Carbazole Dendrimers Research Articles

Interface Modification on TiO2 Electrode Using Dendrimers in Dye-Sensitized Solar Cells

The interface modification of dye-sensitized solar cells (DSSCs) in order to remove I3− on the TiO2 electrodes is important for improving their performance. The suppression of the back electron transfer by a modified interface improves the open-circuit voltage. In this study, we demonstrated that the suppression mechanism using phenylazomethine dendrimers with a triarylamine core (TPA-DPAs) and two other dendrimers, which are a carbazole dendrimer containing a cyclic phenylazomethine of the third generation (CPA-Cz G3) and a half-dendritic phenylazomethine of the fifth generation (Half-DPA G5). Removing I3− and producing I− on the TiO2 electrode by complexation is critical for the suppression of the back electron transfer and promoting the regeneration of the dye in dendrimers having an inner space. Additionally, the presence of various metal compounds in the dendrimers decreased the resistance of the DSSCs, improving fill factor and energy conversion efficiency. We studied that the dendrimer property is changed by the quantitative metal complexation. The fill factor and energy conversion efficiency of the DSSCs are maximized with 0.5 equiv. of SnCl2 in the TPA-DPAs.

Thermally and electrochemically stable amorphous hole-transporting materials based on carbazole dendrimers for electroluminescent devices

Amorphous hole-transporting carbazole dendrimers, 1,4-bis[3,6-di(carbazol-9-yl)carbazol-9-yl]-2,6-di(2-ethylhexyloxy)benzene ( G2CB) and 1,4-bis[3,6-di(carbazol-9-yl)carbazol-9-yl]-9-(2-ethylhexyl)carbazole ( G2CC), were synthesized by a divergent approach involving bromination and Ullmann coupling reactions. Compounds G2CB and G2CC showed high thermal stability ( T g = 206 to 245 °C) and excellent electrochemical reversibility. Double-layer organic light-emitting diodes were fabricated by using G2CB and G2CC as hole-transporting layers (HTLs) and tris(8-quinolinato)aluminum (Alq 3) as light-emissive layer with the device configuration of indium tin oxide/HTL/Alq 3/LiF:Al. Both devices exhibited bright green emission from Alq 3. The device using G2CC as HTL has the best performance with a maximum brightness of 8900 cd/m 2 at 14 V and a low turn-on voltage of 3.5 V.

Synthesis of electrochemically and thermally stable amorphous hole-transporting carbazole dendronized fluorene

A novel amorphous hole-transporting carbazole dendrimer, 2,7-bis[3,6-di(carbazol-9-yl)carbazol-9-yl]-9,9-bis- n-hexylfluorene ( G2CF), was synthesized by a divergent approach involving bromination and Ullmann coupling reactions. G2CF showed UV–vis absorption bands at 304 and 332 nm in chloroform solution and the photoluminescence spectra showed a maximum peak at 373 nm in a bluish-purple region. Differential scanning calorimetry (DSC) and cyclic voltammetry (CV) analysis revealed G2CF was an electrochemically and thermally stable amorphous material with a high glass transition temperature ( T g) of 237 °C. The organic light-emitting device having the structure of ITO/ G2CF/Alq 3/LiF:Al exhibited a bright green emission with a maximum luminescence of 11,000 cd/m 2 at 16 V and a turn-on voltage of 5.4 V.

Electrochemical Deposition of End-Capped Triarylamine and Carbazole Dendrimers: Alternate Technique for the Manufacture of Multilayer Films

We successfully demonstrated layer-by-layer stacking via an electrochemical deposition process using suitable peripheral dendrimers, paving the way to the development of an alternative technique for the fabrication of multilayer devices.

Organic Light-Emitting Diodes with Novel Carbazole Dendrimer as a Photocrosslinking Hole-transfer Layer

Organic Light-Emitting Diodes with Novel Carbazole Dendrimer as a Photocrosslinking Hole-transfer Layer

Novel Hole‐Transport Material for Efficient Polymer Light‐Emitting Diodes by Photoreaction

AbstractSummary: The photo‐crosslinking of carbazole dendrimers was analyzed by UV and IR spectroscopic methods. Photoirradiation results in the formation of a film that is insoluble in toluene and benzene. Time‐of‐flight mass spectrometry studies revealed that the photoirradiation lead to an oligomerization of the dendrimer through crosslinking. The resulting insoluble dendrimer film could be applied as a hole‐transport layer in efficient polymer electroluminescence devices (PLEDs).Luminance‐voltage characteristics for PLEDs wherein PEDOT:PSS and CbzG3 complex with SnCl2 were employed as the hole transport layer (ITO/HTL/EML/Ca/Ag).magnified imageLuminance‐voltage characteristics for PLEDs wherein PEDOT:PSS and CbzG3 complex with SnCl2 were employed as the hole transport layer (ITO/HTL/EML/Ca/Ag).

Synthesis of Asymmetrically Arranged Dendrimers with a Carbazole Dendron and a Phenylazomethine Dendron

Asymmetrically arranged dendrimers with a carbazole dendron and a phenylazomethine dendron were synthesized by the combination of Ullmann reaction and a dehydration reaction in the presence of titanium tetrachloride. Stepwise complexation in the phenylazomethine dendron unit within these dendrimers and SnCl2 suggests a gradient in the electron density associated with the imine groups. The complexation of the dendrimer changes the HOMO/LUMO energy gap of the dendrimer. We show the dendrimers with higher generations have the larger HOMO values. The most electron-rich molecule, Cz3-DPA3, has the highest HOMO value of 5.35 eV and, accordingly, is expected to have the lowest barrier for the hole injection from the ITO electrode (4.6 eV) in OLEDs. However, for the HOMO energy levels of the carbazole dendrimer complex with SnCl2, the energy levels of the carbazoles did not change based on almost the same redox potentials as those of the dendrimers themselves. Using Cz3-DPA3 as a hole-transport layer (HTL), only complexation with metal ions results in the enhanced maximum luminescence from 4041 to 10 640 cd/m2 by only complexing with SnCl2 under the nonoptimized conditions. A complexation leads to a high EL efficiency because of the p-type-doped structure of the dendrimers as a hole-transport layer.

Novel carbazole dendrimers having a metal coordination site as a unique hole‐transport material

AbstractWe have synthesized novel carbazole dendrimers via the cyclotrimerization of aminophenylketones in the presence of titanium tetrachloride. These dendrimers have the ability to assemble metal ions such as Sn2+ and Eu3+ with no significant difference in their generation, suggesting the dendrimer with an interior with a small density up to the third generation. We show the dendrimers with higher generations have the higher HOMO values. The most electron rich molecule, the G3 dendrimer, has the highest HOMO value of −5.2 eV. However, for the HOMO energy levels of the carbazole dendrimer complex with Eu(OTf)3, the energy levels of the carbazoles did not change based on almost the same redox potentials as those of the dendrimers, themselves. Using the carbazole dendrimers and their europium complex, a homogeneous film was produced, which enhanced the performance of the electroluminescence device in comparison with only the dendrimer as the hole‐transporting layer. This approach was managed by a solution process, i.e., the spin‐coating method, without using the coevaporation technique based on the large equilibrium constants of the coordination of metal ions on the imine sites (K = 105 M−1).

Synthesis of Novel Carbazole Dendrimers Having a Metal Coordination Site.

We have synthesized novel carbazole dendrimers via cyclotrimerization. This synthetic procedure to prepare the dendrimers, especially with a higher generation, via the cyclization reaction was found to be an extremely effective method. These dendrimers have the ability to assemble metal ions such as Sn2+ and Eu3+, resulting in a change in its fluorescence property.

Synthesis of Novel Carbazole Dendrimers Having a Metal Coordination Site

Abstract We have synthesized novel carbazole dendrimers via cyclotrimerization. This synthetic procedure to prepare the dendrimers, especially with a higher generation, via the cyclization reaction was found to be an extremely effective method. These dendrimers have the ability to assemble metal ions such as Sn2+ and Eu3+, resulting in a change in its fluorescence property.

Synthesis and properties of polyester dendrimers bearing carbazole groups in their periphery

Polyester dendrimers bearing carbazole units at their peripheries were synthesized by attaching 3,5-bisl4-(9-carbazoly)butoxy]benzoic acid to the peripherical phenoxy groups. The phenoxy-terminated polyester dendrimcrs were synthesized by hydrogenation of the corresponding benzyloxy-terminated polyester dendrimers. The structure of the synthesized compounds was confirmed with IR, 'H NMR. MALDITOF MS and GPC. The reaction conditions for attaching 3,5-bis[4-(9-carbazolyl)butoxy]benzoic acid to the peripherical phenoxy groups of polyester dendrimers were studied. Fluorescence spectra studies showed that there exist strong intramolecular interactions in the carbazole dendrimer molecules.

Multifunctional Hyper-Structured Molecules

AbstractTo fill the gap between molecular design and the architecture of three-dimensional functional structures, we propose novel hyper-structured molecules (HSMs) based on welldefined and topologically controlled molecular systems. To this end we have developed carbazole dendrimers, trimers, cyclic oligomers and chromogenic calix[4]arenes as HSMs. Photorefractivity was selected as the primary target function of these HSMs. Oligomers developed in our laboratory exhibit intrinsic photocarrier generation, transport, electro-optic, film-forming and poling properties. These multifunctional properties allow us to demonstrate optical image processing using optical phase conjugation. The topological shapes of indoaniline-derived calix[4]arenes were studied by hyper-Rayleigh scattering. The two indoaniline moieties in calix[4]arene derivatives were pre-aligned so as to enhance the net molecular hyperpolarizability. Besides dendric oligomers, cyclic oligomers can be used as a molecular platform which allows molecular level tuning of shape, size and topology for superior opto-electronic functions.