Tilt orientationally disordered hexagonal columnar phase of phthalocyanine discotic liquid crystals

Abstract

The structures of the discotic liquid crystalline (LC) phase of metal-free octa-substituted phthalocyanine (Pc) derivatives were investigated using molecular dynamics (MD) simulations. Special attention was paid to the LC phase structure of the non-peripheral octa-hexyl substituted Pc-derivatives that were recently found to show very high carrier mobilities for the discotic LCs. We obtained spontaneous transition to the columnar hexagonal (Col_{h}) LC phase in a melting simulation from the crystal structure obtained using an x-ray diffraction study. In this simulated Col_{h} structure, the Pc-core normal vectors were tilted 47{∘} from the column axis in parallel within each column, but the tilting directions are disordered between columns. We also found that the inter-core distance was not as large as previously suggested (0.4-0.5 nm) but similar to the common value (0.36 nm). This may resolve the contradiction between the high carrier mobility of the non-peripheral substituted Pcs, because larger inter-core separations degrade the mobilities.

Macroscopically aligned molecular stacking structures in mesogenic phthalocyanine derivative films fabricated by heated spin-coating method

“…Since the measured results coincided with the calculated data with the assumed optic axis direction tilting by 24° with respect to incident light, it is considered that the normal vectors of the C6PcH 2 molecules were tilted by 66° with respect to the column axis direction. The obtained tilting angle is in agreement with previously reported value of 64°, which was focused on the single crystals of C6PcH 2 [19,20]. Therefore, although it is the non-equilibrium fabrication method, highly ordered crystalline structure was obtained by simply controlling the process temperature.…”

“…As shown in Fig. 3(a), the strong diffraction peaks were observed at 2θ = 4.9°, which originate from the inter-column distance of the hexagonal columnar structure according to previous reports on the crystalline structure of C6PcH 2 single crystal [19,20]. The diffraction peak intensity depended on the process temperature, and the peaks with the higher-order diffraction were obviously observed when the process temperature was 150 °C.…”

“…From the results of the textures and X-ray diffraction of the films fabricated at the process temperatures corresponding to the LC phase, the anisotropic optical properties based on the planarly aligned columns of C6PcH 2 were prospective. Since the temperature dependence of the crystalline structure of C6PcH 2 was reported [20], it is considered that long crack lines observed in Figs. 2(c) and 2(d) appear upon cooling and direction of crack line have a strong relationship with that of column axis.…”

Liquid crystalline and charge transport properties of novel non-peripherally octasubstituted perfluoroalkylated phthalocyanines

“…25 The DFT calculation of phthalocyanine is reported to show that the spatial distribution of the HOMO is larger than the LUMO at the edge of the phthalocyanine ring (the peripheral sites), 26 and this may provide a possibility of charge hopping from edge to edge of neighbouring phthalocyanine molecules. 28 This phase shows a high degree of molecular contact among columns, which would encourage a two-dimensional transport of carriers and hence help to explain the high mobilities observed for this material. J. Tant et al reported that the rotation angle along the molecular axis normal to the plane is sensitive to the transfer integral in a faceto-face dimer of phthalcyanine where 45 periodicity of electronic splitting energy oscillation is predicted on the symmetry of the phthalocyanine ring.…”

Single crystal growth and X-ray structure analysis of non-peripheral octahexyl phthalocyanine

“…Such high mobility and the photovoltaic property are expected to be related to the self-organized molecular packing structure of C6PcH 2 [14,15]. Therefore, the molecular packing structures of C6PcH 2 in the liquid crystal phase and crystal phase have been previously studied [16][17][18][19].…”