To be or not to be – nematic liquid crystals from shape-persistent V-shaped nematogens with the ‘magic angle’

Abstract

<p>The tetrahedral bending angle in V-shaped nematogens was claimed to be the optimum for finding a biaxial nematic liquid crystal phase. The benzo[1,2-b:4,3-b’]dithiophene core, recently successfully applied as a tetrahedral bending unit in mesogens with lateral flexible chains, is here embedded in a scaffold with only terminal chains, which conventionally promotes the formation of nematic phases at low temperature. A series of new mesogens has been successfully prepared, realising hockey-stick, hockey-stick dimer and V-shaped molecular topologies. Only the hockey-stick mesogens assemble in uniaxial nematic phases over a broad temperature range. Single crystal structure analysis of a hockey-stick and V-shaped compound reveal remarkable similarities with the benzodithiophene core wrapped by aliphatic chains. A model explaining the absence of nematic mesophases in the family of V-shaped, shape-persistent mesogens with terminal aliphatic chains is presented and results in the proposal of a new design for biaxial nematogens.</p