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Two new asymetric D–A–D′ type compounds containing benzophenone and diphenylsulfone as electron accepting core, and acridan and thianthrene as electron donating moieties were design as multifunctional materials. The influence of different acceptor and donor units on thermally activated delayed fluorescence and room temperature phosphorescence was investigated and discussed. The combination of different donors with benzophenone unit resulted in the compound with effective frontier orbital separation, as well as the sustainment of high radiative rate. These statements are both experimentally and theoretically supported using time-resolved photoluminescence spectroscopy and DFT calculations. Deoxygenation experiment revealed higher triplet exciton contribution in the emission of benzophenone derivative, as compared to that of diphenylsulfone-based compound. The films of molecular mixtures of these emitters with 1,3-bis(N-carbazolyl)benzene demonstrated temperature-dependent photoluminescence. The estimated energy gaps between the lowest singlet and triplet states were found to be 0.06 eV and 0.27 eV for benzophenone and diphenylsulfone derivatives, respectively. Due to the relatively high singlet-triplet energy splitting of the diphenylsulfone-based compound, triplet harvesting was detected not only via temperature-stimulated fluorescence but also via room temperature phosphorescence. Displaying effect of triplet harvesting on efficiency of all-organic blue and green OLEDs based on thianthrene and acridan-substituted benzophenone or diphenylsulfone derivatives demonstrated very different maximum external quantum efficiencies of 1.4 and 22.2% respectively.

New derivative acridan and isophthalonitrile (DAcIPN) was designed and synthesized as efficient TADF-type emitter with photoluminescence quantum yield of doped solid-state layer reaching 83%. Tuning of emission and efficiency of TADF emitter was performed by controlling the singlet-triplet energy splitting. Three important effects concerning the solid-state photophysics of TADF emitter was observed and analyzed, providing deep insight on the following new- or opposed-to-established results: (i) the TADF efficiency of DAcIPN in guest-host mixtures is insensitive to the host polarity; (ii) aggregation and (iii) annealing processes were found to respectively reduce and increase the dihedral angle between isophthalonitrile ring and acridan moiety, with strong impacts on the photoluminescence parameters. Thermal annealing of DAcIPN-based systems helps both the diffusion of DAcIPN molecules towards a better phase mixing (disaggregation), and the molecular geometry relaxation towards larger dihedral angles. Organic light-emitting diodes with smaller degree of aggregation of DAcIPN demonstrate outstanding lighting characteristics: brightness of 20700 (at 8 V) and 44900 (at 11 V) cd/m2, maximum current, power and external quantum efficiencies of 68 and 63 cd/A, 62 and 33 lm/W, 22.5 and 17.1%, for green and yellow devices respectively.

Four new derivatives of thianthrene and phenothiazine are reported as emitters for oxygen sensing. They exhibit both fluorescence and phosphorescence at room temperature. Effects of the substitution pattern of phenothiazine moiety on the thermal, electrochemical, emissive and oxygen sensing properties of the compounds are discussed. No phosphorescence at room-temperature was detected for deoxygenated solutions of the compounds. Room temperature phosphorescence of the different intensity was detected for the compounds being in crystalline or amorphous phase and for their dispersions in different polymeric matrices. Fast oxygen response (ca. 0.1 s) of room temperature phosphorescence was observed for only 1 wt.% of the dispersions in polymeric host. The highest oxygen sensitivity, was demonstrated for methylphenothiazinyl-disubstituted thianthrene dispersed in poly(methyl methacrylate). Stern-Volmer constant of 21·10−4 ppm−1 was obtained compared to those of 0.97·10−4, 1.22·10−4 and 2.1·10−4 ppm−1 observed for the dispersions of other compounds. Displaying possibility of oxygen detection by different chromaticity responses of emission of the developed compounds, strong yellowish-green emission with CIE1931 coordinate of (0.294, 0.503) was observed for one sample in the absence of oxygen; while, weak deep-blue emission with CIE1931 coordinate of (0.174, 0.141) was observed for the same sample in oxygen atmosphere.

New donor-acceptor and donor-acceptor-donor compounds based on perfluorobiphenyl electron acceptor and diphenylamine or carbazole as electron-donating units were designed, synthesized and characterized. The influence of the nature and number of electron-donating units on thermal, electrochemical and photophysical properties was studied. The compounds exhibited photoluminescence ranging from near-UV to green region. The solid samples of the compounds demonstrated photoluminescence quantum yields in the range from 0.1 to 0.51.2,7-Dimethoxycarbazole-containing compound was characterized by negligible energy gaps between the lowest singlet and triplet states (0.1 eV) and subsequently showed thermally activated delayed fluorescence (TADF). Carbazolyl-substituted perfluorobiphenyl derivatives showed aggregation-induced emission enhancement and high values of the energies of triplet levels (up to 3.08 eV). The derivatives exhibited from moderate to high temperatures of 5% weight loss up to 356 °C. Electron mobility up to 1.2 × 10−4 cm2 V−1 s−1 at electric field of 7 × 105 V/cm was detected for the studied compounds by time-of-flight measurements. One compound with the best combination of the required properties for the OLED hosts was selected for the fabrication of green TADF-based OLED. The device showed maximum external quantum efficiency of 15.1%. Another compound exhibiting efficient TADF demonstrated oxygen sensitivity with non-linear Stern-Volmer curve which was well fitted by two Stern-Volmer constants of 6.54·10−4 and 7.17·10−6 ppm−1.

The derivatives of carbazole and tetraphenylethylene exhibiting aggregation-induced emission and 4,4′,4′-tris[3-methylphenyl(phenyl)amino]triphenylamine were used for the preparation of organic light-emitting diodes the electroluminescence spectra of which include exciton and exciplex emissions. The low-energy exciplex emission of the electroluminescence spectrum was formed at the interface of the emissive layers. The best fabricated device showed turn-on voltage of 2.7 V for electroluminescence (at 10 cd/m 2 ); maximum current efficiency of 11.5 cd/A, maximum brightness of 17,700 cd/m 2 (at 11 V), and external quantum efficiency of ca. 3.9% with CIE 1931 chromaticity coordinates (0.20, 0.38).

Cationic polymerization of two styrene derivatives containing carbazole moiety with different linking topology, 9-(4-vinylphenyl)carbazole (M1) and 3-(4-vinylphenyl)-9-ethylcarbazole (M2), using 1-chloro-1-phenylethane (PhEtCl)/SnCl4 initiating system has been investigated. It was shown that polymerization of M1, which is characterized by higher electron density on the carbon at the 3 position of carbazolyl group than on vinyl group, proceeds predominantly via step-growth (SG) pathway through addition of protonated monomer/oligomers to 3-position of carbazolyl group (electrophilic aromatic substitution). On the contrary, M2, in which 3-position of carbazolyl group is protected via introduction of 4-vinylphenyl group, polymerized predominantly via chain-growth (CG) pathway through addition of carbocation to double bond of monomer. The polymers synthesized via SG mechanism showed different photophysical characteristics in comparison with corresponding monomer, while in case of polymers prepared via CG mechanism the polymer and monomer have the same absorption and fluorescence profiles.

New tri- or tetraphenylethylene-substituted phenylcarbazole derivatives exhibiting aggregation-induced emission were synthesized by the synthetic route including Pd-catalyzed Suzuki or Buchwald-Hartwig coupling and Heck reactions. The results of evaluation of the thermal, optical, electrochemical, photophysical, and charge-transporting properties of the synthesized derivatives are presented. The compounds possess high thermal stabilities with 5% weight loss temperatures exceeding 350 °C. Some of the synthesized compounds form glasses with glass transition temperature ranging from 77 to 114 °C. Their maximum fluorescence intensity wavelengths are in the range of 472–498 nm. The highest photoluminescence quantum yield of 43.9% was observed for the solid sample of 2-(4-(4-(1,2,2-triphenylvinyl)phenylethenyl)phenyl)-9-ethylcarbazole. The electron photoemission spectra of the films of the synthesized compounds revealed ionization potentials of 5.49–5.74 eV. Hole drift mobilities in the layers of 9-phenylcarbazole para-substituted with tri- or tetraphenylethylene moities reached 10−3 cm2 V−1 s−1 at moderate electric fields, as established by the time-of-flight technique.

New carbazole-based monomers with two reactive functional groups such as epoxypropyl, oxetanyl and vinyloxethyl were synthesized and their cationic photopolymerization was performed. The monomer containing epoxypropyl groups exhibited the highest conversion in photopolymerization (78%). The monomers and polymers exhibited ability of glass formation with the glass transition temperatures up to 98 °C for low-molecular-weight compounds and those observed for polymers ranging from 89 to 150 °C. The synthesized derivatives absorb electromagnetic irradiation in the range of 200–390 nm with the band gaps of 3.14–3.16 eV. The compounds exhibit blue photoluminescence with the intensity maxima at 400 nm. The compounds were found to have high triplet energies of ca. 2.78 eV. The electron photoemission spectra of the layers of the synthesized compounds revealed ionization potentials of 5.20–5.37 eV. The time-of-flight hole drift mobilities of the layers of the compounds exceed 10 − 5 cm 2 /V × s at high electric fields.

A series of twisted-structure carbazole–fluorene tetrads featuring 3,3′-bicarbazole core decorated with singly-bonded carbazole and fluorene end-linkers were synthesized and studied as potential host materials. The tetrads inferred high glass transition temperature (up to 105 °C) and good film-forming properties, which contributed in attaining large hole drift mobilities (up to 10−3 cm2/V/s) in the solution-processed amorphous films. The revealed high triplet energies (up to 2.9 eV) indicated their potential to be utilized as hosts in blue light-emitting devices. Greater sensitivity of the triplet energies to the linking position of peripheral moieties as compared to the sensitivity of the singlets imply new possibilities for the independent tuning of these energies in carbazole–fluorene tetrads.

The impact of linking topology of fluorene-carbazole triads on amplified and spontaneous emission as well as on concentration quenching of emission and charge carrier mobility, i.e. on the properties essential for organic laser application, was investigated. Deep-blue-emitting triads featuring 2,7- substitution pattern and bulky alkyl moieties expressed high emission quantum yield (0.8–0.9) and low concentration quenching, which benefited in attaining large radiative decay rates (∼109 s−1) and rather low amplified spontaneous emission (ASE) threshold (down to 9 kW/cm2) for compound concentrations up to 3 wt % in polymer matrix. Most of the triads expressed carrier drift mobilities close to 10−2 cm2/(V·s) in amorphous films pointing out efficient charge transport essential for reducing threshold current density for lasing. The impact of the position (central or side) of fluorene/carbazole moieties in the triad or the linking position (C-2 or C-3) of the side groups on the ASE threshold and carrier mobility was found to be of little significance. However, a huge advantage of 2,7- substitution pattern over 3,6- pattern for the triads in terms of ASE performance was demonstrated. Importantly, the obtained results suggested a possible trade-off between ASE threshold reduction and carrier mobility enhancement, which may hamper the realization of electrically-driven lasing in organic amorphous films.

The star-shaped compound tri(9-hexylcarbazol-3-yl) amine (THCA) and 4,7-diphenyl-1,10-phenanthroline (Bphen) were used for the preparation of bilayer and bulk exciplex based organic light emitting diodes (OLEDs) in which THCA and Bphen were selected as donor and acceptor components, respectively. The dependencies of the electroluminescence and impedance characteristics of the exciplex type OLEDs depending on the technologies of the formation of the active layers were studied. The correlations between the appearance of negative differential resistance in current–voltage characteristics and negative capacitance observed at low frequencies in impedance spectra of OLEDs with the resonant tunneling of electrons into THCA through Bphen/THCA barrier and generation–recombination processes in THCA were established.

In the field of materials for optoelectronic applications much attention is paid to the derivatives of triphenylamine and carbazole. We report on the electrochemical and spectroelectrochemical properties of two conductive polymers prepared by electropolymerization of two compounds containing either carbazole or triphenylamine moieties. Electrochemical, UV Vis- and EPR-spectroelectrochemical tools were used to study the properties of the polymers. The basic characteristics such as the band gaps, HOMO and LUMO values, absorption and emission maximum wavelengths of the monomers and the polymers are reported and discussed.

Two new carbazole-containing aromatic imides were synthesized by three-step synthetic pathway with the moderate yields up to 76%. The compounds were investigated theoretically. TD-DFT computational studies revealed low singlet-triplet energy differences. The compounds were found to have relatively high thermal stability with 5% mass loss temperatures in the range of 280–310 °C. Phthalimide-based compound exhibited aggregation-induced emission enhancement and thermally activated delayed fluorescence with photoluminescence quantum efficiency of 20% in the solid state. Structure-properties relationship of this compound was investigated and it was found that charge-transfer through space mechanism is responsible for the emission. Series of green-emitting doped and non-doped electroluminescent devices were fabricated based on the carbazole-phthalimide derivative were fabricated to reveal best-performing mCP-doped device demonstrating maximum external quantum efficiency of 2.4% with current efficiency of 6.6 cd/A and power efficiency of 4.0 lm/W with maximum brightness of 8300 cd/m2.

A three-terminal organic light-emitting device with a periodic interrupted middle electrode is developed to allow for an adjustable emission color. The emission results from three independent light-emitting diodes with one diode utilizing exciplex emission. An equivalent electrical circuit is suggested taking the current–voltage characteristics and the direction of current flow through the organic structure into account. Two diodes are formed between the embedded middle electrode and the LiF/Al top and ITO bottom electrode, respectively, and the third diode utilizes that part of the device without the middle-electrode exhibiting exciplex emission. It will be shown that the spectrum of the emitted light can be tuned from blue to orange by controlling the applied potentials to the device terminals.

Twin derivatives with two 9-alkylcarbazol-3-yl fragments were synthesized by the multi-step synthetic rout. The materials were characterized by differential scanning calorimetry and electron photoemission technique. Some of the electro-active derivatives were tested as solution processed hole transporting layers in organic light-emitting diodes with Alq(3) as the emitter. The electroluminescent devices exhibited promising overall performance with a maximal photometric efficiency of about 2.9 cd/A and maximum brightness of 6000 cd/m(2). (C) 2013 Elsevier B.V. All rights reserved.

Synthesis and properties of new dimethyldiphenylamino-substituted carbazoles are reported. A comparative experimental analysis of 2-, 2,7-substituted carbazole derivatives and 3-, 3,6-substituted analogues is performed. Disubstituted carbazole derivatives exhibit more than 2-fold higher glass transition temperatures (99–100 °C) as compared to the monosubstituted compounds (38–40 °C). Dilute solutions of the dimethyldiphenylamino-substituted carbazole compounds are found to emit in the blue region with the fluorescence quantum yield of up to 0.45. More symmetrical molecular geometry of the 2-, 2,7-substituted carbazole compounds favors closer molecular packing in the neat films thereby facilitating exciton migration and migration induced exciton quenching, which results in the significantly reduced excited state decay times (down to sub-nanoseconds) and fluorescence quantum yields (down to 0.04). The 2-, 2,7-substituted carbazole compounds are shown to demonstrate the superiority over 3-, 3,6-substituted compounds by giving rise to extended π-conjugation and expressing over one order of magnitude higher radiative decay rates. The synthesized compounds are electrochemically stable: their cyclic voltammograms show reversible oxidation behavior. The ionization energies of the synthesized compounds are in the range of 5.16–5.28 eV. Hole drift mobilities of the molecular mixtures of dimethyldiphenylamino-substituted carbazoles with bisphenol Z polycarbonate reach 10 −5 cm 2 V −1 s −1 at high electric fields.

The synthesis of a series of carbazole-based monomers incorporating dibenzazepines at the 3 position is reported. Full characterization of their structures is presented. The monomers were subjected to cationic polymerization using BF 3 ·O(C 2 H 5 ) 2 as an initiator. The synthesized low-molar-mass compounds and oligomers were examined by differential scanning calorimetry, UV spectrometry, electron photoemission and time of flight techniques. The electron photoemission spectra of the films of synthesized materials revealed the ionization potentials of 5.12–5.34 eV. Hole drift mobilities of low-molar-mass compounds molecularly dispersed in bisphenol Z polycarbonate range from 2.6 × 10 −8 to 1.7 × 10 −6 cm 2 /V s at high electric fields as it was established by xerographic time of flight technique.

The electroluminescent device ITO/CuI/3,6-di(9-carbazolyl)-9-(2-ethylhexyl)carbazole(TCz1)/Ca/Al in which TCz1 for the first time was used as the emitting layer, was fabricated by means of vacuum deposition. The device emits blue light with a peaks at 388 and 406 nm at 4.5 V, with high current efficiency values (11.5 cd/A) and external quantum efficiency (1.72%).