Liquid-Crystalline Dendrimers Designed by Click Chemistry (original) (raw)
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Chemistry - A European Journal, 1998
Three generations poly(propylene imine) dendrimers with 4, 16, and 64 terminal amine groups have been functionalized with pentyloxycyanobiphenyl and decyloxycyanobiphenyl mesogens. The liquid-crystalline properties of these dendrimers have been studied in detail by differential scanning calorimetry, optical polarization microscopy, and X-ray diffraction. All the mesogenic dendrimers orient into a smectic A mesophase. Thermal properties are influenced to a large extent by the spacer length, showing g 3S A 3I transitions for the dendritic mesogens with the pentyloxy spacers and K 3S A 3I transitions for the ones with a decyloxy spacer. In the latter, the temperature range of the mesophase increases with dendrimer generation. Mesophase formation in the case of the pentyloxy series is more difficult compared with the corresponding decyloxy analogues, when the transition enthalpies and the kinetics of obtaining microscopic textures are considered. The effect of generation on mesophase formation cannot be clearly distinguished, although in the case of the fifth-generation dendrimer with a decyloxy spacer, microscopic textures could be obtained more easily, compared with the lower generations. X-ray diffraction measurements of oriented samples indicate that the cyanobiphenyl endgroups of both series orient into an antiparallel-overlapping interdigitated structure. The observed S A -layer spacings are independent of the dendrimer generation for both spacer lengths, indicating that the dendritic backbone has to adopt a completely distorted conformation, even for the higher generations. Scheme 1. a) Synthesis of functional cyanobiphenyl substituents . b) Synthesis of cyanobiphenyl-functionalized poly(propylene imine) dendrimers. E. W. Meijer et al.
Liquid crystalline dendrimer: Sythesis and Chracterization
Baghdad Science Journal, 2014
A new family of nematic liquid crystal dendrimers derived from 3,5-dihydroxybenzoic acid were synthesized. The synthesis of the dendrimers compounds shows the influence of the dendritic core on the mesomorphic properties. The liquid crystalline properties were studied by polarizing optical microscopy (POM) equipped with a hot stage, the structures of the synthesized compounds characterized using FTIR and 1HNMR spectroscopy.
A Review on Synthesis, Properties, of Liquid Crystal Dendrimers
Al-Nahrain Journal of Science, 2021
This review provides brief information concerning with the dendrimer. The supramolecular organization of selected examples of liquid-crystalline dendrimers within lamellar, columnar and nematic phases is reported. It is shown that tuning of the mesomorphic structure can be achieved by an appropriate molecular design depending upon the chemical nature of the terminal mesogenic groups, dendritic core and dendrimer generation. The pseudospherical shape of a dendrimer arises from its structure, which consists of an internal region (the core) which is connected to repeating units constituting a radial branching pattern.
Triazine-based Dendrimers as Liquid Crystals: Synthesis and Characterization
2009
D ifferent generations of dendritic macromolecules based on triazine were synthesized by the divergent growth approach and functionalization with mesogenic units based on peripherally located dihydroxybiphenyl derivatives. Thermotropic liquid crystal dendrimers, containing poly(ethylene glycol) (PEG) as a core and triazine dendrons with peripherals mesogenic groups were synthesized. First generation (G 1 ) was prepared by coupling of hydroxyl group of PEG with cyanuric chloride in dichloromethane at 0-5ºC. Reaction of compound G 1 with amino group of ethanolamine in dichloromethane resulted G 1.5 . Second generation of linear dendritic compounds (G 2 ) was synthesized using coupling reaction of hydroxyl groups of compound G 1.5 and cyanuric chloride in dichloromethane. Reaction of compound G 2 with amino group of ethanolamine in water/dioxane resulted G 2.5 . The growth of dendrons on the PEG core and their structures were investigated using common spectroscopy methods. In the next step, compounds C n with different alkyl tail groups were synthesized via nucleophilic displacement of bromine from 1-bromoalkane by potassium-4,4'-biphenoxide in DMF. The mesogenic compounds 4-bromo-(4-alkyloxybiphenyl-4'-oxy) butane (C n C 4 Br) were synthesized by reaction with C n and 1,4dibromobutane undergoing S N2 substitution. Liquid crystalline dendrimers (LCD) were synthesized via coupling of hydroxyl group of G 2.5 and bromine from mesogenic units, 4-bromo-(4-alkyloxy-biphenyl-4'-oxy) butane. The liquid crystal property of mesogenic compound has been studied in details with differential scanning calorimetry and optical polarization microscopy. The experiments showed that the thermal properties are influenced with the spacer length.
Using the controlled layer by layer experimental technique via reiterative sequence of chemical reactions carbosilane LC dendrimers with terminal cyanobiphenyl mesogenic groups of generations 1 - 5 were synthesized. Molecular structure and purity of all new compounds were characterized by 1H-NMR spectroscopy and GPC analysis. Thermal behavior of LC dendrimers was investigated by means of polarizing optical microscopy and DSC methods. All LC dendrimers synthesized have mesophases of smectic types over wide temperature region. Values of glass transition temperatures of LC dendrimers do not depend on generation number, but isotropisation temperature raises with increasing of generation number of LC dendrimers. LC dendrimer of generation 5 bearing 128 cyanobiphenyl mesogenic groups displays unusual type of structural polymorphism, which is under investigation.
Multivalent, bifunctional dendrimers prepared by click chemistry
Chemical Communications, 2005
General Methods. Analytical TLC was performed on commercial Merck Plates coated with silica gel GF254 (0.24 mm thick). Silica for flash chromatography was Merck Kieselgel 60 (230-400 mesh, ASTM). 1 H NMR (400 MHz) and 13 C NMR (100 MHz) measurements were performed on a Bruker AC 400, 500 or 600 spectrometer at room temperature. Coupling constants (J) are reported in Hertz, and chemical shifts are reported in parts per million (δ) relative to CHCl 3 (7.26 for 1 H and 77.2 for 13 C) or MeOD (3.31 for 1 H and 49.1 for 13 C as internal reference. Size exclusion chromatography (SEC) was carried out at room temperature on a Waters chromatograph connected to a Waters 410 differential refractometer and six Waters Styragel ® columns (five HR-5 µm and one HMW-20 µm) using THF as eluant (flow rate: 1 mL/min). A Waters 410 Supplementary Material (ESI) for Chemical Communications This journal is © The Royal Society of Chemistry 2005 2 differential refractometer and a 996 photodiode array detector were employed. The molecular weights of the polymers were calculated relative to linear polystyrene standards. Non-aqueous copper(I)-catalyzed cycloaddition were performed in sealed tubes using a SmithCreator microwave reactor (Personal Chemistry Inc.). The modulated differential scanning calorimetry (MDSC) measurements were performed with a TA Instruments DSC 2920 and a ramp rate of 4 degrees per minute. The thermal gravimetric analysis measurements were done with a TA Instruments HiRes TGA 2950, under nitrogen purge, and the ramp rate was 10 degrees per minute. MALDI-TOF mass spectrometry was performed on a PerSeptive Biosystems Voyager DE mass spectrometer operating in linear mode, using dithranol in combination with silver trifluoroacetate as matrix. Nomenclature. The nomenclature used for dendritic structures described in this chapter is as follows: (P) n-[G-X]-FG for dendrons, where P describes the external functional group, either OH for hydroxyl, An for acetonide, Bzl for benzylidene, Acet for acetylene; n indicates the number of chain end functionalities; X indicates the generation number of the dendritic framework and FG describes the functional group at the focal point; either Acet for acetylene, or Az for azide. (P) n-[G-X]-[G-X]-(P) n for triazole linked amphiphilic dendrimers, P describes the external functional group, Cm stands for 7-Diethylaminocoumarin, Mann stands for 1-(2-[1,2,3]-triazolethoxy)-α-Dmannopyranodise.
Chemistry - A European Journal, 2014
Four unconventional triazine-based dendrimers have been prepared and characterized by 1 H and 13 C NMR spectroscopies, mass spectrometry, and elemental analysis. Based on DSC studies, polarizing microscopy, and powder XRD, two of these dendrimers, containing linkers with an odd number of carbon atoms, were observed to display columnar liquid-crystalline phases during thermal treatment. However, the other two dendritic analogues, containing linkers with an even number of carbon atoms, were not observed to behave correspondingly. Based on computer simulation, we reasonably assume that the dendrimers with an odd number of carbon atoms in their linkers distort their molecular shape and adopt two isomeric structures due to asymmetrical congestion. This reduces the molecular p-p face-to-face interaction, which in turn causes the dendrimers to form columnar LC phases during thermal treatment. However, the dendrimers with an even number of carbon atoms in their linkers have more symmetrical skeletons and do not display any liquid-crystalline phase upon thermal treatment. This new strategy should be applicable for eliciting the columnar liquid-crystalline properties of other types of unconventional dendrimers with rigid frameworks.
Liquid-Crystalline Dendritic Networks Derived from Poly(Propylene Imine) (PPI) Dendrimers
Macromol. Rapid Commun., 2005
Dendrimers can be described as well-defined, highly branched molecules that emanate from a central core. As a new class of materials, dendrimers have generated great interest throughout the scientific community. Dendrimers havebeen widely used as building blocks for the construction ofcomplex supramolecular and macromolecular architectureswith precise control of shape and functionality.
New methodologies in the construction of dendritic materials
Chemical Society Reviews, 2009
Dendritic polymers are highly branched polymer structures, with complex, secondary architectures and well-defined spatial location of functional groups. Due to their unique physical and chemical features, applications in areas such as targeted drug-delivery, macromolecular carriers, catalysis, sensors, light harvesting, surface engineering and biomimetic materials have been proposed. However, only a few dendritic materials have been exploited commercially due to time consuming syntheses and the generation of significant waste/presence of unreacted starting materials. This tutorial review describes traditional synthesis of dendritic materials as well as recent advances in synthetic strategies, for example the use of Click chemistry, as a tool to efficiently obtain complex, functional dendritic structures.
Liquid crystalline carbosilane dendrimers: first generation
Liquid Crystals, 2006
An approach to the synthesis of a new class of liquid crystalline (LC) compounds, dendrimers of regular structure with terminal mesogenic groups, was elaborated. LC dendrimers based on the carbosilane dendritic matrix of first generation were synthesized. Cyanobiphenyl, methoxyphenyl benzoate and cholesteryl groups were used as mesogenic fragments. Individuality and structure of all compounds obtained was proved by GPC together with 1Hand 2esi NMR methods. The mesomorphic behaviour and structure of the LC dendrimers synthesized were investigated. It is argued that different mesophases of the smectic type are rcalized in all cases. It is shown that the mesophase type of these compounds essentially depends on the chemical nature of the mesogenic groups.