An alternative convergent synthesis of dendrimers with 2,5-diarylsilole at the core

Dendrimers with 2,5-diarylsilole at the core are readily synthesized by the Ni-catalyzed reaction of 1,1,2,2-tetramethyldisilane and 1,6-diynes having poly(benzyl ether)-dendron units. The dendrimers display, upon excitation of the silole ring, an emission at about 500 nm. The fluorescence quantum yield of the dendrimers increases with increasing the generation of the dendron units. In addition, upon excitation of dendron units in the periphery, the dendrimers also display an emission from the silole ring at the core through the energy transfer from the dendron units to the silole core within the dendrimers.     

Bathochromic shift of the fluorescence spectral maximum with increasing generation of dansyl labeled Newkome type dendrimers

Dansyl moiety attached to the core of Newkome-type dendrimers shows a bathochromic shift of the fluorescence emission spectrum with increase in dendrimer generation. However the E_T(30) plots in different solvents show a decrease in slope with increasing generation. This has been explained in terms of modification of transition energies and progressive shielding of the fluorophore with increasing generation.     

Synthesis and characterization of anthracene-clustering dendrimers: observation of fluorescence resonance energy transfer in the multichromophoric system

A series of anthracene-clustering dendrimers bearing various aliphatic substituents at the terminal positions were synthesized using a direct coupling strategy. A remarkable effect of the side chains was imparted to chemical properties of the dendrimers such as drastically increased solubility. Although the multibranched anthracene arrays in the dendritic architectures exhibited no cooperativity in terms of the absorption feature and behaved as single chromophoric systems, investigations focusing on fluorescence properties revealed that a type of cooperativity was present as expressed in the reduced quantum yields of fluorescence. An alternative approach utilizing time-resolved fluorescence decay measurements clearly demonstrated that the most reasonable mechanism of the cooperative action should involve two discernible channels of intramolecular fluorescence resonance energy transfer (FRET) occurring from one chromophore to the others within and across junctions of the branching units.     

The first examples of anthracene capped chiral carbohydrate derived dendrimers: synthesis, fluorescence and chiroptical properties

The first examples of anthracene capped chiral dendrimers derived from a 1,3,5-trisubstituted aromatic core and carbohydrate units in the interior and periphery are described. Excimer formation was evident from the fluorescence spectrum, and both fluorescence and chiroptical properties indicated that the dendrimer does not undergo aggregation in the ground state.     

Layer-by-layer assembled thin films composed of carboxyl-terminated poly(amidoamine) dendrimer as a pH-sensitive nano-device

Dendrimer-containing multilayer thin films have successfully been prepared by a layer-by-layer deposition of carboxyl-terminated poly(amidoamine) dendrimer (PAMAM–COOH) and poly(methacrylic acid) (PMA) on a solid surface at pH 4.0, while the multilayer film did not form at pH 7.0. The PMA/PAMAM–COOH multilayer films prepared at pH 4.0 are decomposed at neutral pH due to electrostatic repulsion between negatively-charged carboxylate residues. The results suggest that the primary force for the successful deposition of PAMAM–COOH and PMA at pH 4.0 is hydrogen bonding between COOH residues on the surface of the dendrimer and PMA. The multilayer films are decomposed also at strongly acidic pH, suggesting an electrostatic force of attraction between the protonated tertiary amino groups in PAMAM–COOH and a small fraction of COO⁻ residues in PMA contributes in part to the multilayer formation at pH 4.0. The PMA/PAMAM–COOH thin films can accommodate model dyes, Rose Bengal and 5,10,15,20-tetraphenyl-21H,23H-porphinetetrasulfonate, and the release can be controlled by changing pH.     

Poly(benzyl ether) dendrimers with strongly fluorescent distyrylbenzene cores as the fluorophores for peroxyoxalate chemiluminescence: insulating effect of dendritic structures on fluorescent sites

Poly(benzyl ether) dendrimers containing strongly fluorescent distyrylbenzene cores were synthesized, and their fluorescence and electrochemical properties as well as the action as fluorophores in the chemiluminescence reactions were investigated. While all the dendrimers exhibited almost the same properties except for their intensities, a characteristic feature due to the dendritic structure was observed in the electrochemical behaviors. In the peroxyoxalate chemiluminescence reactions using these dendrimers as fluorophores, a bimolecular interaction between the high-energy intermediates and fluorophores was established, and a decrease in the chemiluminescence intensity with an increasing generation was observed, which was connected with the insulating effect of the dendritic structures on the core.     

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.     

Synthesis and photophysical properties of phenothiazine-labeled conjugated dendrimers

A novel class of conjugated dendrimers bearing phenothiazines as peripheral groups and phenylenevinylene-group as a core has been synthesized through the Wittig-Horner reaction in moderate to good yield.     

Synthesis of carbosilane dendrimers with N,N-dimethylaniline as end groups

Carbosilane dendrimers with 4-bromo-N,N-dimethylaniline as end groups were synthesized from methyltrichlorosilane, allyl chloride, magnesium and 4-bromo-N,N-dimethylaniline. All compounds were characterized by 1H NMR, IR, MS.     

Chemiluminescence change of polyphenol dendrimers with different core molecules

Second generation polyphenol dendrimers (PDs) with different core molecules were synthesized, and their chemiluminescence (CL) was measured by reacting the PDs with H2O2 under alkaline conditions. All of the PDs showed a strong CL, more than 120-fold greater than that of gallic acid. Various CL intensities of the PDs were obtained using different core molecules in the PDs. The distance between each dendron in the PD structure is crucial in the PD CL intensity.     

Synthesis and photoresponsive study of azobenzene centered polyamidoamine dendrimers

A new series of novel polyamidoamine (PAMAM) dendrimers 4, 5 and 6 possessing azobenzene units specifically at the core were prepared and their reversible trans/cis photoisomerization properties were studied. PAMAM dendritic wedges as well as azo-based PAMAM dendrimers were fully characterized by means of FT-IR, NMR (¹H and ¹³C), mass spectrometry (MALDI-MS), thermogravimetric and elemental analysis.     

Hydrozirconation of first-generation allyl-functionalized dendrimers and dendrimer model compounds

Several allyl-functionalized dendrimers and mono-functional model compounds have been prepared. These have been hydrozirconated using [Cp₂ZrHCl]_x to give zirconocene terminated dendrimers. These dendrimers have been characterized using spectroscopic techniques, particularly NMR.     

Synthesis of carbosilane dendrons and dendrimers derived from 1,3,5-trihydroxybenzene

Several carbosilane wedges of generations 1-3 have been synthesized, following the divergent method, containing at the focal point a C-Br bond and as peripheral functional groups SiMeCl₂, SiMe(C₃H₅)₂, SiMe₂Cl, SiMe₂H, and ester units SiMe₂{(C₃H₆)N(C₂H₄CO₂Me)₂}. The dendrons functionalized with SiMe(C₃H₅)₂ and SiMe₂{(C₃H₆)N(C₂H₄CO₂Me)₂} groups were used to synthesize spherical dendrimers derived from 1,3,5-(HO)₃C₆H₃, leaving the outer groups unchanged. The allyl dendrimers thus obtained were used as precursors to prepare new dendrimers functionalized with SiMeCl₂, SiMe₂Cl, SiMe₂H, amine units SiMe₂{(C₃H₆)NH₂} and also ester units SiMe₂{(C₃H₆)N(C₂H₄CO₂Me)₂}.     

Synthesis and characterization of dendrons and dendrimers skeleton-constructed with azobenzene moiety

A series of dendrons and dendrimers skeleton-constructed with azobenzene moiety based upon 4-carboxy-4′-(1,2-propanediolether)-azobenzene as an AB₂ monomer, via a convergent approach, proceeding in a repeated stepwise growth manner starting from 4-carboxy-4′-(n-butylether)-azobenzene as a peripheral monomer, were synthesized, and characterized by NMR, FTIR, and MALDI-TOF-MS analysis. Their regular molecular architecture and thus monodispersed molecular weights were confirmed by GPC. The UV-Vis absorbance and ¹H NMR spectrum study indicated that the azobenzene moieties in CHCl₃ solution took fully trans-cis isomerization under UV irradiation, and reversely isomerization back to the trans by visible light irradiation or by heat.     

Synthesis of 1,2,4-triazole dendrimers

A convergent synthetic strategy towards novel 1,2,4-triazole dendrimers, in which 3,5-dichloro-4-(4-methoxyphenyl)-4H-1,2,4-triazole was used as the heterocyclic building block, was successfully explored. Nucleophilic aromatic substitution at this novel AB₂-monomer was used as the key step in the propagation of the heterocyclic dendrons and these dendrons were attached to both a 1,3,5-triazine and a methylene core. The peripheral 1,2,4-triazole could be varied not only by nucleophilic aromatic substitution but also by Suzuki cross-coupling. The presented dendrimers are promising candidates to be used in applications where the large number of heteroatoms can be exploited or a better resistance to the applied conditions is required.     

A new way for the internal functionalization of dendrimers

The selective reaction of amines and hydrazides with only one Cl on each P(S)Cl₂ or P(O)Cl₂ end group of phosphorus dendrimers, followed by the grafting of hydroxybenzaldehyde on the remaining P-Cl functions, and the subsequent growing of the dendrimer from the aldehyde is described. Allyl and pyrene derivatives have been grafted in this way inside the dendrimers during their growing. This constitutes a new way for the internal functionalization of dendrimers.     

A novel nanocomposite material prepared by intercalating photoresponsive dendrimers into a layered double hydroxide

A novel combination for an inorganic-organic nanocomposite material was demonstrated. Anthryl dendron, i.e., poly(amidoamine) dendron with an anthracene chromophore group at the focal point, was incorporated in the interlayer space of ZnAl-NO₃ type layered double hydroxide (LDH) through an anion-exchange reaction. The photoabsorption and fluorescence properties of the resulting material were different from those of the bare anthryl dendron molecule. It was suggested that the change in photochemical properties was due to the organization and π-π interaction of anthracene chromophores within the interlayer of the LDH.     

Synthesis and DSSC application of novel dendrimers with benzothiazole and triazole units

Synthesis of novel dendrimers with benzothiazole as surface group and triazole as branching unit is achieved through click chemistry. The presence of more number of benzothiazole and triazole units increases the molar absorption coefficient and alters the fluorescence as well as electrochemical behaviors in the dendrimers. Dye-sensitized solar cell (DSSC) studies reveal that dendrimers with more number of benzothiazole and triazole groups exhibit better current generating capacity than the dendrimers with lesser number of benzothiazole and triazole groups. Dendrimer 2b shows the maximum current conversion efficiency (η) of 7.1%.     

Nanoscale substrate recognition by porphyrin dendrimers with patched structures

Dendrimer technology has enabled us to build macromolecules with nanosized defined structures. By introducing unsymmetrical patched structures in dendrimers, sophisticated artificial receptors exhibiting nanoscale substrate recognition can be obtained. In this review article, our recent studies on molecular recognition by porphyrin dendrimers with patched structures are summarized. Three topics are presented: (1) oligopeptide-patched dendrimers as a nanoscale receptor of cytochrome c protein; (2) pocket dendrimers as a nanoscale receptor for bimolecular guest accommodation; and (3) energy transfer in unsymmetrical dendrimers. These dendrimers nicely mimic proteins and enzymes, and also act as photofunctional artificial receptors, in which porphyrin’s strong photoabsorption and intense fluorescence signals can respond sensitively to the substrate binding.     

Synthesis, characterization, and electroluminescent properties of star shaped donor-acceptor dendrimers with carbazole dendrons as peripheral branches and heterotriangulene as central core

Luminescent and redox-active heterotriangulene-based dendrimers (G1 and G2) of first and second generation have been synthesized, and their photophysical properties, oxidation behaviors, and applications in organic light emitting diodes (OLEDs) have been investigated. The dendrimers show efficient aggregation-induced emissions originated from the carbazole dendrons, heterotriangulene core, intramolecular charge-transfer (ICT), and intermolecular aggregation absorptions. Highest-occupied molecular orbital and lowest-unoccupied molecular orbital (HOMO and LUMO) values were acquired using UV-vis spectroscopy and cyclic voltammetry. The OLEDs fabricated with G1 and G2 as non-doping emitters exhibit exclusive aggregation-induced luminescence peaking at 600 and 630 nm, respectively, and demonstrate a good performance with maximum luminance of 1586 cd m⁻² at current efficiency of 5.3 cd A⁻¹ for G1 and 827 cd m⁻² at current efficiency of 6.9 cd A⁻¹ for G2.