Tailoring the Thermotropic Behavior of Tetra-Substituted Phthalocyanines via the Lateral Chains Architecture

Abstract

Four newly synthesized alkoxy tetrasubstituted phthalocyanines (Pcs) were characterized by polarized optical microscopy, differential scanning calorimetry, and X-ray diffraction on oriented samples. It was found that the introduction of lateral alkyl chains branched in the second position renders the material liquid crystalline at room temperature. The studied Pcs exhibit a transition between a columnar hexagonal and a columnar rectangular phase. The tilt of the molecules with respect to the columnar axis in the rectangular phase, as measured by X-ray fiber diffraction, was found to be 15−18°. The columnar structure, and defects therein, in relatively thick spin-coated mesomorphic Pc films were for the first time characterized by tapping mode atomic force microscopy, employing ultra-sharp tips with nanometer-thick whiskers. Spin-coated films reveal layerlike structure with domain boundaries that can induce significant columnar curvature without breaking of the columns. In some instances, the boundaries delimiting different LC domains completely disrupt the columnar structure making the columns in neighboring regions uncorrelated.

Absorption, Photoluminescence, and Polarized Raman Spectra of a Fourfold Alkoxy-Substituted Phthalocyanine Liquid Crystal

“…Grazing incidence X-ray scattering for thin films 48 yields a θ 00 angle (between stack and normal to the surface) of 17°, in agreement with previous literature. 9 All θ angles between |θ 0 À θ 00 | ≈ 0°and |θ 0 þ θ 00 | ≈ 32°would be possible in the absence of correlation between θ 0 and θ 00 . For this reason, the finding that the allowed values of θ are well below the maximum possible angle |θ 0 þ θ 00 | indicates that θ 0 and θ 00 are highly correlated and tend to compensate each other, yielding an arrangement in which the molecular cores are, on average, approximately parallel to surface, as first stated in ref 48.…”

“…This result, which is the first direct constraint on θ, is consistent with the available information on θ 0 and θ 00 . The analysis of the angular dispersion of the X-ray scattering intensity 9 yields a most probable θ 0 angle (between molecular and stack axes) around 15°. This value is in agreement with the results of recent MD simulations 47 for the Col r phase, which exhibit a broad distribution of θ 0 angles between 0 and 25°, with a maximum at 15°.…”

Using spin polarised positive muons for studying guest molecule partitioning in soft matter structures

“…33). Morphological features in the form of striations forming a crosshatch [126,127] are attributed to the columnar rectangular phase, A 8 . A typical fan-shaped texture resulting from the thermomechanical undulation of the columns [128,129] was observed from the columnar hexagonal phase, E 10 .…”

Doping and photo-induced current in discotic liquid crystals thin films: Long-time and temperature effects

“…DLCs are formed by a rigid aromatic core and highly flexible peripheral chains, which provide solubility and drive self-organizing properties of these materials in columns forming different mesophases [13,14].…”

“…The relevant properties arise from their self-assembling behavior governed by a combination of the strong p-p overlap between individual molecules [15] and the interaction of peripheral functional groups, which allow the formation of the columnar mesophases [13][14][15][16]. Many theoretical studies have been performed in order to extract the molecular parameters that have direct influence on the electrical transport [5,[17][18][19].…”