Thioxanthone-based thermally activated delayed fluorescence emitters showing fast reverse intersystem crossing for efficient organic light-emitting diodes with small efficiency roll-off

Thermally activated delayed fluorescence-based organic light-emitting diodes (TADF OLEDs) usually suffer from severe efficiency roll-off at high brightness which is considered to originate from slow reverse intersystem crossing (RISC) and resulting long-lived triplet excitons. The development of TADF molecules with very fast RISC is an effective approach to overcome this issue. Here, we report two TADF molecules (MCz-TXO, DMCz-TXO) having thioxanthone as an acceptor unit to introduce heavy atom effect. Theoretical calculations predict that both molecules will achieve close energy level matching of the charge-transfer and locally excited triplet states (3CT and 3LE, respectively), together with a small energy gap between 3CT and the lowest excited singlet state. The newly designed molecule, MCz-TXO, showed an extremely large rate constant of RISC (kRISC) of 6.4×107 s− 1, one of the largest kRISC values among all reported pure organic TADF emitters. Moreover, DMCz-TXO showed not only a large kRISC but also a large rate constant of radiative decay both exceeding 107 s− 1, offering a sub-microsecond-scale delayed lifetime (~ 0.8 µs). These thioxanthone-based emitters exhibited great device performances with suppressed efficiency roll-offs at high luminance when applied to OLEDs.

Influence of Seed Layer Surface Position on Morphology and Photocatalysis Efficiency of ZnO Nanorods and Nanoflowers

ZnO nanorods and nanoflowers were synthesized by a hydrothermal method via different surface substrate positions at 120°C for 3 h as a growth time. The influence of seed layer surface position on the growth of ZnO nanostructures was observed by the variation of ZnO morphologies from nanorods to nanoflowers. Both analyses XRD and EDS proved the pure wurtzite phase with high crystallinity quality and preferential growth along the c-axis. As displayed from the scanning of surface morphology through SEM, a large amount of ZnO nanorods and nanoflowers were deposited on the full substrate surface. Diverse ZnO photocatalysts were used to study the photodegradation of Methylene Blue (MB) dye by UV light. The organic dye MB was decolorized by the most efficient photocatalyst among the ZnO-tested nanostructures. The results showed an improvement of the degradability of this dye from 54% to 81% for ZnO nanoflowers compared to nanorods. Thus, ZnO nanoflowers are the best photocatalyst which have the high efficiency photodegradation and the large rate constant.

Research on the Preparation and Mechanism of the Organic Montmorillonite and Its Application in Drilling Fluid

The study focused on the relation of structure, property, and application of composite prepared by organic cation intercalated montmorillonite (Mt). Herein a new kind of green and steady ionic liquid, 1-hexadecyl-3-methylimidazolium chloride monohydrate (C12mimCl), was chosen as the intercalated agent. This study used molecular dynamics (MD) modeling to examine the interlayer microstructures of montmorillonite intercalated with C12mimCl. The C12mimCl intercalation was relatively fast with a large rate constant. The process was affected by the initial concentration of the solution; the basal spacing increased to 2.08 nm after intercalation. The coordination of electrostatic interaction and hydrogen bonding expelled water molecules out of the clay gallery and bound the layer together, which led to the dehydration of clay. The intercalation of C12minCl into Mt interlayer space affected rheology of the system and improved various properties. This organic clay composite was environmentally friendly and could be used in drilling fluid system. These models provided insights into the prediction of synthesized organic cationic-clay microstructure and guidelines for relevant engineering applications.

Bioactivity of [6R]-5-formyltetrahydrofolate, an unnatural isomer, in humans and Enterococcus hirae, and cytochrome c oxidation of 10-formyltetrahydrofolate to 10-formyldihydrofolate

The bio-inactive C-6 isomer, [6R]-5-formyl-tetrahydrofolate (5-HCO-H4F), is not found in Nature. An oral dose of 13.5µmol of [6R]-5-HCO-H4F in humans results in the appearance of the naturally occurring [6S]-5-methyl-tetrahydrofolate and relatively large amounts of other bioactive folates in plasma. The removal of the asymmetry at C-6 could account for these results. Two oxidized cytochrome c [cyt c (Fe3+)] molecules oxidize one 10-formyl-tetrahydrofolate (10-HCO-H4F) with second-order kinetics and a rate constant of 1.3×;104 M-1·s-1. The folate product of this oxidation reaction is 10-formyl-dihydrofolate (10-HCO-H2F), which has no C-6 asymmetric centre and is therefore bioactive. The folate-requiring bacterium, Enterococcus hirae, does not normally biosynthesize cytochromes but does so when given an exogenous source of haem (e.g. haemin). E. hirae grown in haemin-supplemented media for 3 days utilizes both [6R]- and [6S]-5-HCO-H4F in contrast to that grown in control medium, which utilizes only the [6S] isomer. Since known chemical reactions form 10-HCO-H4F from 5-HCO-H4F, the unusually large rate constant for the oxidation of 10-HCO-H4F by cyt c (Fe3+) may account for the unexpected bioactivity of [6R]-5-HCO-H4F in humans and in E. hirae grown in haemin-containing media. We used an unnatural C-6 folate isomer as a tool to reveal the possible in vivo oxidation of 10-HCO-H4F to 10-HCO-H2F; however, nothing precludes this oxidation from occurring in vivo with the natural C-6 isomer.