Evidence for lateral chain conformation change in the solid phase of substituted nematogens

Abstract A new homologous series of 4-(4-chlorobenzoyloxy)-2-alkoxy-3-methyl-4′-(4-trans-pentyl-cyclohexanoyloxy) azobenzenes has been synthesized. These compounds contain four rings in the main core, a lateral alkoxy branch and an adjacent lateral methyl group on one inner ring. They present a large nematic range and a solid-solid phase transition for the first members of the series. The crystal structures of two similar compounds containing a lateral butoxy chain have been solved. The HM4 compound (C31H33N2O5Cl) is derived from the series, but does not have the terminal pentyl chain while the PM4 compound (C36H43N2O5Cl) possesses this terminal chain. HM4 and PM4 crystallize, respectively, in P21/c (Z = 4) and P1 (Z = 2) space groups. The final reliability factors are R = 0.138 for HM4 (the terminal cyclohexyl ring is largely disordered) and R = 0.041 for PM4, for 2204 and 1963 observed reflections, respectively. The four ring central core is linear and rigid for both compounds. The conformation of the b...