Remarkable stabilisation of the intercalated smectic phases of nonsymmetric dimers by <i>tert</i>-butyl groups

The synthesis and characterisation of two groups nonsymmetric dimers, the 1-(4-cyanobiphenyl-4‘−yloxy)-ω-(4-butyl, 4-(1-methylpropyl) or 4-t-butylanilinebenzylidene-4’−oxy)alkanes, 1-(4-cyanobiphenyl-4‘−yl)-ω-(4-butyl, are reported. length parity flexible spacer is varied. tert-butyl homologues show higher melting points than corresponding sec-butyl n-butyl substituted suggesting that chain branching improves packing efficiency within crystalline structure. branched have a stronger tendency to exhibit smectic phases n-butyl-substituted for longer spacers exclusively smectic. A comparison nematic-isotropic transition temperatures (TNI) dimers containing different terminal chains possible one set materials, reveals large reduction in TNI on passing from sec-butyl-substituted, but much smaller decrease changing tert-butyl. trend observed A-isotropic which value homologue, only marginally lower dimer. This surprising behaviour interpreted terms ability group pack more efficiently into intercalated phase as increases.