Anosmia, the loss of smell, is a common and often the sole symptom of COVID-19. The onset of the sequence of pathobiological events leading to olfactory dysfunction remains obscure. Here, we have developed a postmortem bedside surgical procedure to harvest endoscopically samples of respiratory and olfactory mucosae and whole olfactory bulbs. Our cohort of 85 cases included COVID-19 patients who died a few days after infection with SARS-CoV-2, enabling us to catch the virus while it was still replicating. We found that sustentacular cells are the major target cell type in the olfactory mucosa. We failed to find evidence for infection of olfactory sensory neurons, and the parenchyma of the olfactory bulb is spared as well. Thus, SARS-CoV-2 does not appear to be a neurotropic virus. We postulate that transient insufficient support from sustentacular cells triggers transient olfactory dysfunction in COVID-19. Olfactory sensory neurons would become affected without getting infected. ll

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361wileyonlinelibrary.com phosphorescent OLEDs (PhOLEDs) with both high external quantum effi ciency (EQE) and power effi ciency (PE) by tuning the electrical balance, confi ning the excitons in the emitting layer (EML), and reducing the operating voltage of the devices. For example, a large number of host materials with higher triplet (T 1 ) level than that of a blue emitter have been synthesized for a blue EML, and the mixed host systems or dual EMLs have been utilized to achieve good charge balance and exciton confi nement. [24][25][26][27][28][29] New electron or hole transporting materials with high T 1 level adjacent to an EML have also been introduced to confi ne excitons in the EML. [ 5,8,18,[30][31][32][33][34] Moreover, the electrical doping in the injection layers and synthesis of organic materials with high mobility and proper energy level were reported to reduce the operating voltage. [ 14,17,23,31,32,34 ] As a result, the highly effi cient blue PhOLED with a maximum EQE of 30% was reported, [ 22 ] but the device showed large effi ciency rolloff at high luminance and high driving voltage. There are still challenging issues to realize blue PhOLEDs with high EQE, PE, and low effi ciency roll-off at the same time.Use of an exciplex forming co-host is a promising approach to resolve the issues. The effi cient energy transfer from an exciplex forming co-host to phosphorescent dye resulted in high effi ciencies approaching the theoretical limits, low driving voltages, and low effi ciency roll-offs, simultaneously, with a simple structured device. [34][35][36][37][38][39][40] Green, orange and red PhOLEDs and a fl uorescent OLED with EQEs over 30% have been reported, [35][36][37][38][39][40][41][42] but these exciplex forming systems are not applicable to blue dopants because of the higher T 1 level of blue dopants than the T 1 level of exciplexes.The following is required for an exciplex forming co-host for effi cient phosphorescent OLEDs: 1) T 1 level of an exciplex has to be lower than those of the consisting molecules in order to confi ne the excitation energy in the exciplex state, not to be transferred to the consisting molecules, and 2) T 1 level of an exciplex has to be higher than that of a phosphorescent dopant to utilize the energy transfer from the exciplex to a blue dopant. However, seeking for an ideal exciplex system meeting the requirements for a blue dopant seemed to be a challenging issue. [43][44][45] The exciplex forming co-host with phosphorescent dopant system has potential to realize highly effi cient phosphorescent organic light emitting didoes (PhOLEDs). However, the exciplex forming co-host for blue phosphorescent OLEDs has been rarely introduced because of higher triplet level of the blue dopant than green and red dopants. In this work, a novel exciplex forming co-host with high triplet energy level is developed by mixing a phosphine oxide based electron transporting material, PO-T2T, and a hole transporting material, N , N ′-dicarbazolyl-3,5-benzene (mCP). Photo-physical analysi...

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A high-efficiency blue-emitting organic light-emitting diode (OLED) approaching theoretical efficiency using an exciplex-forming co-host composed of N,N'-dicarbazolyl-3,5-benzene (mCP) and bis-4,6-(3,5-di-3-pyridylphenyl)- 2-methylpyrimidine (B3PYMPM) is fabricated. Iridium(III)bis[(4,6-difluorophenyl)- pyridinato-N,C2']picolinate (FIrpic) is used as the emitter, which turns out to have a preferred horizontal dipole orientation in the emitting layer. The OLED shows a maximum external quantum efficiency of 29.5% (a maximum current efficiency of 62.2 cd A(-1) ), which is in perfect agreement with the theoretical prediction.