We report polarization-analyzed, resonant x-ray diffraction at the sulfur K edge performed upon free-standing liquid-crystal films. Our studies of the thiobenzoate liquid-crystal enantiomer 10OTBBB1M7 yield the polarization states of resonant satellite peaks arising from characteristic superlattices in the chiral smectic-C (SmC(*)) variant phases, including the antiferroelectric SmC(*)(A), ferrielectric SmC(*)(FI1) and SmC(*)(FI2), as well as SmC(*)(alpha). The observed polarizations agree with the clock model of chiral smectic-C variants, and rule out other proposals made to date for these structures. Data from the 10OTBBB1M7 racemate also support the clock model. Our resonant diffraction results from a thiophene liquid-crystal compound reveal the same superlattice periodicities seen in corresponding antiferroelectric and ferrielectric phases of 10OTBBB1M7.

The phase transition temperatures, birefringence and visco-elastic coefficient of several high birefringence isothiocyanato tolane compounds were evaluated. The polarizability of these compounds was calculated by the Austin Model 1 (AM1) and Modified Neglect of Diatomic Overlap (MNDO) methods. Using these compounds, we have formulated a eutectic mixture exhibiting a wide nematic range and high figure of merit.

The majority of low molar mass calamitic mesogenic systems in the literature contain linear cores based on the 1,4-disubstituted phenyl ring. Heterocyclic cores such as thiophene impart unique physical properties as their slightly bent structure leads to features including a reduced packing ability (generally giving rise to lower melting points than their phenyl counterparts), a medium to strong lateral dipole, high anisotropy of the polarizability, low viscosity etc. This critical review describes the most recent synthetic methodology that has been used to prepare thiophene, 1,3-thiazole, and 1,3,4-thiadiazole-based mesogenic materials.

The structures of the liquid crystalline chiral subphases exhibited by several materials containing either a selenium or sulphur atom have been investigated using a resonant x-ray scattering technique. This technique provides a unique structural probe for the ferroelectric, ferrielectric, antiferroelectric, and SmC(*)(alpha) phases. An analysis of the scattering features allows the structural models of the different subphases to be distinguished, in addition to providing a measurement of the helical pitch. This paper reports resonant scattering features in the antiferroelectric hexatic phase, the three- and four-layer intermediate phases, the antiferroelectric and ferroelectric phases and the SmC(*)(alpha) phase. The helicoidal pitch has been measured from the scattering peaks in the four-layer intermediate phase as well as in the antiferroelectric and ferroelectric phases. In the SmC(*)(alpha) phase, an investigation into the helical structure has revealed a pitch ranging from 5 to 54 layers in different materials. Further, a strong resonant scattering signal has been observed in mixtures of a selenium containing material with as much as 90% nonresonant material.

The optical anisotropies, polarisabilities, refractive indices and order parameters of 4-cyanophenyl and 4-isothiocyanatophenyl 4'-butylsulfanylbenzoates with oxy-and thio-substitution in all possible combinations in the ester link have been measured and the results are discussed in terms of the position and number of sulfur atoms in the ester linkage. The S-aryl thio-and dithio-benzoates have greater polarisabilities than the corresponding 0-aryl esters; the differences between 0-aryl and S-aryl thiobenzoates are discussed in terms of the electronegativity and structural changes caused by substitution with sulfur. 2 15 5 X=NCS 6 X=CN 16 X=CN 17 X=NCS Scheme 3 Reagents: 3a, (i) Mg, carbon disulfide, (ii) HC1; 3b, N,N'dicyclohexylcarbodiimide, 4-(dimethy1amino)pyridine 15 10 X=CN 12 x = w s 18 X=CN 19 X = NCS Scheme 4 Reagents: 4a, N,N'-dicyclohexylcarbodiimide, 4-(dimethylamino) pyridine Paper 4/02841D;