Dendron Groups Research Articles

Orange-red and saturated red thermally activated delayed fluorescent dendrimers for non-doped solution-processed OLEDs

Two thermally activated delayed fluorescence (TADF) dendritic emitters with orange-red and saturated red emission, respectively, were obtained by coupled diphenylamine-carbazole dendron groups as donor with di(pyridin-3-yl)methanone as accepter. The two TADF dendrimers of tBuDPACz-DPyM and MeODPACz-DPyM exhibited small energy gaps between the singlet and triplet excited states (0.04 vs 0.03 eV). As a consequence, the tBuDPACz-DPyM non-doped solution-processed organic light-emitting devices (OLED) exhibited high current efficiency of 2.36 cd A−1 and external quantum efficiency of 1.82% with low turn-on voltage 3.4 V as well as a lower efficiency roll-off. Moreover, Commission Internationale de L'Éclairage (CIE) coordinates of two OLED devices were (0.56, 0.43) and (0.62, 0.37) for tBuDPACz-DPyM and MeODPACz-DPyM respectively.

Self-assembled binary chromophores with enhanced electro-optic activity and alignment stability

Four nonlinear optical chromophores FD1-2 and HD1-2 based on dialkyl aniline donor have been synthesized. The donor and bridge part of the chromophores were substituted with aromatic dendron (HD) or fluoroaromatic dendron (FD) groups. Self-assembly strategy through π-π stacking of HD/FD groups was adopted to increase the poling efficiency and long-term stability of the materials. The film FD2/HD2 shown large EO coefficient value of 275 pm/V. After annealing at room temperature for 1000 h, about 91% of the initial r33 values could be still maintained for the poled films of FD2/HD2, compare to only 53% left for film FD2.

Advances in the design of self-supported ion-conducting membranes-new family of columnar liquid crystalline polyamines. Part 1: Copolymer synthesis and membrane preparation

Poly[2-(aziridin-1-yl)ethanol] (PAZE) is a suitable polyamine candidate which can be dendronised with 3,4,5-tris[4-(n-dodecan-1-yloxy)benzyloxy]benzoic acid (TAP) in order to obtain liquid crystalline columnar polyamines, as previously reported. However, the resulting copolymers evidenced a strong tendency to crystallise which leads to the detriment of columnar phase stability and the mechanical properties of the resulting polymeric membranes. In order to overcome this drawback, we successfully prepared LC columnar polyamines based on poly[2-(aziridin-1-yl)ethanol] modified with both TAP and benzoyl chloride at different extents. The presence of the dendron group induces self-assembling into a columnar structure, due to an exo-recognition of the side-chain dendrons, while the benzoyl group is expected to inhibit polymer crystallinity. All copolymers, except one, have lower melting points and exhibit higher clearing temperatures (Tc), when compared to the LC polyamines obtained by modification of PAZE with TAP only, reported in previous studies. In all cases they exhibited LC columnar mesophases after annealing, as inferred by DSC, XRD and POM.When casted as membranes, these columnar copolyamines can be homeotropically oriented under thermal treatment at optimal conditions, as was confirmed by X-ray diffraction studies at low 2θ angles. Additionally, SEM microscopy was used in order to evaluate the morphology of the prepared membranes.

Solvent Effect on Fluorescence Properties of Stilbene Dendrimer Surrounded by Benzyl-Ether Dendrons

Abstract The fluorescence maximum of the fourth generation of stilbene-cored dendrimer (trans-G4) was affected by solvent polarity. These results indicated that the core of even higher generation dendrimer was not isolated from solvent molecules and the environment of the dendrimer core is constructed by both surrounding dendron groups and penetrated solvent molecules.

Preparation of amphiphilic diblock copolymers with pendant hydrophilic phosphorylcholine and hydrophobic dendron groups and their self-association behavior in water

Generation 3.5 poly(amido amine) dendron (G3.5) with 16 n-butyl terminal groups containing an acrylamide monomer (AaUG3.5) was prepared by condensation between an amino focal group in G3.5 and 11-acrylamidoundecanoic acid. AaUG3.5 was polymerized using poly(2-methacryloyloxyethyl phosphorylcholine) (pMPC)-based macro-chain transfer agent via reversible addition-fragmentation chain transfer (RAFT) radical polymerization to obtain amphiphilic diblock copolymers with different compositions. The diblock copolymers (PmDn) were composed of a hydrophilic pMPC block and hydrophobic pendant dendron-bearing block, where P and D represent pMPC and pAaUG3.5, respectively, and m and n represent the degree of polymerization for each block, respectively. P296D1 and P98D3 formed vesicles and large compound micelles and vesicles, respectively, which was confirmed by light scattering measurements and transmission electron microscopic (TEM) observations. The large compound micelles formed from P98D3 could not incorporate hydrophilic guest polymer molecules, because the aggregates did not have a hydrophilic hollow core. In contrast, the vesicles formed from P269D1 could incorporate hydrophilic guest polymer molecules into the hollow core. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4923–4931

Photoisomerization and energy transfer in naphthalene-terminated stilbene dendrimers

Naphthalene-terminated stilbene dendrimers, the largest stilbene dendrimers to date, underwent photoisomerization via highly efficient energy transfer from the dendron group to the core stilbene. It was also demonstrated that the energy transfer efficiency in these dendrimers may be controlled by light, utilizing trans-cis isomerization as the key photoreaction.

Dual Aggregation Behavior of Porphyrin‐Cored Thiophene Dendrimers

Two porphyrin-cored thiophene dendrimers T(3T)P and T(7T)P have been successfully synthesized and characterized by UV-vis and fluorescence measurements. The self-assembly of these two water-insoluble free base porphyrins to form both intrinsic H- and J-aggregates has been reported for the first time. This intrinsic behavior is in contrast to the use of surfactants, dyes, and metal ions to induce aggregation behavior on most porphyrin systems. This work emphasizes the importance of controlling the size, solvent, and extent of conjugation of polythiophene dendron groups in porphyrin systems. These materials may yet be applied to polythiophene or porphyrin blend system in energy conversion devices with the light-harvesting properties of the polythiophene dendrons.

Synthesis of nonlinear optical chromophore and the preparation of attenuated total reflectance modulator

A new nonlinear optical chromophore with strong electron‐withdrawing acceptor and rigid–flexible dendron was synthesized. An electro‐optic (EO) attenuated total reflectance modulator was prepared to measure the EO coefficient of the films. Modification of the tricyanopyrroline chromophore with rigid–flexible dendron group provided reduction of dipole–dipole interactions and improvement of its solubility. As the chromophore loading increased, there was a great improvement on the macroscopic EO response of the polymeric materials obtained by incorporating this chromophore as a guest in amorphous polycarbonate. The largest EO coefficient was 42 pm/V at 1310 nm. Copyright © 2011 John Wiley & Sons, Ltd.

Enhanced poling efficiency in rigid-flexible dendritic nonlinear optical chromophores

A series of nonlinear optical chromophores with the strong electron-withdrawing tricyanopyrroline (TCP) acceptor and rigid-flexible dendron was synthesized and their thermal and optical properties were investigated. Modification of the TCP chromophore with rigid-flexible dendron groups provides reduction of dipole–dipole interactions and thus great improvement of the macroscopic electro-optic (EO) response of the polymeric materials obtained by incorporating these derivatives as a guest in a high Tg amorphous polycarbonate (APC). The best result was obtained with chromophore Lj-Dr1, with three rigid-flexible dendrons, which shows the largest EO activity (39 pm V−1 at 1,310 nm). Furthermore, all chromophores in this study possess good processability and exhibit high thermal decomposition temperatures (highest T d = 300 °C).

Dendronized polymers via Diels–Alder “click” reaction

AbstractA modular approach toward the synthesis of polymers containing dendron groups as side chains is developed using the Diels–Alder “click” reaction. For this purpose, a styrene‐based polymer appended with anthracene groups as reactive side chains was synthesized. First through third‐generation polyester dendrons containing furan‐protected maleimide groups at their focal point were synthesized. Facile, reagent‐free, thermal Diels–Alder cycloaddition between the anthracene‐containing polymer and latent‐reactive dendrons leads to quantitative functionalization of the polymer chains to afford dendronized polymers. The efficiency of this functionalization step was monitored using 1H and 13C NMR spectroscopy and FTIR and UV–vis spectrometry. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 410–416, 2010

Cyclic Self‐Assembled Structures of Chlorophyll Dyes on HOPG by the Dendron Wedge Effect

A molecular cake: Zinc chlorins with different dendron wedges can form linear or circular self-assembled structures with different molecular packing. In particular, zinc chlorins with six alkyl chains in the dendron group self-assemble into hexameric cyclic structures on HOPG (see picture). Such cyclic structures are reminiscent of (bacterio)chlorophyll organization in natural light-harvesting systems.

Photocarrier Transport Property of Phenylene-vinylene Dendrimer Studied by Time-of-Flight Method

The photocarrier transport property of the three-generation dendrimer, which is composed of phenylene-vinylene as the dendron group and triphenylamine as the surface group G3D3-PV(TPA), was studied by the time of flight (TOF) method using a sandwich-type cell of indium-tin-oxide (ITO)/G3D3-PV(TPA)/Mg-Al. The photocurrent decay shows that hole transport occurs stronger than electron transport, and dispersive transport is observed in the dendrimer film. The mobility at 25 °C exhibits negative electric field dependence, and the intrinsic mobility at zero electric field is 7.1 × 10−5 cm2/(V.s). This is faster than that of linear poly(p-phenylene-vinylene). Besides this, the result is one order smaller than that of poly(3-hexylthiophene), but faster than those of poly(3-dodecylthiophene) and poly(3-octadecylthiophene). The result indicates that one of the important parameters for the carrier transport is the average distance between π-conjugated molecules. The fact that the carrier hopping of the G3D3-PV(TPA) dendrimer occurs effectively implies the structure would be a disk shape since the phenylene-vinylene dendron sites of the different dendrimer molecule are estimated to be close to each other.

High-efficiency solution processable electrophosphorescent iridium complexes bearing polyphenylphenyl dendron ligands

Abstract We report the synthesis and electrophosphorescent behavior of a series of novel iridium complex materials (Complexes A–F ), which are composed of ligands bearing polyphenylphenyl dendron groups and acetylacetonate. Yellow to saturated red organic light-emitting diodes (OLEDs) based on these newly developed Ir complexes were fabricated through solution process by doping the complex materials into polyvinyl carbazole (PVK)/2-(4-biphenylyl)-5-(4- tert -butylphenyl)-1,3,4-oxadiazole (PBD) matrices. The emission wavelengths of the materials could be effectively tuned from 549 nm to 640 nm by changing the conjugation of the ligands either through incorporating additional aromatic segment (e.g. phenyl or fluorenyl group) onto the basic dendron ligand or fusing two of the phenyl rings on the polyphenylphenyl dendron group. High performance devices with the configuration of ITO/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) (50 nm)/PVK:PBD (40%):Ir complex (6%) (70 nm)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) (12 nm)/Alq 3 (20 nm)/Mg:Ag (150 nm) have been demonstrated. For example, when Complex B was used as the emissive layer, maximum current efficiency of 34.0 cd/A and external quantum efficiency of 10.3% have been achieved. When 1,3,5-tris( N -phenylbenzimidazol-2-yl) benzene (TPBI) was used as the block layer, the efficiencies can be further improved to 46.3 cd/A and 13.9%, respectively. These solution processed OLED devices demonstrated quite stable EL efficiencies over a large range of current density, which indicated that triplet–triplet annihilation in electrophosphorescence could be effectively suppressed by incorporation of the polyphenylphenyl dendron structure into iridium complexes.

Janus-type dendrimer-like poly(ethylene oxide)s.

A straightforward and original methodology allowing the synthesis of Janus-type dendrimer-like poly(ethylene oxide)s (PEOs) carrying orthogonal functional groups on their surface is described. The use of 3-allyloxy-1,2-propanediol (1) as a latent AB2-type heterofunctional initiator of anionic ring-opening polymerization (AROP) of ethylene oxide (EO) and of selective branching agents of PEO chain ends served to construct the two dendrons of these dendrimer-like PEOs, following a divergent pathway. Thus, the first PEO generation of the first dendron was grown by AROP from 1 followed by the reaction of the corresponding alpha-allyl,omega,omega'-bishydroxy- heterofunctional PEO derivative with 2-(3'-chloromethybenzyloxymethyl)-2-methyl-5,5-dimethyl-1,3-dioxane (2) used as a branching agent. This afforded the dendron A with four latent peripheral hydroxyls protected in the form of two ketal rings. The remaining alpha-allylic double bond of the PEO thus prepared was transformed into two hydroxyl groups using OsO4 in order to create the first PEO generation of the dendron B by AROP of EO. Allyl chloride (3) was then used as another (latent) branching agent to react with the terminal hydroxyl of the corresponding PEO chains. Deprotection under acidic conditions of the ketal groups of dendron A, followed by AROP of EO, afforded the second PEO generation on this face. This alternate and divergent procedure, combining AROP of EO and selective branching of PEO branches, could be readily iterated, one dendron after the other up to the generation six, leading to a Janus-type dendrimer-like PEO exhibiting a total mass of around 300 kg/mol and possessing 64 peripheral groups on each face. The possibility of orthogonal functionalization of the surfaces of such Janus-type dendritic PEOs was exploited. Indeed, a dendron of generation 4 was functionalized with hydroxyl functions at its periphery, whereas the other was end-capped with either tertiary amino or disulfide groups. In a variant of this strategy, azido groups and acetylene could also be orthogonally introduced at the periphery of the fourth generation Janus-type dendrimer-like PEO and subjected to polycondensation by a 1,3-dipolar cycloaddition reaction. This afforded a necklace-like covalent assembly of dendrimer-like PEOs through the formation of stable [1,2,3]-triazole linkages.

Fabrication of fluorescent nanoparticles of dendronized perylenediimide by laser ablation in water

Highly fluorescent organic nanoparticles with size of about 300 nm were prepared by nanosecond laser ablation of micrometer-sized powder of dendronized perylenediimide dispersed in water. The nanoparticle colloidal solution provided a fluorescence quantum yield of 0.58. The absorption and emission spectral studies demonstrated that the bulky dendron groups at the side bays of perylenediimide chromophore efficiently suppress the interchromophoric interactions in the nanoparticles. Fluorescence measurement on several single nanoparticles underlines that the prepared nanoparticles are bright and photo-stable enough to be a useful probe for single particle fluorescence investigation.

Characterization and optical properties of tetrapyrazinoporphyrazines with phenylene dendron group

The treatment of the ethynyl compound 3 with one equivalent of 3,4-bis-(4-methoxyphenyl)-2,5-diphenyl-cyclopenta-2,4-dienone in degassed p-xylene afforded the corresponding 2,3-dicyanopyrazine derivatives containing a phenylene dendron group ( 4). The absorption spectra of the tetrapyrazinoporphyrazinato copper complexes ( 5) with long alkyl groups dramatically changed due to molecular aggregation depending on the polarity of the solvent. The variation in their aggregation behaviors depending on the polarity of the solvent was well correlated with their chemical structures.

Toward understanding the effect of substitutes and solvents on entropic and enthalpic elasticity of single dendronized copolymers

Using single molecule force spectroscopy (SMFS), we have investigated the single chain elasticity of a series of dendronized copolymers, whose original backbone is styryl dendron and maleic anhydride. The amilysis reaction of maleic anhydride introduces amide and carboxyl side groups. Hence, the copolymer bears three type side groups, Fréchet type dendrons, amides and carboxyls. The single chain elasticity of the polymers in tetrahydrofuran (THF) and chloroform (CHCl3) has been obtained, respectively. There is no hysteresis between the stretching and relaxing force curves of individual polymer chain, indicating that the elongation is carried out at the equilibrium condition. The force curves can be fitted well by the modified freely jointed chain model, which suggests that the elongation of the polymer chain is controlled by the entropic elasticity in the low-force region but dominated by enthalpic elasticity in the high-force region. The polymer with first-generation dendrons shows different elasticities in the two solvents, which should result from the different hydrogen bonds of the dendronized copolymer in two solvents. When the dendron groups are changed to be second and third generations, the single chain elasticity of the polymers is the same in two solvents. Hence, the elasticity of the polymer chain can be different depending on the properties of side groups and solvents.

Photoinduced intermolecular electron transfer and energy transfer of C60 dendrimers

Abstract Photoinduced intermolecular electron-transfer and energy-transfer processes of the fullerodendrimers with two poly(amidoamine)dendron groups of 0.5-th, 1.5-th and 2.5-th generations have been investigated by laser flash photolysis. The rate constants and quantum yields of photoinduced electron transfer with the added aromatic amine donors in PhCN tend to decrease with the dendron generation, indicating that the bulky dendron groups act as barriers for the donor molecules to approach the C60 moiety in the center of the dendrimers. The decreases in the rate constants of triplet energy transfer processes vs. O2 and β-carotene with the dendron generation are smaller than those of electron-transfer process, probably because effective encounter radii for energy transfer are larger than those for electron transfer; hence, less sensitive to dendrimer generation. A kinetic model for intermolecular electron-transfer and energy-transfer of fullerodendrimers was proposed. To cite this article: Yasuyuki Araki et al., C. R. Chimie 9 (2006).

Photo-promoting Fabrication of Silver Nanoparticles in the Presence of Anthracenyl-Focal PAMAM Dendrons

Silver nanoparticles protected by first to third generation poly(amido amine) dendrons with an anthracenyl-focal point were fabricated by photo-promotion of silver ions in aqueous dendron solutions. The reaction solutions colored from light to deep brown and displayed a broad plasmon band at 450 nm, indicating the formation of silver nanoparticles. The formation of particles progressed with time, although it slowed down at the light-shielding (dark) condition. The light-promoted electron transfer from amine groups of dendron to silver ions through anthracenyl moiety might concern to the formation of silver nanoparticles. According to the images of transmission electron microscopy, the shape of nanoparticles was not only spherical (15–20 nm in size) but also polygonal (20–35 nm in size). It was confirmed from the crystallographic analysis of electron diffraction patterns that the polygon was a hexagonal-close-packing (hcp) single crystal, whereas the crystal structure of spherical nanoparticles was face-centered-cubic (fcc). The reaction was fastest when the second generation dendron was used, indicating the competition of increasing number of amine groups and reducing efficiency of photo-promoted electron transfer with generation.

Poly(p‐phenylenevinylene) presenting pendent pentaphenylene dendron groups for light‐emitting diodes

AbstractWe have synthesized, using the Gilch method, a novel poly(p‐phenylenevinylene) derivative (PPV‐PP) containing two pendent pentaphenylene dendritic wedges, and have characterized its structure and properties. The incorporated side chain pentaphenylene dendrons serve as solubilizing groups, prevent π‐stacking interactions from occurring between the polymer main chains, and suppress the formation of excimers in the solid state. Photoluminescence studies indicate that efficient intramolecular energy transfer occurred from the photoexcited pentaphenylene groups to the poly(p‐phenylenevinylene) backbone. The polymer film exhibits a maximum emission at 510 nm and had a photoluminescence efficiency of 46%, which is similar to that measured in dilute solution. The photoluminescence spectra remained almost unchanged after thermal annealing at 150 °C for 20 h, and displayed inhibited excimer formation. Polymer light‐emitting diodes that we fabricated in the configuration ITO/PEDOT/PPV‐PP/Mg:Ag/Ag exhibited a maximum emission peak at 513 nm, corresponding to the green region [x = 0.30 and y = 0.62 in the Commission Internationale de L'Eclairage (CIE) chromaticity coordinates]. The maximum brightness and maximum luminance efficiency were 1562 cd/m2 and 1.93 cd/A, respectively. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5147–5155, 2005