The effect of a triple bond in a terminal chain on the mesomorphic properties of rod-like mesogens was studied by replacing a straight alkyl chain with a terminal 1,2-alkynyl chain in some esters and thioesters of the type:[GRAPHICS]or by incorporating the triple bond into an alkyl ester chain in esters and thioesters of the types:[GRAPHICS]The triple bond should provide increased rigidity to the triple bond region but increased flexibility at the adjacent single bond. These should have opposite effects on the mesomorphic properties. The first compounds were synthesized by esterification of the appropriate alkynylbenzoic acids with various phenols or thiols using the carbodiimide method. Detailed syntheses are provided for the alkynylbenzoic acids. Preparation of the alkynyl ester compounds was by acylation of the precursor hydroxyl esters or thioesters using either the acid chloride or carbodiimide method. The synthesis of the phenolic or thiolic ester intermediates, usually using a protection group, is described. Mesomorphic properties of these new esters and thioesters were determined using hot stage polarizing microscopy and DSC and compared with those for the known parent compounds. Fewer mesophases having shorter temperature ranges and lower transition temperatures were usually observed. Some of the intermediate phenols or benzyl ethers were also studied. Long chain benzyloxy esters showed a nematic phase as did some of the hydroxy thioesters but no mesophases were observed in the hydroxy esters.

Small quantities of the floppy bimesogen di(4PPB5)3Si were dissolved in an anticlinic liquid crystal consisting of a mixture of left-handed and right-handed TFMHPOBC, with enantiomer excess X=0.2 . The bimesogen dopant was found to promote anticlinic order with an anticlinic interaction coefficient per molecule udopant smaller than, but of the same order as, that of the rigid bent-core dopant P-7PIMB. For both dopants udopant was found to be much larger than that due to a pair of TFMHPOBC molecules in adjacent layers. The results are examined in terms of both the flexibility of the group linking the two legs of each dopant, as well as their chemical structure.

Small quantities of the bent-core mesogen P-7PIMB were dissolved in an anticlinic liquid crystal consisting of a mixture of left- and right-handed TFMHPOBC, with enantiomer excess X=0.2. The bent-core dopant promotes anticlinic order at higher temperatures, but becomes less effective in suppressing the synclinic phase at the reentrant synclinic transition due to an orientational transition of the dopant within the calamitic TFMHPOBC matrix. Measurements of the anticlinic-synclinic electric-field switching threshold as a function of temperature and dopant concentration facilitate a determination of the component of the anticlinic interaction coefficient U that is due to the bent-core dopant. It is found that the value of U per bent-core molecule is much larger than the corresponding value for a pair of TFMHPOBC molecules in adjacent smectic layers.

A limited selection of ring modified diphenyldiacetylenes of the typewhere A = ,Y =CnH2n+1, CF3, F, COMe, NH2, and NMe2, and A = -[GRAPHICS], trans and cis with Y=F and trans with Y=C3H7, were synthesized. Mesomorphic properties were determined by hot stage polarizing microscopy and DSC. These properties were generally poorer than those found in the parent benzene compounds. This was also true of some pyrimidine analogues reported earlier. Birefringence values also decreased as expected.

A variety of terminal chain modifications (Y) were made on the diacetylenes[GRAPHICS]in which X = CnH2n+1, C12H25O and F, and Y = CH2CH(Me)C2H5, COCH3, C = CC5H11, CnF2n+1 (sic) CnH2n+1 and CH = CHCO2C3H7. Mesomorphic properties were determined by hot stage polarizing microscopy and DSC. These were compared with those for the dialkyl analogues (X = CmH2m+1, Y = CnH2n+1) and a series of 1- and 2-olefins (Y = CH = CHCnH2n+1 and CH2CH = CHCnH2n+1). The 1-olefin series showed wider range nematics than the dialkyl compounds, whereas the above modifications showed either narrow range nematic phases, no mesophase or higher melting temperatures. New transition temperature and enthalpy data are provided for some of the dialkyl and F-alkyl compounds previously reported, for comparisons. Preliminary birefringence data are also included along with the results of some heat and UV stability studies.

Small quantities of the bent-core mesogen P-7PIMB were dissolved in an anticlinic liquid crystal consisting of a mixture of left- and right-handed TFMHPOBC, with enantiomer excess X=0.2. For bent-core concentrations above C=3 wt %, differential scanning calorimetry shows the disappearance of the higher temperature synclinic phase, as well as the appearance of a new peak at a low temperature T c. Polarized infrared absorption measurements indicate that the new DSC peak is due to an orientational transition of the bent-core molecules, analogous to the transition previously observed in a smectic A matrix. For T>T c the plane of the bent-core molecules lies in the tilt plane of the anticlinic matrix, with the arrow (the symmetry axis) of the bent-core molecules parallel to the smectic layers. For T<T c we deduce that the bent-core molecules lie within a single smectic layer, with the polar tilt of the arrow approximately equal to the polar tilt of the TFMHPOBC molecule and the vector connecting the two ends of the bent-core molecule perpendicular to the anticlinic tilt plane. Additionally, T c was found to be an increasing function of bent-core concentration.

New diphenyldiacetylenes of the type with A, B = H and/or F; m = 0, 1; n = 1–4; and X = C n H2n+1, F, CF3 or CN were synthesized and their mesomorphic properties determined by hot stage polarizing microscopy and DSC. When m = 0, all of these compounds showed only a nematic phase except when X = CF3 when both nematic and smectic A phases were seen. Both clearing and melting temperatures were higher than those reported for substitution with the corresponding alkyl chains but the much larger increase in clearing temperatures produced considerably wider nematic phases. Eutectic mixtures of a few of these olefins yielded nematic materials also having much wider temperature ranges and higher clearing temperatures than the eutectic mixtures of the alkyl compounds, while retaining their high birefringence and low viscosities. Such materials are of interest for beam-steering devices. Four of the diacetylenes with m = 1 (A, B = H) were also prepared (X = C6H13, F, n= 2, 3). When X was C6H13 (n=2), the nematic range was smaller in the 2- than in the 1-olefin but wider than in the alkyl series. When X=F, either no nematic phase or a monotropic one was observed, whereas the 1-olefins gave a much wider nematic phase. Both transition temperatures were lower than those for the corresponding 1-olefin and alkyl analogues. The compound with X=C6H13 and n=2 had a melting temperature below room temperature.

Liquid crystals (LCs) with diazo linkages have high dielectric and optical anisotropy. Two newly synthesized liquid crystalline compounds were dissolved in room temperature LC hosts, E7 and PTTP-24/36, to assess their properties. It was found that these mixtures have higher birefringence, larger dielectric anisotropy, and better elastic properties than the hosts. Satisfactory viscoelastic coefficients were also obtained for these mixtures, showing that they are promising LC materials for applications in the near IR region.