Dendron Generation Research Articles

A Horner-Wadsworth-Emmons approach to dipolar and non-dipolar poly(phenylenevinylene)dendrimers

The synthesis of first generation phenylenevinylene dendrimers is described. The Horner-Wadsworth-Emmons reaction is used for this purpose. The reported methodology permits the preparation of dipolar and non-dipolar structures. A second generation dendron bearing peripheral electron donor groups is also reported.

Molecular Structure−Property Relationships for Electron-Transfer Rate Attenuation in Redox-Active Core Dendrimers

Two series of redox-active, iron−sulfur core dendrimers of the general structure (nBu4N)2[Fe4S4(S-Dend)4] (Dend = dendrons of generations 1 through 4) were prepared. Heterogeneous electron-transfer rate constants indicated that the rigid series of dendrimers were more effective at attenuating the rate of electron transfer than were the flexible series of dendrimers. These results were rationalized using computationally derived models which indicated an offset and mobile iron−sulfur core in the flexible series of molecules and a more central and relatively immobile iron−sulfur core in the rigid series of molecules. Further consideration of these data indicated that, while the dendrimers containing rigid ligands had better encapsulated redox cores for a given molecular weight, these molecules had higher electron-transfer rates for a given molecular radius.

A Novel Attempt to Control the Aggregation Number of Dendrons with a Saccharide

Abstract New dendrons containing a saccharide core were synthesized. In organic solvents these dendrons formed self-assembled particles due to the hydrogen-bonding interaction and the particle size decreased with the increase in the generation of dendrons. In this system the saccharide moieties provide a driving-force for aggregation whereas the dendritic moieties provide steric crowding for deaggregation. These two opposing effects balance with each other to control the particle size.

How Dendrons Stiffen Polymer Chains: A SANS Study

The conformation of various polystyrene chains with first (G-1), second (G-2), and third generation (G-3) Fréchet-type dendrons at the repeat unit has been investigated with small-angle neutron scattering. The increased density of the attached dendrons leads to a systematically greater cross-sectional chain diameter D. Bulky, high generation dendrons force the polymer backbone out of its all-trans conformation. The measured statistical Kuhn segment length initially increases in proportion to the chain diameter and then to a greater degree due to steric overcrowding and the concomitantly higher bending rigidity. The introduction of charges further leads to chain expansion and the development of interchain correlations. High molecular weight (G-2) chains develop fully excluded-volume chain properties with a Flory exponent of v = 0.57 and a critical exponent γ = 0.86 which is related to the enhancement of chain configurations with widely separated chain ends.

Concave reagents 29 [1] Dendrimer fixed concave pyridine

A concave pyridine 1c has been attached to dendrimers of the Frechet type by an ethylenoxide linker on the convex outside of the catalyst. Two generations of dendrons [G-1]-OH, [G-2]-OH,[G-1]-Brand [G-2]-Br and of dendrimers with 4,4′-dihydroxybiphenyl (3) and 1,1,1-tris(4-hydroxyphenyl)ethane (4) as di- and trivalent cores [G-1]2–[C2], [G-1]3–[C3] and [G-2]3–[C3] have been synthesized. The resulting molecules possess up to twelve concave catalytic pyridine centers on the outside of the molecules, and can be used as selective catalysts in the base catalyzed addition of alcohols to diphenylketene.

Preparation of Poly(ether ketone) Dendrons with Graded Structures

New highly branched poly(ether ketone) dendrons, with graded structures, were synthesized by the convergent approach using aromatic nucleophilic substitution reactions. Four kinds of compounds3,5-bis(4-fluorobenzoyl)anisole, 1; 4-methoxy-3‘,5‘-bis(4-fluorobenzoyl)-biphenyl, 2; 4-methoxy-3‘ ‘,5‘ ‘-bis(4-fluorobenzoyl)-p-terphenyl, 3; and 4-methoxy-3‘ ‘‘,5‘ ‘‘-bis(4-fluorobenzoyl)-p-quaterphenyl, 4(numberedin the order of the phenylene length) were used as the building blocks, where the methoxy groups were the protected form of hydroxy groups. The reactions of 1 with phenol gave the first generation dendron, G1. Next, after the methoxy group of G1 was converted to the hydroxy derivative, G1−OH by the reaction with aluminum chloride, the resultant phenol functionality of G1−OH was allowed to react with 2 to yield the second generation dendron: G2. By repeating the procedure, further generations G3 and G4, were prepared using 3 and 4 as the building block, respectively. The 1H and 13C NMR spectra were consis...

Dendritic Pseudorotaxanes.

Self-organization is the key. A series of dendritic pseudorotaxanes were efficiently constructed from complementary building blocks-namely, a three-armed, triply charged ammonium salt and the first, second, and third generations of benzyl ether dendrons bearing the dibenzo[24]crown-8 moiety. The pseudorotaxane arising from the third-generation dendron is shown in the picture.

Layered Dendritic Block Copolymers.

A star-shaped molecule and a layered structure are displayed by the title compound, where the layers consist of high molecular weight polymers. A core molecule that is functionalized by six hydroxyl groups acts as the initiator for the ring-opening polymerization of ε-caprolactone, leading to a six-arm star polymer. The second layer of the dendritic block copolymer with 12, 24, or 48 hydroxyl groups (depending on the dendron generation in use) is obtained by the linkage of chain ends with functionalized dendrons. These macromoleculse act as "macroinitiators" for the construction of a further layer of poly(ε-caprolatone), the third generation of dendritic block copolymers.

Second harmonic generation of dipolar dendrons in the assembled thin films

Dendritic macromolecules, called ‘dendrons’, having a branching structure modified with an electron donor/acceptor functionalized azobenzene chromophore have been synthesized. The structurally different dendrons possess a different number, 1, 3, 7, and 15, of chromophore units. The second harmonic generation (SHG) of dendrons was measured in the molecular assembled thin films prepared by the Langmuir–Blodgett (LB) transfer technique. The SHG results indicated that dendrons could be highly organized in these films, where film structure and molecular orientation were analogous to those in the conventional SHG active LB films. The SHG intensity for these molecular organized thin films revealed that the individual chromophores in dendrons were oriented non-centrosymmetrically and coherently contributed to the increase in their molecular hyperpolarizability. The SHG activity became larger as the number of branching units of dendrons increased. The highest molecular hyperpolarizability was found to be 4000×10−30 esu for a dendron containing 15 chromopholic units. The SHG result suggested that the structure of dendrons synthesized was uniaxally dipolar, and that there was a particular merit in this structure for the generation of SHG.

ChemInform Abstract: Monofunctionalized Dendrons of Different Generations as Reagents for the Introduction of Dendritic Substituents

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

First steps towards alternating copolymers from a functionalized [1.1.1]propellane and dendronized acrylates

The synthesis of some alternating copolymers from a tert-butyl(dimethyl)silyl protected hydroxymethyl substituted [1.1.1]propellane and acrylates carrying Frechet-type dendrons of the first and second generation is described. A copolymer with a second generation dendron at every repeat unit was obtained with M w = 43 700 as determined via gel permeation chromatography.

Self-assembling bis-dendritic peptides: design, synthesis and characterization of oxalyl-linked bis-glutamyl peptides [Glu(n)(CO2Me)n + 1-CO-]2; n = 1,3,7.

Three generations of glutamic acid dendrons [Glu(n),(CO2Me)n + 1; n = 1, 3, 7] have been joined together head-to-head by an oxalyl unit to form highly sterically congested bis-Glu-dendritic peptides with gelling properties. The single crystal X-ray structure of the first generation bis-dendritic peptide showed an extended hydrogen-bonded chiral tape with modest nonlinear optical activity.

Monofunktionalisierte Dendrons verschiedener Generationen - als Reagenzien zur Einf�hrung dendritischer Reste

Monofunctionalized Dendrons of Different Generations – as Reagents for the Introduction of Dendritic Substituents In recent years dendrimers become more and more important not only in organic chemistry. They represent a new class of molecules with unique characteristic features. But dendrimers represent not only designed molecular architecture. They stand for a new concept in chemistry. They can be used to alter the properties of already existing molecular skeletons or they can be used to transfer new properties to a classical functional unit. This means that functionalized dendrimers and dendrons (dendritic building blocks) can be regarded as reagents for the preparation of new compounds with dendritic properties. In this article the synthesis and the practical use of appropriate dendritic reagents is explained. Furthermore we introduce the new technical terms „{n} dendryl-”︁ for dendritic substituents of n generations and „dendriagent”︁ which stands for dendritic reagents. Moreover we give a short outlook on future developments.

Preparation of Chromophoric Dipolar Dendrons as Second-Order Nonlinear Optical Material

AbstractDendritic macromolecules, called “dendrons,” having a branching structure modified with an electron donor/acceptor functionalized azobenzene chromophore have been synthesized. The structurally different dendrons possess different numbers, 1, 3, 7, and 15, of chromophore units. The second harmonic generation (SHG) of dendrons was measured in the molecular oriented thin films prepared by the Langmuir-Blodgett film transfer technique. In such structurally organized thin films, individual chromophores coherently contribute to the increase in the molecular hyperpolarizability of dendrons. The SHG activity became large as the numbers of branching units of dendrons increased. The highest molecular hyperpolarizability was found to be <8000×10−30 esu for dendron containing 15 chromophoric units. The SHG results suggest that the structure of dendrons synthesized is uniaxially dipolar, and that there is a particular merit in this structure for the generation of SHG.

Synthesis of a Series of Focally-Substituted Organothiol Dendrons

The synthesis of new organothiol-functionalized dendrons of generation 1−4 is described. Several modifications to the original method for preparation of dendrons are detailed that were found to improve the yield and aid in scale-up. A particularly advantageous method for preparation of an aromatic thiol is reported and is employed in this reaction sequence. Several uses of these dendrons are anticipated and briefly described.

Convergent synthesis of starburst poly(ether ketone) dendrons

New highly branched starburst poly(ether ketone) dendrons were synthesized by the convergent approach through aromatic nucleophilic substitution reactions. 3,5-Bis(4-fluorobenzoyl)anisole was used as the building block, where the methoxy group was a protected form of the hydroxy group. The reaction of the building block with phenol gave the first-generation dentron (G1). Next, after the methoxy group was converted to a hydroxy group by reaction with aluminum chloride, the resulting phenol functionality of G1-OH was allowed to react with the building block to yield the second-generation dendron (G2). By repeating these procedures G3 and G4 generation dendrons possessing 8 and 16 phenoxy groups, respectively, at the periphery position were obtained