Differently substituted benzonitriles for non-doped OLEDs

DG acknowledges to the ERDF PostDoc grant No. 1.1.1.2/VIAA/1/16/177 . This research was funded by the European Regional Development Fund according to the supported activity ‘Research Projects Implemented by World-class Researcher Groups’ under Measure No. 01.2.2-LMT-K-718 .Towards highly efficient doping-free organic light-emitting diodes, five benzonitrile-based emitters with different substitution pattern were designed exploiting symmetrical donor-acceptor-donor and asymmetrical donor-acceptor-donor* structures. As it was predicted by theoretical calculations, different thermally activated delayed fluorescence of different energy with relatively high absolute quantum yields (11–42%) was detected for non-doped films of the studied compounds. The smallest singlet-triplet energy splitting of 0.05 eV thus the most efficient TADF was estimated for the film of compound with the asymmetrical donor-acceptor-donor* structure containing carbazole and acridan donor moieties. Thermogravimetry revealed sublimation of the materials with the onset temperatures in the range of 350–383 °C. Glass transition temperatures of the molecular materials were in the range of 82–94 °C. Tuning of hole injection properties of these compounds in solid-state was demonstrated. Their ionization potential was in range from 5.8 to 6.0 eV. Strong effect of different substitutions was observed on hole mobilities of the layers of compounds. They were found to be in the wide range from 3 × 10−7 cm2V−1s−1 to 1 × 10−4 cm2V−1s−1. Electron mobility values of the compounds were found to be comparable and ranged from 1.5 × 10−4 cm2V−1s−1 to 3 × 10−4 cm2V−1s−1 at electric field of 6.9 × 105 Vcm−1. Reflecting effect of substitution pattern of benzonitrile on electroluminescent properties of OLEDs, maximum external quantum efficiencies in the range from 1.6 to 5% as well as maximum brightness in the wide range from 1200 to 22600 cd/m2 were observed for the devices based on the doping-free light-emitting layerEuropean Regional Development Fund 1.1.1.2/VIAA/1/16/177; European Regional Development Fund 01.2.2-LMT-K-718; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²https://www.sciencedirect.com/science/article/pii/S014372081931238

Differently substituted benzonitriles for non-doped OLEDs

DG acknowledges to the ERDF PostDoc grant No. 1.1.1.2/VIAA/1/16/177 . This research was funded by the European Regional Development Fund according to the supported activity ‘Research Projects Implemented by World-class Researcher Groups’ under Measure No. 01.2.2-LMT-K-718 .Towards highly efficient doping-free organic light-emitting diodes, five benzonitrile-based emitters with different substitution pattern were designed exploiting symmetrical donor-acceptor-donor and asymmetrical donor-acceptor-donor* structures. As it was predicted by theoretical calculations, different thermally activated delayed fluorescence of different energy with relatively high absolute quantum yields (11–42%) was detected for non-doped films of the studied compounds. The smallest singlet-triplet energy splitting of 0.05 eV thus the most efficient TADF was estimated for the film of compound with the asymmetrical donor-acceptor-donor* structure containing carbazole and acridan donor moieties. Thermogravimetry revealed sublimation of the materials with the onset temperatures in the range of 350–383 °C. Glass transition temperatures of the molecular materials were in the range of 82–94 °C. Tuning of hole injection properties of these compounds in solid-state was demonstrated. Their ionization potential was in range from 5.8 to 6.0 eV. Strong effect of different substitutions was observed on hole mobilities of the layers of compounds. They were found to be in the wide range from 3 × 10−7 cm2V−1s−1 to 1 × 10−4 cm2V−1s−1. Electron mobility values of the compounds were found to be comparable and ranged from 1.5 × 10−4 cm2V−1s−1 to 3 × 10−4 cm2V−1s−1 at electric field of 6.9 × 105 Vcm−1. Reflecting effect of substitution pattern of benzonitrile on electroluminescent properties of OLEDs, maximum external quantum efficiencies in the range from 1.6 to 5% as well as maximum brightness in the wide range from 1200 to 22600 cd/m2 were observed for the devices based on the doping-free light-emitting layerEuropean Regional Development Fund 1.1.1.2/VIAA/1/16/177; European Regional Development Fund 01.2.2-LMT-K-718; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²https://www.sciencedirect.com/science/article/pii/S014372081931238

Methoxycarbazolyl-disubstituted dibenzofuranes as holes- and electrons-transporting hosts for phosphorescent and TADF-based OLEDs

This research was funded by European Social Fund (Project No 09.3.3-LMT-K-712-02-0105). DG acknowledges to the ERDF PostDoc grant No. 1.1.1.2/VIAA/1/16/177.In the search of universal host materials for organic light emitting diodes a new series of bipolar host materials containing methoxy-substituted carbazoles as the electron-donating and dibenzofuran as an electron-accepting units were designed and synthesized. Different linking topologies and number of methoxy groups attached to carbazolyl moiety were used to understand the impact of the strength of the donor moiety on the thermal, optical, photophysical, electrochemical and electroluminescent properties. The synthesized compounds exhibited relatively high thermal stability with 5% weight loss temperatures exceeding 378 °C and formed molecular glasses with high glass-transition temperatures ranging from 120 to 148 °C. High triplet energy values of 2.86–2.96 eV were estimated for dilute THF solutions at 77K. Hole and electron drift mobilities estimated using time-of-flight technique in solid layers approached 10−4 cm2V−1s−1 at high electric fields exceeding 3.6 × 105 V cm−1. The synthesized methoxy-carbazole based compounds were tested as hosts in electrophosphorescent and TADF organic light-emitting diodes reaching luminance of 53000 cd m−2 and external quantum efficiency of 12.5%, in the best case.European Social Fund 09.3.3-LMT-K-712-02-0105; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²https://www.sciencedirect.com/science/article/pii/S014372081931162

Effect of donor substituents on thermally activated delayed fluorescence of diphenylsulfone derivatives

This research was funded by the European Social Fund according to the activity ‘Improvement of researchers’ qualification by implementing world-class R&D projects’ of Measure No. 09.3.3-LMT-K-712. DG acknowledges to the ERDF PostDoc project No. 1.1.1.2/VIAA/1/16/177;Diphenylsulfones substituted by acridan, carbazole, phenothiazine and phenoxazine moieties were synthesized and characterized by thermal analysis, UV-, steady-state and time-resolved luminescent spectrometries, cyclic voltametry. Quantum chemical calculations on the molecular level were performed to interpret photophysical properties of the derivatives. Structural parameters, electronic properties, HOMO-LUMO gaps, molecular orbital densities, ionization potentials, reorganization energies were determined. The lowest excitation energies and the wavelengths of absorption maxima were also estimated using the time-dependent density functional theory. All the compounds were found to be capabale to form glasses with glass transition temperatures ranging from 82° to 91°C. They exhibited high thermal stabilities, with 5% weight loss temperatures exceeding 385 °C. Strong solvatochromism arising from the intramolecular charge transfer in the excited state was evidenced by bathochromic shifts of emission maxima with increasing solvent polarity. The compounds containing acridan and phenoxazine moieties showed relatively high photoluminescence quantum yield (up to 35%) in the non-doped solid state, long delayed fluorescence lifetime (in µs range) and small singlet-triplet energy splitting (ΔEST) that is attributed to thermally activated delayed fluorescence. These compounds were tested as emissive species for the fabrication of OLEDs. The sky-blue and green devices showed maximum brightness of 3200 and 12300 cd/m2 and maximum external quantum efficiency of 6.3% and 6.9%, respectively.European Social Fund 09.3.3-LMT-K-712; European Regional Development Fund 1.1.1.2/VIAA/1/16/177; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Role of the alkylation patterning in the performance of OTFTs: the case of thiophene-functionalized triindoles

Organic semiconductors have emerged as potential alternatives to conventional inorganic materials due to their numerous assets and applications. In this context, the star-shaped triindole core stands as a promising system to design new organic materials with enticing charge-transporting properties. Herein, we present the synthesis of three thiophene-containing triindole derivatives that feature N-alkyl chains of different lengths, from methyl to decyl. The impact of the alkylation patterning on the crystallinity of the thin films and their resultant performance as semiconductor have been analyzed. All derivatives displayed p-type semiconductor properties, as demonstrated via both TOF measurements and integration in organic thin-film transistor (OTFT) devices. The attachment of longer alkyl chains and the functionalization of the silicon substrate with octadecyltrichlorosilane (OTS) prompted better OTFT characteristics, with a hole mobility value up to 5 × 10-4 cm2 V-1 s-1. As elucidated from the single crystal, this core is arranged in a convenient cofacial packing that maximizes the p-overlapping. The analysis of the thin films also corroborates that derivatives possessing longer N-alkyl chains confer a higher degree of order and a more adequate morphology.Peer ReviewedPostprint (published version

Multifunctional derivatives of dimethoxy-substituted triphenylamine containing different acceptor moieties

This project has received funding from the Research Council of Lithuania (LMTLT), Agreement No. [S-LZ-19-2]. This research was funded by the Région Centre, the Tunisian ministry of research, University of Monastir and the French ministry of Higher Education and Research. J. Bouclé would like to thank the Sigma-Lim LabEx environment for financial supports, and the PLATINOM facility at XLIM laboratory regarding device fabrication and characterizations. DG acknowledges the Lithuanian Academy of Sciences for the financial support.Two compounds, having dimethoxy-substituted triphenylamino groups and fragments of cyanoacrylic acid or rhodanine-3-acetic acid were prepared and characterized. Their optical, photophysical, thermal, electrochemical, photoelectrical and nonlinear optical properties were investigated. Both derivatives showed ability of glass-formation with glass transition temperatures of 83 and 61 °C. They showed comparable ionization potential values of ca. 5.20 eV. The compounds showed Kerr and two photon absorption effects. The dye containing a rhodanine-3-acetic acid fragment, namely 2-((E)-5-(4-(diphenylamino)benzylidene)-tetrahydro-4-oxo-2-thioxothiophen-3-yl)acetic acid, exhibited a promising power conversion efficiency of 2.09% in dye-sensitized solar cells using the spiro-OMeTAD as hole transporting compound.Research Council of Lithuania Agreement No. [S-LZ-19-2]; Région Centre; Tunisian ministry of research; University of Monastir; French ministry of Higher Education and Research; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

An ambipolar BODIPY derivative for a white exciplex OLED and cholesteric liquid crystal laser toward multifunctional devices

A new interface engineering method is demonstrated for the preparation of an efficient white organic light-emitting diode (WOLED) by embedding an ultrathin layer of the novel ambipolar red emissive compound 4,4-difluoro-2,6-di(4-hexylthiopen-2-yl)-1,3,5,7,8-pentamethyl-4-bora-3a,4a-diaza-s-indacene (bThBODIPY) in the exciplex formation region. The compound shows a hole and electron mobility of 3.3 × 10–4 and 2 × 10–4 cm2 V–1 s–1, respectively, at electric fields higher than 5.3 × 105 V cm–1. The resulting WOLED exhibited a maximum luminance of 6579 cd m–2 with CIE 1931 color coordinates (0.39; 0.35). The bThBODIPY dye is also demonstrated to be an effective laser dye for a cholesteric liquid crystal (ChLC) laser. New construction of the ChLC laser, by which a flat capillary with an optically isotropic dye solution is sandwiched between two dye-free ChLC cells, provides photonic lasing at a wavelength well matched with that of a dye-doped planar ChLC cell

Diphenylsulfone-based hosts for electroluminescent devices: Effect of donor substituents

DG acknowledges to the ERDF PostDoc project No. 1.1.1.2/VIAA/1/16/177. This work was supported by the project of scientific co-operation program between Latvia, Lithuania and Taiwan ?Polymeric Emitters with Controllable Thermally Activated Delayed Fluorescence for Solution-processable OLEDs? (grant No. S-LLT-19-4). Support of the Lithuanian Academy of Sciences is gratefully acknowledged; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²In this work, we report on a series of diphenylsulfone derivatives substituted by 2-(trifluoromethyl)-phenothiazinyl, 10,11-dihydro-5H-dibenz[b,f]azepinyl, 5H-dibenz[b,f]azepinyl, 4-methoxy-carbazolyl and 1,2,3,4-tetrahydrocarbazolyl moieties. Utilization of such donating units provided high triplet levels (2.99–3.12 eV) of the designed compounds. The compounds were characterized by glass-forming properties (with glass transition temperatures of 68–162 °C) and ionization potentials of 5.61–5.99 eV. Depending on the donor substitution pattern, either hole or electron transport was observed for the studied compounds with charge mobilities in the range from 5.3 × 10−6 to 2.8 × 10−4 cm2/V at electric fields higher than 3.1·105 V/cm. Hosting properties of the compounds were studied using widely known emitter exhibiting thermally activated delayed fluorescence. Among the studied compounds, bis(4-(4-methoxy-9H-carbazole-9-yl)phenyl)sulfone showed the best performances in both guest:host solid films (photoluminescence quantum yield of 87%) and electroluminescent devices (maximum external quantum efficiency over 20%).ERDF PostDoc project No. 1.1.1.2/VIAA/1/16/177; Scientific cooperation program grant No. S-LLT-19-4; Lithuanian Academy of Science

TADF versus TTA emission mechanisms in acridan and carbazole-substituted dibenzo[a,c]phenazines: Towards triplet harvesting emitters and hosts

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Satisfying both interfacial- and bulk requirements for organic photovoltaics: Bridged-triphenylamines with extended p-conjugated systems as efficient new molecules

© 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.Peer Reviewe