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The synthesis and optoelectronic properties of four simple-structure thioxanthone derivatives employing thioxanthone as an acceptor unit, coupled with moieties having very different electron-donating abilities such as phenoxazine, 3,6-di-tert-butylcarbazole, 3,7-di-tert-butylphenothiazine, or 2,7-di-tert-butyl-9,9-dimethylacridane, are reported. The compounds form molecular glasses with glass transition temperatures reaching 116 °C. Ionization potentials of the compounds estimated by photoelectron emission method range from 5.42 to 5.74 eV. Thioxanthone derivatives containing 3,6-tert-butylcarbazole or 2,7-di-tert-butyl-9,9-dimethylacridane moieties with weak electron-donating strengths were characterized by bipolar charge transport with relatively close hole and electron mobility values of 6.8 × 10-5/2.4 × 10-5 and 3.1 × 10-5/4.6 × 10-6 cm2/(V s) recorded at 3.6 × 105 V/cm. The other compounds demonstrated hole-transporting properties. The films of thioxanthones containing phenoxazine or 2,7-di-tert-butyl-9,9-dimethylacridane moieties showed efficient thermally activated delayed fluorescence with a photoluminescence quantum yield of up to 50% due to the solid-state luminescence enhancement. Organic-light-emitting diodes containing the synthesized compounds as emitters showed very different external quantum efficiencies (0.9-10.3%) and blue, sky blue, green, or yellow electroluminescence colors, thus reflecting the effects of donor substituents.

White vertical organic permeable-base light-emitting transistors based on a newly developed blue emitter 4,6-bis(4-(9H-carbazol-9-yl)phenyl)pyrimidine-5-carbonitrile with orange exciplex forming ability is developed.

Aiming to design bipolar red TADF emitters with high electron mobility, D–A compounds were synthesized with 1,8-naphthalimide as an acceptor and phenoxazine, 3,7-di-tert-butylphenothiazine or 2,7-di-tert-butyldimethyl-9,10-dihydroacridine as donors.

Here, we report on three new triphenylamine-based enamines synthesized by condensation of an appropriate primary amine with 2,2-diphenylacetaldehyde and characterized by experimental techniques and density functional theory (DFT) computations. Experimental results allow highlighting attractive properties including solid-state ionization potential in the range of 5.33-5.69 eV in solid-state and hole mobilities exceeding 10(-3) cm(2)/V.s, which are higher than those in spiro-OMeTAD at the same electric fields. DFT-based analysis points to the presence of several conformers close in energy at room temperature. The newly synthesized hole-transporting materials (HTMs) were used in perovskite solar cells and exhibited performances comparable to that of spiro-OMeTAD. The device containing one newly synthesized hole-transporting enamine was characterized by a power conversion efficiency of 18.4%. Our analysis indicates that the perovskite-HTM interface dominates the properties of perovskite solar cells. PL measurements indicate smaller efficiency for perovskite-to-new HTM hole transfer as compared to spiro-OMeTAD. Nevertheless, the comparable power conversion efficiencies and simple synthesis of the new compounds make them attractive candidates for utilization in perovskite solar cells.

Fused chalcogenophenocarbazoles bearing a trimethylsilylpropyl substituent at the nitrogen atom of carbazole were synthesized starting with 2,7-dibromocarbazole by subsequent alkylation, iodination at positions 3 and 6, Sonogashira coupling and, finally, creation of thiophene and selenophene rings. Depending on the heteroatom and its charge, the compounds were characterized by fluorescence resulting from recombination of either locally excited, intramolecular charge-transfer or hybridized local and charge-transfer (HLCT) states. This is the first report on dual emission of HLCT character observed for chalcogenophenocarbazoles.

Two new analogues of a popular host material, meta-bis(N-carbazolyl)phenylene (mCP), bearing either methoxy- (mCP-OMe) or tert-butyl (mCP-t-Bu) substituents at C-3 and C-6 positions of carbazole moieties were synthesized and characterized. These materials exhibit higher glass-transition temperatures (79 and 145 °C) than mCP (67 °C). They show reversibility upon electrochemical oxidation while preserving high enough triplet energy levels (2.86 and 2.97 eV). The vacuum-deposited layer of mCP-t-Bu showed hole mobility of 8 × 10−3 cm2V−1s−1 at the electric field of 1.2 × 105 Vcm−1. This value is more than by one order of magnitude higher than that of mCP. The new compounds were tested as hosts for commercial emitters: blue phosphor, bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III) (FIrpic), green and blue thermally-activated delayed fluorescence (TADF) emitters 1,2,3,5-tetrakis(9-carbazolyl)-4,6-dicyanobenzene (4CzIPN) and bis[4-(9,9-dimethyl-9,10-dihydroacridin-10-yl)phenyl]sulfone (DMAC-DPS). Blue phosphorescent OLED based on mCP-t-Bu as the host showed up to 22.0% external quantum efficiency. When doping 4CzIPN into mCP-OMe host, a broad emission with peaks at 388, 514, and 572 nm was observed.

New efficient carbazole-based emitters containing tetra-/triphenylethene units were developed for boosting efficiency of non-doped fluorescent organic light-emitting diodes. Comparable study of the properties of derivatives containing one or two tetra-/triphenylethenyl units was performed using various experimental and theoretical techniques. Depending on the substitution pattern, emitters exhibited strong blue or green emission, which was enhanced by aggregation. Compounds with two substituents showed higher glass transition temperatures (up to 120 °C) and lower ionization potentials (of ca. 5.15 eV) comparing to mono substituted derivatives. Time-of-flight hole drift mobility values of the studied compounds with two substituents reached 10−3 cm2/V at high electric fields. Non-doped fluorescent OLEDs based on carbazole derivative containing two tetraphenylethenyl units demonstrated extremely high external quantum efficiency as for simple fluorescent organic light-emitting devices, which reached 5.32%.

Naphthyl substituted triphenylamine and its derivatives with bromine atoms were synthesized and investigated. The respective glass transition temperatures of the materials were estimated to be in a range 65–137 °C, which can provide morphologically-stable amorphous films for applications in organic light emitting diodes. The compounds possess adequate ionization potentials (5.5–5.75 eV), high hole drift mobilities (>10−3 cm2/V·s) and suitable triplet energies (∼2.4 eV), which make them suitable hole transporting materials for use in red phosphorescent organic light-emitting diodes. A superior peak efficiency of 17.9% (31.4 cd/A and 26.9 lm/W) was achieved in a device having hole transporting layer of tris[4-(1-naphthyl)phenyl]amine. Furthermore, the device gave efficiencies of 17.7% and 16.6% recorded at luminance levels of 102 and 103 cd/m2. The efficiency drop from the maximum to the value recorded at the luminance of 103 cd/m2 for the device was only 7%.

Two electroactive compounds, bearing 2,3-dimethylindole donor moiety and tetrafluorostyrene acceptor moiety, were designed and synthesized by employing one-step nucleophilic aromatic substitution r...

Two derivatives of tetrafluorophenylcarbazole and tri/tetraphenylethylene displaying aggregation-induced emission enhancement were synthesized and investigated by theoretical and experimental tools. The synthesized compounds exhibit efficient emission in solid state with fluorescence intensity maxima at 511 and 502 nm and photoluminescence quantum yields of 57 and 27%. They exhibit high thermal stability with 5% weight loss temperatures of 362 and 314 °C and glass-forming properties with glass-transition temperatures of 112 and 80 °C. Ionization potentials measured by photoelectron emission spectrometry were found to be comparable (5.83 and 5.87 eV). The layers of the compounds showed bipolar charge-transporting properties with balanced electron and hole mobilities reaching 10–3 cm2/V s at high electric fields. Exciplex-host-based OLEDs containing one or two emitting layers of tetraphenylethenyl-containing emitter were fabricated and showed more than 50% higher external quantum efficiency as compared to t...

Two compounds, bearing benzophenone unit as an acceptor core, tetrahydrocarbazole, and 2-phenylindole donor moieties, were designed and synthesized by employing one-step nucleophilic aromatic substitution reaction. Their photophysical properties, based on theoretical calculations and experimental measurements, as well as electrochemical and photoelectrical properties are discussed. These compounds feature aggregation induced enhanced emission characteristic and high triplet energy values exceeding 2.8 eV.

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.

Derivatives of indolo[3,2-b]carbazole containing differently substituted triphenyl ethenyl moieties were synthesized and characterized as multifunctional materials for optoelectronic devices. A structure-properties relationship of the compounds was studied. Alteration of the substituents of triphenyl ethenyl moiety (H-, Ph-, CN-) afforded to modify thermal, photophysical and charge-transporting properties of the compounds. The synthesized compounds demonstrated high thermal stability with the 5% weight loss temperatures reaching 453 °C. Indolo[3,2-b]carbazoles mono- and disubstituted with tetraphenyl ethenyl groups exhibited polymorphism with two melting peaks at 211/216 °C and 236/245 °C, respectively. Modification of the substitution pattern resulted in the changes of emission of the solid films from blue centered at 471 nm to yellow peaking at 583 nm. Addition of the tetraphenylethylene and triphenyl acrylonitrile fragments resulted in aggregation induced emission (AIE) or aggregation enhanced emission (AEE). The solutions of AIE/AEE-active compounds exhibited low photoluminescence quantum yields which did not reach 1%, while the solid films demonstrated the highly boosted values of 23–35%. Hole mobilities of ca. 10−3 cm2/V × s were observed for tri(tetra)phenyl ethenyl substituted indolo[3,2-b]carbazoles compounds. The compounds containing acrylonitrile moieties exhibited bipolar charge transport with drift mobilities of ca. 10−5 cm2/V × s. The synthesized compounds showed promising electroluminescent properties as fluorescent emitters. OLEDs containing these emitters showed maximum external fluorescent quantum efficiency up to 3.0% and maximum brightness up to 18 800 cd/m2. They also demonstrated lasing properties. Using the most promising compound dissolved in cholesteric liquid crystal, laser beam at 515 nm with full width at half maximum of ca. 3.5 nm was generated.

Atom-transfer radical polymerization of 9-(4-vinylphenyl)carbazole (M1) and 9-(2,3,5,6-tetrafluoro-4-vinylphenyl)carbazole (M2) has been investigated using CuCl/N,N,N′,N′′,N′′-pentamethyldiethylenetriamine as catalyst and ethyl 2-bromoisobutyrate as an initiator. The polymerization of the monomers proceeded in a living fashion affording polymers with controlled molecular weight (Mn = 5000 g mol−1 to 32000 g mol−1) and relatively low polydispersity (Đ = 1.2–1.5). The kinetic investigations showed that M2 polymerized at the faster rate as compared to M1. Block copolymers were successfully prepared starting from the polymerization of more reactive M2 followed by addition of M1. The same initiating system also induced living radical copolymerization of these monomers giving random copolymers. Usage of tetrafunctional initiator pentaerythritol tetrakis(2-bromoisobutyrate) in conjunction with CuCl/N,N,N′,N′′,N′′-pentamethyldiethylenetriamine as catalyst allowed to synthesize star-shaped linear and random copolymers from M1 and M2 with controlled molecular weight (up to Mn = 25000 g mol−1) and low polydispersity (Đ

Aiming to design blue fluorescent emitters with high photoluminescence quantum yields in solid-state, nitrogen-containing heteroaromatic 9,9-dimethylacridine was refined by tetraphenylethene and triphenylethene. Six tetra-/triphenylethene-substituted 9,9-dimethylacridines were synthesized by the Buchwald-Hartwig method with relatively high yields. Showing effects of substitution patterns, all emitters demonstrated high fluorescence quantum yields of 26&ndash, 53% in non-doped films and 52&ndash, 88% in doped films due to the aggregation induced/enhanced emission (AIE/AIEE) phenomena. In solid-state, the emitters emitted blue (451&ndash, 481 nm) without doping and deep-blue (438&ndash, 445 nm) with doping while greenish-yellow emission was detected for two compounds with additionally attached cyano-groups. The ionization potentials of the derivatives were found to be in the relatively wide range of 5.43&ndash, 5.81 eV since cyano-groups were used in their design. Possible applications of the emitters were demonstrated in non-doped and doped organic light-emitting diodes with up to 2.3 % external quantum efficiencies for simple fluorescent devices. In the best case, deep-blue electroluminescence with chromaticity coordinates of (0.16, 0.10) was close to blue color standard (0.14, 0.08) of the National Television System Committee.

© Elsevier. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/ In the domain of organic photovoltaic (OPV) devices, the design of new materials faces the extraordinary challenge to satisfy two opposite requirements: the new materials should exhibit weak intermolecular interactions at the donor-acceptor interface, but strong intermolecular interactions and good charge transport properties in the bulk. In an effort to progress in this direction, here we present three new diphenylethenyl substituted derivatives of methylene-bridged triphenylamine, synthesized by condensation of dimethylmethylene-bridged triphenylamines with 2,2-diphenylacetaldehyde. The synthesized compounds were found to be capable of glass formation with glass transition temperatures in the range of 65–130¿°C. The ionization potentials of these derivatives were found to be in the range of 5.29–5.68¿eV. The time-of-flight hole drift mobilities measured at room temperature well exceeded 10-2¿cm [2]/Vs for all the synthesized compounds. By combining the compounds with fullerene C70 acceptor in bilayer organic solar cells, a power conversion efficiency of 1.9% was obtained. Density functional methods-based calculations indicate that this result can be explained by considering edge-on orientations at the donor-acceptor interface. In this case, the designed architecture of the compounds has an effect to sufficiently “hide” the donor HOMO from a direct and easy contact with C70 LUMO(s), thus maintaining low level of geminate donor-acceptor charge recombination, without losing hole-transport properties in the donor bulk. These two design strategies operate consequently in different parts of the molecules, which is central to the success of the new compounds. Our study shows consequently a possible strategy for a simultaneous improvement of both interfacial- and bulk properties of molecules for OPV applications.

The synthesis of new iridium(III) complexes containing a 2-(benzo[b]selenophen-2-yl)pyridine ligand is reported along with their photophysical, thermal, electrochemical and electroluminescent properties. These complexes are characterized by deep red phosphorescence with photoluminescence quantum yields exceeding 31% in the solid state. Solid layers of the complexes were characterized by ionization potentials of 5.17–5.27 eV and electron affinities of 2.87–2.95 eV. Their thermal and electrochemical stabilities were proved by cyclic voltammetry and thermogravimetric analysis. Deep red selenium-based iridium phosphorescent emitters were used in red electroluminescent devices which were characterized by a deep red color with Commission Internationale de l’Eclairage (CIE 1931) chromaticity coordinates (x, y) of (0.69, 0.31). This color is deeper than that defined by the red color standard (0.67, 0.33) of the National Television System Committee (NTSC) or CIE 1931 of (0.68, 0.32) of the widely known red phospho...

Electron withdrawing groups F or CF3 were attached to 6-methyl-4-diphenylquinoline (medpq) ligand. The effect of this substitution on photophysical and electroluminescent properties of four phosphorescent iridium(III) complexes containing the two upgraded medpq ligands and 2-(2-pyridyl) benzimidazole or 2-(1H-tetrazol-5-yl) pyridine ligand was comparatively investigated. All complexes emitted strong phosphorescence with absolute quantum efficiency of deoxygenated toluene solutions higher than 50% and the lifetime of 1.068–1.88 microseconds observed for neat films at 77 K. The orange phosphorescence of CF3-substituted complexes was slight shifted to higher energy region in comparison to that of the corresponding F-containing complexes. The ionization potentials detected by photoelectron emission spectroscopy for solid-state samples of the complexes were practically the same (5.91–6.04 eV). Exploiting the same device structure, phosphorescent organic light-emitting diodes (PhOLEDs) containing a CF3-substituted complex exhibited maximum external quantum efficiency of 10.33% in contrast to 5.36% observed for PhOLEDs based on a F-containing complex.

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.

A series of new indolyl-substituted carbazole derivatives were synthesized and their properties were studied. All the final compounds form molecular glasses. They absorb electromagnetic radiation i...

Three new bipolar star-shaped derivatives of 2,4,6-triphenyl-1,3,5-triazine containing carbazolyl groups were designed, synthesized and characterized. All the materials possess high thermal stability and high glass transition temperatures ranging 97–226 °C. Photophysical study of the dilute solutions and neat films of the synthesized compounds was performed. Lippert–Mataga plots revealed linear dependence of Stokes shifts on the orientation polarizability for all the compounds. The dilute solutions of the triazine derivatives exhibited high photoluminescence quantum yields reaching 0.85, while for the neat films photoluminescence efficiency of 0.20–0.33 was observed. Ionization potentials of the solid layers of carbazole-triazine adducts estimated by photoelectron spectroscopy were found to be in the range of 5.49–5.97 eV. Hole drift mobility of the materials well exceeded the magnitude of 10−3 cm2 V−1 s−1 at an electric field of 6.4 · 105 V/cm. The selected compounds were tested as light emitting materials in organic light emitting diodes based on host-guest systems.

New triphenylethylene-based derivatives, containing 2,6-di-tert-butylcarbazole or 9,9-dimethyl-9,10-dihydroacridine as donor moieties and phenylene or tetrafluorophenylene linking bridges were synthesised by Heck coupling and characterized. The synthesized compounds emitted blue light in the solid state with emission maxima in the range of 478–487 nm and photoluminescence quantum yields of 16–29%. In thermogravimetric analysis they demonstrated sublimation with 5% weight loss temperatures in the range of 307–355 °C. They exhibited glass-forming properties with glass-transition temperatures of 89–123 °C. The solid-state ionization potentials and electrochemical band gaps ranged from 5.88 to 6.37 eV and from 3.30 to 3.57 eV, respectively. Three compounds demonstrated bipolar semiconducting properties. Derivative of triphenylethylene and 2,6-di-tert-butylcarbazole with phenylene bridge showed highest hole and electron drift mobilities reaching 3.07 × 10−3 cm2/Vs and 4.2 × 10−3 cm2/Vs respectively at high electric field. Utilizing compounds in organic light‐emitting diodes as emitters external quantum efficiency of 2% was observed.

Two 3,3‘-bicarbazole derivatives, with triphenylsilyl and toluenesulfonyl moieties attached to 9,9‘-positions were synthesized and their properties were studied. The compounds exhibited high triplet energies of 2.9 eV which made them useful for efficient triplet exciton harvesting. The compound containing triphenylsilyl moieties was found to have bipolar charge-transporting properties which makes it a good candidate for employment as a host in phosphorescent organic light emitting diodes. A series of green and red devices with the newly synthesized host and phosphorescent emitters were fabricated and the performance of the hist was compared with that of 1,3-bis(N-carbazolyl)benzene (mCP). Triphenylsilyl-substituted 3,3‘-bicarbazole was found to be competitive host with the widely used host mCP. Green and red phosphorescent organic light emitting diodes containing this host showed maximum external quantum efficiencies of 13.8 and 7.7%, respectively.

The anionic ring-opening polymerization of carbazole-containing monomers, (9-carbazolylmethyl)thiirane (M1) and (3,6-di-tert-butyl-9-carbazolylmethyl)thiirane (M2), with hexanethiol or pentaerythritol tetrakis(3-mercaptopropionate) (PETMP) as initiators and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as catalyst at 20 °C in tetrahydrofuran or N,N-dimethylformamide as solvents has been studied. The polymerization of these monomers proceeds in a living fashion affording linear and star-shaped polymers with controlled molecular weight (Mn = 4000–15,000 g mol−1) and relatively low polydispersity (Đ

This paper primarily deals with the development of highly efficient phosphorescent iridium (III) complex based on benzoimidazophenanthridine as main ligand. The potential of this complex, as phosphorescent emitter for optoelectronic applications, was screened by different methods, including luminescence spectrometry, cyclic voltammetry, thermogravimetric analysis, differential scanning calorimetry as well as photoelectron emission spectrometry. The possible application of the developed complex in single-colour vacuum-deposited organic light emitting diodes (OLEDs) exhibiting warm orange electrophosphorescence was demonstrated. The device was characterized with CIE1931 colour coordinates of (0.539, 0.459), colour temperature of 2088 K and maximum external quantum efficiency of 17.5%. Good performance in OLEDs can be partly explained by efficient orange phosphorescence with quantum yield of 60% at room temperature. This paper also deals with the development of white hybrid solution-processable organic light-emitting devices, exploiting ultralow concentration of newly synthesized iridium (III) complex as phosphorescent dopant in combination with blue fluorescencent emitter(host), and green emitter exhibiting thermally activated delayed fluorescence emitter. It was designed and fabricated by spin coating white hybrid devices, and was characterized by high quality (human-eyes-friendly) electroluminescence achieving CIE1931 coordinates of (0.335, 0.392), colour temperature of 2910 K and colour rendering index of 72 as well as high maximum external quantum efficiency of 8.7%.

With the aim of developing all-organic bipolar semiconductors with high charge mobility and efficient E-type fluorescence (so-called TADF) as environmentally friendly light-emitting materials for optoelectronic applications, four noble metals-free dyes with linear and V-shapes were designed using accepting pyridine-3,5-dicarbonitrile and donating carbazole units. By exploiting a donor-acceptor design strategy and using moieties with different donating and accepting abilities, TADF emitters with a wide variety of molecular weights were synthesized to achieve the optimum combination of charge-transporting and fluorescent properties in one TADF molecule. Depending on molecule structures, different TADF emitters capable of emitting in the range from 453 to 550 nm with photoluminescence quantum yields up to 98 % for the solutions in oxygen-free toluene were obtained. All compounds showed bipolar charge-transport. Hole mobility of 2.8×10-3 cm2 /Vs at 7×105 V cm-1 was observed for the compound containing two di-tert-butyl-substituted carbazole moieties. The compounds were tested in both non-doped and doped organic light-emitting diodes using different hosts. It was shown that the developed TADF emitters are suitable for different color devices with electroluminescence ranging from blue to yellow and with brightness, maximum current and external quantum efficiencies exceeding 10 000 cd m-2 , 15 cd/A, and 7 %, respectively.

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.

Materials based on triphenylamino core linked with different alkoxyphenyl-substituents through olefinic spacers were synthesised, and their thermal, photophysical and photoelectrical properties were investigated. The synthesized compounds showed relatively good thermal stability. Derivatives containing shorter alkyl chains displayed glass-forming ability, while the compounds containing flexible alkyl termini demonstrated liquid-crystalline behaviour. Flexible alkyl substituents at the periphery of triphenylamine derivatives prevented the close packing of chromophores and hence, they showed relatively similar absorption and fluorescence in thin-films and solutions. Reduction in fluorescence quantum yield in thin-films upon decreasing the size of peripheral alkyl substituents confirmed enhanced intermolecular interactions and in turn, suggested migration-induced exciton quenching at nonradiative decay sites. Ionization potentials of thin solid layers estimated by photoelectron emission spectroscopy ranged from 5.21 to 5.47 eV. Hole-drift mobility of ethyl substituted triphenylamine measured using xerographic time-of-flight (XTOF) method was 1.3 × 10−3 cm2 V−1 s−1 at an electric field of 106 Vcm−1.

Three star-shaped molecules, having 2,4,6-triphenyl-1,3,5-triazine core and fluorene side arms linked through different linkages, were designed and synthesized. The obtained compounds were characterized by UV and fluorescence spectroscopies, differential scanning calorimetry, thermogravimetric analysis, cyclic voltammetry, time-of-flight and CELIV techniques. All the three star-shaped compounds possess high thermal stability with the temperatures of the onsets of thermal degradation around 400 °C and glass formation ability with close glass transition temperatures (56–61 °C). The synthesized compounds show broadband absorption with the absorption maxima of dilute solutions in the range of 350–382 nm. Dilute solutions of the fluorenyl-substituted derivatives of 2,4,6-triphenyl-1,3,5-triazine showed monomer fluorescence with fluorescence quantum yields ranging from 0.50 to 0.70. The theoretical DFT calculations showed that the geometry, optical and electrochemical properties of the synthesized star-shaped molecules depend on their linking topologies. Thus, completely flat star-shaped molecules, in which the donor and acceptor moieties are linked through the linking bridges having double and triple bonds, are characterized by smaller optical band gap and bathochromic shift compared to the derivative with twisted skeleton in which the chromophores are linked directly via single bond. The best charge-transporting properties were shown by the compound in which 2,4,6-triphenyl-1,3,5-triazine and 2-[9,9-bis(2-ethylhexyl)-9 H -fluorene] moieties are linked via the linking bridges containing ethenyl linkages. Hole mobility of the amorphous layer of this compound reached 1.9 × 10 −3 cm/V s at an electric field of 1.15 × 10 6 V/cm.

The synthesis of indolo[3,2- b ]carbazole-based mono- and dihydrazones with reactive vinylbenzyl or vinyloxyethyl functional groups at the nitrogen atom of hydrazine moiety is reported. The thermal, optical, photophysical, electrochemical and photoelectrical properties of the synthesized compounds are described. They exhibit moderate thermal stability with 5% weight loss temperatures ranging from 273 to 343 °C. Self-polymerization of the monomers with vinylbenzyl functional groups starts at around 180 °C. The values of ionization potentials of the compounds measured by cyclic voltammetry are in the range of 4.94–5.00 eV and those estimated by electron photoemission in air range from 4.99 to 5.21 eV. Electron affinities range from −2.28 to −2.23 eV. The molecular structure of these hydrazones allows stable amorphous films to be prepared and the hole drift mobilities of the films exceed 10 −3 cm 2 /V s at high electric fields.

The starburst carbazole derivative and phosphorescent bis-cyclometalated iridium(III) complex (IC2) were used for the preparation of multilayered “warm-white” organic light-emitting diodes (OLEDs), the emission spectra of which are modulated by the thickness of the phosphorescent layer. It was shown that the electroluminescence spectra of the fabricated devices are more extended into the visible region compared with the photoluminescence spectra of both component materials. The observed extension of the electroluminescence spectra can be assigned to the phosphorescent emission of the low-energy exciplex formed at the interface of the emissive layers. The quantum-chemical calculations performed by the DFT and (TD) DFT methods support the formation of the low-energy triplet exciplex at the interface of the IC2 layer and the neighboring layer of the starshaped carbazole-based compound, (4,4′,4″-tris[3-methylphenyl(phenyl)amino] triphenylamine, tri(9-hexylcarbazol-3-yl)amine (THCA). Indeed, the triplet excite...

A new series of monomers consisting of electron-deficient tetrafluorobenzene fragment and electron-donating units such as carbazole, di-tert-butyl carbazole, 9,9-dimethyl acridan and phenothiazine was prepared. Polymers containing well-defined donor-acceptor side chains were obtained via classical free radical polymerization of previously synthesized monomers. Comparative study of photophysical, electrochemical and thermal properties of the synthesized compounds was carried out. It was shown, that emission colour of the compounds from violet to yellow can be effectively adjusted by manipulation of the connected electron-donating fragments. The energy gaps of the compounds can also be fine-tuned by changing the moieties linked to the para-position of pentafluorostyrene moiety. Experimental optical energy gap values varied from 3.57 eV and 3.62 eV for carbazole based monomer and polymer to 2.99 eV and 3.24 for phenothiazine based monomer and polymer. Band gap values of polymers were found to be close to those of the corresponding monomers. The monomers demonstrated violet to yellow fluorescence in the solid state with quantum yields ranging from 1 to 22%. The solid films of polymers demonstrated blue to greenish fluorescence in the region of 456–512 nm with fluorescence quantum yields varying from 1 to 9 %. Monomers exhibited aggregation induced emission enhancement. Pholuminescence quantum yields of their solid samples were found to be higher than those of dilute solutions. Polymers exhibited higher thermal stability, in respect to the corresponding monomers, with 5% weigh loss temperatures reaching 411 °C.

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.

Naphthalimide-substituted derivatives of fluorene were synthesized by Suzuki–Miyaura coupling reactions. Most of the synthesized materials were found to constitute glasses with glass transition temperatures ranging from 30 to 76 °C as characterized by differential scanning calorimetry. Their initial weight loss temperatures range from 315 to 466 °C. Dilute solutions of the naphthalimide-substituted derivatives of fluorene in nonpolar solvents were found to emit in the blue region with high quantum yield ranging from 0.47 to 0.69, while in the solid state fluorescence quantum yields were found to be in the range of 0.06–0.25. Fluorenes possessing two naphthalimide moieties exhibited higher values of the fluorescence quantum yield due to enhanced oscillator strength of the transition. The derivatives of fluorene containing naphthalimide moieties exhibited pronounced positive solvatochromic behaviour in polar solvents indicating on charge-transfer character of the lowest excited states. Fluorescence red shift in dimethylsulfoxide is found of 94 nm, while the fluorescence quantum yield is increasing with polarity from 0.47 in cyclohexane to 0.84 in dimethylsulfoxide. Such untypical enhancement of fluorescence quantum yield is accounted to reduced intersystem crossing in polar solvents, which is proved by almost 10 fold increase in the values of nonradiative decay rate for compounds dissolved in polar solvents. Time-of-flight electron drift mobilities of the layer of 2,7-di((N-octyl-1,8-naphthalimide)-4-yl)-9,9-dioctyl-9H-fluorene in air at 25 °C appproach 1.2 × 10−3 cm2 V−1 s−1 at an eletric field of 6.4 × 105 Vcm−1.

Triazine derived organic materials possessing various donor-chromophores at the periphery have been designed, synthesized and characterized. The synthesized compounds formed molecular glasses. Their glass transition temperatures ranged from 148 to 235 °C. The compounds demonstrated high thermal stability. The onset temperatures of their thermal decomposition exceeded 390 °C. The fluorenyl- and carbazolyl-substituted triazine derivatives were shown to be highly fluorescent in solutions and rigid polymer matrices with fluorescence quantum yields being in the range of 0.73–0.82. The phenothiazinyl-substituted triazine derivative showed moderate fluorescence quantum yields in dilute solution ( η = 0.25) or polymer matrix ( η = 0.50). Photophysical studies of phenothiazinyl-substituted triazine derivative in media of different rigidity and polarity revealed its twisted intramolecular charge transfer character. Neat films of the triazine compounds displayed significant fluorescence quenching accompanied by a non-exponential excited-state decay profile which was attributed to migration-assisted exciton quenching at non-radiative decay sites in disordered media. Differential pulse voltammetry studies of the synthesized materials showed that the nature of donor-substituents attached to the triazine core can influence their redox behaviour. Investigation by cyclic voltammetry revealed that the synthesized materials can be used as monomers to prepare high dimensional conjugated polymers by electro-oxidation. Spectroelectrochemical investigation of electro-oxidation products suggested the formation of charged species like polarons or bipolarons.

Diversity of the (opto)electronic devices in which the derivatives of triphenylamine are used requires thorough knowledge of the structure–properties relationship of this class of organic semiconductors. Diphenylethenyl- or methylphenylethenyl-substituted triphenylamines were prepared by condensation of methoxy-substituted triphenylamines with 2,2-diphenylacetaldehyde or 2-phenylpropionaldehyde, respectively. Diphenylethenyl-substituted triphenylamines form molecular glasses with glass transition temperatures up to 50 °C. Increasing the number of phenylethenyl substituents resulted in suppression of intramolecular motions of the triphenylamine core, thereby significantly (up to 48%) enhancing fluorescence quantum yield of the derivatives in solutions. The enhancement was more pronounced for diphenylethenyl-substituted triphenylamines. The ionization potentials of the synthesized materials do not depend on the number and the structure of substituents and are ca. 5.3 eV. Hole drift mobility of the glassy la...

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.

Arylfluorenyl-substituted triphenylamines were prepared by acid promoted Friedel-Crafts-type substitution reaction. The synthesized compounds were found to be capable of glass formation with glass transition temperatures above 152 °C. The ionization potentials of the layers of the derivatives were found to be in the range of 5.25–5.41 eV. Time-of-flight hole and electron drift mobility values of the layer of tris[3-methoxy-4-(9-phenyl-9-fluorenyl)phenyl]amine well exceeded 10 −3 cm 2 /V at high electric fields at room temperature. The results obtained by means of density functional theory calculations were used to discuss on the charge-transporting and optical properties of the compounds. Deep blue exciplexes formed by the newly synthesized arylfluorenyl-substituted triphenylamines and the known electron-transporting materials 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) or 4,7-diphenyl-1,10-phenanthroline (Bphen) were discovered and studied. Based on these exciplexes, we propose an original structure of cold white OLED with CIE chromaticity coordinates ranging from (0.286, 0.378) to (0.24, 0.29) depending on applied voltages. Electroluminescence spectra of cold white OLED consist of deep blue and green emissions which originate from bulk and interface. The origin of green emission is thermally activated delayed fluorescence (TADF) from exciplex formed between 4,4′,4″-tris[3-methylphenyl(phenyl)amino]triphenylamine (m-MTDATA) and Bphen. Based on the newly discovered exciplex emitters, deep blue OLED with the electroluminescence maximum at 428 nm and with CIE chromaticity coordinates of (0.179; 0.104) was fabricated. The cold white and deep blue devices showed external quantum efficiencies of 2.55% and 1.2%, respectively.

Phosphorescent bis-cyclometallated iridium (III) complexes based on 2-phenyl-1,2,3-benzotriazole with additional donoric diphenylamine or carbazole moieties were synthesized, studied and tested as phosphorescent materials in the single-layer phosphorescent organic light emitting diodes. These single-layer devices were fabricated employing a simple technological approach, based upon the simultaneous vacuum deposition from one crucible of host material and the corresponding phosphorescent 1,2,3-triazole-based iridium complexes. Red and orange electrophosphorescent single-layer devices with current efficiencies of 5.3 cd/A and 6.8 cd/A respectively are reported. Results of the impedance spectroscopy suggest that the proposed method of formation of the working layer provides homogeneous distribution of molecular guest in the matrix of host.