Two new spirobifluorene (SF)‐centered donors (D) DPSF and DTSF are developed to blend with acceptor (A) CN‐T2T for exciplex formation. The transient photoluminescence characterizations of pristine donor and D:A blended films verify the donor aggregates emissions that lead to relatively low photoluminescence quantum yield (PLQY) of exciplex emission. However, the charge recombination at lower energy exciplex state leads the device with DPSF:CN‐T2T blend to give electroluminescence (EL) λmax of 584 nm and external quantum efficiency (EQE) of 6.0%. The DPSF:CN‐T2T exciplex excitons are efficiently extracted by a D‐A‐D‐type fluorescence emitter TTDSF comprising thienothiadiazole core and SF peripherals via Förster energy transfer to give near‐infrared (NIR) emission (760 nm, PLQY 26%). After the electron‐transporting layer thickness optimization, the device with DPSF:CN‐T2T: 7 wt.% TTDSF as emitting layer affords EL λmax 774 nm and EQE up to 5.3%, one of the best cases in NIR organic light‐emitting diodes (OLEDs). More importantly, the device stability has been examined to display an excellent lifetime (LT95 > 200 hours). This work manifests the judicious combination of an exciplex‐forming co‐host system and a designated NIR emitter equipping with a high quinoidal core and rigid peripheral SF groups that can realize an efficient NIR OLED.

The carbazole of a model compound CPTBF was replaced by αand β-carboline to give donors α-CPTBF and β-CPTBF, respectively. The introduction of carboline leads the new donors to have deeper highest occupied molecular orbital (HOMO) energy levels. Different electron acceptors were tested, among them, a new acceptor, 3,4-CN, was found to give exciplexes with efficient green emissions that are blue-shifted as compared to that of model CPTBF:3,4-CN system. The exciplex formations of α-CPTBF:3,4-CN and β-CPTBF:3,4-CN blends were verified with the significantly red-shifted emissions different from those of constituent donor and acceptor together with the delayed fluorescent observed by time-resolved PL decay experiments. The organic light-emitting diode (OLED) devices with α-CPTBF:3,4-CN and β-CPTBF:3,4-CN blends as the emitting layer showed a maximum external quantum (EQE) of 7.57 and 7.34%, respectively, which is higher as compared to that (EQE = 6.87%) of the model device employing CPTBF:3,4-CN. These results were attributed to the higher exciplex photoluminescence quantum yields due to the higher delay fluorescence components, deeper HOMO, and higher triplet energy of the carboline donors. In addition, the β-CPTBF:3,4-CN exciplex-based OLED exhibited better efficiency roll-off at higher luminesce due to more charge balance with less polaron formation, which was analyzed with time-resolved EL.

Pacific bluefin tuna (PBT) is a long-lived, migratory apex predator that travels across vast areas of the North Pacific Ocean. Concentrations of the neurotoxin methylmercury (MeHg) are high in large PBT and increase with fish age. Mercury stable isotope ratios recorded in PBT muscle tissue show a major shift in the source of MeHg between juvenile PBT in the eastern North Pacific Ocean reported in a previous study and adult PBT (age 5 to more than 27 yr) from the west. In addition, a gradual increase in the accumulation of MeHg from epipelagic prey from the Kuroshio extension in adult PBT as they grow was observed. Finally, MeHg stable isotopes indicate that MeHg in the western North Pacific Ocean has a different source or undergoes different transformations before entering the oceanic food web than in the central and eastern North Pacific. These findings may help identify the source of the high concentrations of MeHg in PBT and other top predators from the western North Pacific Ocean.

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