Crystalline Behavior and Structure of a Liquid Crystal Compound, 5-{[4′-(((Pentyl)oxy)-4-biphenylyl)carbonyl]oxy}-1-pentyne

Abstract

Single crystals of two liquid crystal compounds, 5-{[4′-(((pentyl)oxy)-4-biphenylyl)carbonyl]oxy}-1-pentyne (A3EO5) and 5-{[(4′-nonyloxy-4-biphenylyl)carbonyl]oxy}-1-pentyne (A3EO9), have been prepared by solution growth technique. The morphologies and structures of A3EO5 and A3EO9 crystals were investigated by wide angle X-ray diffraction (WXRD), atom force microscope (AFM) and transmission electron microscope (TEM). In contrast to the same series of compounds which have a longer alkyl tail, 5-{[(4′-heptoxy-4-biphenylyl)carbonyl]oxy}-1-pentyne (A3EO7), 5-{[(4′-heptoxy-4-biphenylyl)oxy]carbonyl}-1-pentyne (A3E′O7) and A3EO9, A3EO5 shows strikingly different crystalline behavior. The former three compounds have only one crystal form, whereas A3EO5 exhibits polymorphism. Specifically, A3EO5 crystals grown from toluene solution show two crystal forms. The first one is crystal I which adopts a monoclinic P112/m space group with unit cell parameters of a5.79 Å, b8.34 Å, c43.92 Å, γ96°, and the other one is crystal II which adopts a monoclinic P112 space group with unit cell parameters of a5.55 Å, b7.38 Å, c31.75 Å, γ94°. When using dioxane as the solvent to grow A3EO5 crystal, we can selectively obtain crystal I. A3EO5 melt-grown crystals also have two crystal forms which derive from crystal I and crystal II, respectively. The different crystalline behavior of the compounds should correlate with their different electron dipole moment resulting from the different length of alkyl tail.