Mesomorphic behaviour of N-benzoyl-N′-aryl thioureas liquid crystalline compounds

A series of N-benzoyl-N′-aryl thiourea derivatives bearing alkoxy groups in terminal positions have been prepared and investigated for their potential liquid crystals properties. It was found that only the compounds which have only two alkoxy chains show calamitic mesomorphic behaviour, with nematic, smectic A and C phases being displayed. The type and stability of these mesophases are greatly influenced by the alkyl chain length. Successive introduction of additional alkoxy groups on the benzoyl moiety led to a significant decrease of the clearing points and suppression of the mesogenic character. Using of branched alkyl chain, 2-ethyl-hexyl, instead of normal alkyl group, led to the disappearance of mesogenic behaviour together with the lowering of the clearing temperature. The influence of chain length and number of chains is discussed.