Effect of the Phobic Segregation between Fluorinated and Perhydrogenated Chains on the Supramolecular Organization in Ionic Aromatic Dendrimers (original) (raw)
Related papers
Macromolecules, 2000
A systematic study of the influence of generation number on the phase behavior of LC dendrimers is presented. For this purpose, phase behaviors and structures of first to fifth generations of liquid crystalline (LC) carbosilane dendrimers with 8, 16, 32, 64, and 128 terminal cyanobiphenyl groups were investigated. Investigation of thermal behavior of the LC dendrimers by means of polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction experiments reveals smectic-type mesophases over a wide temperature region. It is shown that with increasing generation number the isotropization temperature increases whereas the enthalpy of this phase transition decreases. The strongest influence of spherical molecular architecture on the phase behavior of the LC dendrimers appears at high generations. In the case of LC dendrimer of the fifth generation, it leads to the formation of two levels of a structural organization. This dendrimer forms different supramolecular nanostructures of columnar type in addition to smectic-like arrangement of mesogenic groups. Possible structures of all mesophases formed are discussed.
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.
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.
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.
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.
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.
Structural Investigation of Carbosilane Liquid Crystalline Dendrimers
The Journal of Physical Chemistry B, 2008
X-ray and neutron scattering investigations have been made on two series of liquid crystal dendrimers. The low generations (first to fourth) predominantly show smectic phases. The fifth generation shows a tendency to form columnar phases and two different types have been observed. The transition from smectic to columnar has been explained in terms of the distance between the dendritic core and the mesogenic units. As the generation number is increased, the distance increases until it becomes greater than the maximum length of the flexible spacers causing a change in molecular shape and the formation of columnar phases. Although the materials are nearly monodisperse, the small variation in the number of mesogens per molecule gives rise to some subtle structural effects. Two coexisting structures have been observed over large temperature ranges in some materials and small angle neutron scattering indicates that there is some microphase segregation which is a reversible function of temperature.
Liquid-Crystalline Dendrimers Designed by Click Chemistry
Macromolecules, 2016
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.