Synthesis and mesomorphic properties of α-methylstilbene-based liquid crystals

Abstract

Six series of α-methylstilbene-based liquid crystals, i.e. 4-(4-alkylphenyl)-4′-amino-α-methylstilbenes (2a–e), 4-(4-alkylphenyl)-4′-cyano-α-methylstilbenes (3a–e), 4-(4-alkylphenyl)-4′-isothiocyanato-α-methylstilbenes (4a–e), 4′-(trans-4-alkylcyclohexyl)-4-fluoro-α-methylstilbenes (5a–e), 4′-(trans-4-alkylcyclohexyl)-4-amino-α-methylstilbenes (7a–e) and 4′-(trans-4-alkylcyclohexyl)-4-isothiocyanato-α-methylstilbenes (8a–e) were synthesised. All of these α-methylstilbene-based compounds exhibit an enantiotropic nematic phase. Some of the 4-(4-alkylphenyl)-4′-isothiocyanato-α-methylstilbenes with longer alkyl chains exhibit a smectic A phase. All of the liquid crystals obtained exhibit a wide nematic range and high birefringence of 0.16–0.46. Both series of isothiocyanato-based, liquid crystal compounds 4a–e and 8a–e containing α-methylstilbenes revealed much lower melting points and clearing temperatures than their cyano and amino homologues.

Keywords:

• α-methylstilbene liquid crystals
• isothiocyanato liquid crystals
• high birefringence

Acknowledgement

The authors are grateful to the National Science Council of the Republic of China and the Ministry of Education (MOE ATU Program) for financial support of this work.