Crystal Structures of Helical Columnar pi-Conjugated Systems and Biodegradable Polyester

Crystal structures of helical columnar pi-conjugated systems, namely helicene-bisquinone and dendronized perylene bisimide derivative as well as of a biodegradable aliphatic polyester, namely poly-9-hydroxynonanoate, have been resolved by means of fibre X-ray diffraction. Enantiopure and racemic helicene-bisquinones are found to be organized into columnar liquid crystalline phases. The internal structure of the columns is 132 hollow helix with the asymmetric unit comprised of six-molecules, hence of 78 molecules and two turns in a period of 112 Å. The long-range order among the columns is found to be laterally high but longitudinally - low. This is the first atomic-level determination of a helical columnar liquid crystalline phase. The crystal structure of N,N’-di-(3,4,5-dodecyloxy-oxyphenylethyl)-perylene bisimide is approximated by distorted helical columns arranged within an orthorhombic unit cell with lattice parameters a = 70.2 ± 0.02 Å, b = 41.1 ± 0.02 Å, and c = 45.5 ± 0.02 Å. The space group is determined to be P212121. The internal structure of the columns is approximated by 61 helices. The structure is based on four-molecule repeat units (tetramers). There are 24 molecules and two turns in a 45.51 Å period of the distorted 6-fold helix. The tetramer is comprised of 2 dimers (two boat-shaped molecules placed side-by-side) facing each other in the tetramer. The rotation angle between the dimers within the tetramer is 100°. Charge mobility along the columns has been found to depend critically on the detailed molecular packing. The crystal structure of poly-9-hydroxynonanoate is established to be polyethylene-like except that the ester groups are randomly distributed throughout the lattice. The molecular chain of poly-9-hydroxynonanoate is determined to possess planar zigzag conformation with two such chains arranged within an orthorhombic unit cell with lattice parameters, a = 7.47 ± 0.02 Å, b = 5.00 ± 0.02 Å and c = 2.47 ± 0.02 Å. The space group is determined to be Pnam. The angle between the C-C-C... zigzag plane of poly-9-hydroxynonanoate and the b-axis is determined to be 32.7°. Torsion of carbonyl group at this particular angle between the C-C-C... zigzag plane of poly-9-hydroxynonanoate and the b-axis is determined to be 0°. Hitherto this is the first time that a space group for aliphatic polyester of the type [-(CH2)n-CO-O-]x with even number of methylene units between successive ester groups is determined because poly-9-hydroxynonanoate is the first to show Bragg reflections on the non-equatorial layer line.