Efficient preparation of single-layer two-dimensional (2D) transition metal dichalcogenides, especially molybdenum disulfide (MoS), offers readily available 2D surface in nanoscale to template various materials to form nanocomposites with van der Waals heterostructures (vdWHs), opening up a new dimension for the design of functional electronic and optoelectronic materials and devices. Here, we report the tunable memory properties of the facilely prepared [6,6]-phenyl-C-butyric acid methyl ester (PCBM)-MoS nanocomposites in a conventional diode device structure, where the vdWHs dominate the electric characteristics of the devices for various memory behaviors depending on different surface deposition ratios of PCBM on MoS nanosheets. Both nonvolatile WORM and flash memory devices have been realized using the new developed PCBM-MoS 2D composites. Specially, the flash characteristic devices show rewritable resistive switching with low switching voltages (∼2 V), high current on/off ratios (∼3 × 10), and superior electrical bistability (>10 s). This research, through successfully allocating massive vdWHs on the MoS surface for organic/inorganic 2D nanocomposites, illustrates the great potential of 2D vdWHs in rectifying the electronic properties for high-performance memory devices and paves a way for the design of promising 2D nanocomposites with electronically active vdWHs for advanced device applications.

A new series of N-P[double bond, length as m-dash]Se resonance-based fluorescent molecules were developed and used for the detection of hypochlorous acid (HClO) with rapid response and high selectivity. These Se-containing molecules can selectively detect trace amounts of HClO in nM, showing significantly strengthened fluorescence due to the enhanced resonance variation with an increased distance between the fluorophore and Se. The design of N-P[double bond, length as m-dash]Se resonance molecules in donor-resonance-acceptor (D-r-A) architectures could be an important way to develop high-performance turn-on fluorescent probes for HClO detection.

Rational design and selection of suitable donor and acceptor components for optimal thermally activated delayed fluorescence (TADF) exciplex-type emitters or hosts is presently challenging. Here, we constructed successfully a blue-emitting bulk exciplex system with efficient TADF emission and high triplet energy (E T) based on a donor of 4,4′,4′′-tris [3-methylphenyl­(phenyl)­amino]­triphenylamine and an acceptor of 1,3,5-tri (m-pyrid-3-yl-phenyl)­benzene. Systematic experimental and theoretical studies show that the matched frontier orbital energy levels, high E T, facile intersystem crossing, high oscillator strength of the exciplex, and efficient energy transfer channels should be the main considerations during the design of high-performance exciplex-type TADF emitters and bipolar host materials. Therefore, this bulk exciplex system can behave not only as blue emitters for organic light-emitting diodes (OLEDs) but also as universal hosts for the green, yellow, and red phosphorescent OLEDs (PhOLEDs). Impressively, even under a very low guest doping level of 2 wt %, the PhOLEDs exhibit very low turn-on voltages (∼2.2 V) and high maximum external quantum efficiencies up to 18.5%. These promising device results, along with the theoretical understandings, could shed important light on the rational design of exciplex systems and their applications as either TADF emitters or bipolar host materials for high-performance and low-cost OLEDs.