Dendrimeric triphenylbenzenes: helical versus zig-zag arrangement in columnar mesophases

Obsiye, Abdirashid; Wöhrle, Tobias; Haenle, Johannes Christian; Bühlmeyer, Andrea

doi:10.1080/02678292.2017.1360523

Cited by 14 publications

(2 citation statements)

References 48 publications

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“…The shape-persistent mesogens 19c have to distort conformationally in order to avoid steric congestions and to fill space efficiently. Later other shape-persistent stars were shown to follow similar helical self-assemblies. − With the aim of using the intrinsic void favorably to generate donor–acceptor structures and release torsional strain, we envisioned and synthesized dyads 20 and 21 with fullerenes attached to the inner stilbene scaffold via flexible spacers to avoid macroscopic segregation (Figure ).…”

Section: Shape-persistent Mesogens and Free Spacementioning

confidence: 99%

Free Space in Liquid Crystals—Molecular Design, Generation, and Usage

et al. 2019

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Conspectus In the last 50 years, an important aim of molecular and materials design has been the generation of space for the uptake of guest molecules in macrocycles and cryptands, in dendrimers as monomolecular containers, and recently in porous networks like metal–organic and covalent organic frameworks. Such molecular, oligomeric, and polymeric materials can be applied for sensing, separation, catalysis, drug delivery, and gas storage, among others. The common goal is the recognition of molecules and their uptake into and release from an appropriate space. Typically, completely empty space is unfavorable in crystalline materials. Therefore, the elimination of molecules from the cavities is often accompanied by the collapse of the cavities, that is, by a change in the molecular conformation. In contrast to this solid matter, in which the cavities are rationally designed by covalent or coordinative bonds, liquid crystals (LCs) are fluid materials with high molecular mobility. Thus, the proposal of empty space in LCs is certainly a scientific provocation. However, various recent publications on columnar mesophases claim the existence of pores with low electron density or even completely empty space on the basis of X-ray and solid-state NMR studies. Although the latter may be debated, there are many examples in which LCs take up dopants such as polymerizable monomers in disclination lines, perdeuterated chains in the interstices between columns, or electron acceptors to fill mesogens with incommensurate building blocks, which eventually stabilize the LC phases. It seems that in LC science the generation and usage of free space has been studied only occasionally and were lucky discoveries rather than investigations based on rational design. This Account summarizes the research on the formal generation of void in LCs and highlights that rational design of molecules can lead to unconventional mesophases by efficient filling of the provided space, as was shown with shuttlecock mesogens and discotic mesogens related to the concept of complementary polytopic interactions. The topic was recently further developed by the investigation of shape-persistent star mesogens. Despite the formally empty space between their arms, they all form columnar liquid crystals. Such shape-persistent oligo(phenylenevinylene) molecules fill the void and efficiently nanosegregate by helical packing in columns and deformation of the molecular scaffold at the expense of the torsional energy. This inspired us to fill the intrinsic free space by guest molecules either via supramolecular or covalent bonds or just by physical mixing in order to avoid the increase in torsional energy and to stabilize the structure. This strategy led to complex filled liquid-crystalline matter with high structural control and may in the future be used for the design of organic electronic materials that are easily alignable for device applications.

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Section: Shape-persistent Mesogens and Free Spacementioning

confidence: 99%

Free Space in Liquid Crystals—Molecular Design, Generation, and Usage

et al. 2019

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“…Star‐shaped 1,3,5‐triphenylbenzenes such as 4 (Scheme ) belong to the class of shape‐persistent hekates which are able to form columnar mesophases . Space‐filling between the three arms is achieved either by helical twisting along the columnar axis or by incorporation of bulky guest molecules covalently or non‐covalently bound to the star, giving rise to unique self‐assembled structures , …”

Section: Introductionmentioning

confidence: 99%

Columnar Propeller‐Like 1,3,5‐Triphenylbenzenes: Probing the Effect of Chlorine on the Suzuki Cross‐Coupling and Liquid Crystalline Properties

et al. 2020

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Suzuki cross-couplings either between chlorinated N-methyliminodiacetic acid (MIDA)-protected aryl boronates and 1,3,5-tribromobenzene or between chlorinated aryl bromides and phenyltrisboronic species to star-shaped 1,3,5-triphenylbenzenes with different substitution patterns and chloro substituents at the outer phenyl rings were studied. The chlorinated precursors required for the respective reaction were synthesized and characterized. Depending on the used coupling reaction target triphenylbenzenes were isolated in yields between 42 % and 88 %. Their mesomorphic properties were in- [a] 2190 fluenced by the substitution pattern and number of peripheral chlorine atoms. Triphenylbenzene with 3,5-alkoxy substitution and H in para-position self-assembled into either columnar hexagonal (Col h ) mesophases or a soft crystal. While threefold chloro substitution in meta-position of the outer phenyl rings led to stable room temperature Col ho phases, triphenylbenzenes with threefold para-chloro or 3,5-dichloro substitution were non-mesomorphic. Based on X-ray diffraction data a helical packing model for the observed phases similar to that of related alkoxy-substituted triphenylbenzenes was proposed.properties and a decrease of phase transition temperatures were independently reported for bent-core liquid crystals by Twieg [9,10] and for ionic liquid crystals by Binnemans. [11] Scheme 1. Selected liquid crystalline pseudoazulenes (1, 2) and indene derivative 3. [7,8] Scheme 2. dated. To study the effects in more detail, convenient synthetic access to (poly)chlorinated triphenylbenzenes 5 is required. In contrast to the plethora of well-explored Suzuki-Miyaura crosscoupling of aryl halides with aryl boron species, [21][22][23][24][25] the use of di-and poly-chlorinated reactants has been mostly devoted to access polychlorinated biphenyl (PCB) derivatives for ecotoxicity and analytical property studies. [26][27][28][29][30][31][32][33] In order to get access to triphenylbenzenes 5 we followed two synthetic strategies involving a cross-coupling as the key step (Scheme 3). Compound 5 is derived either from Suzuki-Miyaura cross-coupling between aryl boronic species 6 [e.g., N-methyliminodiacetic acid (MIDA) boronates [34][35][36][37][38][39] ] and 1,3,5-tribromobenzene 7 (route A) or alternatively, by the connection of aryl bromides 8 and 1,3,5-phenyltrisboronic species 9 (e.g., pinacol boronate) (route B). The results towards the synthesis of compounds 5 and study of their mesomorphic properties are reported below. Scheme 4. Synthesis of precursors 6 and 8 (numbering for NMR assignment; for details see also the Supporting Information). 2191Scheme 3. Retrosynthetic pathways to star-shaped triphenylbenzenes 5.

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Rigid‐Flexible Coupled Dendritic Molecule Doping: General Approach to Activate Commercial Polymers into Harsh Condition‐Tolerant Multi‐Reusable Strong Supramolecular Adhesives

Feng,

Lin,

Zhang

et al. 2024

Angewandte Chemie

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Developing functional adhesives combining strong adhesion, good recyclability and diverse harsh‐condition adaptability is a grand challenge. Here, we introduce a general dendritic molecule doping strategy to activate commercial polymers into a new family of supramolecular adhesives integrating high adhesion strength, ultralow temperature, water resistant and multi‐reusable properties. Our method involves rational design of a new rigid‐flexible coupled dendritic molecule ‐ M4C8OH as a versatile dopant, while simple M4C8OH doping into commercial polymers can modulate internal and external non‐covalent interaction to enable H‐bonding enhanced interchain cross‐linking for tough cohesion along with enhanced interphase interaction. This endows 20 wt% M4C8OH‐doped polycaprolactone (PCL) adhesives (PCL‐M4C8OH) with improved adhesion strength on various substrates with the maximum increase up to 2.87 times that of PCL. In particular, the adhesion strengths of PCL‐M4C8OH on polymethyl methacrylate at 25 °C and ‐196 °C reach 4.67 and 3.58 MPa ‐ 1.9 and 2.3 times those of PCL and superior to diverse commercial adhesives and most reported adhesives. PCL‐M4C8OH also displays markedly‐improved multi‐usability and tolerance against ultralow temperature and diverse wet environments. Mechanism studies reveal the crucial role of M4C8OH molecular structures toward superior adhesion. Our method can be expanded to other polymer matrices, yielding diverse new supramolecular adhesives.

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Dendrimeric triphenylbenzenes: helical versus zig-zag arrangement in columnar mesophases

Cited by 14 publications

References 48 publications

Free Space in Liquid Crystals—Molecular Design, Generation, and Usage

Free Space in Liquid Crystals—Molecular Design, Generation, and Usage

Columnar Propeller‐Like 1,3,5‐Triphenylbenzenes: Probing the Effect of Chlorine on the Suzuki Cross‐Coupling and Liquid Crystalline Properties

Rigid‐Flexible Coupled Dendritic Molecule Doping: General Approach to Activate Commercial Polymers into Harsh Condition‐Tolerant Multi‐Reusable Strong Supramolecular Adhesives

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