Poly(propylene imine) dendrimers functionalized with stilbene or 1,4-distyrylbenzene chromophores

Two generations of dendritic nanoparticles were prepared, which contain (E)-stilbene or (E,E)-1,4-distyrylbenzene chromophores in the 4 or 8 terminal positions of the propylene imine dendrons. The compounds show a highly efficient photoreactivity. On prolonged irradiation all stilbenoid chromophores were destroyed by oligomerization (crosslinking) and the typical absorption and fluorescence of the chromophores disappeared completely.     

Novel highly fluorescent dendritic chiral amines: synthesis and optical properties

An efficient approach to dendritic chiral amines through the allylation of optically active imines bearing chiral auxiliaries were developed. The addition of allylic zinc catalyzed by CeC1₃·7H₂O to chiral imines derived from 2-thiophenecarboxaldehyde and α-amino acid esters conveniently and efficiently afforded the corresponding homoallylic amines with excellent diastereoselectivity. Such addition reactions employing diimines or triimines of the polycyclic aromatic derivatives also produced the chrial multiallylic dendritic amines with the similar diastereoselectivity. The investigation of their photophysical properties including UV-vis absorption and fluorescence spectra as well as circular dichroism (CD) indicated that it did not affect the absorption of the precursors to induce the chiral auxiliaries; however, that the whole molecules exhibited the obvious CD behaviors.     

Synthesis of phosphorus dendrimers bearing chromophoric end groups: toward organic blue light-emitting diodes

Several series of phosphorus dendrimers decorated by potential fluorescent end groups (naphthalene, anthracene, and pyrene) have been synthesized. Unexpectedly, we found that it is absolutely necessary to link the fluorophore to the dendrimer through an alkyl link, and not directly through heteroelements such as oxygen or nitrogen, in order to preserve the fluorescence. One series of dendrimers from generation 1 (6 pyrene end groups) to generation 4 (48 pyrene end groups) has been tested for the elaboration of organic light-emitting diodes (OLEDs). The threshold voltage for the emission of light is high (over 20 V), however, electroluminescence is observed in all cases.     

Rhodium or ruthenium units peripherally coordinated to carbosilane dendrimers functionalized with P-stereogenic monophosphines

Carbosilane dendrimers containing P-stereogenic monophosphines as terminal groups, Dend-{CH₂PPhR}_n (R = 2-biphenylyl or 9-phenanthryl), were reacted with [RhCl(COD)]₂ or [RuCl₂(p-cymene)]₂ to afford the corresponding chiral metalladendrimers Dend-{CH₂PPhR(RhCl(COD))}_n or Dend-{CH₂PPhR(RuCl₂(p-cymene))}_n, respectively. Attempts to obtain the first generation Ru-dendrimer for R = 2-biphenylyl proved unsuccessful, probably due to the steric hindrance of R. Complete characterization of these species was achieved by multinuclear NMR spectra, including 2D experiments, mass spectrometry, and optical rotation determinations. The catalytic properties of the rhodium dendrimers were tested in the hydrogenation of dimethylitaconate and those of the ruthenium derivatives in the asymmetric hydrogen transfer of acetophenone. The following model chiral compounds, (CH₃)₃Si{CH₂PPhR(RhCl(COD))} and (CH₃)₃Si{CH₂PPhR(RuCl₂(p-cymene))}, were prepared in order to detect potential dendritic effects. All compounds were active in the catalytic conditions tested, but low or null e.e. were found.     

Exclusion chromatography of polypropylenamine dendrimers

Size-exclusion chromatography of polypropylenamine (POPAM) dendrimers is investigated. The nitrile-terminated half-generations can be analysed on polystyrene-divinylbenzene-based column packings using tetrahydrofuran as a mobile phase. Several basic and acidic aqueous phase systems were compared for exclusion chromatography of POPAM-amine dendrimers. The optimum system consists of a reversed-phase silica stationary phase deactivated by tetraazacyclotetradecane and a mobile phase of 0.25 M formic acid at 60°C. Several by-products were identified by thermospray mass spectrometric detection.     

Water-soluble azobenzene dendrimers

Water-soluble azobenzene-cored dendrimers 4-6 were synthesized as potential photoresponsive micelles to which the aggregation is triggered by photoirradiation. In the absorption spectra, the π- absorption band of the dendrimers largely blue-shifted with increasing the generation due to the shielding effect of surrounding dendron on the interaction between the core azobenzene and solvent water. Not only the surrounding dendron groups suppressed the E-to-Z photoisomerization, but also the rate of thermal Z-to-E isomerization depended on the generation of the dendrimer. Furthermore, we have observed a novel temperature dependence of the rate constant of the thermal isomerization.     

Convergent synthesis of second generation CCK-functional dendrimers

This paper describes the facile synthesis and characterization of novel dendrimers bearing 9 and 12 CCK pepfide fragments on the surface by a convergent method. The structures of dendrimers are characterized by NMR and MS spectrum.     

Dielectric relaxation in carbosilane dendrimers with cyanobiphenyl end groups

Carbosilane dendrimers of generation 1 and 2 are functionalized with mesogenic end groups (cyanobiphenyl) via spacers of 5 and 11 carbons. The dielectric relaxation is measured over broad frequency (1 Hz–1 GHz) and temperature (170–470 K) ranges. Two relaxation regimes are observed and characterized as δ and β relaxation. The δ relaxation is nearly a single Debye process and varies strongly with temperature. The S_E to S_A transition observed for the dendrimers with long spacers causes a jump in the relaxation rate of the δ process. The β process displays an Arrhenius-type temperature dependence with an activation energy of 35 kJ/mol. The relaxation time depends on spacer length. The dielectric relaxation reflects the mutual distortion of the dendrimer scaffold and the smectic layers. Received: 9 June 1999 Accepted in revised form: 21 July 1999     

Preparation of functionalized primary chiral amines and amides via an enantioselective three-component synthesis of propargylamines

A general preparation of functionalized primary chiral amines and amides from propargylamines has been developed. The chirality is established by an enantioselective three-component reaction of an aldehyde, a terminal alkyne and a secondary amine in the presence of copper(I) bromide/Quinap as the catalytic system leading to chiral propargylamines in high yields and enantioselectivities. Functionalization and reduction leads to various primary amines and amides.     

New synthesis of trifluorinated amines from 1-bromopropargylic amines in superacid

Treatment of 1-bromopropargylic amines affords the corresponding 1,1,1-trifluoro in one step in HF-SbF₅ medium. 1-Bromo-1,1-difluoro or 2-bromo-1,1,1-trifluoro derivatives could also be prepared, depending on the reaction conditions.     

Stereoselective synthesis of N-heterocycles: application of the asymmetric Cu-catalyzed addition of Et2Zn to functionalized alkyl and aryl imines

The preparation of N-heterocycles from alkyl- and aryl-substituted imines is described. The key step involves a copper-catalyzed addition of diethylzinc to functionalized alkyl-substituted imines that were generated in situ from the sulfinic acid adducts. The nucleophilic addition products were then converted to 2-substituted pyrrolidines and piperidines. Aryl-substituted imines were transformed into enantioenriched 1- and 1,4-substituted tetrahydroisoquinolines.     

Catalysis by titanocene-functionalized polymer-supported dendrimers

A series of variously-functionalized first-, second-, and third-generation dendrimers have been prepared and linked via a biphenyl core to a bis-styryl moiety suitable for use as a crosslinker in polymerization. Attachment of titanocene moieties to the first-generation system and copolymerization with styrene affords polymeric disks that exhibit catalytic properties superior to comparable solution-phase systems in a multicomponent coupling of chlorosilanes with Grignards to give bis-allylic silanes.     

Synthesis and photophysical properties of triphenylamine-based dendrimers with 1,3,5-triphenylbenzene cores

Two new conjugated dendrimers bearing a triphenylamine moiety as dendrons and 1,3,5-triphenylbenzene as a core have been synthesized through a convergent synthetic strategy. These conjugated dendrimers have high fluorescence quantum yields and exhibit similar absorption and emission behaviors in solutions and in solid films, which demonstrate that these dendrimers form good amorphous states.     

Accelerated methods of synthesis of phosphorus-containing dendrimers

In order to shorten the long and tedious synthesis of dendrimers, several improvements have been proposed. This paper is a review of the improved methods recently published concerning the synthesis of phosphorus-containing dendrimers. It describes first the synthesis of hyperbranched polymers and their comparison with real dendrimers obtained from the same monomer. Then, the influence of the modification of the core of dendrimers is shown. In a third part, the use of dendrons is illustrated by several examples; they allow for instance to built a generation 8 directly from a generation 3 dendrimer. The last part describes the use of branched monomers of types AB₂ and CD₂, in which A reacts only with D and B reacts only with C. These reactions do not need any protecting groups, and the only by-products are H₂O and N₂. Using these monomers, the 4th generation is obtained in only four steps, instead of 8 for classical methods. This method has been improved by using more branched monomers AB₅ and CD₅, built from the cyclotriphosphazene. In this case, a dendrimer having 750 end groups is obtained in only three steps. The A (NH₂), B (PPh₂), C (N₃) and D (CHO) functions are identical in all cases, and they allow a real “Lego” chemistry, as shown by the synthesis of CA₂ and DB₂ monomers, also used for the accelerated synthesis of dendrimers.     

Symmetrical and unsymmetrical incorporation of active biological monomers on the surface of phosphorus dendrimers

Phosphorus-containing dendrimers are attractive carriers for the delivery of bioactive molecules due to their very particular architecture, globular shape and chemical and physical properties. Herein we report a simple synthetic approach of ethacrynic acid derivatives loaded-phosphorus dendrimers by symmetrical grafting of ethacrynic acid analogues by nucleophilic substitution of each chlorine of P(S)Cl₂ end groups. We report also for the first time an unsymmetrical grafting of two different phenol derivatives by a selective substitution of one chlorine of P(S)Cl₂ end group followed by the grafting of the second phenol.     

Epoxy-based polymer bearing activated azo dye (methyl orange) units: novel colorimetric indicator for amines

Novel epoxy-based polymer 2-bearing activated azo dye, 4-(4-sulphophenylazo)-N,N-dimethylaniline (methyl orange), moieties were synthesised by post-azo-coupling reaction of poly(hydroxy ether amine) 1 and investigated sensory responses towards amines. The reversible protonation–deprotonation chemistry of activated azobenzene moiety makes it of potential use as a colorimetric indicator for amines.     

Synthesis, characterization and optical response of polyene-cored stilbenoid dendrimers

The synthesis of first- and second-generation dendrimers bearing phenylenevinylene chromophores within the dendritic branches (stilbenoid dendrimers) and polyenes (3 and 5 double bonds) as cores is described. A preliminary study of the optical properties of the resulting compounds was conducted by UV/vis and fluorescence spectroscopy.     

Convergent synthesis of dendrimers based on 1,3,3-trisubstituted 2-oxindoles

Dendrons and dendrimers were convergently prepared using an isatin as AB₂ monomer by superelectrophilic arylation in trifluoromethanesulfonic acid. This strategy has the advantage that incomplete reactions of the AB₂ monomer are minimized, thus simplifying purification. As the obtained dendrons/dendrimers are analogues of the hyperbranched polymers with a degree of branching of 100% developed earlier in our group, an opportunity is created to compare the latter with their structurally perfect counterparts.     

Model studies towards liquid crystalline dendrimers with mesogenic repeat units throughout the structure

Model studies towards liquid crystal dendrimers in which the mesogenic units are based on alkoxyalkylbiphenyls and repeat through the structure are described; the parent monomers show smectic mesophases demonstrating the suitability of the motifs.     

Liquid crystalline dendrimers based on cinnamates and coumarins

New poly(propylene imine) (PPI) dendrimers modified at the periphery with mesomorphic 4-cyanobiphenyl units and cinnamate- or coumarin-based photoactive moieties were synthesised and structurally characterised. The photoactive moieties were structurally designed to be liquid crystalline compatible and to reduce the tendency towards crystallisation of the final material. Thermal and liquid crystal properties were studied by POM, DSC, TGA and XRD. The results show that all dendrimers displayed a smectic A mesophase. Dendrimers with high transparency in the visible region but with different absorption spectra were obtained, rendering materials that are easy to monitor in light-irradiation experiments.