Effect of fluorine on the photovoltaic properties of 2,1,3-benzothiadiazole-based alternating conjugated polymers by changing the position and number of fluorine atoms.

Fluorination is one of the most effective ways to manipulate molecular packing, optical bandgap and molecular energy levels in organic semiconductor materials. In this work, different number of fluorine atoms was introduced into the acceptor moiety 2,2'-dithiophene linked 2,1,3-benzothiadiazole, utilizing the alkylthiophene modified dithieno[2,3-d:2',3'-d']benzo[1,2-b:4,5-b] (DTBDT) as the donor unit, three polymers: PDTBDT-0F-BTs, PDTBDT-2F-BTs and PDTBDT-6F-FBTs were synthesized. With the number of fluorine atoms in each repeat unit of polymers varying from 0 to 2 and then up to 6, PDTBDT-0F-BTs, PDTBDT-2F-BTs and PDTBDT-6F-FBTs exhibited gradually downshifted energy levels and improved dielectric constants (εr) from 3.4 to 4.3 to 5.8, further successively increased charge transport mobilities. As a result, the power conversion efficiency (PCE) of the bulk heterojunction organic photovoltaic devices (BHJ-OPV) from the blend films of aforementioned polymers paired with PC71BM were gradually increased from 1.69 for PDTBDT-0F-BTs to 1.89 for PDTBDT-2F-BTs and then to 5.28 for PDTBDT-6F-FBTs. The results show that the continuous insertion of fluorine atoms into the repeating units of the benzothiadiazole conjugated polymer leads to the deepening of HOMO energy level, the increase of εr and the increase of charge mobility, which improve the efficiency of charge transfer and electron collection, thus improving the photovoltaic performance of BHJ-OPV.

Color Revolution: Prospects and Challenges of Quantum-Dot Light-Emitting Diode Display Technologies.

Light-emitting diodes (LEDs) based on colloidal quantum-dots (QDs) such as CdSe, InP, and ZnSeTe feature a unique advantage of narrow emission linewidth of ≈20 nm, which can produce highly accurate colors, making them a highly promising technology for the realization of displays with Rec. 2020 color gamut. With the rapid development in the past decades, the performances of red and green QLEDs have been remarkably improved, and their efficiency and lifetime can almost meet industrial requirements. However, the industrialization of QLED displays still faces many challenges; for example, (1) the device mechanisms including the charge injection/transport/leakage, exciton quenching, and device degradation are still unclear, which fundamentally limit QLED performance improvement; (2) the blue performances including the efficiency, chromaticity, and stability are relatively low, which are still far from the requirements of practical applications; (3) the color patterning processes including the ink-jet printing, transfer printing, and photolithography are still immature, which restrict the manufacturing of high resolution full-color QLED displays. Here, the recent advancements attempting to address the above challenges of QLED displays are specifically reviewed. After a brief overview of QLED development history, device structure/principle, and performances, the main focus is to investigate the recent discoveries on device mechanisms with an emphasis on device degradation. Then recent progress is introduced in blue QLEDs and color patterning. Finally, the opportunities, challenges, solutions, and future research directions of QLED displays are summarized.

Electron-Induced Degradation in Blue Quantum-Dot Light-Emitting Diodes.

The poor stability of blue quantum-dot (QD) light-emitting diodes (B-QLEDs) hinders their application in displays. To improve the stability of B-QLEDs, the degradation mechanism should be revealed. Here, the degradation mechanism of B-QLEDs is investigated by monitoring the changes occurring in the QDs and the hole transport layers (HTL) during device operation, respectively. It is revealed that the accumulation of electrons within the QDs is responsible for the degradation of the devices. On the one hand, the accumulated electrons induce the detachment of oleic acid ligands, leading to permanent damage to the stability of B-QDs. On the other hand, the accumulated electrons leak into the HTL or recombine at the HTL/QDs interface, leading to the degradation of HTL. The formation of surface defects in B-QDs and the decomposition of HTL contribute to the degradation of B-QLEDs. The results reveal the strong dependence of B-QLEDs stability on the accumulated electrons, the QDs and the HTL, which can help researchers to develop effective design strategies for improving the lifespan of B-QLEDs.

An evaluation of the efficacy of percutaneous reduction and screw fixation without bone grafting in Sanders Type-II and Type-III displaced intra-articular calcaneal fractures.

BACKGROUND: The aim of this retrospective monocentric study was to investigate the clinical efficacy of percutaneous reduction and screw fixation without bone grafting in Sanders Type-II and Type-III displaced intra-articular calcaneal fractures (DIACFs). METHODS: The medical records of calcaneal fractures patients who were admitted to our department from January 2018 to January 2020 were retrospectively reviewed, and those meeting the inclusion criteria were fnally included for analysis. All patients were treated with percutaneous reduction and screw fixation, and no patients received bone grafting. The radiologic parameters evaluated included the BÖhler angle and the calcaneal height. In addition, the American Orthopaedic Foot and Ankle Society (AOFAS) hindfoot scores, Maryland Foot Score (MFS), and visual analog scale (VAS) score were determined. RESULTS: Thirty-eight patients with Sanders Type-II and Type-III DIACFs were finally included, including 30 males and 8 females aged 21 to 61 years [(42.6 ± 9.6) years]. According to the Essex-Lopresti classification, 27 of the fractures were the tongue type, and 11 were the joint compression type. According to the Sanders classification, 27 of the fractures were type II, and 11 were type III. Immediately postoperatively, the calcaneal height had recovered to 39.8 ± 2.1 mm, the BÖhler angle had recovered from 4.2° ± 13.6° preoperatively to 27.2° ± 3.4° (P = 0.000). All patients were followed up for 18-42 months [(25.2 ± 9.5) months]. All fractures healed. No differences were found in the outcome measures six-months postoperatively (BÖhler angle, p = 0.24; calcaneal height, p = 0.82) or at final follow-up (BÖhler angle, p = 0.33; calcaneal height, p = 0.28) compared to the immediately postoperative values. At the final follow-up, the AOFAS score was 91.7 ± 7.4 points, with an excellent and good rate of 92.1%; the MFS was 90.3 ± 7.8 points, with an excellent and good rate of 92.1%; and the VAS score was 2.2 ± 1.5 points. None of the patients had incision complications, and one patient developed traumatic arthritis. CONCLUSION: Percutaneous reduction and screw fixation without bone grafting in Sanders Type-II and Type-III DIACFs can achieve good recovery and maintenance of the BÖhler angle and calcaneal height. Moreover, it has the advantage of a low complication rate.

A facile microwave-assisted synthesis of highly crystalline red carbon dots by adjusting the reaction solvent for white light-emitting diodes.

Microwave approach has been widely used for the synthesis of fluorescent carbon dots (CDs) due to its advantages of short reaction time and homogeneous heating. Currently, it is still difficult to synthesize red light-emitting CDs (R-CDs) via the microwave-assisted method at atmospheric pressure. Herein, we report a solvent-controlled synthesis of R-CDs using domestic microwave. As a result, for an ammonium citrate tribasic, formamide and glycerol blend reaction solvent, the R-CDs with emission peak of 622 nm were achieved and exhibited a photoluminescence (PL) quantum yield of 37.4% and excitation-independent PL emission spectrum. During the formation process of R-CDs, glycerol and formamide not only promote the carbonization of ammonium citrate tribasic, but can also enhance the crystalline nature of CDs. Finally, the warm white light-emitting diode (WLED) with a high colour rendering index (CRI) of 90.9 and Commission Internationale de L'Eclairage (CIE) coordinates of (0.344, 0.333) was realized by combining conventional yellow YAG:Ce phosphor and R-CDs/mesoporous silica (MPS) composites with a blue chip. This result demonstrates a low-cost R-CD synthetic method for potential substitution for red phosphor materials in solid-state lighting applications.

The DmtA methyltransferase contributes to Aspergillus flavus conidiation, sclerotial production, aflatoxin biosynthesis and virulence.

DNA methylation is essential for epigenetic regulation of gene transcription and development in many animals, plants and fungi. We investigated whether DNA methylation plays a role in the development and secondary metabolism of Aspergillus flavus, identified the DmtA methyltransferase from A. flavus, and produced a dmtA knock-out mutant by replacing the dmtA coding sequence with the pyrG selectable marker. The A. flavus dmtA null mutant lines produced white fluffy mycelium in liquid medium, and displayed a slightly flavescent conidial pigmentation compared with the normal yellow of the wild-type strain when grown on agar. The ΔdmtA lines exhibited decreased conidiation and aflatoxin (AF) biosynthesis, compared with the wild-type line, suggesting that the DmtA knock-out affected the transcriptional level of genes in the AF cluster. In particular, sclerotia development and host colonization were altered in the dmtA null mutants. Green fluorescent protein tagging at the C-terminus of DmtA showed that DmtA localized to the nucleus and cytoplasm. DNA methylation content measurements in the dmtA mutants revealed no widespread DNA methylation in the mutants or wild-type lines. Thus, our findings suggest that DmtA, apart from being a C-5 cytosine methyltransferase in A. flavus, contributes to asexual development, aflatoxin biosynthesis, sclerotial production and virulence.

sRNA profiling in Aspergillus flavus reveals differentially expressed miRNA-like RNAs response to water activity and temperature.

Small non-coding RNA (sRNA) in various organisms remains a mysterious subject. Although microRNAs (miRNAs) have been intensively investigated in plants and animals, the study of miRNAs in fungi has been limited. Only microRNA-like RNAs (milRNAs) have been reported in several filamentous fungi. In this study, Illumina deep sequencing was performed to characterize the sRNA in Aspergillus flavus and to evaluate their responses to water activity and temperature. Global expression analysis showed an extensively differential expression of sRNA loci in A. flavus under different temperature or water activities. In addition, a total of 135 milRNAs were identified in A. flavus. The milRNA profiles obtained in deep sequencing were further validated by RT-qPCR assay. The presence and differential expression of milRNAs under different temperature or water activities in A. flavus imply that milRNAs might play important roles in the mycotoxin biosynthesis and mycelium growth in fungi A. flavus.