Dendritic Host Research Articles

Alkoxy-capped carbazole dendrimers as host materials for highly efficient narrowband electroluminescence by solution process

Narrowband electroluminescence from multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters have attracted much attention owing to their potential in developing high-resolution organic light-emitting diode (OLED) displays. However, host materials used for MR-TADF emitters are mainly focused on small molecules that are relying on vacuum deposition for device fabrication. Here, we demonstrate the design of novel host materials with dendritic structures consisting of a non-conjugated adamantane core and four alkoxy-capped carbazole dendrons in periphery for solution-processed MR-TADF OLEDs with highly efficient narrowband electroluminescence. By introducing electron-donating n-butoxy capping groups to carbazole units and using the second-generation dendrons instead of the first-generation ones, triplet energies for the dendritic hosts are kept at higher than 2.80 eV, but the highest occupied molecular orbital (HOMO) levels can be considerably elevated from −5.51 to −5.19 eV, leading to barrier-free hole injection from anode to emissive layer. Solution-processed OLEDs based on the alkoxy-capped dendritic host and B,N-containing MR-TADF emitter reveal narrowband emission with full-width at half-maximum of 42 nm, together with low turn-on voltage of 2.8 V, maximum external quantum efficiency of 24.2% and power efficiency of 95.0 lm W−1, which represent the promising device efficiencies for narrowband electroluminescence by solution process.

Elevating the triplet level of carbazolyl benzonitrile-based dendritic hosts by suppressing intramolecular charge transfer for solution-processed blue thermally activated delayed fluorescence OLEDs

Realizing appropriate and excellent solution-processed thermally activated delayed fluorescence host materials is of great consequence to the development of low-cost, large-area OLED displays, as the doped devices mostly yield better efficiency than the undoped devices. Herein, two carbazolyl benzonitrile-based dendritic host materials were designed and synthesized by inserting phenyl bridges to 2,4,6-tri(9H-carbazol-9-yl) benzonitrile (3CzBN) and encapsulating flexible alkyl chains. The phenyl bridge extended the backbone of acceptor unit and donor unit respectively, allowed for a better separation of the HOMO and LUMO orbital and weakened intramolecular charge transfer, which endowed high triplet level of 3.01 eV, 2.85 eV for 3CzPhCN-O-Cz and 3PhCzCN-O-Cz. The introduction of the peripheral alkyl chains resulted in better solubility and film-forming ability. These features made the host materials suitable for fabricating blue solution-processed devices. The experimental results proved that the device performance was better when the phenyl bridge was inserted between the accepter unit and the center benzene ring than when it was introduced between the donor unit and the center benzene ring, which paved the way toward achieving high triplet level host materials for solution-processed OLEDs.

Cyclohexane-cored dendritic host materials with high triplet energy for efficient solution-processed blue thermally activated delayed fluorescence OLEDs

Two dendritic host materials (CH-2D1 and CH-2D2) are developed by using non-conjugated cyclohexane core and two first/second generation carbazole dendrons, which show excellent solubility in organic solvents, high thermal stability and high triplet energy (ET) of 2.78–2.84 eV, making them suitable for fabrication of solution-processed blue thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs). Compared to CH-2D1 with the first-generation carbazole dendron which shows low-lying highest occupied molecular orbital (HOMO) energy level of −5.48 eV, CH-2D2 with the second-generation carbazole dendrons exhibits higher HOMO level of −5.37 eV, which is more favourable for hole injection from the anode to the emissive layers. Consequently, solution-processed blue TADF OLEDs utilizing CH-2D2 as host show promising device performance with a low turn-on voltage of 3.4 V, maximum external quantum efficiency of 17.8%, maximum luminous efficiency of 41.3 cd A−1 and power efficiency of 33.9 lm W−1, which can compare with the most efficient solution-processed blue TADF OLEDs based on small-molecule and polymer hosts. These results indicate that dendritic host materials with well-defined chemical structure and good solubility are an attractive approach―beyond the soluble small-molecule hosts and polymer hosts―for the development of efficient solution-processed TADF OLEDs.

Multivalency in a Dendritic Host–Guest System

Multivalency is an important instrument in the supramolecular chemistry toolkit for the creation of strong specific interactions. In this paper we investigate the multivalency effect in a dendritic host–guest system using molecular dynamics simulations. Specifically, we consider urea–adamantyl decorated poly(propyleneimine) dendrimers that together with compatible mono-, bi-, and tetravalent ureidoacetic acid guests can form dynamic patchy nanoparticles. First, we simulate the self-assembly of these particles into macromolecular nanostructures, showing guest-controlled reduction of dendrimer aggregation. Subsequently, we systematically study guest concentration dependent multivalent binding. At low guest concentrations multivalency of the guests clearly increases relative binding as tethered headgroups bind more often than free guests’ headgroups. We find that despite an abundance of binding sites, most of the tethered headgroups bind in close proximity, irrespective of the spacer length; nevertheless, longer spacers do increase binding. At high guest concentrations the dendrimer becomes saturated with bound headgroups, independent of guest valency. However, in direct competition the tetravalent guests prevail over the monovalent ones. This demonstrates the benefit of multivalency at high as well as low concentrations.

Solution processible triphenylphosphine-oxide-cored dendritic hosts featuring thermally activated delayed fluorescence for power-efficient blue electrophosphorescent devices

A series of phosphine oxide based dendritic hosts have been developed. Compare with conventional dendritic host H2, the new hosts not only maintain high T1 but also have a small ΔEST and bring higher device performance.

Dendritic host materials with non-conjugated adamantane cores for efficient solution-processed blue thermally activated delayed fluorescence OLEDs

Dendritic hosts containing non-conjugated adamantane cores are developed for solution-processed blue TADF OLEDs with a maximum external quantum efficiency of 18.3%.

High-Energy-Level Blue Phosphor for Solution-Processed White Organic Light-Emitting Diodes with Efficiency Comparable to Fluorescent Tubes

SummaryA high-energy-level blue phosphor FIr-p-OC8 has been developed for solution-processed white organic light-emitting diodes (WOLEDs) with comparable fluorescent tube efficiency. Benefiting from the electron-donating nature of the introduced alkoxy, FIr-p-OC8 shows not only efficient blue light but also elevated highest occupied molecular orbital/lowest unoccupied molecular orbital levels to well match the dendritic host H2. Consequently, the hole scattering between FIr-p-OC8 and H2 can be prevented to favor the direct exciton formation on the blue phosphor, leading to reduced driving voltage and thus improved power efficiency. By exploiting this approach, a maximum power efficiency of 68.5 lm W−1 is achieved for FIr-p-OC8-based white devices, slightly declining to 47.0 lm W−1 at a practical luminance of 1,000 cd m−2. This efficiency can be further raised to 96.3 lm W−1 @ 1,000 cd m−2 when a half-sphere is applied to increase light out-coupling. We believe that our results can compete with commercial fluorescent tubes, representing an important progress in solution-processed WOLEDs.

UV light- and thermo-responsive supramolecular aggregates with tunable morphologies from the inclusion complexation of dendritic/linear polymers

UV light- and thermo-responsive supramolecular aggregates with tunable morphologies were obtained through the inclusion complexation between a β-CD containing dendritic host polymer and an azobenzene containing linear guest polymer. Morphologies of the aggregates could be adjusted by changing the molar ratio of host/guest polymers in the supramolecular polymers.

Recent Advances in Solution‐Processable Dendrimers for Highly Efficient Phosphorescent Organic Light‐Emitting Diodes (PHOLEDs)

AbstractPhosphorescent dendrimers together with dendritic host materials have inherent advantages in achieving highly efficient phosphorescent organic light‐emitting diodes (PHOLEDs) with low‐cost, solution‐processed device fabrication. Recently, much research effort has been devoted to developing these dendritic materials in the field of electroluminescence (EL). In this Focus Review, the major advances in this line of research are summarized and discussed. The crucial roles played by these dendritic organic electronic materials in coping with the key issues in the field of PHOLEDs have been specially emphasized. These include alleviating the triplet‐triplet annihilation effect through the site‐isolation effect associated with the dendritic structures, promoting charge‐carrier injection/transporting ability and ambipolar properties through functionalized dendrons, fulfilling simple PHOLEDs with high EL efficiencies, obtaining self‐hosting phosphorescent emitters, and avoiding undesired energy transfer process from phosphorescent cores to the dendrons. In addition, the future perspectives and ongoing challenges of this research frontier are also highlighted.

Synthesis and Characterization of Carbazole-Based Dendritic Host with Triphenylamine Core

Synthesis and Characterization of Carbazole-Based Dendritic Host with Triphenylamine Core

A carbazole-based dendritic host material for efficient solution-processed blue phosphorescent OLEDs

A dendritic host material 4,4-bis[3,6-bis(3,6-di-tert-butylcarbazol-9-yl)-carbazol-9-yl]-biphenyl for solution-processed blue phosphorescent organic light-emitting devices was designed and synthesized. Owing to the decrease of the π conjugation length of biphenyl moiety in molecule structure, this carbazole derived derivative shows high triplet energy. Furthermore, the thermal, photophysical and electrochemical properties of 4,4-bis[3,6-bis(3,6-di-tert-butylcarbazol-9-yl)-carbazol-9-yl]-biphenyl were investigated. The high triplet energy of 4,4-bis[3,6-bis(3,6-di-tert-butylcarbazol-9-yl)-carbazol-9-yl]-biphenyl ensures efficient energy transfer from the host to the triplet emitter iridium(III) bis(4,6-difluorophenylpyridinato)picolinate. The single layer device using the carbazole derivatives as the host for iridium(III) bis(4,6-difluorophenylpyridinato)picolinate showed the maximum luminance efficiencies of 5.8 cd A −1 , and a maximum external quantum efficiency 2.8%. The efficiency of the carbazole derivative based device was almost 3 times higher than the corresponding 1,3-bis(9-carbazolyl)benzene based device. ► A novel host material Cz-CBP for solution processed blue PhOLEDs was synthesized. ► Cz-CBP possesses high triplet energy and extremely high glass-transition temperature. ► The luminance efficiency of Cz-CBP based device was nearly 3 times higher than of mCP with the same structure.

Synthesis of carbazole-based dendrimer: host material for highly efficient solution-processed blue organic electrophosphorescent diodes

This paper reports the synthesis and physical properties of two novel carbazole-based dendritic host materials Cz-CCP and Cz-mCP for solution-processed blue phosphorescent organic light-emitting devices (PhOLEDs). These dendritic hosts exhibit high triplet energy (≥2.85 eV), excellent film-forming ability (with low root-mean-square (rms) values less than 0.2 nm), high glass-transition temperatures in the range of 242–248 °C, and the appropriate HOMO energy levels (−5.33–−5.35 eV) facilitating the transfer of holes from Poly(3,4-ethylenedioxythiophene):Poly(styrene-4-sulfonate) (PEDOT:PSS) to the emitting layer. The single-layer device using Cz-CCP and Cz-mCP as the host for the phosphorescence emitter iridium(III) bis(4,6-difluorophenylpyridinato)-picolinate (FIrpic) showed the maximum luminance efficiencies of 9.6 and 10.8 cd A−1, respectively. By introducing a thin 1,3,5-tris(1-phenyl-1H-benzo[d]imidazol-2-yl)benzene (TPBI) electron-transporting and exciton-confining layer, the maximum efficiency of the solution-processed double-layer device based on Cz-CCP and Cz-mCP can be further improved to 20.5 and 22.7 cd A−1, and maximum external quantum efficiencies as high as 10.2% and 11.5%, respectively. These results demonstrated that the newly synthesized, carbazole-based dendritic host materials are advantageous for fabrication of highly efficient blue PhOLEDs.

High‐Efficiency Single Emissive Layer White Organic Light‐Emitting Diodes Based on Solution‐Processed Dendritic Host and New Orange‐Emitting Iridium Complex

An extremely high-efficiency solution-processed white organic light-emitting diode (WOLED) is successfully developed by simultaneously using an ideal dendritic host material and a novel efficient orange phosphorescent iridium complex. The optimized device exhibits forward-viewing efficiencies of 70.6 cd A(-1) , 26.0%, and 47.6 lm W(-1) at a luminance of 100 cd m(-2) , respectively, promising the low-cost solution-processed WOLEDs a bright future as the next generation of illumination sources.

Tailoring uptake and release of ATP by dendritic glycopolymer/PNIPAAm hydrogel hybrids: first approaches towards multicompartment release systems

A multicompartment release system is described which combines the advantages of dendritic architectures and hydrogels to enhance the desired delivery features in complex biological compartments. Here, a hydrogel hosts dendritic glycopolymers as nanocontainers and a delivery system for drug molecules. The dendritic glycopolymer used consists of a hyperbranched poly(ethylene imine) with a maltose shell and acts as a host for the guest molecule adenosine triphosphate disodium salt hydrate (ATP). The ATP uptake and release from the dendritic host have been elucidated in detail with dependence on the dendritic glycostructure and pH. The complex interactions within the three components ATP, dendritic glycopolymer and hydrogel have been evaluated and could be fine-tuned. A selective release at pH 5.4–7.4 only of ATP from the multicompartment release system ATP@dendritic glycopolymer@hydrogel has been achieved when a boronic acid containing hydrogel was used which allowed chemical binding between the maltose units from the dendritic glycopolymer and the boronic acid (BA) units in the hydrogel. However, when using a hydrogel without BA units, simultaneous release of ATP and the dendritic glycopolymer scaffold from the ATP@dendritic glycopolymer@hydrogel multicompartment release system is observed in the pH range 2–7.4. This multicompartment release system can be applied in complex biological environments with changing pH values and has potential in biomedical applications and sensory devices.

Star-shaped dendritic hosts based on carbazole moieties for highly efficient blue phosphorescent OLEDs

An efficient carbazole-based dendritic host material Cz-TCB for solution processed blue phosphorescent organic light-emitting devices (PhOLEDs) was designed and synthesized. The nonplanar star-shaped configuration of Cz-TCB limited the effective extension of their π-conjugation, leading to the same triplet energy of 2.86 eV. No noticeable signals of Cz-TCB related to glass transition is observed in the DSC curves. Atomic force microscopy (AFM) measurements indicate the excellent thermal and morphological stability of the dendrimer. The performance of the novel host material based devices is far superior to those of the corresponding 1,3,5-tri(N-carbazolyl)benzene (TCB) based devices, which is outstanding for a solution-processed blue PhOLED. The best performance of iridium(III) bis(4,6-(di-fluorophenyl)-pyridinato-N,C′ (FIrpic) based devices show a turn-on voltage of 4.6 V, a maximum external quantum efficiency of 13.0%, and a maximum luminance efficiency of 25.7 cd A−1. Moreover, the best performance of iridium(III) tris(3,5-difluoro-4-cyanophenyl)pyridinato-N,C′ (FCNIrpic) based deep-blue-emitting devices exhibits a turn-on voltage of 5.7 V, a maximum efficiency of 10.9 cd A−1, and a maximum external quantum efficiency 6.4%. Our results demonstrate a promising approach to well-designed dendritic host materials for solution-processed blue PhOLEDs.

Host–guest chemistry of dendrimers in the gas phase

Since the early days of dendrimer chemistry, mass spectrometry has been an important analytical method for determining the purity and the detection of defects in dendrimers. Meanwhile, growing evidence demonstrates the great potential of mass spectrometry for the investigation of non-covalent dendritic host–guest complexes. Mass spectrometry provides an efficient means to isolate them in the high vacuum inside a mass spectrometer under environment-free conditions. Gas-phase chemistry is particularly beneficial for exploring the intrinsic properties which cannot easily be studied in solution. This mini-review highlights the versatility of gas-phase chemistry for (1) screening the specificity and stability of multivalent dendritic host–guest complexes depending on the nature of the guests, (2) revealing a dendritic effect during dendrimer–tweezer complex fragmentation and (3) monitoring an intra complex movement of small guests along the dendrimer periphery.

Dendritic effects of crown ether-functionalized dendrimers on the solvent extraction of metal ions

The ability of a series of crown ether-functionalized dendrimers to function as alkali metal picrate extraction agents is assessed by liquid–liquid extraction and 1H NMR titration experiments. Crown ether-functionalized dendrimers that contain Fréchet-type poly(benzyl ether) dendrons of different generation as building blocks display different extraction characteristics toward alkali metal cations. Positive and negative dendritic effects depending on the generation of the dendrimer are assigned in the complexation behaviour of the dendritic host compounds.

Encapsulation of nanoparticles using linear–dendritic macromolecules

Benzyl alcohol and Rose Bengal were loaded and entrapped using linear–dendritic macromolecules by two procedures. In the first procedure, benzyl alcohol was attached to the end functional groups of linear–dendritic macromolecules by ester bonds to afford linear–dendritic–host conjugates. In the second procedure, entrapment was based on physical interactions between Rose Bengal and linear–dendritic macromolecules; this procedure is known as complexation method. Loading and binding capacity of different linear–dendritic macromolecules was investigated using 1H nuclear magnetic resonance (NMR) and UV spectroscopy methods. It was found the loading or binding capacity of linear–dendritic macromolecules depends on their generation, so that higher generations have higher loading or binding capacity. Diameter of nanocarriers was investigated using dynamic light scattering (DLS) experiments, and it was between 16 and 50 nm for different nanocarriers. Release of guest molecules from nanocarriers was evaluated at pH 1, 7.4, and 10.

Structural Elucidation of Dendritic Host–Guest Complexes by X-ray Crystallography and Molecular Dynamics Simulations

The multiple monovalent binding of adamantyl-urea poly(propyleneimine) dendrimers with carboxylic acid-urea guests was investigated using molecular dynamics simulations and X-ray crystallography to better understand the structure and behavior of the dynamic multivalent complex in solution. The results from the two methods are consistent and suggest a preferred molecular picture of this complicated aggregate of multiple components. The guest molecules can bind to the dendrimer in a variety of ways although most involve hydrogen-bonding interactions between urea groups of the dendrimer with urea and/or carboxylic acid groups of the guest. In addition, acid-base interactions between the carboxylic acid of the guest and the tertiary amine in the interior of the dendritic host are present. Our proposed structure gives important information about the predominant dynamic interactions between the host and guest and illustrates how they fit together and interact with each other.

Dendritic Host Molecules with a Polycationic Core and an Outer Shell of Dodecyl Groups

AbstractThe synthesis of a topologically new type of dendrimer is presented in which a permanently positively charged core is decorated with a shell that is apolar and aliphatic in nature. The novel polyionic dendrimers were successfully applied as hosts for a predefined number of anionic guests, as is shown for the dye methyl orange. The aliphatic periphery of the dendrimers efficiently shields the ion pairs and renders the dendrimers fully soluble in organic solvents that are as apolar as hexane and, furthermore, provides them with an interesting phase behavior that appears not to be sensitive to the type of anion associated with it.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)