Rational Design of Bipolar Host and Thermally Activated Delayed Fluorescence Materials in Donor-Acceptor Molecular Architecture: A Theoretical Study.

Donor-acceptor (D-A) molecules have drawn massive attention recently in the design of high-performance materials, but the underlying reasons for the magic abilities of D-A architecture in building very different organic semiconductors are still unclear. Here, based on a series of experimentally bipolar host and thermally activated delayed fluorescence (TADF) molecules with the same donor but different acceptor units, it was found that TADF emitters have more effective charge transfer between donor and acceptor units than bipolar host molecules. More efficient conjugation effects between the donor and acceptor units of host materials were identified from the lower dihedral angles of the D-A structure, smaller and even negative charge transfer amount, shorter charge-transfer length, and larger hole-electron overlap extent. These findings with in-depth insights into different interaction models of donor and acceptor units shed important light on the molecular design of TADF emitters and bipolar materials in a D-A architecture.

Improving the performance of OLEDs by controlling the molecular orientation in charge carrier transport layers.

The transition dipole moment (TDM) orientation in the emission layer (EML) of organic light-emitting diodes (OLEDs) have attracted increasing attention from many researchers. But the study point at the molecular orientation in the hole transport layer (HTL) and electron transport layer (ETL) was not reported widely. In this paper, the molecular orientation of HTLs and ETLs were controlled by the deposition rate. The angle-dependent PL spectra and the variable angle spectroscopic ellipsometry (VASE) were used for evaluating the molecular orientation of B3PYMPM and TAPC, respectively. We found that fast deposition rate can boost preferentially vertical molecular orientation in both molecules and facilitate the hole and electron mobility, which was tested by the current density-voltage and capacitance-voltage curves of HODs and EODs. Moreover, the HTLs and ETLs were employed in OLED devices to verify the influence of molecular orientation on charge carrier mobility, which determined the performance of OLEDs significantly.

Antioxidant Activity of Docosahexaenoic Acid (DHA) and Its Regulatory Roles in Mitochondria.

Reactive oxygen species (ROS) are single-electron-bearing oxidation-reduction products that are mainly produced in mitochondria. Excessive ROS accumulation may lead to oxidative damage. Docosahexaenoic acid (DHA) is an essential component of brain phospholipids and is mainly derived from the diet. Its antioxidant activities have been extensively studied. However, its regulatory roles in mitochondria and the underlying mechanism remain to be elucidated. In this study, the DHA's effect on cellular antioxidant capacity and mitochondrial functions was examined in HepG2 cells. The results showed that 100 µM DHA decreased cellular and mitochondrial ROS levels to 75.2 ± 9.4% (P < 0.05) and 55.1 ± 1.4% (P < 0.01), respectively. It also increased the total antioxidant capacity by 55.6 ± 0.1 and 49.2 ± 1.1% (P < 0.05), based on ABTS and FRAP assay results, respectively. Consistently, it increased the activities and gene expression of major antioxidant enzymes by at least 35 and 40% (P < 0.05), respectively. Furthermore, DHA promoted mitochondrial functions and biogenesis. These data suggested that DHA's antioxidant activity can be attributed to its enhancement of mitochondrial functions and biogenesis. This study may shed light on the molecular mechanisms underlying DHA's function in improving resistance to and relieving the symptoms of chronic disease.

Solution-processed PEDOT:PSS:GO/Ag NWs composite electrode for flexible organic light-emitting diodes.

Flexible organic light emitting diodes (OLEDs) have attracted considerable attention for the reason of light weight, high mechanical flexibility in display and lighting. The most widely used transparent anode indium tin oxide (ITO) is unsuitable for flexible OLEDs because of its easy cracking upon bending. In this paper, we proposed a simple two steps solution processing method to fabricate flexible PEDOT:PSS:GO/Ag NWs composite electrodes. The optimized PEDOT:PSS:GO/Ag NWs composite electrode exhibits an optical transmittance of 88.7% at a wavelength of 550 nm and a low sheet resistance of 17 Ω/sq, which arecomparable to that of ITO. With PEDOT:PSS:GO/Ag NWs composite electrodes, the turn on voltage, current density and maximum brightness of OLEDs based on composite electrode were 2.1 V, 6.2 cd/A and 22894 cd/m2, respectively, which were superior to that OLED based on ITO anode. The enhanced performance of OLEDs based on composite anode mainly attributed to the lower sheet resistance, smoother surface of the composite anode and the far surface plasma resonance (Far SPR) effect, a lower waveguide optical loss because of the introduction of Ag NWs in the electrode.