Deuteron NMR study of dynamics and order in the columnar phase of a fluorinated discotic liquid crystal

Benzopyrano-Fused Phenanthridine-Based Columnar Mesogens: Synthesis, Self-organization and Charge-Transport Properties

Columnar mesogens constitute a fascinating class of supramolecular nano-architectures owing to the exceptional properties induced by their self-assembling behavior. Extending the π-conjugated core in such systems by incorporating heteroatoms extensively influences their mesomorphic, photophysical properties, etc., presenting them as potential candidates for optoelectronic applications. In the present work, a series of novel nitrogen and oxygen-incorporated chromenonaphthophenanthridine-based elliptical dimers have been synthesized through tandem Pictet-Spengler cyclization followed by ipso-aromatic substitution in one-pot. Mesophase characterization has been carried out by employing POM, DSC, and X-ray diffraction studies. Photophysical properties were investigated using UV-vis and emission spectroscopy. Furthermore, the charge transport properties were analyzed by time-of-flight measurements, and the observed ambipolar mobilities were found to be of the order of 10^-3  cm²  V^-1  s^-1 . The high solubility, excellent thermal stability, self-organizing properties, and ambipolar charge transport characteristics make them promising candidates for applications in organic electronics.

Fluorination-Induced Evolution of Columnar Packing in Fluorous Triphenylenes and Benzotriphenylenes

Use of D_3h -symmetrical triphenylene (TRPH) as a substrate for high-temperature radical reactions with C₄ F₈ I₂ under varying conditions resulted in the introduction of four types of fluorinated substituents: ω-C₄ F₈ H, c-C₄ F₈ , c-C₄ F₄ , and c-C₄ HF₃ . In contrast to the previous work on direct (poly)substitutions with R_F groups in polycyclic aromatic hydrocarbons (PAHs), in this work regiospecificity, selectivity, and high yield were achieved for TRPH(C₄ F₈ ) and TRPH(C₄ F₈ )₃ . New single-crystal structural data for seven compounds combined with literature crystallographic data allowed for the first detailed and precise analysis of the effects of fluorous substituent types, their number, and their position(s) on the TRPH core on the solid-state packing, and more specifically, the degree of π-π overlap between neighboring molecules, which is linked to charge transport properties. Comparison of isostructural partially fluorinated benzotriphenylenes, 2,3-TRPH(C₄ F₄ ) and 2,3-TRPH(C₄ HF₃ ), revealed an unexpectedly large (30 %) drop of π-π overlap, when only one fluorine atom was replaced with the hydrogen atom in a C₄ F₄ moiety. Theoretical and potentially practical implications of this work may include further testing and elaboration of computational methods describing solid-state interactions and predictions of transport properties of organic semiconductors, and further advances in the molecular design of high-performing TRPH-based organic materials and supramolecular architectures for organic optoelectronics.

Phase equilibria, fluid structure, and diffusivity of a discotic liquid crystal

Molecular Dynamics simulations were performed for the Gay-Berne discotic fluid parameterized by GB(0.345, 0.2, 1.0, 2.0). The volumetric phase diagram exhibits isotropic (IL), nematic (ND), and two columnar phases characterized by radial distribution functions: the transversal fluid structure varies between a hexagonal columnar (CD) phase (at higher temperatures and pressures) and a rectangular columnar (CO) phase (at lower temperatures and pressures). The slab-wise analysis of fluid dynamics suggests the formation of grain-boundary defects in the CO phase. Longitudinal fluid structure is highly periodic with narrow peaks for the CO phase, suggestive of a near-crystalline (yet diffusive) system, but is only short-ranged for the CD phase. The IL phase does not exhibit anisotropic diffusion. Transversal diffusion is more favorable in the ND phase at all times, but only favorable at short times for the columnar phases. In the columnar phases, a crossover occurs where longitudinal diffusion is favored over transversal diffusion at intermediate-to-long timescales. The anomalous diffusivity is pronounced in both columnar phases, with three identifiable contributions: (a) the rattling of discogens within a transient "interdigitation" cage, (b) the hopping of discogens across columns, and (c) the drifting motion of discogens along the orientation of the director.

Molecular self-diffusion in a columnar liquid crystalline phase determined by deuterium NMR

We report translational diffusion coefficients in a columnar phase of a discotic liquid crystal formed by a triphenylene-based compound. The experiments were performed using 2H stimulated-echo-type pulsed-field-gradient spin-echo NMR applied to a chain-deuterated sample. The diffusion coefficients were found in the range of 1x10(-14)-4x10(-14) m2/s, three orders of magnitude lower than in the isotopic phase of the same compound. This, together with the high activation energy obtained in columnar phase, indicates that the diffusion is dominated by solidlike jump processes.