Carbon dendron nano-chains with π-extended conjugation based on end-capped N,N-dimethylamino in linear 1,4-phenylethynyl or in 1,5-naphthylethynyl subunits: fluorescence analysis

The synthesis of dendrons with the end-capped 5-(N,N-dimethylamino)naphthyl-1-ethynyl unit connected to conjugated naphthylethynyl or p-phenylethynyl chains, as the branches of the 1,3,5-substituted benzene core, have been undertaken by heterocoupling reaction between 1,3,5-triiodobenzene and the convenient end-capped 5-(N,N-dimethylamino)naphthylacetylene or 5-(N,N-dimethylamino)naphthylethynylphenylacetylene in the presence of the palladium-copper catalyst system, in excellent yields. The influence of the alternating naphthylethynyl-phenylethynyl chains on the fluorescence emission radiation, in the dendron structures, has been analyzed.     

Second-harmonic properties of dendritic polymers skeleton-constructed with azobenzene moiety used for nonlinear optical materials

A series of dendrons and dendrimers skeleton-constructed with azobenzene moiety were synthesized and doped in a high T_g polycarbonate (PC) as a host for nonlinear optical (NLO) materials. The optimal loading density and poling conditions were investigated using UV-vis spectral and second-harmonic generation (SHG) measurements. The results showed that the dendrons and dendrimers have good solubility in PC host, which increased with the generation increased. Moreover, the SHG measurements indicated that the dendrons possess higher nonlinearity than the dendrimers. The chromophores of lower generation dendrons were easier to orient along the poling electric field and gave a cone shape with the azobenzene branching units, which coherently contributed to the molecular hyperpolarizability and resulted in the higher SHG intensity. The temporal stability of the dendrons with 15% loading density was also investigated, and showed that the decaying in nonlinearity was slower for higher generation dendrons.     

Photoresponsive organogels: an amino acid-based dendron functionalized with p-nitrocinnamate

An amino acid-based dendron 1, synthesized and focally functionalized with p-nitrocinnamate, can self-assemble into fibrous network in common organic solvents at low concentration. The most remarkable character of the gel from 1 is photoresponse besides thermo-reversible response. Upon irradiation with UV light at 365 nm, gel to sol transition occurred resulting from the photodimerization of p-nitrocinnamate groups. On the other hand, when the obtained solution was further exposed to short wavelength of UV light at 254 nm, the gel re-formed because of the photocleavage reaction.     

Crowned dendron: ion-responsive flexibility of macromolecules induced by integrated crown ether moieties

Polybenzyl ether type dendrons bearing the crown ether moieties at the periphery, namely, crowned dendrons were synthesized, and the effect of complex formation on their flexibility with metal-ion binding properties was examined. Upon addition of Na⁺, ¹H NMR spectra of the crowned dendrons in CD₃CN were significantly broadened, reflecting the flexibility restriction of the crowned dendrons by the complex formation with Na⁺. Such a significant flexibility restriction was observed only with Na⁺, although ESI-MS studies revealed that the crowned dendrons formed 1:2 complexes (a metal ion:the crown ether moiety) regardless of the kind of metal ions. The flexibility restriction became significant with increasing dendron generation on the basis of ¹H NMR spectra and spin-lattice relaxation time (T₁) measurements. Binding constants of the crowned dendrons with metal ions in CD₃CN decreased with the increase of the dendron generation, reflecting an influence of the charge repulsion as well as a dendrimer effect to cause the steric hindrance. The examination of UV-vis absorption spectra for complexes of the crowned dendron with metal picrates in THF displayed the formation of a loose ion-pair complex with Na⁺, namely, a typical sandwich type complex. However, in CH₃CN, all metal picrates were solvated to be in a loose ion-pair even without complex formation. These results suggested that the control of macromolecular flexibility with metal ions is feasible by the integration of crown ether moieties with a dendritic structure.     

Interaction between glutathione and glutathione-S-transferase on dendron self-assembled controlled pore glass beads

Controlled pore glass beads were modified with a conical shaped dendron and interaction between immobilized glutathione on top of the dendron and glutathione-S-transferase (GST) in cell lysate was examined. SDS-PAGE chromatogram showed that the dendron modified beads were effective not only in binding the corresponding proteins such as GST and GST-fused proteins but also in suppressing the nonspecific binding of proteins. Dramatic increase of ligand utilization (ca. 30%) was observed in comparison with the conventional approaches. Molecular weight dependence of the beads is comparable to that of Sepharose 4B.     

Interfacial assembly and host-guest interaction of anthracene-conjugated L-glutamate dendron with cyclodextrin at the air/water interface

The interfacial assembly of photo-induced dimerization of atypical anthracene-containing amphiphilic dendron and host-guest interaction with γ-cyclodextrin has been investigated.It has been proved that even without long alkyl chain the amphiphilic dendron could still form stable Langmuir monolayer at the air/water interface.Through the host-guest interaction,γ-cyclodextrin can be used to encapsulate two headgroups of amphiphilic dendron in the antiparallel direction.However,the formed host-guest complex was sensitive to the surface pressure.Slight compression of surface pressure led amphiphilic dendron to reassemble into nanofibers through the strong π-π stacking between headgroups.On the other hand,under in sitv irradiation,the amphiphilic dendron was stabilized in the cavity of γ-cyclodextrin through headgroup dimerization and the host-guest complex further irregularly aggregated to nanoparticles.Meanwhile,γ-cyclodextrin,as a silencer,blocked the supramolecular chirality transfer.Our conclusion was demonstrated through UV/vis,FT-IR,CD spectrum and AFM images,respectively.     

Phosphorus-Containing Dendrimers: Towards Applications

The properties and applications of phosphorus-containing dendritic macromolecules in various fields, including material science and biology, are reported.     

Continuous intra- and intermolecular energy transfer in light-harvesting gels from natural amino acids-based dendrons

The gels and co-gels from glycine (Gly) and glutamic acid (Glu)-based dendrons with either tyrosine (Tyr) or tryptophan (Trp), two of the luminescent amino acid residues in natural proteins, at the focal point were prepared (Tyr-AB₄ and Trp-AB₄). It was found that such gels, especially the co-gels from Tyr-AB₄/Trp-AB₄, showed a high efficient energy transfer (ET) and light-harvesting behaviors. Moreover, luminescent gels with tunable emission ranging from blue to green were also observed owing to the cascade intra- and intermolecular ET from dendritic gelators to the guest molecules (PDNS) in the host-guest gel sample (co-gel with PDNS as the guest molecule), which mimicked the natural light-harvesting systems.     

A double heteroatom Mitsunobu coupling with amino hydroxybenzoic acids on solid phase: a novel application of the Mitsunobu reaction to form dendron building blocks

A new highly efficient double heteroatom Mitsunobu coupling with amino hydroxybenzoic acids on solid phase is described. The synthetic routes reported in this work are general and applicable for the preparation of diverse building blocks, controlling protection, arm length, chirality, and peripheral functional groups. These novel units can form unusual dendritic architectures, which could be incorporated into specific complex structures, expanding the scope of dendrimer science.     

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}.