The synthesis and characterization of four dendron-containing tetraphenylethylenes (TPEs), 1(1)-1(4), were synthesized, along with a TPE compound that contained four OCH(2) Ph groups (referred to as 1(0)) for comparison. Photophysical studies revealed that the TPE core became emissive after linking dendrons onto its periphery. Moreover, the fluorescence intensity was significantly enhanced when high-generation dendrons were linked onto the TPE core; the fluorescence intensity increased in the following order: 1(1)<1(2)<1(3)<1(4). This phenomenon was tentatively attributed to an enhancement in the energy barrier for internal rotation and torsion of the TPE core to which four dendrons were connected. In addition, the photocyclization of the TPE core into the respective 9,10-diphenylphenanthrene was facilitated when high-generation dendrons were linked to the TPE core. Again, the photocycliztion reactivity increased in the following order: 1(1)<1(2)<1(3)<1(4). We found that the fluorescence and photocyclization reactivity of TPE could be modulated by covalent interactions with dendrons, and such modulation was strongly dependent on the dendron-generation. 相似文献
Synthesis and characterization of gold‐nanoparticle‐cored dendrimers (NCDs), in which the dendrons are attached to the gold core through gold–carbon bonds, are described. Synthesis of these materials involved the simultaneous reduction of HAuCl4 and a Fréchet‐type dendron with a diazonium group at the focal point, all in an organic solvent such as toluene. These materials possess a nanometer‐sized gold core surrounded by a shell of polyaryl ether dendrons, which are connected radially to the core. The NCDs were characterized by TEM, thermogravimetric analysis (TGA), and IR, UV, and NMR spectroscopic techniques. Average particle diameter of the NCDs ranged from 4.7 to 5.5 nm for the different generations. All NCDs exhibit the characteristic plasmon absorption of gold nanoparticles at 520 nm. Average numbers of dendrons per NCD in AuGn were calculated using results from TGA and TEM studies. Multiple layering of the dendrons is proposed as a possible reason for the high dendron/NCD value. 相似文献
A series of tunable G0–G3 dendritic 2,2′‐bis(diphenylphosphino)‐1,1′‐binaphthyl (BINAP) ligands was prepared by attaching polyaryl ether dendrons onto the four phenyl rings on the P atoms. Their ruthenium complexes were employed in the asymmetric hydrogenation of β‐ketoesters, α‐ketoesters, and α‐ketoamides to reveal the effects of dendron size on the catalytic properties. The second‐ and third‐generation catalysts exhibited excellent enantioselectivities, which are remarkably higher than those obtained from the small molecular catalysts and the first‐generation catalyst. Molecular modeling indicates that the incorporation of bulky dendritic wedges can influence the steric environments around the metal center. In addition, the ruthenium catalyst bearing a second‐generation dendritic ligand could be recycled and reused seven times without any obvious decrease in enantioselectivity. 相似文献
A novel series of pyrene dendronized porphyrins bearing two and four pyrenyl groups (Py(2)-TMEG1 and Py(4)-TMEG2) were successfully synthesized. First and second generation Fréchet type dendrons (Py(2)-G1OH and Py(4)-G2OH) were prepared from 1-pyrenylbutanol and 3,5-dihydroxybenzyl alcohol. These compounds were further linked to a trimesitylphenylporphyrin containing a butyric acid spacer via an esterification reaction to obtain the desired products. Dendrons and dendronized porphyrins were fully characterized by FTIR and (1)H NMR spectroscopy and their molecular weights were determined by matrix-assisted laser desorption ionization time of flight mass spectrometry. Their optical and photophysical properties were studied by absorption and fluorescence spectroscopies. The formation of dynamic excimers was detected in the pyrene-labeled dendrons, with more excimer being produced in the higher generation dendron. The fluorescence spectra of the pyrene dendronized porphyrins exhibited a significant decrease in the amount of pyrene monomer and excimer emission, jointly with the appearance of a new emission band at 661 nm characteristic of porphyrin emission, an indication that fluorescence resonance energy transfer (FRET) occurred from one of the excited pyrene species to the porphyrin. The FRET efficiency was found to be almost quantitative ranging between 97% and 99% depending on the construct. Model Free analysis of the fluorescence decays acquired with the pyrene monomer, excimer, and porphyrin core established that only residual pyrene excimer formation in the dendrons could occur before FRET from the excited pyrene monomer to the ground-state porphyrin core. 相似文献
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. 相似文献
The effect of branching point structures and densities is studied between azido‐containing hyperbranched polymers and cross‐linked nanogels on their loading efficiency of alkynyl‐containing dendron molecules. Hyperbranched polymers that contained “T”‐shaped branching linkage from which three chains radiated out and cross‐linked nanogels that contained “X”‐shaped branching linkage with four radiating chains are synthesized in microemulsion using either atom transfer radical polymerization (ATRP) or conventional radical polymerization (RP) technique. Both polymers have similar density of azido groups in the structure and exhibit similar hydrodynamic diameter in latexes before purification. Subsequent copper‐catalyzed azide–alkyne cycloaddition reactions between these polymers and alkynyl‐containing dendrons in various sizes (G1–G3) demonstrate an order of dendron loading efficiencies (i.e., final conversion of alkynyl‐containing dendron) as hyperbranched polymers > nanogels synthesized by ATRP > nanogels synthesized by RP. Decreasing the branching density or using smaller dendron molecules increases the click efficiency of both polymers. When G2 dendrons with a molecular weight of 627 Da are used to click with the hyperbranched polymers composed of 100% inimer, a maximum loading efficiency of G2 in the loaded hyperbranched polymer is 58% of G2 by weight. These results represent the first comparison between hyperbranched polymers and cross‐linked nanogels to explore the effect of branching structures on their loading efficiencies.
A series of 2,2‐bis(hydroxymethyl)propionic acid dendrons of generation 2 through 8 having a strained cyclooctyne at the core and hydroxy groups at the periphery were prepared by a divergent method and used to functionalize azide‐decorated α‐chymotrypsin. The ability of the appended dendrons to selectively block enzyme activity (through a molecular sieving effect) was investigated using a small molecule substrate (benzoyl‐l ‐tyrosine p‐nitroanilide), as well as two proteins of different size (casein and bovine serum albumin). Additionally, the ability of dendrons to block complexation with a chymotrypsin antagonist, α‐antichymotrypsin, was investigated, and it was found that the dendron coating effectively prevented inhibition by this antagonist. We found that a critical generation is required to achieve efficient sieving with bis‐MPA dendrons, which illustrates the importance of macromolecular architecture and size in the shielding of proteins. 相似文献
A series of dendrons bearing various number of fluorenyl donor groups have been synthesized. First, the reference compound 2-(bromomethyl)-9H-fluorene (8) with one fluorenyl unit, then dendron 10, with two fluorenyl arms, and finally new generation dendrons, 11 and 12, bearing four peripheral fluorenyl arms were synthesized and characterized. A series of different generations of porphyrin dendrimers, obtained from these dendrons are also presented. Preliminary results on higher generation dendrimers are reported as well. Under mild basic conditions, surprisingly, a new compound 1 incorporating a fluorenyl unit in the cycle and three pendant fluorenyl arms was obtained by an intramolecular reaction of brominated tetrapod dendron 12. 相似文献
A facile divergent synthesis of a phosphorus-containing dendron containing 1,5-diaminonaphthalene is described. The phosphorus-containing dendron, functionalized with a 1,5-diaminonaphthalene unit at the core and phenolic OH groups grafted at the periphery, has been accomplished in a versatile, simple fashion, using Schiff's condensation and nucleophilic substitution reactions with POCl3, 3-hydroxy-benzaldehyde, 4-hydroxy-benzaldehyde, and 3-amino-phenol iteratively. The structures of intermediate dendrons were characterized by infrared, NMR (1H, 13C, and 31P), liquid chromatography–mass spectrometry, and C, H, N analysis. The structure of the final dendron (6) was confirmed by infrared, NMR (1H, 13C, and 31P), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and C, H, N analysis. The thermal stability and degradation of the resulting final dendron was checked by thermal gravitometric analysis/differential thermal analysis. 相似文献
The synthesis of first‐ and second‐generation dendrons with defined ratios of orthogonally protected amine groups in the periphery ((benzyloxy)carbonyl (Cbz) and (tert‐butoxy)carbonyl (Boc) protection) and the degree to which they can be selectively removed are described. The reaction conditions required for these deprotections were applied to methacrylic acid (= 2‐methylprop‐2‐enoic acid) based dendronized polymers carrying the same peripheral protecting groups to investigate whether they have any detrimental interference with the polymer skeleton. Specifically it was explored whether dendrons attached to the backbone could possibly be cleaved off as a whole (de‐dendronization). Finally it was investigated how de‐dendronizations can be used for quantifying both the dendron‐structure perfection and the polymer‐backbone configurations. 相似文献
Three diastereomeric second‐generation (G2) dendrons were prepared by using (2S,4S)‐, (2S,4R)‐, and (2R,4S)‐4‐aminoprolines on the multigram scale with highly optimized and fully reproducible solution‐phase methods. The peripheral 4‐aminoproline branching units of all the dendrons have the 2S,4S configuration throughout, whereas those units at the focal point have the 2S,4S, 2S,4R, and 2R,4S configurations. These latter configurations led to the dendrons being named (2S,4S)‐ 1 , (2S,4R)‐ 1 , and (2R,4S)‐ 1 , respectively. The 4‐aminoproline derivatives used in this study are new, although many closely related compounds exist. Their syntheses were optimized. The dendron assembly involved amide coupling, the efficiency of which was also optimized by employing the following well‐known reagents: EDC/HOBt, DCC/HOSu, TBTA/HOBt, TBTU/HOBt, BOP/HOBt, pentafluorophenol, and PyBOP/HOBt. It was found that the use of PyBOP is by far the best for dendrons (2S,4S)‐ 1 and (2R,4S)‐ 1 , and pentafluorophenol active ester is best for (2S,4R)‐ 1 . Because of their multigram scale, all couplings were done in solution instead of by solid‐phase procedures. Purifications were, nevertheless, easy. The optical purities of the key intermediates as well as the three G2 dendrons were analyzed by chiral HPLC analysis. These novel, diastereomeric second‐generation dendrons have a rather compact and conformationally highly rigid structure that makes them interesting candidates for applications, for example, in the field of dendronized polymers and in organocatalysis. 相似文献
Syntheses of several examples of a new type of trivalent building blocks for the preparation of aliphatic polyester dendrimers are presented. Starting from the well-known mono-O-benzylidenepentaerythritol, AB3 type acid dendrons can be obtained in high yield in only two steps. Other triprotected bis-2,2-(hydroxymethyl)-3-hydroxypropanoic acid derivatives with varying protecting groups were also synthesized readily. This type of dendron was used in combination with 2,2′-bis(hydroxymethyl) propanoic acid (bis-HMPA) divalent dendrons to produce low generation mixed polyester dendrimers with increased number of branching points. 相似文献
A series of supramolecular assemblies of types [Ag8( L )4](PF6)8 and [Ag4( L )2](PF6)4, obtained from the tetraphenylethylene (TPE) bridged tetrakis(1,2,4‐triazolium) salts H4‐L(PF6)4 and AgI ions, is described. The assembly type obtained dependends on the N‐wingtip substituents of H4‐L(PF6)4. Changes in the lengths of the N4‐wingtip substituents enables controlled formation of assemblies with either [Ag4( L )2](PF6)4 or [Ag8( L )4](PF6)8 stoichiometry. The molecular structures of selected [Ag8( L )4](PF6)8 and [Ag4( L )2](PF6)4 assemblies were determined by X‐ray diffraction analyses. While H4‐ L (PF6)4 does not exhibit fluorescence in solution, their tetra‐NHC (NHC=N‐heterocyclic carbene) assemblies do upon NHC–metal coordination. Upon irradiation, all assemblies undergo a light‐induced, supramolecule‐to‐supramolecule structural transformation by an oxidative photocyclization involving phenyl groups of the TPE core, resulting in a significant change of the luminescence properties. 相似文献
FTIR and FT-Raman spectra of four generations of phosphorus-containing dendrons with terminal aldehyde or PCl groups have been recorded and analyzed. Their spectral patterns are determined by the ratio T/R (T, the number of terminal groups; R, the number of repeated units). Bands assigned to the core, repeated units and terminal groups were separated by the difference spectroscopy method. The optimized geometry, frequencies and intensity of IR bands of G(1v) generation dendron with terminal aldehyde groups were obtained by the density functional theory (DFT). It was found that the internal skeleton of molecules exists in a single stable conformation with planar O-C(6)H(4)-CHN-N(CH(3))-P(S) fragments, but terminal groups may adopt the t,g,g- and t,-g,g-rotational isomers. The t,-g,g-conformer is 0.74 kcal/mol less stable compared to the t,g,g-conformer. The bond length and bond angles obtained by DFT show the best agreement with experimental data. Relying on DFT calculations a complete assignment of vibrations is proposed for different parts of the studied dendrons. The calculated frequencies and intensity of IR bands of the t,g,g- and t,-g,g-conformers of G(1v) are found to be in reasonable agreement with the experimental results. The most reactive site in dendron is the core function and vinyl group is preferred for nucleophilic attack. In dendrimer the most reactive are the terminal groups. 相似文献