Nematic Dendrimers Based on Carbosilazane Cores

Elsäßer, R.; Mehl, Georg H.; Goodby, John W.; Veith, Michael

doi:10.1002/1521-3773(20010716)40:14<2688::aid-anie2688>3.0.co;2-s

Cited by 46 publications

(18 citation statements)

References 21 publications

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“…As for the carbosilazane dendrimers (N C = 3, N B = 2), two series (G0-G2) with laterally attached mesogenic units were reported. Depending on the mesogenic unit, these dendrimers exhibit a single room temperature N phase 53 or a N-SmC and a N-Col dimorphism on increasing generation. 54 Thus, the ''side-on'' attachment of mesogenic groups appears to be an excellent strategy to induce pure N systems, although, due to the strong tendency of the core to phase separate as the generation increases, the strongly segregated smectic and columnar supramolecular organizations were inescapably formed.…”

Section: Liquid-crystalline Dendrimersmentioning

confidence: 99%

Liquid crystalline dendrimers

et al. 2007

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In recent years, there has been an increasing interest in the field of liquid crystalline dendrimers. Such a fast development is, among other things, driven by the multiple possibilities offered by combining the mesomorphic properties of single mesogenic subunits with the supermolecular and versatile architectures of dendrimers to yield a new class of highly functional materials. The induction and the control of the mesomorphic properties (phase type and stability) in dendrimers can be achieved by a dedicated molecular design which depends on the chemical nature and structure of both the functional groups and the dendritic matrix. In particular, the intrinsic connectivity of the dendrimer such as the multivalency of the focal core and the multiplicity of the branches, both controlling the geometrical rate of growth, or the dendritic generation, plays a crucial role and influences at various stages the subtle relationships between the supermolecular structure and the mesophase structure and stability. In this critical review article, an account of the various types of dendritic systems that form liquid-crystalline mesophases along with a description of the self-organization of representative case-study supermolecules into liquid crystalline mesophases will be discussed. Some basics of thermotropic liquid crystals and dendrimers will be given in the introduction. Then, in the following sections, selected examples including side-chain, main-chain, fullerodendrimers, shape-persistent dendrimers, supramolecular dendromesogens and metallodendrimers, as representative families of LC dendrimers, will be described. In the conclusion some further developments will be highlighted. This review will not cover liquid crystalline hyperbranched and dendronized polymers that might be considered as being somehow less structurally "perfect".

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Section: Liquid-crystalline Dendrimersmentioning

confidence: 99%

Liquid crystalline dendrimers

et al. 2007

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“…Side-chain and main-chain liquid-crystal polymers [3] have internal flexible linkages as an intrinsic part of their structure. Dendrimers [4] and multipodes [5] have flexible linking chains as part of threedimensional (3D) macromolecular structures that can also form liquid-crystal phases. The simplest molecular structure having core flexibility is a dimer structure in which two semirigid mesogenic groups are connected by a flexible chain.…”

Section: Introductionmentioning

confidence: 99%

Phase behavior and properties of the liquid-crystal dimer 1′′,7′′-bis(4-cyanobiphenyl-4′-yl) heptane: A twist-bend nematic liquid crystal

et al. 2011

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The liquid-crystal dimer 1'',7''-bis(4-cyanobiphenyl-4'-yl)heptane (CB7CB) exhibits two liquid-crystalline mesophases on cooling from the isotropic phase. The high-temperature phase is nematic; the identification and characterization of the other liquid-crystal phase is reported in this paper. It is concluded that the low-temperature mesophase of CB7CB is a new type of uniaxial nematic phase having a nonuniform director distribution composed of twist-bend deformations. The techniques of small-angle x-ray scattering, modulated differential scanning calorimetry, and dielectric spectroscopy have been applied to establish the nature of the nematic-nematic phase transition and the structural features of the twist-bend nematic phase. In addition, magnetic resonance studies (electron-spin resonance and (2)H nuclear magnetic resonance) have been used to investigate the orientational order and director distribution in the liquid-crystalline phases of CB7CB. The synthesis of a specifically deuterated sample of CB7CB is reported, and measurements showed a bifurcation of the quadrupolar splitting on entering the low-temperature mesophase from the high-temperature nematic phase. This splitting could be interpreted in terms of the chirality of the twist-bend structure of the director. Calculations using an atomistic model and the surface interaction potential with Monte Carlo sampling have been carried out to determine the conformational distribution and predict dielectric and elastic properties in the nematic phase. The former are in agreement with experimental measurements, while the latter are consistent with the formation of a twist-bend nematic phase.

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“…Important studies in dendritic liquid crystals to understand various aspects of mesophase evolution include: (i) changes in the dendrimer types, such as, carbosilane, PAMAM, PPI, and siloxane, and a homologous series of poly(propyl ether imine) (PETIM) dendrimers and changes in the dendrimer generations; (ii) varying linker lengths connecting the dendrimer backbone and the mesogenic moiety; (iii) varying alkyl chain length at the peripheries; (iv) the mode of attachment of the mesogenic moiety to the dendrimer, such as, side on or end on; (v) changing the shape of mesogenic moieties, such as, linear, radial and banana shaped and the degree of branching in the core . In the studies of dendritic LCs, to the best of our knowledge, no work has been reported so far which deals with the study of change in the mesophase by varying the flexibility and shape of the linkers within one particular dendrimer generation.…”

Section: Introductionmentioning

confidence: 99%

Connector type‐controlled mesophase structures in poly(propyl ether imine) dendritic liquid crystals of identical dendrimer generations

Kumar

Rao

Prasad

et al. 2017

J. Polym. Sci. Part A: Polym. Chem.

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Poly(propyl ether imine) (PETIM) dendrimers of one to three generations are used as dendritic cores to identify the influence of varying connector types that connect the dendritic core with peripheral mesogens on the emerging liquid crystalline (LC) properties. The LC properties vary in these dendritic liquid crystals, even when the dendrimer generations and thus the number of peripheral mesogenic moieties remain identical. PETIM dendrimer generations one to three, ester and amide connectors varying with succinates, phthalates, and succinamides, are studied herein. Cholesteryl moieties are installed at the peripheries through the above connectors to induce mesogenic properties. These modified dendritic liquid crystals reveal a layered mesophase structure in most ester and amide connector‐derivatives, whereas a third‐generation phthalate ester dendrimer favors a rectangular columnar mesophase structure. A transition from layered to a rectangular columnar structure results by a mere change in the connector varying between a succinate or succinamide or phthalate, within one particular dendrimer generation and without altering the underlying dendrimer core or the number of mesogenic moieties. The study demonstrates that in dendritic liquid crystals with essentially identical chemical constitutions, a change in the connector type connecting the mesogen with the dendrimer core is sufficient to change the mesophase structures. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3665–3678

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Nematic Dendrimers Based on Carbosilazane Cores

Cited by 46 publications

References 21 publications

Liquid crystalline dendrimers

Liquid crystalline dendrimers

Phase behavior and properties of the liquid-crystal dimer 1′′,7′′-bis(4-cyanobiphenyl-4′-yl) heptane: A twist-bend nematic liquid crystal

Connector type‐controlled mesophase structures in poly(propyl ether imine) dendritic liquid crystals of identical dendrimer generations

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