Dendrimer Films Research Articles

Effect of Red Emissive Ligand Number on Dendronized Solution‐Processable Iridium(III) Complexes for Organic Light‐Emitting Diodes

AbstractTris‐bidentate iridium(III) complexes used in organic light‐emitting diodes (OLEDs) are typically homoleptic or heteroleptic with three or two identical emissive ligands, respectively. Herein red phosphorescence emitting dendrimers composed of first generation biphenyl dendrons, 2‐ethylhexyloxy surface groups and an iridium(III) complex core with three, two or one emissive [4‐phenyl]−2‐[thiophen‐2‐yl]quinoline ligands are reported. The dendrimers have similar photoluminescence quantum yields (PLQYs) in solution (84–88%), neat film (23–25%) and when blended with tris(4‐carbazoyl‐9‐ylphenyl)amine (72–73%), enabling the effect of the number of emissive ligands on OLED performance to be determined. The external quantum efficiency (EQE) of OLEDs composed of neat dendrimer films increased with decreasing number of emissive ligands, with the device composed of the dendrimer having a single emissive ligand having an EQE of 9.2%, which is almost double that expected from a bottom emitting device and a film PLQY of 25 ± 3.6%. The emission is Lambertian and the higher‐than‐expected EQE is ascribed to alignment of the single emissive ligand being optimal for light‐outcoupling. The EQE of OLEDs containing the blend film also increased with decreasing emissive number of ligands (maximum EQE = 15.4%).

Real-time detection of TNT analogues in water using fluorescent dendrimer films

Thin fluorescent dendrimer films detect 2,4,6-trinitrotoluene (TNT) and its analogues dissolved in water.

Density Multiplication of Highly Periodic Sub-5 nm Supramolecular Dendrimer Cylinders on Block Copolymer Lamellar-Assisted High-Resolution Patterns.

Density multiplication in nanopatterning is one of the most efficient techniques for increasing the resolution of the inherent patterns. Thus far, most of the density multiplication techniques integrate bottom-up (or top-down) patterning onto guide patterns prepared by the top-down approach. Although the bottom-up approach exhibits several advantages of cost-effectiveness and high resolution, very few studies have reported bottom-up patterning within a bottom-up template. In this study, the density multiplication of supramolecular cylinders into a block copolymer (BCP)-based guide lamellar pattern is demonstrated by the directed self-assembly (DSA) of a dendrimer and BCPs for the first time. Supramolecular cylinders of sub-5 nm scale are confined into trenches based on 50 and 100 nm scales of a lamellar polystyrene (PS)-poly(methyl methacrylate) (PMMA) BCP, which led to 10×-level to 20×-level density multiplication. Moreover, the orientation of the dendrimer is dependent on the dendrimer film thickness, and the corresponding mechanism is revealed. Notably, the strong guiding effect from the high-resolution guide patterns improved the ordering behavior in the highly curved pattern. Graphoepitaxy via the confinement of an ultrahigh-resolution dendrimer into the guide pattern based on BCP demonstrates promise as a density multiplication method for generating highly ordered nanostructures and complex structures.

Structure and Mechanical Response of Polybutylcarbosilane Dendrimers Confined in a Flat Slit: Effect of Molecular Architecture and Generation Number.

Due to the absence of specific interactions, carbosilane dendrimers are ideal models to study the effect of a hyperbranched regular structure on the molecular response to external influences. In this work, we have studied the conformational behavior of single polybutylcarbosilane dendrimers under confinement between impermeable flat surfaces using atomistic molecular dynamics simulations. Dendrimers of different generations belonging to two homologous series with a tetra-functional core and three- and four-functional branches were simulated. The analysis of the dependence of the internal energy of the dendrimers on the wall distance allowed us to determine the critical degree of compression at which the dendrimers are able to change their shape without energy loss. The effects of generation number and branching functionality on the number of wall contacts, density distribution and shape changes were elucidated. It was found that for high generation dendrimers, the inner layers are not accessible for external interaction. It was shown that the excess stresses occurring at high compressions are concentrated in the structural center of the dendrimer. The nature of the elastic response, which is strongly nonlinear, was analyzed at different compressions depending on the dendrimer architecture and generation. We believe that our results are useful for further studies of dendrimer films under compression and can also serve as a basis for developing model concepts to describe the dynamics of dendrimer melts.

Enhanced adsorption films of dendrimers on mild steel for super protection

ABSTRACT This study employed metronidazole skeletons based on the target branched molecules (TBMs) for achieving efficient anti-corrosion of mild steel in HCl solution. In contrast, the reference linear molecules (RLMs) carrying a single metronidazole framework were also made. The excellent corrosion resistance performance of the target dendrimers for mild steel electrodes in HCl solution was demonstrated. It is shown that the TBMs displayed a superior anti-corrosion effect for mild steel over RLMs in HCl medium at 298 K (at 0.15 mol/L, TBM1, 97.70% versus RLM1, 90.89%). It is shown that the standard Gibbs free energy changes of the adsorption of the TBMs on mild steel surface are below −33 kJ/mol (TBM1, −34.58 kJ/mol), thus an enhanced adsorption film was formed.

Poly(amidoamine) Dendrimer as an Interfacial Dipole Modification in Crystalline Silicon Solar Cells.

Poly(amidoamine) (PAMAM) dendrimers are used to modify the interface of metal-semiconductor junctions. The large number of protonated amines contributes to the formation of a dipole layer, which finally serves to form electron-selective contacts in silicon heterojunction solar cells. By modification of the work function of the contacts, the addition of the PAMAM dendrimer interlayer quenches Fermi level pinning, thus creating an ohmic contact between the metal and the semiconductor. This is supported by the observation of a low contact resistivity of 4.5 mΩ cm2, the shift in work function, and the n-type behavior of PAMAM dendrimer films on the surface of crystalline silicon. A silicon heterojunction solar cell containing the PAMAM dendrimer interlayer is presented, which achieved a power conversion efficiency of 14.5%, an increase of 8.3% over the reference device without the dipole interlayer.

Strengthened adsorption films of double antibiotic medicines skeletons-based dendrimers on copper surface: Molecular dynamics simulation and intensified anti effects of algae, bacteria and corrosion

In this study, an approach was proposed to achieve super anti-effects of alga, bacteria and corrosion for copper surface by employing strengthened adsorption films of dendritic compounds having double antibiotic medicine xacins skeletons. Thus, two new target dendritic compounds based on goal-orientation were prepared with the linear reference molecules carrying a single xacin segment. The adsorption of the studied compounds on copper surface was analyzed based on molecular modeling and material dynamic simulation. Furthermore, the spontaneous adsorption of copper surface of these molecules was performed in mixed DMSO/H2O (80/20, v/v). The copper surface adsorbed by the target molecules showed superior antialgae performance of Chlorella, and the maximum diameters of bacteriostatic zones against E. coli and S. aureus reached about 3.5 cm and 2.8 cm. Besides, the dynamic polarization and electrochemical impedance spectroscopy show that the target compounds achieved over 96% corrosion inhibition efficiency at 0.100 mM in 0.5 M H2SO4 solution. The adsorption of copper surface of the target molecules was deeply characterized such as X-ray photoelectron spectroscopy (XPS), which revealed that the target molecules are chemically adsorbed on the metal surface through the complexation of heteroatoms with metals.

Effect of dendrimer surface groups on the properties of phosphorescent emissive films

Fac -tris[2-phenylpyridinato- C 2 , N ]iridium(III) [Ir(ppy) 3 ] is a well-known phosphorescent material for organic light-emitting diodes (OLEDs) and while uniform thin films can be formed using evaporation under high vacuum, it is not sufficiently soluble to enable it to be processed from solution. Ir(ppy) 3 -cored dendrimers with solubilizing surface groups can be processed from solution to form good quality neat or guest:host blends, even when the host has relatively poor solubility. In this manuscript, we report the effect of adding different solubilizing surface groups, namely 2-ethylhexyloxy, n -propyl or t -butyl to first generation dendrons attached to the Ir(ppy) 3 core on the optoelectronic properties of neat and blend films with tris(4-carbazoyl-9-ylphenyl)amine (TCTA). The different dendrons were found to have minimal effect on the photoluminescence spectra and efficiency of energy transfer from the host to the guest in the blend films. The hole mobility of neat films of the solution-processed Ir(ppy) 3 -cored dendrimer films was around 10 −6 cm 2 V −1 s −1 , which was an order of magnitude less than Ir(ppy) 3 films formed by evaporation. Blending the dendrimers with TCTA at a concentration of 11 mol% (the concentration of the highest film photoluminescence quantum yield) led to an order of magnitude decrease in the hole mobility compared to the neat films. However, despite the relatively low mobilities, simple two-layer OLEDs composed of a blend light-emitting layer and an electron transporting layer were found to reach a maximum EQE of 11.1% at a luminance of 1000 cd m −2 for a film with a PLQY of 60%. • Ir(ppy)3-cored dendrimers with solubilising surface groups are solution processed. • Good quality guest:host blend films formed with poorly soluble TCTA host. • Dendron type was found to have minimal effect on the host to guest energy transfer. • Charge mobility in dendrimer:TCTA blends less than in neat film. • Simple two-layer OLEDs had maximum EQEs of 11.1% at a luminance of 1000 cd m-2.

Arylazopyrazole-Based Dendrimer Solar Thermal Fuels: Stable Visible Light Storage and Controllable Heat Release.

Solar thermal fuels offer a closed cycle and a renewable energy storage strategy by harvesting photon energy within the chemical conformations of molecules and retrieving energy by an induced release of heat. However, the majority of reports are limited to the ultraviolet light storage, which potentially interferes with the surrounding environment and reduces the material lifetime. Here, we present a novel arylazopyrazole (AAP)-containing dendrimer that not only addresses the hindrance of visible light storage for solar thermal fuels but also exhibits outstanding performances of abundant energy conversion and stable storage, which are attributed to the substantial absorbance in visible wavelengths of para-thiomethyl-substituted AAP groups and the stability of cis isomers, respectively. The energy density of the dendrimer fuel after efficiently harvesting blue light (405 nm) is as high as 0.14 MJ kg-1 (67 kJ mol-1), and the storage half-life of the fabricated dendrimer film can reach up to 12.9 days. Moreover, the heat release of the dendrimer film can be triggered by different stimuli (light and heat). The dendrimer film displays a 6.5 °C temperature difference between trans isomers and cis isomers during green light irradiation. Our work provides a fascinating avenue to fabricate visible light storage solar thermal fuels and unlocks the possibility of developing natural sunlight storage in the future.

Covalent and noncovalent films made up of sulfonimide-based dendrimers

Dendrimers are unique macromolecules composed of branched monomers that are characterized by monodispersity, biocompatibility, and multivalent surfaces and are synthesized by the stepwise addition of repetitive units. Over recent years, dendrimers have been attractive materials as detecting agents, targeting components, imaging agents, or pharmaceutically active compounds. This study demonstrates the possibility of the formation and transfer of thin sulfonimide dendrimer films of different generations to solid surfaces using the Langmuir-Blodgett technique. The surface of sulfonimide dendrimers was functionalized with naphthalene end groups (from 4 to 64 groups). The developed noncovalent and covalent films showed the expected different contact angles due to the presence of the naphthyl groups attached to the dendrimer side, which can bond intramolecularly or intermolecularly. Changing the number of naphthyl groups allows control of the hydrophobic properties of the films, providing an opportunity to create two types of films with covalent and noncovalent bonding. The difference in contact angle between the 2nd and 5th generations of dendrimers was approximately 33°. The low-cost formation of such transparent water-repellent film imparting water repellency to a substrate while maintaining its inherent properties, such as color and morphology, can protect glass and painted surfaces from excessive humidity.

Sub‐5 nm Dendrimer Directed Self‐Assembly with Large‐Area Uniform Alignment by Graphoepitaxy

AbstractDirected self‐assembly (DSA) using soft materials is an important method for producing periodic nanostructures because it is a simple, cost‐effective process for fabricating high‐resolution patterns. Most of the previously reported DSA methods exploit the self‐assembly of block copolymers, which generates a wide range of nanostructures. In this study, cylinders obtained from supramolecular dendrimer films with a high resolution (<5 nm) exhibit planar ordering over a macroscopic area via guiding topographical templates with a high aspect ratio (>10) and high spatial resolution (≈20 nm) of guiding line patterns. Theoretical and experimental studies reveal that this property is related to geometrical anchoring on the meniscus region and physical surface anchoring on the sidewall. Furthermore, this DSA of dendrimer cylinders is demonstrated by the non‐regular geometry of the patterned template. The macroscopic planar alignment of the dendrimer nanostructure reveals an extremely small feature size (≈4.7 nm) on the wafer scale (>16 cm2). This study is expected to open avenues for the production of a large family of supramolecular dendrimers with different phases and feature dimensions oriented by the DSA approach.

Self-Perforated Hydrogel Nanomembranes Facilitate Structural Analysis of Proteins by Electron Cryo-Microscopy.

We developed a method to improve specimen preparation for electron cryo-microscopy of membrane proteins. The method features a perforated hydrogel nanomembrane that stabilizes the thin film of aqueous buffer spanning the holes of holey carbon films, while at the same time preventing the depletion of protein molecules from these holes. The membrane is obtained by cross-linking of thiolated polyglycerol dendrimer films on gold, which self-perforate upon transfer to holey carbon substrates, forming a sub-micron-sized hydrogel network. The perforated nanomembrane improves the distribution of the protein molecules in the ice considerably. This facilitates data acquisition as demonstrated with two eukaryotic membrane protein complexes.

Quantitative interpretation of PAMAM dendrimers adsorption on silica surface

Understanding the dendrimer-solid support interaction is of great importance for dendrimer-based drug delivery system design. The maximum surface coverage on a hydrophilic silica surface was determined using the quartz crystal microbalance with dissipation monitoring (QCM-D) and multi-parametric surface plasmon resonance (MP-SPR) methods: the adsorption process depends on ionic strength and pH of solutions. The effectiveness of G6 adsorption is mainly determined by the range of electrostatic inter-dendrimer interactions and dendrimer-silica surface interactions. Changes in ionic strength have a strong effect on the binding affinity of dendrimers to the surface. The trends in the binding affinity and the surface saturation amount correspond well with the degree of change of protonation of the adsorbed molecules. The development of new research techniques makes it possible to attain a more profound understanding of the self-assembling behaviour of dendrimers. The comparison of QCM-D and MP-SPR allowed the estimation that the dendrimer film contains approximately 70% water. These results indicate that 6th generation PAMAM dendrimers form very hydrated films on silica surfaces. In this case the number of water molecules associated per dendrimer molecule varied from 10,450 to 9,200. The hydration of dendrimer films seems to be a crucial aspect of their implementation. This data confirmed that dendrimers are very promising candidates for many biological applications.

Sugar-sensitive dendrimer films as a sacrificial layer for the preparation of freestanding multilayer films

Multilayer thin films composed of poly(vinyl alcohol) (PVA) and phenylboronic acid-bearing poly(amidoamine) dendrimer (PBA-PAMAM) were used as a sacrificial layer for constructing freestanding polyelectrolyte films consisting of poly(styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH). Freestanding (PSS/PAH)15 films were successfully released from substrate by exposing composite (PVA/PBA-PAMAM)n/(PSS/PAH)15 films (n=5 and 10) to sorbitol solutions under mild conditions at pH7.0–9.0. The film release was accelerated in solutions of higher sorbitol concentrations at pH9.0 as well as in solutions with lower concentration of NaCl. The results were rationalized based on the scission of boronate ester bonds between PBA-PAMAM and PVA in the (PVA/PBA-PAMAM)n layer due to a competitive binding of sorbitol to PBA-PAMAM.

Novel “signal-on” electrochemiluminescence biosensor for the detection of PSA based on resonance energy transfer

Here, we propose a simple and novel “signal-on” electrochemiluminescence (ECL) biosensor based on resonance energy transfer (RET) for detection of prostate specific antigen (PSA). The system is composed of Multi-walled carbon nanotubes (MWCNT), polyamidoamine (PAMAM) dendrimer and Au nanoparticles (NPs) film on glassy carbon electrode (GCE) to improve the electron transfer, provide abundant amine group for the immobilization of biomolecules, and amplify the ECL signal. After that, Au nanorods (Au NRs) labeled peptide is modified on electrode surface to serve as ECL-RET acceptor due to the excellent overlap between the ECL emission spectrum of Ru(bpy)32+ and the absorption spectrum of Au NRs, leading to the significant decrement of ECL signal. Upon the sensing cleavage of peptide with PSA, both Au NRs and peptide are released from electrode surface, resulting in the high recovery efficiency of ECL signal. The proposed approach exhibits a wide linear range from 0.1pg/mL to 10ng/mL with a detection limit of 0.03pg/mL. Results revealed that the recoveries were in a range from 95% to 108%, indicating good accuracy of the proposed method for PSA detection. In addition, the proposed biosensor exhibited well specificity for the detection of PSA.

Piezoelectric sensor for sensitive determination of metal ions based on the phosphate-modified dendrimer

Heavy metal ions arising from human activities are retained strongly in water; therefore public water supplies must be monitored regularly to ensure the timely detection of potential problems. A phosphate-modified dendrimer film was investigated on a quartz crystal microbalance (QCM) for sensing metal ions in water at room temperature in this study. The chemical structures and sensing properties were characterized by Fourier transform infrared spectroscopy and QCM measurement, respectively. This phosphate-modified dendrimer sensor can directly detect metal ions in aqueous solutions. This novel sensor was evaluated for its capacity to sense various metal ions. The sensor exhibited a higher sensitivity level and shorter response time to copper(II) ions than other sensors. The linear detection range of the prepared QCM based on the phosphate-modified dendrimer was 0.0001 ∼ 1 μM Cu(II) ions (R2 = 0.98). The detection properties, including sensitivity, response time, selectivity, reusability, maximum adsorption capacity, and adsorption equilibrium constants, were also investigated.

ChemInform Abstract: Synthesis of Optically Active, X‐Shaped, Conjugated Compounds and Dendrimers Based on Planar Chiral [2.2]Paracyclophane, Leading to Highly Emissive Circularly Polarized Luminescence.

Optically active, Frechet-type dendrimers containing an emissive X-shaped π-electron system as the core unit were synthesized. Gram-scale optical resolution and transformations of 4,7,12,15-tetrasubstituted [2.2]paracyclophanes were also carried out. The high-generation dendrons effectively absorbed UV light and transferred energy to the core, resulting in high photoluminescence (PL) from the core. In addition, the dendrons sufficiently isolated the emissive X-shaped conjugated core and bright emission was observed from both thin films and solutions. Intense circularly polarized luminescence (CPL) was observed from the thin film. The dendrimer films exhibited excellent optical properties, such as large molar extinction coefficients, high fluorescence quantum efficiencies, intense PL and CPL, and large CPL dissymmetry factors.

Synthesis of Optically Active, X-Shaped, Conjugated Compounds and Dendrimers Based on Planar Chiral [2.2]Paracyclophane, Leading to Highly Emissive Circularly Polarized Luminescence.

Optically active, Fréchet-type dendrimers containing an emissive X-shaped π-electron system as the core unit were synthesized. Gram-scale optical resolution and transformations of 4,7,12,15-tetrasubstituted [2.2]paracyclophanes were also carried out. The high-generation dendrons effectively absorbed UV light and transferred energy to the core, resulting in high photoluminescence (PL) from the core. In addition, the dendrons sufficiently isolated the emissive X-shaped conjugated core and bright emission was observed from both thin films and solutions. Intense circularly polarized luminescence (CPL) was observed from the thin film. The dendrimer films exhibited excellent optical properties, such as large molar extinction coefficients, high fluorescence quantum efficiencies, intense PL and CPL, and large CPL dissymmetry factors.

Detection of Cu(II) Ion in Water Using a Quartz Crystal Microbalance

Drinking water from a tap is a source of potential exposure to environmental contaminants. This requires that public water supplies should be regularly monitored for heavy metals. Many of heavy metal ions are retained and accumulated in water strongly. Consequently it has entered the food chain to threaten human health. A quartz crystal microbalance (QCM) based on a phosphate-modified dendrimer film was investigated for direct detection of Cu(II) metal ion in water. This QCM sensor exhibited the high sensitivity and the short response time to Cu(II) metal ion.

Phosphorescence quenching of fac-tris(2-phenylpyridyl)iridium(iii) complexes in thin films on dielectric surfaces.

We study the influence of the film thickness on the time-resolved phosphorescence and the luminescence quantum yield of fac-tris(2-phenylpyridyl)iridium(iii) [Ir(ppy)3]-cored dendrimers deposited on dielectric substrates. A correlation is observed between the surface quenching velocity and the quenching rate by intermolecular interactions in the bulk film, which suggests that both processes are controlled by dipole-dipole interactions between Ir(ppy)3 complexes at the core of the dendrimers. It is also found that the surface quenching velocity decreases as the refractive index of the substrate is increased. This can be explained by partial screening of dipole-dipole interactions by the dielectric environment.