Mesogenic Benzothiazole Derivatives with a Polar Nitro Substituent†

Abstract

Two new mesogenic homologous series containing 6-nitrobenzothiazole moiety at the terminus of the molecule, viz 2-(4′-n-alkoxyphenylazo)-6-nitrobenzothiazoles and 2-[4′-(4”-n alkoxybenzoyloxy) phenylazo]-6-nitrobenzothiazoles were synthesized. The molecular structures of these new compounds of both the series have been characterized by elemental analysis, FTIR, and NMR spectral studies. The mesomorphic behavior has been studied using mainly polarized microscopy and in some cases differential scanning calorimetry as well. All the nine compounds of the series I are mesogenic and exhibit only the smectic A mesophase. In series II, all the twelve members synthesized exhibit enantiotropic mesomorphism. This series exhibits enantiotropic nematic mesophase from methoxy to n-heptyloxy derivatives. The smectic C mesophase commences from methoxy derivative, and persist up to n-butyloxy derivative, whereas the smectic A mesophase enters from the n-butyloxy derivative, and remains up to the last member synthesized. The mesomorphic properties of the present series are compared with other structurally related series to evaluate the effect of the benzothiazole ring and the polar nitro substituent on mesomorphism.