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.     

Thiophene‐cored 2,2‐bis(methylol)propionic acid dendrimers for optical‐power‐limiting applications

The synthesis and characterization of dendron‐coated 2,5‐bis(phenylethynyl)thiophene chromophores are described. The dendrimers were grown divergently on the arylthiophene core with the versatile anhydride of 2,2‐bis(methylol)propionic acid. The arylthiophene core was synthesized with Sonogashira coupling reactions. Structurally well‐defined dendrimers up to the fourth generation were grown, as confirmed by size exclusion chromatography, NMR, and matrix‐assisted laser desorption/ionization time‐of‐flight analysis. The different dendritic substitution did not influence the absorption spectra of the compounds in or near the visible region. Solutions of arylthiophenes had good transparency at wavelengths greater than 400 nm. The dendritic thiophenes exhibited an optical‐power limit at the laser wavelength of 532 nm. However, the magnitude of the optical‐power limit of these compounds was slightly lower than that of a nondendritic arylthiophene with n‐pentyl substituents. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1177–1187, 2005     

Single‐Crystalline Optical Microcavities from Luminescent Dendrimers

Microcrystallites are promising minute mirrorless laser sources. A variety of luminescent organic compounds have been exploited along this line, but dendrimers have been inapplicable owing to their fragility and extremely poor crystallinity. Now, a dendrimer family that overcomes these difficulties is presented. First‐, second‐, and third‐generation carbazole (Cz) dendrimers with a carbon‐bridged oligo(phenylenevinylene) (COPV2) core (GnCOPV2, n=1–3) assemble to form microcrystals. The COPV2 cores align uni/bidirectionally in the crystals while the Cz units in G2‐ and G3COPV2 align omnidirectionally. The dendrons work as light‐harvesting antennas that absorb non‐polarized light and transfer it to the COPV2 core, from which a polarized luminescence radiates. Furthermore, these crystals act as laser resonators, where the lasing thresholds are strongly coupled with the crystal morphology and the orientation of COPV2, which is in contrast with the conventional amorphous dendrimers.     

Deep‐red light‐emitting phosphorescent dendrimer encapsulated tris‐[2‐benzo[b]thiophen‐2‐yl‐pyridyl] iridium (III) core for light‐emitting device applications

New deep‐red light‐emitting phosphorescent dendrimers with hole‐transporting carbazole dendrons were synthesized by reacting tris(2‐benzo[b]thiophen‐2‐yl‐pyridyl) iridium (III) complex with carbazolyl dendrons by DCC‐catalyzed esterification. The resulting first‐, second‐, and third‐generation dendrimers were found to be highly efficient as solution‐processable emitting materials and for use in host‐free electrophosphorescent light‐emitting diodes. We fabricated a host‐free dendrimer EL device with configuration ITO/PEDOT:PSS (40 nm)/dendrimer (55 nm)/BCP (10 nm)/Alq₃ (40 nm)/LiF (1 nm)/Al (100 nm) and characterized the device performance. The multilayered devices showed luminance of 561 cd/m² at 383.4 mA/cm² (12 V) for 15 , 1302 cd/m² at 321.3 mA/cm² (14 V) for 16 , and 422 cd/m² at 94.4 mA/cm² (18 V) for 17 . The third‐generation dendrimer, 17 (η_ext = 6.12% at 7.5 V), showed the highest external quantum efficiency (EQE) with an increase in the density of the light‐harvesting carbazole dendron. Three dendrimers exhibited considerably pure deep‐red emission with CIE 1931 (Commission International de L'Eclairage) chromaticity coordinates of x = 0.70, y = 0.30. The CIE coordinates remained very stable with the current density. The integration of rigid hole‐transporting dendrons and phosphorescent complexes provides a new route to design highly efficient solution‐processable materials for dendrimer light‐emitting diode (DLED) applications. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7517–7533, 2008     

外围含对-硝基偶氮苯介晶基团的椭球型硅碳烷树状物

Novel carbosilane liquid crystalline dendrimers based on 1,6-hexanediol were prepared. Using the precursors Gn-C1 （n = 1-3） with Si-C1 bonds on the periphery as dendritic scaffolds and 4-[4-（6-hydroxyhexyloxy）phenylazo]- nitrobenzene as mesogenic group, a series of carbosilane liquid crystalline dendrimers from the first to the third generation were synthesized. These carbosilane liquid crystalline dendrimers showed smectic phase.     

Phenylacetylene Dendrimers Containing a Fluorene Core: Synthesis and Spectroscopic Studies

Phenylacetylene dendrimers 9 – 11 containing fluorene as the core with a larger HOMO‐LUMO energy gap were synthesized and characterized. Their structure and properties were studied by UV, FL, ¹H NMR, MS etc. These novel phenylacetylene dendrimers exhibit unique photophysical properties. They exist a new absorption band around 340 nm whose molar coefficient decreases with increasing generation. The band‐gaps of 9 – 11 are 3.54, 3.43 and 3.02 respectively. The fluorescence quantum yield of 10 is as high as 0.61.     

Synthesis and Characterization of Gold‐Nanoparticle‐Cored Dendrimers Stabilized by Metal–Carbon Bonds

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 AuG_n 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.     

2,3,4,5‐Tetraphenylsilole‐Based Conjugated Polymers: Synthesis,Optical Properties,and as Sensors for Explosive Compounds

A series of linear 2,5‐tetraphenylsilole‐vinylene‐type polymers were successfully synthesized for the first time. The tetraphenylsilole moieties were linked at their 2,5‐positions through a vinylene bridge with p‐dialkoxybenzenes to obtain polymer PSVB and with 3,6‐carbazole to obtain polymer PSVC . For comparison, 2,5‐tetraphenylsilole‐ethyne‐type polymer PSEB was also synthesized, in which the vinylene bridge of PSVB was replaced with an ethyne bridge. Very interestingly, the bridging group (vinylene or ethyne) had a significant effect on the photophysical properties of the corresponding polymers. The fluorescence peak of PSEB at 504 nm in solution originated from the emission of its silole moieties, whereas PSVB and PSVC emitted yellow light and no blueish–green emission from the silole moieties was observed, thus demonstrating that the emissions of PSVB and PSVC were due to their polymer backbones. More importantly, the 2,5‐tetraphenylsilole‐ethyne polymer exhibited a pronounced aggregation‐enhanced emission (AEE) effect but the 2,5‐tetraphenylsilole‐vinylene polymer was AEE‐inactive. Moreover, both AEE‐active 2,5‐tetraphenylsilole‐ethyne polymer and AEE‐inactive 2,5‐tetraphenylsilole‐vinylene polymers were successfully applied as fluorescent chemosensors for the detection of explosive compounds.     

Shape‐Persistent Oligothienylene–Ethynylene‐Based Dendrimers: Synthesis,Spectroscopy and Electrochemical Characterization

A series of novel structurally well‐defined oligothienylene–ethynylene‐based dendritic macromolecules up to the 3rd generation (G3) were successfully synthesized by a combination of Pd‐catalyzed Sonogashira‐type cross‐coupling and oxidative homocoupling steps. Oxidative homocoupling of dendrons successfully afforded dendrimers up to the 2nd generation (G2). In contrast, the G3 dendrimer was effectively prepared by a four‐fold Sonogashira‐type cross‐coupling reaction. All compounds showed broad and structureless absorption and emission spectra arising from the presence of different π‐conjugated chromophores. With increasing generation, a bathochromic shift of the π–π* absorption band and an increase of the absorption coefficient were observed. The insertion of ethynylene groups into the conjugated dendrimer backbone resulted in a hypsochromic shift compared to all‐thiophene dendrimers reported earlier by our group. All dendritic compounds are fluorescent and showed moderate quantum efficiencies due to an effective intramolecular charge‐transfer (ICT) process. Cyclic voltammetry measurements also revealed the presence of multiple π‐conjugative pathways that show very broad oxidation waves for higher generations. HOMO–LUMO energy levels of these dendrons and dendrimers were estimated from optical and redox measurements and the calculated band gaps were within the range of 3.3 to 2.4 eV, typical for oligo‐ and polythiophenes. Electrochemical polymerizations of several desilylated compounds were performed and characterization of the films is reported. Preliminary bulk heterojunction solar cells that utilise these ethynylated dendrimers as the donor and [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM[60]) as the acceptor showed moderate efficiencies ranging from 0.18–0.64 %.     

Luminescence properties of soluble 2,2′,7,7′‐Tetrakis(2‐(9‐hexyl‐9H‐carbazol‐3‐yl)‐vinyl)‐9,9′‐spirobifluorene‐labeled dendrimers: Photoluminescence and electroluminescence

New light emitting dendrimers were synthesized by reacting 3,5‐bis‐(3,5‐bis‐benzyloxy‐benzyloxy)‐benzoic acid or 3,5‐bis‐[3,5‐bis‐(3,5‐bis‐benzyloxy‐benzyloxy)‐benzyloxy]‐benzoic acid with a carbazolyl vinyl spirobifluorene moiety. A blue‐emitting core dye was encapsulated by multibenzyloxy dendrons, and two dendrimers having different densities of dendrons were prepared. Photoluminescence (PL) studies of the dendrimers demonstrated that at the higher density of benzyloxy dendrons, the featureless vibronic transitions were improved, causing lesser excimer emission. The similarity of the solution and solid emission spectra of the larger dendrimer, 10 , revealed the suppression of molecular aggregation in the solid film, which is attributed to the presence of the bulky benzyloxy dendrons. The electroluminescence spectra of multilayered devices made using 10 predominantly exhibited blue emissions; similar emission was observed in the PL spectra of its thin film. The multilayered devices made using 3 , 9 , and 10 showed luminances of 1021 cd m^?2 at 5 V, 916 cd m^?2 at 6 V, and 851 cd m^?2 at 6.5 V, respectively. The largest dendrimer, 10 , bearing a greater number of benzyloxy dendrons, exhibited a blue‐like emission with CIE 1931 chromaticity coordinates of x = 0.16 and y = 0.13, which is due to the influence of a higher shielding effect. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 501–514, 2008     

Single-Crystalline Optical Microcavities from Luminescent Dendrimers

Microcrystallites are promising minute mirrorless laser sources. A variety of luminescent organic compounds have been exploited along this line, but dendrimers have been inapplicable owing to their fragility and extremely poor crystallinity. Now, a dendrimer family that overcomes these difficulties is presented. First-, second-, and third-generation carbazole (Cz) dendrimers with a carbon-bridged oligo(phenylenevinylene) (COPV2) core (GnCOPV2, n=1–3) assemble to form microcrystals. The COPV2 cores align uni/bidirectionally in the crystals while the Cz units in G2- and G3COPV2 align omnidirectionally. The dendrons work as light-harvesting antennas that absorb non-polarized light and transfer it to the COPV2 core, from which a polarized luminescence radiates. Furthermore, these crystals act as laser resonators, where the lasing thresholds are strongly coupled with the crystal morphology and the orientation of COPV2, which is in contrast with the conventional amorphous dendrimers.     

Searching for new host compounds: synthesis and characterization of novel crown ether-functionalized dendrimers

Novel lipophilic dendrimers as host compounds, that is, 7-15, containing crown ether moieties with different sizes as the core, surrounded by first, second or third generation poly(aromatic ether) wedges, were synthesized by the use of bis(bromomethyl)-substituted crown ethers and Fréchet-type poly(benzyl ether) dendrons as building blocks. The compounds were fully characterized.     

Designing poly(amido amine) dendrimers containing core diversities by click chemistry of the propargyl focal point poly(amido amine) dendrons

General, fast, efficient, and inexpensive methods for the synthesis of poly (amido amine) (PAMAM) dendrimers having core diversities were elaborated. In all syntheses, the major step involved an inexpensive 1,3‐dipolar cycloaddition reaction between an alkyne and an azide in the presence of Cu(I) species, which is known as the best example of click chemistry. The propargyl‐functionalized PAMAM dendrons are obtained by the divergent approach using propargylamine as an alkyne‐focal point. Three core building blocks, 1,3,5‐tris(azidomethyl)benzene, N,N,N′,N′‐tetra(azidopropylamidoethyl)‐1,2‐diaminoethane, and 4,4′‐(3,5‐bis(azidopropyloxy)benzyloxy)bisphenyl, were designed and synthesized to serve as the azide functionalities for dendrimer growth via click reactions with the alkyne‐dendrons. These three building blocks were employed together with the propargyl‐functionalized PAMAM dendrons in a convergent strategy to synthesize three kinds of PAMAM dendrimers with different core units. This novel and pivotal strategy using an efficient click methodology provides the fast and efficient synthesis of the PAMAM dendrimers with the tailed made core units. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1083–1097, 2008     

Divergent synthesis and self‐assembly of amphiphilic polymeric dendrons with selective degradable linkages

Enhancing the structural complexity and functionality of the building blocks allows the construction of supramolecular assemblies. In this work, we demonstrate a strategy for the design and synthesis of complex macromolecular architectures. We use atom transfer radical polymerization to produce well‐defined polymers with telechelic end‐group functionality, and “click” them together to form functional 3rd generation dendrons, and incorporated degradable linkages and certain functionality at the polymer chain‐ends of each generation. The 3rd generation polymeric dendrons consisted of homopolymer polystyrene (PSTY) with either four solketals or eight alcohols, diblock PSTY and poly(t‐butyl acrylate), and amphiphilic diblock. The peripheral ends consisting of alcohols create functionalization points for further chemical modification or chemical coupling and the cleavable linkages between the 2nd and 3rd generations all provide the first steps toward smart nanostructures. Importantly, we can synthesize these dendrons in pure form. The self‐assembly of the amphiphilic dendrons (the inner and outer generations consisting of PSTY and polyacrylic acid, respectively) in water produced micelles of uniform size with an aggregation number of 43 dendrons per micelle. The size of the micelles was small (D_H =20.7 nm) and comparable to the size found by transmission electron microscopy (14–18 nm). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1533–1547, 2008     

New Calix[4]arene‐Cored Peripherally Functionalized Dendrimers: Synthesis and Conformational Characteristics

New calixarene‐based dendrimers, containing calix[4]arene as the core and different generations of Fréchet‐type poly(benzyl ether) dendrons as building blocks, which possess either Br‐atoms or COO^tBu groups at their surface were synthesized and presented herein for the first time. The new calix[4]arene‐cored dendritic macromolecules were fully characterized and found to prefer strictly the cone conformation.     

Photoresponsive nanocarriers based on PAMAM dendrimers with a o‐nitrobenzyl shell

Gn (n = 3, 4, and 5) poly(amidoamine) (PAMAM) dendrimers were synthesized and peripherally modified with photocleavable o‐nitrobenzyl (NB) groups by reacting o‐nitrobenzaldehyde with the terminal amine groups of PAMAM dendrimers, followed by reducing the imine to amine groups with NaBH₄. The NB‐modified dendrimers, Gn‐NB (n = 3, 4, and 5), were characterized by nuclear magnetic resonance and fourier transform infrared spectroscopy. The results showed that the NB groups were successfully attached on the periphery of the dendrimers with near 100% grafting efficiency. Such a photosensitive NB shell could be cut off on irradiation with 365 nm ultraviolet (UV) light. The encapsulation and release of guest molecules, that is, salicylic acid (SA) and adriamycin (ADR), by Gn‐NB were explored. The encapsulation capability of these dendrimers was found to increase as the guest molecular size was decreased and have dependence on the generation of dendrimers as well. For both of SA and ADR, the average encapsulation numbers per dendrimer decreased in the order of G4‐NB > G5‐NB > G3‐NB, indicating that the fourth generation dendrimer was a better container for the guest molecules. The rate of SA release was found to be greater with UV irradiation than that without, suggesting that the NB‐shelled PAMMAM dendrimers could function as a molecular container/box with photoresponsive characteristics. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 551–557, 2010     

Divergent synthesis of segmented carbosilane dendrimers

A number of carbosilane copolymers of the first through third generations has been synthesized via the divergent approach. Each molecule of these compounds contains two pairs of dendrons—segments that have the same poly(propylenesilyl) carbosilane dendritic architecture but differ in the generation number and the amount and type of terminal groups (n-decyl or allyl). The target dendrimers have been isolated as individual compounds via preparative gel-permeation chromatography, and their structure has been studied by ¹H NMR spectroscopy.     

2,2′:3′,2′′‐Terthiophene‐Based all‐Thiophene Dendrons and Dendrimers: Synthesis,Structural Characterization,and Properties

The synthesis of generational dendritic oligothiophenes (DOTs) has been successfully achieved by a divergent/convergent approach that involves halogenation, boronation, and palladium‐catalyzed Suzuki coupling reactions. The key point in the presented synthetic approach is the use of trimethylsilyl (TMS) protecting groups, which allow for the core‐lithiation and subsequent boronation of the dendrons and for the peripheral ipso‐substitution with iodine monochloride or N‐bromosuccimide. In addition, the TMS protecting groups can be completely removed by using tetrabutylammonium fluoride, thus yielding only‐thiophene‐based dendrons and dendrimers. Due to their highly branched structure, all these synthesized DOTs are soluble in organic solvents. Chemical structures were confirmed by NMR spectroscopic, mass spectrometric, and elemental analysis. Concentration‐dependent ¹H NMR spectroscopic investigations revealed that the higher generation compounds tend to aggregate in solution. Such an aggregation behavior was further confirmed by measuring with MALDI‐TOF MS. Both MALDI‐TOF MS and gel‐permeation chromatography (GPC) analyses confirmed the monodispersity of the DOTs. Furthermore, GPC results revealed that these DOT molecules adopt a condensed globular molecular shape. Their optical and electronic properties were also investigated. The results indicated that these DOTs comprise various conjugated α‐oligothiophenes with different chain lengths, which results in the higher generation compounds showing broad and featureless UV/Vis absorption spectra and ill‐defined redox waves.     

Synthesis,Structural Characterization,and Thermoresponsivity of Hybrid Supramolecular Dendrimers Bearing a Polyoxometalate Core

A series of cationic dendrons bearing triethylene glycol monomethyl ether terminal groups of different generations have been synthesized and used to encapsulate an inorganic polyanionic cluster [K_12.5Na_1.5(NaP₅W₃₀O₁₁₀)] through electrostatic interactions. The resulting dendritic cation–encapsulated polyoxometalate (POM) complexes, cluster–dendrimers, are soluble in water and exhibit lower critical solution temperatures (LCST). The thermoresponsivities of these complexes in aqueous solutions were studied by turbidimetry and variable‐temperature ¹H NMR spectroscopy. The observed cloud points show a remarkable dependence on the generation of the dendrons. Complexes composed of first‐generation dendrons exhibit no obvious thermoresponsive properties, but for complexes bearing second‐generation dendrons, the LCST decreases as the number of dendritic cations around the POM cluster increases. Complexes composed of third‐generation cations underwent reversible aggregation and disaggregation upon heating and cooling, respectively. This thermally induced self‐aggregation was characterized by DLS and TEM. In addition, the effects of salt and solvent on the LCST were investigated. This research demonstrates a new type of thermoresponsive dendritic organic–inorganic hybrid complex and provides a general route to the endowment of POMs with temperature‐sensitive properties through electrostatic interactions.     

The Pt‐Organometallic Version of Perigraniline: Going Blue

Four conjugated push–pull organometallic polymers ( [Pt]‐AQ )_n ( [Pt] = trans‐bis(phenylacetylene)bis(tributylphosphine)platinum(II); AQ = 2‐bromo‐, 2,6‐dibromo‐, 2,6‐diamino‐, and unsubstituted anthraquinone diimine) were prepared and characterized by UV–vis spectroscopy and electrochemistry. A low‐energy charge transfer, CT, band ( [Pt] *→ AQ ; confirmed by density functional theory calculations), was found in the 445–500 nm window rather than the expected red‐shifted range above 630 nm. X‐ray structures of four model compounds reveal that steric hindrance induces large dihedral angles between the C₆H₄ and NCC₂ planes, rendering π‐orbital overlap difficult between the [Pt] and AQ units. The position of the CT band is mainly driven the reduction potential of the anthraquinone diimine unit.