Abstract
Shape-persistent conjugated mesogens with oligothiophene arms of different lengths have been synthesized. Such mesogens possess free intrinsic space between their conjugated arms. They form columnar liquid-crystalline phases, in which the void is filled by dense helical packing in the neat phase similar to an oligo(phenylene vinylene) derivative of equal size. The void can also be compensated by the inclusion of the small acceptor molecule 2,4,7-trinitrofluorenone. In solution, the acceptor interacts with the core as the largest π-surface, while in the solid material, it is incorporated between the arms and sandwiched by the star-shaped neighbours along the columnar assemblies. The TNF acceptors are not nanosegregated from the star-shaped donors, thus the liquid crystal structure converts to a nano-reservoir for TNF (endo-receptor). These host-guest arrangements are confirmed by comprehensive X-ray scattering experiments and solid-state NMR spectroscopy. This results in ordered columnar hexagonal phases at high temperatures, which change to helical columnar mesophases or to columnar soft crystals at room temperature.
Highlights
The void can be compensated by the inclusion of the small acceptor molecule 2,4,7-trinitrofluorenone
This results in ordered columnar hexagonal phases at high temperatures, which change to helical columnar mesophases or to columnar soft crystals at room temperature
It undergoes a transition from a mobile columnar liquid crystal (LC) phase into a soft crystal, in which the conjugated arms are segregated from the anthracene guests in a cable-like structure with six alternating segments
Summary
The TNF mixtures are studied in solution as well as for 1 : 1, 1 : 2 and 1 : 3 mixtures in the solid state These materials were subjected to a detailed structural analysis using X-ray scattering (XRS) and solid-state NMR. While XRS is one of the key techniques in the analysis of liquid-crystalline materials, the sensitivity of solid-state NMR to intra- and intermolecular proximities as well as dynamics makes the two techniques highly complementary probing long- and short-range order, respectively, for a broad range of materials[36,37] and liquid crystals in particular.[25,38,39] We found that while in solution the acceptors on average interact with the most planar centre of the star to form weak donor-acceptor complexes, they fill the space between the arms in the solid state. That these star mesogens are liquidcrystalline nano-reservoirs for up to three guest molecules per LC-host in the columnar structures
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