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Recently, numerous efforts have been devoted to sky blue or greenish blue organic light-emitting diodes (OLEDs), nevertheless, the deep blue and pure blue OLEDs still remain a formidable challenge. Herein, a series of deep blue and pure blue donor–acceptor–donor (D–A–D) type emitters, namely Cz-DMTD, PhCz-DMTD and TMCz-DMTD, were constructed. For PhCz-DMTD which exhibited no delayed fluorescence component, the extended delocalization of donors and the enhancement of oscillator strength were both observed through theoretical calculation. For methyl-engineered TMCz-DMTD, the degenerate charge transfer singlet excited (1CT) and triplet excited (3CT) states and localized triplet excited (3LE) state endowed a thermally activated delayed fluorescence (TADF) character. Moreover, PhCz-DMTD and TMCz-DMTD based OLEDs displayed emission with Commission Internationale de l'Eclairage (CIE) coordinates of (0.164, 0.077) and (0.157, 0.107) and with maximum external quantum efficiencies (EQEmax) of 4.6% and 8.7%, respectively. It is the first time that the electroluminescence wavelength of TMCz based OLEDs reached below 450 nm with a CIEy below 0.11. Molecular engineering of the carbazole moiety is expected to provide a valuable strategy for molecular design of more deep blue emitters. [ABSTRACT FROM AUTHOR]

Non-electronic wearables that utilize skin-interfaced microfluidic technology have revolutionized the collection and analysis of human sweat, providing valuable biochemical information and indicating body hydration status. However, existing microfluidic devices often require constant monitoring of data during sweat assessment, thereby impeding the user experience and potentially missing anomalous physiological events, such as excessive sweating. Moreover, the complex manufacturing process hampers the scalability and large-scale production of such devices. Herein, we present a self-feedback microfluidic device with a unique dehydration reminder through a cost-effective "CAD-to-3D device" approach. It incorporates two independent systems for sweat collection and thermal feedback, including serpentine microchannels, reservoirs, petal-like bursting valves and heating chambers. The device operates by sequentially collecting sweat in the channels and reservoirs, and then activating thermal stimulators in the heating chambers through breaking the valves, initiating a chemical exothermic reaction. Human trials validate that the devices effectively alert users to potential dehydration by inducing skin thermal sensations triggered by sweat sampling. The proposed device offers facile scalability and customizable fabrication, and holds promise for managing hydration strategies in real-world scenarios, benefiting individuals engaged in sporting activities or exposed to high-temperature settings. [ABSTRACT FROM AUTHOR]

Two novel heteroleptic iridium complexes containing 4-phenylquinazoline (pqz) as a cyclometalating ligand, namely Ir1 and Ir2, are designed and synthesized. Methoxy groups are incorporated into the 6- and 7-sites of pqz rings to tune the physical properties and the emission performance of the complexes. The introduction of methoxy groups in Ir1 and Ir2 causes a slight blue shift by 3–5 nm relative to the reference complex Ir(pqz)2(acac) (630 nm), and moderate photoluminescence quantum yields of 0.35 and 0.38 and short lifetimes of 0.79 and 0.64 μs, respectively, are obtained. Ir1 and Ir2 are used as doped emitters to fabricate phosphorescence organic light-emitting diodes and pure red electroluminescence (EL) is achieved. In comparison with the reference complex Ir(pqz)2(acac), dramatically improved EL performance with color purity and efficiencies are realized for both Ir1 and Ir2. In particular, the Ir2 device exhibits a maximum external quantum efficiency of 26.22% with Commission Internationale de l'Eclairage (CIE) coordinates of (0.65, 0.34), which is close to the best efficiencies reported for other pqz based red iridium phosphors but advantageous in terms of a simple device structure with a single emitting layer. [ABSTRACT FROM AUTHOR]

Blue iridium phosphors are always precious and desirable for both fundamental research and industrial applications in organic light-emitting diodes (OLEDs). Three heteroleptic cyclometalated iridium(III) complexes, namely, Ir1, Ir2 and Ir3, incorporating 2-(3,5-bis(trifluoromethyl)phenyl)-pyrimidine (tfmphpm) or 2-(2,4-difluorophenyl)-pyrimidine (dfppm) as the main ligand, and 2-(3-(trifluoromethyl)-1H-pyrazol-5-yl)pyridine (fppz) or 2-(5-(4-(trifluoromethyl)phenyl)-2H-1,2,4-triazol-3-yl)pyridine (Htaz) as the ancillary ligand, were developed for application in OLEDs. Owing to the introduction of the strong-field CF3-containing ancillary ligand and the incorporation of electron-withdrawing F or CF3 groups on the HOMO-lying C-related aromatic rings of the C^N cyclometalating ligands, the phosphorescence of these Ir(III) complexes peaked at 457–459 nm. In comparison with the well-known commercial sky-blue iridium complex FIrpic (bis(4′,6′-difluorophenylpyridinato) iridium(III) picolinate, 475 nm), the phosphorescence of these complexes is hypsochromically shifted by 16–18 nm, more closely approaching standard blue light. They have high phosphorescence quantum yields in solution. The phosphorescent OLEDs employing these complexes as doped emitters display impressive performance. In particular, the PhOLED based on Ir3 achieves an outstanding maximum external quantum efficiency of 21.23% with Commission Internationale de l'Eclairage (CIE) coordinates of (0.15, 0.26), which is about 27% higher than that of the control device using FIrpic as a dopant (16.63%). [ABSTRACT FROM AUTHOR]