Synthesis, transition temperatures, and optical properties of various 2,6-disubstituted naphthalenes and related 1-benzothiophenes with butylsulfanyl and cyano or isothiocyanato terminal groups

Fourteen compounds based on 2,6-disubstituted naphthalenes or related 1-benzothiophene moieties with butylsulfanyl and cyano or isothiocyanato terminal groups have been synthesised. The transition temperatures of the compounds and their refractive indices have been determined and the derived values for the optical anisotropies, polarisabilities and order parameters have been calculated. With one exception (which also shows a smectic A phase), all the compounds with naphthyl and phenyl groups are solely nematogenic; for these compounds the naphthyl unit gives an average increase in TN-I value and melting point of 72 and 20 degrees C respectively compared to the values for the compounds with a phenyl in place of the naphthyl unit. The incorporation of a 2,5-thiophene unit in place of phenyl lowers TN-I and when it is part of a 1-benzothiophene unit the depression is even greater. The naphthalene compounds increase the values of optical anisotropy by approximately 0.04, compared to the phenyl systems, mainly because they increase the refractive index of thee-ray (n(parallel to;) values); compound 12 has an exceptionally high optical anisotropy (Delta n value) of 0.54.