Significantly Enhanced Thermotropic Liquid Crystalline Columnar Mesophases in Stereoregular Polymethylenes with Discotic Triphenylene Side Groups

Abstract

Side-chain discotic liquid crystalline polymers (SDLCPs) with discotic (disclike) mesogens (discogens) attached as side groups through flexible spacers constitute a class of fascinating organic polymer semiconducting materials. While so far almost all reported SDLCPs belong to conventional C2 polymers based on polymerization of vinyl monomers, limiting their structure diversities, substitution density, and efficiency promotion. In this article we present the synthesis of a series of syndiotactic polymethylene SDLCPs of Pm(TPn) with discotic triphenylene (TP) side groups of variant peripheral alkoxy substituents (n = 6, 4, 10) and different length alkyl spacers (m = 3, 4, 6, 8, 10, 12) through an indirect two-step rhodium-complex-catalyzed C1 carbene polymerization pathway. The thermal properties and ordered organization structures of the precursor polymers and polymethylene SDLCPs have been systematically investigated with differential scanning calorimetry (DSC) and polarized optical microscopy (POM), especially through synchrotron radiation variable-temperature small/wide-angle X-ray scattering (SAXS/WAXS) analyses. All of the series C1-type syndiotactic polymethylenes with high densely substituted TP side groups exhibit various hierarchical ordered columnar mesophases comparable to that of the typical side-chain C2 polymers of well-defined polyacrylates with TP discogens. Moreover, they possess a remarkably broadened temperature range of columnar structures persistent to very high temperatures in virtue of the stiff helical polymethylene backbone. This work provides a feasible route to prepare the C1-type SDLCPs with high densely substituted functional side groups and may offer an in-depth understanding for the hierarchical organization of ordered columnar structures with significantly increased thermal stability.

Liquid Crystalline Polyimide Films with High Intrinsic Thermal Conductivities and Robust Toughness

“…For the pre LC-PI I films, an incomplete DSC endothermic peak appears during the heating process, and the peak vertex does not appear before 400 °C. The endothermic peak is due to the gradual transformation of the pre LC-PI I films from amorphous phase to liquid crystal phase . The POM images show that the pre LC-PI I films exhibit no bright spots in the viewshed during the process of heating to 350 °C and the pink color is the background color generated by the crossed polarizer, showing the amorphous state of the samples (Figure a 1 ∼ a 4 ).…”

“…The endothermic peak is due to the gradual transformation of the preLC-PI I films from amorphous phase to liquid crystal phase. 53 The POM images show that the preLC-PI I films exhibit no bright spots in the viewshed during the process of heating to 350 °C and the pink color is the background color generated by the crossed polarizer, showing the amorphous state of the samples (Figure 2a 1 ∼a 4 ). When the temperature continues to rise to 400 °C, there are very few scattered bright yellow spots (preLC-PI liquid crystals, Figure 2a 5 ).…”

Enhanced Conductivity and Thermochromic Luminescence in Hydrogen Bond-Stabilized Columnar Liquid Crystals

“…The molecular design of 9C n - ester -TCS and 9C n - amide -TCS was inspired by the excellent optical characteristics as well as appealing electrical properties in orderly assembled cyanostilbene derivatives ,− and was further guided by our experience on discotic columnar LCs. − Because the electrical conductivity requires substantial structural rigidity to generate charge transport pathways via intermolecular π–π interactions, while bright luminescence in solid favors distorted molecular conformation to limit nonradiative deactivation, we here designed a quasi-discotic three-arm TCS fluorophore core with specific stereo geometry and moderate π-conjugation effect for the aforementioned issue of synchronous improvement of both conductivity and luminescence performance. X-ray revealed that the star-shaped TCS core exhibits a nonplanar quasi-discotic shape and the phenyl rings adopt a trans conformation relative to one another (Figure d).…”

Processing-Dependent Lamellar Polymorphism of Hyperbranched Liquid-Crystalline Polymer with Variable Light Emission

“…As shown in Figure , we herein report a HLCP by employing π-conjugated α-cyanostilbene (CS) as the mesogenic unit, glutamate as the branching point, and decyl chain as the flexible spacer to induce liquid crystallinity. The molecular design was guided by our experience on the hierarchical self-assembly of LC polymers − and their fluorescence functionality , and was also benefiting from the two following considerations: (i) Incorporation of noncovalent interactions (such as π–π stacking of the aromatics, , local dipole coupling generated by the lateral polar cyano group, , and hydrogen bond introduced by the glutamate group) in HLCP may promote inter/intramolecular stacking assembly of the CS mesogens and then enable controlled modification of mesomorphic structures by regulation of assembly pathways. (ii) The aggregation-enhanced emission characteristic of the CS mesogen − would endow the resulting HLCP with solid-state fluorescence, which is much sensitive to the molecular packing arrangement, thus allowing for an efficient measure in monitoring the mutable assembly structures, and vice versa, providing a way to tune the light emission by structural engineering. , Eventually, the obtained HLCP self-assembled into ordered lamellar smectic phases and exhibited processing-dependent lamellar polymorphism, enabling a control of the molecular packing arrangement in the assembled lamellar arrays and thus a way to tune the multicolored light emission by various processing methods.…”