabutane) and poly(1-silabutane) with pendant mesogenic groups