Molecular Structure and Smectic Properties: Thermal Properties of Some Liquid Crystals Having a Nitro Group at the Terminal Position

Abstract

Abstract The thermal properties of ortho (o)-, meta (m)-, and para(p)-nitrophenyl 4-(4-alkoxybenzoyloxy)benzoates (1), 4-(4-alkoxyphenoxycarbonyl)phenyl o-, m-, p-nitrobenzoates (2), 4-(4-alkoxybenzoyloxy)phenyl o-, m-, p-nitrobenzoates (3), o-, m-, p-nitrophenyl 4-(4-alkoxyphenoxycarbonyl)benzoates (4), and some related compounds have been reported. For the p-nitro derivatives of compounds 1–4 the smectic A phase having a partially bilayer arrangement (SAd ) commences from the hexyloxy, nonyloxy, pentyloxy, and nonyloxy homologs, respectively, where the smectic A-nematic transition temperatures are almost independent of the orientation of the ester linkages. The p-nitro derivatives of compounds 2 and 3 also show two kinds of smectic A phases having bilayer (SA2 ) and/or monolayer (SA 1) arrangements at low temperature. All the m-nitro derivatives show smectic A phases, where 2 and probably 4 have the SA 2 phase, and 1 and 3 show the SA 1 one. The o-nitro derivatives fof compounds 2 and 4 show the SA 2 phase which commences from the nonyloxy homologs. The dielectric properties for m- and o-nitro derivatives have been examined. The results are discussed in terms of polar interactions around the substituents and linkages.