Jurate Simokaitiene

Synthesis and Properties of Methoxyphenyl-Substituted Derivatives of Indolo[3,2-b]carbazole

The synthesis and full characterization of new derivatives of indolo[3,2-b]carbazole with differently substituted phenyl groups at nitrogen atoms is reported. Comparative study on their thermal, optical electrochemical, and photoelectrical properties is presented. The synthesized compounds are electrochemically stable. Their highest occupied molecular orbital energy values range from -5.14 to -5.07 eV. The electron photoemission spectra of the films of synthesized materials revealed the ionization potentials of 5.31-5.47 eV. Hole drift mobility of the amorphous film of 5,11-bis(3-methoxyphenyl)-6-pentyl-5,11-dihydroindolo[3,2-b]carbazole exceed 10(-3) cm(2)/V·s at high electric fields, as it was established by xerographic time-of-flight technique. In contrast to diphenylamino substituted derivatives of carbazole, no effect of the position of methoxy groups on the photoelectrical properties was observed for the synthesized methoxyphenyl-substituted derivatives of indolo[3,2-b]carbazole. The indolo[3,2-b]carbazole core has a larger resonance structure that includes 3 phenyl rings, and thus the energy gap of the HOMO and LUMO π orbitals is lower as compared to that of carbazoles. With a larger energy difference between the phenyl substituents and the core moiety, the indolo[3,2-b]carbazole derivatives studied all have a weaker coupling between the phenyl group and a much weaker dependence of the molecular properties on the position of substituents on the phenyl groups as compared to those observed in substituted carbazoles.

Influence of methoxy groups on the properties of 1,1-bis(4-aminophenyl)cyclohexane based arylamines: experimental and theoretical approach

Three new isomeric cyclohexylidene linked triphenylamines containing methoxy groups in different positions were synthesized via Ullmann coupling from 1,1-bis(4-aminophenyl)cyclohexane and respective aryl iodides. Thermal behaviour, optical and photoelectrical properties of the obtained materials were investigated. Calculations based on the density functional methods (DFT) were also carried out in order to better understand structure–property relationships. Methoxy-substituted derivatives of 1,1-bis(4-aminophenyl)cyclohexane show lower ionization potentials and higher hole drift mobilities than the corresponding derivative having no methoxy groups. The ionization potentials of the solid samples of the methoxy-substituted compounds established by the electron photoemission technique are in the range of 5.34–5.55 eV. Hole-drift mobility values of the amorphous layers of the methoxy-substituted materials established by the time-of-flight technique range from 4.0 × 10−4 to 1.2 × 10−3 cm2 V−1 s−1 at the electric field of 106 V cm−1. The highest hole mobilities were observed for the para-substituted derivative. Theoretical results suggest that the hole mobility in the bulk materials is driven by the electronic coupling parameter whilst the reorganization energy parameter predicts the wrong mobility trend. The role of the methoxy groups is found to be related to the well-known mesomeric (π-donor) effect and the possibility to establish C–H⋯π(Ph) and C–H⋯X (X = O, N) hydrogen bonds. The effect of these properties on the enhanced Stokes shifts of the para-methoxy-substituted compound, on the decrease of the ionization potentials for the methoxy substituted compounds as compared to the non-substituted one, and on the enhanced possibility to establish considerable electronic couplings between adjacent molecules is discussed in detail.

Carbazole based polymers as hosts for blue iridium emitters: synthesis, photophysics and high efficiency PLEDs

This article reports the synthesis of new carbazole based polymers and their application as hosts in sky-blue polymer light emitting devices (PLEDs) with a solution-processed emitting layer doped with a cyclometalated Ir(III) complex. We systematically investigate their effect on the PLED performance. A current efficiency of 19.7 cd A−1 and a brightness of 1850 cd m−2 were achieved with these polymers. The roll-off in electrophosphorescent quantum efficiency in PLEDs was shown to arise mainly from triplet–triplet annihilation between dopants in the hosts with tert-butyl groups. It has been shown that in the devices with hosts without tert-butyl groups the efficiency roll-off is additionally affected by electric field quenching. In these carbazole based polymers, triplet dimers are formed and tert-butyl groups do not limit the intermolecular interactions to prevent triplet dimer formation, nevertheless tert-butyl groups reduce charge transport.

Synthesis and characterisation of a carbazole-based bipolar exciplex-forming compound for efficient and color-tunable OLEDs

A new ambipolar fluorophore, 3,6-di(4,4′-dimethoxydiphenylaminyl)-9-(1-naphthyl)carbazole, was synthesized and its physical properties were studied by differential scanning calorimetry, thermogravimetric analysis, UV-vis absorption, luminescence and photoelectron emission spectroscopy, cyclic voltammetry and a time of flight method. The latter technique indicates that the compound demonstrates bipolar semiconducting properties. Using the synthesized compound as an emissive material, a single-layer OLED with an electroluminescence spectrum containing a voltage-dependent electroplex emission band in the region of 550–650 nm was fabricated. Another OLED was fabricated with an additional electron transporting bathophenanthroline layer that forms a direct interface with the layer of 3,6-di(4,4′-dimethoxydiphenylaminyl)-9-(1-naphthyl)carbazole. A strong exciplex-type band in the electroluminescence spectrum of this OLED with an emission maximum at ca. 540 nm was observed. The electroluminescence spectra of both devices were found to be clearly dependent on the applied bias. This effect can be useful for the development of efficient and colour-tunable OLEDs.

P-152: Efficient Blue Phosphorescent OLEDs Employing Novel Oligocarbazoles as High-Triplet-Energy Host Materials

A series of 3(6),9′-linked oligocarbazoles with large triplet energies and morphological stability are reported as host materials for electrophosphorescence. In such oligocarbazoles, the triplet excitation is confined within one carbazole unit, leading to a new molecular design strategy for large-triplet-energy and high morphological stability hosts. Using these hosts, efficient blue phosphorescent OLEDs having efficiencies up to 15%, 31 cd/A and 28 lm/W are demonstrated.

Photopolymerization of neopentyl glycol diglycidylether and its compositions with 9-(2-oxiranylmethyl) carbazole

Photopolymerization of neopentyl glycol diglycidylether (NPG) initiated with diphenyl iodonium tetrafluoroborate (TB) in bulk has been studied. The influence of concentration of the photoinitiator on the rate of polymerization and monomer conversion is discussed. The initiator exponent was established for the photopolymerization of NPG with TB. Photopolymerization of the compositions consisting of NPG and 9-(2-oxiranylmethyl) carbazole (OMC) initiated with TB has been studied. It was established that OMC undergoes both homopolymerization and copolymerization during the UV irradiation of the composition. The effect of the temperature on the rate and conversion of epoxy groups for the photopolymerization of NPG alone and in the presence of OMC has been examined. It was established that 9-vinylcarbazole (VCz) acts as synergist of NPG photopolymerization as well of photopolymerization of the composition of NPG and OMC.

Synthesis and Properties of Triindole-Based Monomers and Polymers

New star-shaped derivatives of 10,15-dihydro-5H-diindolo[3,2-a:3′,2′-c]carbazole (triindole) with reactive functional groups are synthesized. Triindole monomers were found to have similar profiles of absorption and fluorescence spectra due to the presence of the same chromophore. The ionization potentials of the monomers are found to be comparable (5.37–5.53 eV). Hole drift mobilities of the amorphous layers of oxetane and vinyl ether molecularly dispersed in bisphenol Z polycarbonate (50%) exceed 10−5cm2/Vs at high electric fields. Cationic photocross-linking of triindole containing oxirane, oxetane and vinyl ether initiated with diphenyliodoniun tetrafluorborate is carried out.

Carbazole Derivative Based Near Ultraviolet Organic Light Emitting Diode with ZnMgO:Al Anode Layer

We demonstrate the fabrication and properties of an near ultraviolet organic light emitting diode (UV OLED) that contains 2,7-di(9-carbazolyl)-9-(2-ethylhexyl)carbazole organic emitting layer and aluminum-doped magnesium zinc oxide (ZnMgO:Al) layer as transparent electrode. The obtained ZnMgO:Al layer is transparent for the wavelengths longer than 325 nm and has low resistivity of the order of 10-3 Ωcm. The UV OLED device turns on at the applied voltage of 9 V.

Hole-Transporting Carbazole-Based Imines

Carbazole-based imines were synthesized by the reactions of 3-amino-9-ethylcarbazole with heteroaromatic aldehydes (3-formyl-9-ethylcarbazole or 3-formyl-10-(2-ethylhexyl)phenothiazine) or with 4,4′-bis(dimethylamino)benzophenone. The characterization of the derivatives synthesized by 1H NMR and IR spectroscopy as well as by MS spectrometry is presented. The electron photoemission spectra of thin layers of the materials were recorded and the ionization potentials of ca 5.3 eV were established. Hole drift mobilities in the layers of bisphenol Z polycarbonate containing 50% of the electro-active material reached 4 × 10−6 cm2/Vs at an electric field of 1.4 × 106 V/cm.

ZnMgO:Al Anode layer for organic light emitting diode based on carbazole derivative

We demonstrate the fabrication and properties of an near ultraviolet organic light emitting diode (UV OLED) that contains 2,7-di(9-carbazolyl)-9-(2-ethylhexyl)carbazole organic emitting layer and aluminumdoped magnesium zinc oxide (ZnMgO:Al) layer as transparent electrode. The obtained ZnMgO:Al layer is transparent for the wavelengths longer than 325 nm and has low resistivity of the order of 10−3 Ωcm. The UV OLED device turns on at the applied voltage of 9 V.