Ramunas Lygaitis

Hole-Transporting Glass-Forming 3,3′-Dicarbazyl-Based Hydrazones

ABSTRACT 3,3′-Di(9-(4-butylphenyl)carbazyl) and 3,3′-di(9-ethylcarbazyl)-based hydrazones were synthesized by the multi-step synthetic route including oxidative dimerization of 9-(4-butylphenyl)carbazole and 9-ethylcarbazole, formylation of the dimmers obtained and the reactions of the formyl derivatives with different hydrazines. The chemical structure of the compounds was confirmed by 1HNMR, IR and mass spectroscopy. The hydrazones synthesized form stable glasses with the glass transition temperatures exceeding 140°C. The values of ionisation potentials measured by electron photoemission technique are in the range of 5,21–5,4 eV. The hole drift mobilities in the films of the 50% solid solutions of the hydrazones in bisphenol Z polycarbonate established by the xerographic time-of-flight technique exceed 10−5 cm2/Vs at high electric fields.

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.

9-Phenylcarbazole–Based Hydrazone Twin Compounds as P-Type Organic Semiconductors

Hole transporting glass-forming low-molar-mass hydrazones containing 9-phenylcarbazole moiety were synthesized and characterized by NMR-, infrared- and mass spectrometries. The thermal, optical and photoelectrical properties of the synthesized compounds are reported. Compounds containing 1,3-benzendithiol linking bridge were isolated as amorphous materials therefore differential scanning calorimetry experiments revealed glass transitions approximately at 60°C. The ionization potentials of the synthesized compounds were measured by electron photoemission technique in air range from 5.23 eV to 5.4 eV. Hole drift mobilities in the films of the solid solutions of some of the synthesized hydrazones in bisphenol Z polycarbonate measured by the time-of-flight technique exceed 10−5 cm2 V−1 s−1 at high electric fields.

9-(4-Methoxyphenyl) Carbazolyl-Containing Hydrazones for Optoelectronic Applications

ABSTRACT 9-(4-methoxyphenyl)carbazolyl-containing hydrazones were prepared by multi-step synthetic route including Ullmann coupling of carbazole with 4-iodoanisole, formylation of 9-(4-methoxyphenyl)carbazole by Vilsmeier reaction and the condensation of mono- or dicarbaldehydes obtainexd with differently substituted hydrazines. All the hydrazones synthesized form glasses with the glass transition temperatures ranging from 56 to 110°C. Their ionization potentials established by electron photoemission technique are in the range 5.3–5.47 eV. Hole drift mobilities of 50% solid solutions of the hydrazones in polycarbonate established by the xerographic time-of-flight technique exceed 10−5 cm2/Vs at high electric fields.

Polyethers containing 3,6-diarylcarbazolyl groups as polymeric materials for hole transporting layers of OLEDs

Several polyethers containing pendent 3,6-diarylcarbazolyl moieties have been synthesized by the multi-step synthetic routes. Full characterization of their structures is presented. The polymers represent materials of high thermal stability with initial thermal degradation temperatures exceeding 419 °C. The glass transition temperatures of the amorphous materials were in the range of 66–108 °C. The electron photoemission spectra of thin layers of the polymers showed ionization potentials in the range of 5.47–5.69 eV. Hole transporting properties of the polymeric materials were tested in the structures of organic light emitting diodes with Alq3 as the green emitter. The device containing hole transporting layers of the polymer with 3,6-di(4-biphenyl)carbazolyl moieties exhibited the best overall performance with a maximum photometric efficiency of about 2.3 cd/A and maximum brightness exceeding 2630 cd/m2.

Formation and Electrical Properties of Metal/Organic Semiconductor/Si Heterostructures Based on Naphthalene Diimide-Based Compounds

We report on the synthesis of two naphthalene diimide-based organic derivatives: POANT containing electronically isolated 1,4,5,8-naphthalenetetracarboxylic diimide units and FCAND – a low-molar-mass compound with two different (fluorenone and 1,4,5,8-naphthalenetetracarboxylic diimide) electron-accepting units. Initial decomposition temperatures of 305°C and 390°C were indicated for FCAND and POANT, respectively. Organic semiconductor/Si heterostructures have been prepared by using spin coating (POANT, PEPK) and thermal evaporation in vacuum (FCAND). All heterojunctions demonstrated nonlinear I-U dependences and defined rectifying properties. The Schottky thermoionic emission model has been applied to explain the carrier transport and to estimate the barrier height and the ideality factor n of heterojunctions.

Intramolecular charge transfer in bipolar molecules for electron and hole transporting materials

The excited state relaxation of 6-(9H-carbazole)hexyl-9,10,10-trioxo-9H-3-thioxanthenecarboxyl (CHTT) molecules containing electron donating and electron accepting groups was investigated in solutions by means of picosecond pump–probe absorption spectroscopy. The excitation energy and charge transfer between electrondonating and electronaccepting molecule fragments takes place under molecular excitation and determine the excited state relaxation dynamics.

Synthesis and properties of glass-forming 2-substituted perimidines

ABSTRACT 2-Substituted perimidine derivatives were synthesized by condensation of 1,8-diaminonaphthalene and the different formyl derivatives. Alkylation of the intermediate compounds was performed using microwave irradiation using potassium and cesium carbonate as a base. The synthesized compounds were characterised by UV and luminescence spectroscopies, cyclic voltammetry, thermogravimetry, differential scanning calorimetry. They exhibit relatively high thermal stability with the temperatures of the onset of thermal degradation ranging from 230 to 392°C. Most of the synthesized perimidines are capabale to form glasses with glass transition temperatures up to 197°C. The alkyl group attached to the perimidinyl moiety influences the conformation of the molecules and consequently the absorption and emission spectra. The values of ionization potential of the layers of the synthesized derivatives range from 5.26 to 5.52 eV.

Electroactive Twin Compounds Containing Trioxothioxanthene Electron Accepting Moieties

Three dimeric molecules based on trioxothioxanthene and benzotriazole moieties were synthesized by alkylation and esterification reactions. The chemical structures of the compounds were confirmed by 1HNMR, IR spectroscopies and mass spectrometry. Dilute solutions of trioxothioxanthene and benzotriazole-based compounds in THF absorb electromagnetic radiation in the region of 230–320 nm. 1,10-Bis-(9,10,10-trioxothioxanthen-3-yl-carboxy)decane can be transformed into the glassy state with the glass transition temperature of 35°C. It is capable of transporting negative charges. Electron drift mobility in the layers of trioxothioxanthene-based twin compound molecularly dispersed in PC-Z approaches 10−6 cm2/Vs at an electric field of 1 × 106 V/cm.