Liquid-Crystalline Dendrimers Designed by Click Chemistry

Abstract

Liquid-crystalline dendrimers have been prepared from second-generation Percec-type poly(benzyl ether) dendrons or second-generation poly(aryl ester) dendrons carrying cyanobiphenyl mesogens. The Janus dendrimer, which combines the two types of dendromesogens, has also been synthesized. Those compounds have been prepared under copper-catalyzed azide−alkyne cycloaddition conditions. The mesomorphic properties have been studied by thermal analysis (POM, DSC) and small-angle X-ray scattering. Smectic A, nematic, and columnar phases have been observed depending on the dendritic building blocks. The click reaction has proven to be a powerful and elegant synthetic tool for the design of complex dendritic liquid-crystalline architectures. ■ INTRODUCTIONThe development of nanoscale devices with specific properties (e.g., optical, magnetic, redox properties) obtained by the selfassembly of functional building blocks requires important efforts in the molecular design.1,2 In this context, liquid crystals are a class of materials of particular interest due to their controllable self-organization behavior.3 Structural engineering at the molecular level, by designing mesomorphic units with accurate shape, length, polarity, or chirality, is the key step to modulate the self-organization process and tune the physicochemical properties of the target supramolecular architectures.4,5 Thus, the development of complex liquid-crystalline nanostructures with tailor-made and high performance properties requires effective and versatile synthetic tools.The copper-catalyzed azide−alkyne "click" cycloaddition (CuAAC) 6−8 is of interest as it requires mild reaction conditions and simple work-up procedures, tolerates a wide range of functional groups, and leads to high yields. Thus, the CuAAC reaction was applied for the synthesis and modification of various supramolecular architectures such as gels, and dendrimers, 55 were also prepared by applying this chemical transformation.In the field of liquid crystals, we successfully applied the CuAAC reaction for the synthesis of liquid-crystalline gold nanoparticles: first-and second-generation mesomorphic cyanobiphenyl-based dendrons were grafted onto the gold core, and the formation of smectic A phases was observed. 56,57 We also reported hexadducts of [60]fullerene (C 60 ) prepared by clicking 12 chiral or achiral first-generation poly(benzyl ether) dendrons onto a C 60 derivative. 58 The materials gave rise to supramolecular helical columns.The aim of this study is to exploit the click chemistry as an effective and elegant approach for the assembly of two dendrons leading to novel liquid-crystalline dendrimers. This strategy, which allows to connect dendrons with identical, similar, or different properties, is an interesting way to design liquid-crystalline dendrimers with tailor-made self-assembly properties based on the characteristics of each individual dendron.We report, herein, the synthesis, characterization, and mesomorphic properties of three clicked dendrimers (1−3, Figures ...

A mini review of the synthesis of poly-1,2,3-triazole-based functional materials

“…4) could also be used as a raw material for construction of triazole modules and then formation of dendrimer-like liquid crystal. 29 Various characterizations including a polarizing microscopy, etc., indicated that the dendritic polymer exhibited a columnar nematic liquid crystal structure. This nding thus opens up a new avenue to liquid crustal materials.…”

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

“…Among them, hyperbranched polymers have been well-studied in developing various nano/microscopic supramolecular structures, , but usually do not crystallize or assemble into ordered molecular solids due to their intrinsic structural irregularity and highly branched architectures. The incorporation of mesogenic units into hyperbranched polymer scaffold has demonstrated an ability to show liquid-crystalline (LC) mesomorphism. − Most of hyperbranched LC polymers (HLCPs) can merely generate orientationally ordered nematic mesophase, − while some higher ordered smectic, columnar, cubic, and even liquid quasi-crystalline structures that usually observed in their analogues of structurally perfect dendrimers remain a contemporary challenge. This underdeveloped situation in HLCPs largely limits the diversification in their structures and functions, − whereas self-assembly of hyperbranched polymers can become more expected in this case where both three-dimensional dendritic architecture and facile one-pot synthesis are desired. , The shape-variable nature of the highly branched spheroidic morphology allows for various modes of packing, − and the irregularity (or distribution) in structure and molecular weight provides additional possibilities to affect the crystalline process, , which would result in the observation of various phases. − Thus, our intention here is to develop a well-organizable HLCP and to tune the optoelectronic property through control of the self-assembled hierarchical structures by regulation of the kinetics involved processing pathways.…”

Preparation and Characterization of Poly-1,2,3-triazole with Chiral 2(5H)-Furanone Moiety as Potential Optical Brightening Agents

“…Generally, the trans state of the stilbene molecule is more stable than the cis state. 3 As shown in Figure 5, the UV–vis spectra of multiblock copolymers 2a – e were measured in THF solution. According to Figure 5, their most intense absorption bands were below 280 nm in the ultraviolet region, arising from the π–π* transition localized on the 2(5 H )-furanone ring within each polymer.…”