ABSTRACT
The spontaneous orientation polarization (SOP) of a permanent dipole moment of the molecule induces a giant surface potential (GSP) in an organic semiconductor film, and GSP is expected to be a crucial parameter for understanding the operational mechanism of organic light-emitting diodes (OLEDs). This study demonstrates that the voltage-dependent migration of a carrier recombination zone induced by a polar electron transporting layer (ETL) having a positive SOP causes a decline in the overall performance of the OLED in triplet-triplet upconversion (TTU) based on OLEDs. Specifically, the TTU efficiency in an OLED with 2,2',2â³-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) as the ETL decreased by 20% due to the reduction of electrically generated triplet exciton density. This decrease resulted in a lower external electroluminescence (EL) quantum efficiency (EQE) of 5.4% at 1 mA cm-2, while the OLED with a nonpolar ETL resulted in an EQE of around 8.1% at 1 mA cm-2. We confirmed a shift in the recombination zone from the current density dependence of the EL spectra in the OLEDs. Our results indicate that the fixed carrier recombination zone near a hole transport layer and an emitting layer (HTL/EML) strongly enhanced the TTU process, while the polar EML/ETL interface induced the migration of the recombination zone depending on voltage, resulting in the decrease of triplet exciton density.
ABSTRACT
Honeybee larvae have been recognized as nutrient-rich food in many countries. Although glycogen, a storage form of glucose in animals, is synthesized in honeybee larvae, there is no information on the structure of glycan and its biological activity. In this study, we successfully extracted glycogen from honeybee larvae using hot water extraction and investigated the structure and biological activity of glycan. It was found that the molecular weight of glycogen from honeybee larvae is higher than that of glycogen from bovine liver and oysters. In addition, treatment of RAW264.7 cells with glycogen from honeybee larvae resulted in a much higher production of tumor necrosis factor (TNF)-α and interleukin (IL)-6 than treatment with glycogen from either bovine liver or oysters. These results suggest that the high molecular weight glycogen from honeybee larvae is a functional food ingredient with immunomodulatory activity.
