Bicarbazole-Benzophenone Based Twisted Donor-Acceptor Derivatives as Potential Blue TADF Emitters for OLEDs.

Over the past few decades, organic light-emitting diodes (OLEDs) find applications in smartphones, televisions, and the automotive sector. However, this technology is still not perfect, and its application for lighting purposes has been slow. For further development of the OLEDs, we designed twisted donor-acceptor-type electroactive bipolar derivatives using benzophenone and bicarbazole as building blocks. Derivatives were synthesized through the reaction of 4-fluorobenzophenone with various mono-alkylated 3,3'-bicarbazoles. We have provided a comprehensive structural characterization of these compounds. The new materials are amorphous and exhibit suitable glass transition temperatures ranging from 57 to 102 °C. They also demonstrate high thermal stability, with decomposition temperatures reaching 400 °C. The developed compounds exhibit elevated photoluminescence quantum yields (PLQY) of up to 75.5% and favourable HOMO-LUMO levels, along with suitable triplet-singlet state energy values. Due to their good solubility and suitable film-forming properties, all the compounds were evaluated as blue TADF emitters dispersed in commercial 4,4'-bis(N-carbazolyl)-1,10-biphenyl (CBP) host material and used for the formation of emissive layer of organic light-emitting diodes (OLEDs) in concentration-dependent experiments. Out of these experiments, the OLED with 15 wt% of the emitting derivative 4-(9'-{2-ethylhexyl}-[3,3']-bicarbazol-9-yl)benzophenone exhibited superior performance. It attained a maximum brightness of 3581 cd/m2, a current efficacy of 5.7 cd/A, a power efficacy of 4.1 lm/W, and an external quantum efficacy of 2.7%.

Pyridinyl-Carbazole Fragments Containing Host Materials for Efficient Green and Blue Phosphorescent OLEDs.

Pyridinyl-carbazole fragments containing low molar mass compounds as host derivatives H1 and H2 were synthesized, investigated, and used for the preparation of electro-phosphorescent organic light-emitting devices (PhOLEDs). The materials demonstrated high stability against thermal decomposition with the decomposition temperatures of 361-386 °C and were suitable for the preparation of thin amorphous and homogeneous layers with very high values of glass transition temperatures of 127-139 °C. It was determined that triplet energy values of the derivatives are, correspondingly, 2.82 eV for the derivative H1 and 2.81 eV for the host H2. The new derivatives were tested as hosts of emitting layers in blue, as well as in green phosphorescent OLEDs. The blue device with 15 wt.% of the iridium(III)[bis(4,6-difluorophenyl)-pyridinato-N,C2']picolinate (FIrpic) emitter doping ratio in host material H2 exhibited the best overall characteristics with a power efficiency of 24.9 lm/W, a current efficiency of 23.9 cd/A, and high value of 10.3% of external quantum efficiency at 100 cd/m2. The most efficient green PhOLED with 10 wt% of Ir(ppy)3 {tris(2-phenylpyridine)iridium(III)} in the H2 host showed a power efficiency of 34.1 lm/W, current efficiency of 33.9 cd/A, and a high value of 9.4% for external quantum efficiency at a high brightness of 1000 cd/m2, which is required for lighting applications. These characteristics were obtained in non-optimized PhOLEDs under an ordinary laboratory atmosphere and could be improved in the optimization process. The results demonstrate that some of the new host materials are very promising components for the development of efficient phosphorescent devices.

Application of rape pod sealants to reduce adverse environmental impacts.

BACKGROUND: Rape (Brassica napus L.) is a major global oilseed crop characterized by its high potential as an alimentary oil and in biodiesel production. The two most popular pod sealants (PS) used to reduce rape pod shattering are products in the pinolene range (di-1-p-menthene) and latex polymer products. Reports on the effective preservation of seed yield by these products are fairly contradictory. With this in mind, an experimental PS (PS4) that contained the active agents acrylic and trisiloxane was developed. RESULTS: Comparative experimental trials of the developed PS4 and three other PS (PS1, PS2 and PS3) containing active agents that are generally used for sealant production were conducted. The studies showed that the static and dynamic surface tension of PS4 was the lowest at the same concentration (2.0 g kg-1 ), consequently demonstrating the lowest spray drift. The chemical substances from PS had not penetrated the rape seeds in any of the PSs. CONCLUSION: The results indicate that treatment with PS4 exerts a beneficial effect in reducing rape seed yield loss (68-104 kg ha-1 in 2014 and 194-305 kg ha-1 in 2015) compared to other investigated PS. © 2017 Society of Chemical Industry.

The Influence of Bacteria-Inoculated Mineral Fertilizer on the Productivity and Profitability of Spring Barley Cultivation.

The heavy use of mineral fertilizers causes imbalances in the biological processes that take place in soil. Therefore, it is necessary to develop more effective fertilizers or fertilizer complexes that ensure agricultural productivity and soil conservation. There is currently a lack of knowledge regarding the effectiveness of biologically enriched, complex mineral fertilizers for spring barley fertilization. The hypothesis of this study was that bacteria-enriched (Paenibacillus azotofixans, Bacillus megaterium, Bacillus mucilaginosus, and Bacillus mycoides), complex mineral fertilizers (N5P20.5K36) have significant impacts on the yield and potential for economic use of spring barley. Experimental studies were carried out for three years (2020-2022) with sandy loam soil in southern Lithuania. Four different spring barley fertilization scenarios (SCs) were investigated. In SC-1 (control), complex mineral fertilizer (N5P20.5K36) was not applied. In the other SCs, spring barley was sown with a drill and fertilizers were incorporated locally during the sowing operation: fertilization scenario SC-2 used 300 kg ha-1, SC-3 used 150 kg ha-1 preceded by a bacteria-inoculated complex mineral fertilizer (N5P20.5K36), and SC-4 used 300 kg ha-1 with the same bacterial complex. The results showed that the bacterial inoculant increased the efficiency of the mineral fertilizer and had an effect on plant growth in barley. For three consecutive years in the same plots, the bacterial inoculant showed significant positive effects on grain yield (changes of 8.1% in 2020, 6.8% in 2021, and 17.3% in 2022 between SC-2 and SC-4). Comparing the several different fertilizer scenarios from an economic point of view, it was observed that the highest profit per hectare was obtained with SC-4 in all three years of the study. Comparing SC-4 and SC-2, an increase of 13.7% was observed in 2020, followed by 9.1% and 41.9% in 2021 and in 2022, respectively. This study will be useful for farmers, biological inoculant manufacturers, and scientists researching the effectiveness of biological inoculants for growing agricultural crops. We found that it is possible to increase the yield of barley (7-17%) using the same rate of mineral fertilization by enriching it with bacterial inoculants. Further studies should be conducted to determine the effects of the bacterial inoculant on crop yield and soil over a period longer than 3 years.

Effect of substituent structure in fluorene based compounds: Experimental and theoretical study.

Fluorene-based low molar weight derivatives were synthesized in Suzuki reactions by using key starting materials 9-benzylidene-2,7-dibromofluorene or 3-(2,7-dibromofluoren-9-ylmethylen)-9-ethylcarbazole and various aryl boronic acids. Photophysical properties of the compounds were investigated in different solutions as well as in solid state. The thermal investigations showed that the obtained compounds are highly thermally stable with temperatures of 5% mass loss (T5%) in the range of 311-432 °C. Some of the compounds also exhibited very high glass transition temperatures exceeding 125 °C. The presented molecules were electrochemically active and showed the energy band gap below 2.97 eV. The investigations were supported by DFT calculations and the photovoltaic ability of the presented compounds was tested in the organic-inorganic solar cells.